Adding upstream version 115.8.0esr.upstream/115.8.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

118 files changed, 29744 insertions, 0 deletions

diff --git a/xpcom/io/Base64.cpp b/xpcom/io/Base64.cpp
new file mode 100644
index 0000000000..4bd0394ecb
--- /dev/null
+++ b/xpcom/io/Base64.cpp
@@ -0,0 +1,780 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "Base64.h"
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/UniquePtrExtensions.h"
+#include "nsIInputStream.h"
+#include "nsString.h"
+#include "nsTArray.h"
+
+#include "plbase64.h"
+
+namespace {
+
+// BEGIN base64 encode code copied and modified from NSPR
+const unsigned char* const base =
+  (unsigned char*)"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+                  "abcdefghijklmnopqrstuvwxyz"
+                  "0123456789+/";
+
+// The Base64 encoder assumes all characters are less than 256; for 16-bit
+// strings, that means assuming that all characters are within range, and
+// masking off high bits if necessary.
+template <typename T>
+uint8_t CharTo8Bit(T aChar) {
+  return uint8_t(aChar);
+}
+
+template <typename SrcT, typename DestT>
+static void Encode3to4(const SrcT* aSrc, DestT* aDest) {
+  uint32_t b32 = (uint32_t)0;
+  int i, j = 18;
+
+  for (i = 0; i < 3; ++i) {
+    b32 <<= 8;
+    b32 |= CharTo8Bit(aSrc[i]);
+  }
+
+  for (i = 0; i < 4; ++i) {
+    aDest[i] = base[(uint32_t)((b32 >> j) & 0x3F)];
+    j -= 6;
+  }
+}
+
+template <typename SrcT, typename DestT>
+static void Encode2to4(const SrcT* aSrc, DestT* aDest) {
+  uint8_t src0 = CharTo8Bit(aSrc[0]);
+  uint8_t src1 = CharTo8Bit(aSrc[1]);
+  aDest[0] = base[(uint32_t)((src0 >> 2) & 0x3F)];
+  aDest[1] = base[(uint32_t)(((src0 & 0x03) << 4) | ((src1 >> 4) & 0x0F))];
+  aDest[2] = base[(uint32_t)((src1 & 0x0F) << 2)];
+  aDest[3] = DestT('=');
+}
+
+template <typename SrcT, typename DestT>
+static void Encode1to4(const SrcT* aSrc, DestT* aDest) {
+  uint8_t src0 = CharTo8Bit(aSrc[0]);
+  aDest[0] = base[(uint32_t)((src0 >> 2) & 0x3F)];
+  aDest[1] = base[(uint32_t)((src0 & 0x03) << 4)];
+  aDest[2] = DestT('=');
+  aDest[3] = DestT('=');
+}
+
+template <typename SrcT, typename DestT>
+static void Encode(const SrcT* aSrc, uint32_t aSrcLen, DestT* aDest) {
+  while (aSrcLen >= 3) {
+    Encode3to4(aSrc, aDest);
+    aSrc += 3;
+    aDest += 4;
+    aSrcLen -= 3;
+  }
+
+  switch (aSrcLen) {
+    case 2:
+      Encode2to4(aSrc, aDest);
+      break;
+    case 1:
+      Encode1to4(aSrc, aDest);
+      break;
+    case 0:
+      break;
+    default:
+      MOZ_ASSERT_UNREACHABLE("coding error");
+  }
+}
+
+// END base64 encode code copied and modified from NSPR.
+
+template <typename T>
+struct EncodeInputStream_State {
+  unsigned char c[3];
+  uint8_t charsOnStack;
+  typename T::char_type* buffer;
+};
+
+template <typename T>
+nsresult EncodeInputStream_Encoder(nsIInputStream* aStream, void* aClosure,
+                                   const char* aFromSegment, uint32_t aToOffset,
+                                   uint32_t aCount, uint32_t* aWriteCount) {
+  MOZ_ASSERT(aCount > 0, "Er, what?");
+
+  EncodeInputStream_State<T>* state =
+      static_cast<EncodeInputStream_State<T>*>(aClosure);
+
+  // We consume the whole data always.
+  *aWriteCount = aCount;
+
+  // If we have any data left from last time, encode it now.
+  uint32_t countRemaining = aCount;
+  const unsigned char* src = (const unsigned char*)aFromSegment;
+  if (state->charsOnStack) {
+    MOZ_ASSERT(state->charsOnStack == 1 || state->charsOnStack == 2);
+
+    // Not enough data to compose a triple.
+    if (state->charsOnStack == 1 && countRemaining == 1) {
+      state->charsOnStack = 2;
+      state->c[1] = src[0];
+      return NS_OK;
+    }
+
+    uint32_t consumed = 0;
+    unsigned char firstSet[4];
+    if (state->charsOnStack == 1) {
+      firstSet[0] = state->c[0];
+      firstSet[1] = src[0];
+      firstSet[2] = src[1];
+      firstSet[3] = '\0';
+      consumed = 2;
+    } else /* state->charsOnStack == 2 */ {
+      firstSet[0] = state->c[0];
+      firstSet[1] = state->c[1];
+      firstSet[2] = src[0];
+      firstSet[3] = '\0';
+      consumed = 1;
+    }
+
+    Encode(firstSet, 3, state->buffer);
+    state->buffer += 4;
+    countRemaining -= consumed;
+    src += consumed;
+    state->charsOnStack = 0;
+
+    // Nothing is left.
+    if (!countRemaining) {
+      return NS_OK;
+    }
+  }
+
+  // Encode as many full triplets as possible.
+  uint32_t encodeLength = countRemaining - countRemaining % 3;
+  MOZ_ASSERT(encodeLength % 3 == 0, "Should have an exact number of triplets!");
+  Encode(src, encodeLength, state->buffer);
+  state->buffer += (encodeLength / 3) * 4;
+  src += encodeLength;
+  countRemaining -= encodeLength;
+
+  if (countRemaining) {
+    // We should never have a full triplet left at this point.
+    MOZ_ASSERT(countRemaining < 3, "We should have encoded more!");
+    state->c[0] = src[0];
+    state->c[1] = (countRemaining == 2) ? src[1] : '\0';
+    state->charsOnStack = countRemaining;
+  }
+
+  return NS_OK;
+}
+
+mozilla::Result<uint32_t, nsresult> CalculateBase64EncodedLength(
+    const size_t aBinaryLen, const uint32_t aPrefixLen = 0) {
+  mozilla::CheckedUint32 res = aBinaryLen;
+  // base 64 encoded length is 4/3rds the length of the input data, rounded up
+  res += 2;
+  res /= 3;
+  res *= 4;
+  res += aPrefixLen;
+  if (!res.isValid()) {
+    return mozilla::Err(NS_ERROR_FAILURE);
+  }
+  return res.value();
+}
+
+template <typename T>
+nsresult EncodeInputStream(nsIInputStream* aInputStream, T& aDest,
+                           uint32_t aCount, uint32_t aOffset) {
+  nsresult rv;
+  uint64_t count64 = aCount;
+
+  if (!aCount) {
+    rv = aInputStream->Available(&count64);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+    // if count64 is over 4GB, it will be failed at the below condition,
+    // then will return NS_ERROR_OUT_OF_MEMORY
+    aCount = (uint32_t)count64;
+  }
+
+  const auto base64LenOrErr = CalculateBase64EncodedLength(count64, aOffset);
+  if (base64LenOrErr.isErr()) {
+    // XXX For some reason, it was NS_ERROR_OUT_OF_MEMORY here instead of
+    // NS_ERROR_FAILURE, so we keep that.
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  auto handleOrErr = aDest.BulkWrite(base64LenOrErr.inspect(), aOffset, false);
+  if (handleOrErr.isErr()) {
+    return handleOrErr.unwrapErr();
+  }
+
+  auto handle = handleOrErr.unwrap();
+
+  EncodeInputStream_State<T> state{
+      .c = {'\0', '\0', '\0'},
+      .charsOnStack = 0,
+      .buffer = handle.Elements() + aOffset,
+  };
+
+  while (aCount > 0) {
+    uint32_t read = 0;
+
+    rv = aInputStream->ReadSegments(&EncodeInputStream_Encoder<T>,
+                                    (void*)&state, aCount, &read);
+    if (NS_FAILED(rv)) {
+      if (rv == NS_BASE_STREAM_WOULD_BLOCK) {
+        MOZ_CRASH("Not implemented for async streams!");
+      }
+      if (rv == NS_ERROR_NOT_IMPLEMENTED) {
+        MOZ_CRASH("Requires a stream that implements ReadSegments!");
+      }
+      return rv;
+    }
+
+    if (!read) {
+      break;
+    }
+
+    aCount -= read;
+  }
+
+  // Finish encoding if anything is left
+  if (state.charsOnStack) {
+    Encode(state.c, state.charsOnStack, state.buffer);
+    state.buffer += 4;
+  }
+
+  // If we encountered EOF before reading aCount bytes, the resulting string
+  // could be shorter than predicted, so determine the length from the state.
+  size_t trueLength = state.buffer - handle.Elements();
+  handle.Finish(trueLength, false);
+
+  return NS_OK;
+}
+
+// Maps an encoded character to a value in the Base64 alphabet, per
+// RFC 4648, Table 1. Invalid input characters map to UINT8_MAX.
+
+static const uint8_t kBase64DecodeTable[] = {
+    // clang-format off
+  /* 0 */  255, 255, 255, 255, 255, 255, 255, 255,
+  /* 8 */  255, 255, 255, 255, 255, 255, 255, 255,
+  /* 16 */ 255, 255, 255, 255, 255, 255, 255, 255,
+  /* 24 */ 255, 255, 255, 255, 255, 255, 255, 255,
+  /* 32 */ 255, 255, 255, 255, 255, 255, 255, 255,
+  /* 40 */ 255, 255, 255,
+  62 /* + */,
+  255, 255, 255,
+  63 /* / */,
+
+  /* 48 */ /* 0 - 9 */ 52, 53, 54, 55, 56, 57, 58, 59,
+  /* 56 */ 60, 61, 255, 255, 255, 255, 255, 255,
+
+  /* 64 */ 255, /* A - Z */ 0, 1, 2, 3, 4, 5, 6,
+  /* 72 */ 7, 8, 9, 10, 11, 12, 13, 14,
+  /* 80 */ 15, 16, 17, 18, 19, 20, 21, 22,
+  /* 88 */ 23, 24, 25, 255, 255, 255, 255, 255,
+  /* 96 */ 255, /* a - z */ 26, 27, 28, 29, 30, 31, 32,
+  /* 104 */ 33, 34, 35, 36, 37, 38, 39, 40,
+  /* 112 */ 41, 42, 43, 44, 45, 46, 47, 48,
+  /* 120 */ 49, 50, 51, 255, 255, 255, 255, 255,
+};
+static_assert(mozilla::ArrayLength(kBase64DecodeTable) == 0x80);
+// clang-format on
+
+template <typename T>
+[[nodiscard]] bool Base64CharToValue(T aChar, uint8_t* aValue) {
+  size_t index = static_cast<uint8_t>(aChar);
+  if (index >= mozilla::ArrayLength(kBase64DecodeTable)) {
+    *aValue = 255;
+    return false;
+  }
+  *aValue = kBase64DecodeTable[index];
+  return *aValue != 255;
+}
+
+static const char kBase64URLAlphabet[] =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+static_assert(mozilla::ArrayLength(kBase64URLAlphabet) == 0x41);
+
+// Maps an encoded character to a value in the Base64 URL alphabet, per
+// RFC 4648, Table 2. Invalid input characters map to UINT8_MAX.
+static const uint8_t kBase64URLDecodeTable[] = {
+    // clang-format off
+  255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255,
+  62 /* - */,
+  255, 255,
+  52, 53, 54, 55, 56, 57, 58, 59, 60, 61, /* 0 - 9 */
+  255, 255, 255, 255, 255, 255, 255,
+  0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
+  16, 17, 18, 19, 20, 21, 22, 23, 24, 25, /* A - Z */
+  255, 255, 255, 255,
+  63 /* _ */,
+  255,
+  26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41,
+  42, 43, 44, 45, 46, 47, 48, 49, 50, 51, /* a - z */
+  255, 255, 255, 255, 255,
+};
+static_assert(mozilla::ArrayLength(kBase64URLDecodeTable) == 0x80);
+// clang-format on
+
+bool Base64URLCharToValue(char aChar, uint8_t* aValue) {
+  uint8_t index = static_cast<uint8_t>(aChar);
+  if (index >= mozilla::ArrayLength(kBase64URLDecodeTable)) {
+    *aValue = 255;
+    return false;
+  }
+  *aValue = kBase64URLDecodeTable[index];
+  return *aValue != 255;
+}
+
+}  // namespace
+
+namespace mozilla {
+
+nsresult Base64EncodeInputStream(nsIInputStream* aInputStream,
+                                 nsACString& aDest, uint32_t aCount,
+                                 uint32_t aOffset) {
+  return EncodeInputStream<nsACString>(aInputStream, aDest, aCount, aOffset);
+}
+
+nsresult Base64EncodeInputStream(nsIInputStream* aInputStream, nsAString& aDest,
+                                 uint32_t aCount, uint32_t aOffset) {
+  return EncodeInputStream<nsAString>(aInputStream, aDest, aCount, aOffset);
+}
+
+nsresult Base64Encode(const char* aBinary, uint32_t aBinaryLen,
+                      char** aBase64) {
+  if (aBinaryLen == 0) {
+    *aBase64 = (char*)moz_xmalloc(1);
+    (*aBase64)[0] = '\0';
+    return NS_OK;
+  }
+
+  const auto base64LenOrErr = CalculateBase64EncodedLength(aBinaryLen);
+  if (base64LenOrErr.isErr()) {
+    return base64LenOrErr.inspectErr();
+  }
+  const uint32_t base64Len = base64LenOrErr.inspect();
+
+  *aBase64 = nullptr;
+
+  // Add one byte for null termination.
+  UniqueFreePtr<char[]> base64((char*)malloc(base64Len + 1));
+  if (!base64) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  Encode(aBinary, aBinaryLen, base64.get());
+  base64[base64Len] = '\0';
+
+  *aBase64 = base64.release();
+  return NS_OK;
+}
+
+template <bool Append = false, typename T, typename U>
+static nsresult Base64EncodeHelper(const T* const aBinary,
+                                   const size_t aBinaryLen, U& aBase64) {
+  if (aBinaryLen == 0) {
+    if (!Append) {
+      aBase64.Truncate();
+    }
+    return NS_OK;
+  }
+
+  const uint32_t prefixLen = Append ? aBase64.Length() : 0;
+  const auto base64LenOrErr =
+      CalculateBase64EncodedLength(aBinaryLen, prefixLen);
+  if (base64LenOrErr.isErr()) {
+    return base64LenOrErr.inspectErr();
+  }
+  const uint32_t base64Len = base64LenOrErr.inspect();
+
+  auto handleOrErr = aBase64.BulkWrite(base64Len, prefixLen, false);
+  if (handleOrErr.isErr()) {
+    return handleOrErr.unwrapErr();
+  }
+
+  auto handle = handleOrErr.unwrap();
+
+  Encode(aBinary, aBinaryLen, handle.Elements() + prefixLen);
+  handle.Finish(base64Len, false);
+  return NS_OK;
+}
+
+nsresult Base64EncodeAppend(const char* aBinary, uint32_t aBinaryLen,
+                            nsAString& aBase64) {
+  return Base64EncodeHelper<true>(aBinary, aBinaryLen, aBase64);
+}
+
+nsresult Base64EncodeAppend(const char* aBinary, uint32_t aBinaryLen,
+                            nsACString& aBase64) {
+  return Base64EncodeHelper<true>(aBinary, aBinaryLen, aBase64);
+}
+
+nsresult Base64EncodeAppend(const nsACString& aBinary, nsACString& aBase64) {
+  return Base64EncodeHelper<true>(aBinary.BeginReading(), aBinary.Length(),
+                                  aBase64);
+}
+
+nsresult Base64EncodeAppend(const nsACString& aBinary, nsAString& aBase64) {
+  return Base64EncodeHelper<true>(aBinary.BeginReading(), aBinary.Length(),
+                                  aBase64);
+}
+
+nsresult Base64Encode(const char* aBinary, uint32_t aBinaryLen,
+                      nsACString& aBase64) {
+  return Base64EncodeHelper(aBinary, aBinaryLen, aBase64);
+}
+
+nsresult Base64Encode(const char* aBinary, uint32_t aBinaryLen,
+                      nsAString& aBase64) {
+  return Base64EncodeHelper(aBinary, aBinaryLen, aBase64);
+}
+
+nsresult Base64Encode(const nsACString& aBinary, nsACString& aBase64) {
+  return Base64EncodeHelper(aBinary.BeginReading(), aBinary.Length(), aBase64);
+}
+
+nsresult Base64Encode(const nsACString& aBinary, nsAString& aBase64) {
+  return Base64EncodeHelper(aBinary.BeginReading(), aBinary.Length(), aBase64);
+}
+
+nsresult Base64Encode(const nsAString& aBinary, nsAString& aBase64) {
+  return Base64EncodeHelper(aBinary.BeginReading(), aBinary.Length(), aBase64);
+}
+
+template <typename T, typename U, typename Decoder>
+static bool Decode4to3(const T* aSrc, U* aDest, Decoder aToVal) {
+  uint8_t w, x, y, z;
+  if (!aToVal(aSrc[0], &w) || !aToVal(aSrc[1], &x) || !aToVal(aSrc[2], &y) ||
+      !aToVal(aSrc[3], &z)) {
+    return false;
+  }
+  aDest[0] = U(uint8_t(w << 2 | x >> 4));
+  aDest[1] = U(uint8_t(x << 4 | y >> 2));
+  aDest[2] = U(uint8_t(y << 6 | z));
+  return true;
+}
+
+template <typename T, typename U, typename Decoder>
+static bool Decode3to2(const T* aSrc, U* aDest, Decoder aToVal) {
+  uint8_t w, x, y;
+  if (!aToVal(aSrc[0], &w) || !aToVal(aSrc[1], &x) || !aToVal(aSrc[2], &y)) {
+    return false;
+  }
+  aDest[0] = U(uint8_t(w << 2 | x >> 4));
+  aDest[1] = U(uint8_t(x << 4 | y >> 2));
+  return true;
+}
+
+template <typename T, typename U, typename Decoder>
+static bool Decode2to1(const T* aSrc, U* aDest, Decoder aToVal) {
+  uint8_t w, x;
+  if (!aToVal(aSrc[0], &w) || !aToVal(aSrc[1], &x)) {
+    return false;
+  }
+  aDest[0] = U(uint8_t(w << 2 | x >> 4));
+  return true;
+}
+
+template <typename SrcT, typename DestT>
+static nsresult Base64DecodeHelper(const SrcT* aBase64, uint32_t aBase64Len,
+                                   DestT* aBinary, uint32_t* aBinaryLen) {
+  MOZ_ASSERT(aBinary);
+
+  const SrcT* input = aBase64;
+  uint32_t inputLength = aBase64Len;
+  DestT* binary = aBinary;
+  uint32_t binaryLength = 0;
+
+  // Handle trailing '=' characters.
+  if (inputLength && (inputLength % 4 == 0)) {
+    if (aBase64[inputLength - 1] == SrcT('=')) {
+      if (aBase64[inputLength - 2] == SrcT('=')) {
+        inputLength -= 2;
+      } else {
+        inputLength -= 1;
+      }
+    }
+  }
+
+  while (inputLength >= 4) {
+    if (!Decode4to3(input, binary, Base64CharToValue<SrcT>)) {
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    input += 4;
+    inputLength -= 4;
+    binary += 3;
+    binaryLength += 3;
+  }
+
+  switch (inputLength) {
+    case 3:
+      if (!Decode3to2(input, binary, Base64CharToValue<SrcT>)) {
+        return NS_ERROR_INVALID_ARG;
+      }
+      binaryLength += 2;
+      break;
+    case 2:
+      if (!Decode2to1(input, binary, Base64CharToValue<SrcT>)) {
+        return NS_ERROR_INVALID_ARG;
+      }
+      binaryLength += 1;
+      break;
+    case 1:
+      return NS_ERROR_INVALID_ARG;
+    case 0:
+      break;
+    default:
+      MOZ_CRASH("Too many characters leftover");
+  }
+
+  aBinary[binaryLength] = DestT('\0');
+  *aBinaryLen = binaryLength;
+
+  return NS_OK;
+}
+
+nsresult Base64Decode(const char* aBase64, uint32_t aBase64Len, char** aBinary,
+                      uint32_t* aBinaryLen) {
+  // Check for overflow.
+  if (aBase64Len > UINT32_MAX / 3) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Don't ask PR_Base64Decode to decode the empty string.
+  if (aBase64Len == 0) {
+    *aBinary = (char*)moz_xmalloc(1);
+    (*aBinary)[0] = '\0';
+    *aBinaryLen = 0;
+    return NS_OK;
+  }
+
+  *aBinary = nullptr;
+  *aBinaryLen = (aBase64Len * 3) / 4;
+
+  // Add one byte for null termination.
+  UniqueFreePtr<char[]> binary((char*)malloc(*aBinaryLen + 1));
+  if (!binary) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  nsresult rv =
+      Base64DecodeHelper(aBase64, aBase64Len, binary.get(), aBinaryLen);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  *aBinary = binary.release();
+  return NS_OK;
+}
+
+template <typename T, typename U>
+static nsresult Base64DecodeString(const T& aBase64, U& aBinary) {
+  aBinary.Truncate();
+
+  // Check for overflow.
+  if (aBase64.Length() > UINT32_MAX / 3) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Don't decode the empty string
+  if (aBase64.IsEmpty()) {
+    return NS_OK;
+  }
+
+  uint32_t binaryLen = ((aBase64.Length() * 3) / 4);
+
+  auto handleOrErr = aBinary.BulkWrite(binaryLen, 0, false);
+  if (handleOrErr.isErr()) {
+    // Must not touch the handle if failing here, but we
+    // already truncated the string at the top, so it's
+    // unchanged.
+    return handleOrErr.unwrapErr();
+  }
+
+  auto handle = handleOrErr.unwrap();
+
+  nsresult rv = Base64DecodeHelper(aBase64.BeginReading(), aBase64.Length(),
+                                   handle.Elements(), &binaryLen);
+  if (NS_FAILED(rv)) {
+    // Retruncate to match old semantics of this method.
+    handle.Finish(0, true);
+    return rv;
+  }
+
+  handle.Finish(binaryLen, true);
+  return NS_OK;
+}
+
+nsresult Base64Decode(const nsACString& aBase64, nsACString& aBinary) {
+  return Base64DecodeString(aBase64, aBinary);
+}
+
+nsresult Base64Decode(const nsAString& aBase64, nsAString& aBinary) {
+  return Base64DecodeString(aBase64, aBinary);
+}
+
+nsresult Base64Decode(const nsAString& aBase64, nsACString& aBinary) {
+  return Base64DecodeString(aBase64, aBinary);
+}
+
+nsresult Base64URLDecode(const nsACString& aBase64,
+                         Base64URLDecodePaddingPolicy aPaddingPolicy,
+                         FallibleTArray<uint8_t>& aBinary) {
+  // Don't decode empty strings.
+  if (aBase64.IsEmpty()) {
+    aBinary.Clear();
+    return NS_OK;
+  }
+
+  // Check for overflow.
+  uint32_t base64Len = aBase64.Length();
+  if (base64Len > UINT32_MAX / 3) {
+    return NS_ERROR_FAILURE;
+  }
+  const char* base64 = aBase64.BeginReading();
+
+  // The decoded length may be 1-2 bytes over, depending on the final quantum.
+  uint32_t binaryLen = (base64Len * 3) / 4;
+
+  // Determine whether to check for and ignore trailing padding.
+  bool maybePadded = false;
+  switch (aPaddingPolicy) {
+    case Base64URLDecodePaddingPolicy::Require:
+      if (base64Len % 4) {
+        // Padded input length must be a multiple of 4.
+        return NS_ERROR_INVALID_ARG;
+      }
+      maybePadded = true;
+      break;
+
+    case Base64URLDecodePaddingPolicy::Ignore:
+      // Check for padding only if the length is a multiple of 4.
+      maybePadded = !(base64Len % 4);
+      break;
+
+    // If we're expecting unpadded input, no need for additional checks.
+    // `=` isn't in the decode table, so padded strings will fail to decode.
+    default:
+      MOZ_FALLTHROUGH_ASSERT("Invalid decode padding policy");
+    case Base64URLDecodePaddingPolicy::Reject:
+      break;
+  }
+  if (maybePadded && base64[base64Len - 1] == '=') {
+    if (base64[base64Len - 2] == '=') {
+      base64Len -= 2;
+    } else {
+      base64Len -= 1;
+    }
+  }
+
+  if (NS_WARN_IF(!aBinary.SetCapacity(binaryLen, mozilla::fallible))) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  aBinary.SetLengthAndRetainStorage(binaryLen);
+  uint8_t* binary = aBinary.Elements();
+
+  for (; base64Len >= 4; base64Len -= 4) {
+    if (!Decode4to3(base64, binary, Base64URLCharToValue)) {
+      return NS_ERROR_INVALID_ARG;
+    }
+    base64 += 4;
+    binary += 3;
+  }
+
+  if (base64Len == 3) {
+    if (!Decode3to2(base64, binary, Base64URLCharToValue)) {
+      return NS_ERROR_INVALID_ARG;
+    }
+    binary += 2;
+  } else if (base64Len == 2) {
+    if (!Decode2to1(base64, binary, Base64URLCharToValue)) {
+      return NS_ERROR_INVALID_ARG;
+    }
+    binary += 1;
+  } else if (base64Len) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // Set the length to the actual number of decoded bytes.
+  aBinary.TruncateLength(binary - aBinary.Elements());
+  return NS_OK;
+}
+
+nsresult Base64URLEncode(uint32_t aBinaryLen, const uint8_t* aBinary,
+                         Base64URLEncodePaddingPolicy aPaddingPolicy,
+                         nsACString& aBase64) {
+  aBase64.Truncate();
+  // Don't encode empty strings.
+  if (aBinaryLen == 0) {
+    return NS_OK;
+  }
+
+  // Allocate a buffer large enough to hold the encoded string with padding.
+  const auto base64LenOrErr = CalculateBase64EncodedLength(aBinaryLen);
+  if (base64LenOrErr.isErr()) {
+    return base64LenOrErr.inspectErr();
+  }
+  const uint32_t base64Len = base64LenOrErr.inspect();
+
+  auto handleOrErr = aBase64.BulkWrite(base64Len, 0, false);
+  if (handleOrErr.isErr()) {
+    return handleOrErr.unwrapErr();
+  }
+
+  auto handle = handleOrErr.unwrap();
+
+  char* base64 = handle.Elements();
+
+  uint32_t index = 0;
+  for (; index + 3 <= aBinaryLen; index += 3) {
+    *base64++ = kBase64URLAlphabet[aBinary[index] >> 2];
+    *base64++ = kBase64URLAlphabet[((aBinary[index] & 0x3) << 4) |
+                                   (aBinary[index + 1] >> 4)];
+    *base64++ = kBase64URLAlphabet[((aBinary[index + 1] & 0xf) << 2) |
+                                   (aBinary[index + 2] >> 6)];
+    *base64++ = kBase64URLAlphabet[aBinary[index + 2] & 0x3f];
+  }
+
+  uint32_t remaining = aBinaryLen - index;
+  if (remaining == 1) {
+    *base64++ = kBase64URLAlphabet[aBinary[index] >> 2];
+    *base64++ = kBase64URLAlphabet[((aBinary[index] & 0x3) << 4)];
+  } else if (remaining == 2) {
+    *base64++ = kBase64URLAlphabet[aBinary[index] >> 2];
+    *base64++ = kBase64URLAlphabet[((aBinary[index] & 0x3) << 4) |
+                                   (aBinary[index + 1] >> 4)];
+    *base64++ = kBase64URLAlphabet[((aBinary[index + 1] & 0xf) << 2)];
+  }
+
+  uint32_t length = base64 - handle.Elements();
+  if (aPaddingPolicy == Base64URLEncodePaddingPolicy::Include) {
+    if (length % 4 == 2) {
+      *base64++ = '=';
+      *base64++ = '=';
+      length += 2;
+    } else if (length % 4 == 3) {
+      *base64++ = '=';
+      length += 1;
+    }
+  } else {
+    MOZ_ASSERT(aPaddingPolicy == Base64URLEncodePaddingPolicy::Omit,
+               "Invalid encode padding policy");
+  }
+
+  handle.Finish(length, false);
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/io/Base64.h b/xpcom/io/Base64.h
new file mode 100644
index 0000000000..0a9b3a0305
--- /dev/null
+++ b/xpcom/io/Base64.h
@@ -0,0 +1,93 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_Base64_h__
+#define mozilla_Base64_h__
+
+#include "nsString.h"
+
+class nsIInputStream;
+
+namespace mozilla {
+
+[[nodiscard]] nsresult Base64EncodeInputStream(nsIInputStream* aInputStream,
+                                               nsACString& aDest,
+                                               uint32_t aCount,
+                                               uint32_t aOffset = 0);
+[[nodiscard]] nsresult Base64EncodeInputStream(nsIInputStream* aInputStream,
+                                               nsAString& aDest,
+                                               uint32_t aCount,
+                                               uint32_t aOffset = 0);
+
+// Encode 8-bit data of a given length and append the Base64 encoded data to
+// aBase64.
+[[nodiscard]] nsresult Base64EncodeAppend(const char* aBinary,
+                                          uint32_t aBinaryLen,
+                                          nsAString& aBase64);
+[[nodiscard]] nsresult Base64EncodeAppend(const char* aBinary,
+                                          uint32_t aBinaryLen,
+                                          nsACString& aBase64);
+[[nodiscard]] nsresult Base64EncodeAppend(const nsACString& aBinary,
+                                          nsACString& aBase64);
+[[nodiscard]] nsresult Base64EncodeAppend(const nsACString& aBinary,
+                                          nsAString& aBase64);
+
+[[nodiscard]] nsresult Base64Encode(const char* aBinary, uint32_t aBinaryLen,
+                                    char** aBase64);
+[[nodiscard]] nsresult Base64Encode(const char* aBinary, uint32_t aBinaryLen,
+                                    nsACString& aBase64);
+[[nodiscard]] nsresult Base64Encode(const char* aBinary, uint32_t aBinaryLen,
+                                    nsAString& aBase64);
+[[nodiscard]] nsresult Base64Encode(const nsACString& aBinary,
+                                    nsACString& aBase64);
+[[nodiscard]] nsresult Base64Encode(const nsACString& aBinary,
+                                    nsAString& aBase64);
+
+// The high bits of any characters in aBinary are dropped.
+[[nodiscard]] nsresult Base64Encode(const nsAString& aBinary,
+                                    nsAString& aBase64);
+
+[[nodiscard]] nsresult Base64Decode(const char* aBase64, uint32_t aBase64Len,
+                                    char** aBinary, uint32_t* aBinaryLen);
+[[nodiscard]] nsresult Base64Decode(const nsACString& aBase64,
+                                    nsACString& aBinary);
+
+// The high bits of any characters in aBase64 are dropped.
+[[nodiscard]] nsresult Base64Decode(const nsAString& aBase64,
+                                    nsAString& aBinary);
+[[nodiscard]] nsresult Base64Decode(const nsAString& aBase64,
+                                    nsACString& aBinary);
+
+enum class Base64URLEncodePaddingPolicy {
+  Include,
+  Omit,
+};
+
+/**
+ * Converts |aBinary| to an unpadded, Base64 URL-encoded string per RFC 4648.
+ * Aims to encode the data in constant time. The caller retains ownership
+ * of |aBinary|.
+ */
+[[nodiscard]] nsresult Base64URLEncode(
+    uint32_t aBinaryLen, const uint8_t* aBinary,
+    Base64URLEncodePaddingPolicy aPaddingPolicy, nsACString& aBase64);
+
+enum class Base64URLDecodePaddingPolicy {
+  Require,
+  Ignore,
+  Reject,
+};
+
+/**
+ * Decodes a Base64 URL-encoded |aBase64| into |aBinary|.
+ */
+[[nodiscard]] nsresult Base64URLDecode(
+    const nsACString& aBase64, Base64URLDecodePaddingPolicy aPaddingPolicy,
+    FallibleTArray<uint8_t>& aBinary);
+
+}  // namespace mozilla
+
+#endif
diff --git a/xpcom/io/CocoaFileUtils.h b/xpcom/io/CocoaFileUtils.h
new file mode 100644
index 0000000000..4055787fb6
--- /dev/null
+++ b/xpcom/io/CocoaFileUtils.h
@@ -0,0 +1,46 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// This namespace contains methods with Obj-C/Cocoa implementations. The header
+// is C/C++ for inclusion in C/C++-only files.
+
+#ifndef CocoaFileUtils_h_
+#define CocoaFileUtils_h_
+
+#include "nscore.h"
+#include "nsString.h"
+#include <CoreFoundation/CoreFoundation.h>
+
+namespace CocoaFileUtils {
+
+nsresult RevealFileInFinder(CFURLRef aUrl);
+nsresult OpenURL(CFURLRef aUrl);
+nsresult GetFileCreatorCode(CFURLRef aUrl, OSType* aCreatorCode);
+nsresult SetFileCreatorCode(CFURLRef aUrl, OSType aCreatorCode);
+nsresult GetFileTypeCode(CFURLRef aUrl, OSType* aTypeCode);
+nsresult SetFileTypeCode(CFURLRef aUrl, OSType aTypeCode);
+
+// Can be called off of the main thread.
+void AddOriginMetadataToFile(const CFStringRef filePath,
+                             const CFURLRef sourceURL,
+                             const CFURLRef referrerURL);
+// Can be called off of the main thread.
+void AddQuarantineMetadataToFile(const CFStringRef filePath,
+                                 const CFURLRef sourceURL,
+                                 const CFURLRef referrerURL,
+                                 const bool isFromWeb,
+                                 const bool createProps = false);
+// Can be called off of the main thread.
+void CopyQuarantineReferrerUrl(const CFStringRef aFilePath,
+                               nsAString& aReferrer);
+
+CFURLRef GetTemporaryFolderCFURLRef();
+
+CFURLRef GetProductDirectoryCFURLRef(bool aLocal);
+
+}  // namespace CocoaFileUtils
+
+#endif
diff --git a/xpcom/io/CocoaFileUtils.mm b/xpcom/io/CocoaFileUtils.mm
new file mode 100644
index 0000000000..b906365a2b
--- /dev/null
+++ b/xpcom/io/CocoaFileUtils.mm
@@ -0,0 +1,289 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+// vim:set ts=2 sts=2 sw=2 et cin:
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "CocoaFileUtils.h"
+#include "nsCocoaFeatures.h"
+#include "nsCocoaUtils.h"
+#include <Cocoa/Cocoa.h>
+#include "nsObjCExceptions.h"
+#include "nsDebug.h"
+#include "nsString.h"
+#include "mozilla/MacStringHelpers.h"
+
+namespace CocoaFileUtils {
+
+nsresult RevealFileInFinder(CFURLRef url) {
+  NS_OBJC_BEGIN_TRY_BLOCK_RETURN;
+
+  if (NS_WARN_IF(!url)) return NS_ERROR_INVALID_ARG;
+
+  NSAutoreleasePool* ap = [[NSAutoreleasePool alloc] init];
+  BOOL success = [[NSWorkspace sharedWorkspace] selectFile:[(NSURL*)url path]
+                                  inFileViewerRootedAtPath:@""];
+  [ap release];
+
+  return (success ? NS_OK : NS_ERROR_FAILURE);
+
+  NS_OBJC_END_TRY_BLOCK_RETURN(NS_ERROR_FAILURE);
+}
+
+nsresult OpenURL(CFURLRef url) {
+  NS_OBJC_BEGIN_TRY_BLOCK_RETURN;
+
+  if (NS_WARN_IF(!url)) return NS_ERROR_INVALID_ARG;
+
+  NSAutoreleasePool* ap = [[NSAutoreleasePool alloc] init];
+  BOOL success = [[NSWorkspace sharedWorkspace] openURL:(NSURL*)url];
+  [ap release];
+
+  return (success ? NS_OK : NS_ERROR_FAILURE);
+
+  NS_OBJC_END_TRY_BLOCK_RETURN(NS_ERROR_FAILURE);
+}
+
+nsresult GetFileCreatorCode(CFURLRef url, OSType* creatorCode) {
+  NS_OBJC_BEGIN_TRY_BLOCK_RETURN;
+
+  if (NS_WARN_IF(!url) || NS_WARN_IF(!creatorCode)) return NS_ERROR_INVALID_ARG;
+
+  nsAutoreleasePool localPool;
+
+  NSString* resolvedPath = [[(NSURL*)url path] stringByResolvingSymlinksInPath];
+  if (!resolvedPath) {
+    return NS_ERROR_FAILURE;
+  }
+
+  NSDictionary* dict = [[NSFileManager defaultManager] attributesOfItemAtPath:resolvedPath
+                                                                        error:nil];
+  if (!dict) {
+    return NS_ERROR_FAILURE;
+  }
+
+  NSNumber* creatorNum = (NSNumber*)[dict objectForKey:NSFileHFSCreatorCode];
+  if (!creatorNum) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *creatorCode = [creatorNum unsignedLongValue];
+  return NS_OK;
+
+  NS_OBJC_END_TRY_BLOCK_RETURN(NS_ERROR_FAILURE);
+}
+
+nsresult SetFileCreatorCode(CFURLRef url, OSType creatorCode) {
+  NS_OBJC_BEGIN_TRY_BLOCK_RETURN;
+
+  if (NS_WARN_IF(!url)) return NS_ERROR_INVALID_ARG;
+
+  NSAutoreleasePool* ap = [[NSAutoreleasePool alloc] init];
+  NSDictionary* dict =
+      [NSDictionary dictionaryWithObject:[NSNumber numberWithUnsignedLong:creatorCode]
+                                  forKey:NSFileHFSCreatorCode];
+  BOOL success = [[NSFileManager defaultManager] setAttributes:dict
+                                                  ofItemAtPath:[(NSURL*)url path]
+                                                         error:nil];
+  [ap release];
+  return (success ? NS_OK : NS_ERROR_FAILURE);
+
+  NS_OBJC_END_TRY_BLOCK_RETURN(NS_ERROR_FAILURE);
+}
+
+nsresult GetFileTypeCode(CFURLRef url, OSType* typeCode) {
+  NS_OBJC_BEGIN_TRY_BLOCK_RETURN;
+
+  if (NS_WARN_IF(!url) || NS_WARN_IF(!typeCode)) return NS_ERROR_INVALID_ARG;
+
+  nsAutoreleasePool localPool;
+
+  NSString* resolvedPath = [[(NSURL*)url path] stringByResolvingSymlinksInPath];
+  if (!resolvedPath) {
+    return NS_ERROR_FAILURE;
+  }
+
+  NSDictionary* dict = [[NSFileManager defaultManager] attributesOfItemAtPath:resolvedPath
+                                                                        error:nil];
+  if (!dict) {
+    return NS_ERROR_FAILURE;
+  }
+
+  NSNumber* typeNum = (NSNumber*)[dict objectForKey:NSFileHFSTypeCode];
+  if (!typeNum) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *typeCode = [typeNum unsignedLongValue];
+  return NS_OK;
+
+  NS_OBJC_END_TRY_BLOCK_RETURN(NS_ERROR_FAILURE);
+}
+
+nsresult SetFileTypeCode(CFURLRef url, OSType typeCode) {
+  NS_OBJC_BEGIN_TRY_BLOCK_RETURN;
+
+  if (NS_WARN_IF(!url)) return NS_ERROR_INVALID_ARG;
+
+  NSAutoreleasePool* ap = [[NSAutoreleasePool alloc] init];
+  NSDictionary* dict = [NSDictionary dictionaryWithObject:[NSNumber numberWithUnsignedLong:typeCode]
+                                                   forKey:NSFileHFSTypeCode];
+  BOOL success = [[NSFileManager defaultManager] setAttributes:dict
+                                                  ofItemAtPath:[(NSURL*)url path]
+                                                         error:nil];
+  [ap release];
+  return (success ? NS_OK : NS_ERROR_FAILURE);
+
+  NS_OBJC_END_TRY_BLOCK_RETURN(NS_ERROR_FAILURE);
+}
+
+// Can be called off of the main thread.
+void AddOriginMetadataToFile(const CFStringRef filePath, const CFURLRef sourceURL,
+                             const CFURLRef referrerURL) {
+  typedef OSStatus (*MDItemSetAttribute_type)(MDItemRef, CFStringRef, CFTypeRef);
+  static MDItemSetAttribute_type mdItemSetAttributeFunc = NULL;
+
+  static bool did_symbol_lookup = false;
+  if (!did_symbol_lookup) {
+    did_symbol_lookup = true;
+
+    CFBundleRef metadata_bundle = ::CFBundleGetBundleWithIdentifier(CFSTR("com.apple.Metadata"));
+    if (!metadata_bundle) {
+      return;
+    }
+
+    mdItemSetAttributeFunc = (MDItemSetAttribute_type)::CFBundleGetFunctionPointerForName(
+        metadata_bundle, CFSTR("MDItemSetAttribute"));
+  }
+  if (!mdItemSetAttributeFunc) {
+    return;
+  }
+
+  MDItemRef mdItem = ::MDItemCreate(NULL, filePath);
+  if (!mdItem) {
+    return;
+  }
+
+  CFMutableArrayRef list = ::CFArrayCreateMutable(kCFAllocatorDefault, 2, NULL);
+  if (!list) {
+    ::CFRelease(mdItem);
+    return;
+  }
+
+  // The first item in the list is the source URL of the downloaded file.
+  if (sourceURL) {
+    ::CFArrayAppendValue(list, ::CFURLGetString(sourceURL));
+  }
+
+  // If the referrer is known, store that in the second position.
+  if (referrerURL) {
+    ::CFArrayAppendValue(list, ::CFURLGetString(referrerURL));
+  }
+
+  mdItemSetAttributeFunc(mdItem, kMDItemWhereFroms, list);
+
+  ::CFRelease(list);
+  ::CFRelease(mdItem);
+}
+
+// Can be called off of the main thread.
+static CFMutableDictionaryRef CreateQuarantineDictionary(const CFURLRef aFileURL,
+                                                         const bool aCreateProps) {
+  CFDictionaryRef quarantineProps = NULL;
+  if (aCreateProps) {
+    quarantineProps = ::CFDictionaryCreate(NULL, NULL, NULL, 0, &kCFTypeDictionaryKeyCallBacks,
+                                           &kCFTypeDictionaryValueCallBacks);
+  } else {
+    Boolean success = ::CFURLCopyResourcePropertyForKey(aFileURL, kCFURLQuarantinePropertiesKey,
+                                                        &quarantineProps, NULL);
+    // If there aren't any quarantine properties then the user probably
+    // set up an exclusion and we don't need to add metadata.
+    if (!success || !quarantineProps) {
+      return NULL;
+    }
+  }
+
+  // We don't know what to do if the props aren't a dictionary.
+  if (::CFGetTypeID(quarantineProps) != ::CFDictionaryGetTypeID()) {
+    ::CFRelease(quarantineProps);
+    return NULL;
+  }
+
+  // Make a mutable copy of the properties.
+  CFMutableDictionaryRef mutQuarantineProps =
+      ::CFDictionaryCreateMutableCopy(kCFAllocatorDefault, 0, (CFDictionaryRef)quarantineProps);
+  ::CFRelease(quarantineProps);
+
+  return mutQuarantineProps;
+}
+
+// Can be called off of the main thread.
+void AddQuarantineMetadataToFile(const CFStringRef filePath, const CFURLRef sourceURL,
+                                 const CFURLRef referrerURL, const bool isFromWeb,
+                                 const bool createProps /* = false */) {
+  CFURLRef fileURL =
+      ::CFURLCreateWithFileSystemPath(kCFAllocatorDefault, filePath, kCFURLPOSIXPathStyle, false);
+
+  CFMutableDictionaryRef mutQuarantineProps = CreateQuarantineDictionary(fileURL, createProps);
+  if (!mutQuarantineProps) {
+    ::CFRelease(fileURL);
+    return;
+  }
+
+  // Add metadata that the OS couldn't infer.
+
+  if (!::CFDictionaryGetValue(mutQuarantineProps, kLSQuarantineTypeKey)) {
+    CFStringRef type = isFromWeb ? kLSQuarantineTypeWebDownload : kLSQuarantineTypeOtherDownload;
+    ::CFDictionarySetValue(mutQuarantineProps, kLSQuarantineTypeKey, type);
+  }
+
+  if (!::CFDictionaryGetValue(mutQuarantineProps, kLSQuarantineOriginURLKey) && referrerURL) {
+    ::CFDictionarySetValue(mutQuarantineProps, kLSQuarantineOriginURLKey, referrerURL);
+  }
+
+  if (!::CFDictionaryGetValue(mutQuarantineProps, kLSQuarantineDataURLKey) && sourceURL) {
+    ::CFDictionarySetValue(mutQuarantineProps, kLSQuarantineDataURLKey, sourceURL);
+  }
+
+  // Set quarantine properties on file.
+  ::CFURLSetResourcePropertyForKey(fileURL, kCFURLQuarantinePropertiesKey, mutQuarantineProps,
+                                   NULL);
+
+  ::CFRelease(fileURL);
+  ::CFRelease(mutQuarantineProps);
+}
+
+// Can be called off of the main thread.
+void CopyQuarantineReferrerUrl(const CFStringRef aFilePath, nsAString& aReferrer) {
+  CFURLRef fileURL =
+      ::CFURLCreateWithFileSystemPath(kCFAllocatorDefault, aFilePath, kCFURLPOSIXPathStyle, false);
+
+  CFMutableDictionaryRef mutQuarantineProps = CreateQuarantineDictionary(fileURL, false);
+  ::CFRelease(fileURL);
+  if (!mutQuarantineProps) {
+    return;
+  }
+
+  CFTypeRef referrerRef = ::CFDictionaryGetValue(mutQuarantineProps, kLSQuarantineOriginURLKey);
+  if (referrerRef && ::CFGetTypeID(referrerRef) == ::CFURLGetTypeID()) {
+    // URL string must be copied prior to releasing the dictionary.
+    mozilla::CopyCocoaStringToXPCOMString(
+        (NSString*)::CFURLGetString(static_cast<CFURLRef>(referrerRef)), aReferrer);
+  }
+
+  ::CFRelease(mutQuarantineProps);
+}
+
+CFURLRef GetTemporaryFolderCFURLRef() {
+  NSString* tempDir = ::NSTemporaryDirectory();
+  return tempDir == nil ? NULL : (CFURLRef)[NSURL fileURLWithPath:tempDir isDirectory:YES];
+}
+
+CFURLRef GetProductDirectoryCFURLRef(bool aLocal) {
+  NSSearchPathDirectory folderType = aLocal ? NSCachesDirectory : NSLibraryDirectory;
+  NSFileManager* manager = [NSFileManager defaultManager];
+  return static_cast<CFURLRef>([[manager URLsForDirectory:folderType
+                                                inDomains:NSUserDomainMask] firstObject]);
+}
+
+}  // namespace CocoaFileUtils
diff --git a/xpcom/io/FileDescriptorFile.cpp b/xpcom/io/FileDescriptorFile.cpp
new file mode 100644
index 0000000000..6398a89760
--- /dev/null
+++ b/xpcom/io/FileDescriptorFile.cpp
@@ -0,0 +1,442 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FileDescriptorFile.h"
+
+#include "mozilla/ipc/FileDescriptorUtils.h"
+#include "mozilla/ipc/URIUtils.h"
+#include "mozilla/net/NeckoChild.h"
+#include "nsNetUtil.h"
+#include "nsProxyRelease.h"
+#include "nsThreadUtils.h"
+#include "private/pprio.h"
+#include "SerializedLoadContext.h"
+
+namespace mozilla {
+namespace net {
+
+NS_IMPL_ISUPPORTS(FileDescriptorFile, nsIFile)
+
+LazyLogModule gFDFileLog("FDFile");
+#undef DBG
+#define DBG(...) MOZ_LOG(gFDFileLog, LogLevel::Debug, (__VA_ARGS__))
+
+FileDescriptorFile::FileDescriptorFile(const FileDescriptor& aFD,
+                                       nsIFile* aFile) {
+  MOZ_ASSERT(aFD.IsValid());
+  auto platformHandle = aFD.ClonePlatformHandle();
+  mFD = FileDescriptor(platformHandle.get());
+  mFile = aFile;
+}
+
+FileDescriptorFile::FileDescriptorFile(const FileDescriptorFile& aOther) {
+  auto platformHandle = aOther.mFD.ClonePlatformHandle();
+  mFD = FileDescriptor(platformHandle.get());
+  aOther.mFile->Clone(getter_AddRefs(mFile));
+}
+
+//-----------------------------------------------------------------------------
+// FileDescriptorFile::nsIFile functions that we override logic for
+//-----------------------------------------------------------------------------
+
+NS_IMETHODIMP
+FileDescriptorFile::Clone(nsIFile** aFileOut) {
+  RefPtr<FileDescriptorFile> fdFile = new FileDescriptorFile(*this);
+  fdFile.forget(aFileOut);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::OpenNSPRFileDesc(int32_t aFlags, int32_t aMode,
+                                     PRFileDesc** aRetval) {
+  // Remove optional OS_READAHEAD flag so we test against PR_RDONLY
+  aFlags &= ~nsIFile::OS_READAHEAD;
+
+  // Remove optional/deprecated DELETE_ON_CLOSE flag
+  aFlags &= ~nsIFile::DELETE_ON_CLOSE;
+
+  // All other flags require write access to the file and
+  // this implementation only provides read access.
+  if (aFlags != PR_RDONLY) {
+    DBG("OpenNSPRFileDesc flags error (%" PRIu32 ")\n", aFlags);
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  if (!mFD.IsValid()) {
+    DBG("OpenNSPRFileDesc error: no file descriptor\n");
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  auto platformHandle = mFD.ClonePlatformHandle();
+  *aRetval = PR_ImportFile(PROsfd(platformHandle.release()));
+
+  if (!*aRetval) {
+    DBG("OpenNSPRFileDesc Clone failure\n");
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  return NS_OK;
+}
+
+//-----------------------------------------------------------------------------
+// FileDescriptorFile::nsIFile functions that we delegate to underlying nsIFile
+//-----------------------------------------------------------------------------
+
+nsresult FileDescriptorFile::GetLeafName(nsAString& aLeafName) {
+  return mFile->GetLeafName(aLeafName);
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetNativeLeafName(nsACString& aLeafName) {
+  return mFile->GetNativeLeafName(aLeafName);
+}
+
+NS_IMETHODIMP FileDescriptorFile::GetDisplayName(nsAString& aLeafName) {
+  return mFile->GetDisplayName(aLeafName);
+}
+
+nsresult FileDescriptorFile::GetTarget(nsAString& aRetVal) {
+  return mFile->GetTarget(aRetVal);
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetNativeTarget(nsACString& aRetVal) {
+  return mFile->GetNativeTarget(aRetVal);
+}
+
+nsresult FileDescriptorFile::GetPath(nsAString& aRetVal) {
+  return mFile->GetPath(aRetVal);
+}
+
+PathString FileDescriptorFile::NativePath() { return mFile->NativePath(); }
+
+NS_IMETHODIMP
+FileDescriptorFile::Equals(nsIFile* aOther, bool* aRetVal) {
+  return mFile->Equals(aOther, aRetVal);
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::Contains(nsIFile* aOther, bool* aRetVal) {
+  return mFile->Contains(aOther, aRetVal);
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetParent(nsIFile** aParent) {
+  return mFile->GetParent(aParent);
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetPersistentDescriptor(nsACString& aPersistentDescriptor) {
+  return mFile->GetPersistentDescriptor(aPersistentDescriptor);
+}
+
+//-----------------------------------------------------------------------------
+// FileDescriptorFile::nsIFile functions that are not currently supported
+//-----------------------------------------------------------------------------
+
+nsresult FileDescriptorFile::Append(const nsAString& aNode) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::AppendNative(const nsACString& aFragment) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::Normalize() { return NS_ERROR_NOT_IMPLEMENTED; }
+
+NS_IMETHODIMP
+FileDescriptorFile::Create(uint32_t aType, uint32_t aPermissions,
+                           bool aSkipAncestors) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+nsresult FileDescriptorFile::SetLeafName(const nsAString& aLeafName) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::SetNativeLeafName(const nsACString& aLeafName) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+nsresult FileDescriptorFile::InitWithPath(const nsAString& aPath) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::InitWithNativePath(const nsACString& aPath) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::InitWithFile(nsIFile* aFile) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+nsresult FileDescriptorFile::AppendRelativePath(const nsAString& aNode) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::AppendRelativeNativePath(const nsACString& aFragment) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::SetPersistentDescriptor(
+    const nsACString& aPersistentDescriptor) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetRelativeDescriptor(nsIFile* aFromFile,
+                                          nsACString& aRetVal) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::SetRelativeDescriptor(nsIFile* aFromFile,
+                                          const nsACString& aRelativeDesc) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetRelativePath(nsIFile* aFromFile, nsACString& aRetVal) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::SetRelativePath(nsIFile* aFromFile,
+                                    const nsACString& aRelativePath) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+nsresult FileDescriptorFile::CopyTo(nsIFile* aNewParentDir,
+                                    const nsAString& aNewName) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::CopyToNative(nsIFile* aNewParent,
+                                 const nsACString& aNewName) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+nsresult FileDescriptorFile::CopyToFollowingLinks(nsIFile* aNewParentDir,
+                                                  const nsAString& aNewName) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::CopyToFollowingLinksNative(nsIFile* aNewParent,
+                                               const nsACString& aNewName) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+nsresult FileDescriptorFile::MoveTo(nsIFile* aNewParentDir,
+                                    const nsAString& aNewName) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::MoveToNative(nsIFile* aNewParent,
+                                 const nsACString& aNewName) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::MoveToFollowingLinks(nsIFile* aNewParent,
+                                         const nsAString& aNewName) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::MoveToFollowingLinksNative(nsIFile* aNewParent,
+                                               const nsACString& aNewName) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::RenameTo(nsIFile* aNewParentDir,
+                             const nsAString& aNewName) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::RenameToNative(nsIFile* aNewParentDir,
+                                   const nsACString& aNewName) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::Remove(bool aRecursive, uint32_t* aRemoveCount) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetPermissions(uint32_t* aPermissions) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::SetPermissions(uint32_t aPermissions) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetPermissionsOfLink(uint32_t* aPermissionsOfLink) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::SetPermissionsOfLink(uint32_t aPermissions) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetLastAccessedTime(PRTime* aLastAccessedTime) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::SetLastAccessedTime(PRTime aLastAccessedTime) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetLastAccessedTimeOfLink(PRTime* aLastAccessedTime) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::SetLastAccessedTimeOfLink(PRTime aLastAccessedTime) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetLastModifiedTime(PRTime* aLastModTime) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::SetLastModifiedTime(PRTime aLastModTime) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetLastModifiedTimeOfLink(PRTime* aLastModTimeOfLink) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::SetLastModifiedTimeOfLink(PRTime aLastModTimeOfLink) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetCreationTime(PRTime* aCreationTime) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetCreationTimeOfLink(PRTime* aCreationTime) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetFileSize(int64_t* aFileSize) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::SetFileSize(int64_t aFileSize) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetFileSizeOfLink(int64_t* aFileSize) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::Exists(bool* aRetVal) { return NS_ERROR_NOT_IMPLEMENTED; }
+
+NS_IMETHODIMP
+FileDescriptorFile::IsWritable(bool* aRetVal) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::IsReadable(bool* aRetVal) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::IsExecutable(bool* aRetVal) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::IsHidden(bool* aRetVal) { return NS_ERROR_NOT_IMPLEMENTED; }
+
+NS_IMETHODIMP
+FileDescriptorFile::IsDirectory(bool* aRetVal) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::IsFile(bool* aRetVal) { return NS_ERROR_NOT_IMPLEMENTED; }
+
+NS_IMETHODIMP
+FileDescriptorFile::IsSymlink(bool* aRetVal) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::IsSpecial(bool* aRetVal) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::CreateUnique(uint32_t aType, uint32_t aAttributes) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetDirectoryEntriesImpl(nsIDirectoryEnumerator** aEntries) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::OpenANSIFileDesc(const char* aMode, FILE** aRetVal) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::Load(PRLibrary** aRetVal) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetDiskSpaceAvailable(int64_t* aDiskSpaceAvailable) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::GetDiskCapacity(int64_t* aDiskCapacity) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+FileDescriptorFile::Reveal() { return NS_ERROR_NOT_IMPLEMENTED; }
+
+NS_IMETHODIMP
+FileDescriptorFile::Launch() { return NS_ERROR_NOT_IMPLEMENTED; }
+
+}  // namespace net
+}  // namespace mozilla
diff --git a/xpcom/io/FileDescriptorFile.h b/xpcom/io/FileDescriptorFile.h
new file mode 100644
index 0000000000..1d0fbad2d8
--- /dev/null
+++ b/xpcom/io/FileDescriptorFile.h
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef _FileDescriptorFile_h
+#define _FileDescriptorFile_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/ipc/FileDescriptor.h"
+#include "nsIFile.h"
+#include "private/pprio.h"
+
+namespace mozilla {
+namespace net {
+
+/**
+ * A limited implementation of nsIFile that wraps a FileDescriptor object
+ * allowing the file to be read from. Added to allow a child process to use
+ * an nsIFile object for a file it does not have access to on the filesystem
+ * but has been provided a FileDescriptor for from the parent. Many nsIFile
+ * methods are not implemented and this is not intended to be a general
+ * purpose file implementation.
+ */
+class FileDescriptorFile final : public nsIFile {
+  typedef mozilla::ipc::FileDescriptor FileDescriptor;
+
+ public:
+  FileDescriptorFile(const FileDescriptor& aFD, nsIFile* aFile);
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIFILE
+
+ private:
+  ~FileDescriptorFile() = default;
+
+  FileDescriptorFile(const FileDescriptorFile& other);
+
+  // regular nsIFile object, that we forward most calls to.
+  nsCOMPtr<nsIFile> mFile;
+  FileDescriptor mFD;
+};
+
+}  // namespace net
+}  // namespace mozilla
+
+#endif  // _FileDescriptorFile_h
diff --git a/xpcom/io/FilePreferences.cpp b/xpcom/io/FilePreferences.cpp
new file mode 100644
index 0000000000..1d96c72810
--- /dev/null
+++ b/xpcom/io/FilePreferences.cpp
@@ -0,0 +1,373 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FilePreferences.h"
+
+#include "mozilla/Atomics.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/StaticMutex.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/TextUtils.h"
+#include "mozilla/Tokenizer.h"
+#include "nsAppDirectoryServiceDefs.h"
+#include "nsDirectoryServiceDefs.h"
+#include "nsDirectoryServiceUtils.h"
+#include "nsString.h"
+
+namespace mozilla {
+namespace FilePreferences {
+
+static StaticMutex sMutex;
+
+static bool sBlockUNCPaths = false;
+typedef nsTArray<nsString> WinPaths;
+
+static WinPaths& PathAllowlist() MOZ_REQUIRES(sMutex) {
+  sMutex.AssertCurrentThreadOwns();
+
+  static WinPaths sPaths MOZ_GUARDED_BY(sMutex);
+  return sPaths;
+}
+
+#ifdef XP_WIN
+const auto kDevicePathSpecifier = u"\\\\?\\"_ns;
+
+typedef char16_t char_path_t;
+#else
+typedef char char_path_t;
+#endif
+
+// Initially false to make concurrent consumers acquire the lock and sync.
+// The plain bool is synchronized with sMutex, the atomic one is for a quick
+// check w/o the need to acquire the lock on the hot path.
+static bool sForbiddenPathsEmpty = false;
+static Atomic<bool, Relaxed> sForbiddenPathsEmptyQuickCheck{false};
+
+typedef nsTArray<nsTString<char_path_t>> Paths;
+static StaticAutoPtr<Paths> sForbiddenPaths;
+
+static Paths& ForbiddenPaths() {
+  sMutex.AssertCurrentThreadOwns();
+  if (!sForbiddenPaths) {
+    sForbiddenPaths = new nsTArray<nsTString<char_path_t>>();
+    ClearOnShutdown(&sForbiddenPaths);
+  }
+  return *sForbiddenPaths;
+}
+
+static void AllowUNCDirectory(char const* directory) {
+  nsCOMPtr<nsIFile> file;
+  NS_GetSpecialDirectory(directory, getter_AddRefs(file));
+  if (!file) {
+    return;
+  }
+
+  nsString path;
+  if (NS_FAILED(file->GetTarget(path))) {
+    return;
+  }
+
+  // The allowlist makes sense only for UNC paths, because this code is used
+  // to block only UNC paths, hence, no need to add non-UNC directories here
+  // as those would never pass the check.
+  if (!StringBeginsWith(path, u"\\\\"_ns)) {
+    return;
+  }
+
+  StaticMutexAutoLock lock(sMutex);
+
+  if (!PathAllowlist().Contains(path)) {
+    PathAllowlist().AppendElement(path);
+  }
+}
+
+void InitPrefs() {
+  sBlockUNCPaths =
+      Preferences::GetBool("network.file.disable_unc_paths", false);
+
+  nsTAutoString<char_path_t> forbidden;
+#ifdef XP_WIN
+  Preferences::GetString("network.file.path_blacklist", forbidden);
+#else
+  Preferences::GetCString("network.file.path_blacklist", forbidden);
+#endif
+
+  StaticMutexAutoLock lock(sMutex);
+
+  if (forbidden.IsEmpty()) {
+    sForbiddenPathsEmptyQuickCheck = (sForbiddenPathsEmpty = true);
+    return;
+  }
+
+  ForbiddenPaths().Clear();
+  TTokenizer<char_path_t> p(forbidden);
+  while (!p.CheckEOF()) {
+    nsTString<char_path_t> path;
+    Unused << p.ReadUntil(TTokenizer<char_path_t>::Token::Char(','), path);
+    path.Trim(" ");
+    if (!path.IsEmpty()) {
+      ForbiddenPaths().AppendElement(path);
+    }
+    Unused << p.CheckChar(',');
+  }
+
+  sForbiddenPathsEmptyQuickCheck =
+      (sForbiddenPathsEmpty = ForbiddenPaths().Length() == 0);
+}
+
+void InitDirectoriesAllowlist() {
+  // NS_GRE_DIR is the installation path where the binary resides.
+  AllowUNCDirectory(NS_GRE_DIR);
+  // NS_APP_USER_PROFILE_50_DIR and NS_APP_USER_PROFILE_LOCAL_50_DIR are the two
+  // parts of the profile we store permanent and local-specific data.
+  AllowUNCDirectory(NS_APP_USER_PROFILE_50_DIR);
+  AllowUNCDirectory(NS_APP_USER_PROFILE_LOCAL_50_DIR);
+}
+
+namespace {  // anon
+
+template <typename TChar>
+class TNormalizer : public TTokenizer<TChar> {
+  typedef TTokenizer<TChar> base;
+
+ public:
+  typedef typename base::Token Token;
+
+  TNormalizer(const nsTSubstring<TChar>& aFilePath, const Token& aSeparator)
+      : TTokenizer<TChar>(aFilePath), mSeparator(aSeparator) {}
+
+  bool Get(nsTSubstring<TChar>& aNormalizedFilePath) {
+    aNormalizedFilePath.Truncate();
+
+    // Windows UNC paths begin with double separator (\\)
+    // Linux paths begin with just one separator (/)
+    // If we want to use the normalizer for regular windows paths this code
+    // will need to be updated.
+#ifdef XP_WIN
+    if (base::Check(mSeparator)) {
+      aNormalizedFilePath.Append(mSeparator.AsChar());
+    }
+#endif
+
+    if (base::Check(mSeparator)) {
+      aNormalizedFilePath.Append(mSeparator.AsChar());
+    }
+
+    while (base::HasInput()) {
+      if (!ConsumeName()) {
+        return false;
+      }
+    }
+
+    for (auto const& name : mStack) {
+      aNormalizedFilePath.Append(name);
+    }
+
+    return true;
+  }
+
+ private:
+  bool ConsumeName() {
+    if (base::CheckEOF()) {
+      return true;
+    }
+
+    if (CheckCurrentDir()) {
+      return true;
+    }
+
+    if (CheckParentDir()) {
+      if (!mStack.Length()) {
+        // This means there are more \.. than valid names
+        return false;
+      }
+
+      mStack.RemoveLastElement();
+      return true;
+    }
+
+    nsTDependentSubstring<TChar> name;
+    if (base::ReadUntil(mSeparator, name, base::INCLUDE_LAST) &&
+        name.Length() == 1) {
+      // this means an empty name (a lone slash), which is illegal
+      return false;
+    }
+    mStack.AppendElement(name);
+
+    return true;
+  }
+
+  bool CheckParentDir() {
+    typename nsTString<TChar>::const_char_iterator cursor = base::mCursor;
+    if (base::CheckChar('.') && base::CheckChar('.') && CheckSeparator()) {
+      return true;
+    }
+
+    base::mCursor = cursor;
+    return false;
+  }
+
+  bool CheckCurrentDir() {
+    typename nsTString<TChar>::const_char_iterator cursor = base::mCursor;
+    if (base::CheckChar('.') && CheckSeparator()) {
+      return true;
+    }
+
+    base::mCursor = cursor;
+    return false;
+  }
+
+  bool CheckSeparator() { return base::Check(mSeparator) || base::CheckEOF(); }
+
+  Token const mSeparator;
+  nsTArray<nsTDependentSubstring<TChar>> mStack;
+};
+
+#ifdef XP_WIN
+bool IsDOSDevicePathWithDrive(const nsAString& aFilePath) {
+  if (!StringBeginsWith(aFilePath, kDevicePathSpecifier)) {
+    return false;
+  }
+
+  const auto pathNoPrefix =
+      nsDependentSubstring(aFilePath, kDevicePathSpecifier.Length());
+
+  // After the device path specifier, the rest of file path can be:
+  // - starts with the volume or drive. e.g. \\?\C:\...
+  // - UNCs. e.g. \\?\UNC\Server\Share\Test\Foo.txt
+  // - device UNCs. e.g. \\?\server1\e:\utilities\\filecomparer\...
+  // The first case should not be blocked by IsBlockedUNCPath.
+  if (!StartsWithDiskDesignatorAndBackslash(pathNoPrefix)) {
+    return false;
+  }
+
+  return true;
+}
+#endif
+
+}  // namespace
+
+bool IsBlockedUNCPath(const nsAString& aFilePath) {
+  typedef TNormalizer<char16_t> Normalizer;
+  if (!sBlockUNCPaths) {
+    return false;
+  }
+
+  if (!StringBeginsWith(aFilePath, u"\\\\"_ns)) {
+    return false;
+  }
+
+#ifdef XP_WIN
+  // ToDo: We don't need to check this once we can check if there is a valid
+  // server or host name that is prefaced by "\\".
+  // https://docs.microsoft.com/en-us/dotnet/standard/io/file-path-formats
+  if (IsDOSDevicePathWithDrive(aFilePath)) {
+    return false;
+  }
+#endif
+
+  nsAutoString normalized;
+  if (!Normalizer(aFilePath, Normalizer::Token::Char('\\')).Get(normalized)) {
+    // Broken paths are considered invalid and thus inaccessible
+    return true;
+  }
+
+  StaticMutexAutoLock lock(sMutex);
+
+  for (const auto& allowedPrefix : PathAllowlist()) {
+    if (StringBeginsWith(normalized, allowedPrefix)) {
+      if (normalized.Length() == allowedPrefix.Length()) {
+        return false;
+      }
+      if (normalized[allowedPrefix.Length()] == L'\\') {
+        return false;
+      }
+
+      // When we are here, the path has a form "\\path\prefixevil"
+      // while we have an allowed prefix of "\\path\prefix".
+      // Note that we don't want to add a slash to the end of a prefix
+      // so that opening the directory (no slash at the end) still works.
+      break;
+    }
+  }
+
+  return true;
+}
+
+#ifdef XP_WIN
+const char kPathSeparator = '\\';
+#else
+const char kPathSeparator = '/';
+#endif
+
+bool IsAllowedPath(const nsTSubstring<char_path_t>& aFilePath) {
+  typedef TNormalizer<char_path_t> Normalizer;
+
+  // An atomic quick check out of the lock, because this is mostly `true`.
+  if (sForbiddenPathsEmptyQuickCheck) {
+    return true;
+  }
+
+  StaticMutexAutoLock lock(sMutex);
+
+  if (sForbiddenPathsEmpty) {
+    return true;
+  }
+
+  // If sForbidden has been cleared at shutdown, we must avoid calling
+  // ForbiddenPaths() again, as that will recreate the array and we will leak.
+  if (!sForbiddenPaths) {
+    return true;
+  }
+
+  nsTAutoString<char_path_t> normalized;
+  if (!Normalizer(aFilePath, Normalizer::Token::Char(kPathSeparator))
+           .Get(normalized)) {
+    // Broken paths are considered invalid and thus inaccessible
+    return false;
+  }
+
+  for (const auto& prefix : ForbiddenPaths()) {
+    if (StringBeginsWith(normalized, prefix)) {
+      if (normalized.Length() > prefix.Length() &&
+          normalized[prefix.Length()] != kPathSeparator) {
+        continue;
+      }
+      return false;
+    }
+  }
+
+  return true;
+}
+
+#ifdef XP_WIN
+bool StartsWithDiskDesignatorAndBackslash(const nsAString& aAbsolutePath) {
+  // aAbsolutePath can only be (in regular expression):
+  // UNC path: ^\\\\.*
+  // A single backslash: ^\\.*
+  // A disk designator with a backslash: ^[A-Za-z]:\\.*
+  return aAbsolutePath.Length() >= 3 && IsAsciiAlpha(aAbsolutePath.CharAt(0)) &&
+         aAbsolutePath.CharAt(1) == L':' &&
+         aAbsolutePath.CharAt(2) == kPathSeparator;
+}
+#endif
+
+void testing::SetBlockUNCPaths(bool aBlock) { sBlockUNCPaths = aBlock; }
+
+void testing::AddDirectoryToAllowlist(nsAString const& aPath) {
+  StaticMutexAutoLock lock(sMutex);
+  PathAllowlist().AppendElement(aPath);
+}
+
+bool testing::NormalizePath(nsAString const& aPath, nsAString& aNormalized) {
+  typedef TNormalizer<char16_t> Normalizer;
+  Normalizer normalizer(aPath, Normalizer::Token::Char('\\'));
+  return normalizer.Get(aNormalized);
+}
+
+}  // namespace FilePreferences
+}  // namespace mozilla
diff --git a/xpcom/io/FilePreferences.h b/xpcom/io/FilePreferences.h
new file mode 100644
index 0000000000..ee80429047
--- /dev/null
+++ b/xpcom/io/FilePreferences.h
@@ -0,0 +1,40 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsAString.h"
+
+namespace mozilla {
+namespace FilePreferences {
+
+void InitPrefs();
+void InitDirectoriesAllowlist();
+bool IsBlockedUNCPath(const nsAString& aFilePath);
+
+#ifdef XP_WIN
+bool IsAllowedPath(const nsAString& aFilePath);
+#else
+bool IsAllowedPath(const nsACString& aFilePath);
+#endif
+
+#ifdef XP_WIN
+bool StartsWithDiskDesignatorAndBackslash(const nsAString& aAbsolutePath);
+#endif
+
+extern const char kPathSeparator;
+#ifdef XP_WIN
+extern const nsLiteralString kDevicePathSpecifier;
+#endif
+
+namespace testing {
+
+void SetBlockUNCPaths(bool aBlock);
+void AddDirectoryToAllowlist(nsAString const& aPath);
+bool NormalizePath(nsAString const& aPath, nsAString& aNormalized);
+
+}  // namespace testing
+
+}  // namespace FilePreferences
+}  // namespace mozilla
diff --git a/xpcom/io/FileUtilsWin.cpp b/xpcom/io/FileUtilsWin.cpp
new file mode 100644
index 0000000000..9c0bc6faa2
--- /dev/null
+++ b/xpcom/io/FileUtilsWin.cpp
@@ -0,0 +1,139 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FileUtilsWin.h"
+
+#include <windows.h>
+#include <psapi.h>
+
+#include "base/process_util.h"
+#include "mozilla/ProfilerLabels.h"
+#include "mozilla/Unused.h"
+#include "nsWindowsHelpers.h"
+
+namespace {
+
+// Scoped type used by HandleToFilename
+struct ScopedMappedViewTraits {
+  typedef void* type;
+  static void* empty() { return nullptr; }
+  static void release(void* aPtr) {
+    if (aPtr) {
+      mozilla::Unused << UnmapViewOfFile(aPtr);
+    }
+  }
+};
+typedef mozilla::Scoped<ScopedMappedViewTraits> ScopedMappedView;
+
+}  // namespace
+
+namespace mozilla {
+
+bool HandleToFilename(HANDLE aHandle, const LARGE_INTEGER& aOffset,
+                      nsAString& aFilename) {
+  AUTO_PROFILER_LABEL("HandletoFilename", OTHER);
+
+  aFilename.Truncate();
+  // This implementation is nice because it uses fully documented APIs that
+  // are available on all Windows versions that we support.
+  nsAutoHandle fileMapping(
+      CreateFileMapping(aHandle, nullptr, PAGE_READONLY, 0, 1, nullptr));
+  if (!fileMapping) {
+    return false;
+  }
+  ScopedMappedView view(MapViewOfFile(fileMapping, FILE_MAP_READ,
+                                      aOffset.HighPart, aOffset.LowPart, 1));
+  if (!view) {
+    return false;
+  }
+  nsAutoString mappedFilename;
+  DWORD len = 0;
+  SetLastError(ERROR_SUCCESS);
+  do {
+    mappedFilename.SetLength(mappedFilename.Length() + MAX_PATH);
+    len = GetMappedFileNameW(GetCurrentProcess(), view, mappedFilename.get(),
+                             mappedFilename.Length());
+  } while (!len && GetLastError() == ERROR_INSUFFICIENT_BUFFER);
+  if (!len) {
+    return false;
+  }
+  mappedFilename.Truncate(len);
+  return NtPathToDosPath(mappedFilename, aFilename);
+}
+
+template <class T>
+struct RVAMap {
+  RVAMap(HANDLE map, DWORD offset) {
+    SYSTEM_INFO info;
+    GetSystemInfo(&info);
+
+    DWORD alignedOffset =
+        (offset / info.dwAllocationGranularity) * info.dwAllocationGranularity;
+
+    MOZ_ASSERT(offset - alignedOffset < info.dwAllocationGranularity, "Wtf");
+
+    mRealView = ::MapViewOfFile(map, FILE_MAP_READ, 0, alignedOffset,
+                                sizeof(T) + (offset - alignedOffset));
+
+    mMappedView =
+        mRealView
+            ? reinterpret_cast<T*>((char*)mRealView + (offset - alignedOffset))
+            : nullptr;
+  }
+  ~RVAMap() {
+    if (mRealView) {
+      ::UnmapViewOfFile(mRealView);
+    }
+  }
+  operator const T*() const { return mMappedView; }
+  const T* operator->() const { return mMappedView; }
+
+ private:
+  const T* mMappedView;
+  void* mRealView;
+};
+
+uint32_t GetExecutableArchitecture(const wchar_t* aPath) {
+  nsAutoHandle file(::CreateFileW(aPath, GENERIC_READ, FILE_SHARE_READ, nullptr,
+                                  OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL,
+                                  nullptr));
+  if (!file) {
+    return base::PROCESS_ARCH_INVALID;
+  }
+
+  nsAutoHandle map(
+      ::CreateFileMappingW(file, nullptr, PAGE_READONLY, 0, 0, nullptr));
+  if (!map) {
+    return base::PROCESS_ARCH_INVALID;
+  }
+
+  RVAMap<IMAGE_DOS_HEADER> peHeader(map, 0);
+  if (!peHeader) {
+    return base::PROCESS_ARCH_INVALID;
+  }
+
+  RVAMap<IMAGE_NT_HEADERS> ntHeader(map, peHeader->e_lfanew);
+  if (!ntHeader) {
+    return base::PROCESS_ARCH_INVALID;
+  }
+
+  switch (ntHeader->FileHeader.Machine) {
+    case IMAGE_FILE_MACHINE_I386:
+      return base::PROCESS_ARCH_I386;
+    case IMAGE_FILE_MACHINE_AMD64:
+      return base::PROCESS_ARCH_X86_64;
+    case IMAGE_FILE_MACHINE_ARM64:
+      return base::PROCESS_ARCH_ARM_64;
+    case IMAGE_FILE_MACHINE_ARM:
+    case IMAGE_FILE_MACHINE_ARMNT:
+    case IMAGE_FILE_MACHINE_THUMB:
+      return base::PROCESS_ARCH_ARM;
+    default:
+      return base::PROCESS_ARCH_INVALID;
+  }
+}
+
+}  // namespace mozilla
diff --git a/xpcom/io/FileUtilsWin.h b/xpcom/io/FileUtilsWin.h
new file mode 100644
index 0000000000..4a59820d08
--- /dev/null
+++ b/xpcom/io/FileUtilsWin.h
@@ -0,0 +1,147 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_FileUtilsWin_h
+#define mozilla_FileUtilsWin_h
+
+#include <windows.h>
+
+#include "mozilla/Scoped.h"
+#include "nsString.h"
+
+namespace mozilla {
+
+inline bool EnsureLongPath(nsAString& aDosPath) {
+  nsAutoString inputPath(aDosPath);
+  while (true) {
+    DWORD requiredLength = GetLongPathNameW(
+        inputPath.get(), reinterpret_cast<wchar_t*>(aDosPath.BeginWriting()),
+        aDosPath.Length());
+    if (!requiredLength) {
+      return false;
+    }
+    if (requiredLength < aDosPath.Length()) {
+      // When GetLongPathNameW deems the last argument too small,
+      // it returns a value, but when you pass that value back, it's
+      // satisfied and returns a number that's one smaller. If the above
+      // check was == instead of <, the loop would go on forever with
+      // GetLongPathNameW returning oscillating values!
+      aDosPath.Truncate(requiredLength);
+      return true;
+    }
+    aDosPath.SetLength(requiredLength);
+  }
+}
+
+inline bool NtPathToDosPath(const nsAString& aNtPath, nsAString& aDosPath) {
+  aDosPath.Truncate();
+  if (aNtPath.IsEmpty()) {
+    return true;
+  }
+  constexpr auto symLinkPrefix = u"\\??\\"_ns;
+  uint32_t ntPathLen = aNtPath.Length();
+  uint32_t symLinkPrefixLen = symLinkPrefix.Length();
+  if (ntPathLen >= 6 && aNtPath.CharAt(5) == L':' &&
+      ntPathLen >= symLinkPrefixLen &&
+      Substring(aNtPath, 0, symLinkPrefixLen).Equals(symLinkPrefix)) {
+    // Symbolic link for DOS device. Just strip off the prefix.
+    aDosPath = aNtPath;
+    aDosPath.Cut(0, 4);
+    return true;
+  }
+  nsAutoString logicalDrives;
+  while (true) {
+    DWORD requiredLength = GetLogicalDriveStringsW(
+        logicalDrives.Length(),
+        reinterpret_cast<wchar_t*>(logicalDrives.BeginWriting()));
+    if (!requiredLength) {
+      return false;
+    }
+    if (requiredLength < logicalDrives.Length()) {
+      // When GetLogicalDriveStringsW deems the first argument too small,
+      // it returns a value, but when you pass that value back, it's
+      // satisfied and returns a number that's one smaller. If the above
+      // check was == instead of <, the loop would go on forever with
+      // GetLogicalDriveStringsW returning oscillating values!
+      logicalDrives.Truncate(requiredLength);
+      // logicalDrives now has the format "C:\\\0D:\\\0Z:\\\0". That is,
+      // the sequence drive letter, colon, backslash, U+0000 repeats.
+      break;
+    }
+    logicalDrives.SetLength(requiredLength);
+  }
+
+  const char16_t* cur = logicalDrives.BeginReading();
+  const char16_t* end = logicalDrives.EndReading();
+  nsString targetPath;
+  targetPath.SetLength(MAX_PATH);
+  wchar_t driveTemplate[] = L" :";
+  while (cur < end) {
+    // Unfortunately QueryDosDevice doesn't support the idiom for querying the
+    // output buffer size, so it may require retries.
+    driveTemplate[0] = *cur;
+    DWORD targetPathLen = 0;
+    SetLastError(ERROR_SUCCESS);
+    while (true) {
+      targetPathLen = QueryDosDeviceW(
+          driveTemplate, reinterpret_cast<wchar_t*>(targetPath.BeginWriting()),
+          targetPath.Length());
+      if (targetPathLen || GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
+        break;
+      }
+      targetPath.SetLength(targetPath.Length() * 2);
+    }
+    if (targetPathLen) {
+      // Need to use wcslen here because targetPath contains embedded NULL chars
+      size_t firstTargetPathLen = wcslen(targetPath.get());
+      const char16_t* pathComponent =
+          aNtPath.BeginReading() + firstTargetPathLen;
+      bool found = _wcsnicmp(char16ptr_t(aNtPath.BeginReading()),
+                             targetPath.get(), firstTargetPathLen) == 0 &&
+                   *pathComponent == L'\\';
+      if (found) {
+        aDosPath = driveTemplate;
+        aDosPath += pathComponent;
+        return EnsureLongPath(aDosPath);
+      }
+    }
+    // Find the next U+0000 within the logical string
+    while (*cur) {
+      // This loop skips the drive letter, the colon
+      // and the backslash.
+      cur++;
+    }
+    // Skip over the U+0000 that ends a drive entry
+    // within the logical string
+    cur++;
+  }
+  // Try to handle UNC paths. NB: This must happen after we've checked drive
+  // mappings in case a UNC path is mapped to a drive!
+  constexpr auto uncPrefix = u"\\\\"_ns;
+  constexpr auto deviceMupPrefix = u"\\Device\\Mup\\"_ns;
+  if (StringBeginsWith(aNtPath, deviceMupPrefix)) {
+    aDosPath = uncPrefix;
+    aDosPath += Substring(aNtPath, deviceMupPrefix.Length());
+    return true;
+  }
+  constexpr auto deviceLanmanRedirectorPrefix =
+      u"\\Device\\LanmanRedirector\\"_ns;
+  if (StringBeginsWith(aNtPath, deviceLanmanRedirectorPrefix)) {
+    aDosPath = uncPrefix;
+    aDosPath += Substring(aNtPath, deviceLanmanRedirectorPrefix.Length());
+    return true;
+  }
+  return false;
+}
+
+bool HandleToFilename(HANDLE aHandle, const LARGE_INTEGER& aOffset,
+                      nsAString& aFilename);
+
+uint32_t GetExecutableArchitecture(const wchar_t* aPath);
+
+}  // namespace mozilla
+
+#endif  // mozilla_FileUtilsWin_h
diff --git a/xpcom/io/FixedBufferOutputStream.cpp b/xpcom/io/FixedBufferOutputStream.cpp
new file mode 100644
index 0000000000..1c841bb91f
--- /dev/null
+++ b/xpcom/io/FixedBufferOutputStream.cpp
@@ -0,0 +1,161 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FixedBufferOutputStream.h"
+
+#include "mozilla/RefPtr.h"
+#include "mozilla/StreamBufferSinkImpl.h"
+#include "nsStreamUtils.h"
+#include "nsString.h"
+
+namespace mozilla {
+
+FixedBufferOutputStream::FixedBufferOutputStream(
+    UniquePtr<StreamBufferSink>&& aSink)
+    : mSink(std::move(aSink)),
+      mMutex("FixedBufferOutputStream::mMutex"),
+      mOffset(0),
+      mWriting(false),
+      mClosed(false) {}
+
+// static
+RefPtr<FixedBufferOutputStream> FixedBufferOutputStream::Create(
+    size_t aLength) {
+  MOZ_ASSERT(aLength);
+
+  return MakeRefPtr<FixedBufferOutputStream>(MakeUnique<BufferSink>(aLength));
+}
+
+// static
+RefPtr<FixedBufferOutputStream> FixedBufferOutputStream::Create(
+    size_t aLength, const mozilla::fallible_t&) {
+  MOZ_ASSERT(aLength);
+
+  auto sink = BufferSink::Alloc(aLength);
+
+  if (NS_WARN_IF(!sink)) {
+    return nullptr;
+  }
+
+  return MakeRefPtr<FixedBufferOutputStream>(std::move(sink));
+}
+
+// static
+RefPtr<FixedBufferOutputStream> FixedBufferOutputStream::Create(
+    mozilla::Span<char> aBuffer) {
+  return MakeRefPtr<FixedBufferOutputStream>(
+      MakeUnique<nsBorrowedSink>(aBuffer));
+}
+
+// static
+RefPtr<FixedBufferOutputStream> FixedBufferOutputStream::Create(
+    UniquePtr<StreamBufferSink>&& aSink) {
+  return MakeRefPtr<FixedBufferOutputStream>(std::move(aSink));
+}
+
+nsDependentCSubstring FixedBufferOutputStream::WrittenData() {
+  MutexAutoLock autoLock(mMutex);
+
+  return mSink->Slice(mOffset);
+}
+
+NS_IMPL_ISUPPORTS(FixedBufferOutputStream, nsIOutputStream)
+
+NS_IMETHODIMP
+FixedBufferOutputStream::Close() {
+  MutexAutoLock autoLock(mMutex);
+
+  if (mWriting) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  mClosed = true;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+FixedBufferOutputStream::Flush() { return NS_OK; }
+
+NS_IMETHODIMP
+FixedBufferOutputStream::StreamStatus() {
+  MutexAutoLock autoLock(mMutex);
+  return mClosed ? NS_BASE_STREAM_CLOSED : NS_OK;
+}
+
+NS_IMETHODIMP
+FixedBufferOutputStream::Write(const char* aBuf, uint32_t aCount,
+                               uint32_t* _retval) {
+  return WriteSegments(NS_CopyBufferToSegment, const_cast<char*>(aBuf), aCount,
+                       _retval);
+}
+
+NS_IMETHODIMP
+FixedBufferOutputStream::WriteFrom(nsIInputStream* aFromStream, uint32_t aCount,
+                                   uint32_t* _retval) {
+  return WriteSegments(NS_CopyStreamToSegment, aFromStream, aCount, _retval);
+}
+
+NS_IMETHODIMP
+FixedBufferOutputStream::WriteSegments(nsReadSegmentFun aReader, void* aClosure,
+                                       uint32_t aCount, uint32_t* _retval) {
+  MOZ_ASSERT(_retval);
+
+  MutexAutoLock autoLock(mMutex);
+
+  if (mWriting) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  if (mClosed) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  size_t length = mSink->Data().Length();
+  size_t offset = mOffset;
+
+  MOZ_ASSERT(length >= offset, "Bad stream state!");
+
+  size_t maxCount = length - offset;
+  if (maxCount == 0) {
+    *_retval = 0;
+    return NS_OK;
+  }
+
+  if (aCount > maxCount) {
+    aCount = maxCount;
+  }
+
+  mWriting = true;
+
+  nsresult rv;
+
+  {
+    MutexAutoUnlock autoUnlock(mMutex);
+
+    rv = aReader(this, aClosure, mSink->Data().Elements() + offset, 0, aCount,
+                 _retval);
+  }
+
+  mWriting = false;
+
+  if (NS_SUCCEEDED(rv)) {
+    MOZ_ASSERT(*_retval <= aCount,
+               "Reader should not read more than we asked it to read!");
+    mOffset += *_retval;
+  }
+
+  // As defined in nsIOutputStream.idl, do not pass reader func errors.
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+FixedBufferOutputStream::IsNonBlocking(bool* _retval) {
+  *_retval = true;
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/io/FixedBufferOutputStream.h b/xpcom/io/FixedBufferOutputStream.h
new file mode 100644
index 0000000000..db7fba3c3a
--- /dev/null
+++ b/xpcom/io/FixedBufferOutputStream.h
@@ -0,0 +1,78 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_FixedBufferOutputStream_h
+#define mozilla_FixedBufferOutputStream_h
+
+#include <cstddef>
+#include "mozilla/fallible.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/Span.h"
+#include "mozilla/UniquePtr.h"
+#include "nsIOutputStream.h"
+#include "nsStringFwd.h"
+
+template <class T>
+class RefPtr;
+
+namespace mozilla {
+
+class StreamBufferSink;
+
+// An output stream so you can read your potentially-async input stream into
+// a contiguous buffer using NS_AsyncCopy. Back when streams were more
+// synchronous and people didn't know blocking I/O was bad, if you wanted to
+// read a stream into a flat buffer, you could use NS_ReadInputStreamToString
+// or NS_ReadInputStreamToBuffer.  But those don't work with async streams.
+// This can be used to replace hand-rolled Read/AsyncWait() loops.  Because you
+// specify the expected size up front, the buffer is pre-allocated so wasteful
+// reallocations can be avoided.
+class FixedBufferOutputStream final : public nsIOutputStream {
+  template <typename T, typename... Args>
+  friend RefPtr<T> MakeRefPtr(Args&&... aArgs);
+
+ public:
+  // Factory method to get a FixedBufferOutputStream by allocating a char buffer
+  // with the given length.
+  static RefPtr<FixedBufferOutputStream> Create(size_t aLength);
+
+  // Factory method to get a FixedBufferOutputStream by allocating a char buffer
+  // with the given length, fallible version.
+  static RefPtr<FixedBufferOutputStream> Create(size_t aLength,
+                                                const mozilla::fallible_t&);
+
+  // Factory method to get a FixedBufferOutputStream from a preallocated char
+  // buffer. The output stream doesn't take ownership of the char buffer, so the
+  // char buffer must outlive the output stream (to avoid a use-after-free).
+  static RefPtr<FixedBufferOutputStream> Create(mozilla::Span<char> aBuffer);
+
+  // Factory method to get a FixedBufferOutputStream from an arbitrary
+  // StreamBufferSink.
+  static RefPtr<FixedBufferOutputStream> Create(
+      UniquePtr<StreamBufferSink>&& aSink);
+
+  nsDependentCSubstring WrittenData();
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIOUTPUTSTREAM
+
+ private:
+  explicit FixedBufferOutputStream(UniquePtr<StreamBufferSink>&& aSink);
+
+  ~FixedBufferOutputStream() = default;
+
+  const UniquePtr<StreamBufferSink> mSink;
+
+  Mutex mMutex;
+
+  size_t mOffset MOZ_GUARDED_BY(mMutex);
+  bool mWriting MOZ_GUARDED_BY(mMutex);
+  bool mClosed MOZ_GUARDED_BY(mMutex);
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_FixedBufferOutputStream_h
diff --git a/xpcom/io/InputStreamLengthHelper.cpp b/xpcom/io/InputStreamLengthHelper.cpp
new file mode 100644
index 0000000000..9a767f9229
--- /dev/null
+++ b/xpcom/io/InputStreamLengthHelper.cpp
@@ -0,0 +1,258 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "InputStreamLengthHelper.h"
+#include "mozilla/dom/WorkerCommon.h"
+#include "nsIAsyncInputStream.h"
+#include "nsIInputStream.h"
+#include "nsNetCID.h"
+#include "nsServiceManagerUtils.h"
+
+namespace mozilla {
+
+namespace {
+
+class AvailableEvent final : public Runnable {
+ public:
+  AvailableEvent(nsIInputStream* stream,
+                 const std::function<void(int64_t aLength)>& aCallback)
+      : Runnable("mozilla::AvailableEvent"),
+        mStream(stream),
+        mCallback(aCallback),
+        mSize(-1) {
+    mCallbackTarget = GetCurrentSerialEventTarget();
+    MOZ_ASSERT(NS_IsMainThread());
+  }
+
+  NS_IMETHOD
+  Run() override {
+    // ping
+    if (!NS_IsMainThread()) {
+      uint64_t size = 0;
+      if (NS_WARN_IF(NS_FAILED(mStream->Available(&size)))) {
+        mSize = -1;
+      } else {
+        mSize = (int64_t)size;
+      }
+
+      mStream = nullptr;
+
+      nsCOMPtr<nsIRunnable> self(this);  // overly cute
+      mCallbackTarget->Dispatch(self.forget(), NS_DISPATCH_NORMAL);
+      mCallbackTarget = nullptr;
+      return NS_OK;
+    }
+
+    // pong
+    std::function<void(int64_t aLength)> callback;
+    callback.swap(mCallback);
+    callback(mSize);
+    return NS_OK;
+  }
+
+ private:
+  nsCOMPtr<nsIInputStream> mStream;
+  std::function<void(int64_t aLength)> mCallback;
+  nsCOMPtr<nsIEventTarget> mCallbackTarget;
+
+  int64_t mSize;
+};
+
+}  // namespace
+
+/* static */
+bool InputStreamLengthHelper::GetSyncLength(nsIInputStream* aStream,
+                                            int64_t* aLength) {
+  MOZ_ASSERT(aStream);
+  MOZ_ASSERT(aLength);
+
+  *aLength = -1;
+
+  // Sync length access.
+  nsCOMPtr<nsIInputStreamLength> streamLength = do_QueryInterface(aStream);
+  if (streamLength) {
+    int64_t length = -1;
+    nsresult rv = streamLength->Length(&length);
+
+    // All good!
+    if (NS_SUCCEEDED(rv)) {
+      *aLength = length;
+      return true;
+    }
+
+    // Already closed stream or an error occurred.
+    if (rv == NS_BASE_STREAM_CLOSED ||
+        NS_WARN_IF(rv == NS_ERROR_NOT_AVAILABLE) ||
+        NS_WARN_IF(rv != NS_BASE_STREAM_WOULD_BLOCK)) {
+      return true;
+    }
+  }
+
+  nsCOMPtr<nsIAsyncInputStreamLength> asyncStreamLength =
+      do_QueryInterface(aStream);
+  if (asyncStreamLength) {
+    // GetAsyncLength should be used.
+    return false;
+  }
+
+  // We cannot calculate the length of an async stream.
+  nsCOMPtr<nsIAsyncInputStream> asyncStream = do_QueryInterface(aStream);
+  if (asyncStream) {
+    return false;
+  }
+
+  // For main-thread only, we want to avoid calling ::Available() for blocking
+  // streams.
+  if (NS_IsMainThread()) {
+    bool nonBlocking = false;
+    if (NS_WARN_IF(NS_FAILED(aStream->IsNonBlocking(&nonBlocking)))) {
+      // Let's return -1. There is nothing else we can do here.
+      return true;
+    }
+
+    if (!nonBlocking) {
+      return false;
+    }
+  }
+
+  // Fallback using available().
+  uint64_t available = 0;
+  nsresult rv = aStream->Available(&available);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    // Let's return -1. There is nothing else we can do here.
+    return true;
+  }
+
+  *aLength = (int64_t)available;
+  return true;
+}
+
+/* static */
+void InputStreamLengthHelper::GetAsyncLength(
+    nsIInputStream* aStream,
+    const std::function<void(int64_t aLength)>& aCallback) {
+  MOZ_ASSERT(aStream);
+  MOZ_ASSERT(aCallback);
+
+  // We don't want to allow this class to be used on workers because we are not
+  // using the correct Runnable types.
+  MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread() ||
+                        !dom::IsCurrentThreadRunningWorker());
+
+  RefPtr<InputStreamLengthHelper> helper =
+      new InputStreamLengthHelper(aStream, aCallback);
+
+  // Let's be sure that we don't call ::Available() on main-thread.
+  if (NS_IsMainThread()) {
+    nsCOMPtr<nsIInputStreamLength> streamLength = do_QueryInterface(aStream);
+    nsCOMPtr<nsIAsyncInputStreamLength> asyncStreamLength =
+        do_QueryInterface(aStream);
+    if (!streamLength && !asyncStreamLength) {
+      // We cannot calculate the length of an async stream. We must fix the
+      // caller if this happens.
+#ifdef DEBUG
+      nsCOMPtr<nsIAsyncInputStream> asyncStream = do_QueryInterface(aStream);
+      MOZ_DIAGNOSTIC_ASSERT(!asyncStream);
+#endif
+
+      bool nonBlocking = false;
+      if (NS_SUCCEEDED(aStream->IsNonBlocking(&nonBlocking)) && !nonBlocking) {
+        nsCOMPtr<nsIEventTarget> target =
+            do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID);
+        MOZ_ASSERT(target);
+
+        RefPtr<AvailableEvent> event = new AvailableEvent(aStream, aCallback);
+        target->Dispatch(event.forget(), NS_DISPATCH_NORMAL);
+        return;
+      }
+    }
+  }
+
+  // Let's go async in order to have similar behaviors for sync and async
+  // nsIInputStreamLength implementations.
+  GetCurrentSerialEventTarget()->Dispatch(helper, NS_DISPATCH_NORMAL);
+}
+
+InputStreamLengthHelper::InputStreamLengthHelper(
+    nsIInputStream* aStream,
+    const std::function<void(int64_t aLength)>& aCallback)
+    : Runnable("InputStreamLengthHelper"),
+      mStream(aStream),
+      mCallback(aCallback) {
+  MOZ_ASSERT(aStream);
+  MOZ_ASSERT(aCallback);
+}
+
+InputStreamLengthHelper::~InputStreamLengthHelper() = default;
+
+NS_IMETHODIMP
+InputStreamLengthHelper::Run() {
+  // Sync length access.
+  nsCOMPtr<nsIInputStreamLength> streamLength = do_QueryInterface(mStream);
+  if (streamLength) {
+    int64_t length = -1;
+    nsresult rv = streamLength->Length(&length);
+
+    // All good!
+    if (NS_SUCCEEDED(rv)) {
+      ExecCallback(length);
+      return NS_OK;
+    }
+
+    // Already closed stream or an error occurred.
+    if (rv == NS_BASE_STREAM_CLOSED ||
+        NS_WARN_IF(rv == NS_ERROR_NOT_AVAILABLE) ||
+        NS_WARN_IF(rv != NS_BASE_STREAM_WOULD_BLOCK)) {
+      ExecCallback(-1);
+      return NS_OK;
+    }
+  }
+
+  // Async length access.
+  nsCOMPtr<nsIAsyncInputStreamLength> asyncStreamLength =
+      do_QueryInterface(mStream);
+  if (asyncStreamLength) {
+    nsresult rv =
+        asyncStreamLength->AsyncLengthWait(this, GetCurrentSerialEventTarget());
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      ExecCallback(-1);
+    }
+
+    return NS_OK;
+  }
+
+  // Fallback using available().
+  uint64_t available = 0;
+  nsresult rv = mStream->Available(&available);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    ExecCallback(-1);
+    return NS_OK;
+  }
+
+  ExecCallback((int64_t)available);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+InputStreamLengthHelper::OnInputStreamLengthReady(
+    nsIAsyncInputStreamLength* aStream, int64_t aLength) {
+  ExecCallback(aLength);
+  return NS_OK;
+}
+
+void InputStreamLengthHelper::ExecCallback(int64_t aLength) {
+  MOZ_ASSERT(mCallback);
+
+  std::function<void(int64_t aLength)> callback;
+  callback.swap(mCallback);
+
+  callback(aLength);
+}
+
+NS_IMPL_ISUPPORTS_INHERITED(InputStreamLengthHelper, Runnable,
+                            nsIInputStreamLengthCallback)
+
+}  // namespace mozilla
diff --git a/xpcom/io/InputStreamLengthHelper.h b/xpcom/io/InputStreamLengthHelper.h
new file mode 100644
index 0000000000..1f44c70fe3
--- /dev/null
+++ b/xpcom/io/InputStreamLengthHelper.h
@@ -0,0 +1,57 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_InputStreamLengthHelper_h
+#define mozilla_InputStreamLengthHelper_h
+
+#include <functional>
+
+#include "nsISupportsImpl.h"
+#include "nsIInputStreamLength.h"
+#include "nsThreadUtils.h"
+
+class nsIInputStream;
+
+namespace mozilla {
+
+// This class helps to retrieve the stream's length.
+
+class InputStreamLengthHelper final : public Runnable,
+                                      public nsIInputStreamLengthCallback {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+
+  // This is one of the 2 entry points of this class. It returns false if the
+  // length cannot be taken synchronously.
+  static bool GetSyncLength(nsIInputStream* aStream, int64_t* aLength);
+
+  // This is one of the 2 entry points of this class. The callback is executed
+  // asynchronously when the length is known.
+  static void GetAsyncLength(
+      nsIInputStream* aStream,
+      const std::function<void(int64_t aLength)>& aCallback);
+
+ private:
+  NS_DECL_NSIINPUTSTREAMLENGTHCALLBACK
+
+  InputStreamLengthHelper(
+      nsIInputStream* aStream,
+      const std::function<void(int64_t aLength)>& aCallback);
+
+  ~InputStreamLengthHelper();
+
+  NS_IMETHOD
+  Run() override;
+
+  void ExecCallback(int64_t aLength);
+
+  nsCOMPtr<nsIInputStream> mStream;
+  std::function<void(int64_t aLength)> mCallback;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_InputStreamLengthHelper_h
diff --git a/xpcom/io/InputStreamLengthWrapper.cpp b/xpcom/io/InputStreamLengthWrapper.cpp
new file mode 100644
index 0000000000..9ba4968ad2
--- /dev/null
+++ b/xpcom/io/InputStreamLengthWrapper.cpp
@@ -0,0 +1,345 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "InputStreamLengthWrapper.h"
+#include "mozilla/ipc/InputStreamUtils.h"
+#include "nsISeekableStream.h"
+#include "nsStreamUtils.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+NS_IMPL_ADDREF(InputStreamLengthWrapper);
+NS_IMPL_RELEASE(InputStreamLengthWrapper);
+
+NS_INTERFACE_MAP_BEGIN(InputStreamLengthWrapper)
+  NS_INTERFACE_MAP_ENTRY(nsIInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsICloneableInputStream,
+                                     mWeakCloneableInputStream || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(
+      nsIIPCSerializableInputStream,
+      mWeakIPCSerializableInputStream || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsISeekableStream,
+                                     mWeakSeekableInputStream || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsITellableStream,
+                                     mWeakTellableInputStream || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIAsyncInputStream,
+                                     mWeakAsyncInputStream || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIInputStreamCallback,
+                                     mWeakAsyncInputStream || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY(nsIInputStreamLength)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIInputStream)
+NS_INTERFACE_MAP_END
+
+/* static */
+already_AddRefed<nsIInputStream> InputStreamLengthWrapper::MaybeWrap(
+    already_AddRefed<nsIInputStream> aInputStream, int64_t aLength) {
+  nsCOMPtr<nsIInputStream> inputStream = std::move(aInputStream);
+  MOZ_ASSERT(inputStream);
+
+  nsCOMPtr<nsIInputStreamLength> length = do_QueryInterface(inputStream);
+  if (length) {
+    return inputStream.forget();
+  }
+
+  nsCOMPtr<nsIAsyncInputStreamLength> asyncLength =
+      do_QueryInterface(inputStream);
+  if (asyncLength) {
+    return inputStream.forget();
+  }
+
+  nsCOMPtr<nsIAsyncInputStream> asyncStream = do_QueryInterface(inputStream);
+  if (!asyncStream) {
+    return inputStream.forget();
+  }
+
+  inputStream = new InputStreamLengthWrapper(inputStream.forget(), aLength);
+  return inputStream.forget();
+}
+
+InputStreamLengthWrapper::InputStreamLengthWrapper(
+    already_AddRefed<nsIInputStream> aInputStream, int64_t aLength)
+    : mWeakCloneableInputStream(nullptr),
+      mWeakIPCSerializableInputStream(nullptr),
+      mWeakSeekableInputStream(nullptr),
+      mWeakTellableInputStream(nullptr),
+      mWeakAsyncInputStream(nullptr),
+      mLength(aLength),
+      mConsumed(false),
+      mMutex("InputStreamLengthWrapper::mMutex") {
+  MOZ_ASSERT(mLength >= 0);
+
+  nsCOMPtr<nsIInputStream> inputStream = std::move(aInputStream);
+  SetSourceStream(inputStream.forget());
+}
+
+InputStreamLengthWrapper::InputStreamLengthWrapper()
+    : mWeakCloneableInputStream(nullptr),
+      mWeakIPCSerializableInputStream(nullptr),
+      mWeakSeekableInputStream(nullptr),
+      mWeakTellableInputStream(nullptr),
+      mWeakAsyncInputStream(nullptr),
+      mLength(-1),
+      mConsumed(false),
+      mMutex("InputStreamLengthWrapper::mMutex") {}
+
+InputStreamLengthWrapper::~InputStreamLengthWrapper() = default;
+
+void InputStreamLengthWrapper::SetSourceStream(
+    already_AddRefed<nsIInputStream> aInputStream) {
+  MOZ_ASSERT(!mInputStream);
+
+  mInputStream = std::move(aInputStream);
+
+  nsCOMPtr<nsICloneableInputStream> cloneableStream =
+      do_QueryInterface(mInputStream);
+  if (cloneableStream && SameCOMIdentity(mInputStream, cloneableStream)) {
+    mWeakCloneableInputStream = cloneableStream;
+  }
+
+  nsCOMPtr<nsIIPCSerializableInputStream> serializableStream =
+      do_QueryInterface(mInputStream);
+  if (serializableStream && SameCOMIdentity(mInputStream, serializableStream)) {
+    mWeakIPCSerializableInputStream = serializableStream;
+  }
+
+  nsCOMPtr<nsISeekableStream> seekableStream = do_QueryInterface(mInputStream);
+  if (seekableStream && SameCOMIdentity(mInputStream, seekableStream)) {
+    mWeakSeekableInputStream = seekableStream;
+  }
+
+  nsCOMPtr<nsITellableStream> tellableStream = do_QueryInterface(mInputStream);
+  if (tellableStream && SameCOMIdentity(mInputStream, tellableStream)) {
+    mWeakTellableInputStream = tellableStream;
+  }
+
+  nsCOMPtr<nsIAsyncInputStream> asyncInputStream =
+      do_QueryInterface(mInputStream);
+  if (asyncInputStream && SameCOMIdentity(mInputStream, asyncInputStream)) {
+    mWeakAsyncInputStream = asyncInputStream;
+  }
+}
+
+// nsIInputStream interface
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::Close() {
+  NS_ENSURE_STATE(mInputStream);
+  return mInputStream->Close();
+}
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::Available(uint64_t* aLength) {
+  NS_ENSURE_STATE(mInputStream);
+  return mInputStream->Available(aLength);
+}
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::StreamStatus() {
+  NS_ENSURE_STATE(mInputStream);
+  return mInputStream->StreamStatus();
+}
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::Read(char* aBuffer, uint32_t aCount,
+                               uint32_t* aReadCount) {
+  NS_ENSURE_STATE(mInputStream);
+  mConsumed = true;
+  return mInputStream->Read(aBuffer, aCount, aReadCount);
+}
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::ReadSegments(nsWriteSegmentFun aWriter,
+                                       void* aClosure, uint32_t aCount,
+                                       uint32_t* aResult) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::IsNonBlocking(bool* aNonBlocking) {
+  NS_ENSURE_STATE(mInputStream);
+  return mInputStream->IsNonBlocking(aNonBlocking);
+}
+
+// nsICloneableInputStream interface
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::GetCloneable(bool* aCloneable) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakCloneableInputStream);
+  mWeakCloneableInputStream->GetCloneable(aCloneable);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::Clone(nsIInputStream** aResult) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakCloneableInputStream);
+
+  nsCOMPtr<nsIInputStream> clonedStream;
+  nsresult rv = mWeakCloneableInputStream->Clone(getter_AddRefs(clonedStream));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsCOMPtr<nsIInputStream> stream =
+      new InputStreamLengthWrapper(clonedStream.forget(), mLength);
+
+  stream.forget(aResult);
+  return NS_OK;
+}
+
+// nsIAsyncInputStream interface
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::CloseWithStatus(nsresult aStatus) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakAsyncInputStream);
+
+  mConsumed = true;
+  return mWeakAsyncInputStream->CloseWithStatus(aStatus);
+}
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::AsyncWait(nsIInputStreamCallback* aCallback,
+                                    uint32_t aFlags, uint32_t aRequestedCount,
+                                    nsIEventTarget* aEventTarget) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakAsyncInputStream);
+
+  nsCOMPtr<nsIInputStreamCallback> callback = aCallback ? this : nullptr;
+  {
+    MutexAutoLock lock(mMutex);
+
+    if (NS_WARN_IF(mAsyncWaitCallback && aCallback &&
+                   mAsyncWaitCallback != aCallback)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    mAsyncWaitCallback = aCallback;
+  }
+
+  return mWeakAsyncInputStream->AsyncWait(callback, aFlags, aRequestedCount,
+                                          aEventTarget);
+}
+
+// nsIInputStreamCallback
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::OnInputStreamReady(nsIAsyncInputStream* aStream) {
+  MOZ_ASSERT(mInputStream);
+  MOZ_ASSERT(mWeakAsyncInputStream);
+  MOZ_ASSERT(mWeakAsyncInputStream == aStream);
+
+  nsCOMPtr<nsIInputStreamCallback> callback;
+  {
+    MutexAutoLock lock(mMutex);
+    // We have been canceled in the meanwhile.
+    if (!mAsyncWaitCallback) {
+      return NS_OK;
+    }
+
+    callback.swap(mAsyncWaitCallback);
+  }
+
+  MOZ_ASSERT(callback);
+  return callback->OnInputStreamReady(this);
+}
+
+// nsIIPCSerializableInputStream
+
+void InputStreamLengthWrapper::SerializedComplexity(uint32_t aMaxSize,
+                                                    uint32_t* aSizeUsed,
+                                                    uint32_t* aPipes,
+                                                    uint32_t* aTransferables) {
+  InputStreamHelper::SerializedComplexity(mInputStream, aMaxSize, aSizeUsed,
+                                          aPipes, aTransferables);
+}
+
+void InputStreamLengthWrapper::Serialize(
+    mozilla::ipc::InputStreamParams& aParams, uint32_t aMaxSize,
+    uint32_t* aSizeUsed) {
+  MOZ_ASSERT(mInputStream);
+  MOZ_ASSERT(mWeakIPCSerializableInputStream);
+
+  InputStreamLengthWrapperParams params;
+  InputStreamHelper::SerializeInputStream(mInputStream, params.stream(),
+                                          aMaxSize, aSizeUsed);
+  params.length() = mLength;
+  params.consumed() = mConsumed;
+
+  aParams = params;
+}
+
+bool InputStreamLengthWrapper::Deserialize(
+    const mozilla::ipc::InputStreamParams& aParams) {
+  MOZ_ASSERT(!mInputStream);
+  MOZ_ASSERT(!mWeakIPCSerializableInputStream);
+
+  if (aParams.type() != InputStreamParams::TInputStreamLengthWrapperParams) {
+    NS_ERROR("Received unknown parameters from the other process!");
+    return false;
+  }
+
+  const InputStreamLengthWrapperParams& params =
+      aParams.get_InputStreamLengthWrapperParams();
+
+  nsCOMPtr<nsIInputStream> stream =
+      InputStreamHelper::DeserializeInputStream(params.stream());
+  if (!stream) {
+    NS_WARNING("Deserialize failed!");
+    return false;
+  }
+
+  SetSourceStream(stream.forget());
+
+  mLength = params.length();
+  mConsumed = params.consumed();
+
+  return true;
+}
+
+// nsISeekableStream
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::Seek(int32_t aWhence, int64_t aOffset) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakSeekableInputStream);
+
+  mConsumed = true;
+  return mWeakSeekableInputStream->Seek(aWhence, aOffset);
+}
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::SetEOF() {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakSeekableInputStream);
+
+  mConsumed = true;
+  return mWeakSeekableInputStream->SetEOF();
+}
+
+// nsITellableStream
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::Tell(int64_t* aResult) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakTellableInputStream);
+
+  return mWeakTellableInputStream->Tell(aResult);
+}
+
+// nsIInputStreamLength
+
+NS_IMETHODIMP
+InputStreamLengthWrapper::Length(int64_t* aLength) {
+  NS_ENSURE_STATE(mInputStream);
+  *aLength = mLength;
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/io/InputStreamLengthWrapper.h b/xpcom/io/InputStreamLengthWrapper.h
new file mode 100644
index 0000000000..a11a808fa7
--- /dev/null
+++ b/xpcom/io/InputStreamLengthWrapper.h
@@ -0,0 +1,84 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef InputStreamLengthWrapper_h
+#define InputStreamLengthWrapper_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Mutex.h"
+#include "nsCOMPtr.h"
+#include "nsIAsyncInputStream.h"
+#include "nsICloneableInputStream.h"
+#include "nsIIPCSerializableInputStream.h"
+#include "nsISeekableStream.h"
+#include "nsIInputStreamLength.h"
+
+namespace mozilla {
+
+// A wrapper keeps an inputStream together with its length.
+// This class can be used for nsIInputStreams that do not implement
+// nsIInputStreamLength.
+
+class InputStreamLengthWrapper final : public nsIAsyncInputStream,
+                                       public nsICloneableInputStream,
+                                       public nsIIPCSerializableInputStream,
+                                       public nsISeekableStream,
+                                       public nsIInputStreamCallback,
+                                       public nsIInputStreamLength {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINPUTSTREAM
+  NS_DECL_NSIASYNCINPUTSTREAM
+  NS_DECL_NSICLONEABLEINPUTSTREAM
+  NS_DECL_NSIIPCSERIALIZABLEINPUTSTREAM
+  NS_DECL_NSISEEKABLESTREAM
+  NS_DECL_NSITELLABLESTREAM
+  NS_DECL_NSIINPUTSTREAMCALLBACK
+  NS_DECL_NSIINPUTSTREAMLENGTH
+
+  // This method creates a InputStreamLengthWrapper around aInputStream if
+  // this doesn't implement nsIInputStreamLength or
+  // nsIInputStreamAsyncLength interface, but it implements
+  // nsIAsyncInputStream. For this kind of streams,
+  // InputStreamLengthHelper is not able to retrieve the length. This
+  // method will make such streams ready to be used with
+  // InputStreamLengthHelper.
+  static already_AddRefed<nsIInputStream> MaybeWrap(
+      already_AddRefed<nsIInputStream> aInputStream, int64_t aLength);
+
+  // The length here will be used when nsIInputStreamLength::Length() is called.
+  InputStreamLengthWrapper(already_AddRefed<nsIInputStream> aInputStream,
+                           int64_t aLength);
+
+  // This CTOR is meant to be used just for IPC.
+  InputStreamLengthWrapper();
+
+ private:
+  ~InputStreamLengthWrapper();
+
+  void SetSourceStream(already_AddRefed<nsIInputStream> aInputStream);
+
+  nsCOMPtr<nsIInputStream> mInputStream;
+
+  // Raw pointers because these are just QI of mInputStream.
+  nsICloneableInputStream* mWeakCloneableInputStream;
+  nsIIPCSerializableInputStream* mWeakIPCSerializableInputStream;
+  nsISeekableStream* mWeakSeekableInputStream;
+  nsITellableStream* mWeakTellableInputStream;
+  nsIAsyncInputStream* mWeakAsyncInputStream;
+
+  int64_t mLength;
+  bool mConsumed;
+
+  mozilla::Mutex mMutex;
+
+  // This is used for AsyncWait and it's protected by mutex.
+  nsCOMPtr<nsIInputStreamCallback> mAsyncWaitCallback MOZ_GUARDED_BY(mMutex);
+};
+
+}  // namespace mozilla
+
+#endif  // InputStreamLengthWrapper_h
diff --git a/xpcom/io/NonBlockingAsyncInputStream.cpp b/xpcom/io/NonBlockingAsyncInputStream.cpp
new file mode 100644
index 0000000000..00e8598d86
--- /dev/null
+++ b/xpcom/io/NonBlockingAsyncInputStream.cpp
@@ -0,0 +1,388 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "NonBlockingAsyncInputStream.h"
+#include "mozilla/ipc/InputStreamUtils.h"
+#include "nsIAsyncInputStream.h"
+#include "nsICloneableInputStream.h"
+#include "nsIInputStream.h"
+#include "nsIIPCSerializableInputStream.h"
+#include "nsISeekableStream.h"
+#include "nsStreamUtils.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+class NonBlockingAsyncInputStream::AsyncWaitRunnable final
+    : public CancelableRunnable {
+  RefPtr<NonBlockingAsyncInputStream> mStream;
+  nsCOMPtr<nsIInputStreamCallback> mCallback;
+
+ public:
+  AsyncWaitRunnable(NonBlockingAsyncInputStream* aStream,
+                    nsIInputStreamCallback* aCallback)
+      : CancelableRunnable("AsyncWaitRunnable"),
+        mStream(aStream),
+        mCallback(aCallback) {}
+
+  NS_IMETHOD
+  Run() override {
+    mStream->RunAsyncWaitCallback(this, mCallback.forget());
+    return NS_OK;
+  }
+
+  nsresult Cancel() override {
+    mStream = nullptr;
+    return NS_OK;
+  }
+};
+
+NS_IMPL_ADDREF(NonBlockingAsyncInputStream);
+NS_IMPL_RELEASE(NonBlockingAsyncInputStream);
+
+NonBlockingAsyncInputStream::WaitClosureOnly::WaitClosureOnly(
+    AsyncWaitRunnable* aRunnable, nsIEventTarget* aEventTarget)
+    : mRunnable(aRunnable), mEventTarget(aEventTarget) {}
+
+NS_INTERFACE_MAP_BEGIN(NonBlockingAsyncInputStream)
+  NS_INTERFACE_MAP_ENTRY(nsIInputStream)
+  NS_INTERFACE_MAP_ENTRY(nsIAsyncInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsICloneableInputStream,
+                                     mWeakCloneableInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIIPCSerializableInputStream,
+                                     mWeakIPCSerializableInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsISeekableStream,
+                                     mWeakSeekableInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsITellableStream,
+                                     mWeakTellableInputStream)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIInputStream)
+NS_INTERFACE_MAP_END
+
+/* static */
+nsresult NonBlockingAsyncInputStream::Create(
+    already_AddRefed<nsIInputStream> aInputStream,
+    nsIAsyncInputStream** aResult) {
+  MOZ_DIAGNOSTIC_ASSERT(aResult);
+
+  nsCOMPtr<nsIInputStream> inputStream = std::move(aInputStream);
+
+  bool nonBlocking = false;
+  nsresult rv = inputStream->IsNonBlocking(&nonBlocking);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  MOZ_DIAGNOSTIC_ASSERT(nonBlocking);
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+  nsCOMPtr<nsIAsyncInputStream> asyncInputStream =
+      do_QueryInterface(inputStream);
+  MOZ_DIAGNOSTIC_ASSERT(!asyncInputStream);
+#endif  // MOZ_DIAGNOSTIC_ASSERT_ENABLED
+
+  RefPtr<NonBlockingAsyncInputStream> stream =
+      new NonBlockingAsyncInputStream(inputStream.forget());
+
+  stream.forget(aResult);
+  return NS_OK;
+}
+
+NonBlockingAsyncInputStream::NonBlockingAsyncInputStream(
+    already_AddRefed<nsIInputStream> aInputStream)
+    : mInputStream(std::move(aInputStream)),
+      mWeakCloneableInputStream(nullptr),
+      mWeakIPCSerializableInputStream(nullptr),
+      mWeakSeekableInputStream(nullptr),
+      mWeakTellableInputStream(nullptr),
+      mLock("NonBlockingAsyncInputStream::mLock"),
+      mClosed(false) {
+  MOZ_ASSERT(mInputStream);
+
+  nsCOMPtr<nsICloneableInputStream> cloneableStream =
+      do_QueryInterface(mInputStream);
+  if (cloneableStream && SameCOMIdentity(mInputStream, cloneableStream)) {
+    mWeakCloneableInputStream = cloneableStream;
+  }
+
+  nsCOMPtr<nsIIPCSerializableInputStream> serializableStream =
+      do_QueryInterface(mInputStream);
+  if (serializableStream && SameCOMIdentity(mInputStream, serializableStream)) {
+    mWeakIPCSerializableInputStream = serializableStream;
+  }
+
+  nsCOMPtr<nsISeekableStream> seekableStream = do_QueryInterface(mInputStream);
+  if (seekableStream && SameCOMIdentity(mInputStream, seekableStream)) {
+    mWeakSeekableInputStream = seekableStream;
+  }
+
+  nsCOMPtr<nsITellableStream> tellableStream = do_QueryInterface(mInputStream);
+  if (tellableStream && SameCOMIdentity(mInputStream, tellableStream)) {
+    mWeakTellableInputStream = tellableStream;
+  }
+}
+
+NonBlockingAsyncInputStream::~NonBlockingAsyncInputStream() = default;
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::Close() {
+  RefPtr<AsyncWaitRunnable> waitClosureOnlyRunnable;
+  nsCOMPtr<nsIEventTarget> waitClosureOnlyEventTarget;
+
+  {
+    MutexAutoLock lock(mLock);
+
+    if (mClosed) {
+      // Here we could return NS_BASE_STREAM_CLOSED as well, but just to avoid
+      // warning messages, let's make everybody happy with a NS_OK.
+      return NS_OK;
+    }
+
+    mClosed = true;
+
+    NS_ENSURE_STATE(mInputStream);
+    nsresult rv = mInputStream->Close();
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      mWaitClosureOnly.reset();
+      return rv;
+    }
+
+    // If we have a WaitClosureOnly runnable, it's time to use it.
+    if (mWaitClosureOnly.isSome()) {
+      waitClosureOnlyRunnable = std::move(mWaitClosureOnly->mRunnable);
+      waitClosureOnlyEventTarget = std::move(mWaitClosureOnly->mEventTarget);
+
+      mWaitClosureOnly.reset();
+
+      // Now we want to dispatch the asyncWaitCallback.
+      mAsyncWaitCallback = waitClosureOnlyRunnable;
+    }
+  }
+
+  if (waitClosureOnlyRunnable) {
+    if (waitClosureOnlyEventTarget) {
+      waitClosureOnlyEventTarget->Dispatch(waitClosureOnlyRunnable,
+                                           NS_DISPATCH_NORMAL);
+    } else {
+      waitClosureOnlyRunnable->Run();
+    }
+  }
+
+  return NS_OK;
+}
+
+// nsIInputStream interface
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::Available(uint64_t* aLength) {
+  nsresult rv = mInputStream->Available(aLength);
+  // Don't issue warnings for legal condition NS_BASE_STREAM_CLOSED.
+  if (rv == NS_BASE_STREAM_CLOSED || NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // Nothing more to read. Let's close the stream now.
+  if (*aLength == 0) {
+    MutexAutoLock lock(mLock);
+    mInputStream->Close();
+    mClosed = true;
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::StreamStatus() {
+  return mInputStream->StreamStatus();
+}
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::Read(char* aBuffer, uint32_t aCount,
+                                  uint32_t* aReadCount) {
+  return mInputStream->Read(aBuffer, aCount, aReadCount);
+}
+
+namespace {
+
+class MOZ_RAII ReadSegmentsData {
+ public:
+  ReadSegmentsData(NonBlockingAsyncInputStream* aStream,
+                   nsWriteSegmentFun aFunc, void* aClosure)
+      : mStream(aStream), mFunc(aFunc), mClosure(aClosure) {}
+
+  NonBlockingAsyncInputStream* mStream;
+  nsWriteSegmentFun mFunc;
+  void* mClosure;
+};
+
+nsresult ReadSegmentsWriter(nsIInputStream* aInStream, void* aClosure,
+                            const char* aFromSegment, uint32_t aToOffset,
+                            uint32_t aCount, uint32_t* aWriteCount) {
+  ReadSegmentsData* data = static_cast<ReadSegmentsData*>(aClosure);
+  return data->mFunc(data->mStream, data->mClosure, aFromSegment, aToOffset,
+                     aCount, aWriteCount);
+}
+
+}  // namespace
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::ReadSegments(nsWriteSegmentFun aWriter,
+                                          void* aClosure, uint32_t aCount,
+                                          uint32_t* aResult) {
+  ReadSegmentsData data(this, aWriter, aClosure);
+  return mInputStream->ReadSegments(ReadSegmentsWriter, &data, aCount, aResult);
+}
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::IsNonBlocking(bool* aNonBlocking) {
+  *aNonBlocking = true;
+  return NS_OK;
+}
+
+// nsICloneableInputStream interface
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::GetCloneable(bool* aCloneable) {
+  NS_ENSURE_STATE(mWeakCloneableInputStream);
+  return mWeakCloneableInputStream->GetCloneable(aCloneable);
+}
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::Clone(nsIInputStream** aResult) {
+  NS_ENSURE_STATE(mWeakCloneableInputStream);
+
+  nsCOMPtr<nsIInputStream> clonedStream;
+  nsresult rv = mWeakCloneableInputStream->Clone(getter_AddRefs(clonedStream));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsCOMPtr<nsIAsyncInputStream> asyncStream;
+  rv = Create(clonedStream.forget(), getter_AddRefs(asyncStream));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  asyncStream.forget(aResult);
+  return NS_OK;
+}
+
+// nsIAsyncInputStream interface
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::CloseWithStatus(nsresult aStatus) {
+  return Close();
+}
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::AsyncWait(nsIInputStreamCallback* aCallback,
+                                       uint32_t aFlags,
+                                       uint32_t aRequestedCount,
+                                       nsIEventTarget* aEventTarget) {
+  RefPtr<AsyncWaitRunnable> runnable;
+  {
+    MutexAutoLock lock(mLock);
+
+    mWaitClosureOnly.reset();
+    mAsyncWaitCallback = nullptr;
+
+    if (!aCallback) {
+      // Canceling previous callbacks, which is done above.
+      return NS_OK;
+    }
+
+    // Maybe the stream is already closed.
+    if (!mClosed) {
+      uint64_t length;
+      nsresult rv = mInputStream->Available(&length);
+      if (NS_SUCCEEDED(rv) && length == 0) {
+        mInputStream->Close();
+        mClosed = true;
+      }
+    }
+
+    runnable = new AsyncWaitRunnable(this, aCallback);
+    if ((aFlags & nsIAsyncInputStream::WAIT_CLOSURE_ONLY) && !mClosed) {
+      mWaitClosureOnly.emplace(runnable, aEventTarget);
+      return NS_OK;
+    }
+
+    mAsyncWaitCallback = runnable;
+  }
+
+  MOZ_ASSERT(runnable);
+
+  if (aEventTarget) {
+    return aEventTarget->Dispatch(runnable.forget());
+  }
+
+  return runnable->Run();
+}
+
+// nsIIPCSerializableInputStream
+
+void NonBlockingAsyncInputStream::SerializedComplexity(
+    uint32_t aMaxSize, uint32_t* aSizeUsed, uint32_t* aPipes,
+    uint32_t* aTransferables) {
+  InputStreamHelper::SerializedComplexity(mInputStream, aMaxSize, aSizeUsed,
+                                          aPipes, aTransferables);
+}
+
+void NonBlockingAsyncInputStream::Serialize(
+    mozilla::ipc::InputStreamParams& aParams, uint32_t aMaxSize,
+    uint32_t* aSizeUsed) {
+  MOZ_ASSERT(mWeakIPCSerializableInputStream);
+  InputStreamHelper::SerializeInputStream(mInputStream, aParams, aMaxSize,
+                                          aSizeUsed);
+}
+
+bool NonBlockingAsyncInputStream::Deserialize(
+    const mozilla::ipc::InputStreamParams& aParams) {
+  MOZ_CRASH("NonBlockingAsyncInputStream cannot be deserialized!");
+  return true;
+}
+
+// nsISeekableStream
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::Seek(int32_t aWhence, int64_t aOffset) {
+  NS_ENSURE_STATE(mWeakSeekableInputStream);
+  return mWeakSeekableInputStream->Seek(aWhence, aOffset);
+}
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::SetEOF() {
+  NS_ENSURE_STATE(mWeakSeekableInputStream);
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+// nsITellableStream
+
+NS_IMETHODIMP
+NonBlockingAsyncInputStream::Tell(int64_t* aResult) {
+  NS_ENSURE_STATE(mWeakTellableInputStream);
+  return mWeakTellableInputStream->Tell(aResult);
+}
+
+void NonBlockingAsyncInputStream::RunAsyncWaitCallback(
+    NonBlockingAsyncInputStream::AsyncWaitRunnable* aRunnable,
+    already_AddRefed<nsIInputStreamCallback> aCallback) {
+  nsCOMPtr<nsIInputStreamCallback> callback = std::move(aCallback);
+
+  {
+    MutexAutoLock lock(mLock);
+    if (mAsyncWaitCallback != aRunnable) {
+      // The callback has been canceled in the meantime.
+      return;
+    }
+
+    mAsyncWaitCallback = nullptr;
+  }
+
+  callback->OnInputStreamReady(this);
+}
+
+}  // namespace mozilla
diff --git a/xpcom/io/NonBlockingAsyncInputStream.h b/xpcom/io/NonBlockingAsyncInputStream.h
new file mode 100644
index 0000000000..453ac2eafc
--- /dev/null
+++ b/xpcom/io/NonBlockingAsyncInputStream.h
@@ -0,0 +1,85 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef NonBlockingAsyncInputStream_h
+#define NonBlockingAsyncInputStream_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/Mutex.h"
+#include "nsCOMPtr.h"
+#include "nsIAsyncInputStream.h"
+#include "nsICloneableInputStream.h"
+#include "nsIIPCSerializableInputStream.h"
+#include "nsISeekableStream.h"
+
+// This class aims to wrap a non-blocking and non-async inputStream and expose
+// it as nsIAsyncInputStream.
+// Probably you don't want to use this class directly. Instead use
+// NS_MakeAsyncNonBlockingInputStream() as it will handle different stream
+// variants without requiring you to special-case them yourself.
+
+namespace mozilla {
+
+class NonBlockingAsyncInputStream final : public nsIAsyncInputStream,
+                                          public nsICloneableInputStream,
+                                          public nsIIPCSerializableInputStream,
+                                          public nsISeekableStream {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINPUTSTREAM
+  NS_DECL_NSIASYNCINPUTSTREAM
+  NS_DECL_NSICLONEABLEINPUTSTREAM
+  NS_DECL_NSIIPCSERIALIZABLEINPUTSTREAM
+  NS_DECL_NSISEEKABLESTREAM
+  NS_DECL_NSITELLABLESTREAM
+
+  // |aInputStream| must be a non-blocking, non-async inputSteam.
+  static nsresult Create(already_AddRefed<nsIInputStream> aInputStream,
+                         nsIAsyncInputStream** aAsyncInputStream);
+
+ private:
+  explicit NonBlockingAsyncInputStream(
+      already_AddRefed<nsIInputStream> aInputStream);
+  ~NonBlockingAsyncInputStream();
+
+  class AsyncWaitRunnable;
+
+  void RunAsyncWaitCallback(AsyncWaitRunnable* aRunnable,
+                            already_AddRefed<nsIInputStreamCallback> aCallback);
+
+  nsCOMPtr<nsIInputStream> mInputStream;
+
+  // Raw pointers because these are just QI of mInputStream.
+  nsICloneableInputStream* MOZ_NON_OWNING_REF mWeakCloneableInputStream;
+  nsIIPCSerializableInputStream* MOZ_NON_OWNING_REF
+      mWeakIPCSerializableInputStream;
+  nsISeekableStream* MOZ_NON_OWNING_REF mWeakSeekableInputStream;
+  nsITellableStream* MOZ_NON_OWNING_REF mWeakTellableInputStream;
+
+  Mutex mLock;
+
+  struct WaitClosureOnly {
+    WaitClosureOnly(AsyncWaitRunnable* aRunnable, nsIEventTarget* aEventTarget);
+
+    RefPtr<AsyncWaitRunnable> mRunnable;
+    nsCOMPtr<nsIEventTarget> mEventTarget;
+  };
+
+  // This is set when AsyncWait is called with a callback and with
+  // WAIT_CLOSURE_ONLY as flag.
+  // This is protected by mLock.
+  Maybe<WaitClosureOnly> mWaitClosureOnly MOZ_GUARDED_BY(mLock);
+
+  // This is protected by mLock.
+  RefPtr<AsyncWaitRunnable> mAsyncWaitCallback MOZ_GUARDED_BY(mLock);
+
+  // This is protected by mLock.
+  bool mClosed MOZ_GUARDED_BY(mLock);
+};
+
+}  // namespace mozilla
+
+#endif  // NonBlockingAsyncInputStream_h
diff --git a/xpcom/io/SlicedInputStream.cpp b/xpcom/io/SlicedInputStream.cpp
new file mode 100644
index 0000000000..c64af8e9dd
--- /dev/null
+++ b/xpcom/io/SlicedInputStream.cpp
@@ -0,0 +1,668 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "SlicedInputStream.h"
+#include "mozilla/ipc/InputStreamUtils.h"
+#include "mozilla/CheckedInt.h"
+#include "mozilla/ScopeExit.h"
+#include "nsISeekableStream.h"
+#include "nsStreamUtils.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+NS_IMPL_ADDREF(SlicedInputStream);
+NS_IMPL_RELEASE(SlicedInputStream);
+
+NS_INTERFACE_MAP_BEGIN(SlicedInputStream)
+  NS_INTERFACE_MAP_ENTRY(nsIInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsICloneableInputStream,
+                                     mWeakCloneableInputStream || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(
+      nsIIPCSerializableInputStream,
+      mWeakIPCSerializableInputStream || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsISeekableStream,
+                                     mWeakSeekableInputStream || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsITellableStream,
+                                     mWeakTellableInputStream || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIAsyncInputStream,
+                                     mWeakAsyncInputStream || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIInputStreamCallback,
+                                     mWeakAsyncInputStream || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIInputStreamLength,
+                                     mWeakInputStreamLength || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(
+      nsIAsyncInputStreamLength, mWeakAsyncInputStreamLength || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(
+      nsIInputStreamLengthCallback,
+      mWeakAsyncInputStreamLength || !mInputStream)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIInputStream)
+NS_INTERFACE_MAP_END
+
+SlicedInputStream::SlicedInputStream(
+    already_AddRefed<nsIInputStream> aInputStream, uint64_t aStart,
+    uint64_t aLength)
+    : mWeakCloneableInputStream(nullptr),
+      mWeakIPCSerializableInputStream(nullptr),
+      mWeakSeekableInputStream(nullptr),
+      mWeakTellableInputStream(nullptr),
+      mWeakAsyncInputStream(nullptr),
+      mWeakInputStreamLength(nullptr),
+      mWeakAsyncInputStreamLength(nullptr),
+      mStart(aStart),
+      mLength(aLength),
+      mCurPos(0),
+      mClosed(false),
+      mAsyncWaitFlags(0),
+      mAsyncWaitRequestedCount(0),
+      mMutex("SlicedInputStream::mMutex") {
+  nsCOMPtr<nsIInputStream> inputStream = std::move(aInputStream);
+  SetSourceStream(inputStream.forget());
+}
+
+SlicedInputStream::SlicedInputStream()
+    : mWeakCloneableInputStream(nullptr),
+      mWeakIPCSerializableInputStream(nullptr),
+      mWeakSeekableInputStream(nullptr),
+      mWeakTellableInputStream(nullptr),
+      mWeakAsyncInputStream(nullptr),
+      mWeakInputStreamLength(nullptr),
+      mWeakAsyncInputStreamLength(nullptr),
+      mStart(0),
+      mLength(0),
+      mCurPos(0),
+      mClosed(false),
+      mAsyncWaitFlags(0),
+      mAsyncWaitRequestedCount(0),
+      mMutex("SlicedInputStream::mMutex") {}
+
+SlicedInputStream::~SlicedInputStream() = default;
+
+void SlicedInputStream::SetSourceStream(
+    already_AddRefed<nsIInputStream> aInputStream) {
+  MOZ_ASSERT(!mInputStream);
+
+  mInputStream = std::move(aInputStream);
+
+  nsCOMPtr<nsICloneableInputStream> cloneableStream =
+      do_QueryInterface(mInputStream);
+  if (cloneableStream && SameCOMIdentity(mInputStream, cloneableStream)) {
+    mWeakCloneableInputStream = cloneableStream;
+  }
+
+  nsCOMPtr<nsIIPCSerializableInputStream> serializableStream =
+      do_QueryInterface(mInputStream);
+  if (serializableStream && SameCOMIdentity(mInputStream, serializableStream)) {
+    mWeakIPCSerializableInputStream = serializableStream;
+  }
+
+  nsCOMPtr<nsISeekableStream> seekableStream = do_QueryInterface(mInputStream);
+  if (seekableStream && SameCOMIdentity(mInputStream, seekableStream)) {
+    mWeakSeekableInputStream = seekableStream;
+  }
+
+  nsCOMPtr<nsITellableStream> tellableStream = do_QueryInterface(mInputStream);
+  if (tellableStream && SameCOMIdentity(mInputStream, tellableStream)) {
+    mWeakTellableInputStream = tellableStream;
+  }
+
+  nsCOMPtr<nsIAsyncInputStream> asyncInputStream =
+      do_QueryInterface(mInputStream);
+  if (asyncInputStream && SameCOMIdentity(mInputStream, asyncInputStream)) {
+    mWeakAsyncInputStream = asyncInputStream;
+  }
+
+  nsCOMPtr<nsIInputStreamLength> streamLength = do_QueryInterface(mInputStream);
+  if (streamLength && SameCOMIdentity(mInputStream, streamLength)) {
+    mWeakInputStreamLength = streamLength;
+  }
+
+  nsCOMPtr<nsIAsyncInputStreamLength> asyncStreamLength =
+      do_QueryInterface(mInputStream);
+  if (asyncStreamLength && SameCOMIdentity(mInputStream, asyncStreamLength)) {
+    mWeakAsyncInputStreamLength = asyncStreamLength;
+  }
+}
+
+uint64_t SlicedInputStream::AdjustRange(uint64_t aRange) {
+  CheckedUint64 range(aRange);
+  range += mCurPos;
+
+  // Let's remove extra length from the end.
+  if (range.isValid() && range.value() > mStart + mLength) {
+    aRange -= XPCOM_MIN((uint64_t)aRange, range.value() - (mStart + mLength));
+  }
+
+  // Let's remove extra length from the begin.
+  if (mCurPos < mStart) {
+    aRange -= XPCOM_MIN((uint64_t)aRange, mStart - mCurPos);
+  }
+
+  return aRange;
+}
+
+// nsIInputStream interface
+
+NS_IMETHODIMP
+SlicedInputStream::Close() {
+  NS_ENSURE_STATE(mInputStream);
+
+  mClosed = true;
+  return mInputStream->Close();
+}
+
+NS_IMETHODIMP
+SlicedInputStream::Available(uint64_t* aLength) {
+  NS_ENSURE_STATE(mInputStream);
+
+  if (mClosed) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  nsresult rv = mInputStream->Available(aLength);
+  if (rv == NS_BASE_STREAM_CLOSED) {
+    mClosed = true;
+    return rv;
+  }
+
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  *aLength = AdjustRange(*aLength);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SlicedInputStream::StreamStatus() {
+  NS_ENSURE_STATE(mInputStream);
+
+  if (mClosed) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  nsresult rv = mInputStream->StreamStatus();
+  if (rv == NS_BASE_STREAM_CLOSED) {
+    mClosed = true;
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+SlicedInputStream::Read(char* aBuffer, uint32_t aCount, uint32_t* aReadCount) {
+  *aReadCount = 0;
+
+  if (mClosed) {
+    return NS_OK;
+  }
+
+  if (mCurPos < mStart) {
+    nsCOMPtr<nsISeekableStream> seekableStream =
+        do_QueryInterface(mInputStream);
+    if (seekableStream) {
+      nsresult rv =
+          seekableStream->Seek(nsISeekableStream::NS_SEEK_SET, mStart);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      mCurPos = mStart;
+    } else {
+      char buf[4096];
+      while (mCurPos < mStart) {
+        uint32_t bytesRead;
+        uint64_t bufCount = XPCOM_MIN(mStart - mCurPos, (uint64_t)sizeof(buf));
+        nsresult rv = mInputStream->Read(buf, bufCount, &bytesRead);
+        if (NS_SUCCEEDED(rv) && bytesRead == 0) {
+          mClosed = true;
+          return rv;
+        }
+
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return rv;
+        }
+
+        mCurPos += bytesRead;
+      }
+    }
+  }
+
+  // Let's reduce aCount in case it's too big.
+  if (mCurPos + aCount > mStart + mLength) {
+    aCount = mStart + mLength - mCurPos;
+  }
+
+  // Nothing else to read.
+  if (!aCount) {
+    return NS_OK;
+  }
+
+  nsresult rv = mInputStream->Read(aBuffer, aCount, aReadCount);
+  if (NS_SUCCEEDED(rv) && *aReadCount == 0) {
+    mClosed = true;
+    return rv;
+  }
+
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  mCurPos += *aReadCount;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SlicedInputStream::ReadSegments(nsWriteSegmentFun aWriter, void* aClosure,
+                                uint32_t aCount, uint32_t* aResult) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+SlicedInputStream::IsNonBlocking(bool* aNonBlocking) {
+  NS_ENSURE_STATE(mInputStream);
+  return mInputStream->IsNonBlocking(aNonBlocking);
+}
+
+// nsICloneableInputStream interface
+
+NS_IMETHODIMP
+SlicedInputStream::GetCloneable(bool* aCloneable) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakCloneableInputStream);
+
+  *aCloneable = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SlicedInputStream::Clone(nsIInputStream** aResult) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakCloneableInputStream);
+
+  nsCOMPtr<nsIInputStream> clonedStream;
+  nsresult rv = mWeakCloneableInputStream->Clone(getter_AddRefs(clonedStream));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsCOMPtr<nsIInputStream> sis =
+      new SlicedInputStream(clonedStream.forget(), mStart, mLength);
+
+  sis.forget(aResult);
+  return NS_OK;
+}
+
+// nsIAsyncInputStream interface
+
+NS_IMETHODIMP
+SlicedInputStream::CloseWithStatus(nsresult aStatus) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakAsyncInputStream);
+
+  mClosed = true;
+  return mWeakAsyncInputStream->CloseWithStatus(aStatus);
+}
+
+NS_IMETHODIMP
+SlicedInputStream::AsyncWait(nsIInputStreamCallback* aCallback, uint32_t aFlags,
+                             uint32_t aRequestedCount,
+                             nsIEventTarget* aEventTarget) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakAsyncInputStream);
+
+  nsCOMPtr<nsIInputStreamCallback> callback = aCallback ? this : nullptr;
+
+  uint32_t flags = aFlags;
+  uint32_t requestedCount = aRequestedCount;
+
+  {
+    MutexAutoLock lock(mMutex);
+
+    if (NS_WARN_IF(mAsyncWaitCallback && aCallback &&
+                   mAsyncWaitCallback != aCallback)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    mAsyncWaitCallback = aCallback;
+
+    // If we haven't started retrieving data, let's see if we can seek.
+    // If we cannot seek, we will do consecutive reads.
+    if (mCurPos < mStart && mWeakSeekableInputStream) {
+      nsresult rv = mWeakSeekableInputStream->Seek(
+          nsISeekableStream::NS_SEEK_SET, mStart);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      mCurPos = mStart;
+    }
+
+    mAsyncWaitFlags = aFlags;
+    mAsyncWaitRequestedCount = aRequestedCount;
+    mAsyncWaitEventTarget = aEventTarget;
+
+    // If we are not at the right position, let's do an asyncWait just internal.
+    if (mCurPos < mStart) {
+      flags = 0;
+      requestedCount = mStart - mCurPos;
+    }
+  }
+
+  return mWeakAsyncInputStream->AsyncWait(callback, flags, requestedCount,
+                                          aEventTarget);
+}
+
+// nsIInputStreamCallback
+
+NS_IMETHODIMP
+SlicedInputStream::OnInputStreamReady(nsIAsyncInputStream* aStream) {
+  MOZ_ASSERT(mInputStream);
+  MOZ_ASSERT(mWeakAsyncInputStream);
+  MOZ_ASSERT(mWeakAsyncInputStream == aStream);
+
+  nsCOMPtr<nsIInputStreamCallback> callback;
+  uint32_t asyncWaitFlags = 0;
+  uint32_t asyncWaitRequestedCount = 0;
+  nsCOMPtr<nsIEventTarget> asyncWaitEventTarget;
+
+  {
+    MutexAutoLock lock(mMutex);
+
+    // We have been canceled in the meanwhile.
+    if (!mAsyncWaitCallback) {
+      return NS_OK;
+    }
+
+    auto raii = MakeScopeExit([&] {
+      mMutex.AssertCurrentThreadOwns();
+      mAsyncWaitCallback = nullptr;
+      mAsyncWaitEventTarget = nullptr;
+    });
+
+    asyncWaitFlags = mAsyncWaitFlags;
+    asyncWaitRequestedCount = mAsyncWaitRequestedCount;
+    asyncWaitEventTarget = mAsyncWaitEventTarget;
+
+    // If at the end of this locked block, the callback is not null, it will be
+    // executed, otherwise, we are going to exec another AsyncWait().
+    callback = mAsyncWaitCallback;
+
+    if (mCurPos < mStart) {
+      char buf[4096];
+      nsresult rv = NS_OK;
+      while (mCurPos < mStart) {
+        uint32_t bytesRead;
+        uint64_t bufCount = XPCOM_MIN(mStart - mCurPos, (uint64_t)sizeof(buf));
+        rv = mInputStream->Read(buf, bufCount, &bytesRead);
+        if (NS_SUCCEEDED(rv) && bytesRead == 0) {
+          mClosed = true;
+          break;
+        }
+
+        if (rv == NS_BASE_STREAM_WOULD_BLOCK) {
+          asyncWaitFlags = 0;
+          asyncWaitRequestedCount = mStart - mCurPos;
+          // Here we want to exec another AsyncWait().
+          callback = nullptr;
+          break;
+        }
+
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          break;
+        }
+
+        mCurPos += bytesRead;
+      }
+
+      // Now we are ready to do the 'real' asyncWait.
+      if (mCurPos >= mStart) {
+        // We don't want to nullify the callback now, because it will be needed
+        // at the next ::OnInputStreamReady.
+        raii.release();
+        callback = nullptr;
+      }
+    }
+  }
+
+  if (callback) {
+    return callback->OnInputStreamReady(this);
+  }
+
+  return mWeakAsyncInputStream->AsyncWait(
+      this, asyncWaitFlags, asyncWaitRequestedCount, asyncWaitEventTarget);
+}
+
+// nsIIPCSerializableInputStream
+
+void SlicedInputStream::SerializedComplexity(uint32_t aMaxSize,
+                                             uint32_t* aSizeUsed,
+                                             uint32_t* aPipes,
+                                             uint32_t* aTransferables) {
+  InputStreamHelper::SerializedComplexity(mInputStream, aMaxSize, aSizeUsed,
+                                          aPipes, aTransferables);
+
+  // If we're going to be serializing a pipe to transfer the sliced data, and we
+  // are getting no efficiency improvements from transferables, stream this
+  // sliced input stream directly as a pipe to avoid streaming data which will
+  // be sliced off anyway.
+  if (*aPipes > 0 && *aTransferables == 0) {
+    *aSizeUsed = 0;
+    *aPipes = 1;
+    *aTransferables = 0;
+  }
+}
+
+void SlicedInputStream::Serialize(mozilla::ipc::InputStreamParams& aParams,
+                                  uint32_t aMaxSize, uint32_t* aSizeUsed) {
+  MOZ_ASSERT(mInputStream);
+  MOZ_ASSERT(mWeakIPCSerializableInputStream);
+
+  uint32_t sizeUsed = 0, pipes = 0, transferables = 0;
+  SerializedComplexity(aMaxSize, &sizeUsed, &pipes, &transferables);
+  if (pipes > 0 && transferables == 0) {
+    InputStreamHelper::SerializeInputStreamAsPipe(this, aParams);
+    return;
+  }
+
+  SlicedInputStreamParams params;
+  InputStreamHelper::SerializeInputStream(mInputStream, params.stream(),
+                                          aMaxSize, aSizeUsed);
+  params.start() = mStart;
+  params.length() = mLength;
+  params.curPos() = mCurPos;
+  params.closed() = mClosed;
+
+  aParams = params;
+}
+
+bool SlicedInputStream::Deserialize(
+    const mozilla::ipc::InputStreamParams& aParams) {
+  MOZ_ASSERT(!mInputStream);
+  MOZ_ASSERT(!mWeakIPCSerializableInputStream);
+
+  if (aParams.type() != InputStreamParams::TSlicedInputStreamParams) {
+    NS_ERROR("Received unknown parameters from the other process!");
+    return false;
+  }
+
+  const SlicedInputStreamParams& params = aParams.get_SlicedInputStreamParams();
+
+  nsCOMPtr<nsIInputStream> stream =
+      InputStreamHelper::DeserializeInputStream(params.stream());
+  if (!stream) {
+    NS_WARNING("Deserialize failed!");
+    return false;
+  }
+
+  SetSourceStream(stream.forget());
+
+  mStart = params.start();
+  mLength = params.length();
+  mCurPos = params.curPos();
+  mClosed = params.closed();
+
+  return true;
+}
+
+// nsISeekableStream
+
+NS_IMETHODIMP
+SlicedInputStream::Seek(int32_t aWhence, int64_t aOffset) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakSeekableInputStream);
+
+  int64_t offset;
+  nsresult rv;
+
+  switch (aWhence) {
+    case NS_SEEK_SET:
+      offset = mStart + aOffset;
+      break;
+    case NS_SEEK_CUR:
+      // mCurPos could be lower than mStart if the reading has not started yet.
+      offset = XPCOM_MAX(mStart, mCurPos) + aOffset;
+      break;
+    case NS_SEEK_END: {
+      uint64_t available;
+      rv = mInputStream->Available(&available);
+      if (rv == NS_BASE_STREAM_CLOSED) {
+        mClosed = true;
+        return rv;
+      }
+
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      offset = XPCOM_MIN(mStart + mLength, available) + aOffset;
+      break;
+    }
+    default:
+      return NS_ERROR_ILLEGAL_VALUE;
+  }
+
+  if (offset < (int64_t)mStart || offset > (int64_t)(mStart + mLength)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  rv = mWeakSeekableInputStream->Seek(NS_SEEK_SET, offset);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  mCurPos = offset;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SlicedInputStream::SetEOF() {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakSeekableInputStream);
+
+  mClosed = true;
+  return mWeakSeekableInputStream->SetEOF();
+}
+
+// nsITellableStream
+
+NS_IMETHODIMP
+SlicedInputStream::Tell(int64_t* aResult) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakTellableInputStream);
+
+  int64_t tell = 0;
+
+  nsresult rv = mWeakTellableInputStream->Tell(&tell);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (tell < (int64_t)mStart) {
+    *aResult = 0;
+    return NS_OK;
+  }
+
+  *aResult = tell - mStart;
+  if (*aResult > (int64_t)mLength) {
+    *aResult = mLength;
+  }
+
+  return NS_OK;
+}
+
+// nsIInputStreamLength
+
+NS_IMETHODIMP
+SlicedInputStream::Length(int64_t* aLength) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakInputStreamLength);
+
+  nsresult rv = mWeakInputStreamLength->Length(aLength);
+  if (rv == NS_BASE_STREAM_CLOSED) {
+    mClosed = true;
+    return rv;
+  }
+
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (*aLength == -1) {
+    return NS_OK;
+  }
+
+  *aLength = (int64_t)AdjustRange((uint64_t)*aLength);
+  return NS_OK;
+}
+
+// nsIAsyncInputStreamLength
+
+NS_IMETHODIMP
+SlicedInputStream::AsyncLengthWait(nsIInputStreamLengthCallback* aCallback,
+                                   nsIEventTarget* aEventTarget) {
+  NS_ENSURE_STATE(mInputStream);
+  NS_ENSURE_STATE(mWeakAsyncInputStreamLength);
+
+  nsCOMPtr<nsIInputStreamLengthCallback> callback = aCallback ? this : nullptr;
+  {
+    MutexAutoLock lock(mMutex);
+    mAsyncWaitLengthCallback = aCallback;
+  }
+
+  return mWeakAsyncInputStreamLength->AsyncLengthWait(callback, aEventTarget);
+}
+
+// nsIInputStreamLengthCallback
+
+NS_IMETHODIMP
+SlicedInputStream::OnInputStreamLengthReady(nsIAsyncInputStreamLength* aStream,
+                                            int64_t aLength) {
+  MOZ_ASSERT(mInputStream);
+  MOZ_ASSERT(mWeakAsyncInputStreamLength);
+  MOZ_ASSERT(mWeakAsyncInputStreamLength == aStream);
+
+  nsCOMPtr<nsIInputStreamLengthCallback> callback;
+  {
+    MutexAutoLock lock(mMutex);
+
+    // We have been canceled in the meanwhile.
+    if (!mAsyncWaitLengthCallback) {
+      return NS_OK;
+    }
+
+    callback.swap(mAsyncWaitLengthCallback);
+  }
+
+  if (aLength != -1) {
+    aLength = (int64_t)AdjustRange((uint64_t)aLength);
+  }
+
+  MOZ_ASSERT(callback);
+  return callback->OnInputStreamLengthReady(this, aLength);
+}
+
+}  // namespace mozilla
diff --git a/xpcom/io/SlicedInputStream.h b/xpcom/io/SlicedInputStream.h
new file mode 100644
index 0000000000..30b6c118ab
--- /dev/null
+++ b/xpcom/io/SlicedInputStream.h
@@ -0,0 +1,102 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef SlicedInputStream_h
+#define SlicedInputStream_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Mutex.h"
+#include "nsCOMPtr.h"
+#include "nsIAsyncInputStream.h"
+#include "nsICloneableInputStream.h"
+#include "nsIIPCSerializableInputStream.h"
+#include "nsISeekableStream.h"
+#include "nsIInputStreamLength.h"
+
+namespace mozilla {
+
+// A wrapper for a slice of an underlying input stream.
+
+class SlicedInputStream final : public nsIAsyncInputStream,
+                                public nsICloneableInputStream,
+                                public nsIIPCSerializableInputStream,
+                                public nsISeekableStream,
+                                public nsIInputStreamCallback,
+                                public nsIInputStreamLength,
+                                public nsIAsyncInputStreamLength,
+                                public nsIInputStreamLengthCallback {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINPUTSTREAM
+  NS_DECL_NSIASYNCINPUTSTREAM
+  NS_DECL_NSICLONEABLEINPUTSTREAM
+  NS_DECL_NSIIPCSERIALIZABLEINPUTSTREAM
+  NS_DECL_NSISEEKABLESTREAM
+  NS_DECL_NSITELLABLESTREAM
+  NS_DECL_NSIINPUTSTREAMCALLBACK
+  NS_DECL_NSIINPUTSTREAMLENGTH
+  NS_DECL_NSIASYNCINPUTSTREAMLENGTH
+  NS_DECL_NSIINPUTSTREAMLENGTHCALLBACK
+
+  // Create an input stream whose data comes from a slice of aInputStream.  The
+  // slice begins at aStart bytes beyond aInputStream's current position, and
+  // extends for a maximum of aLength bytes.  If aInputStream contains fewer
+  // than aStart bytes, reading from SlicedInputStream returns no data.  If
+  // aInputStream contains more than aStart bytes, but fewer than aStart +
+  // aLength bytes, reading from SlicedInputStream returns as many bytes as can
+  // be consumed from aInputStream after reading aLength bytes.
+  //
+  // aInputStream should not be read from after constructing a
+  // SlicedInputStream wrapper around it.
+
+  SlicedInputStream(already_AddRefed<nsIInputStream> aInputStream,
+                    uint64_t aStart, uint64_t aLength);
+
+  // This CTOR is meant to be used just for IPC.
+  SlicedInputStream();
+
+ private:
+  ~SlicedInputStream();
+
+  void SetSourceStream(already_AddRefed<nsIInputStream> aInputStream);
+
+  uint64_t AdjustRange(uint64_t aRange);
+
+  nsCOMPtr<nsIInputStream> mInputStream;
+
+  // Raw pointers because these are just QI of mInputStream.
+  nsICloneableInputStream* mWeakCloneableInputStream;
+  nsIIPCSerializableInputStream* mWeakIPCSerializableInputStream;
+  nsISeekableStream* mWeakSeekableInputStream;
+  nsITellableStream* mWeakTellableInputStream;
+  nsIAsyncInputStream* mWeakAsyncInputStream;
+  nsIInputStreamLength* mWeakInputStreamLength;
+  nsIAsyncInputStreamLength* mWeakAsyncInputStreamLength;
+
+  uint64_t mStart;
+  uint64_t mLength;
+  uint64_t mCurPos;
+
+  bool mClosed;
+
+  // These four are used for AsyncWait. They are protected by mutex because
+  // touched on multiple threads.
+  nsCOMPtr<nsIInputStreamCallback> mAsyncWaitCallback MOZ_GUARDED_BY(mMutex);
+  nsCOMPtr<nsIEventTarget> mAsyncWaitEventTarget MOZ_GUARDED_BY(mMutex);
+  uint32_t mAsyncWaitFlags MOZ_GUARDED_BY(mMutex);
+  uint32_t mAsyncWaitRequestedCount MOZ_GUARDED_BY(mMutex);
+
+  // This is use for nsIAsyncInputStreamLength::AsyncWait.
+  // This is protected by mutex.
+  nsCOMPtr<nsIInputStreamLengthCallback> mAsyncWaitLengthCallback
+      MOZ_GUARDED_BY(mMutex);
+
+  Mutex mMutex;
+};
+
+}  // namespace mozilla
+
+#endif  // SlicedInputStream_h
diff --git a/xpcom/io/SnappyCompressOutputStream.cpp b/xpcom/io/SnappyCompressOutputStream.cpp
new file mode 100644
index 0000000000..ebe9e1073c
--- /dev/null
+++ b/xpcom/io/SnappyCompressOutputStream.cpp
@@ -0,0 +1,259 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/SnappyCompressOutputStream.h"
+
+#include <algorithm>
+#include "nsStreamUtils.h"
+#include "snappy/snappy.h"
+
+namespace mozilla {
+
+NS_IMPL_ISUPPORTS(SnappyCompressOutputStream, nsIOutputStream);
+
+// static
+const size_t SnappyCompressOutputStream::kMaxBlockSize = snappy::kBlockSize;
+
+SnappyCompressOutputStream::SnappyCompressOutputStream(
+    nsIOutputStream* aBaseStream, size_t aBlockSize)
+    : mBaseStream(aBaseStream),
+      mBlockSize(std::min(aBlockSize, kMaxBlockSize)),
+      mNextByte(0),
+      mCompressedBufferLength(0),
+      mStreamIdentifierWritten(false) {
+  MOZ_ASSERT(mBlockSize > 0);
+
+  // This implementation only supports sync base streams.  Verify this in debug
+  // builds.  Note, this can be simpler than the check in
+  // SnappyUncompressInputStream because we don't have to deal with the
+  // nsStringInputStream oddness of being non-blocking and sync.
+#ifdef DEBUG
+  bool baseNonBlocking;
+  nsresult rv = mBaseStream->IsNonBlocking(&baseNonBlocking);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+  MOZ_ASSERT(!baseNonBlocking);
+#endif
+}
+
+size_t SnappyCompressOutputStream::BlockSize() const { return mBlockSize; }
+
+NS_IMETHODIMP
+SnappyCompressOutputStream::Close() {
+  if (!mBaseStream) {
+    return NS_OK;
+  }
+
+  nsresult rv = Flush();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  mBaseStream->Close();
+  mBaseStream = nullptr;
+
+  mBuffer = nullptr;
+  mCompressedBuffer = nullptr;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SnappyCompressOutputStream::Flush() {
+  if (!mBaseStream) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  nsresult rv = FlushToBaseStream();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  mBaseStream->Flush();
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SnappyCompressOutputStream::StreamStatus() {
+  if (!mBaseStream) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+  return mBaseStream->StreamStatus();
+}
+
+NS_IMETHODIMP
+SnappyCompressOutputStream::Write(const char* aBuf, uint32_t aCount,
+                                  uint32_t* aResultOut) {
+  return WriteSegments(NS_CopyBufferToSegment, const_cast<char*>(aBuf), aCount,
+                       aResultOut);
+}
+
+NS_IMETHODIMP
+SnappyCompressOutputStream::WriteFrom(nsIInputStream*, uint32_t, uint32_t*) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+SnappyCompressOutputStream::WriteSegments(nsReadSegmentFun aReader,
+                                          void* aClosure, uint32_t aCount,
+                                          uint32_t* aBytesWrittenOut) {
+  *aBytesWrittenOut = 0;
+
+  if (!mBaseStream) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  if (!mBuffer) {
+    mBuffer.reset(new (fallible) char[mBlockSize]);
+    if (NS_WARN_IF(!mBuffer)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+  }
+
+  while (aCount > 0) {
+    // Determine how much space is left in our flat, uncompressed buffer.
+    MOZ_ASSERT(mNextByte <= mBlockSize);
+    uint32_t remaining = mBlockSize - mNextByte;
+
+    // If it is full, then compress and flush the data to the base stream.
+    if (remaining == 0) {
+      nsresult rv = FlushToBaseStream();
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      // Now the entire buffer should be available for copying.
+      MOZ_ASSERT(!mNextByte);
+      remaining = mBlockSize;
+    }
+
+    uint32_t numToRead = std::min(remaining, aCount);
+    uint32_t numRead = 0;
+
+    nsresult rv = aReader(this, aClosure, &mBuffer[mNextByte],
+                          *aBytesWrittenOut, numToRead, &numRead);
+
+    // As defined in nsIOutputStream.idl, do not pass reader func errors.
+    if (NS_FAILED(rv)) {
+      return NS_OK;
+    }
+
+    // End-of-file
+    if (numRead == 0) {
+      return NS_OK;
+    }
+
+    mNextByte += numRead;
+    *aBytesWrittenOut += numRead;
+    aCount -= numRead;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SnappyCompressOutputStream::IsNonBlocking(bool* aNonBlockingOut) {
+  *aNonBlockingOut = false;
+  return NS_OK;
+}
+
+SnappyCompressOutputStream::~SnappyCompressOutputStream() { Close(); }
+
+nsresult SnappyCompressOutputStream::FlushToBaseStream() {
+  MOZ_ASSERT(mBaseStream);
+
+  // Lazily create the compressed buffer on our first flush.  This
+  // allows us to report OOM during stream operation.  This buffer
+  // will then get re-used until the stream is closed.
+  if (!mCompressedBuffer) {
+    mCompressedBufferLength = MaxCompressedBufferLength(mBlockSize);
+    mCompressedBuffer.reset(new (fallible) char[mCompressedBufferLength]);
+    if (NS_WARN_IF(!mCompressedBuffer)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+  }
+
+  // The first chunk must be a StreamIdentifier chunk.  Write it out
+  // if we have not done so already.
+  nsresult rv = MaybeFlushStreamIdentifier();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // Compress the data to our internal compressed buffer.
+  size_t compressedLength;
+  rv = WriteCompressedData(mCompressedBuffer.get(), mCompressedBufferLength,
+                           mBuffer.get(), mNextByte, &compressedLength);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  MOZ_ASSERT(compressedLength > 0);
+
+  mNextByte = 0;
+
+  // Write the compressed buffer out to the base stream.
+  uint32_t numWritten = 0;
+  rv = WriteAll(mCompressedBuffer.get(), compressedLength, &numWritten);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  MOZ_ASSERT(compressedLength == numWritten);
+
+  return NS_OK;
+}
+
+nsresult SnappyCompressOutputStream::MaybeFlushStreamIdentifier() {
+  MOZ_ASSERT(mCompressedBuffer);
+
+  if (mStreamIdentifierWritten) {
+    return NS_OK;
+  }
+
+  // Build the StreamIdentifier in our compressed buffer.
+  size_t compressedLength;
+  nsresult rv = WriteStreamIdentifier(
+      mCompressedBuffer.get(), mCompressedBufferLength, &compressedLength);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // Write the compressed buffer out to the base stream.
+  uint32_t numWritten = 0;
+  rv = WriteAll(mCompressedBuffer.get(), compressedLength, &numWritten);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  MOZ_ASSERT(compressedLength == numWritten);
+
+  mStreamIdentifierWritten = true;
+
+  return NS_OK;
+}
+
+nsresult SnappyCompressOutputStream::WriteAll(const char* aBuf, uint32_t aCount,
+                                              uint32_t* aBytesWrittenOut) {
+  *aBytesWrittenOut = 0;
+
+  if (!mBaseStream) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  uint32_t offset = 0;
+  while (aCount > 0) {
+    uint32_t numWritten = 0;
+    nsresult rv = mBaseStream->Write(aBuf + offset, aCount, &numWritten);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+    offset += numWritten;
+    aCount -= numWritten;
+    *aBytesWrittenOut += numWritten;
+  }
+
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/io/SnappyCompressOutputStream.h b/xpcom/io/SnappyCompressOutputStream.h
new file mode 100644
index 0000000000..895691034b
--- /dev/null
+++ b/xpcom/io/SnappyCompressOutputStream.h
@@ -0,0 +1,68 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_SnappyCompressOutputStream_h__
+#define mozilla_SnappyCompressOutputStream_h__
+
+#include "mozilla/Attributes.h"
+#include "mozilla/UniquePtr.h"
+#include "nsCOMPtr.h"
+#include "nsIOutputStream.h"
+#include "nsISupportsImpl.h"
+#include "SnappyFrameUtils.h"
+
+namespace mozilla {
+
+class SnappyCompressOutputStream final : public nsIOutputStream,
+                                         protected detail::SnappyFrameUtils {
+ public:
+  // Maximum compression block size.
+  static const size_t kMaxBlockSize;
+
+  // Construct a new blocking output stream to compress data to
+  // the given base stream.  The base stream must also be blocking.
+  // The compression block size may optionally be set to a value
+  // up to kMaxBlockSize.
+  explicit SnappyCompressOutputStream(nsIOutputStream* aBaseStream,
+                                      size_t aBlockSize = kMaxBlockSize);
+
+  // The compression block size.  To optimize stream performance
+  // try to write to the stream in segments at least this size.
+  size_t BlockSize() const;
+
+ private:
+  virtual ~SnappyCompressOutputStream();
+
+  nsresult FlushToBaseStream();
+  nsresult MaybeFlushStreamIdentifier();
+  nsresult WriteAll(const char* aBuf, uint32_t aCount,
+                    uint32_t* aBytesWrittenOut);
+
+  nsCOMPtr<nsIOutputStream> mBaseStream;
+  const size_t mBlockSize;
+
+  // Buffer holding copied uncompressed data.  This must be copied here
+  // so that the compression can be performed on a single flat buffer.
+  mozilla::UniquePtr<char[]> mBuffer;
+
+  // The next byte in the uncompressed data to copy incoming data to.
+  size_t mNextByte;
+
+  // Buffer holding the resulting compressed data.
+  mozilla::UniquePtr<char[]> mCompressedBuffer;
+  size_t mCompressedBufferLength;
+
+  // The first thing written to the stream must be a stream identifier.
+  bool mStreamIdentifierWritten;
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIOUTPUTSTREAM
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_SnappyCompressOutputStream_h__
diff --git a/xpcom/io/SnappyFrameUtils.cpp b/xpcom/io/SnappyFrameUtils.cpp
new file mode 100644
index 0000000000..c606794fd9
--- /dev/null
+++ b/xpcom/io/SnappyFrameUtils.cpp
@@ -0,0 +1,241 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/SnappyFrameUtils.h"
+
+#include "crc32c.h"
+#include "mozilla/EndianUtils.h"
+#include "nsDebug.h"
+#include "snappy/snappy.h"
+
+namespace {
+
+using mozilla::NativeEndian;
+using mozilla::detail::SnappyFrameUtils;
+
+SnappyFrameUtils::ChunkType ReadChunkType(uint8_t aByte) {
+  if (aByte == 0xff) {
+    return SnappyFrameUtils::StreamIdentifier;
+  } else if (aByte == 0x00) {
+    return SnappyFrameUtils::CompressedData;
+  } else if (aByte == 0x01) {
+    return SnappyFrameUtils::UncompressedData;
+  } else if (aByte == 0xfe) {
+    return SnappyFrameUtils::Padding;
+  }
+
+  return SnappyFrameUtils::Reserved;
+}
+
+void WriteChunkType(char* aDest, SnappyFrameUtils::ChunkType aType) {
+  unsigned char* dest = reinterpret_cast<unsigned char*>(aDest);
+  if (aType == SnappyFrameUtils::StreamIdentifier) {
+    *dest = 0xff;
+  } else if (aType == SnappyFrameUtils::CompressedData) {
+    *dest = 0x00;
+  } else if (aType == SnappyFrameUtils::UncompressedData) {
+    *dest = 0x01;
+  } else if (aType == SnappyFrameUtils::Padding) {
+    *dest = 0xfe;
+  } else {
+    *dest = 0x02;
+  }
+}
+
+void WriteUInt24(char* aBuf, uint32_t aVal) {
+  MOZ_ASSERT(!(aVal & 0xff000000));
+  uint32_t tmp = NativeEndian::swapToLittleEndian(aVal);
+  memcpy(aBuf, &tmp, 3);
+}
+
+uint32_t ReadUInt24(const char* aBuf) {
+  uint32_t val = 0;
+  memcpy(&val, aBuf, 3);
+  return NativeEndian::swapFromLittleEndian(val);
+}
+
+// This mask is explicitly defined in the snappy framing_format.txt file.
+uint32_t MaskChecksum(uint32_t aValue) {
+  return ((aValue >> 15) | (aValue << 17)) + 0xa282ead8;
+}
+
+}  // namespace
+
+namespace mozilla {
+namespace detail {
+
+using mozilla::LittleEndian;
+
+// static
+nsresult SnappyFrameUtils::WriteStreamIdentifier(char* aDest,
+                                                 size_t aDestLength,
+                                                 size_t* aBytesWrittenOut) {
+  if (NS_WARN_IF(aDestLength < (kHeaderLength + kStreamIdentifierDataLength))) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  WriteChunkType(aDest, StreamIdentifier);
+  aDest[1] = 0x06;  // Data length
+  aDest[2] = 0x00;
+  aDest[3] = 0x00;
+  aDest[4] = 0x73;  // "sNaPpY"
+  aDest[5] = 0x4e;
+  aDest[6] = 0x61;
+  aDest[7] = 0x50;
+  aDest[8] = 0x70;
+  aDest[9] = 0x59;
+
+  static_assert(kHeaderLength + kStreamIdentifierDataLength == 10,
+                "StreamIdentifier chunk should be exactly 10 bytes long");
+  *aBytesWrittenOut = kHeaderLength + kStreamIdentifierDataLength;
+
+  return NS_OK;
+}
+
+// static
+nsresult SnappyFrameUtils::WriteCompressedData(char* aDest, size_t aDestLength,
+                                               const char* aData,
+                                               size_t aDataLength,
+                                               size_t* aBytesWrittenOut) {
+  *aBytesWrittenOut = 0;
+
+  size_t neededLength = MaxCompressedBufferLength(aDataLength);
+  if (NS_WARN_IF(aDestLength < neededLength)) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  size_t offset = 0;
+
+  WriteChunkType(aDest, CompressedData);
+  offset += kChunkTypeLength;
+
+  // Skip length for now and write it out after we know the compressed length.
+  size_t lengthOffset = offset;
+  offset += kChunkLengthLength;
+
+  uint32_t crc = ComputeCrc32c(
+      ~0, reinterpret_cast<const unsigned char*>(aData), aDataLength);
+  uint32_t maskedCrc = MaskChecksum(crc);
+  LittleEndian::writeUint32(aDest + offset, maskedCrc);
+  offset += kCRCLength;
+
+  size_t compressedLength;
+  snappy::RawCompress(aData, aDataLength, aDest + offset, &compressedLength);
+
+  // Go back and write the data length.
+  size_t dataLength = compressedLength + kCRCLength;
+  WriteUInt24(aDest + lengthOffset, dataLength);
+
+  *aBytesWrittenOut = kHeaderLength + dataLength;
+
+  return NS_OK;
+}
+
+// static
+nsresult SnappyFrameUtils::ParseHeader(const char* aSource,
+                                       size_t aSourceLength,
+                                       ChunkType* aTypeOut,
+                                       size_t* aDataLengthOut) {
+  if (NS_WARN_IF(aSourceLength < kHeaderLength)) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  *aTypeOut = ReadChunkType(aSource[0]);
+  *aDataLengthOut = ReadUInt24(aSource + kChunkTypeLength);
+
+  return NS_OK;
+}
+
+// static
+nsresult SnappyFrameUtils::ParseData(char* aDest, size_t aDestLength,
+                                     ChunkType aType, const char* aData,
+                                     size_t aDataLength,
+                                     size_t* aBytesWrittenOut,
+                                     size_t* aBytesReadOut) {
+  switch (aType) {
+    case StreamIdentifier:
+      return ParseStreamIdentifier(aDest, aDestLength, aData, aDataLength,
+                                   aBytesWrittenOut, aBytesReadOut);
+
+    case CompressedData:
+      return ParseCompressedData(aDest, aDestLength, aData, aDataLength,
+                                 aBytesWrittenOut, aBytesReadOut);
+
+    // TODO: support other snappy chunk types
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unsupported snappy framing chunk type.");
+      return NS_ERROR_NOT_IMPLEMENTED;
+  }
+}
+
+// static
+nsresult SnappyFrameUtils::ParseStreamIdentifier(char*, size_t,
+                                                 const char* aData,
+                                                 size_t aDataLength,
+                                                 size_t* aBytesWrittenOut,
+                                                 size_t* aBytesReadOut) {
+  *aBytesWrittenOut = 0;
+  *aBytesReadOut = 0;
+  if (NS_WARN_IF(aDataLength != kStreamIdentifierDataLength ||
+                 aData[0] != 0x73 || aData[1] != 0x4e || aData[2] != 0x61 ||
+                 aData[3] != 0x50 || aData[4] != 0x70 || aData[5] != 0x59)) {
+    return NS_ERROR_CORRUPTED_CONTENT;
+  }
+  *aBytesReadOut = aDataLength;
+  return NS_OK;
+}
+
+// static
+nsresult SnappyFrameUtils::ParseCompressedData(char* aDest, size_t aDestLength,
+                                               const char* aData,
+                                               size_t aDataLength,
+                                               size_t* aBytesWrittenOut,
+                                               size_t* aBytesReadOut) {
+  *aBytesWrittenOut = 0;
+  *aBytesReadOut = 0;
+  size_t offset = 0;
+
+  uint32_t readCrc = LittleEndian::readUint32(aData + offset);
+  offset += kCRCLength;
+
+  size_t uncompressedLength;
+  if (NS_WARN_IF(!snappy::GetUncompressedLength(
+          aData + offset, aDataLength - offset, &uncompressedLength))) {
+    return NS_ERROR_CORRUPTED_CONTENT;
+  }
+
+  if (NS_WARN_IF(aDestLength < uncompressedLength)) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  if (NS_WARN_IF(!snappy::RawUncompress(aData + offset, aDataLength - offset,
+                                        aDest))) {
+    return NS_ERROR_CORRUPTED_CONTENT;
+  }
+
+  uint32_t crc = ComputeCrc32c(
+      ~0, reinterpret_cast<const unsigned char*>(aDest), uncompressedLength);
+  uint32_t maskedCrc = MaskChecksum(crc);
+  if (NS_WARN_IF(readCrc != maskedCrc)) {
+    return NS_ERROR_CORRUPTED_CONTENT;
+  }
+
+  *aBytesWrittenOut = uncompressedLength;
+  *aBytesReadOut = aDataLength;
+
+  return NS_OK;
+}
+
+// static
+size_t SnappyFrameUtils::MaxCompressedBufferLength(size_t aSourceLength) {
+  size_t neededLength = kHeaderLength;
+  neededLength += kCRCLength;
+  neededLength += snappy::MaxCompressedLength(aSourceLength);
+  return neededLength;
+}
+
+}  // namespace detail
+}  // namespace mozilla
diff --git a/xpcom/io/SnappyFrameUtils.h b/xpcom/io/SnappyFrameUtils.h
new file mode 100644
index 0000000000..923994c661
--- /dev/null
+++ b/xpcom/io/SnappyFrameUtils.h
@@ -0,0 +1,80 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_SnappyFrameUtils_h__
+#define mozilla_SnappyFrameUtils_h__
+
+#include <cstddef>
+
+#include "mozilla/Attributes.h"
+#include "nsError.h"
+
+namespace mozilla {
+namespace detail {
+
+//
+// Utility class providing primitives necessary to build streams based
+// on the snappy compressor.  This essentially abstracts the framing format
+// defined in:
+//
+//  other-licences/snappy/src/framing_format.txt
+//
+// NOTE: Currently only the StreamIdentifier and CompressedData chunks are
+//       supported.
+//
+class SnappyFrameUtils {
+ public:
+  enum ChunkType {
+    Unknown,
+    StreamIdentifier,
+    CompressedData,
+    UncompressedData,
+    Padding,
+    Reserved,
+    ChunkTypeCount
+  };
+
+  static const size_t kChunkTypeLength = 1;
+  static const size_t kChunkLengthLength = 3;
+  static const size_t kHeaderLength = kChunkTypeLength + kChunkLengthLength;
+  static const size_t kStreamIdentifierDataLength = 6;
+  static const size_t kCRCLength = 4;
+
+  static nsresult WriteStreamIdentifier(char* aDest, size_t aDestLength,
+                                        size_t* aBytesWrittenOut);
+
+  static nsresult WriteCompressedData(char* aDest, size_t aDestLength,
+                                      const char* aData, size_t aDataLength,
+                                      size_t* aBytesWrittenOut);
+
+  static nsresult ParseHeader(const char* aSource, size_t aSourceLength,
+                              ChunkType* aTypeOut, size_t* aDataLengthOut);
+
+  static nsresult ParseData(char* aDest, size_t aDestLength, ChunkType aType,
+                            const char* aData, size_t aDataLength,
+                            size_t* aBytesWrittenOut, size_t* aBytesReadOut);
+
+  static nsresult ParseStreamIdentifier(char* aDest, size_t aDestLength,
+                                        const char* aData, size_t aDataLength,
+                                        size_t* aBytesWrittenOut,
+                                        size_t* aBytesReadOut);
+
+  static nsresult ParseCompressedData(char* aDest, size_t aDestLength,
+                                      const char* aData, size_t aDataLength,
+                                      size_t* aBytesWrittenOut,
+                                      size_t* aBytesReadOut);
+
+  static size_t MaxCompressedBufferLength(size_t aSourceLength);
+
+ protected:
+  SnappyFrameUtils() = default;
+  virtual ~SnappyFrameUtils() = default;
+};
+
+}  // namespace detail
+}  // namespace mozilla
+
+#endif  // mozilla_SnappyFrameUtils_h__
diff --git a/xpcom/io/SnappyUncompressInputStream.cpp b/xpcom/io/SnappyUncompressInputStream.cpp
new file mode 100644
index 0000000000..2872c8c7a2
--- /dev/null
+++ b/xpcom/io/SnappyUncompressInputStream.cpp
@@ -0,0 +1,386 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/SnappyUncompressInputStream.h"
+
+#include <algorithm>
+#include "nsIAsyncInputStream.h"
+#include "nsStreamUtils.h"
+#include "snappy/snappy.h"
+
+namespace mozilla {
+
+NS_IMPL_ISUPPORTS(SnappyUncompressInputStream, nsIInputStream);
+
+// Putting kCompressedBufferLength inside a function avoids a static
+// constructor.
+static size_t CompressedBufferLength() {
+  static size_t kCompressedBufferLength =
+      detail::SnappyFrameUtils::MaxCompressedBufferLength(snappy::kBlockSize);
+
+  MOZ_ASSERT(kCompressedBufferLength > 0);
+  return kCompressedBufferLength;
+}
+
+SnappyUncompressInputStream::SnappyUncompressInputStream(
+    nsIInputStream* aBaseStream)
+    : mBaseStream(aBaseStream),
+      mUncompressedBytes(0),
+      mNextByte(0),
+      mNextChunkType(Unknown),
+      mNextChunkDataLength(0),
+      mNeedFirstStreamIdentifier(true) {
+  // This implementation only supports sync base streams.  Verify this in debug
+  // builds.  Note, this is a bit complicated because the streams we support
+  // advertise different capabilities:
+  //  - nsFileInputStream - blocking and sync
+  //  - nsStringInputStream - non-blocking and sync
+  //  - nsPipeInputStream - can be blocking, but provides async interface
+#ifdef DEBUG
+  bool baseNonBlocking;
+  nsresult rv = mBaseStream->IsNonBlocking(&baseNonBlocking);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+  if (baseNonBlocking) {
+    nsCOMPtr<nsIAsyncInputStream> async = do_QueryInterface(mBaseStream);
+    MOZ_ASSERT(!async);
+  }
+#endif
+}
+
+NS_IMETHODIMP
+SnappyUncompressInputStream::Close() {
+  if (!mBaseStream) {
+    return NS_OK;
+  }
+
+  mBaseStream->Close();
+  mBaseStream = nullptr;
+
+  mUncompressedBuffer = nullptr;
+  mCompressedBuffer = nullptr;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SnappyUncompressInputStream::Available(uint64_t* aLengthOut) {
+  if (!mBaseStream) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  // If we have uncompressed bytes, then we are done.
+  *aLengthOut = UncompressedLength();
+  if (*aLengthOut > 0) {
+    return NS_OK;
+  }
+
+  // Otherwise, attempt to uncompress bytes until we get something or the
+  // underlying stream is drained.  We loop here because some chunks can
+  // be StreamIdentifiers, padding, etc with no data.
+  uint32_t bytesRead;
+  do {
+    nsresult rv = ParseNextChunk(&bytesRead);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+    *aLengthOut = UncompressedLength();
+  } while (*aLengthOut == 0 && bytesRead);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SnappyUncompressInputStream::StreamStatus() {
+  if (!mBaseStream) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  // If we have uncompressed bytes, then we're still open.
+  if (UncompressedLength() > 0) {
+    return NS_OK;
+  }
+
+  // Otherwise we'll need to read from the underlying stream, so check it
+  return mBaseStream->StreamStatus();
+}
+
+NS_IMETHODIMP
+SnappyUncompressInputStream::Read(char* aBuf, uint32_t aCount,
+                                  uint32_t* aBytesReadOut) {
+  return ReadSegments(NS_CopySegmentToBuffer, aBuf, aCount, aBytesReadOut);
+}
+
+NS_IMETHODIMP
+SnappyUncompressInputStream::ReadSegments(nsWriteSegmentFun aWriter,
+                                          void* aClosure, uint32_t aCount,
+                                          uint32_t* aBytesReadOut) {
+  *aBytesReadOut = 0;
+
+  if (!mBaseStream) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  nsresult rv;
+
+  // Do not try to use the base stream's ReadSegements here.  Its very
+  // unlikely we will get a single buffer that contains all of the compressed
+  // data and therefore would have to copy into our own buffer anyways.
+  // Instead, focus on making efficient use of the Read() interface.
+
+  while (aCount > 0) {
+    // We have some decompressed data in our buffer.  Provide it to the
+    // callers writer function.
+    if (mUncompressedBytes > 0) {
+      MOZ_ASSERT(mUncompressedBuffer);
+      uint32_t remaining = UncompressedLength();
+      uint32_t numToWrite = std::min(aCount, remaining);
+      uint32_t numWritten;
+      rv = aWriter(this, aClosure, &mUncompressedBuffer[mNextByte],
+                   *aBytesReadOut, numToWrite, &numWritten);
+
+      // As defined in nsIInputputStream.idl, do not pass writer func errors.
+      if (NS_FAILED(rv)) {
+        return NS_OK;
+      }
+
+      // End-of-file
+      if (numWritten == 0) {
+        return NS_OK;
+      }
+
+      *aBytesReadOut += numWritten;
+      mNextByte += numWritten;
+      MOZ_ASSERT(mNextByte <= mUncompressedBytes);
+
+      if (mNextByte == mUncompressedBytes) {
+        mNextByte = 0;
+        mUncompressedBytes = 0;
+      }
+
+      aCount -= numWritten;
+
+      continue;
+    }
+
+    // Otherwise uncompress the next chunk and loop.  Any resulting data
+    // will set mUncompressedBytes which we check at the top of the loop.
+    uint32_t bytesRead;
+    rv = ParseNextChunk(&bytesRead);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // If we couldn't read anything and there is no more data to provide
+    // to the caller, then this is eof.
+    if (bytesRead == 0 && mUncompressedBytes == 0) {
+      return NS_OK;
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SnappyUncompressInputStream::IsNonBlocking(bool* aNonBlockingOut) {
+  *aNonBlockingOut = false;
+  return NS_OK;
+}
+
+SnappyUncompressInputStream::~SnappyUncompressInputStream() { Close(); }
+
+nsresult SnappyUncompressInputStream::ParseNextChunk(uint32_t* aBytesReadOut) {
+  // There must not be any uncompressed data already in mUncompressedBuffer.
+  MOZ_ASSERT(mUncompressedBytes == 0);
+  MOZ_ASSERT(mNextByte == 0);
+
+  nsresult rv;
+  *aBytesReadOut = 0;
+
+  // Lazily create our two buffers so we can report OOM during stream
+  // operation.  These allocations only happens once.  The buffers are reused
+  // until the stream is closed.
+  if (!mUncompressedBuffer) {
+    mUncompressedBuffer.reset(new (fallible) char[snappy::kBlockSize]);
+    if (NS_WARN_IF(!mUncompressedBuffer)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+  }
+
+  if (!mCompressedBuffer) {
+    mCompressedBuffer.reset(new (fallible) char[CompressedBufferLength()]);
+    if (NS_WARN_IF(!mCompressedBuffer)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+  }
+
+  // We have no decompressed data and we also have not seen the start of stream
+  // yet. Read and validate the StreamIdentifier chunk.  Also read the next
+  // header to determine the size of the first real data chunk.
+  if (mNeedFirstStreamIdentifier) {
+    const uint32_t firstReadLength =
+        kHeaderLength + kStreamIdentifierDataLength + kHeaderLength;
+    MOZ_ASSERT(firstReadLength <= CompressedBufferLength());
+
+    rv = ReadAll(mCompressedBuffer.get(), firstReadLength, firstReadLength,
+                 aBytesReadOut);
+    if (NS_WARN_IF(NS_FAILED(rv)) || *aBytesReadOut == 0) {
+      return rv;
+    }
+
+    rv = ParseHeader(mCompressedBuffer.get(), kHeaderLength, &mNextChunkType,
+                     &mNextChunkDataLength);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+    if (NS_WARN_IF(mNextChunkType != StreamIdentifier ||
+                   mNextChunkDataLength != kStreamIdentifierDataLength)) {
+      return NS_ERROR_CORRUPTED_CONTENT;
+    }
+    size_t offset = kHeaderLength;
+
+    mNeedFirstStreamIdentifier = false;
+
+    size_t numRead;
+    size_t numWritten;
+    rv = ParseData(mUncompressedBuffer.get(), snappy::kBlockSize,
+                   mNextChunkType, &mCompressedBuffer[offset],
+                   mNextChunkDataLength, &numWritten, &numRead);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+    MOZ_ASSERT(numWritten == 0);
+    MOZ_ASSERT(numRead == mNextChunkDataLength);
+    offset += numRead;
+
+    rv = ParseHeader(&mCompressedBuffer[offset], *aBytesReadOut - offset,
+                     &mNextChunkType, &mNextChunkDataLength);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    return NS_OK;
+  }
+
+  // We have no compressed data and we don't know how big the next chunk is.
+  // This happens when we get an EOF pause in the middle of a stream and also
+  // at the end of the stream.  Simply read the next header and return.  The
+  // chunk body will be read on the next entry into this method.
+  if (mNextChunkType == Unknown) {
+    rv = ReadAll(mCompressedBuffer.get(), kHeaderLength, kHeaderLength,
+                 aBytesReadOut);
+    if (NS_WARN_IF(NS_FAILED(rv)) || *aBytesReadOut == 0) {
+      return rv;
+    }
+
+    rv = ParseHeader(mCompressedBuffer.get(), kHeaderLength, &mNextChunkType,
+                     &mNextChunkDataLength);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    return NS_OK;
+  }
+
+  // We have no decompressed data, but we do know the size of the next chunk.
+  // Read at least that much from the base stream.
+  uint32_t readLength = mNextChunkDataLength;
+  MOZ_ASSERT(readLength <= CompressedBufferLength());
+
+  // However, if there is enough data in the base stream, also read the next
+  // chunk header.  This helps optimize the stream by avoiding many small reads.
+  uint64_t avail;
+  rv = mBaseStream->Available(&avail);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  if (avail >= (readLength + kHeaderLength)) {
+    readLength += kHeaderLength;
+    MOZ_ASSERT(readLength <= CompressedBufferLength());
+  }
+
+  rv = ReadAll(mCompressedBuffer.get(), readLength, mNextChunkDataLength,
+               aBytesReadOut);
+  if (NS_WARN_IF(NS_FAILED(rv)) || *aBytesReadOut == 0) {
+    return rv;
+  }
+
+  size_t numRead;
+  size_t numWritten;
+  rv = ParseData(mUncompressedBuffer.get(), snappy::kBlockSize, mNextChunkType,
+                 mCompressedBuffer.get(), mNextChunkDataLength, &numWritten,
+                 &numRead);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  MOZ_ASSERT(numRead == mNextChunkDataLength);
+
+  mUncompressedBytes = numWritten;
+
+  // If we were unable to directly read the next chunk header, then clear
+  // our internal state.  We will have to perform a small read to get the
+  // header the next time we enter this method.
+  if (*aBytesReadOut <= mNextChunkDataLength) {
+    mNextChunkType = Unknown;
+    mNextChunkDataLength = 0;
+    return NS_OK;
+  }
+
+  // We got the next chunk header.  Parse it so that we are ready to for the
+  // next call into this method.
+  rv = ParseHeader(&mCompressedBuffer[numRead], *aBytesReadOut - numRead,
+                   &mNextChunkType, &mNextChunkDataLength);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+nsresult SnappyUncompressInputStream::ReadAll(char* aBuf, uint32_t aCount,
+                                              uint32_t aMinValidCount,
+                                              uint32_t* aBytesReadOut) {
+  MOZ_ASSERT(aCount >= aMinValidCount);
+
+  *aBytesReadOut = 0;
+
+  if (!mBaseStream) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  uint32_t offset = 0;
+  while (aCount > 0) {
+    uint32_t bytesRead = 0;
+    nsresult rv = mBaseStream->Read(aBuf + offset, aCount, &bytesRead);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    // EOF, but don't immediately return.  We need to validate min read bytes
+    // below.
+    if (bytesRead == 0) {
+      break;
+    }
+
+    *aBytesReadOut += bytesRead;
+    offset += bytesRead;
+    aCount -= bytesRead;
+  }
+
+  // Reading zero bytes is not an error.  Its the expected EOF condition.
+  // Only compare to the minimum valid count if we read at least one byte.
+  if (*aBytesReadOut != 0 && *aBytesReadOut < aMinValidCount) {
+    return NS_ERROR_CORRUPTED_CONTENT;
+  }
+
+  return NS_OK;
+}
+
+size_t SnappyUncompressInputStream::UncompressedLength() const {
+  MOZ_ASSERT(mNextByte <= mUncompressedBytes);
+  return mUncompressedBytes - mNextByte;
+}
+
+}  // namespace mozilla
diff --git a/xpcom/io/SnappyUncompressInputStream.h b/xpcom/io/SnappyUncompressInputStream.h
new file mode 100644
index 0000000000..c61ec321a9
--- /dev/null
+++ b/xpcom/io/SnappyUncompressInputStream.h
@@ -0,0 +1,89 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_SnappyUncompressInputStream_h__
+#define mozilla_SnappyUncompressInputStream_h__
+
+#include "mozilla/Attributes.h"
+#include "mozilla/UniquePtr.h"
+#include "nsCOMPtr.h"
+#include "nsIInputStream.h"
+#include "nsISupportsImpl.h"
+#include "SnappyFrameUtils.h"
+
+namespace mozilla {
+
+class SnappyUncompressInputStream final : public nsIInputStream,
+                                          protected detail::SnappyFrameUtils {
+ public:
+  // Construct a new blocking stream to uncompress the given base stream.  The
+  // base stream must also be blocking.  The base stream does not have to be
+  // buffered.
+  explicit SnappyUncompressInputStream(nsIInputStream* aBaseStream);
+
+ private:
+  virtual ~SnappyUncompressInputStream();
+
+  // Parse the next chunk of data.  This may populate mBuffer and set
+  // mBufferFillSize.  This should not be called when mBuffer already
+  // contains data.
+  nsresult ParseNextChunk(uint32_t* aBytesReadOut);
+
+  // Convenience routine to Read() from the base stream until we get
+  // the given number of bytes or reach EOF.
+  //
+  // aBuf           - The buffer to write the bytes into.
+  // aCount         - Max number of bytes to read. If the stream closes
+  //                  fewer bytes my be read.
+  // aMinValidCount - A minimum expected number of bytes.  If we find
+  //                  fewer than this many bytes, then return
+  //                  NS_ERROR_CORRUPTED_CONTENT.  If nothing was read due
+  //                  due to EOF (aBytesReadOut == 0), then NS_OK is returned.
+  // aBytesReadOut  - An out parameter indicating how many bytes were read.
+  nsresult ReadAll(char* aBuf, uint32_t aCount, uint32_t aMinValidCount,
+                   uint32_t* aBytesReadOut);
+
+  // Convenience routine to determine how many bytes of uncompressed data
+  // we currently have in our buffer.
+  size_t UncompressedLength() const;
+
+  nsCOMPtr<nsIInputStream> mBaseStream;
+
+  // Buffer to hold compressed data.  Must copy here since we need a large
+  // flat buffer to run the uncompress process on. Always the same length
+  // of SnappyFrameUtils::MaxCompressedBufferLength(snappy::kBlockSize)
+  // bytes long.
+  mozilla::UniquePtr<char[]> mCompressedBuffer;
+
+  // Buffer storing the resulting uncompressed data.  Exactly snappy::kBlockSize
+  // bytes long.
+  mozilla::UniquePtr<char[]> mUncompressedBuffer;
+
+  // Number of bytes of uncompressed data in mBuffer.
+  size_t mUncompressedBytes;
+
+  // Next byte of mBuffer to return in ReadSegments().  Must be less than
+  // mBufferFillSize
+  size_t mNextByte;
+
+  // Next chunk in the stream that has been parsed during read-ahead.
+  ChunkType mNextChunkType;
+
+  // Length of next chunk's length that has been determined during read-ahead.
+  size_t mNextChunkDataLength;
+
+  // The stream must begin with a StreamIdentifier chunk.  Are we still
+  // expecting it?
+  bool mNeedFirstStreamIdentifier;
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINPUTSTREAM
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_SnappyUncompressInputStream_h__
diff --git a/xpcom/io/SpecialSystemDirectory.cpp b/xpcom/io/SpecialSystemDirectory.cpp
new file mode 100644
index 0000000000..fcb366aede
--- /dev/null
+++ b/xpcom/io/SpecialSystemDirectory.cpp
@@ -0,0 +1,748 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "SpecialSystemDirectory.h"
+#include "nsString.h"
+#include "nsDependentString.h"
+#include "nsIXULAppInfo.h"
+
+#if defined(XP_WIN)
+
+#  include <windows.h>
+#  include <stdlib.h>
+#  include <stdio.h>
+#  include <string.h>
+#  include <direct.h>
+#  include <shlobj.h>
+#  include <knownfolders.h>
+#  include <guiddef.h>
+
+#elif defined(XP_UNIX)
+
+#  include <limits.h>
+#  include <unistd.h>
+#  include <stdlib.h>
+#  include <sys/param.h>
+#  include "prenv.h"
+#  if defined(MOZ_WIDGET_COCOA)
+#    include "CFTypeRefPtr.h"
+#    include "CocoaFileUtils.h"
+#  endif
+#  if defined(MOZ_WIDGET_GTK)
+#    include "mozilla/WidgetUtilsGtk.h"
+#  endif
+
+#endif
+
+#ifndef MAXPATHLEN
+#  ifdef PATH_MAX
+#    define MAXPATHLEN PATH_MAX
+#  elif defined(MAX_PATH)
+#    define MAXPATHLEN MAX_PATH
+#  elif defined(_MAX_PATH)
+#    define MAXPATHLEN _MAX_PATH
+#  elif defined(CCHMAXPATH)
+#    define MAXPATHLEN CCHMAXPATH
+#  else
+#    define MAXPATHLEN 1024
+#  endif
+#endif
+
+#if defined(XP_WIN)
+
+static nsresult GetKnownFolder(GUID* aGuid, nsIFile** aFile) {
+  if (!aGuid) {
+    return NS_ERROR_FAILURE;
+  }
+
+  PWSTR path = nullptr;
+  SHGetKnownFolderPath(*aGuid, 0, nullptr, &path);
+
+  if (!path) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsresult rv = NS_NewLocalFile(nsDependentString(path), true, aFile);
+
+  CoTaskMemFree(path);
+  return rv;
+}
+
+static nsresult GetWindowsFolder(int aFolder, nsIFile** aFile) {
+  WCHAR path_orig[MAX_PATH + 3];
+  WCHAR* path = path_orig + 1;
+  BOOL result = SHGetSpecialFolderPathW(nullptr, path, aFolder, true);
+
+  if (!result) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Append the trailing slash
+  int len = wcslen(path);
+  if (len == 0) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+  if (len > 1 && path[len - 1] != L'\\') {
+    path[len] = L'\\';
+    path[++len] = L'\0';
+  }
+
+  return NS_NewLocalFile(nsDependentString(path, len), true, aFile);
+}
+
+#  if WINVER < 0x0601
+__inline HRESULT SHLoadLibraryFromKnownFolder(REFKNOWNFOLDERID aFolderId,
+                                              DWORD aMode, REFIID riid,
+                                              void** ppv) {
+  *ppv = nullptr;
+  IShellLibrary* plib;
+  HRESULT hr = CoCreateInstance(CLSID_ShellLibrary, nullptr,
+                                CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&plib));
+  if (SUCCEEDED(hr)) {
+    hr = plib->LoadLibraryFromKnownFolder(aFolderId, aMode);
+    if (SUCCEEDED(hr)) {
+      hr = plib->QueryInterface(riid, ppv);
+    }
+    plib->Release();
+  }
+  return hr;
+}
+#  endif
+
+#  if defined(MOZ_THUNDERBIRD) || defined(MOZ_SUITE)
+/*
+ * Return the default save-to location for the Windows Library passed in
+ * through aFolderId.
+ */
+static nsresult GetLibrarySaveToPath(int aFallbackFolderId,
+                                     REFKNOWNFOLDERID aFolderId,
+                                     nsIFile** aFile) {
+  RefPtr<IShellLibrary> shellLib;
+  RefPtr<IShellItem> savePath;
+  SHLoadLibraryFromKnownFolder(aFolderId, STGM_READ, IID_IShellLibrary,
+                               getter_AddRefs(shellLib));
+
+  if (shellLib && SUCCEEDED(shellLib->GetDefaultSaveFolder(
+                      DSFT_DETECT, IID_IShellItem, getter_AddRefs(savePath)))) {
+    wchar_t* str = nullptr;
+    if (SUCCEEDED(savePath->GetDisplayName(SIGDN_FILESYSPATH, &str))) {
+      nsAutoString path;
+      path.Assign(str);
+      path.Append('\\');
+      nsresult rv = NS_NewLocalFile(path, false, aFile);
+      CoTaskMemFree(str);
+      return rv;
+    }
+  }
+
+  return GetWindowsFolder(aFallbackFolderId, aFile);
+}
+#  endif
+
+/**
+ * Provides a fallback for getting the path to APPDATA or LOCALAPPDATA by
+ * querying the registry when the call to SHGetSpecialFolderPathW is unable to
+ * provide these paths (Bug 513958).
+ */
+static nsresult GetRegWindowsAppDataFolder(bool aLocal, nsIFile** aFile) {
+  HKEY key;
+  LPCWSTR keyName =
+      L"Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Shell Folders";
+  DWORD res = ::RegOpenKeyExW(HKEY_CURRENT_USER, keyName, 0, KEY_READ, &key);
+  if (res != ERROR_SUCCESS) {
+    return NS_ERROR_FAILURE;
+  }
+
+  WCHAR path[MAX_PATH + 2];
+  DWORD type, size;
+  res = RegQueryValueExW(key, (aLocal ? L"Local AppData" : L"AppData"), nullptr,
+                         &type, (LPBYTE)&path, &size);
+  ::RegCloseKey(key);
+  // The call to RegQueryValueExW must succeed, the type must be REG_SZ, the
+  // buffer size must not equal 0, and the buffer size be a multiple of 2.
+  if (res != ERROR_SUCCESS || type != REG_SZ || size == 0 || size % 2 != 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Append the trailing slash
+  int len = wcslen(path);
+  if (len > 1 && path[len - 1] != L'\\') {
+    path[len] = L'\\';
+    path[++len] = L'\0';
+  }
+
+  return NS_NewLocalFile(nsDependentString(path, len), true, aFile);
+}
+
+#endif  // XP_WIN
+
+#if defined(XP_UNIX)
+static nsresult GetUnixHomeDir(nsIFile** aFile) {
+#  if defined(ANDROID)
+  // XXX no home dir on android; maybe we should return the sdcard if present?
+  return NS_ERROR_FAILURE;
+#  else
+  return NS_NewNativeLocalFile(nsDependentCString(PR_GetEnv("HOME")), true,
+                               aFile);
+#  endif
+}
+
+static nsresult GetUnixSystemConfigDir(nsIFile** aFile) {
+#  if defined(ANDROID)
+  return NS_ERROR_FAILURE;
+#  else
+  nsAutoCString appName;
+  if (nsCOMPtr<nsIXULAppInfo> appInfo =
+          do_GetService("@mozilla.org/xre/app-info;1")) {
+    MOZ_TRY(appInfo->GetName(appName));
+  } else {
+    appName.AssignLiteral(MOZ_APP_BASENAME);
+  }
+
+  ToLowerCase(appName);
+
+  nsDependentCString sysConfigDir;
+  if (PR_GetEnv("XPCSHELL_TEST_PROFILE_DIR")) {
+    const char* mozSystemConfigDir = PR_GetEnv("MOZ_SYSTEM_CONFIG_DIR");
+    if (mozSystemConfigDir) {
+      sysConfigDir.Assign(nsDependentCString(mozSystemConfigDir));
+    }
+  }
+#    if defined(MOZ_WIDGET_GTK)
+  if (sysConfigDir.IsEmpty() && mozilla::widget::IsRunningUnderFlatpak()) {
+    sysConfigDir.Assign(nsLiteralCString("/app/etc"));
+  }
+#    endif
+  if (sysConfigDir.IsEmpty()) {
+    sysConfigDir.Assign(nsLiteralCString("/etc"));
+  }
+  MOZ_TRY(NS_NewNativeLocalFile(sysConfigDir, true, aFile));
+  MOZ_TRY((*aFile)->AppendNative(appName));
+  return NS_OK;
+#  endif
+}
+
+/*
+  The following license applies to the xdg_user_dir_lookup function:
+
+  Copyright (c) 2007 Red Hat, Inc.
+
+  Permission is hereby granted, free of charge, to any person
+  obtaining a copy of this software and associated documentation files
+  (the "Software"), to deal in the Software without restriction,
+  including without limitation the rights to use, copy, modify, merge,
+  publish, distribute, sublicense, and/or sell copies of the Software,
+  and to permit persons to whom the Software is furnished to do so,
+  subject to the following conditions:
+
+  The above copyright notice and this permission notice shall be
+  included in all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+  BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+  ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+  CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+  SOFTWARE.
+*/
+
+static char* xdg_user_dir_lookup(const char* aType) {
+  FILE* file;
+  char* home_dir;
+  char* config_home;
+  char* config_file;
+  char buffer[512];
+  char* user_dir;
+  char* p;
+  char* d;
+  int len;
+  int relative;
+
+  home_dir = getenv("HOME");
+
+  if (!home_dir) {
+    goto error;
+  }
+
+  config_home = getenv("XDG_CONFIG_HOME");
+  if (!config_home || config_home[0] == 0) {
+    config_file =
+        (char*)malloc(strlen(home_dir) + strlen("/.config/user-dirs.dirs") + 1);
+    if (!config_file) {
+      goto error;
+    }
+
+    strcpy(config_file, home_dir);
+    strcat(config_file, "/.config/user-dirs.dirs");
+  } else {
+    config_file =
+        (char*)malloc(strlen(config_home) + strlen("/user-dirs.dirs") + 1);
+    if (!config_file) {
+      goto error;
+    }
+
+    strcpy(config_file, config_home);
+    strcat(config_file, "/user-dirs.dirs");
+  }
+
+  file = fopen(config_file, "r");
+  free(config_file);
+  if (!file) {
+    goto error;
+  }
+
+  user_dir = nullptr;
+  while (fgets(buffer, sizeof(buffer), file)) {
+    /* Remove newline at end */
+    len = strlen(buffer);
+    if (len > 0 && buffer[len - 1] == '\n') {
+      buffer[len - 1] = 0;
+    }
+
+    p = buffer;
+    while (*p == ' ' || *p == '\t') {
+      p++;
+    }
+
+    if (strncmp(p, "XDG_", 4) != 0) {
+      continue;
+    }
+    p += 4;
+    if (strncmp(p, aType, strlen(aType)) != 0) {
+      continue;
+    }
+    p += strlen(aType);
+    if (strncmp(p, "_DIR", 4) != 0) {
+      continue;
+    }
+    p += 4;
+
+    while (*p == ' ' || *p == '\t') {
+      p++;
+    }
+
+    if (*p != '=') {
+      continue;
+    }
+    p++;
+
+    while (*p == ' ' || *p == '\t') {
+      p++;
+    }
+
+    if (*p != '"') {
+      continue;
+    }
+    p++;
+
+    relative = 0;
+    if (strncmp(p, "$HOME/", 6) == 0) {
+      p += 6;
+      relative = 1;
+    } else if (*p != '/') {
+      continue;
+    }
+
+    if (relative) {
+      user_dir = (char*)malloc(strlen(home_dir) + 1 + strlen(p) + 1);
+      if (!user_dir) {
+        goto error2;
+      }
+
+      strcpy(user_dir, home_dir);
+      strcat(user_dir, "/");
+    } else {
+      user_dir = (char*)malloc(strlen(p) + 1);
+      if (!user_dir) {
+        goto error2;
+      }
+
+      *user_dir = 0;
+    }
+
+    d = user_dir + strlen(user_dir);
+    while (*p && *p != '"') {
+      if ((*p == '\\') && (*(p + 1) != 0)) {
+        p++;
+      }
+      *d++ = *p++;
+    }
+    *d = 0;
+  }
+error2:
+  fclose(file);
+
+  if (user_dir) {
+    return user_dir;
+  }
+
+error:
+  return nullptr;
+}
+
+static const char xdg_user_dirs[] =
+    "DESKTOP\0"
+    "DOCUMENTS\0"
+    "DOWNLOAD\0"
+    "MUSIC\0"
+    "PICTURES\0"
+    "PUBLICSHARE\0"
+    "TEMPLATES\0"
+    "VIDEOS";
+
+static const uint8_t xdg_user_dir_offsets[] = {0, 8, 18, 27, 33, 42, 54, 64};
+
+static nsresult GetUnixXDGUserDirectory(SystemDirectories aSystemDirectory,
+                                        nsIFile** aFile) {
+  char* dir = xdg_user_dir_lookup(
+      xdg_user_dirs +
+      xdg_user_dir_offsets[aSystemDirectory - Unix_XDG_Desktop]);
+
+  nsresult rv;
+  nsCOMPtr<nsIFile> file;
+  bool exists;
+  if (dir) {
+    rv = NS_NewNativeLocalFile(nsDependentCString(dir), true,
+                               getter_AddRefs(file));
+    free(dir);
+
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    rv = file->Exists(&exists);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    if (!exists) {
+      rv = file->Create(nsIFile::DIRECTORY_TYPE, 0755);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    }
+  } else if (Unix_XDG_Desktop == aSystemDirectory) {
+    // for the XDG desktop dir, fall back to HOME/Desktop
+    // (for historical compatibility)
+    nsCOMPtr<nsIFile> home;
+    rv = GetUnixHomeDir(getter_AddRefs(home));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    rv = home->Clone(getter_AddRefs(file));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    rv = file->AppendNative("Desktop"_ns);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    rv = file->Exists(&exists);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // fallback to HOME only if HOME/Desktop doesn't exist
+    if (!exists) {
+      file = home;
+    }
+  } else {
+    // no fallback for the other XDG dirs
+    return NS_ERROR_FAILURE;
+  }
+
+  *aFile = nullptr;
+  file.swap(*aFile);
+
+  return NS_OK;
+}
+#endif
+
+nsresult GetSpecialSystemDirectory(SystemDirectories aSystemSystemDirectory,
+                                   nsIFile** aFile) {
+#if defined(XP_WIN)
+  WCHAR path[MAX_PATH];
+#else
+  char path[MAXPATHLEN];
+#endif
+
+  switch (aSystemSystemDirectory) {
+    case OS_CurrentWorkingDirectory:
+#if defined(XP_WIN)
+      if (!_wgetcwd(path, MAX_PATH)) {
+        return NS_ERROR_FAILURE;
+      }
+      return NS_NewLocalFile(nsDependentString(path), true, aFile);
+#else
+      if (!getcwd(path, MAXPATHLEN)) {
+        return NS_ERROR_FAILURE;
+      }
+#endif
+
+#if !defined(XP_WIN)
+      return NS_NewNativeLocalFile(nsDependentCString(path), true, aFile);
+#endif
+
+    case OS_TemporaryDirectory:
+#if defined(XP_WIN)
+    {
+      DWORD len = ::GetTempPathW(MAX_PATH, path);
+      if (len == 0) {
+        break;
+      }
+      return NS_NewLocalFile(nsDependentString(path, len), true, aFile);
+    }
+#elif defined(MOZ_WIDGET_COCOA)
+    {
+      return GetOSXFolderType(kUserDomain, kTemporaryFolderType, aFile);
+    }
+
+#elif defined(XP_UNIX)
+    {
+      static const char* tPath = nullptr;
+      if (!tPath) {
+        tPath = PR_GetEnv("TMPDIR");
+        if (!tPath || !*tPath) {
+          tPath = PR_GetEnv("TMP");
+          if (!tPath || !*tPath) {
+            tPath = PR_GetEnv("TEMP");
+            if (!tPath || !*tPath) {
+              tPath = "/tmp/";
+            }
+          }
+        }
+      }
+      return NS_NewNativeLocalFile(nsDependentCString(tPath), true, aFile);
+    }
+#else
+      break;
+#endif
+#if defined(MOZ_WIDGET_COCOA)
+    case Mac_SystemDirectory: {
+      return GetOSXFolderType(kClassicDomain, kSystemFolderType, aFile);
+    }
+    case Mac_UserLibDirectory: {
+      return GetOSXFolderType(kUserDomain, kDomainLibraryFolderType, aFile);
+    }
+    case Mac_HomeDirectory: {
+      return GetOSXFolderType(kUserDomain, kDomainTopLevelFolderType, aFile);
+    }
+    case Mac_DefaultDownloadDirectory: {
+      nsresult rv = GetOSXFolderType(kUserDomain, kDownloadsFolderType, aFile);
+      if (NS_FAILED(rv)) {
+        return GetOSXFolderType(kUserDomain, kDesktopFolderType, aFile);
+      }
+      return NS_OK;
+    }
+    case Mac_UserDesktopDirectory: {
+      return GetOSXFolderType(kUserDomain, kDesktopFolderType, aFile);
+    }
+    case Mac_LocalApplicationsDirectory: {
+      return GetOSXFolderType(kLocalDomain, kApplicationsFolderType, aFile);
+    }
+    case Mac_UserPreferencesDirectory: {
+      return GetOSXFolderType(kUserDomain, kPreferencesFolderType, aFile);
+    }
+    case Mac_PictureDocumentsDirectory: {
+      return GetOSXFolderType(kUserDomain, kPictureDocumentsFolderType, aFile);
+    }
+    case Mac_DefaultScreenshotDirectory: {
+      auto prefValue = CFTypeRefPtr<CFPropertyListRef>::WrapUnderCreateRule(
+          CFPreferencesCopyAppValue(CFSTR("location"),
+                                    CFSTR("com.apple.screencapture")));
+
+      if (!prefValue || CFGetTypeID(prefValue.get()) != CFStringGetTypeID()) {
+        return GetOSXFolderType(kUserDomain, kPictureDocumentsFolderType,
+                                aFile);
+      }
+
+      nsAutoString path;
+      mozilla::Span<char16_t> data =
+          path.GetMutableData(CFStringGetLength((CFStringRef)prefValue.get()));
+      CFStringGetCharacters((CFStringRef)prefValue.get(),
+                            CFRangeMake(0, data.Length()),
+                            reinterpret_cast<UniChar*>(data.Elements()));
+
+      return NS_NewLocalFile(path, true, aFile);
+    }
+#elif defined(XP_WIN)
+    case Win_SystemDirectory: {
+      int32_t len = ::GetSystemDirectoryW(path, MAX_PATH);
+
+      // Need enough space to add the trailing backslash
+      if (!len || len > MAX_PATH - 2) {
+        break;
+      }
+      path[len] = L'\\';
+      path[++len] = L'\0';
+
+      return NS_NewLocalFile(nsDependentString(path, len), true, aFile);
+    }
+
+    case Win_WindowsDirectory: {
+      int32_t len = ::GetWindowsDirectoryW(path, MAX_PATH);
+
+      // Need enough space to add the trailing backslash
+      if (!len || len > MAX_PATH - 2) {
+        break;
+      }
+
+      path[len] = L'\\';
+      path[++len] = L'\0';
+
+      return NS_NewLocalFile(nsDependentString(path, len), true, aFile);
+    }
+
+    case Win_ProgramFiles: {
+      return GetWindowsFolder(CSIDL_PROGRAM_FILES, aFile);
+    }
+
+    case Win_HomeDirectory: {
+      nsresult rv = GetWindowsFolder(CSIDL_PROFILE, aFile);
+      if (NS_SUCCEEDED(rv)) {
+        return rv;
+      }
+
+      int32_t len;
+      if ((len = ::GetEnvironmentVariableW(L"HOME", path, MAX_PATH)) > 0) {
+        // Need enough space to add the trailing backslash
+        if (len > MAX_PATH - 2) {
+          break;
+        }
+
+        path[len] = L'\\';
+        path[++len] = L'\0';
+
+        rv = NS_NewLocalFile(nsDependentString(path, len), true, aFile);
+        if (NS_SUCCEEDED(rv)) {
+          return rv;
+        }
+      }
+
+      len = ::GetEnvironmentVariableW(L"HOMEDRIVE", path, MAX_PATH);
+      if (0 < len && len < MAX_PATH) {
+        WCHAR temp[MAX_PATH];
+        DWORD len2 = ::GetEnvironmentVariableW(L"HOMEPATH", temp, MAX_PATH);
+        if (0 < len2 && len + len2 < MAX_PATH) {
+          wcsncat(path, temp, len2);
+        }
+
+        len = wcslen(path);
+
+        // Need enough space to add the trailing backslash
+        if (len > MAX_PATH - 2) {
+          break;
+        }
+
+        path[len] = L'\\';
+        path[++len] = L'\0';
+
+        return NS_NewLocalFile(nsDependentString(path, len), true, aFile);
+      }
+      break;
+    }
+    case Win_Programs: {
+      return GetWindowsFolder(CSIDL_PROGRAMS, aFile);
+    }
+
+    case Win_Downloads: {
+      // Defined in KnownFolders.h.
+      GUID folderid_downloads = {
+          0x374de290,
+          0x123f,
+          0x4565,
+          {0x91, 0x64, 0x39, 0xc4, 0x92, 0x5e, 0x46, 0x7b}};
+      nsresult rv = GetKnownFolder(&folderid_downloads, aFile);
+      // On WinXP, there is no downloads folder, default
+      // to 'Desktop'.
+      if (NS_ERROR_FAILURE == rv) {
+        rv = GetWindowsFolder(CSIDL_DESKTOP, aFile);
+      }
+      return rv;
+    }
+
+    case Win_Favorites: {
+      return GetWindowsFolder(CSIDL_FAVORITES, aFile);
+    }
+    case Win_Desktopdirectory: {
+      return GetWindowsFolder(CSIDL_DESKTOPDIRECTORY, aFile);
+    }
+    case Win_Cookies: {
+      return GetWindowsFolder(CSIDL_COOKIES, aFile);
+    }
+    case Win_Appdata: {
+      nsresult rv = GetWindowsFolder(CSIDL_APPDATA, aFile);
+      if (NS_FAILED(rv)) {
+        rv = GetRegWindowsAppDataFolder(false, aFile);
+      }
+      return rv;
+    }
+    case Win_LocalAppdata: {
+      nsresult rv = GetWindowsFolder(CSIDL_LOCAL_APPDATA, aFile);
+      if (NS_FAILED(rv)) {
+        rv = GetRegWindowsAppDataFolder(true, aFile);
+      }
+      return rv;
+    }
+#  if defined(MOZ_THUNDERBIRD) || defined(MOZ_SUITE)
+    case Win_Documents: {
+      return GetLibrarySaveToPath(CSIDL_MYDOCUMENTS, FOLDERID_DocumentsLibrary,
+                                  aFile);
+    }
+#  endif
+#endif  // XP_WIN
+
+#if defined(XP_UNIX)
+    case Unix_HomeDirectory:
+      return GetUnixHomeDir(aFile);
+
+    case Unix_XDG_Desktop:
+    case Unix_XDG_Download:
+      return GetUnixXDGUserDirectory(aSystemSystemDirectory, aFile);
+
+    case Unix_SystemConfigDirectory:
+      return GetUnixSystemConfigDir(aFile);
+#endif
+
+    default:
+      break;
+  }
+  return NS_ERROR_NOT_AVAILABLE;
+}
+
+#if defined(MOZ_WIDGET_COCOA)
+nsresult GetOSXFolderType(short aDomain, OSType aFolderType,
+                          nsIFile** aLocalFile) {
+  nsresult rv = NS_ERROR_FAILURE;
+
+  if (aFolderType == kTemporaryFolderType) {
+    NS_NewLocalFile(u""_ns, true, aLocalFile);
+    nsCOMPtr<nsILocalFileMac> localMacFile(do_QueryInterface(*aLocalFile));
+    if (localMacFile) {
+      rv = localMacFile->InitWithCFURL(
+          CocoaFileUtils::GetTemporaryFolderCFURLRef());
+    }
+    return rv;
+  }
+
+  OSErr err;
+  FSRef fsRef;
+  err = ::FSFindFolder(aDomain, aFolderType, kCreateFolder, &fsRef);
+  if (err == noErr) {
+    NS_NewLocalFile(u""_ns, true, aLocalFile);
+    nsCOMPtr<nsILocalFileMac> localMacFile(do_QueryInterface(*aLocalFile));
+    if (localMacFile) {
+      rv = localMacFile->InitWithFSRef(&fsRef);
+    }
+  }
+  return rv;
+}
+#endif
diff --git a/xpcom/io/SpecialSystemDirectory.h b/xpcom/io/SpecialSystemDirectory.h
new file mode 100644
index 0000000000..e760b0ae26
--- /dev/null
+++ b/xpcom/io/SpecialSystemDirectory.h
@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef _SPECIALSYSTEMDIRECTORY_H_
+#define _SPECIALSYSTEMDIRECTORY_H_
+
+#include "nscore.h"
+#include "nsIFile.h"
+
+#ifdef MOZ_WIDGET_COCOA
+#  include "nsILocalFileMac.h"
+#  include "prenv.h"
+#endif
+
+enum SystemDirectories {
+  OS_TemporaryDirectory = 2,
+  // 3 Used to be OS_CurrentProcessDirectory, which we never actually
+  //   supported getting...
+  OS_CurrentWorkingDirectory = 4,
+
+  Mac_SystemDirectory = 101,
+  Mac_UserLibDirectory = 102,
+  Mac_HomeDirectory = 103,
+  Mac_DefaultDownloadDirectory = 104,
+  Mac_UserDesktopDirectory = 105,
+  Mac_LocalApplicationsDirectory = 106,
+  Mac_UserPreferencesDirectory = 107,
+  Mac_PictureDocumentsDirectory = 108,
+  Mac_DefaultScreenshotDirectory = 109,
+
+  Win_SystemDirectory = 201,
+  Win_WindowsDirectory = 202,
+  Win_HomeDirectory = 203,
+  Win_Programs = 205,
+  Win_Favorites = 209,
+  Win_Desktopdirectory = 213,
+  Win_Appdata = 221,
+  Win_Cookies = 223,
+  Win_LocalAppdata = 224,
+  Win_ProgramFiles = 225,
+  Win_Downloads = 226,
+#if defined(MOZ_THUNDERBIRD) || defined(MOZ_SUITE)
+  Win_Documents = 228,
+#endif
+
+  Unix_HomeDirectory = 303,
+  Unix_XDG_Desktop = 304,
+  Unix_XDG_Download = 306,
+  Unix_SystemConfigDirectory = 307
+};
+
+nsresult GetSpecialSystemDirectory(SystemDirectories aSystemSystemDirectory,
+                                   nsIFile** aFile);
+#ifdef MOZ_WIDGET_COCOA
+nsresult GetOSXFolderType(short aDomain, OSType aFolderType,
+                          nsIFile** aLocalFile);
+#endif
+
+#endif
diff --git a/xpcom/io/StreamBufferSink.h b/xpcom/io/StreamBufferSink.h
new file mode 100644
index 0000000000..bf00527aea
--- /dev/null
+++ b/xpcom/io/StreamBufferSink.h
@@ -0,0 +1,29 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_StreamBufferSink_h
+#define mozilla_StreamBufferSink_h
+
+#include <cstddef>
+#include "mozilla/Span.h"
+#include "nsString.h"
+
+namespace mozilla {
+
+class StreamBufferSink {
+ public:
+  virtual mozilla::Span<char> Data() = 0;
+
+  nsDependentCSubstring Slice(size_t aOffset) {
+    return nsDependentCSubstring(Data().First(aOffset));
+  }
+
+  virtual ~StreamBufferSink() = default;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_StreamBufferSink_h
diff --git a/xpcom/io/StreamBufferSinkImpl.h b/xpcom/io/StreamBufferSinkImpl.h
new file mode 100644
index 0000000000..9fba413ef2
--- /dev/null
+++ b/xpcom/io/StreamBufferSinkImpl.h
@@ -0,0 +1,49 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_StreamBufferSinkImpl_h
+#define mozilla_StreamBufferSinkImpl_h
+
+#include "mozilla/Buffer.h"
+#include "mozilla/StreamBufferSink.h"
+#include "mozilla/UniquePtr.h"
+
+namespace mozilla {
+
+class BufferSink final : public StreamBufferSink {
+ public:
+  explicit BufferSink(Buffer<char>&& aBuffer) : mBuffer(std::move(aBuffer)) {}
+
+  explicit BufferSink(size_t aLength) : mBuffer(aLength) {}
+
+  static UniquePtr<BufferSink> Alloc(size_t aLength) {
+    auto maybeBuffer = Buffer<char>::Alloc(aLength);
+    if (!maybeBuffer) {
+      return nullptr;
+    }
+
+    return MakeUnique<BufferSink>(maybeBuffer.extract());
+  }
+
+  mozilla::Span<char> Data() override { return mBuffer.AsWritableSpan(); }
+
+ private:
+  Buffer<char> mBuffer;
+};
+
+class nsBorrowedSink final : public StreamBufferSink {
+ public:
+  explicit nsBorrowedSink(mozilla::Span<char> aBuffer) : mBuffer(aBuffer) {}
+
+  mozilla::Span<char> Data() override { return mBuffer; }
+
+ private:
+  mozilla::Span<char> mBuffer;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_StreamBufferSinkImpl_h
diff --git a/xpcom/io/StreamBufferSource.h b/xpcom/io/StreamBufferSource.h
new file mode 100644
index 0000000000..f0a3d30eea
--- /dev/null
+++ b/xpcom/io/StreamBufferSource.h
@@ -0,0 +1,61 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_StreamBufferSource_h
+#define mozilla_StreamBufferSource_h
+
+#include <cstddef>
+#include "ErrorList.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/Span.h"
+#include "nsISupportsImpl.h"
+#include "nsString.h"
+
+namespace mozilla {
+
+class StreamBufferSource {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(StreamBufferSource)
+
+  virtual Span<const char> Data() = 0;
+
+  virtual nsresult GetData(nsACString& aString) {
+    Span<const char> data = Data();
+    if (!aString.Assign(data.Elements(), data.Length(), fallible)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    return NS_OK;
+  }
+
+  virtual bool Owning() = 0;
+
+  virtual size_t SizeOfExcludingThisIfUnshared(MallocSizeOf aMallocSizeOf) {
+    return SizeOfExcludingThisEvenIfShared(aMallocSizeOf);
+  }
+  size_t SizeOfIncludingThisIfUnshared(MallocSizeOf aMallocSizeOf) {
+    if (mRefCnt > 1) {
+      return 0;
+    }
+    size_t n = aMallocSizeOf(this);
+    n += SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+    return n;
+  }
+
+  virtual size_t SizeOfExcludingThisEvenIfShared(
+      MallocSizeOf aMallocSizeOf) = 0;
+  size_t SizeOfIncludingThisEvenIfShared(MallocSizeOf aMallocSizeOf) {
+    size_t n = aMallocSizeOf(this);
+    n += SizeOfExcludingThisEvenIfShared(aMallocSizeOf);
+    return n;
+  }
+
+ protected:
+  virtual ~StreamBufferSource() = default;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_StreamBufferSource_h
diff --git a/xpcom/io/StreamBufferSourceImpl.h b/xpcom/io/StreamBufferSourceImpl.h
new file mode 100644
index 0000000000..0d04adcc24
--- /dev/null
+++ b/xpcom/io/StreamBufferSourceImpl.h
@@ -0,0 +1,82 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_StreamBufferSourceImpl_h
+#define mozilla_StreamBufferSourceImpl_h
+
+#include "mozilla/StreamBufferSource.h"
+
+#include "nsTArray.h"
+
+namespace mozilla {
+
+class nsTArraySource final : public StreamBufferSource {
+ public:
+  explicit nsTArraySource(nsTArray<uint8_t>&& aArray)
+      : mArray(std::move(aArray)) {}
+
+  Span<const char> Data() override {
+    return Span{reinterpret_cast<const char*>(mArray.Elements()),
+                mArray.Length()};
+  }
+
+  bool Owning() override { return true; }
+
+  size_t SizeOfExcludingThisEvenIfShared(MallocSizeOf aMallocSizeOf) override {
+    return mArray.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  }
+
+ private:
+  const nsTArray<uint8_t> mArray;
+};
+
+class nsCStringSource final : public StreamBufferSource {
+ public:
+  explicit nsCStringSource(nsACString&& aString)
+      : mString(std::move(aString)) {}
+
+  Span<const char> Data() override { return mString; }
+
+  nsresult GetData(nsACString& aString) override {
+    if (!aString.Assign(mString, fallible)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    return NS_OK;
+  }
+
+  bool Owning() override { return true; }
+
+  size_t SizeOfExcludingThisIfUnshared(MallocSizeOf aMallocSizeOf) override {
+    return mString.SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+  }
+
+  size_t SizeOfExcludingThisEvenIfShared(MallocSizeOf aMallocSizeOf) override {
+    return mString.SizeOfExcludingThisEvenIfShared(aMallocSizeOf);
+  }
+
+ private:
+  const nsCString mString;
+};
+
+class nsBorrowedSource final : public StreamBufferSource {
+ public:
+  explicit nsBorrowedSource(Span<const char> aBuffer) : mBuffer(aBuffer) {}
+
+  Span<const char> Data() override { return mBuffer; }
+
+  bool Owning() override { return false; }
+
+  size_t SizeOfExcludingThisEvenIfShared(MallocSizeOf aMallocSizeOf) override {
+    return 0;
+  }
+
+ private:
+  const Span<const char> mBuffer;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_StreamBufferSourceImpl_h
diff --git a/xpcom/io/components.conf b/xpcom/io/components.conf
new file mode 100644
index 0000000000..0c4f44b712
--- /dev/null
+++ b/xpcom/io/components.conf
@@ -0,0 +1,42 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+Classes = [
+    {
+        'name': 'Directory',
+        'js_name': 'dirsvc',
+        'cid': '{f00152d0-b40b-11d3-8c9c-000064657374}',
+        'contract_ids': ['@mozilla.org/file/directory_service;1'],
+        'interfaces': ['nsIDirectoryService', 'nsIProperties'],
+        'legacy_constructor': 'nsDirectoryService::Create',
+        'headers': ['nsDirectoryService.h'],
+    },
+    {
+        'cid': '{565e3a2c-1dd2-11b2-8da1-b4cef17e568d}',
+        'contract_ids': ['@mozilla.org/io/multiplex-input-stream;1'],
+        'legacy_constructor': 'nsMultiplexInputStreamConstructor',
+        'headers': ['nsMultiplexInputStream.h'],
+    },
+    {
+        'cid': '{e4a0ee4e-0775-457b-9118-b3ae97a7c758}',
+        'contract_ids': ['@mozilla.org/pipe;1'],
+        'legacy_constructor': 'nsPipeConstructor',
+        'headers': ['/xpcom/io/nsPipe.h'],
+    },
+    {
+        'cid': '{7225c040-a9bf-11d3-a197-0050041caf44}',
+        'contract_ids': ['@mozilla.org/scriptableinputstream;1'],
+        'legacy_constructor': 'nsScriptableInputStream::Create',
+        'headers': ['nsScriptableInputStream.h'],
+    },
+    {
+        'cid': '{0abb0835-5000-4790-af28-61b3ba17c295}',
+        'contract_ids': ['@mozilla.org/io/string-input-stream;1'],
+        'legacy_constructor': 'nsStringInputStreamConstructor',
+        'headers': ['/xpcom/build/XPCOMModule.h'],
+        'processes': ProcessSelector.ALLOW_IN_SOCKET_PROCESS,
+    },
+]
diff --git a/xpcom/io/crc32c.c b/xpcom/io/crc32c.c
new file mode 100644
index 0000000000..3494945c0f
--- /dev/null
+++ b/xpcom/io/crc32c.c
@@ -0,0 +1,154 @@
+/*
+ * Based on file found here:
+ *
+ *   https://svnweb.freebsd.org/base/stable/10/sys/libkern/crc32.c?revision=256281
+ */
+
+/*-
+ *  COPYRIGHT (C) 1986 Gary S. Brown.  You may use this program, or
+ *  code or tables extracted from it, as desired without restriction.
+ */
+
+/*
+ *  First, the polynomial itself and its table of feedback terms.  The
+ *  polynomial is
+ *  X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0
+ *
+ *  Note that we take it "backwards" and put the highest-order term in
+ *  the lowest-order bit.  The X^32 term is "implied"; the LSB is the
+ *  X^31 term, etc.  The X^0 term (usually shown as "+1") results in
+ *  the MSB being 1
+ *
+ *  Note that the usual hardware shift register implementation, which
+ *  is what we're using (we're merely optimizing it by doing eight-bit
+ *  chunks at a time) shifts bits into the lowest-order term.  In our
+ *  implementation, that means shifting towards the right.  Why do we
+ *  do it this way?  Because the calculated CRC must be transmitted in
+ *  order from highest-order term to lowest-order term.  UARTs transmit
+ *  characters in order from LSB to MSB.  By storing the CRC this way
+ *  we hand it to the UART in the order low-byte to high-byte; the UART
+ *  sends each low-bit to hight-bit; and the result is transmission bit
+ *  by bit from highest- to lowest-order term without requiring any bit
+ *  shuffling on our part.  Reception works similarly
+ *
+ *  The feedback terms table consists of 256, 32-bit entries.  Notes
+ *
+ *      The table can be generated at runtime if desired; code to do so
+ *      is shown later.  It might not be obvious, but the feedback
+ *      terms simply represent the results of eight shift/xor opera
+ *      tions for all combinations of data and CRC register values
+ *
+ *      The values must be right-shifted by eight bits by the "updcrc
+ *      logic; the shift must be unsigned (bring in zeroes).  On some
+ *      hardware you could probably optimize the shift in assembler by
+ *      using byte-swap instructions
+ *      polynomial $edb88320
+ *
+ *
+ * CRC32 code derived from work by Gary S. Brown.
+ */
+
+#include "crc32c.h"
+
+/* CRC32C routines, these use a different polynomial */
+/*****************************************************************/
+/*                                                               */
+/* CRC LOOKUP TABLE                                              */
+/* ================                                              */
+/* The following CRC lookup table was generated automagically    */
+/* by the Rocksoft^tm Model CRC Algorithm Table Generation       */
+/* Program V1.0 using the following model parameters:            */
+/*                                                               */
+/*    Width   : 4 bytes.                                         */
+/*    Poly    : 0x1EDC6F41L                                      */
+/*    Reverse : TRUE.                                            */
+/*                                                               */
+/* For more information on the Rocksoft^tm Model CRC Algorithm,  */
+/* see the document titled "A Painless Guide to CRC Error        */
+/* Detection Algorithms" by Ross Williams                        */
+/* (ross@guest.adelaide.edu.au.). This document is likely to be  */
+/* in the FTP archive "ftp.adelaide.edu.au/pub/rocksoft".        */
+/*                                                               */
+/*****************************************************************/
+
+static const uint32_t crc32Table[256] = {
+	0x00000000L, 0xF26B8303L, 0xE13B70F7L, 0x1350F3F4L,
+	0xC79A971FL, 0x35F1141CL, 0x26A1E7E8L, 0xD4CA64EBL,
+	0x8AD958CFL, 0x78B2DBCCL, 0x6BE22838L, 0x9989AB3BL,
+	0x4D43CFD0L, 0xBF284CD3L, 0xAC78BF27L, 0x5E133C24L,
+	0x105EC76FL, 0xE235446CL, 0xF165B798L, 0x030E349BL,
+	0xD7C45070L, 0x25AFD373L, 0x36FF2087L, 0xC494A384L,
+	0x9A879FA0L, 0x68EC1CA3L, 0x7BBCEF57L, 0x89D76C54L,
+	0x5D1D08BFL, 0xAF768BBCL, 0xBC267848L, 0x4E4DFB4BL,
+	0x20BD8EDEL, 0xD2D60DDDL, 0xC186FE29L, 0x33ED7D2AL,
+	0xE72719C1L, 0x154C9AC2L, 0x061C6936L, 0xF477EA35L,
+	0xAA64D611L, 0x580F5512L, 0x4B5FA6E6L, 0xB93425E5L,
+	0x6DFE410EL, 0x9F95C20DL, 0x8CC531F9L, 0x7EAEB2FAL,
+	0x30E349B1L, 0xC288CAB2L, 0xD1D83946L, 0x23B3BA45L,
+	0xF779DEAEL, 0x05125DADL, 0x1642AE59L, 0xE4292D5AL,
+	0xBA3A117EL, 0x4851927DL, 0x5B016189L, 0xA96AE28AL,
+	0x7DA08661L, 0x8FCB0562L, 0x9C9BF696L, 0x6EF07595L,
+	0x417B1DBCL, 0xB3109EBFL, 0xA0406D4BL, 0x522BEE48L,
+	0x86E18AA3L, 0x748A09A0L, 0x67DAFA54L, 0x95B17957L,
+	0xCBA24573L, 0x39C9C670L, 0x2A993584L, 0xD8F2B687L,
+	0x0C38D26CL, 0xFE53516FL, 0xED03A29BL, 0x1F682198L,
+	0x5125DAD3L, 0xA34E59D0L, 0xB01EAA24L, 0x42752927L,
+	0x96BF4DCCL, 0x64D4CECFL, 0x77843D3BL, 0x85EFBE38L,
+	0xDBFC821CL, 0x2997011FL, 0x3AC7F2EBL, 0xC8AC71E8L,
+	0x1C661503L, 0xEE0D9600L, 0xFD5D65F4L, 0x0F36E6F7L,
+	0x61C69362L, 0x93AD1061L, 0x80FDE395L, 0x72966096L,
+	0xA65C047DL, 0x5437877EL, 0x4767748AL, 0xB50CF789L,
+	0xEB1FCBADL, 0x197448AEL, 0x0A24BB5AL, 0xF84F3859L,
+	0x2C855CB2L, 0xDEEEDFB1L, 0xCDBE2C45L, 0x3FD5AF46L,
+	0x7198540DL, 0x83F3D70EL, 0x90A324FAL, 0x62C8A7F9L,
+	0xB602C312L, 0x44694011L, 0x5739B3E5L, 0xA55230E6L,
+	0xFB410CC2L, 0x092A8FC1L, 0x1A7A7C35L, 0xE811FF36L,
+	0x3CDB9BDDL, 0xCEB018DEL, 0xDDE0EB2AL, 0x2F8B6829L,
+	0x82F63B78L, 0x709DB87BL, 0x63CD4B8FL, 0x91A6C88CL,
+	0x456CAC67L, 0xB7072F64L, 0xA457DC90L, 0x563C5F93L,
+	0x082F63B7L, 0xFA44E0B4L, 0xE9141340L, 0x1B7F9043L,
+	0xCFB5F4A8L, 0x3DDE77ABL, 0x2E8E845FL, 0xDCE5075CL,
+	0x92A8FC17L, 0x60C37F14L, 0x73938CE0L, 0x81F80FE3L,
+	0x55326B08L, 0xA759E80BL, 0xB4091BFFL, 0x466298FCL,
+	0x1871A4D8L, 0xEA1A27DBL, 0xF94AD42FL, 0x0B21572CL,
+	0xDFEB33C7L, 0x2D80B0C4L, 0x3ED04330L, 0xCCBBC033L,
+	0xA24BB5A6L, 0x502036A5L, 0x4370C551L, 0xB11B4652L,
+	0x65D122B9L, 0x97BAA1BAL, 0x84EA524EL, 0x7681D14DL,
+	0x2892ED69L, 0xDAF96E6AL, 0xC9A99D9EL, 0x3BC21E9DL,
+	0xEF087A76L, 0x1D63F975L, 0x0E330A81L, 0xFC588982L,
+	0xB21572C9L, 0x407EF1CAL, 0x532E023EL, 0xA145813DL,
+	0x758FE5D6L, 0x87E466D5L, 0x94B49521L, 0x66DF1622L,
+	0x38CC2A06L, 0xCAA7A905L, 0xD9F75AF1L, 0x2B9CD9F2L,
+	0xFF56BD19L, 0x0D3D3E1AL, 0x1E6DCDEEL, 0xEC064EEDL,
+	0xC38D26C4L, 0x31E6A5C7L, 0x22B65633L, 0xD0DDD530L,
+	0x0417B1DBL, 0xF67C32D8L, 0xE52CC12CL, 0x1747422FL,
+	0x49547E0BL, 0xBB3FFD08L, 0xA86F0EFCL, 0x5A048DFFL,
+	0x8ECEE914L, 0x7CA56A17L, 0x6FF599E3L, 0x9D9E1AE0L,
+	0xD3D3E1ABL, 0x21B862A8L, 0x32E8915CL, 0xC083125FL,
+	0x144976B4L, 0xE622F5B7L, 0xF5720643L, 0x07198540L,
+	0x590AB964L, 0xAB613A67L, 0xB831C993L, 0x4A5A4A90L,
+	0x9E902E7BL, 0x6CFBAD78L, 0x7FAB5E8CL, 0x8DC0DD8FL,
+	0xE330A81AL, 0x115B2B19L, 0x020BD8EDL, 0xF0605BEEL,
+	0x24AA3F05L, 0xD6C1BC06L, 0xC5914FF2L, 0x37FACCF1L,
+	0x69E9F0D5L, 0x9B8273D6L, 0x88D28022L, 0x7AB90321L,
+	0xAE7367CAL, 0x5C18E4C9L, 0x4F48173DL, 0xBD23943EL,
+	0xF36E6F75L, 0x0105EC76L, 0x12551F82L, 0xE03E9C81L,
+	0x34F4F86AL, 0xC69F7B69L, 0xD5CF889DL, 0x27A40B9EL,
+	0x79B737BAL, 0x8BDCB4B9L, 0x988C474DL, 0x6AE7C44EL,
+	0xBE2DA0A5L, 0x4C4623A6L, 0x5F16D052L, 0xAD7D5351L
+};
+
+// NOTE: See source URL at top of this file for multitable implementation which
+//       offers a performance boost at the cost of ~8KB of static tables.
+
+uint32_t
+ComputeCrc32c(uint32_t crc, const void *buf, size_t size)
+{
+	const uint8_t *p = buf;
+
+
+	while (size--)
+		crc = crc32Table[(crc ^ *p++) & 0xff] ^ (crc >> 8);
+
+	return crc;
+}
diff --git a/xpcom/io/crc32c.h b/xpcom/io/crc32c.h
new file mode 100644
index 0000000000..2830c28659
--- /dev/null
+++ b/xpcom/io/crc32c.h
@@ -0,0 +1,26 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef crc32c_h
+#define crc32c_h
+
+#include <stdint.h>
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Compute a CRC32c as defined in RFC3720.  This is a different polynomial than
+// what is used in the crc for zlib, etc.  Typical usage to calculate a new CRC:
+//
+//    ComputeCrc32c(~0, buffer, bufferLength);
+//
+uint32_t ComputeCrc32c(uint32_t aCrc, const void* aBuf, size_t aSize);
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // crc32c_h
diff --git a/xpcom/io/moz.build b/xpcom/io/moz.build
new file mode 100644
index 0000000000..97fe1663ab
--- /dev/null
+++ b/xpcom/io/moz.build
@@ -0,0 +1,162 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+XPIDL_SOURCES += [
+    "nsIAsyncInputStream.idl",
+    "nsIAsyncOutputStream.idl",
+    "nsIBinaryInputStream.idl",
+    "nsIBinaryOutputStream.idl",
+    "nsICloneableInputStream.idl",
+    "nsIConverterInputStream.idl",
+    "nsIConverterOutputStream.idl",
+    "nsIDirectoryEnumerator.idl",
+    "nsIDirectoryService.idl",
+    "nsIFile.idl",
+    "nsIInputStream.idl",
+    "nsIInputStreamLength.idl",
+    "nsIInputStreamPriority.idl",
+    "nsIInputStreamTee.idl",
+    "nsIIOUtil.idl",
+    "nsILineInputStream.idl",
+    "nsILocalFileWin.idl",
+    "nsIMultiplexInputStream.idl",
+    "nsIObjectInputStream.idl",
+    "nsIObjectOutputStream.idl",
+    "nsIOutputStream.idl",
+    "nsIPipe.idl",
+    "nsIRandomAccessStream.idl",
+    "nsISafeOutputStream.idl",
+    "nsIScriptableBase64Encoder.idl",
+    "nsIScriptableInputStream.idl",
+    "nsISeekableStream.idl",
+    "nsIStorageStream.idl",
+    "nsIStreamBufferAccess.idl",
+    "nsIStringStream.idl",
+    "nsITellableStream.idl",
+    "nsIUnicharInputStream.idl",
+    "nsIUnicharLineInputStream.idl",
+    "nsIUnicharOutputStream.idl",
+]
+
+if CONFIG["MOZ_WIDGET_TOOLKIT"] == "cocoa":
+    XPIDL_SOURCES += [
+        "nsILocalFileMac.idl",
+    ]
+
+if CONFIG["MOZ_WIDGET_TOOLKIT"] == "windows":
+    EXPORTS += ["nsLocalFileWin.h"]
+    EXPORTS.mozilla += [
+        "FileUtilsWin.h",
+    ]
+    SOURCES += [
+        "FileUtilsWin.cpp",
+        "nsLocalFileWin.cpp",
+    ]
+else:
+    EXPORTS += ["nsLocalFileUnix.h"]
+    SOURCES += [
+        "nsLocalFileUnix.cpp",
+    ]
+
+XPIDL_MODULE = "xpcom_io"
+
+XPCOM_MANIFESTS += [
+    "components.conf",
+]
+
+EXPORTS += [
+    "FileDescriptorFile.h",
+    "nsAnonymousTemporaryFile.h",
+    "nsAppDirectoryServiceDefs.h",
+    "nsDirectoryService.h",
+    "nsDirectoryServiceDefs.h",
+    "nsDirectoryServiceUtils.h",
+    "nsEscape.h",
+    "nsLinebreakConverter.h",
+    "nsLocalFile.h",
+    "nsLocalFileCommon.h",
+    "nsMultiplexInputStream.h",
+    "nsNativeCharsetUtils.h",
+    "nsScriptableInputStream.h",
+    "nsStorageStream.h",
+    "nsStreamUtils.h",
+    "nsStringStream.h",
+    "nsUnicharInputStream.h",
+    "nsWildCard.h",
+    "SpecialSystemDirectory.h",
+]
+
+EXPORTS.mozilla += [
+    "Base64.h",
+    "FilePreferences.h",
+    "FixedBufferOutputStream.h",
+    "InputStreamLengthHelper.h",
+    "InputStreamLengthWrapper.h",
+    "NonBlockingAsyncInputStream.h",
+    "SlicedInputStream.h",
+    "SnappyCompressOutputStream.h",
+    "SnappyFrameUtils.h",
+    "SnappyUncompressInputStream.h",
+    "StreamBufferSink.h",
+    "StreamBufferSinkImpl.h",
+    "StreamBufferSource.h",
+    "StreamBufferSourceImpl.h",
+]
+
+UNIFIED_SOURCES += [
+    "Base64.cpp",
+    "crc32c.c",
+    "FileDescriptorFile.cpp",
+    "FilePreferences.cpp",
+    "FixedBufferOutputStream.cpp",
+    "InputStreamLengthHelper.cpp",
+    "InputStreamLengthWrapper.cpp",
+    "NonBlockingAsyncInputStream.cpp",
+    "nsAnonymousTemporaryFile.cpp",
+    "nsAppFileLocationProvider.cpp",
+    "nsBinaryStream.cpp",
+    "nsDirectoryService.cpp",
+    "nsEscape.cpp",
+    "nsInputStreamTee.cpp",
+    "nsIOUtil.cpp",
+    "nsLinebreakConverter.cpp",
+    "nsLocalFileCommon.cpp",
+    "nsMultiplexInputStream.cpp",
+    "nsNativeCharsetUtils.cpp",
+    "nsPipe3.cpp",
+    "nsScriptableBase64Encoder.cpp",
+    "nsScriptableInputStream.cpp",
+    "nsSegmentedBuffer.cpp",
+    "nsStorageStream.cpp",
+    "nsStreamUtils.cpp",
+    "nsStringStream.cpp",
+    "nsUnicharInputStream.cpp",
+    "nsWildCard.cpp",
+    "SlicedInputStream.cpp",
+    "SnappyCompressOutputStream.cpp",
+    "SnappyFrameUtils.cpp",
+    "SnappyUncompressInputStream.cpp",
+    "SpecialSystemDirectory.cpp",
+]
+
+if CONFIG["MOZ_WIDGET_TOOLKIT"] == "cocoa":
+    SOURCES += [
+        "CocoaFileUtils.mm",
+    ]
+
+DEFINES["MOZ_APP_BASENAME"] = '"%s"' % CONFIG["MOZ_APP_BASENAME"]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
+
+if CONFIG["OS_ARCH"] == "Linux" and "lib64" in CONFIG["libdir"]:
+    DEFINES["HAVE_USR_LIB64_DIR"] = True
+
+LOCAL_INCLUDES += [
+    "!..",
+    "../build",
+]
diff --git a/xpcom/io/nsAnonymousTemporaryFile.cpp b/xpcom/io/nsAnonymousTemporaryFile.cpp
new file mode 100644
index 0000000000..1c9dce57d5
--- /dev/null
+++ b/xpcom/io/nsAnonymousTemporaryFile.cpp
@@ -0,0 +1,264 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsAnonymousTemporaryFile.h"
+#include "nsXULAppAPI.h"
+#include "nsCOMPtr.h"
+#include "nsString.h"
+#include "prio.h"
+#include "SpecialSystemDirectory.h"
+
+#ifdef XP_WIN
+#  include "nsIObserver.h"
+#  include "nsIObserverService.h"
+#  include "mozilla/ResultExtensions.h"
+#  include "mozilla/Services.h"
+#  include "nsIUserIdleService.h"
+#  include "nsISimpleEnumerator.h"
+#  include "nsIFile.h"
+#  include "nsITimer.h"
+#  include "nsCRT.h"
+
+#endif
+
+using namespace mozilla;
+
+// We store the temp files in the system temp dir.
+//
+// On Windows systems in particular we use a sub-directory of the temp
+// directory, because:
+//   1. DELETE_ON_CLOSE is unreliable on Windows, in particular if we power
+//      cycle (and perhaps if we crash) the files are not deleted. We store
+//      the temporary files in a known sub-dir so that we can find and delete
+//      them easily and quickly.
+//   2. On Windows NT the system temp dir is in the user's $HomeDir/AppData,
+//      so we can be sure the user always has write privileges to that
+//      directory; if the sub-dir for our temp files was in some shared location
+//      and was created by a privileged user, it's possible that other users
+//      wouldn't have write access to that sub-dir. (Non-Windows systems
+//      don't store their temp files in a sub-dir, so this isn't an issue on
+//      those platforms).
+//   3. Content processes can access the system temp dir
+//      (NS_GetSpecialDirectory fails on NS_APP_USER_PROFILE_LOCAL_50_DIR
+//      for content process for example, which is where we previously stored
+//      temp files on Windows). This argument applies to all platforms, not
+//      just Windows.
+static nsresult GetTempDir(nsIFile** aTempDir) {
+  if (NS_WARN_IF(!aTempDir)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  nsCOMPtr<nsIFile> tmpFile;
+  nsresult rv =
+      GetSpecialSystemDirectory(OS_TemporaryDirectory, getter_AddRefs(tmpFile));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+#ifdef XP_WIN
+  // On windows DELETE_ON_CLOSE is unreliable, so we store temporary files
+  // in a subdir of the temp dir and delete that in an idle service observer
+  // to ensure it's been cleared.
+  rv = tmpFile->AppendNative(nsDependentCString("mozilla-temp-files"));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  rv = tmpFile->Create(nsIFile::DIRECTORY_TYPE, 0700);
+  if (rv != NS_ERROR_FILE_ALREADY_EXISTS && NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+#endif
+
+  tmpFile.forget(aTempDir);
+
+  return NS_OK;
+}
+
+nsresult NS_OpenAnonymousTemporaryNsIFile(nsIFile** aFile) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  if (NS_WARN_IF(!aFile)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsresult rv;
+  nsCOMPtr<nsIFile> tmpFile;
+  rv = GetTempDir(getter_AddRefs(tmpFile));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // Give the temp file a name with a random element. CreateUnique will also
+  // append a counter to the name if it encounters a name collision. Adding
+  // a random element to the name reduces the likelihood of a name collision,
+  // so that CreateUnique() doesn't end up trying a lot of name variants in
+  // its "try appending an incrementing counter" loop, as file IO can be
+  // expensive on some mobile flash drives.
+  nsAutoCString name("mozilla-temp-");
+  name.AppendInt(rand());
+
+  rv = tmpFile->AppendNative(name);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = tmpFile->CreateUnique(nsIFile::NORMAL_FILE_TYPE, 0600);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  tmpFile.forget(aFile);
+  return NS_OK;
+}
+
+nsresult NS_OpenAnonymousTemporaryFile(PRFileDesc** aOutFileDesc) {
+  nsCOMPtr<nsIFile> tmpFile;
+  nsresult rv = NS_OpenAnonymousTemporaryNsIFile(getter_AddRefs(tmpFile));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = tmpFile->OpenNSPRFileDesc(PR_RDWR | nsIFile::DELETE_ON_CLOSE, PR_IRWXU,
+                                 aOutFileDesc);
+
+  return rv;
+}
+
+#ifdef XP_WIN
+
+// On Windows we have an idle service observer that runs some time after
+// startup and deletes any stray anonymous temporary files...
+
+// Duration of idle time before we'll get a callback whereupon we attempt to
+// remove any stray and unused anonymous temp files.
+#  define TEMP_FILE_IDLE_TIME_S 30
+
+// The nsAnonTempFileRemover is created in a timer, which sets an idle observer.
+// This is expiration time (in ms) which initial timer is set for (3 minutes).
+#  define SCHEDULE_TIMEOUT_MS 3 * 60 * 1000
+
+#  define XPCOM_SHUTDOWN_TOPIC "xpcom-shutdown"
+
+// This class adds itself as an idle observer. When the application has
+// been idle for about 30 seconds we'll get a notification, whereupon we'll
+// attempt to delete ${TempDir}/mozilla-temp-files/. This is to ensure all
+// temp files that were supposed to be deleted on application exit were actually
+// deleted, as they may not be if we previously crashed. See bugs 572579 and
+// 785662. This is only needed on some versions of Windows,
+// nsIFile::DELETE_ON_CLOSE works on other platforms.
+// This class adds itself as a shutdown observer so that it can cancel the
+// idle observer and its timer on shutdown. Note: the observer and idle
+// services hold references to instances of this object, and those references
+// are what keep this object alive.
+class nsAnonTempFileRemover final : public nsIObserver, public nsINamed {
+ public:
+  NS_DECL_ISUPPORTS
+
+  nsAnonTempFileRemover() {}
+
+  nsresult Init() {
+    // We add the idle observer in a timer, so that the app has enough
+    // time to start up before we add the idle observer. If we register the
+    // idle observer too early, it will be registered before the fake idle
+    // service is installed when running in xpcshell, and this interferes with
+    // the fake idle service, causing xpcshell-test failures.
+    MOZ_TRY_VAR(mTimer, NS_NewTimerWithObserver(this, SCHEDULE_TIMEOUT_MS,
+                                                nsITimer::TYPE_ONE_SHOT));
+
+    // Register shutdown observer so we can cancel the timer if we shutdown
+    // before the timer runs.
+    nsCOMPtr<nsIObserverService> obsSrv = services::GetObserverService();
+    if (NS_WARN_IF(!obsSrv)) {
+      return NS_ERROR_FAILURE;
+    }
+    return obsSrv->AddObserver(this, XPCOM_SHUTDOWN_TOPIC, false);
+  }
+
+  void Cleanup() {
+    // Cancel timer.
+    if (mTimer) {
+      mTimer->Cancel();
+      mTimer = nullptr;
+    }
+    // Remove idle service observer.
+    nsCOMPtr<nsIUserIdleService> idleSvc =
+        do_GetService("@mozilla.org/widget/useridleservice;1");
+    if (idleSvc) {
+      idleSvc->RemoveIdleObserver(this, TEMP_FILE_IDLE_TIME_S);
+    }
+    // Remove shutdown observer.
+    nsCOMPtr<nsIObserverService> obsSrv = services::GetObserverService();
+    if (obsSrv) {
+      obsSrv->RemoveObserver(this, XPCOM_SHUTDOWN_TOPIC);
+    }
+  }
+
+  NS_IMETHODIMP Observe(nsISupports* aSubject, const char* aTopic,
+                        const char16_t* aData) {
+    if (nsCRT::strcmp(aTopic, NS_TIMER_CALLBACK_TOPIC) == 0 &&
+        NS_FAILED(RegisterIdleObserver())) {
+      Cleanup();
+    } else if (nsCRT::strcmp(aTopic, OBSERVER_TOPIC_IDLE) == 0) {
+      // The user has been idle for a while, clean up the temp files.
+      // The idle service will drop its reference to this object after
+      // we exit, destroying this object.
+      RemoveAnonTempFileFiles();
+      Cleanup();
+    } else if (nsCRT::strcmp(aTopic, XPCOM_SHUTDOWN_TOPIC) == 0) {
+      Cleanup();
+    }
+    return NS_OK;
+  }
+
+  NS_IMETHODIMP GetName(nsACString& aName) {
+    aName.AssignLiteral("nsAnonTempFileRemover");
+    return NS_OK;
+  }
+
+  nsresult RegisterIdleObserver() {
+    // Add this as an idle observer. When we've been idle for
+    // TEMP_FILE_IDLE_TIME_S seconds, we'll get a notification, and we'll then
+    // try to delete any stray temp files.
+    nsCOMPtr<nsIUserIdleService> idleSvc =
+        do_GetService("@mozilla.org/widget/useridleservice;1");
+    if (!idleSvc) {
+      return NS_ERROR_FAILURE;
+    }
+    return idleSvc->AddIdleObserver(this, TEMP_FILE_IDLE_TIME_S);
+  }
+
+  void RemoveAnonTempFileFiles() {
+    nsCOMPtr<nsIFile> tmpDir;
+    nsresult rv = GetTempDir(getter_AddRefs(tmpDir));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return;
+    }
+
+    // Remove the directory recursively.
+    tmpDir->Remove(true);
+  }
+
+ private:
+  ~nsAnonTempFileRemover() {}
+
+  nsCOMPtr<nsITimer> mTimer;
+};
+
+NS_IMPL_ISUPPORTS(nsAnonTempFileRemover, nsIObserver, nsINamed)
+
+nsresult CreateAnonTempFileRemover() {
+  // Create a temp file remover. If Init() succeeds, the temp file remover is
+  // kept alive by a reference held by the observer service, since the temp file
+  // remover is a shutdown observer. We only create the temp file remover if
+  // we're running in the main process; there's no point in doing the temp file
+  // removal multiple times per startup.
+  if (!XRE_IsParentProcess()) {
+    return NS_OK;
+  }
+  RefPtr<nsAnonTempFileRemover> tempRemover = new nsAnonTempFileRemover();
+  return tempRemover->Init();
+}
+
+#endif
diff --git a/xpcom/io/nsAnonymousTemporaryFile.h b/xpcom/io/nsAnonymousTemporaryFile.h
new file mode 100644
index 0000000000..8e900dda4c
--- /dev/null
+++ b/xpcom/io/nsAnonymousTemporaryFile.h
@@ -0,0 +1,39 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#pragma once
+
+#include "prio.h"
+#include "nscore.h"
+#include "nsIFile.h"
+
+/**
+ * OpenAnonymousTemporaryFile
+ *
+ * Creates and opens a temporary file which has a random name. Callers have no
+ * control over the file name, and the file is opened in a temporary location
+ * which is appropriate for the platform.
+ *
+ * Upon success, aOutFileDesc contains an opened handle to the temporary file.
+ * The caller is responsible for closing the file when they're finished with it.
+ *
+ * The file will be deleted when the file handle is closed. On non-Windows
+ * platforms the file will be unlinked before this function returns. On Windows
+ * the OS supplied delete-on-close mechanism is unreliable if the application
+ * crashes or the computer power cycles unexpectedly, so unopened temporary
+ * files are purged at some time after application startup.
+ *
+ */
+nsresult NS_OpenAnonymousTemporaryFile(PRFileDesc** aOutFileDesc);
+
+/**
+ * OpenAnonymousTemporaryNsIFile
+ *
+ * Similar to the previous function, it returns a nsIFile. Note that the nsIFile
+ * will not be deleted automagically. The callee has to call aFile->Remove() in
+ * order to remove the temporary file.
+ */
+nsresult NS_OpenAnonymousTemporaryNsIFile(nsIFile** aFile);
diff --git a/xpcom/io/nsAppDirectoryServiceDefs.h b/xpcom/io/nsAppDirectoryServiceDefs.h
new file mode 100644
index 0000000000..521dbe0d50
--- /dev/null
+++ b/xpcom/io/nsAppDirectoryServiceDefs.h
@@ -0,0 +1,102 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsAppDirectoryServiceDefs_h___
+#define nsAppDirectoryServiceDefs_h___
+
+//========================================================================================
+//
+// Defines property names for directories available from standard
+// nsIDirectoryServiceProviders. These keys are not guaranteed to exist because
+// the nsIDirectoryServiceProviders which provide them are optional.
+//
+// Keys whose definition ends in "DIR" or "FILE" return a single nsIFile (or
+// subclass). Keys whose definition ends in "LIST" return an nsISimpleEnumerator
+// which enumerates a list of file objects.
+//
+// System and XPCOM level properties are defined in nsDirectoryServiceDefs.h.
+//
+//========================================================================================
+
+// --------------------------------------------------------------------------------------
+// Files and directories which exist on a per-product basis
+// --------------------------------------------------------------------------------------
+
+#define NS_APP_APPLICATION_REGISTRY_FILE "AppRegF"
+#define NS_APP_APPLICATION_REGISTRY_DIR "AppRegD"
+
+#define NS_APP_DEFAULTS_50_DIR "DefRt"  // The root dir of all defaults dirs
+#define NS_APP_PREF_DEFAULTS_50_DIR "PrfDef"
+
+#define NS_APP_USER_PROFILES_ROOT_DIR \
+  "DefProfRt"  // The dir where user profile dirs live.
+#define NS_APP_USER_PROFILES_LOCAL_ROOT_DIR \
+  "DefProfLRt"  // The dir where user profile temp dirs live.
+
+#define NS_APP_RES_DIR "ARes"
+#define NS_APP_CHROME_DIR "AChrom"
+
+#define NS_APP_CHROME_DIR_LIST "AChromDL"
+
+// --------------------------------------------------------------------------------------
+// Files and directories which exist on a per-profile basis
+// These locations are typically provided by the profile mgr
+// --------------------------------------------------------------------------------------
+
+// In a shared profile environment, prefixing a profile-relative
+// key with NS_SHARED returns a location that is shared by
+// other users of the profile. Without this prefix, the consumer
+// has exclusive access to this location.
+
+#define NS_SHARED "SHARED"
+
+#define NS_APP_PREFS_50_DIR "PrefD"  // Directory which contains user prefs
+#define NS_APP_PREFS_50_FILE "PrefF"
+#define NS_APP_PREFS_DEFAULTS_DIR_LIST "PrefDL"
+#define NS_APP_PREFS_OVERRIDE_DIR \
+  "PrefDOverride"  // Directory for per-profile defaults
+
+#define NS_APP_USER_PROFILE_50_DIR "ProfD"
+#define NS_APP_USER_PROFILE_LOCAL_50_DIR "ProfLD"
+
+#define NS_APP_USER_CHROME_DIR "UChrm"
+
+#define NS_APP_USER_PANELS_50_FILE "UPnls"
+#define NS_APP_CACHE_PARENT_DIR "cachePDir"
+
+#define NS_APP_INSTALL_CLEANUP_DIR \
+  "XPIClnupD"  // location of xpicleanup.dat xpicleanup.exe
+
+#define NS_APP_INDEXEDDB_PARENT_DIR "indexedDBPDir"
+
+#define NS_APP_PERMISSION_PARENT_DIR "permissionDBPDir"
+
+#if defined(MOZ_CONTENT_TEMP_DIR)
+//
+// NS_APP_CONTENT_PROCESS_TEMP_DIR refers to a directory that is read and
+// write accessible from a sandboxed content process. The key may be used in
+// either process, but the directory is intended to be used for short-lived
+// files that need to be saved to the filesystem by the content process and
+// don't need to survive browser restarts. The directory is reset on startup.
+//
+// When MOZ_CONTENT_TEMP_DIR is defined and sandboxing is enabled (versus
+// manually disabled via prefs), the content process replaces NS_OS_TEMP_DIR
+// with NS_APP_CONTENT_PROCESS_TEMP_DIR so that legacy code in content
+// attempting to write to NS_OS_TEMP_DIR will write to
+// NS_APP_CONTENT_PROCESS_TEMP_DIR instead. When MOZ_SANDBOX is
+// defined but sandboxing is disabled, NS_APP_CONTENT_PROCESS_TEMP_DIR
+// falls back to NS_OS_TEMP_DIR in both content and chrome processes.
+//
+// New code should avoid writing to the filesystem from the content process
+// and should instead proxy through the parent process whenever possible.
+//
+// At present, all sandboxed content processes use the same directory for
+// NS_APP_CONTENT_PROCESS_TEMP_DIR, but that should not be relied upon.
+//
+#  define NS_APP_CONTENT_PROCESS_TEMP_DIR "ContentTmpD"
+#endif  // defined(MOZ_SANDBOX)
+
+#endif  // nsAppDirectoryServiceDefs_h___
diff --git a/xpcom/io/nsAppFileLocationProvider.cpp b/xpcom/io/nsAppFileLocationProvider.cpp
new file mode 100644
index 0000000000..aedaad1b4f
--- /dev/null
+++ b/xpcom/io/nsAppFileLocationProvider.cpp
@@ -0,0 +1,333 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsAppFileLocationProvider.h"
+#include "nsAppDirectoryServiceDefs.h"
+#include "nsDirectoryServiceDefs.h"
+#include "nsEnumeratorUtils.h"
+#include "nsAtom.h"
+#include "nsIDirectoryService.h"
+#include "nsIFile.h"
+#include "nsString.h"
+#include "nsSimpleEnumerator.h"
+#include "prenv.h"
+#include "nsCRT.h"
+#if defined(MOZ_WIDGET_COCOA)
+#  include <Carbon/Carbon.h>
+#  include "CocoaFileUtils.h"
+#  include "nsILocalFileMac.h"
+#elif defined(XP_WIN)
+#  include <windows.h>
+#  include <shlobj.h>
+#elif defined(XP_UNIX)
+#  include <unistd.h>
+#  include <stdlib.h>
+#  include <sys/param.h>
+#endif
+
+// WARNING: These hard coded names need to go away. They need to
+// come from localizable resources
+
+#if defined(MOZ_WIDGET_COCOA)
+#  define APP_REGISTRY_NAME "Application Registry"_ns
+#  define ESSENTIAL_FILES "Essential Files"_ns
+#elif defined(XP_WIN)
+#  define APP_REGISTRY_NAME "registry.dat"_ns
+#else
+#  define APP_REGISTRY_NAME "appreg"_ns
+#endif
+
+// define default product directory
+#define DEFAULT_PRODUCT_DIR nsLiteralCString(MOZ_USER_DIR)
+
+#define DEFAULTS_DIR_NAME "defaults"_ns
+#define DEFAULTS_PREF_DIR_NAME "pref"_ns
+#define RES_DIR_NAME "res"_ns
+#define CHROME_DIR_NAME "chrome"_ns
+
+//*****************************************************************************
+// nsAppFileLocationProvider::Constructor/Destructor
+//*****************************************************************************
+
+nsAppFileLocationProvider::nsAppFileLocationProvider() = default;
+
+//*****************************************************************************
+// nsAppFileLocationProvider::nsISupports
+//*****************************************************************************
+
+NS_IMPL_ISUPPORTS(nsAppFileLocationProvider, nsIDirectoryServiceProvider)
+
+//*****************************************************************************
+// nsAppFileLocationProvider::nsIDirectoryServiceProvider
+//*****************************************************************************
+
+NS_IMETHODIMP
+nsAppFileLocationProvider::GetFile(const char* aProp, bool* aPersistent,
+                                   nsIFile** aResult) {
+  if (NS_WARN_IF(!aProp)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsCOMPtr<nsIFile> localFile;
+  nsresult rv = NS_ERROR_FAILURE;
+
+  *aResult = nullptr;
+  *aPersistent = true;
+
+  if (nsCRT::strcmp(aProp, NS_APP_APPLICATION_REGISTRY_DIR) == 0) {
+    rv = GetProductDirectory(getter_AddRefs(localFile));
+  } else if (nsCRT::strcmp(aProp, NS_APP_APPLICATION_REGISTRY_FILE) == 0) {
+    rv = GetProductDirectory(getter_AddRefs(localFile));
+    if (NS_SUCCEEDED(rv)) {
+      rv = localFile->AppendNative(APP_REGISTRY_NAME);
+    }
+  } else if (nsCRT::strcmp(aProp, NS_APP_DEFAULTS_50_DIR) == 0) {
+    rv = CloneMozBinDirectory(getter_AddRefs(localFile));
+    if (NS_SUCCEEDED(rv)) {
+      rv = localFile->AppendRelativeNativePath(DEFAULTS_DIR_NAME);
+    }
+  } else if (nsCRT::strcmp(aProp, NS_APP_PREF_DEFAULTS_50_DIR) == 0) {
+    rv = CloneMozBinDirectory(getter_AddRefs(localFile));
+    if (NS_SUCCEEDED(rv)) {
+      rv = localFile->AppendRelativeNativePath(DEFAULTS_DIR_NAME);
+      if (NS_SUCCEEDED(rv)) {
+        rv = localFile->AppendRelativeNativePath(DEFAULTS_PREF_DIR_NAME);
+      }
+    }
+  } else if (nsCRT::strcmp(aProp, NS_APP_USER_PROFILES_ROOT_DIR) == 0) {
+    rv = GetDefaultUserProfileRoot(getter_AddRefs(localFile));
+  } else if (nsCRT::strcmp(aProp, NS_APP_USER_PROFILES_LOCAL_ROOT_DIR) == 0) {
+    rv = GetDefaultUserProfileRoot(getter_AddRefs(localFile), true);
+  } else if (nsCRT::strcmp(aProp, NS_APP_RES_DIR) == 0) {
+    rv = CloneMozBinDirectory(getter_AddRefs(localFile));
+    if (NS_SUCCEEDED(rv)) {
+      rv = localFile->AppendRelativeNativePath(RES_DIR_NAME);
+    }
+  } else if (nsCRT::strcmp(aProp, NS_APP_CHROME_DIR) == 0) {
+    rv = CloneMozBinDirectory(getter_AddRefs(localFile));
+    if (NS_SUCCEEDED(rv)) {
+      rv = localFile->AppendRelativeNativePath(CHROME_DIR_NAME);
+    }
+  } else if (nsCRT::strcmp(aProp, NS_APP_INSTALL_CLEANUP_DIR) == 0) {
+    // This is cloned so that embeddors will have a hook to override
+    // with their own cleanup dir.  See bugzilla bug #105087
+    rv = CloneMozBinDirectory(getter_AddRefs(localFile));
+  }
+
+  if (localFile && NS_SUCCEEDED(rv)) {
+    localFile.forget(aResult);
+    return NS_OK;
+  }
+
+  return rv;
+}
+
+nsresult nsAppFileLocationProvider::CloneMozBinDirectory(nsIFile** aLocalFile) {
+  if (NS_WARN_IF(!aLocalFile)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  nsresult rv;
+
+  if (!mMozBinDirectory) {
+    // Get the mozilla bin directory
+    // 1. Check the directory service first for NS_XPCOM_CURRENT_PROCESS_DIR
+    //    This will be set if a directory was passed to NS_InitXPCOM
+    // 2. If that doesn't work, set it to be the current process directory
+    nsCOMPtr<nsIProperties> directoryService(
+        do_GetService(NS_DIRECTORY_SERVICE_CONTRACTID, &rv));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    rv =
+        directoryService->Get(NS_XPCOM_CURRENT_PROCESS_DIR, NS_GET_IID(nsIFile),
+                              getter_AddRefs(mMozBinDirectory));
+    if (NS_FAILED(rv)) {
+      rv = directoryService->Get(NS_OS_CURRENT_PROCESS_DIR, NS_GET_IID(nsIFile),
+                                 getter_AddRefs(mMozBinDirectory));
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    }
+  }
+
+  nsCOMPtr<nsIFile> aFile;
+  rv = mMozBinDirectory->Clone(getter_AddRefs(aFile));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  NS_IF_ADDREF(*aLocalFile = aFile);
+  return NS_OK;
+}
+
+//----------------------------------------------------------------------------------------
+// GetProductDirectory - Gets the directory which contains the application data
+// folder
+//
+// UNIX   : ~/.mozilla/
+// WIN    : <Application Data folder on user's machine>\Mozilla
+// Mac    : :Documents:Mozilla:
+//----------------------------------------------------------------------------------------
+nsresult nsAppFileLocationProvider::GetProductDirectory(nsIFile** aLocalFile,
+                                                        bool aLocal) {
+  if (NS_WARN_IF(!aLocalFile)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsresult rv;
+  bool exists;
+  nsCOMPtr<nsIFile> localDir;
+
+#if defined(MOZ_WIDGET_COCOA)
+  NS_NewLocalFile(u""_ns, true, getter_AddRefs(localDir));
+  if (!localDir) {
+    return NS_ERROR_FAILURE;
+  }
+  nsCOMPtr<nsILocalFileMac> localDirMac(do_QueryInterface(localDir));
+
+  rv = localDirMac->InitWithCFURL(
+      CocoaFileUtils::GetProductDirectoryCFURLRef(aLocal));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+#elif defined(XP_WIN)
+  nsCOMPtr<nsIProperties> directoryService =
+      do_GetService(NS_DIRECTORY_SERVICE_CONTRACTID, &rv);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  const char* prop = aLocal ? NS_WIN_LOCAL_APPDATA_DIR : NS_WIN_APPDATA_DIR;
+  rv = directoryService->Get(prop, NS_GET_IID(nsIFile),
+                             getter_AddRefs(localDir));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+#elif defined(XP_UNIX)
+  rv = NS_NewNativeLocalFile(nsDependentCString(PR_GetEnv("HOME")), true,
+                             getter_AddRefs(localDir));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+#else
+#  error dont_know_how_to_get_product_dir_on_your_platform
+#endif
+
+  rv = localDir->AppendRelativeNativePath(DEFAULT_PRODUCT_DIR);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  rv = localDir->Exists(&exists);
+
+  if (NS_SUCCEEDED(rv) && !exists) {
+    rv = localDir->Create(nsIFile::DIRECTORY_TYPE, 0700);
+  }
+
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  localDir.forget(aLocalFile);
+
+  return rv;
+}
+
+//----------------------------------------------------------------------------------------
+// GetDefaultUserProfileRoot - Gets the directory which contains each user
+// profile dir
+//
+// UNIX   : ~/.mozilla/
+// WIN    : <Application Data folder on user's machine>\Mozilla\Profiles
+// Mac    : :Documents:Mozilla:Profiles:
+//----------------------------------------------------------------------------------------
+nsresult nsAppFileLocationProvider::GetDefaultUserProfileRoot(
+    nsIFile** aLocalFile, bool aLocal) {
+  if (NS_WARN_IF(!aLocalFile)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsresult rv;
+  nsCOMPtr<nsIFile> localDir;
+
+  rv = GetProductDirectory(getter_AddRefs(localDir), aLocal);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+#if defined(MOZ_WIDGET_COCOA) || defined(XP_WIN)
+  // These 3 platforms share this part of the path - do them as one
+  rv = localDir->AppendRelativeNativePath("Profiles"_ns);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  bool exists;
+  rv = localDir->Exists(&exists);
+  if (NS_SUCCEEDED(rv) && !exists) {
+    rv = localDir->Create(nsIFile::DIRECTORY_TYPE, 0775);
+  }
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+#endif
+
+  localDir.forget(aLocalFile);
+
+  return rv;
+}
+
+//*****************************************************************************
+// nsAppFileLocationProvider::nsIDirectoryServiceProvider
+//*****************************************************************************
+
+class nsAppDirectoryEnumerator : public nsSimpleEnumerator {
+ public:
+  /**
+   * aKeyList is a null-terminated list of properties which are provided by
+   * aProvider They do not need to be publicly defined keys.
+   */
+  nsAppDirectoryEnumerator(nsIDirectoryServiceProvider* aProvider,
+                           const char* aKeyList[])
+      : mProvider(aProvider), mCurrentKey(aKeyList) {}
+
+  const nsID& DefaultInterface() override { return NS_GET_IID(nsIFile); }
+
+  NS_IMETHOD HasMoreElements(bool* aResult) override {
+    while (!mNext && *mCurrentKey) {
+      bool dontCare;
+      nsCOMPtr<nsIFile> testFile;
+      (void)mProvider->GetFile(*mCurrentKey++, &dontCare,
+                               getter_AddRefs(testFile));
+      mNext = testFile;
+    }
+    *aResult = mNext != nullptr;
+    return NS_OK;
+  }
+
+  NS_IMETHOD GetNext(nsISupports** aResult) override {
+    if (NS_WARN_IF(!aResult)) {
+      return NS_ERROR_INVALID_ARG;
+    }
+    *aResult = nullptr;
+
+    bool hasMore;
+    HasMoreElements(&hasMore);
+    if (!hasMore) {
+      return NS_ERROR_FAILURE;
+    }
+
+    *aResult = mNext;
+    NS_IF_ADDREF(*aResult);
+    mNext = nullptr;
+
+    return *aResult ? NS_OK : NS_ERROR_FAILURE;
+  }
+
+ protected:
+  nsCOMPtr<nsIDirectoryServiceProvider> mProvider;
+  const char** mCurrentKey;
+  nsCOMPtr<nsIFile> mNext;
+};
diff --git a/xpcom/io/nsAppFileLocationProvider.h b/xpcom/io/nsAppFileLocationProvider.h
new file mode 100644
index 0000000000..d2fd9cf651
--- /dev/null
+++ b/xpcom/io/nsAppFileLocationProvider.h
@@ -0,0 +1,45 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsAppFileLocationProvider_h
+#define nsAppFileLocationProvider_h
+
+#include "nsIDirectoryService.h"
+#include "nsCOMPtr.h"
+#include "mozilla/Attributes.h"
+
+class nsIFile;
+
+//*****************************************************************************
+// class nsAppFileLocationProvider
+//*****************************************************************************
+
+class nsAppFileLocationProvider final : public nsIDirectoryServiceProvider {
+ public:
+  nsAppFileLocationProvider();
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIDIRECTORYSERVICEPROVIDER
+
+ private:
+  ~nsAppFileLocationProvider() = default;
+
+ protected:
+  nsresult CloneMozBinDirectory(nsIFile** aLocalFile);
+  /**
+   * Get the product directory. This is a user-specific directory for storing
+   * application settings (e.g. the Application Data directory on windows
+   * systems).
+   * @param aLocal If true, should try to get a directory that is only stored
+   *               locally (ie not transferred with roaming profiles)
+   */
+  nsresult GetProductDirectory(nsIFile** aLocalFile, bool aLocal = false);
+  nsresult GetDefaultUserProfileRoot(nsIFile** aLocalFile, bool aLocal = false);
+
+  nsCOMPtr<nsIFile> mMozBinDirectory;
+};
+
+#endif
diff --git a/xpcom/io/nsBinaryStream.cpp b/xpcom/io/nsBinaryStream.cpp
new file mode 100644
index 0000000000..555edf5345
--- /dev/null
+++ b/xpcom/io/nsBinaryStream.cpp
@@ -0,0 +1,1007 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * This file contains implementations of the nsIBinaryInputStream and
+ * nsIBinaryOutputStream interfaces.  Together, these interfaces allows reading
+ * and writing of primitive data types (integers, floating-point values,
+ * booleans, etc.) to a stream in a binary, untagged, fixed-endianness format.
+ * This might be used, for example, to implement network protocols or to
+ * produce architecture-neutral binary disk files, i.e. ones that can be read
+ * and written by both big-endian and little-endian platforms.  Output is
+ * written in big-endian order (high-order byte first), as this is traditional
+ * network order.
+ *
+ * @See nsIBinaryInputStream
+ * @See nsIBinaryOutputStream
+ */
+#include <algorithm>
+#include <string.h>
+
+#include "nsBinaryStream.h"
+
+#include "mozilla/EndianUtils.h"
+#include "mozilla/PodOperations.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/Span.h"
+#include "mozilla/UniquePtr.h"
+
+#include "nsCRT.h"
+#include "nsString.h"
+#include "nsISerializable.h"
+#include "nsIClassInfo.h"
+#include "nsComponentManagerUtils.h"
+#include "nsIURI.h"       // for NS_IURI_IID
+#include "nsIX509Cert.h"  // for NS_IX509CERT_IID
+
+#include "js/ArrayBuffer.h"  // JS::{GetArrayBuffer{,ByteLength},IsArrayBufferObject}
+#include "js/GCAPI.h"        // JS::AutoCheckCannotGC
+#include "js/RootingAPI.h"  // JS::{Handle,Rooted}
+#include "js/Value.h"       // JS::Value
+
+using mozilla::AsBytes;
+using mozilla::MakeUnique;
+using mozilla::PodCopy;
+using mozilla::Span;
+using mozilla::UniquePtr;
+
+already_AddRefed<nsIObjectOutputStream> NS_NewObjectOutputStream(
+    nsIOutputStream* aOutputStream) {
+  MOZ_ASSERT(aOutputStream);
+  auto stream = mozilla::MakeRefPtr<nsBinaryOutputStream>();
+
+  MOZ_ALWAYS_SUCCEEDS(stream->SetOutputStream(aOutputStream));
+  return stream.forget();
+}
+
+already_AddRefed<nsIObjectInputStream> NS_NewObjectInputStream(
+    nsIInputStream* aInputStream) {
+  MOZ_ASSERT(aInputStream);
+  auto stream = mozilla::MakeRefPtr<nsBinaryInputStream>();
+
+  MOZ_ALWAYS_SUCCEEDS(stream->SetInputStream(aInputStream));
+  return stream.forget();
+}
+
+NS_IMPL_ISUPPORTS(nsBinaryOutputStream, nsIObjectOutputStream,
+                  nsIBinaryOutputStream, nsIOutputStream)
+
+NS_IMETHODIMP
+nsBinaryOutputStream::Flush() {
+  if (NS_WARN_IF(!mOutputStream)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return mOutputStream->Flush();
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::Close() {
+  if (NS_WARN_IF(!mOutputStream)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return mOutputStream->Close();
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::StreamStatus() {
+  if (NS_WARN_IF(!mOutputStream)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return mOutputStream->StreamStatus();
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::Write(const char* aBuf, uint32_t aCount,
+                            uint32_t* aActualBytes) {
+  if (NS_WARN_IF(!mOutputStream)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return mOutputStream->Write(aBuf, aCount, aActualBytes);
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteFrom(nsIInputStream* aInStr, uint32_t aCount,
+                                uint32_t* aResult) {
+  MOZ_ASSERT_UNREACHABLE("WriteFrom");
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteSegments(nsReadSegmentFun aReader, void* aClosure,
+                                    uint32_t aCount, uint32_t* aResult) {
+  MOZ_ASSERT_UNREACHABLE("WriteSegments");
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::IsNonBlocking(bool* aNonBlocking) {
+  if (NS_WARN_IF(!mOutputStream)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return mOutputStream->IsNonBlocking(aNonBlocking);
+}
+
+nsresult nsBinaryOutputStream::WriteFully(const char* aBuf, uint32_t aCount) {
+  if (NS_WARN_IF(!mOutputStream)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  nsresult rv;
+  uint32_t bytesWritten;
+
+  rv = mOutputStream->Write(aBuf, aCount, &bytesWritten);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (bytesWritten != aCount) {
+    return NS_ERROR_FAILURE;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::SetOutputStream(nsIOutputStream* aOutputStream) {
+  if (NS_WARN_IF(!aOutputStream)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  mOutputStream = aOutputStream;
+  mBufferAccess = do_QueryInterface(aOutputStream);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteBoolean(bool aBoolean) { return Write8(aBoolean); }
+
+NS_IMETHODIMP
+nsBinaryOutputStream::Write8(uint8_t aByte) {
+  return WriteFully((const char*)&aByte, sizeof(aByte));
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::Write16(uint16_t aNum) {
+  aNum = mozilla::NativeEndian::swapToBigEndian(aNum);
+  return WriteFully((const char*)&aNum, sizeof(aNum));
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::Write32(uint32_t aNum) {
+  aNum = mozilla::NativeEndian::swapToBigEndian(aNum);
+  return WriteFully((const char*)&aNum, sizeof(aNum));
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::Write64(uint64_t aNum) {
+  nsresult rv;
+  uint32_t bytesWritten;
+
+  aNum = mozilla::NativeEndian::swapToBigEndian(aNum);
+  rv = Write(reinterpret_cast<char*>(&aNum), sizeof(aNum), &bytesWritten);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (bytesWritten != sizeof(aNum)) {
+    return NS_ERROR_FAILURE;
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteFloat(float aFloat) {
+  static_assert(sizeof(float) == sizeof(uint32_t),
+                "False assumption about sizeof(float)");
+  return Write32(*reinterpret_cast<uint32_t*>(&aFloat));
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteDouble(double aDouble) {
+  static_assert(sizeof(double) == sizeof(uint64_t),
+                "False assumption about sizeof(double)");
+  return Write64(*reinterpret_cast<uint64_t*>(&aDouble));
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteStringZ(const char* aString) {
+  uint32_t length;
+  nsresult rv;
+
+  length = strlen(aString);
+  rv = Write32(length);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  return WriteFully(aString, length);
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteWStringZ(const char16_t* aString) {
+  uint32_t length = NS_strlen(aString);
+  nsresult rv = Write32(length);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (length == 0) {
+    return NS_OK;
+  }
+
+#ifdef IS_BIG_ENDIAN
+  rv = WriteBytes(AsBytes(Span(aString, length)));
+#else
+  // XXX use WriteSegments here to avoid copy!
+  char16_t* copy;
+  char16_t temp[64];
+  if (length <= 64) {
+    copy = temp;
+  } else {
+    copy = static_cast<char16_t*>(malloc(length * sizeof(char16_t)));
+    if (!copy) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+  }
+  NS_ASSERTION((uintptr_t(aString) & 0x1) == 0, "aString not properly aligned");
+  mozilla::NativeEndian::copyAndSwapToBigEndian(copy, aString, length);
+  rv = WriteBytes(AsBytes(Span(copy, length)));
+  if (copy != temp) {
+    free(copy);
+  }
+#endif
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteUtf8Z(const char16_t* aString) {
+  return WriteStringZ(NS_ConvertUTF16toUTF8(aString).get());
+}
+
+nsresult nsBinaryOutputStream::WriteBytes(Span<const uint8_t> aBytes) {
+  nsresult rv;
+  uint32_t bytesWritten;
+
+  rv = Write(reinterpret_cast<const char*>(aBytes.Elements()), aBytes.Length(),
+             &bytesWritten);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (bytesWritten != aBytes.Length()) {
+    return NS_ERROR_FAILURE;
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteBytesFromJS(const char* aString, uint32_t aLength) {
+  return WriteBytes(AsBytes(Span(aString, aLength)));
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteByteArray(const nsTArray<uint8_t>& aByteArray) {
+  return WriteBytes(aByteArray);
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteObject(nsISupports* aObject, bool aIsStrongRef) {
+  return WriteCompoundObject(aObject, NS_GET_IID(nsISupports), aIsStrongRef);
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteSingleRefObject(nsISupports* aObject) {
+  return WriteCompoundObject(aObject, NS_GET_IID(nsISupports), true);
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteCompoundObject(nsISupports* aObject,
+                                          const nsIID& aIID,
+                                          bool aIsStrongRef) {
+  nsCOMPtr<nsIClassInfo> classInfo = do_QueryInterface(aObject);
+  nsCOMPtr<nsISerializable> serializable = do_QueryInterface(aObject);
+
+  // Can't deal with weak refs
+  if (NS_WARN_IF(!aIsStrongRef)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  if (NS_WARN_IF(!classInfo) || NS_WARN_IF(!serializable)) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  nsCID cid;
+  nsresult rv = classInfo->GetClassIDNoAlloc(&cid);
+  if (NS_SUCCEEDED(rv)) {
+    rv = WriteID(cid);
+  } else {
+    nsCID* cidptr = nullptr;
+    rv = classInfo->GetClassID(&cidptr);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    rv = WriteID(*cidptr);
+
+    free(cidptr);
+  }
+
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = WriteID(aIID);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return serializable->Write(this);
+}
+
+NS_IMETHODIMP
+nsBinaryOutputStream::WriteID(const nsIID& aIID) {
+  nsresult rv = Write32(aIID.m0);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = Write16(aIID.m1);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = Write16(aIID.m2);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = WriteBytes(aIID.m3);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP_(char*)
+nsBinaryOutputStream::GetBuffer(uint32_t aLength, uint32_t aAlignMask) {
+  if (mBufferAccess) {
+    return mBufferAccess->GetBuffer(aLength, aAlignMask);
+  }
+  return nullptr;
+}
+
+NS_IMETHODIMP_(void)
+nsBinaryOutputStream::PutBuffer(char* aBuffer, uint32_t aLength) {
+  if (mBufferAccess) {
+    mBufferAccess->PutBuffer(aBuffer, aLength);
+  }
+}
+
+NS_IMPL_ISUPPORTS(nsBinaryInputStream, nsIObjectInputStream,
+                  nsIBinaryInputStream, nsIInputStream)
+
+NS_IMETHODIMP
+nsBinaryInputStream::Available(uint64_t* aResult) {
+  if (NS_WARN_IF(!mInputStream)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return mInputStream->Available(aResult);
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::StreamStatus() {
+  if (NS_WARN_IF(!mInputStream)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return mInputStream->StreamStatus();
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::Read(char* aBuffer, uint32_t aCount, uint32_t* aNumRead) {
+  if (NS_WARN_IF(!mInputStream)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  // mInputStream might give us short reads, so deal with that.
+  uint32_t totalRead = 0;
+
+  uint32_t bytesRead;
+  do {
+    nsresult rv = mInputStream->Read(aBuffer, aCount, &bytesRead);
+    if (rv == NS_BASE_STREAM_WOULD_BLOCK && totalRead != 0) {
+      // We already read some data.  Return it.
+      break;
+    }
+
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    totalRead += bytesRead;
+    aBuffer += bytesRead;
+    aCount -= bytesRead;
+  } while (aCount != 0 && bytesRead != 0);
+
+  *aNumRead = totalRead;
+
+  return NS_OK;
+}
+
+// when forwarding ReadSegments to mInputStream, we need to make sure
+// 'this' is being passed to the writer each time. To do this, we need
+// a thunking function which keeps the real input stream around.
+
+// the closure wrapper
+struct MOZ_STACK_CLASS ReadSegmentsClosure {
+  nsCOMPtr<nsIInputStream> mRealInputStream;
+  void* mRealClosure;
+  nsWriteSegmentFun mRealWriter;
+  nsresult mRealResult;
+  uint32_t mBytesRead;  // to properly implement aToOffset
+};
+
+// the thunking function
+static nsresult ReadSegmentForwardingThunk(nsIInputStream* aStream,
+                                           void* aClosure,
+                                           const char* aFromSegment,
+                                           uint32_t aToOffset, uint32_t aCount,
+                                           uint32_t* aWriteCount) {
+  ReadSegmentsClosure* thunkClosure =
+      reinterpret_cast<ReadSegmentsClosure*>(aClosure);
+
+  NS_ASSERTION(NS_SUCCEEDED(thunkClosure->mRealResult),
+               "How did this get to be a failure status?");
+
+  thunkClosure->mRealResult = thunkClosure->mRealWriter(
+      thunkClosure->mRealInputStream, thunkClosure->mRealClosure, aFromSegment,
+      thunkClosure->mBytesRead + aToOffset, aCount, aWriteCount);
+
+  return thunkClosure->mRealResult;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::ReadSegments(nsWriteSegmentFun aWriter, void* aClosure,
+                                  uint32_t aCount, uint32_t* aResult) {
+  if (NS_WARN_IF(!mInputStream)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  ReadSegmentsClosure thunkClosure = {this, aClosure, aWriter, NS_OK, 0};
+
+  // mInputStream might give us short reads, so deal with that.
+  uint32_t bytesRead;
+  do {
+    nsresult rv = mInputStream->ReadSegments(ReadSegmentForwardingThunk,
+                                             &thunkClosure, aCount, &bytesRead);
+
+    if (rv == NS_BASE_STREAM_WOULD_BLOCK && thunkClosure.mBytesRead != 0) {
+      // We already read some data.  Return it.
+      break;
+    }
+
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    thunkClosure.mBytesRead += bytesRead;
+    aCount -= bytesRead;
+  } while (aCount != 0 && bytesRead != 0 &&
+           NS_SUCCEEDED(thunkClosure.mRealResult));
+
+  *aResult = thunkClosure.mBytesRead;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::IsNonBlocking(bool* aNonBlocking) {
+  if (NS_WARN_IF(!mInputStream)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return mInputStream->IsNonBlocking(aNonBlocking);
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::Close() {
+  if (NS_WARN_IF(!mInputStream)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return mInputStream->Close();
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::SetInputStream(nsIInputStream* aInputStream) {
+  if (NS_WARN_IF(!aInputStream)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  mInputStream = aInputStream;
+  mBufferAccess = do_QueryInterface(aInputStream);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::ReadBoolean(bool* aBoolean) {
+  uint8_t byteResult;
+  nsresult rv = Read8(&byteResult);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  *aBoolean = !!byteResult;
+  return rv;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::Read8(uint8_t* aByte) {
+  nsresult rv;
+  uint32_t bytesRead;
+
+  rv = Read(reinterpret_cast<char*>(aByte), sizeof(*aByte), &bytesRead);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (bytesRead != 1) {
+    return NS_ERROR_FAILURE;
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::Read16(uint16_t* aNum) {
+  uint32_t bytesRead;
+  nsresult rv = Read(reinterpret_cast<char*>(aNum), sizeof(*aNum), &bytesRead);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (bytesRead != sizeof(*aNum)) {
+    return NS_ERROR_FAILURE;
+  }
+  *aNum = mozilla::NativeEndian::swapFromBigEndian(*aNum);
+  return rv;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::Read32(uint32_t* aNum) {
+  uint32_t bytesRead;
+  nsresult rv = Read(reinterpret_cast<char*>(aNum), sizeof(*aNum), &bytesRead);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (bytesRead != sizeof(*aNum)) {
+    return NS_ERROR_FAILURE;
+  }
+  *aNum = mozilla::NativeEndian::swapFromBigEndian(*aNum);
+  return rv;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::Read64(uint64_t* aNum) {
+  uint32_t bytesRead;
+  nsresult rv = Read(reinterpret_cast<char*>(aNum), sizeof(*aNum), &bytesRead);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (bytesRead != sizeof(*aNum)) {
+    return NS_ERROR_FAILURE;
+  }
+  *aNum = mozilla::NativeEndian::swapFromBigEndian(*aNum);
+  return rv;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::ReadFloat(float* aFloat) {
+  static_assert(sizeof(float) == sizeof(uint32_t),
+                "False assumption about sizeof(float)");
+  return Read32(reinterpret_cast<uint32_t*>(aFloat));
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::ReadDouble(double* aDouble) {
+  static_assert(sizeof(double) == sizeof(uint64_t),
+                "False assumption about sizeof(double)");
+  return Read64(reinterpret_cast<uint64_t*>(aDouble));
+}
+
+static nsresult WriteSegmentToCString(nsIInputStream* aStream, void* aClosure,
+                                      const char* aFromSegment,
+                                      uint32_t aToOffset, uint32_t aCount,
+                                      uint32_t* aWriteCount) {
+  nsACString* outString = static_cast<nsACString*>(aClosure);
+
+  outString->Append(aFromSegment, aCount);
+
+  *aWriteCount = aCount;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::ReadCString(nsACString& aString) {
+  nsresult rv;
+  uint32_t length, bytesRead;
+
+  rv = Read32(&length);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  aString.Truncate();
+  rv = ReadSegments(WriteSegmentToCString, &aString, length, &bytesRead);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (bytesRead != length) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+// sometimes, WriteSegmentToString will be handed an odd-number of
+// bytes, which means we only have half of the last char16_t
+struct WriteStringClosure {
+  char16_t* mWriteCursor;
+  bool mHasCarryoverByte;
+  char mCarryoverByte;
+};
+
+// there are a few cases we have to account for here:
+// * even length buffer, no carryover - easy, just append
+// * odd length buffer, no carryover - the last byte needs to be saved
+//                                     for carryover
+// * odd length buffer, with carryover - first byte needs to be used
+//                              with the carryover byte, and
+//                              the rest of the even length
+//                              buffer is appended as normal
+// * even length buffer, with carryover - the first byte needs to be
+//                              used with the previous carryover byte.
+//                              this gives you an odd length buffer,
+//                              so you have to save the last byte for
+//                              the next carryover
+
+// same version of the above, but with correct casting and endian swapping
+static nsresult WriteSegmentToString(nsIInputStream* aStream, void* aClosure,
+                                     const char* aFromSegment,
+                                     uint32_t aToOffset, uint32_t aCount,
+                                     uint32_t* aWriteCount) {
+  MOZ_ASSERT(aCount > 0, "Why are we being told to write 0 bytes?");
+  static_assert(sizeof(char16_t) == 2, "We can't handle other sizes!");
+
+  WriteStringClosure* closure = static_cast<WriteStringClosure*>(aClosure);
+  char16_t* cursor = closure->mWriteCursor;
+
+  // we're always going to consume the whole buffer no matter what
+  // happens, so take care of that right now.. that allows us to
+  // tweak aCount later. Do NOT move this!
+  *aWriteCount = aCount;
+
+  // if the last Write had an odd-number of bytes read, then
+  if (closure->mHasCarryoverByte) {
+    // re-create the two-byte sequence we want to work with
+    char bytes[2] = {closure->mCarryoverByte, *aFromSegment};
+    *cursor = *(char16_t*)bytes;
+    // Now the little endianness dance
+    mozilla::NativeEndian::swapToBigEndianInPlace(cursor, 1);
+    ++cursor;
+
+    // now skip past the first byte of the buffer.. code from here
+    // can assume normal operations, but should not assume aCount
+    // is relative to the ORIGINAL buffer
+    ++aFromSegment;
+    --aCount;
+
+    closure->mHasCarryoverByte = false;
+  }
+
+  // this array is possibly unaligned... be careful how we access it!
+  const char16_t* unicodeSegment =
+      reinterpret_cast<const char16_t*>(aFromSegment);
+
+  // calculate number of full characters in segment (aCount could be odd!)
+  uint32_t segmentLength = aCount / sizeof(char16_t);
+
+  // copy all data into our aligned buffer.  byte swap if necessary.
+  // cursor may be unaligned, so we cannot use copyAndSwapToBigEndian directly
+  memcpy(cursor, unicodeSegment, segmentLength * sizeof(char16_t));
+  char16_t* end = cursor + segmentLength;
+  mozilla::NativeEndian::swapToBigEndianInPlace(cursor, segmentLength);
+  closure->mWriteCursor = end;
+
+  // remember this is the modifed aCount and aFromSegment,
+  // so that will take into account the fact that we might have
+  // skipped the first byte in the buffer
+  if (aCount % sizeof(char16_t) != 0) {
+    // we must have had a carryover byte, that we'll need the next
+    // time around
+    closure->mCarryoverByte = aFromSegment[aCount - 1];
+    closure->mHasCarryoverByte = true;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::ReadString(nsAString& aString) {
+  nsresult rv;
+  uint32_t length, bytesRead;
+
+  rv = Read32(&length);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (length == 0) {
+    aString.Truncate();
+    return NS_OK;
+  }
+
+  // pre-allocate output buffer, and get direct access to buffer...
+  if (!aString.SetLength(length, mozilla::fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  WriteStringClosure closure;
+  closure.mWriteCursor = aString.BeginWriting();
+  closure.mHasCarryoverByte = false;
+
+  rv = ReadSegments(WriteSegmentToString, &closure, length * sizeof(char16_t),
+                    &bytesRead);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  NS_ASSERTION(!closure.mHasCarryoverByte, "some strange stream corruption!");
+
+  if (bytesRead != length * sizeof(char16_t)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+nsresult nsBinaryInputStream::ReadBytesToBuffer(uint32_t aLength,
+                                                uint8_t* aBuffer) {
+  uint32_t bytesRead;
+  nsresult rv = Read(reinterpret_cast<char*>(aBuffer), aLength, &bytesRead);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (bytesRead != aLength) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::ReadBytes(uint32_t aLength, char** aResult) {
+  char* s = static_cast<char*>(malloc(aLength));
+  if (!s) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  nsresult rv = ReadBytesToBuffer(aLength, reinterpret_cast<uint8_t*>(s));
+  if (NS_FAILED(rv)) {
+    free(s);
+    return rv;
+  }
+
+  *aResult = s;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::ReadByteArray(uint32_t aLength,
+                                   nsTArray<uint8_t>& aResult) {
+  if (!aResult.SetLength(aLength, mozilla::fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  nsresult rv = ReadBytesToBuffer(aLength, aResult.Elements());
+  if (NS_FAILED(rv)) {
+    aResult.Clear();
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::ReadArrayBuffer(uint64_t aLength,
+                                     JS::Handle<JS::Value> aBuffer,
+                                     JSContext* aCx, uint64_t* aReadLength) {
+  if (!aBuffer.isObject()) {
+    return NS_ERROR_FAILURE;
+  }
+  JS::Rooted<JSObject*> buffer(aCx, &aBuffer.toObject());
+  if (!JS::IsArrayBufferObject(buffer)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  size_t bufferLength = JS::GetArrayBufferByteLength(buffer);
+  if (bufferLength < aLength) {
+    return NS_ERROR_FAILURE;
+  }
+
+  uint32_t bufSize = std::min<uint64_t>(aLength, 4096);
+  UniquePtr<char[]> buf = MakeUnique<char[]>(bufSize);
+
+  uint64_t pos = 0;
+  *aReadLength = 0;
+  do {
+    // Read data into temporary buffer.
+    uint32_t bytesRead;
+    uint32_t amount = std::min<uint64_t>(aLength - pos, bufSize);
+    nsresult rv = Read(buf.get(), amount, &bytesRead);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+    MOZ_ASSERT(bytesRead <= amount);
+
+    if (bytesRead == 0) {
+      break;
+    }
+
+    // Copy data into actual buffer.
+
+    JS::AutoCheckCannotGC nogc;
+    bool isShared;
+    if (bufferLength != JS::GetArrayBufferByteLength(buffer)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    char* data = reinterpret_cast<char*>(
+        JS::GetArrayBufferData(buffer, &isShared, nogc));
+    MOZ_ASSERT(!isShared);  // Implied by JS::GetArrayBufferData()
+    if (!data) {
+      return NS_ERROR_FAILURE;
+    }
+
+    *aReadLength += bytesRead;
+    PodCopy(data + pos, buf.get(), bytesRead);
+
+    pos += bytesRead;
+  } while (pos < aLength);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::ReadObject(bool aIsStrongRef, nsISupports** aObject) {
+  nsCID cid;
+  nsIID iid;
+  nsresult rv = ReadID(&cid);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = ReadID(&iid);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // HACK: Intercept old (pre-gecko6) nsIURI IID, and replace with
+  // the updated IID, so that we're QI'ing to an actual interface.
+  // (As soon as we drop support for upgrading from pre-gecko6, we can
+  // remove this chunk.)
+  static const nsIID oldURIiid = {
+      0x7a22cc0,
+      0xce5,
+      0x11d3,
+      {0x93, 0x31, 0x0, 0x10, 0x4b, 0xa0, 0xfd, 0x40}};
+
+  // hackaround for bug 670542
+  static const nsIID oldURIiid2 = {
+      0xd6d04c36,
+      0x0fa4,
+      0x4db3,
+      {0xbe, 0x05, 0x4a, 0x18, 0x39, 0x71, 0x03, 0xe2}};
+
+  // hackaround for bug 682031
+  static const nsIID oldURIiid3 = {
+      0x12120b20,
+      0x0929,
+      0x40e9,
+      {0x88, 0xcf, 0x6e, 0x08, 0x76, 0x6e, 0x8b, 0x23}};
+
+  // hackaround for bug 1195415
+  static const nsIID oldURIiid4 = {
+      0x395fe045,
+      0x7d18,
+      0x4adb,
+      {0xa3, 0xfd, 0xaf, 0x98, 0xc8, 0xa1, 0xaf, 0x11}};
+
+  if (iid.Equals(oldURIiid) || iid.Equals(oldURIiid2) ||
+      iid.Equals(oldURIiid3) || iid.Equals(oldURIiid4)) {
+    const nsIID newURIiid = NS_IURI_IID;
+    iid = newURIiid;
+  }
+
+  // Hack around bug 1508939
+  // The old CSP serialization can't be handled cleanly when
+  // it's embedded in an old style principal
+  static const nsIID oldCSPiid = {
+      0xb3c4c0ae,
+      0xbd5e,
+      0x4cad,
+      {0x87, 0xe0, 0x8d, 0x21, 0x0d, 0xbb, 0x3f, 0x9f}};
+  if (iid.Equals(oldCSPiid)) {
+    return NS_ERROR_FAILURE;
+  }
+  // END HACK
+
+  // HACK:  Service workers store resource security info on disk in the dom
+  //        Cache API.  When the uuid of the nsIX509Cert interface changes
+  //        these serialized objects cannot be loaded any more.  This hack
+  //        works around this issue.
+
+  // hackaround for bug 1247580 (FF45 to FF46 transition)
+  static const nsIID oldCertIID = {
+      0xf8ed8364,
+      0xced9,
+      0x4c6e,
+      {0x86, 0xba, 0x48, 0xaf, 0x53, 0xc3, 0x93, 0xe6}};
+
+  if (iid.Equals(oldCertIID)) {
+    const nsIID newCertIID = NS_IX509CERT_IID;
+    iid = newCertIID;
+  }
+  // END HACK
+
+  nsCOMPtr<nsISupports> object = do_CreateInstance(cid, &rv);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsCOMPtr<nsISerializable> serializable = do_QueryInterface(object);
+  if (NS_WARN_IF(!serializable)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  rv = serializable->Read(this);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return object->QueryInterface(iid, reinterpret_cast<void**>(aObject));
+}
+
+NS_IMETHODIMP
+nsBinaryInputStream::ReadID(nsID* aResult) {
+  nsresult rv = Read32(&aResult->m0);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = Read16(&aResult->m1);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = Read16(&aResult->m2);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  const uint32_t toRead = sizeof(aResult->m3);
+  uint32_t bytesRead = 0;
+  rv = Read(reinterpret_cast<char*>(&aResult->m3[0]), toRead, &bytesRead);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  if (bytesRead != toRead) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP_(char*)
+nsBinaryInputStream::GetBuffer(uint32_t aLength, uint32_t aAlignMask) {
+  if (mBufferAccess) {
+    return mBufferAccess->GetBuffer(aLength, aAlignMask);
+  }
+  return nullptr;
+}
+
+NS_IMETHODIMP_(void)
+nsBinaryInputStream::PutBuffer(char* aBuffer, uint32_t aLength) {
+  if (mBufferAccess) {
+    mBufferAccess->PutBuffer(aBuffer, aLength);
+  }
+}
diff --git a/xpcom/io/nsBinaryStream.h b/xpcom/io/nsBinaryStream.h
new file mode 100644
index 0000000000..94b92bb746
--- /dev/null
+++ b/xpcom/io/nsBinaryStream.h
@@ -0,0 +1,99 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsBinaryStream_h___
+#define nsBinaryStream_h___
+
+#include "nsCOMPtr.h"
+#include "nsAString.h"
+#include "nsIObjectInputStream.h"
+#include "nsIObjectOutputStream.h"
+#include "nsIStreamBufferAccess.h"
+
+#define NS_BINARYOUTPUTSTREAM_CID                    \
+  { /* 86c37b9a-74e7-4672-844e-6e7dd83ba484 */       \
+    0x86c37b9a, 0x74e7, 0x4672, {                    \
+      0x84, 0x4e, 0x6e, 0x7d, 0xd8, 0x3b, 0xa4, 0x84 \
+    }                                                \
+  }
+
+#define NS_BINARYOUTPUTSTREAM_CONTRACTID "@mozilla.org/binaryoutputstream;1"
+
+// Derive from nsIObjectOutputStream so this class can be used as a superclass
+// by nsObjectOutputStream.
+class nsBinaryOutputStream final : public nsIObjectOutputStream {
+ public:
+  nsBinaryOutputStream() = default;
+
+ protected:
+  friend already_AddRefed<nsIObjectOutputStream> NS_NewObjectOutputStream(
+      nsIOutputStream*);
+
+  // nsISupports methods
+  NS_DECL_ISUPPORTS
+
+  // nsIOutputStream methods
+  NS_DECL_NSIOUTPUTSTREAM
+
+  // nsIBinaryOutputStream methods
+  NS_DECL_NSIBINARYOUTPUTSTREAM
+
+  // nsIObjectOutputStream methods
+  NS_DECL_NSIOBJECTOUTPUTSTREAM
+
+  // Call Write(), ensuring that all proffered data is written
+  nsresult WriteFully(const char* aBuf, uint32_t aCount);
+
+  nsCOMPtr<nsIOutputStream> mOutputStream;
+  nsCOMPtr<nsIStreamBufferAccess> mBufferAccess;
+
+ private:
+  // virtual dtor since subclasses call our Release()
+  virtual ~nsBinaryOutputStream() = default;
+};
+
+#define NS_BINARYINPUTSTREAM_CID                     \
+  { /* c521a612-2aad-46db-b6ab-3b821fb150b1 */       \
+    0xc521a612, 0x2aad, 0x46db, {                    \
+      0xb6, 0xab, 0x3b, 0x82, 0x1f, 0xb1, 0x50, 0xb1 \
+    }                                                \
+  }
+
+#define NS_BINARYINPUTSTREAM_CONTRACTID "@mozilla.org/binaryinputstream;1"
+
+class nsBinaryInputStream final : public nsIObjectInputStream {
+ public:
+  nsBinaryInputStream() = default;
+
+ protected:
+  friend already_AddRefed<nsIObjectInputStream> NS_NewObjectInputStream(
+      nsIInputStream*);
+
+  // nsISupports methods
+  NS_DECL_ISUPPORTS
+
+  // nsIInputStream methods
+  NS_DECL_NSIINPUTSTREAM
+
+  // nsIBinaryInputStream methods
+  NS_DECL_NSIBINARYINPUTSTREAM
+
+  // nsIObjectInputStream methods
+  NS_DECL_NSIOBJECTINPUTSTREAM
+
+  nsCOMPtr<nsIInputStream> mInputStream;
+  nsCOMPtr<nsIStreamBufferAccess> mBufferAccess;
+
+ private:
+  // Shared infrastructure for ReadBytes and ReadByteArray.  Callers
+  // are expected to provide a buffer that can contain aLength bytes.
+  nsresult ReadBytesToBuffer(uint32_t aLength, uint8_t* aBuffer);
+
+  // virtual dtor since subclasses call our Release()
+  virtual ~nsBinaryInputStream() = default;
+};
+
+#endif  // nsBinaryStream_h___
diff --git a/xpcom/io/nsDirectoryService.cpp b/xpcom/io/nsDirectoryService.cpp
new file mode 100644
index 0000000000..f5e841c6ea
--- /dev/null
+++ b/xpcom/io/nsDirectoryService.cpp
@@ -0,0 +1,448 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/ArrayUtils.h"
+
+#include "nsCOMPtr.h"
+#include "nsDirectoryService.h"
+#include "nsLocalFile.h"
+#include "nsDebug.h"
+#include "nsGkAtoms.h"
+#include "nsEnumeratorUtils.h"
+#include "nsThreadUtils.h"
+
+#include "mozilla/SimpleEnumerator.h"
+#include "nsICategoryManager.h"
+#include "nsISimpleEnumerator.h"
+
+#if defined(XP_WIN)
+#  include <windows.h>
+#  include <shlobj.h>
+#  include <stdlib.h>
+#  include <stdio.h>
+#elif defined(XP_UNIX)
+#  include <unistd.h>
+#  include <stdlib.h>
+#  include <sys/param.h>
+#  include "prenv.h"
+#  ifdef MOZ_WIDGET_COCOA
+#    include <CoreServices/CoreServices.h>
+#    include <Carbon/Carbon.h>
+#  endif
+#endif
+
+#include "SpecialSystemDirectory.h"
+#include "nsAppFileLocationProvider.h"
+#include "BinaryPath.h"
+
+using namespace mozilla;
+
+//----------------------------------------------------------------------------------------
+nsresult nsDirectoryService::GetCurrentProcessDirectory(nsIFile** aFile)
+//----------------------------------------------------------------------------------------
+{
+  if (NS_WARN_IF(!aFile)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aFile = nullptr;
+
+  //  Set the component registry location:
+  if (!gService) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (!mXCurProcD) {
+#if defined(ANDROID)
+    // Some callers relying on this fallback make assumptions that don't
+    // hold on Android for BinaryPath::GetFile, so use GRE_HOME instead.
+    const char* greHome = getenv("GRE_HOME");
+    if (!greHome) {
+      return NS_ERROR_FAILURE;
+    }
+    nsresult rv = NS_NewNativeLocalFile(nsDependentCString(greHome), true,
+                                        getter_AddRefs(mXCurProcD));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+#else
+    nsCOMPtr<nsIFile> file;
+    if (NS_SUCCEEDED(BinaryPath::GetFile(getter_AddRefs(file)))) {
+      nsresult rv = file->GetParent(getter_AddRefs(mXCurProcD));
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    }
+#endif
+  }
+  return mXCurProcD->Clone(aFile);
+}  // GetCurrentProcessDirectory()
+
+StaticRefPtr<nsDirectoryService> nsDirectoryService::gService;
+
+nsDirectoryService::nsDirectoryService() : mHashtable(128) {}
+
+nsresult nsDirectoryService::Create(REFNSIID aIID, void** aResult) {
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  if (!gService) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  return gService->QueryInterface(aIID, aResult);
+}
+
+NS_IMETHODIMP
+nsDirectoryService::Init() {
+  MOZ_ASSERT_UNREACHABLE("nsDirectoryService::Init() for internal use only!");
+  return NS_OK;
+}
+
+void nsDirectoryService::RealInit() {
+  NS_ASSERTION(!gService,
+               "nsDirectoryService::RealInit Mustn't initialize twice!");
+
+  gService = new nsDirectoryService();
+
+  // Let the list hold the only reference to the provider.
+  nsAppFileLocationProvider* defaultProvider = new nsAppFileLocationProvider;
+  gService->mProviders.AppendElement(defaultProvider);
+}
+
+nsDirectoryService::~nsDirectoryService() = default;
+
+NS_IMPL_ISUPPORTS(nsDirectoryService, nsIProperties, nsIDirectoryService,
+                  nsIDirectoryServiceProvider, nsIDirectoryServiceProvider2)
+
+NS_IMETHODIMP
+nsDirectoryService::Undefine(const char* aProp) {
+  if (NS_WARN_IF(!aProp)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsDependentCString key(aProp);
+  return mHashtable.Remove(key) ? NS_OK : NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsDirectoryService::GetKeys(nsTArray<nsCString>& aKeys) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+struct MOZ_STACK_CLASS FileData {
+  FileData(const char* aProperty, const nsIID& aUUID)
+      : property(aProperty), data(nullptr), persistent(true), uuid(aUUID) {}
+
+  const char* property;
+  nsCOMPtr<nsISupports> data;
+  bool persistent;
+  const nsIID& uuid;
+};
+
+static bool FindProviderFile(nsIDirectoryServiceProvider* aElement,
+                             FileData* aData) {
+  nsresult rv;
+  if (aData->uuid.Equals(NS_GET_IID(nsISimpleEnumerator))) {
+    // Not all providers implement this iface
+    nsCOMPtr<nsIDirectoryServiceProvider2> prov2 = do_QueryInterface(aElement);
+    if (prov2) {
+      nsCOMPtr<nsISimpleEnumerator> newFiles;
+      rv = prov2->GetFiles(aData->property, getter_AddRefs(newFiles));
+      if (NS_SUCCEEDED(rv) && newFiles) {
+        if (aData->data) {
+          nsCOMPtr<nsISimpleEnumerator> unionFiles;
+
+          NS_NewUnionEnumerator(getter_AddRefs(unionFiles),
+                                (nsISimpleEnumerator*)aData->data.get(),
+                                newFiles);
+
+          if (unionFiles) {
+            unionFiles.swap(*(nsISimpleEnumerator**)&aData->data);
+          }
+        } else {
+          aData->data = newFiles;
+        }
+
+        aData->persistent = false;  // Enumerators can never be persistent
+        return rv == NS_SUCCESS_AGGREGATE_RESULT;
+      }
+    }
+  } else {
+    rv = aElement->GetFile(aData->property, &aData->persistent,
+                           (nsIFile**)&aData->data);
+    if (NS_SUCCEEDED(rv) && aData->data) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+NS_IMETHODIMP
+nsDirectoryService::Get(const char* aProp, const nsIID& aUuid, void** aResult) {
+  if (NS_WARN_IF(!aProp)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  MOZ_ASSERT(NS_IsMainThread(), "Do not call dirsvc::get on non-main threads!");
+
+  nsDependentCString key(aProp);
+
+  nsCOMPtr<nsIFile> cachedFile = mHashtable.Get(key);
+
+  if (cachedFile) {
+    nsCOMPtr<nsIFile> cloneFile;
+    cachedFile->Clone(getter_AddRefs(cloneFile));
+    return cloneFile->QueryInterface(aUuid, aResult);
+  }
+
+  // it is not one of our defaults, lets check any providers
+  FileData fileData(aProp, aUuid);
+
+  for (int32_t i = mProviders.Length() - 1; i >= 0; i--) {
+    if (!FindProviderFile(mProviders[i], &fileData)) {
+      break;
+    }
+  }
+  if (fileData.data) {
+    if (fileData.persistent) {
+      Set(aProp, static_cast<nsIFile*>(fileData.data.get()));
+    }
+    nsresult rv = (fileData.data)->QueryInterface(aUuid, aResult);
+    fileData.data = nullptr;  // AddRef occurs in FindProviderFile()
+    return rv;
+  }
+
+  FindProviderFile(static_cast<nsIDirectoryServiceProvider*>(this), &fileData);
+  if (fileData.data) {
+    if (fileData.persistent) {
+      Set(aProp, static_cast<nsIFile*>(fileData.data.get()));
+    }
+    nsresult rv = (fileData.data)->QueryInterface(aUuid, aResult);
+    fileData.data = nullptr;  // AddRef occurs in FindProviderFile()
+    return rv;
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsDirectoryService::Set(const char* aProp, nsISupports* aValue) {
+  if (NS_WARN_IF(!aProp)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  if (!aValue) {
+    return NS_ERROR_FAILURE;
+  }
+
+  const nsDependentCString key(aProp);
+  return mHashtable.WithEntryHandle(key, [&](auto&& entry) {
+    if (!entry) {
+      nsCOMPtr<nsIFile> ourFile = do_QueryInterface(aValue);
+      if (ourFile) {
+        nsCOMPtr<nsIFile> cloneFile;
+        ourFile->Clone(getter_AddRefs(cloneFile));
+        entry.Insert(std::move(cloneFile));
+        return NS_OK;
+      }
+    }
+    return NS_ERROR_FAILURE;
+  });
+}
+
+NS_IMETHODIMP
+nsDirectoryService::Has(const char* aProp, bool* aResult) {
+  if (NS_WARN_IF(!aProp)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  *aResult = false;
+  nsCOMPtr<nsIFile> value;
+  nsresult rv = Get(aProp, NS_GET_IID(nsIFile), getter_AddRefs(value));
+  if (NS_FAILED(rv)) {
+    return NS_OK;
+  }
+
+  if (value) {
+    *aResult = true;
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsDirectoryService::RegisterProvider(nsIDirectoryServiceProvider* aProv) {
+  if (!aProv) {
+    return NS_ERROR_FAILURE;
+  }
+
+  mProviders.AppendElement(aProv);
+  return NS_OK;
+}
+
+void nsDirectoryService::RegisterCategoryProviders() {
+  nsCOMPtr<nsICategoryManager> catman(
+      do_GetService(NS_CATEGORYMANAGER_CONTRACTID));
+  if (!catman) {
+    return;
+  }
+
+  nsCOMPtr<nsISimpleEnumerator> entries;
+  catman->EnumerateCategory(XPCOM_DIRECTORY_PROVIDER_CATEGORY,
+                            getter_AddRefs(entries));
+
+  for (auto& categoryEntry : SimpleEnumerator<nsICategoryEntry>(entries)) {
+    nsAutoCString contractID;
+    categoryEntry->GetValue(contractID);
+
+    if (nsCOMPtr<nsIDirectoryServiceProvider> provider =
+            do_GetService(contractID.get())) {
+      RegisterProvider(provider);
+    }
+  }
+}
+
+NS_IMETHODIMP
+nsDirectoryService::UnregisterProvider(nsIDirectoryServiceProvider* aProv) {
+  if (!aProv) {
+    return NS_ERROR_FAILURE;
+  }
+
+  mProviders.RemoveElement(aProv);
+  return NS_OK;
+}
+
+// DO NOT ADD ANY LOCATIONS TO THIS FUNCTION UNTIL YOU TALK TO:
+// dougt@netscape.com. This is meant to be a place of xpcom or system specific
+// file locations, not application specific locations.  If you need the later,
+// register a callback for your application.
+
+NS_IMETHODIMP
+nsDirectoryService::GetFile(const char* aProp, bool* aPersistent,
+                            nsIFile** aResult) {
+  nsCOMPtr<nsIFile> localFile;
+  nsresult rv = NS_ERROR_FAILURE;
+
+  *aResult = nullptr;
+  *aPersistent = true;
+
+  RefPtr<nsAtom> inAtom = NS_Atomize(aProp);
+
+  // check to see if it is one of our defaults
+
+  if (inAtom == nsGkAtoms::DirectoryService_CurrentProcess ||
+      inAtom == nsGkAtoms::DirectoryService_OS_CurrentProcessDirectory) {
+    rv = GetCurrentProcessDirectory(getter_AddRefs(localFile));
+  }
+
+  // Unless otherwise set, the core pieces of the GRE exist
+  // in the current process directory.
+  else if (inAtom == nsGkAtoms::DirectoryService_GRE_Directory ||
+           inAtom == nsGkAtoms::DirectoryService_GRE_BinDirectory) {
+    rv = GetCurrentProcessDirectory(getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_OS_TemporaryDirectory) {
+    rv = GetSpecialSystemDirectory(OS_TemporaryDirectory,
+                                   getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_OS_CurrentWorkingDirectory) {
+    rv = GetSpecialSystemDirectory(OS_CurrentWorkingDirectory,
+                                   getter_AddRefs(localFile));
+  }
+#if defined(MOZ_WIDGET_COCOA)
+  else if (inAtom == nsGkAtoms::DirectoryService_SystemDirectory) {
+    rv = GetSpecialSystemDirectory(Mac_SystemDirectory,
+                                   getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_UserLibDirectory) {
+    rv = GetSpecialSystemDirectory(Mac_UserLibDirectory,
+                                   getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::Home) {
+    rv =
+        GetSpecialSystemDirectory(Mac_HomeDirectory, getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_DefaultDownloadDirectory) {
+    rv = GetSpecialSystemDirectory(Mac_DefaultDownloadDirectory,
+                                   getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_OS_DesktopDirectory) {
+    rv = GetSpecialSystemDirectory(Mac_UserDesktopDirectory,
+                                   getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_LocalApplicationsDirectory) {
+    rv = GetSpecialSystemDirectory(Mac_LocalApplicationsDirectory,
+                                   getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_UserPreferencesDirectory) {
+    rv = GetSpecialSystemDirectory(Mac_UserPreferencesDirectory,
+                                   getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_PictureDocumentsDirectory) {
+    rv = GetSpecialSystemDirectory(Mac_PictureDocumentsDirectory,
+                                   getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_DefaultScreenshotDirectory) {
+    rv = GetSpecialSystemDirectory(Mac_DefaultScreenshotDirectory,
+                                   getter_AddRefs(localFile));
+  }
+#elif defined(XP_WIN)
+  else if (inAtom == nsGkAtoms::DirectoryService_SystemDirectory) {
+    rv = GetSpecialSystemDirectory(Win_SystemDirectory,
+                                   getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_WindowsDirectory) {
+    rv = GetSpecialSystemDirectory(Win_WindowsDirectory,
+                                   getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_WindowsProgramFiles) {
+    rv = GetSpecialSystemDirectory(Win_ProgramFiles, getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::Home) {
+    rv =
+        GetSpecialSystemDirectory(Win_HomeDirectory, getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_Programs) {
+    rv = GetSpecialSystemDirectory(Win_Programs, getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_Favorites) {
+    rv = GetSpecialSystemDirectory(Win_Favorites, getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_OS_DesktopDirectory) {
+    rv = GetSpecialSystemDirectory(Win_Desktopdirectory,
+                                   getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_Appdata) {
+    rv = GetSpecialSystemDirectory(Win_Appdata, getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_LocalAppdata) {
+    rv = GetSpecialSystemDirectory(Win_LocalAppdata, getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_WinCookiesDirectory) {
+    rv = GetSpecialSystemDirectory(Win_Cookies, getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_DefaultDownloadDirectory) {
+    rv = GetSpecialSystemDirectory(Win_Downloads, getter_AddRefs(localFile));
+  }
+#elif defined(XP_UNIX)
+  else if (inAtom == nsGkAtoms::Home) {
+    rv = GetSpecialSystemDirectory(Unix_HomeDirectory,
+                                   getter_AddRefs(localFile));
+  } else if (inAtom == nsGkAtoms::DirectoryService_OS_DesktopDirectory) {
+    rv = GetSpecialSystemDirectory(Unix_XDG_Desktop, getter_AddRefs(localFile));
+    *aPersistent = false;
+  } else if (inAtom == nsGkAtoms::DirectoryService_DefaultDownloadDirectory) {
+    rv =
+        GetSpecialSystemDirectory(Unix_XDG_Download, getter_AddRefs(localFile));
+    *aPersistent = false;
+  } else if (inAtom == nsGkAtoms::DirectoryService_OS_SystemConfigDir) {
+    rv = GetSpecialSystemDirectory(Unix_SystemConfigDirectory,
+                                   getter_AddRefs(localFile));
+  }
+#endif
+
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (!localFile) {
+    return NS_ERROR_FAILURE;
+  }
+
+  localFile.forget(aResult);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDirectoryService::GetFiles(const char* aProp, nsISimpleEnumerator** aResult) {
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aResult = nullptr;
+
+  return NS_ERROR_FAILURE;
+}
diff --git a/xpcom/io/nsDirectoryService.h b/xpcom/io/nsDirectoryService.h
new file mode 100644
index 0000000000..49f3c85f51
--- /dev/null
+++ b/xpcom/io/nsDirectoryService.h
@@ -0,0 +1,59 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsDirectoryService_h___
+#define nsDirectoryService_h___
+
+#include "nsIDirectoryService.h"
+#include "nsInterfaceHashtable.h"
+#include "nsIFile.h"
+#include "nsDirectoryServiceDefs.h"
+#include "nsTArray.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/StaticPtr.h"
+
+#define NS_DIRECTORY_SERVICE_CID                     \
+  {                                                  \
+    0xf00152d0, 0xb40b, 0x11d3, {                    \
+      0x8c, 0x9c, 0x00, 0x00, 0x64, 0x65, 0x73, 0x74 \
+    }                                                \
+  }
+
+class nsDirectoryService final : public nsIDirectoryService,
+                                 public nsIProperties,
+                                 public nsIDirectoryServiceProvider2 {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  NS_DECL_NSIPROPERTIES
+
+  NS_DECL_NSIDIRECTORYSERVICE
+
+  NS_DECL_NSIDIRECTORYSERVICEPROVIDER
+
+  NS_DECL_NSIDIRECTORYSERVICEPROVIDER2
+
+  nsDirectoryService();
+
+  static void RealInit();
+  void RegisterCategoryProviders();
+
+  static nsresult Create(REFNSIID aIID, void** aResult);
+
+  static mozilla::StaticRefPtr<nsDirectoryService> gService;
+
+  void SetCurrentProcessDirectory(nsIFile* aFile) { mXCurProcD = aFile; }
+  nsresult GetCurrentProcessDirectory(nsIFile**);
+
+ private:
+  ~nsDirectoryService();
+  nsCOMPtr<nsIFile> mXCurProcD;
+
+  nsInterfaceHashtable<nsCStringHashKey, nsIFile> mHashtable;
+  nsTArray<nsCOMPtr<nsIDirectoryServiceProvider>> mProviders;
+};
+
+#endif
diff --git a/xpcom/io/nsDirectoryServiceDefs.h b/xpcom/io/nsDirectoryServiceDefs.h
new file mode 100644
index 0000000000..9f0368ff06
--- /dev/null
+++ b/xpcom/io/nsDirectoryServiceDefs.h
@@ -0,0 +1,96 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Defines the property names for directories available from
+ * nsIDirectoryService. These dirs are always available even if no
+ * nsIDirectoryServiceProviders have been registered with the service.
+ * Application level keys are defined in nsAppDirectoryServiceDefs.h.
+ *
+ * Keys whose definition ends in "DIR" or "FILE" return a single nsIFile (or
+ * subclass). Keys whose definition ends in "LIST" return an nsISimpleEnumerator
+ * which enumerates a list of file objects.
+ *
+ * Defines listed in this file are FROZEN.  This list may grow.  Each unique
+ * string in this file should have a corresponding atom defined in
+ * StaticAtoms.py (search for "DirectoryService"), regardless of whether it
+ * is defined here due to conditional compilation.
+ */
+
+#ifndef nsDirectoryServiceDefs_h___
+#define nsDirectoryServiceDefs_h___
+
+/* General OS specific locations */
+
+#define NS_OS_HOME_DIR "Home"
+
+#define NS_OS_TEMP_DIR "TmpD"
+#define NS_OS_CURRENT_WORKING_DIR "CurWorkD"
+/* Files stored in this directory will appear on the user's desktop,
+ * if there is one, otherwise it's just the same as "Home"
+ */
+#define NS_OS_DESKTOP_DIR "Desk"
+
+#define NS_OS_DEFAULT_DOWNLOAD_DIR "DfltDwnld"
+
+/* Property returns the directory in which the procces was started from.
+ */
+#define NS_OS_CURRENT_PROCESS_DIR "CurProcD"
+
+/* This location is similar to NS_OS_CURRENT_PROCESS_DIR, however,
+ * NS_XPCOM_CURRENT_PROCESS_DIR can be overriden by passing a "bin
+ * directory" to NS_InitXPCOM().
+ */
+#define NS_XPCOM_CURRENT_PROCESS_DIR "XCurProcD"
+
+/* Property will return the location of the the XPCOM Shared Library.
+ */
+#define NS_XPCOM_LIBRARY_FILE "XpcomLib"
+
+/* Property will return the current location of the GRE directory.
+ * On OSX, this typically points to Contents/Resources in the app bundle.
+ * If no GRE is used, this propery will behave like
+ * NS_XPCOM_CURRENT_PROCESS_DIR.
+ */
+#define NS_GRE_DIR "GreD"
+
+/* Property will return the current location of the GRE-binaries directory.
+ * On OSX, this typically points to Contents/MacOS in the app bundle. On
+ * all other platforms, this will be identical to NS_GRE_DIR.
+ * Since this property is based on the NS_GRE_DIR, if no GRE is used, this
+ * propery will behave like NS_XPCOM_CURRENT_PROCESS_DIR.
+ */
+#define NS_GRE_BIN_DIR "GreBinD"
+
+/* Platform Specific Locations */
+
+#if !defined(XP_UNIX) || defined(MOZ_WIDGET_COCOA)
+#  define NS_OS_SYSTEM_DIR "SysD"
+#endif
+
+#if defined(MOZ_WIDGET_COCOA)
+#  define NS_MAC_USER_LIB_DIR "ULibDir"
+#  define NS_OSX_LOCAL_APPLICATIONS_DIR "LocApp"
+#  define NS_OSX_USER_PREFERENCES_DIR "UsrPrfs"
+#  define NS_OSX_PICTURE_DOCUMENTS_DIR "Pct"
+#elif defined(XP_WIN)
+#  define NS_WIN_WINDOWS_DIR "WinD"
+#  define NS_WIN_PROGRAM_FILES_DIR "ProgF"
+#  define NS_WIN_HOME_DIR NS_OS_HOME_DIR
+#  define NS_WIN_PROGRAMS_DIR "Progs"  // User start menu programs directory!
+#  define NS_WIN_FAVORITES_DIR "Favs"
+#  define NS_WIN_APPDATA_DIR "AppData"
+#  define NS_WIN_LOCAL_APPDATA_DIR "LocalAppData"
+#  define NS_WIN_COOKIES_DIR "CookD"
+#elif defined(XP_UNIX)
+#  define NS_UNIX_HOME_DIR NS_OS_HOME_DIR
+#endif
+
+#if defined(MOZ_WIDGET_GTK)
+#  define NS_OS_SYSTEM_CONFIG_DIR "SysConfD"
+#endif  // defined(MOZ_WIDGET_GTK)
+
+#endif
diff --git a/xpcom/io/nsDirectoryServiceUtils.h b/xpcom/io/nsDirectoryServiceUtils.h
new file mode 100644
index 0000000000..c48bf4e2fe
--- /dev/null
+++ b/xpcom/io/nsDirectoryServiceUtils.h
@@ -0,0 +1,29 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsDirectoryServiceUtils_h___
+#define nsDirectoryServiceUtils_h___
+
+#include "nsIProperties.h"
+#include "nsServiceManagerUtils.h"
+#include "nsCOMPtr.h"
+#include "nsXPCOMCID.h"
+#include "nsIFile.h"
+
+inline nsresult NS_GetSpecialDirectory(const char* aSpecialDirName,
+                                       nsIFile** aResult) {
+  nsresult rv;
+  nsCOMPtr<nsIProperties> serv(
+      do_GetService(NS_DIRECTORY_SERVICE_CONTRACTID, &rv));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  return serv->Get(aSpecialDirName, NS_GET_IID(nsIFile),
+                   reinterpret_cast<void**>(aResult));
+}
+
+#endif
diff --git a/xpcom/io/nsEscape.cpp b/xpcom/io/nsEscape.cpp
new file mode 100644
index 0000000000..c1714c0b9a
--- /dev/null
+++ b/xpcom/io/nsEscape.cpp
@@ -0,0 +1,664 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsEscape.h"
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/BinarySearch.h"
+#include "mozilla/CheckedInt.h"
+#include "mozilla/TextUtils.h"
+#include "nsTArray.h"
+#include "nsCRT.h"
+#include "nsASCIIMask.h"
+
+static const char hexCharsUpper[] = "0123456789ABCDEF";
+static const char hexCharsUpperLower[] = "0123456789ABCDEFabcdef";
+
+static const unsigned char netCharType[256] =
+    // clang-format off
+/*  Bit 0       xalpha      -- the alphas
+**  Bit 1       xpalpha     -- as xalpha but
+**                             converts spaces to plus and plus to %2B
+**  Bit 3 ...   path        -- as xalphas but doesn't escape '/'
+**  Bit 4 ...   NSURL-ref   -- extra encoding for Apple NSURL compatibility.
+**                             This encoding set is used on encoded URL ref
+**                             components before converting a URL to an NSURL
+**                             so we don't include '%' to avoid double encoding.
+*/
+  /*   0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F */
+  {  0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0, /* 0x */
+     0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0, /* 1x */
+  /*       !   "   #   $   %   &   '   (   )   *   +   ,   -   .   /        */
+     0x0,0x8,0x0,0x0,0x8,0x8,0x8,0x8,0x8,0x8,0xf,0xc,0x8,0xf,0xf,0xc, /* 2x */
+  /*   0   1   2   3   4   5   6   7   8   9   :   ;   <   =   >   ?        */
+     0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0x8,0x8,0x0,0x8,0x0,0x8, /* 3x */
+  /*   @   A   B   C   D   E   F   G   H   I   J   K   L   M   N   O        */
+     0x8,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf, /* 4x */
+     /* bits for '@' changed from 7 to 0 so '@' can be escaped   */
+     /* in usernames and passwords in publishing.                */
+  /*   P   Q   R   S   T   U   V   W   X   Y   Z   [   \   ]   ^   _        */
+     0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0x0,0x0,0x0,0x0,0xf, /* 5x */
+  /*   `   a   b   c   d   e   f   g   h   i   j   k   l   m   n   o        */
+     0x0,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf, /* 6x */
+  /*   p   q   r   s   t   u   v   w   x   y   z   {   |   }   ~ DEL        */
+     0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0xf,0x0,0x0,0x0,0x8,0x0, /* 7x */
+     0x0,
+  };
+
+/* decode % escaped hex codes into character values
+ */
+#define UNHEX(C) \
+    ((C >= '0' && C <= '9') ? C - '0' : \
+     ((C >= 'A' && C <= 'F') ? C - 'A' + 10 : \
+     ((C >= 'a' && C <= 'f') ? C - 'a' + 10 : 0)))
+// clang-format on
+
+#define IS_OK(C) (netCharType[((unsigned char)(C))] & (aFlags))
+#define HEX_ESCAPE '%'
+
+static const uint32_t ENCODE_MAX_LEN = 6;  // %uABCD
+
+static uint32_t AppendPercentHex(char* aBuffer, unsigned char aChar) {
+  uint32_t i = 0;
+  aBuffer[i++] = '%';
+  aBuffer[i++] = hexCharsUpper[aChar >> 4];   // high nibble
+  aBuffer[i++] = hexCharsUpper[aChar & 0xF];  // low nibble
+  return i;
+}
+
+static uint32_t AppendPercentHex(char16_t* aBuffer, char16_t aChar) {
+  uint32_t i = 0;
+  aBuffer[i++] = '%';
+  if (aChar & 0xff00) {
+    aBuffer[i++] = 'u';
+    aBuffer[i++] = hexCharsUpper[aChar >> 12];         // high-byte high nibble
+    aBuffer[i++] = hexCharsUpper[(aChar >> 8) & 0xF];  // high-byte low nibble
+  }
+  aBuffer[i++] = hexCharsUpper[(aChar >> 4) & 0xF];  // low-byte high nibble
+  aBuffer[i++] = hexCharsUpper[aChar & 0xF];         // low-byte low nibble
+  return i;
+}
+
+//----------------------------------------------------------------------------------------
+char* nsEscape(const char* aStr, size_t aLength, size_t* aOutputLength,
+               nsEscapeMask aFlags)
+//----------------------------------------------------------------------------------------
+{
+  if (!aStr) {
+    return nullptr;
+  }
+
+  size_t charsToEscape = 0;
+
+  const unsigned char* src = (const unsigned char*)aStr;
+  for (size_t i = 0; i < aLength; ++i) {
+    if (!IS_OK(src[i])) {
+      charsToEscape++;
+    }
+  }
+
+  // calculate how much memory should be allocated
+  // original length + 2 bytes for each escaped character + terminating '\0'
+  // do the sum in steps to check for overflow
+  size_t dstSize = aLength + 1 + charsToEscape;
+  if (dstSize <= aLength) {
+    return nullptr;
+  }
+  dstSize += charsToEscape;
+  if (dstSize < aLength) {
+    return nullptr;
+  }
+
+  // fail if we need more than 4GB
+  if (dstSize > UINT32_MAX) {
+    return nullptr;
+  }
+
+  char* result = (char*)moz_xmalloc(dstSize);
+
+  unsigned char* dst = (unsigned char*)result;
+  if (aFlags == url_XPAlphas) {
+    for (size_t i = 0; i < aLength; ++i) {
+      unsigned char c = *src++;
+      if (IS_OK(c)) {
+        *dst++ = c;
+      } else if (c == ' ') {
+        *dst++ = '+'; /* convert spaces to pluses */
+      } else {
+        *dst++ = HEX_ESCAPE;
+        *dst++ = hexCharsUpper[c >> 4];   /* high nibble */
+        *dst++ = hexCharsUpper[c & 0x0f]; /* low nibble */
+      }
+    }
+  } else {
+    for (size_t i = 0; i < aLength; ++i) {
+      unsigned char c = *src++;
+      if (IS_OK(c)) {
+        *dst++ = c;
+      } else {
+        *dst++ = HEX_ESCAPE;
+        *dst++ = hexCharsUpper[c >> 4];   /* high nibble */
+        *dst++ = hexCharsUpper[c & 0x0f]; /* low nibble */
+      }
+    }
+  }
+
+  *dst = '\0'; /* tack on eos */
+  if (aOutputLength) {
+    *aOutputLength = dst - (unsigned char*)result;
+  }
+
+  return result;
+}
+
+//----------------------------------------------------------------------------------------
+char* nsUnescape(char* aStr)
+//----------------------------------------------------------------------------------------
+{
+  nsUnescapeCount(aStr);
+  return aStr;
+}
+
+//----------------------------------------------------------------------------------------
+int32_t nsUnescapeCount(char* aStr)
+//----------------------------------------------------------------------------------------
+{
+  char* src = aStr;
+  char* dst = aStr;
+
+  char c1[] = " ";
+  char c2[] = " ";
+  char* const pc1 = c1;
+  char* const pc2 = c2;
+
+  if (!*src) {
+    // A null string was passed in.  Nothing to escape.
+    // Returns early as the string might not actually be mutable with
+    // length 0.
+    return 0;
+  }
+
+  while (*src) {
+    c1[0] = *(src + 1);
+    if (*(src + 1) == '\0') {
+      c2[0] = '\0';
+    } else {
+      c2[0] = *(src + 2);
+    }
+
+    if (*src != HEX_ESCAPE || strpbrk(pc1, hexCharsUpperLower) == nullptr ||
+        strpbrk(pc2, hexCharsUpperLower) == nullptr) {
+      *dst++ = *src++;
+    } else {
+      src++; /* walk over escape */
+      if (*src) {
+        *dst = UNHEX(*src) << 4;
+        src++;
+      }
+      if (*src) {
+        *dst = (*dst + UNHEX(*src));
+        src++;
+      }
+      dst++;
+    }
+  }
+
+  *dst = 0;
+  return (int)(dst - aStr);
+
+} /* NET_UnEscapeCnt */
+
+void nsAppendEscapedHTML(const nsACString& aSrc, nsACString& aDst) {
+  // Preparation: aDst's length will increase by at least aSrc's length. If the
+  // addition overflows, we skip this, which is fine, and we'll likely abort
+  // while (infallibly) appending due to aDst becoming too large.
+  mozilla::CheckedInt<nsACString::size_type> newCapacity = aDst.Length();
+  newCapacity += aSrc.Length();
+  if (newCapacity.isValid()) {
+    aDst.SetCapacity(newCapacity.value());
+  }
+
+  for (auto cur = aSrc.BeginReading(); cur != aSrc.EndReading(); cur++) {
+    if (*cur == '<') {
+      aDst.AppendLiteral("&lt;");
+    } else if (*cur == '>') {
+      aDst.AppendLiteral("&gt;");
+    } else if (*cur == '&') {
+      aDst.AppendLiteral("&amp;");
+    } else if (*cur == '"') {
+      aDst.AppendLiteral("&quot;");
+    } else if (*cur == '\'') {
+      aDst.AppendLiteral("&#39;");
+    } else {
+      aDst.Append(*cur);
+    }
+  }
+}
+
+//----------------------------------------------------------------------------------------
+//
+// The following table encodes which characters needs to be escaped for which
+// parts of an URL.  The bits are the "url components" in the enum EscapeMask,
+// see nsEscape.h.
+
+template <size_t N>
+static constexpr void AddUnescapedChars(const char (&aChars)[N],
+                                        uint32_t aFlags,
+                                        std::array<uint32_t, 256>& aTable) {
+  for (size_t i = 0; i < N - 1; ++i) {
+    aTable[static_cast<unsigned char>(aChars[i])] |= aFlags;
+  }
+}
+
+static constexpr std::array<uint32_t, 256> BuildEscapeChars() {
+  constexpr uint32_t kAllModes = esc_Scheme | esc_Username | esc_Password |
+                                 esc_Host | esc_Directory | esc_FileBaseName |
+                                 esc_FileExtension | esc_Param | esc_Query |
+                                 esc_Ref | esc_ExtHandler;
+
+  std::array<uint32_t, 256> table{0};
+
+  // Alphanumerics shouldn't be escaped in all escape modes.
+  AddUnescapedChars("0123456789", kAllModes, table);
+  AddUnescapedChars("ABCDEFGHIJKLMNOPQRSTUVWXYZ", kAllModes, table);
+  AddUnescapedChars("abcdefghijklmnopqrstuvwxyz", kAllModes, table);
+  AddUnescapedChars("!$&()*+,-_~", kAllModes, table);
+
+  // Extra characters which aren't escaped in particular escape modes.
+  AddUnescapedChars(".", esc_Scheme, table);
+  // esc_Username has no additional unescaped characters.
+  AddUnescapedChars("|", esc_Password, table);
+  AddUnescapedChars(".", esc_Host, table);
+  AddUnescapedChars("'./:;=@[]|", esc_Directory, table);
+  AddUnescapedChars("'.:;=@[]|", esc_FileBaseName, table);
+  AddUnescapedChars("':;=@[]|", esc_FileExtension, table);
+  AddUnescapedChars(".:;=@[\\]^`{|}", esc_Param, table);
+  AddUnescapedChars("./:;=?@[\\]^`{|}", esc_Query, table);
+  AddUnescapedChars("#'./:;=?@[\\]^{|}", esc_Ref, table);
+  AddUnescapedChars("#'./:;=?@[]", esc_ExtHandler, table);
+
+  return table;
+}
+
+static constexpr std::array<uint32_t, 256> EscapeChars = BuildEscapeChars();
+
+static bool dontNeedEscape(unsigned char aChar, uint32_t aFlags) {
+  return EscapeChars[(size_t)aChar] & aFlags;
+}
+static bool dontNeedEscape(uint16_t aChar, uint32_t aFlags) {
+  return aChar < EscapeChars.size() ? (EscapeChars[(size_t)aChar] & aFlags)
+                                    : false;
+}
+
+// Temporary static assert to make sure that the rewrite to using
+// `BuildEscapeChars` didn't change the final array in memory.
+// It will be removed in Bug 1750945.
+
+static_assert([]() constexpr {
+  constexpr uint32_t OldEscapeChars[256] =
+      // clang-format off
+//     0      1      2      3      4      5      6      7      8      9      A      B      C      D      E      F
+{
+       0,     0,     0,     0,     0,     0,     0,     0,     0,     0,     0,     0,     0,     0,     0,     0,  // 0x
+       0,     0,     0,     0,     0,     0,     0,     0,     0,     0,     0,     0,     0,     0,     0,     0,  // 1x
+       0,132095,     0,131584,132095,     0,132095,131696,132095,132095,132095,132095,132095,132095,132025,131856,  // 2x   !"#$%&'()*+,-./
+  132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132080,132080,     0,132080,     0,131840,  // 3x  0123456789:;<=>?
+  132080,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,  // 4x  @ABCDEFGHIJKLMNO
+  132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132080,   896,132080,   896,132095,  // 5x  PQRSTUVWXYZ[\]^_
+     384,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,  // 6x  `abcdefghijklmno
+  132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,132095,   896,  1012,   896,132095,     0,  // 7x  pqrstuvwxyz{|}~ DEL
+       0                                                                                                            // 80 to FF are zero
+};
+  // clang-format on
+
+  for (size_t i = 0; i < EscapeChars.size(); ++i) {
+    if (OldEscapeChars[i] != EscapeChars[i]) {
+      return false;
+    }
+  }
+  return true;
+}());
+
+//----------------------------------------------------------------------------------------
+
+/**
+ * Templated helper for URL escaping a portion of a string.
+ *
+ * @param aPart The pointer to the beginning of the portion of the string to
+ *  escape.
+ * @param aPartLen The length of the string to escape.
+ * @param aFlags Flags used to configure escaping. @see EscapeMask
+ * @param aResult String that has the URL escaped portion appended to. Only
+ *  altered if the string is URL escaped or |esc_AlwaysCopy| is specified.
+ * @param aDidAppend Indicates whether or not data was appended to |aResult|.
+ * @return NS_ERROR_INVALID_ARG, NS_ERROR_OUT_OF_MEMORY on failure.
+ */
+template <class T>
+static nsresult T_EscapeURL(const typename T::char_type* aPart, size_t aPartLen,
+                            uint32_t aFlags, const ASCIIMaskArray* aFilterMask,
+                            T& aResult, bool& aDidAppend) {
+  typedef nsCharTraits<typename T::char_type> traits;
+  typedef typename traits::unsigned_char_type unsigned_char_type;
+  static_assert(sizeof(*aPart) == 1 || sizeof(*aPart) == 2,
+                "unexpected char type");
+
+  if (!aPart) {
+    MOZ_ASSERT_UNREACHABLE("null pointer");
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  bool forced = !!(aFlags & esc_Forced);
+  bool ignoreNonAscii = !!(aFlags & esc_OnlyASCII);
+  bool ignoreAscii = !!(aFlags & esc_OnlyNonASCII);
+  bool writing = !!(aFlags & esc_AlwaysCopy);
+  bool colon = !!(aFlags & esc_Colon);
+  bool spaces = !!(aFlags & esc_Spaces);
+
+  auto src = reinterpret_cast<const unsigned_char_type*>(aPart);
+
+  typename T::char_type tempBuffer[100];
+  unsigned int tempBufferPos = 0;
+
+  bool previousIsNonASCII = false;
+  for (size_t i = 0; i < aPartLen; ++i) {
+    unsigned_char_type c = *src++;
+
+    // If there is a filter, we wish to skip any characters which match it.
+    // This is needed so we don't perform an extra pass just to extract the
+    // filtered characters.
+    if (aFilterMask && mozilla::ASCIIMask::IsMasked(*aFilterMask, c)) {
+      if (!writing) {
+        if (!aResult.Append(aPart, i, mozilla::fallible)) {
+          return NS_ERROR_OUT_OF_MEMORY;
+        }
+        writing = true;
+      }
+      continue;
+    }
+
+    // if the char has not to be escaped or whatever follows % is
+    // a valid escaped string, just copy the char.
+    //
+    // Also the % will not be escaped until forced
+    // See bugzilla bug 61269 for details why we changed this
+    //
+    // And, we will not escape non-ascii characters if requested.
+    // On special request we will also escape the colon even when
+    // not covered by the matrix.
+    // ignoreAscii is not honored for control characters (C0 and DEL)
+    //
+    // And, we should escape the '|' character when it occurs after any
+    // non-ASCII character as it may be aPart of a multi-byte character.
+    //
+    // 0x20..0x7e are the valid ASCII characters.
+    if ((dontNeedEscape(c, aFlags) || (c == HEX_ESCAPE && !forced) ||
+         (c > 0x7f && ignoreNonAscii) ||
+         (c >= 0x20 && c < 0x7f && ignoreAscii)) &&
+        !(c == ':' && colon) && !(c == ' ' && spaces) &&
+        !(previousIsNonASCII && c == '|' && !ignoreNonAscii)) {
+      if (writing) {
+        tempBuffer[tempBufferPos++] = c;
+      }
+    } else { /* do the escape magic */
+      if (!writing) {
+        if (!aResult.Append(aPart, i, mozilla::fallible)) {
+          return NS_ERROR_OUT_OF_MEMORY;
+        }
+        writing = true;
+      }
+      uint32_t len = ::AppendPercentHex(tempBuffer + tempBufferPos, c);
+      tempBufferPos += len;
+      MOZ_ASSERT(len <= ENCODE_MAX_LEN, "potential buffer overflow");
+    }
+
+    // Flush the temp buffer if it doesnt't have room for another encoded char.
+    if (tempBufferPos >= mozilla::ArrayLength(tempBuffer) - ENCODE_MAX_LEN) {
+      NS_ASSERTION(writing, "should be writing");
+      if (!aResult.Append(tempBuffer, tempBufferPos, mozilla::fallible)) {
+        return NS_ERROR_OUT_OF_MEMORY;
+      }
+      tempBufferPos = 0;
+    }
+
+    previousIsNonASCII = (c > 0x7f);
+  }
+  if (writing) {
+    if (!aResult.Append(tempBuffer, tempBufferPos, mozilla::fallible)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+  }
+  aDidAppend = writing;
+  return NS_OK;
+}
+
+bool NS_EscapeURL(const char* aPart, int32_t aPartLen, uint32_t aFlags,
+                  nsACString& aResult) {
+  size_t partLen;
+  if (aPartLen < 0) {
+    partLen = strlen(aPart);
+  } else {
+    partLen = aPartLen;
+  }
+
+  return NS_EscapeURLSpan(mozilla::Span(aPart, partLen), aFlags, aResult);
+}
+
+bool NS_EscapeURLSpan(mozilla::Span<const char> aStr, uint32_t aFlags,
+                      nsACString& aResult) {
+  bool appended = false;
+  nsresult rv = T_EscapeURL(aStr.Elements(), aStr.Length(), aFlags, nullptr,
+                            aResult, appended);
+  if (NS_FAILED(rv)) {
+    ::NS_ABORT_OOM(aResult.Length() * sizeof(nsACString::char_type));
+  }
+
+  return appended;
+}
+
+nsresult NS_EscapeURL(const nsACString& aStr, uint32_t aFlags,
+                      nsACString& aResult, const mozilla::fallible_t&) {
+  bool appended = false;
+  nsresult rv = T_EscapeURL(aStr.Data(), aStr.Length(), aFlags, nullptr,
+                            aResult, appended);
+  if (NS_FAILED(rv)) {
+    aResult.Truncate();
+    return rv;
+  }
+
+  if (!appended) {
+    aResult = aStr;
+  }
+
+  return rv;
+}
+
+nsresult NS_EscapeAndFilterURL(const nsACString& aStr, uint32_t aFlags,
+                               const ASCIIMaskArray* aFilterMask,
+                               nsACString& aResult,
+                               const mozilla::fallible_t&) {
+  bool appended = false;
+  nsresult rv = T_EscapeURL(aStr.Data(), aStr.Length(), aFlags, aFilterMask,
+                            aResult, appended);
+  if (NS_FAILED(rv)) {
+    aResult.Truncate();
+    return rv;
+  }
+
+  if (!appended) {
+    if (!aResult.Assign(aStr, mozilla::fallible)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+  }
+
+  return rv;
+}
+
+const nsAString& NS_EscapeURL(const nsAString& aStr, uint32_t aFlags,
+                              nsAString& aResult) {
+  bool result = false;
+  nsresult rv = T_EscapeURL<nsAString>(aStr.Data(), aStr.Length(), aFlags,
+                                       nullptr, aResult, result);
+
+  if (NS_FAILED(rv)) {
+    ::NS_ABORT_OOM(aResult.Length() * sizeof(nsAString::char_type));
+  }
+
+  if (result) {
+    return aResult;
+  }
+  return aStr;
+}
+
+// Starting at aStr[aStart] find the first index in aStr that matches any
+// character that is forbidden by aFunction. Return false if not found.
+static bool FindFirstMatchFrom(const nsString& aStr, size_t aStart,
+                               const std::function<bool(char16_t)>& aFunction,
+                               size_t* aIndex) {
+  for (size_t j = aStart, l = aStr.Length(); j < l; ++j) {
+    if (aFunction(aStr[j])) {
+      *aIndex = j;
+      return true;
+    }
+  }
+  return false;
+}
+
+const nsAString& NS_EscapeURL(const nsString& aStr,
+                              const std::function<bool(char16_t)>& aFunction,
+                              nsAString& aResult) {
+  bool didEscape = false;
+  for (size_t i = 0, strLen = aStr.Length(); i < strLen;) {
+    size_t j;
+    if (MOZ_UNLIKELY(FindFirstMatchFrom(aStr, i, aFunction, &j))) {
+      if (i == 0) {
+        didEscape = true;
+        aResult.Truncate();
+        aResult.SetCapacity(aStr.Length());
+      }
+      if (j != i) {
+        // The substring from 'i' up to 'j' that needs no escaping.
+        aResult.Append(nsDependentSubstring(aStr, i, j - i));
+      }
+      char16_t buffer[ENCODE_MAX_LEN];
+      uint32_t bufferLen = ::AppendPercentHex(buffer, aStr[j]);
+      MOZ_ASSERT(bufferLen <= ENCODE_MAX_LEN, "buffer overflow");
+      aResult.Append(buffer, bufferLen);
+      i = j + 1;
+    } else {
+      if (MOZ_UNLIKELY(didEscape)) {
+        // The tail of the string that needs no escaping.
+        aResult.Append(nsDependentSubstring(aStr, i, strLen - i));
+      }
+      break;
+    }
+  }
+  if (MOZ_UNLIKELY(didEscape)) {
+    return aResult;
+  }
+  return aStr;
+}
+
+bool NS_UnescapeURL(const char* aStr, int32_t aLen, uint32_t aFlags,
+                    nsACString& aResult) {
+  bool didAppend = false;
+  nsresult rv =
+      NS_UnescapeURL(aStr, aLen, aFlags, aResult, didAppend, mozilla::fallible);
+  if (rv == NS_ERROR_OUT_OF_MEMORY) {
+    ::NS_ABORT_OOM(aLen * sizeof(nsACString::char_type));
+  }
+
+  return didAppend;
+}
+
+nsresult NS_UnescapeURL(const char* aStr, int32_t aLen, uint32_t aFlags,
+                        nsACString& aResult, bool& aDidAppend,
+                        const mozilla::fallible_t&) {
+  if (!aStr) {
+    MOZ_ASSERT_UNREACHABLE("null pointer");
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  MOZ_ASSERT(aResult.IsEmpty(),
+             "Passing a non-empty string as an out parameter!");
+
+  uint32_t len;
+  if (aLen < 0) {
+    size_t stringLength = strlen(aStr);
+    if (stringLength >= UINT32_MAX) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    len = stringLength;
+  } else {
+    len = aLen;
+  }
+
+  bool ignoreNonAscii = !!(aFlags & esc_OnlyASCII);
+  bool ignoreAscii = !!(aFlags & esc_OnlyNonASCII);
+  bool writing = !!(aFlags & esc_AlwaysCopy);
+  bool skipControl = !!(aFlags & esc_SkipControl);
+  bool skipInvalidHostChar = !!(aFlags & esc_Host);
+
+  unsigned char* destPtr;
+  uint32_t destPos;
+
+  if (writing) {
+    if (!aResult.SetLength(len, mozilla::fallible)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    destPos = 0;
+    destPtr = reinterpret_cast<unsigned char*>(aResult.BeginWriting());
+  }
+
+  const char* last = aStr;
+  const char* end = aStr + len;
+
+  for (const char* p = aStr; p < end; ++p) {
+    if (*p == HEX_ESCAPE && p + 2 < end) {
+      unsigned char c1 = *((unsigned char*)p + 1);
+      unsigned char c2 = *((unsigned char*)p + 2);
+      unsigned char u = (UNHEX(c1) << 4) + UNHEX(c2);
+      if (mozilla::IsAsciiHexDigit(c1) && mozilla::IsAsciiHexDigit(c2) &&
+          (!skipInvalidHostChar || dontNeedEscape(u, aFlags) || c1 >= '8') &&
+          ((c1 < '8' && !ignoreAscii) || (c1 >= '8' && !ignoreNonAscii)) &&
+          !(skipControl &&
+            (c1 < '2' || (c1 == '7' && (c2 == 'f' || c2 == 'F'))))) {
+        if (MOZ_UNLIKELY(!writing)) {
+          writing = true;
+          if (!aResult.SetLength(len, mozilla::fallible)) {
+            return NS_ERROR_OUT_OF_MEMORY;
+          }
+          destPos = 0;
+          destPtr = reinterpret_cast<unsigned char*>(aResult.BeginWriting());
+        }
+        if (p > last) {
+          auto toCopy = p - last;
+          memcpy(destPtr + destPos, last, toCopy);
+          destPos += toCopy;
+          MOZ_ASSERT(destPos <= len);
+          last = p;
+        }
+        destPtr[destPos] = u;
+        destPos += 1;
+        MOZ_ASSERT(destPos <= len);
+        p += 2;
+        last += 3;
+      }
+    }
+  }
+  if (writing && last < end) {
+    auto toCopy = end - last;
+    memcpy(destPtr + destPos, last, toCopy);
+    destPos += toCopy;
+    MOZ_ASSERT(destPos <= len);
+  }
+
+  if (writing) {
+    aResult.Truncate(destPos);
+  }
+
+  aDidAppend = writing;
+  return NS_OK;
+}
diff --git a/xpcom/io/nsEscape.h b/xpcom/io/nsEscape.h
new file mode 100644
index 0000000000..0e86fe8487
--- /dev/null
+++ b/xpcom/io/nsEscape.h
@@ -0,0 +1,243 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*	First checked in on 98/12/03 by John R. McMullen, derived from
+ * net.h/mkparse.c. */
+
+#ifndef _ESCAPE_H_
+#define _ESCAPE_H_
+
+#include "nscore.h"
+#include "nsError.h"
+#include "nsString.h"
+#include <functional>
+
+/**
+ * Valid mask values for nsEscape
+ * Note: these values are copied in nsINetUtil.idl. Any changes should be kept
+ * in sync.
+ */
+typedef enum {
+  url_All = 0,  // %-escape every byte unconditionally
+  url_XAlphas =
+      1u << 0,  // Normal escape - leave alphas intact, escape the rest
+  url_XPAlphas =
+      1u
+      << 1,  // As url_XAlphas, but convert spaces (0x20) to '+' and plus to %2B
+  url_Path = 1u << 2,     // As url_XAlphas, but don't escape slash ('/')
+  url_NSURLRef = 1u << 3  // Extra URL ref encoding required for Apple's
+                          // NSURL compatibility
+} nsEscapeMask;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Escape the given string according to mask
+ * @param aSstr The string to escape
+ * @param aLength The length of the string to escape
+ * @param aOutputLen A pointer that will be used to store the length of the
+ *        output string, if not null
+ * @param aMask How to escape the string
+ * @return A newly allocated escaped string that must be free'd with
+ *         nsCRT::free, or null on failure
+ * @note: Please, don't use this function. Use NS_Escape instead!
+ */
+char* nsEscape(const char* aStr, size_t aLength, size_t* aOutputLen,
+               nsEscapeMask aMask);
+
+/**
+ * Decodes '%'-escaped hex codes into character values, modifies the parameter,
+ * returns the same buffer
+ */
+char* nsUnescape(char* aStr);
+
+/**
+ * Decodes '%'-escaped hex codes into character values, modifies the parameter
+ * buffer, returns the length of the result (result may contain \0's).
+ */
+int32_t nsUnescapeCount(char* aStr);
+
+#ifdef __cplusplus
+}
+#endif
+
+/**
+ * Infallibly append aSrc to aDst, escaping chars that are problematic for HTML
+ * display.
+ */
+void nsAppendEscapedHTML(const nsACString& aSrc, nsACString& aDst);
+
+/**
+ * NS_EscapeURL/NS_UnescapeURL constants for |flags| parameter:
+ *
+ * Note: These values are copied to nsINetUtil.idl
+ *       Any changes should be kept in sync
+ */
+enum EscapeMask {
+  /** url components **/
+  esc_Scheme = 1u << 0,
+  esc_Username = 1u << 1,
+  esc_Password = 1u << 2,
+  esc_Host = 1u << 3,
+  esc_Directory = 1u << 4,
+  esc_FileBaseName = 1u << 5,
+  esc_FileExtension = 1u << 6,
+  esc_FilePath = esc_Directory | esc_FileBaseName | esc_FileExtension,
+  esc_Param = 1u << 7,
+  esc_Query = 1u << 8,
+  esc_Ref = 1u << 9,
+  /** special flags **/
+  esc_Minimal = esc_Scheme | esc_Username | esc_Password | esc_Host |
+                esc_FilePath | esc_Param | esc_Query | esc_Ref,
+  esc_Forced = 1u << 10,    /* forces escaping of existing escape sequences */
+  esc_OnlyASCII = 1u << 11, /* causes non-ascii octets to be skipped */
+  esc_OnlyNonASCII =
+      1u << 12, /* causes _graphic_ ascii octets (0x20-0x7E)
+                 * to be skipped when escaping. causes all
+                 * ascii octets (<= 0x7F) to be skipped when unescaping */
+  esc_AlwaysCopy =
+      1u << 13, /* copy input to result buf even if escaping is unnecessary */
+  esc_Colon = 1u << 14,       /* forces escape of colon */
+  esc_SkipControl = 1u << 15, /* skips C0 and DEL from unescaping */
+  esc_Spaces = 1u << 16,      /* forces escape of spaces */
+  esc_ExtHandler = 1u << 17   /* For escaping external protocol handler urls.
+                               * Escapes everything except:
+                               * a-z, 0-9 and !#$&'()*+,-./:;=?@[]_~ */
+};
+
+/**
+ * NS_EscapeURL
+ *
+ * Escapes invalid char's in an URL segment.  Has no side-effect if the URL
+ * segment is already escaped, unless aFlags has the esc_Forced bit in which
+ * case % will also be escaped.  Iff some part of aStr is escaped is the
+ * final result appended to aResult.  You can also request that aStr is
+ * always appended to aResult with esc_AlwaysCopy.
+ *
+ * @param aStr     url segment string
+ * @param aLen     url segment string length (-1 if unknown)
+ * @param aFlags   url segment type flag (see EscapeMask above)
+ * @param aResult  result buffer, untouched if aStr is already escaped unless
+ *                 aFlags has esc_AlwaysCopy
+ *
+ * @return true if aResult was written to (i.e. at least one character was
+ *              escaped or esc_AlwaysCopy was requested), false otherwise.
+ */
+bool NS_EscapeURL(const char* aStr, int32_t aLen, uint32_t aFlags,
+                  nsACString& aResult);
+
+bool NS_EscapeURLSpan(mozilla::Span<const char> aStr, uint32_t aFlags,
+                      nsACString& aResult);
+
+/**
+ * Expands URL escape sequences... beware embedded null bytes!
+ *
+ * @param aStr     url string to unescape
+ * @param aLen     length of aStr
+ * @param aFlags   only esc_OnlyNonASCII, esc_SkipControl and esc_AlwaysCopy
+ *                 are recognized
+ * @param aResult  result buffer, untouched if aStr is already unescaped unless
+ *                 aFlags has esc_AlwaysCopy
+ *
+ * @return true if aResult was written to (i.e. at least one character was
+ *              unescaped or esc_AlwaysCopy was requested), false otherwise.
+ */
+bool NS_UnescapeURL(const char* aStr, int32_t aLen, uint32_t aFlags,
+                    nsACString& aResult);
+
+/**
+ * Fallible version of |NS_UnescapeURL|. See above for details.
+ *
+ * @param aAppended Out param: true if aResult was written to (i.e. at least
+ *                  one character was unescaped or esc_AlwaysCopy was
+ *                  requested), false otherwise.
+ */
+nsresult NS_UnescapeURL(const char* aStr, int32_t aLen, uint32_t aFlags,
+                        nsACString& aResult, bool& aAppended,
+                        const mozilla::fallible_t&);
+
+/** returns resultant string length **/
+inline int32_t NS_UnescapeURL(char* aStr) { return nsUnescapeCount(aStr); }
+
+/**
+ * String friendly versions...
+ */
+inline const nsACString& NS_EscapeURL(const nsACString& aStr, uint32_t aFlags,
+                                      nsACString& aResult) {
+  if (NS_EscapeURLSpan(aStr, aFlags, aResult)) {
+    return aResult;
+  }
+  return aStr;
+}
+
+/**
+ * Fallible version of NS_EscapeURL. On success aResult will point to either
+ * the original string or an escaped copy.
+ */
+nsresult NS_EscapeURL(const nsACString& aStr, uint32_t aFlags,
+                      nsACString& aResult, const mozilla::fallible_t&);
+
+// Forward declaration for nsASCIIMask.h
+typedef std::array<bool, 128> ASCIIMaskArray;
+
+/**
+ * The same as NS_EscapeURL, except it also filters out characters that match
+ * aFilterMask.
+ */
+nsresult NS_EscapeAndFilterURL(const nsACString& aStr, uint32_t aFlags,
+                               const ASCIIMaskArray* aFilterMask,
+                               nsACString& aResult, const mozilla::fallible_t&);
+
+inline const nsACString& NS_UnescapeURL(const nsACString& aStr, uint32_t aFlags,
+                                        nsACString& aResult) {
+  if (NS_UnescapeURL(aStr.Data(), aStr.Length(), aFlags, aResult)) {
+    return aResult;
+  }
+  return aStr;
+}
+
+const nsAString& NS_EscapeURL(const nsAString& aStr, uint32_t aFlags,
+                              nsAString& aResult);
+
+/**
+ * Percent-escapes all characters in aStr that occurs in aForbidden.
+ * @param aStr the input URL string
+ * @param aFunction returns true for characters that should be escaped
+ * @param aResult the result if some characters were escaped
+ * @return aResult if some characters were escaped, or aStr otherwise (aResult
+ *         is unmodified in that case)
+ */
+const nsAString& NS_EscapeURL(const nsString& aStr,
+                              const std::function<bool(char16_t)>& aFunction,
+                              nsAString& aResult);
+
+/**
+ * CString version of nsEscape. Returns true on success, false
+ * on out of memory. To reverse this function, use NS_UnescapeURL.
+ */
+inline bool NS_Escape(const nsACString& aOriginal, nsACString& aEscaped,
+                      nsEscapeMask aMask) {
+  size_t escLen = 0;
+  char* esc =
+      nsEscape(aOriginal.BeginReading(), aOriginal.Length(), &escLen, aMask);
+  if (!esc) {
+    return false;
+  }
+  aEscaped.Adopt(esc, escLen);
+  return true;
+}
+
+/**
+ * Inline unescape of mutable string object.
+ */
+inline nsACString& NS_UnescapeURL(nsACString& aStr) {
+  aStr.SetLength(nsUnescapeCount(aStr.BeginWriting()));
+  return aStr;
+}
+
+#endif  //  _ESCAPE_H_
diff --git a/xpcom/io/nsIAsyncInputStream.idl b/xpcom/io/nsIAsyncInputStream.idl
new file mode 100644
index 0000000000..8dbe442663
--- /dev/null
+++ b/xpcom/io/nsIAsyncInputStream.idl
@@ -0,0 +1,105 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIInputStream.idl"
+
+interface nsIInputStreamCallback;
+interface nsIEventTarget;
+
+/**
+ * If an input stream is non-blocking, it may return NS_BASE_STREAM_WOULD_BLOCK
+ * when read.  The caller must then wait for the stream to have some data to
+ * read.  If the stream implements nsIAsyncInputStream, then the caller can use
+ * this interface to request an asynchronous notification when the stream
+ * becomes readable or closed (via the AsyncWait method).
+ *
+ * While this interface is almost exclusively used with non-blocking streams, it
+ * is not necessary that nsIInputStream::isNonBlocking return true.  Nor is it
+ * necessary that a non-blocking nsIInputStream implementation also implement
+ * nsIAsyncInputStream.
+ */
+[scriptable, builtinclass, uuid(a5f255ab-4801-4161-8816-277ac92f6ad1)]
+interface nsIAsyncInputStream : nsIInputStream
+{
+    /**
+     * This method closes the stream and sets its internal status.  If the
+     * stream is already closed, then this method is ignored.  Once the stream
+     * is closed, the stream's status cannot be changed.  Any successful status
+     * code passed to this method is treated as NS_BASE_STREAM_CLOSED, which
+     * has an effect equivalent to nsIInputStream::close.
+     *
+     * NOTE: this method exists in part to support pipes, which have both an
+     * input end and an output end.  If the input end of a pipe is closed, then
+     * writes to the output end of the pipe will fail.  The error code returned
+     * when an attempt is made to write to a "broken" pipe corresponds to the
+     * status code passed in when the input end of the pipe was closed, which
+     * greatly simplifies working with pipes in some cases.
+     *
+     * @param aStatus
+     *        The error that will be reported if this stream is accessed after
+     *        it has been closed.
+     */
+    void closeWithStatus(in nsresult aStatus);
+
+    /**
+     * Asynchronously wait for the stream to be readable or closed.  The
+     * notification is one-shot, meaning that each asyncWait call will result
+     * in exactly one notification callback.  After the OnInputStreamReady event
+     * is dispatched, the stream releases its reference to the
+     * nsIInputStreamCallback object.  It is safe to call asyncWait again from the
+     * notification handler.
+     *
+     * This method may be called at any time (even if read has not been called).
+     * In other words, this method may be called when the stream already has
+     * data to read.  It may also be called when the stream is closed and will NOT
+     * result in an error return, e.g., NS_BASE_STREAM_CLOSED.  If the stream is
+     * already readable or closed when AsyncWait is called, then the
+     * OnInputStreamReady event will be dispatched immediately.  Otherwise, the
+     * event will be dispatched when the stream becomes readable or closed.
+     *
+     * @param aCallback
+     *        This object is notified when the stream becomes ready.  This
+     *        parameter may be null to clear an existing callback.
+     * @param aFlags
+     *        This parameter specifies optional flags passed in to configure
+     *        the behavior of this method.  Pass zero to specify no flags.
+     * @param aRequestedCount
+     *        Wait until at least this many bytes can be read.  This is only
+     *        a suggestion to the underlying stream; it may be ignored.  The
+     *        caller may pass zero to indicate no preference.
+     * @param aEventTarget
+     *        Specify NULL to receive notification on ANY thread (possibly even
+     *        recursively on the calling thread -- i.e., synchronously), or
+     *        specify that the notification be delivered to a specific event
+     *        target.
+     */
+    void asyncWait(in nsIInputStreamCallback aCallback,
+                   in unsigned long aFlags,
+                   in unsigned long aRequestedCount,
+                   in nsIEventTarget aEventTarget);
+
+    /**
+     * If passed to asyncWait, this flag overrides the default behavior,
+     * causing the OnInputStreamReady notification to be suppressed until the
+     * stream becomes closed (either as a result of closeWithStatus/close being
+     * called on the stream or possibly due to some error in the underlying
+     * stream).
+     */
+    const unsigned long WAIT_CLOSURE_ONLY = (1<<0);
+};
+
+/**
+ * This is a companion interface for nsIAsyncInputStream::asyncWait.
+ */
+[function, scriptable, uuid(d1f28e94-3a6e-4050-a5f5-2e81b1fc2a43)]
+interface nsIInputStreamCallback : nsISupports
+{
+    /**
+     * Called to indicate that the stream is either readable or closed.
+     *
+     * @param aStream
+     *        The stream whose asyncWait method was called.
+     */
+    void onInputStreamReady(in nsIAsyncInputStream aStream);
+};
diff --git a/xpcom/io/nsIAsyncOutputStream.idl b/xpcom/io/nsIAsyncOutputStream.idl
new file mode 100644
index 0000000000..88f9d107cf
--- /dev/null
+++ b/xpcom/io/nsIAsyncOutputStream.idl
@@ -0,0 +1,104 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIOutputStream.idl"
+
+interface nsIOutputStreamCallback;
+interface nsIEventTarget;
+
+/**
+ * If an output stream is non-blocking, it may return NS_BASE_STREAM_WOULD_BLOCK
+ * when written to.  The caller must then wait for the stream to become
+ * writable.  If the stream implements nsIAsyncOutputStream, then the caller can
+ * use this interface to request an asynchronous notification when the stream
+ * becomes writable or closed (via the AsyncWait method).
+ *
+ * While this interface is almost exclusively used with non-blocking streams, it
+ * is not necessary that nsIOutputStream::isNonBlocking return true.  Nor is it
+ * necessary that a non-blocking nsIOutputStream implementation also implement
+ * nsIAsyncOutputStream.
+ */
+[scriptable, builtinclass, uuid(beb632d3-d77a-4e90-9134-f9ece69e8200)]
+interface nsIAsyncOutputStream : nsIOutputStream
+{
+    /**
+     * This method closes the stream and sets its internal status.  If the
+     * stream is already closed, then this method is ignored.  Once the stream
+     * is closed, the stream's status cannot be changed.  Any successful status
+     * code passed to this method is treated as NS_BASE_STREAM_CLOSED, which
+     * is equivalent to nsIInputStream::close.
+     *
+     * NOTE: this method exists in part to support pipes, which have both an
+     * input end and an output end.  If the output end of a pipe is closed, then
+     * reads from the input end of the pipe will fail.  The error code returned
+     * when an attempt is made to read from a "closed" pipe corresponds to the
+     * status code passed in when the output end of the pipe is closed, which
+     * greatly simplifies working with pipes in some cases.
+     *
+     * @param aStatus
+     *        The error that will be reported if this stream is accessed after
+     *        it has been closed.
+     */
+    void closeWithStatus(in nsresult reason);
+
+    /**
+     * Asynchronously wait for the stream to be writable or closed.  The
+     * notification is one-shot, meaning that each asyncWait call will result
+     * in exactly one notification callback.  After the OnOutputStreamReady event
+     * is dispatched, the stream releases its reference to the
+     * nsIOutputStreamCallback object.  It is safe to call asyncWait again from the
+     * notification handler.
+     *
+     * This method may be called at any time (even if write has not been called).
+     * In other words, this method may be called when the stream already has
+     * room for more data.  It may also be called when the stream is closed.  If
+     * the stream is already writable or closed when AsyncWait is called, then the
+     * OnOutputStreamReady event will be dispatched immediately.  Otherwise, the
+     * event will be dispatched when the stream becomes writable or closed.
+     *
+     * @param aCallback
+     *        This object is notified when the stream becomes ready.  This
+     *        parameter may be null to clear an existing callback.
+     * @param aFlags
+     *        This parameter specifies optional flags passed in to configure
+     *        the behavior of this method.  Pass zero to specify no flags.
+     * @param aRequestedCount
+     *        Wait until at least this many bytes can be written.  This is only
+     *        a suggestion to the underlying stream; it may be ignored.  The
+     *        caller may pass zero to indicate no preference.
+     * @param aEventTarget
+     *        Specify NULL to receive notification on ANY thread (possibly even
+     *        recursively on the calling thread -- i.e., synchronously), or
+     *        specify that the notification be delivered to a specific event
+     *        target.
+     */
+    void asyncWait(in nsIOutputStreamCallback aCallback,
+                   in unsigned long aFlags,
+                   in unsigned long aRequestedCount,
+                   in nsIEventTarget aEventTarget);
+
+    /**
+     * If passed to asyncWait, this flag overrides the default behavior,
+     * causing the OnOutputStreamReady notification to be suppressed until the
+     * stream becomes closed (either as a result of closeWithStatus/close being
+     * called on the stream or possibly due to some error in the underlying
+     * stream).
+     */
+    const unsigned long WAIT_CLOSURE_ONLY = (1<<0);
+};
+
+/**
+ * This is a companion interface for nsIAsyncOutputStream::asyncWait.
+ */
+[function, scriptable, uuid(40dbcdff-9053-42c5-a57c-3ec910d0f148)]
+interface nsIOutputStreamCallback : nsISupports
+{
+    /**
+     * Called to indicate that the stream is either writable or closed.
+     *
+     * @param aStream
+     *        The stream whose asyncWait method was called.
+     */
+    void onOutputStreamReady(in nsIAsyncOutputStream aStream);
+};
diff --git a/xpcom/io/nsIBinaryInputStream.idl b/xpcom/io/nsIBinaryInputStream.idl
new file mode 100644
index 0000000000..698dbae4f8
--- /dev/null
+++ b/xpcom/io/nsIBinaryInputStream.idl
@@ -0,0 +1,118 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIInputStream.idl"
+
+/**
+ * This interface allows consumption of primitive data types from a "binary
+ * stream" containing untagged, big-endian binary data, i.e. as produced by an
+ * implementation of nsIBinaryOutputStream.  This might be used, for example,
+ * to implement network protocols or to read from architecture-neutral disk
+ * files, i.e. ones that can be read and written by both big-endian and
+ * little-endian platforms.
+ *
+ * @See nsIBinaryOutputStream
+ */
+
+[scriptable, builtinclass, uuid(899b826b-2eb3-469c-8b31-4c29f5d341a6)]
+interface nsIBinaryInputStream : nsIInputStream {
+    void setInputStream(in nsIInputStream aInputStream);
+
+    /**
+     * Read 8-bits from the stream.
+     *
+     * @return that byte to be treated as a boolean.
+     */
+    boolean readBoolean();
+
+    uint8_t read8();
+    uint16_t read16();
+    uint32_t read32();
+    uint64_t read64();
+
+    float readFloat();
+    double readDouble();
+
+    /**
+     * Read an 8-bit pascal style string from the stream.
+     * 32-bit length field, followed by length 8-bit chars.
+     */
+    ACString readCString();
+
+    /**
+     * Read an 16-bit pascal style string from the stream.
+     * 32-bit length field, followed by length PRUnichars.
+     */
+    AString readString();
+
+    /**
+     * Read an opaque byte array from the stream.
+     *
+     * @param aLength the number of bytes that must be read.
+     *
+     * @throws NS_ERROR_FAILURE if it can't read aLength bytes
+     */
+    void readBytes(in uint32_t aLength,
+                   [size_is(aLength), retval] out string aString);
+
+    /**
+     * Read an opaque byte array from the stream, storing the results
+     * as an array of PRUint8s.
+     *
+     * @param aLength the number of bytes that must be read.
+     *
+     * @throws NS_ERROR_FAILURE if it can't read aLength bytes
+     */
+    Array<uint8_t> readByteArray(in uint32_t aLength);
+
+    /**
+     * Read opaque bytes from the stream, storing the results in an ArrayBuffer.
+     *
+     * @param aLength the number of bytes that must be read
+     * @param aArrayBuffer the arraybuffer in which to store the results
+     * Note: passing view.buffer, where view is an ArrayBufferView of an
+     *       ArrayBuffer, is not valid unless view.byteOffset == 0.
+     *
+     * @return The number of bytes actually read into aArrayBuffer.
+     */
+    [implicit_jscontext]
+    uint64_t readArrayBuffer(in uint64_t aLength, in jsval aArrayBuffer);
+};
+
+%{C++
+
+#ifdef MOZILLA_INTERNAL_API
+#include "nsString.h"
+
+inline nsresult
+NS_ReadOptionalCString(nsIBinaryInputStream* aStream, nsACString& aResult)
+{
+    bool nonnull;
+    nsresult rv = aStream->ReadBoolean(&nonnull);
+    if (NS_SUCCEEDED(rv)) {
+        if (nonnull)
+            rv = aStream->ReadCString(aResult);
+        else
+            aResult.Truncate();
+    }
+    return rv;
+}
+
+inline nsresult
+NS_ReadOptionalString(nsIBinaryInputStream* aStream, nsAString& aResult)
+{
+    bool nonnull;
+    nsresult rv = aStream->ReadBoolean(&nonnull);
+    if (NS_SUCCEEDED(rv)) {
+        if (nonnull)
+            rv = aStream->ReadString(aResult);
+        else
+            aResult.Truncate();
+    }
+    return rv;
+}
+#endif
+
+%}
diff --git a/xpcom/io/nsIBinaryOutputStream.idl b/xpcom/io/nsIBinaryOutputStream.idl
new file mode 100644
index 0000000000..caa96eb699
--- /dev/null
+++ b/xpcom/io/nsIBinaryOutputStream.idl
@@ -0,0 +1,103 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIOutputStream.idl"
+
+%{C++
+namespace mozilla {
+template<class ElementType, size_t Extent> class Span;
+}
+%}
+native Bytes(mozilla::Span<const uint8_t>);
+
+/**
+ * This interface allows writing of primitive data types (integers,
+ * floating-point values, booleans, etc.) to a stream in a binary, untagged,
+ * fixed-endianness format.  This might be used, for example, to implement
+ * network protocols or to produce architecture-neutral binary disk files,
+ * i.e. ones that can be read and written by both big-endian and little-endian
+ * platforms.  Output is written in big-endian order (high-order byte first),
+ * as this is traditional network order.
+ *
+ * @See nsIBinaryInputStream
+ */
+
+[scriptable, builtinclass, uuid(204ee610-8765-11d3-90cf-0040056a906e)]
+interface nsIBinaryOutputStream : nsIOutputStream {
+    void setOutputStream(in nsIOutputStream aOutputStream);
+
+    /**
+     * Write a boolean as an 8-bit char to the stream.
+     */
+    void writeBoolean(in boolean aBoolean);
+
+    void write8(in uint8_t aByte);
+    void write16(in uint16_t a16);
+    void write32(in uint32_t a32);
+    void write64(in uint64_t a64);
+
+    void writeFloat(in float aFloat);
+    void writeDouble(in double aDouble);
+
+    /**
+     * Write an 8-bit pascal style string to the stream.
+     * 32-bit length field, followed by length 8-bit chars.
+     */
+    void writeStringZ(in string aString);
+
+    /**
+     * Write a 16-bit pascal style string to the stream.
+     * 32-bit length field, followed by length PRUnichars.
+     */
+    void writeWStringZ(in wstring aString);
+
+    /**
+     * Write an 8-bit pascal style string (UTF8-encoded) to the stream.
+     * 32-bit length field, followed by length 8-bit chars.
+     */
+    void writeUtf8Z(in wstring aString);
+
+    /**
+     * Write an opaque byte array to the stream.
+     */
+    [binaryname(WriteBytesFromJS)]
+    void writeBytes([size_is(aLength)] in string aString,
+                    [optional] in uint32_t aLength);
+
+    /**
+     * Non-scriptable and saner-signature version of the same.
+     */
+    [noscript, nostdcall, binaryname(WriteBytes)]
+    void writeBytesNative(in Bytes aBytes);
+
+    /**
+     * Write an opaque byte array to the stream.
+     */
+    void writeByteArray(in Array<uint8_t> aBytes);
+};
+
+%{C++
+
+inline nsresult
+NS_WriteOptionalStringZ(nsIBinaryOutputStream* aStream, const char* aString)
+{
+    bool nonnull = (aString != nullptr);
+    nsresult rv = aStream->WriteBoolean(nonnull);
+    if (NS_SUCCEEDED(rv) && nonnull)
+        rv = aStream->WriteStringZ(aString);
+    return rv;
+}
+
+inline nsresult
+NS_WriteOptionalWStringZ(nsIBinaryOutputStream* aStream, const char16_t* aString)
+{
+    bool nonnull = (aString != nullptr);
+    nsresult rv = aStream->WriteBoolean(nonnull);
+    if (NS_SUCCEEDED(rv) && nonnull)
+        rv = aStream->WriteWStringZ(aString);
+    return rv;
+}
+
+%}
diff --git a/xpcom/io/nsICloneableInputStream.idl b/xpcom/io/nsICloneableInputStream.idl
new file mode 100644
index 0000000000..adefd0f428
--- /dev/null
+++ b/xpcom/io/nsICloneableInputStream.idl
@@ -0,0 +1,31 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIInputStream.idl"
+
+[scriptable, builtinclass, uuid(8149be1f-44d3-4f14-8b65-a57a5fbbeb97)]
+interface nsICloneableInputStream : nsISupports
+{
+  // Allow streams that implement the interface to determine if cloning
+  // possible at runtime.  For example, this allows wrappers to check if
+  // their base stream supports cloning.
+  [infallible] readonly attribute boolean cloneable;
+
+  // Produce a copy of the current stream in the most efficient way possible.
+  // In this case "copy" means that both the original and cloned streams
+  // should produce the same bytes for all future reads.  Bytes that have
+  // already been consumed from the original stream are not copied to the
+  // clone.  Operations on the two streams should be completely independent
+  // after the clone() occurs.
+  nsIInputStream clone();
+};
+
+// This interface implements cloneWithRange() because for some streams
+// (RemoteLazyInputStream only, so far) are more efficient to produce a sub
+// stream with range than doing clone + SlicedInputStream().
+[scriptable, builtinclass, uuid(ece853c3-aded-4cef-8f51-0d1493d60bd5)]
+interface nsICloneableInputStreamWithRange : nsICloneableInputStream
+{
+  nsIInputStream cloneWithRange(in uint64_t start, in uint64_t length);
+};
diff --git a/xpcom/io/nsIConverterInputStream.idl b/xpcom/io/nsIConverterInputStream.idl
new file mode 100644
index 0000000000..ad1f9bfbc4
--- /dev/null
+++ b/xpcom/io/nsIConverterInputStream.idl
@@ -0,0 +1,45 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIUnicharInputStream.idl"
+
+interface nsIInputStream;
+
+/**
+ * A unichar input stream that wraps an input stream.
+ * This allows reading unicode strings from a stream, automatically converting
+ * the bytes from a selected character encoding.
+ */
+[scriptable, uuid(FC66FFB6-5404-4908-A4A3-27F92FA0579D)]
+interface nsIConverterInputStream : nsIUnicharInputStream {
+    /**
+     * Default replacement char value, U+FFFD REPLACEMENT CHARACTER.
+     */
+    const char16_t DEFAULT_REPLACEMENT_CHARACTER = 0xFFFD;
+
+    /**
+     * Special replacement character value that requests errors to
+     * be treated as fatal.
+     */
+    const char16_t ERRORS_ARE_FATAL = 0;
+
+    /**
+     * Initialize this stream.
+     * @param aStream
+     *        The underlying stream to read from.
+     * @param aCharset
+     *        The character encoding to use for converting the bytes of the
+     *        stream. A null charset will be interpreted as UTF-8.
+     * @param aBufferSize
+     *        How many bytes to buffer.
+     * @param aReplacementChar
+     *        The character to replace unknown byte sequences in the stream
+     *        with. The standard replacement character is U+FFFD.
+     *        A value of 0x0000 will cause an exception to be thrown if unknown
+     *        byte sequences are encountered in the stream.
+     */
+    void init (in nsIInputStream aStream, in string aCharset,
+               in long aBufferSize, in char16_t aReplacementChar);
+};
diff --git a/xpcom/io/nsIConverterOutputStream.idl b/xpcom/io/nsIConverterOutputStream.idl
new file mode 100644
index 0000000000..41faa5332d
--- /dev/null
+++ b/xpcom/io/nsIConverterOutputStream.idl
@@ -0,0 +1,30 @@
+/* vim:set expandtab ts=4 sw=4 sts=4 cin: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIUnicharOutputStream.idl"
+
+interface nsIOutputStream;
+
+/**
+ * This interface allows writing strings to a stream, doing automatic
+ * character encoding conversion.
+ */
+[scriptable, builtinclass, uuid(4b71113a-cb0d-479f-8ed5-01daeba2e8d4)]
+interface nsIConverterOutputStream : nsIUnicharOutputStream
+{
+    /**
+     * Initialize this stream. Must be called before any other method on this
+     * interface, or you will crash. The output stream passed to this method
+     * must not be null, or you will crash.
+     *
+     * @param aOutStream
+     *        The underlying output stream to which the converted strings will
+     *        be written.
+     * @param aCharset
+     *        The character set to use for encoding the characters. A null
+     *        charset will be interpreted as UTF-8.
+     */
+    void init(in nsIOutputStream aOutStream, in string aCharset);
+};
diff --git a/xpcom/io/nsIDirectoryEnumerator.idl b/xpcom/io/nsIDirectoryEnumerator.idl
new file mode 100644
index 0000000000..e8abb81acd
--- /dev/null
+++ b/xpcom/io/nsIDirectoryEnumerator.idl
@@ -0,0 +1,34 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+#include "nsISimpleEnumerator.idl"
+
+interface nsIFile;
+
+/**
+ * This interface provides a means for enumerating the contents of a directory.
+ * It is similar to nsISimpleEnumerator except the retrieved entries are QI'ed
+ * to nsIFile, and there is a mechanism for closing the directory when the
+ * enumeration is complete.
+ */
+[scriptable, uuid(31f7f4ae-6916-4f2d-a81e-926a4e3022ee)]
+interface nsIDirectoryEnumerator : nsISimpleEnumerator
+{
+  /**
+   * Retrieves the next file in the sequence. The "nextFile" element is the
+   * first element upon the first call. This attribute is null if there is no
+   * next element.
+   */
+  readonly attribute nsIFile nextFile;
+
+  /**
+   * Closes the directory being enumerated, releasing the system resource.
+   * @throws NS_OK if the call succeeded and the directory was closed.
+   *         NS_ERROR_FAILURE if the directory close failed.
+   *         It is safe to call this function many times.
+   */
+  void close();
+};
diff --git a/xpcom/io/nsIDirectoryService.idl b/xpcom/io/nsIDirectoryService.idl
new file mode 100644
index 0000000000..99c4324782
--- /dev/null
+++ b/xpcom/io/nsIDirectoryService.idl
@@ -0,0 +1,101 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsIFile;
+interface nsISimpleEnumerator;
+
+/**
+ * nsIDirectoryServiceProvider
+ *
+ * Used by Directory Service to get file locations.
+ */
+
+[scriptable, uuid(bbf8cab0-d43a-11d3-8cc2-00609792278c)]
+interface nsIDirectoryServiceProvider: nsISupports
+{
+ /**
+  * getFile
+  *
+  * Directory Service calls this when it gets the first request for
+  * a prop or on every request if the prop is not persistent.
+  *
+  * @param prop         The symbolic name of the file.
+  * @param persistent   TRUE - The returned file will be cached by Directory
+  *                     Service. Subsequent requests for this prop will
+  *                     bypass the provider and use the cache.
+  *                     FALSE - The provider will be asked for this prop
+  *                     each time it is requested.
+  *
+  * @return             The file represented by the property.
+  *
+  */
+  nsIFile getFile(in string prop, out boolean persistent);
+};
+
+/**
+ * nsIDirectoryServiceProvider2
+ *
+ * An extension of nsIDirectoryServiceProvider which allows
+ * multiple files to be returned for the given key.
+ */
+
+[scriptable, uuid(2f977d4b-5485-11d4-87e2-0010a4e75ef2)]
+interface nsIDirectoryServiceProvider2: nsIDirectoryServiceProvider
+{
+ /**
+  * getFiles
+  *
+  * Directory Service calls this when it gets a request for
+  * a prop and the requested type is nsISimpleEnumerator.
+  *
+  * @param prop         The symbolic name of the file list.
+  *
+  * @return             An enumerator for a list of file locations.
+  *                     The elements in the enumeration are nsIFile
+  * @returnCode         NS_SUCCESS_AGGREGATE_RESULT if this result should be
+  *                     aggregated with other "lower" providers.
+  */
+  nsISimpleEnumerator getFiles(in string prop);
+};
+
+/**
+ * nsIDirectoryService
+ */
+
+[scriptable, uuid(57a66a60-d43a-11d3-8cc2-00609792278c)]
+interface nsIDirectoryService: nsISupports
+{
+ /**
+  * init
+  *
+  * Must be called. Used internally by XPCOM initialization.
+  *
+  */
+  void init();
+
+ /**
+  * registerProvider
+  *
+  * Register a provider with the service.
+  *
+  * @param prov            The service will keep a strong reference
+  *                        to this object. It will be released when
+  *                        the service is released.
+  *
+  */
+  void registerProvider(in nsIDirectoryServiceProvider prov);
+
+ /**
+  * unregisterProvider
+  *
+  * Unregister a provider with the service.
+  *
+  * @param prov
+  *
+  */
+  void unregisterProvider(in nsIDirectoryServiceProvider prov);
+};
diff --git a/xpcom/io/nsIFile.idl b/xpcom/io/nsIFile.idl
new file mode 100644
index 0000000000..535a7a88ee
--- /dev/null
+++ b/xpcom/io/nsIFile.idl
@@ -0,0 +1,597 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+#include "nsIDirectoryEnumerator.idl"
+
+%{C++
+struct PRFileDesc;
+struct PRLibrary;
+#include <stdio.h>
+#include "mozilla/Path.h"
+#include "nsCOMPtr.h"
+#include "nsStringFwd.h"
+namespace mozilla {
+using PathString = nsTString<filesystem::Path::value_type>;
+using PathSubstring = nsTSubstring<filesystem::Path::value_type>;
+} // namespace mozilla
+%}
+
+[ptr] native PRFileDescStar(PRFileDesc);
+[ptr] native PRLibraryStar(PRLibrary);
+[ptr] native FILE(FILE);
+native PathString(mozilla::PathString);
+
+/**
+ * An nsIFile is an abstract representation of a filename. It manages
+ * filename encoding issues, pathname component separators ('/' vs. '\\'
+ * vs. ':') and weird stuff like differing volumes with identical names, as
+ * on pre-Darwin Macintoshes.
+ *
+ * This file has long introduced itself to new hackers with this opening
+ * paragraph:
+ *
+ *    This is the only correct cross-platform way to specify a file.
+ *    Strings are not such a way. If you grew up on windows or unix, you
+ *    may think they are.  Welcome to reality.
+ *
+ * While taking the pose struck here to heart would be uncalled for, one
+ * may safely conclude that writing cross-platform code is an embittering
+ * experience.
+ *
+ * All methods with string parameters have two forms.  The preferred
+ * form operates on UCS-2 encoded characters strings.  An alternate
+ * form operates on characters strings encoded in the "native" charset.
+ *
+ * A string containing characters encoded in the native charset cannot
+ * be safely passed to javascript via xpconnect.  Therefore, the "native
+ * methods" are not scriptable.
+ */
+[scriptable, main_process_scriptable_only, uuid(2fa6884a-ae65-412a-9d4c-ce6e34544ba1), builtinclass]
+interface nsIFile : nsISupports
+{
+    /**
+     *  Create Types
+     *
+     *  NORMAL_FILE_TYPE - A normal file.
+     *  DIRECTORY_TYPE   - A directory/folder.
+     */
+    const unsigned long NORMAL_FILE_TYPE = 0;
+    const unsigned long DIRECTORY_TYPE   = 1;
+
+    /**
+     *  append[Native]
+     *
+     *  This function is used for constructing a descendent of the
+     *  current nsIFile.
+     *
+     *   @param node
+     *       A string which is intended to be a child node of the nsIFile.
+     *       For security reasons, this cannot contain .. and cannot start with
+     *       a directory separator. For the |appendNative| method, the node must
+     *       be in the native filesystem charset.
+     */
+    void append(in AString node);
+    [noscript] void appendNative(in ACString node);
+
+    /**
+     *  Normalize the pathName (e.g. removing .. and . components on Unix).
+     */
+    void normalize();
+
+    /**
+     *  create
+     *
+     *  This function will create a new file or directory in the
+     *  file system. Any nodes that have not been created or
+     *  resolved, will be.  If the file or directory already
+     *  exists create() will return NS_ERROR_FILE_ALREADY_EXISTS.
+     *
+     *   @param type
+     *       This specifies the type of file system object
+     *       to be made.  The only two types at this time
+     *       are file and directory which are defined above.
+     *       If the type is unrecongnized, we will return an
+     *       error (NS_ERROR_FILE_UNKNOWN_TYPE).
+     *
+     *   @param permissions
+     *       The unix style octal permissions.  This may
+     *       be ignored on systems that do not need to do
+     *       permissions.
+     *
+     *   @param skipAncestors
+     *       Optional; if set to true, we'll skip creating
+     *       ancestor directories (and return an error instead).
+     */
+    [must_use] void create(in unsigned long type, in unsigned long permissions,
+                           [optional,default(false)] in bool skipAncestors);
+
+    /**
+     *  Accessor to the leaf name of the file itself.
+     *  For the |nativeLeafName| method, the nativeLeafName must
+     *  be in the native filesystem charset.
+     */
+    attribute AString leafName;
+    [noscript] attribute ACString nativeLeafName;
+
+    /**
+     * The leaf name as displayed in OS-provided file pickers and similar UI.
+     * On Windows and macOS, 'real' leaf names of some directories can be
+     * in English, but the OS will show a different, translated name to users
+     * using a different locale. So folders like "Downloads", "Desktop" and
+     * "Documents" might not normally appear to users with that (English) name,
+     * but with an OS-localized translation. This API will return such a
+     * translation if it exists, or the leafName if it doesn't.
+     * On Linux, this will always be the same as `leafName`.
+     */
+    readonly attribute AString displayName;
+
+    /**
+     *  copyTo[Native]
+     *
+     *  This will copy this file to the specified newParentDir.
+     *  If a newName is specified, the file will be renamed.
+     *  If 'this' is not created we will return an error
+     *  (NS_ERROR_FILE_NOT_FOUND).
+     *
+     *  copyTo may fail if the file already exists in the destination
+     *  directory.
+     *
+     *  copyTo will NOT resolve aliases/shortcuts during the copy.
+     *
+     *   @param newParentDir
+     *       This param is the destination directory. If the
+     *       newParentDir is null, copyTo() will use the parent
+     *       directory of this file. If the newParentDir is not
+     *       empty and is not a directory, an error will be
+     *       returned (NS_ERROR_FILE_DESTINATION_NOT_DIR). For the
+     *       |CopyToNative| method, the newName must be in the
+     *       native filesystem charset.
+     *
+     *   @param newName
+     *       This param allows you to specify a new name for
+     *       the file to be copied. This param may be empty, in
+     *       which case the current leaf name will be used.
+     */
+    void copyTo(in nsIFile newParentDir, in AString newName);
+    [noscript] void CopyToNative(in nsIFile newParentDir, in ACString newName);
+
+    /**
+     *  copyToFollowingLinks[Native]
+     *
+     *  This function is identical to copyTo with the exception that,
+     *  as the name implies, it follows symbolic links.  The XP_UNIX
+     *  implementation always follow symbolic links when copying.  For
+     *  the |CopyToFollowingLinks| method, the newName must be in the
+     *  native filesystem charset.
+     */
+    void copyToFollowingLinks(in nsIFile newParentDir, in AString newName);
+    [noscript] void copyToFollowingLinksNative(in nsIFile newParentDir, in ACString newName);
+
+    /**
+     *  moveTo[Native]
+     *
+     *  A method to move this file or directory to newParentDir.
+     *  If a newName is specified, the file or directory will be renamed.
+     *  If 'this' is not created we will return an error
+     *  (NS_ERROR_FILE_NOT_FOUND).
+     *  If 'this' is a file, and the destination file already exists, moveTo
+     *  will replace the old file.
+     *  This object is updated to refer to the new file.
+     *
+     *  moveTo will NOT resolve aliases/shortcuts during the copy.
+     *  moveTo will do the right thing and allow copies across volumes.
+     *  moveTo will return an error (NS_ERROR_FILE_DIR_NOT_EMPTY) if 'this' is
+     *  a directory and the destination directory is not empty.
+     *  moveTo will return an error (NS_ERROR_FILE_ACCESS_DENIED) if 'this' is
+     *  a directory and the destination directory is not writable.
+     *
+     *   @param newParentDir
+     *       This param is the destination directory. If the
+     *       newParentDir is empty, moveTo() will rename the file
+     *       within its current directory. If the newParentDir is
+     *       not empty and does not name a directory, an error will
+     *       be returned (NS_ERROR_FILE_DESTINATION_NOT_DIR).  For
+     *       the |moveToNative| method, the newName must be in the
+     *       native filesystem charset.
+     *
+     *   @param newName
+     *       This param allows you to specify a new name for
+     *       the file to be moved. This param may be empty, in
+     *       which case the current leaf name will be used.
+     */
+    void moveTo(in nsIFile newParentDir, in AString newName);
+    [noscript] void moveToNative(in nsIFile newParentDir, in ACString newName);
+
+    /**
+     *  moveToFollowingLinks[Native]
+     *
+     *  This function is identical to moveTo with the exception that,
+     *  as the name implies, it follows symbolic links.  The XP_UNIX
+     *  implementation always follows symbolic links when moving.  For
+     *  the |MoveToFollowingLinks| method, the newName ust be in the native
+     *  filesystem charset.
+     */
+    void moveToFollowingLinks(in nsIFile newParentDir, in AString newName);
+    [noscript] void moveToFollowingLinksNative(in nsIFile newParentDir, in ACString newName);
+
+    /**
+     *  renameTo
+     *
+     *  This method is identical to moveTo except that if this file or directory
+     *  is moved to a a different volume, it fails and returns an error
+     *  (NS_ERROR_FILE_ACCESS_DENIED).
+     *  This object will still point to the old location after renaming.
+     */
+    void renameTo(in nsIFile newParentDir, in AString newName);
+    [noscript] void renameToNative(in nsIFile newParentDir, in ACString newName);
+
+    /**
+     *  This will try to delete this file.  The 'recursive' flag
+     *  must be PR_TRUE to delete directories which are not empty.
+     *
+     *  If passed, 'removeCount' will be incremented by the total number of files
+     *  and/or directories removed. Will be 1 unless the 'recursive' flag is
+     *  set. The parameter must be initialized beforehand.
+     *
+     *  This will not resolve any symlinks.
+     */
+    void remove(in boolean recursive, [optional] inout uint32_t removeCount);
+
+    /**
+     *  Attributes of nsIFile.
+     */
+
+    attribute unsigned long permissions;
+    attribute unsigned long permissionsOfLink;
+
+    /**
+     * The last accesss time of the file in milliseconds from midnight, January
+     * 1, 1970 GMT, if available.
+     */
+    attribute PRTime lastAccessedTime;
+    attribute PRTime lastAccessedTimeOfLink;
+
+    /**
+     *  File Times are to be in milliseconds from
+     *  midnight (00:00:00), January 1, 1970 Greenwich Mean
+     *  Time (GMT).
+     */
+    attribute PRTime lastModifiedTime;
+    attribute PRTime lastModifiedTimeOfLink;
+
+    /**
+     * The creation time of file in milliseconds from midnight, January 1, 1970
+     * GMT, if available.
+     *
+     * This attribute is only implemented on Windows and macOS. Accessing this
+     * on another platform will this will throw NS_ERROR_NOT_IMPLEMENTED.
+     */
+    readonly attribute PRTime creationTime;
+    readonly attribute PRTime creationTimeOfLink;
+
+    /**
+     *  WARNING!  On the Mac, getting/setting the file size with nsIFile
+     *  only deals with the size of the data fork.  If you need to
+     *  know the size of the combined data and resource forks use the
+     *  GetFileSizeWithResFork() method defined on nsILocalFileMac.
+     */
+    attribute int64_t fileSize;
+    readonly attribute int64_t fileSizeOfLink;
+
+    /**
+     *  target & path
+     *
+     *  Accessor to the string path.  The native version of these
+     *  strings are not guaranteed to be a usable path to pass to
+     *  NSPR or the C stdlib.  There are problems that affect
+     *  platforms on which a path does not fully specify a file
+     *  because two volumes can have the same name (e.g., mac).
+     *  This is solved by holding "private", native data in the
+     *  nsIFile implementation.  This native data is lost when
+     *  you convert to a string.
+     *
+     *      DO NOT PASS TO USE WITH NSPR OR STDLIB!
+     *
+     *  target
+     *      Find out what the symlink points at.  Will give error
+     *      (NS_ERROR_FILE_INVALID_PATH) if not a symlink.
+     *
+     *  path
+     *      Find out what the nsIFile points at.
+     *
+     *  Note that the ACString attributes are returned in the
+     *  native filesystem charset.
+     *
+     */
+    readonly attribute AString target;
+    [noscript] readonly attribute ACString nativeTarget;
+    readonly attribute AString path;
+    [notxpcom,nostdcall,must_use] PathString nativePath();
+%{C++
+#ifndef XP_WIN
+    nsresult GetNativePath(nsACString& aPath);
+#endif
+    /*
+     * Returns a human-readable path string.
+     */
+    nsCString HumanReadablePath();
+%}
+
+    boolean exists();
+    boolean isWritable();
+    boolean isReadable();
+    boolean isExecutable();
+    boolean isHidden();
+    boolean isDirectory();
+    boolean isFile();
+    boolean isSymlink();
+    /**
+     * Not a regular file, not a directory, not a symlink.
+     */
+    boolean isSpecial();
+
+    /**
+     *  createUnique
+     *
+     *  This function will create a new file or directory in the
+     *  file system. Any nodes that have not been created or
+     *  resolved, will be.  If this file already exists, we try
+     *  variations on the leaf name "suggestedName" until we find
+     *  one that did not already exist.
+     *
+     *  If the search for nonexistent files takes too long
+     *  (thousands of the variants already exist), we give up and
+     *  return NS_ERROR_FILE_TOO_BIG.
+     *
+     *   @param type
+     *       This specifies the type of file system object
+     *       to be made.  The only two types at this time
+     *       are file and directory which are defined above.
+     *       If the type is unrecongnized, we will return an
+     *       error (NS_ERROR_FILE_UNKNOWN_TYPE).
+     *
+     *   @param permissions
+     *       The unix style octal permissions.  This may
+     *       be ignored on systems that do not need to do
+     *       permissions.
+     */
+    [must_use]
+    void createUnique(in unsigned long type, in unsigned long permissions);
+
+    /**
+      * clone()
+      *
+      * This function will allocate and initialize a nsIFile object to the
+      * exact location of the |this| nsIFile.
+      *
+      *   @param file
+      *          A nsIFile which this object will be initialize
+      *          with.
+      *
+      */
+    nsIFile clone();
+
+    /**
+     *  Will determine if the inFile equals this.
+     */
+    boolean equals(in nsIFile inFile);
+
+    /**
+     *  Will determine if inFile is a descendant of this file.
+     *  This routine looks in subdirectories too.
+     */
+    boolean contains(in nsIFile inFile);
+
+    /**
+     *  Parent will be null when this is at the top of the volume.
+     */
+    readonly attribute nsIFile parent;
+
+    /**
+     *  Returns an enumeration of the elements in a directory. Each
+     *  element in the enumeration is an nsIFile.
+     *
+     *   @throws NS_ERROR_FILE_NOT_DIRECTORY if the current nsIFile does
+     *           not specify a directory.
+     */
+    [binaryname(DirectoryEntriesImpl)]
+    readonly attribute nsIDirectoryEnumerator directoryEntries;
+
+    %{C++
+    nsresult GetDirectoryEntries(nsIDirectoryEnumerator** aOut)
+    {
+      return GetDirectoryEntriesImpl(aOut);
+    };
+    %}
+
+    /**
+     *  initWith[Native]Path
+     *
+     *  This function will initialize the nsIFile object.  Any
+     *  internal state information will be reset.
+     *
+     *   @param filePath
+     *       A string which specifies a full file path to a
+     *       location.  Relative paths will be treated as an
+     *       error (NS_ERROR_FILE_UNRECOGNIZED_PATH).  For
+     *       initWithNativePath, the filePath must be in the native
+     *       filesystem charset.
+     */
+    void initWithPath(in AString filePath);
+    [noscript] void initWithNativePath(in ACString filePath);
+
+    /**
+     *  initWithFile
+     *
+     *  Initialize this object with another file
+     *
+     *   @param aFile
+     *       the file this becomes equivalent to
+     */
+    void initWithFile(in nsIFile aFile);
+
+    /**
+     * Flag for openNSPRFileDesc(), to hint to the OS that the file will be
+     * read sequentially with agressive readahead.
+     */
+    const unsigned long OS_READAHEAD = 0x40000000;
+
+    /**
+     * Flag for openNSPRFileDesc(). Deprecated and unreliable!
+     * Instead use NS_OpenAnonymousTemporaryFile() to create a temporary
+     * file which will be deleted upon close!
+     */
+    const unsigned long DELETE_ON_CLOSE = 0x80000000;
+
+    /**
+     * Return the result of PR_Open on the file.  The caller is
+     * responsible for calling PR_Close on the result.  On success, the
+     * returned PRFileDescr must be non-null.
+     *
+     * @param flags the PR_Open flags from prio.h, plus optionally
+     * OS_READAHEAD or DELETE_ON_CLOSE. OS_READAHEAD is a hint to the
+     * OS that the file will be read sequentially with agressive
+     * readahead. DELETE_ON_CLOSE is unreliable on Windows and is deprecated.
+     * Instead use NS_OpenAnonymousTemporaryFile() to create a temporary
+     * file which will be deleted upon close.
+     */
+    [noscript, must_use] PRFileDescStar openNSPRFileDesc(in long flags,
+                                                         in long mode);
+
+    /**
+     * Return the result of fopen on the file.  The caller is
+     * responsible for calling fclose on the result.  On success, the
+     * returned FILE pointer must be non-null.
+     */
+    [noscript, must_use] FILE openANSIFileDesc(in string mode);
+
+    /**
+     * Return the result of PR_LoadLibrary on the file.  The caller is
+     * responsible for calling PR_UnloadLibrary on the result.
+     */
+    [noscript, must_use] PRLibraryStar  load();
+
+    // number of bytes available on disk to non-superuser
+    [must_use] readonly attribute int64_t diskSpaceAvailable;
+
+    // disk capacity in bytes
+    [must_use] readonly attribute int64_t diskCapacity;
+
+    /**
+     *  appendRelative[Native]Path
+     *
+     *  Append a relative path to the current path of the nsIFile object.
+     *
+     *   @param relativeFilePath
+     *       relativeFilePath is a native relative path. For security reasons,
+     *       this cannot contain .. and cannot start with a directory separator.
+     *       For the |appendRelativeNativePath| method, the relativeFilePath
+     *       must be in the native filesystem charset.
+     */
+    void appendRelativePath(in AString relativeFilePath);
+    [noscript] void appendRelativeNativePath(in ACString relativeFilePath);
+
+    /**
+     *  Accessor to a null terminated string which will specify
+     *  the file in a persistent manner for disk storage.
+     *
+     *  The character set of this attribute is undefined.  DO NOT TRY TO
+     *  INTERPRET IT AS HUMAN READABLE TEXT!
+     */
+    [must_use] attribute ACString persistentDescriptor;
+
+    /**
+     *  reveal
+     *
+     *  Ask the operating system to open the folder which contains
+     *  this file or folder. This routine only works on platforms which
+     *  support the ability to open a folder and is run async on Windows.
+     *  This routine must be called on the main.
+     */
+    [must_use] void reveal();
+
+    /**
+     *  launch
+     *
+     *  Ask the operating system to attempt to open the file.
+     *  this really just simulates "double clicking" the file on your platform.
+     *  This routine only works on platforms which support this functionality
+     *  and is run async on Windows.  This routine must be called on the
+     *  main thread.
+     */
+    [must_use] void launch();
+
+    /**
+     *  getRelativeDescriptor
+     *
+     *  Returns a relative file path in an opaque, XP format. It is therefore
+     *  not a native path.
+     *
+     *  The character set of the string returned from this function is
+     *  undefined.  DO NOT TRY TO INTERPRET IT AS HUMAN READABLE TEXT!
+     *
+     *   @param fromFile
+     *       the file from which the descriptor is relative.
+     *       Throws if fromFile is null.
+     */
+    [must_use] ACString getRelativeDescriptor(in nsIFile fromFile);
+
+    /**
+     *  setRelativeDescriptor
+     *
+     *  Initializes the file to the location relative to fromFile using
+     *  a string returned by getRelativeDescriptor.
+     *
+     *   @param fromFile
+     *       the file to which the descriptor is relative
+     *   @param relative
+     *       the relative descriptor obtained from getRelativeDescriptor
+     */
+    [must_use]
+    void setRelativeDescriptor(in nsIFile fromFile, in ACString relativeDesc);
+
+    /**
+     *  getRelativePath
+     *
+     *  Returns a relative file from 'fromFile' to this file as a UTF-8 string.
+     *  Going up the directory tree is represented via "../".  '/' is used as
+     *  the path segment separator.  This is not a native path, since it's UTF-8
+     *  encoded.
+     *
+     *   @param fromFile
+     *       the file from which the path is relative.
+     *       Throws if fromFile is null.
+     */
+    [must_use] AUTF8String getRelativePath(in nsIFile fromFile);
+
+    /**
+     *  setRelativePath
+     *
+     *  Initializes the file to the location relative to fromFile using
+     *  a string returned by getRelativePath.
+     *
+     *   @param fromFile
+     *       the file from which the path is relative
+     *   @param relative
+     *       the relative path obtained from getRelativePath
+     */
+    [must_use]
+    void setRelativePath(in nsIFile fromFile, in AUTF8String relativeDesc);
+};
+
+%{C++
+#ifdef MOZILLA_INTERNAL_API
+#include "nsDirectoryServiceUtils.h"
+#include "nsString.h"
+
+inline std::ostream& operator<<(std::ostream& aOut, const nsIFile& aFile) {
+  nsIFile* file = const_cast<nsIFile*>(&aFile);
+  nsAutoString path;
+  file->GetPath(path);
+  return aOut << "nsIFile { " << path << " }";
+}
+#endif
+%}
diff --git a/xpcom/io/nsIIOUtil.idl b/xpcom/io/nsIIOUtil.idl
new file mode 100644
index 0000000000..589556b367
--- /dev/null
+++ b/xpcom/io/nsIIOUtil.idl
@@ -0,0 +1,34 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsIInputStream;
+interface nsIOutputStream;
+
+/**
+ * nsIIOUtil provdes various xpcom/io-related utility methods.
+ */
+[scriptable, builtinclass, uuid(e8152f7f-4209-4c63-ad23-c3d2aa0c5a49)]
+interface nsIIOUtil : nsISupports
+{
+  /**
+   * Test whether an input stream is buffered.  See nsStreamUtils.h
+   * documentation for NS_InputStreamIsBuffered for the definition of
+   * "buffered" used here and for edge-case behavior.
+   *
+   * @throws NS_ERROR_INVALID_POINTER if null is passed in.
+   */
+  boolean inputStreamIsBuffered(in nsIInputStream aStream);
+
+  /**
+   * Test whether an output stream is buffered.  See nsStreamUtils.h
+   * documentation for NS_OutputStreamIsBuffered for the definition of
+   * "buffered" used here and for edge-case behavior.
+   *
+   * @throws NS_ERROR_INVALID_POINTER if null is passed in.
+   */
+  boolean outputStreamIsBuffered(in nsIOutputStream aStream);
+};
diff --git a/xpcom/io/nsIInputStream.idl b/xpcom/io/nsIInputStream.idl
new file mode 100644
index 0000000000..9a72eaeae2
--- /dev/null
+++ b/xpcom/io/nsIInputStream.idl
@@ -0,0 +1,172 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsIInputStream;
+
+%{C++
+/**
+ * The signature of the writer function passed to ReadSegments. This
+ * is the "consumer" of data that gets read from the stream's buffer.
+ *
+ * @param aInStream stream being read
+ * @param aClosure opaque parameter passed to ReadSegments
+ * @param aFromSegment pointer to memory owned by the input stream.  This is
+ *                     where the writer function should start consuming data.
+ * @param aToOffset amount of data already consumed by this writer during this
+ *                  ReadSegments call.  This is also the sum of the aWriteCount
+ *                  returns from this writer over the previous invocations of
+ *                  the writer by this ReadSegments call.
+ * @param aCount Number of bytes available to be read starting at aFromSegment
+ * @param [out] aWriteCount number of bytes read by this writer function call
+ *
+ * Implementers should return the following:
+ *
+ * @return NS_OK and (*aWriteCount > 0) if consumed some data
+ * @return <any-error> if not interested in consuming any data
+ *
+ * Errors are never passed to the caller of ReadSegments.
+ *
+ * NOTE: returning NS_OK and (*aWriteCount = 0) has undefined behavior.
+ */
+typedef nsresult (*nsWriteSegmentFun)(nsIInputStream *aInStream,
+                                      void *aClosure,
+                                      const char *aFromSegment,
+                                      uint32_t aToOffset,
+                                      uint32_t aCount,
+                                      uint32_t *aWriteCount);
+%}
+
+native nsWriteSegmentFun(nsWriteSegmentFun);
+
+/**
+ * nsIInputStream
+ *
+ * An interface describing a readable stream of data.  An input stream may be
+ * "blocking" or "non-blocking" (see the IsNonBlocking method).  A blocking
+ * input stream may suspend the calling thread in order to satisfy a call to
+ * Close, Available, Read, or ReadSegments.  A non-blocking input stream, on
+ * the other hand, must not block the calling thread of execution.
+ *
+ * NOTE: blocking input streams are often read on a background thread to avoid
+ * locking up the main application thread.  For this reason, it is generally
+ * the case that a blocking input stream should be implemented using thread-
+ * safe AddRef and Release.
+ */
+[scriptable, builtinclass, uuid(53cdbc97-c2d7-4e30-b2c3-45b2ee79db18)]
+interface nsIInputStream : nsISupports
+{
+    /**
+     * Close the stream.  This method causes subsequent calls to Read and
+     * ReadSegments to return 0 bytes read to indicate end-of-file.  Any
+     * subsequent calls to Available or StreamStatus should throw
+     * NS_BASE_STREAM_CLOSED.
+     *
+     * Succeeds (without side effects) if already closed.
+     */
+    void close();
+
+    /**
+     * Determine number of bytes available in the stream.  A non-blocking
+     * stream that does not yet have any data to read should return 0 bytes
+     * from this method (i.e., it must not throw the NS_BASE_STREAM_WOULD_BLOCK
+     * exception).
+     *
+     * In addition to the number of bytes available in the stream, this method
+     * also informs the caller of the current status of the stream.  A stream
+     * that is closed will throw an exception when this method is called.  That
+     * enables the caller to know the condition of the stream before attempting
+     * to read from it.  If a stream is at end-of-file, but not closed, then
+     * this method returns 0 bytes available.  (Note: some nsIInputStream
+     * implementations automatically close when eof is reached; some do not).
+     *
+     * NOTE: Streams implementing nsIAsyncInputStream must automatically close
+     * when eof is reached, as otherwise it is impossible to distinguish between
+     * a stream waiting for more data and a stream at EOF using Available().
+     *
+     * @return number of bytes currently available in the stream.
+     *
+     * @throws NS_BASE_STREAM_CLOSED if the stream is closed normally.
+     * @throws <other-error> if the stream is closed due to some error
+     *   condition
+     */
+    unsigned long long available();
+
+    /**
+     * Check the current status of the stream.  A stream that is closed will
+     * throw an exception when this method is called.  That enables the caller
+     * to know the condition of the stream before attempting to read from it.
+     *
+     * This method will not throw NS_BASE_STREAM_WOULD_BLOCK, even if the stream
+     * is an non-blocking stream with no data. A non-blocking stream that does
+     * not yet have any data to read should return NS_OK.
+     *
+     * NOTE: Unlike available, his method should not block the calling thread
+     * (e.g. to query the state of a file descriptor), even when called on a
+     * blocking stream.
+     *
+     * @throws NS_BASE_STREAM_CLOSED if the stream closed normally
+     * @throws <other-error> if the stream closed with a different status
+     */
+    void streamStatus();
+
+    /**
+     * Read data from the stream.
+     *
+     * @param aBuf the buffer into which the data is to be read
+     * @param aCount the maximum number of bytes to be read
+     *
+     * @return number of bytes read (may be less than aCount).
+     * @return 0 if reached end-of-file
+     *
+     * @throws NS_BASE_STREAM_WOULD_BLOCK if reading from the input stream would
+     *   block the calling thread (non-blocking mode only)
+     * @throws <other-error> on failure
+     *
+     * NOTE: this method should not throw NS_BASE_STREAM_CLOSED.
+     */
+    [noscript] unsigned long read(in charPtr aBuf, in unsigned long aCount);
+
+    /**
+     * Low-level read method that provides access to the stream's underlying
+     * buffer.  The writer function may be called multiple times for segmented
+     * buffers.  ReadSegments is expected to keep calling the writer until
+     * either there is nothing left to read or the writer returns an error.
+     * ReadSegments should not call the writer with zero bytes to consume.
+     *
+     * @param aWriter the "consumer" of the data to be read
+     * @param aClosure opaque parameter passed to writer
+     * @param aCount the maximum number of bytes to be read
+     *
+     * @return number of bytes read (may be less than aCount)
+     * @return 0 if reached end-of-file (or if aWriter refused to consume data)
+     *
+     * @throws NS_BASE_STREAM_WOULD_BLOCK if reading from the input stream would
+     *   block the calling thread (non-blocking mode only)
+     * @throws NS_ERROR_NOT_IMPLEMENTED if the stream has no underlying buffer
+     * @throws <other-error> on failure
+     *
+     * NOTE: this function may be unimplemented if a stream has no underlying
+     * buffer (e.g., socket input stream).
+     *
+     * NOTE: this method should not throw NS_BASE_STREAM_CLOSED.
+     */
+    [noscript] unsigned long readSegments(in nsWriteSegmentFun aWriter,
+                                          in voidPtr aClosure,
+                                          in unsigned long aCount);
+
+    /**
+     * @return true if stream is non-blocking
+     *
+     * NOTE: reading from a blocking input stream will block the calling thread
+     * until at least one byte of data can be extracted from the stream.
+     *
+     * NOTE: a non-blocking input stream may implement nsIAsyncInputStream to
+     * provide consumers with a way to wait for the stream to have more data
+     * once its read method is unable to return any data without blocking.
+     */
+    boolean isNonBlocking();
+};
diff --git a/xpcom/io/nsIInputStreamLength.idl b/xpcom/io/nsIInputStreamLength.idl
new file mode 100644
index 0000000000..f9f685704a
--- /dev/null
+++ b/xpcom/io/nsIInputStreamLength.idl
@@ -0,0 +1,85 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsIEventTarget;
+interface nsIInputStreamLengthCallback;
+
+/**
+ * Note: Instead of using these interfaces directly, consider to use
+ * InputStreamLengthHelper class.
+ */
+
+[uuid(452d059f-9a9c-4434-8839-e10d1405647c)]
+interface nsIInputStreamLength : nsISupports
+{
+  /**
+   * Returns the total length of the stream if known. Otherwise it returns -1.
+   * This is different than calling available() which returns the number of
+   * bytes ready to be read from the stream.
+   * -1 is a valid value for a stream that doesn't know its length. For
+   * instance, a pipe stream could return such value.
+   *
+   * It could throw NS_BASE_STREAM_WOULD_BLOCK if the inputStream is
+   * non-blocking. If this happens, you should use
+   * nsIAsyncInputStreamLength::asyncLengthWait().
+   *
+   * If the stream has already been read (read()/readSegments()/close()/seek()
+   * methods has been called), length() returns NS_ERROR_NOT_AVAILABLE.
+   *
+   * This is not an attribute because a stream can change its length. For
+   * instance, if the stream is a file inputStream and the underlying OS file
+   * changes, its length will change as well.
+   */
+  long long length();
+};
+
+[uuid(b63f9ecf-4668-44a3-93bd-72dbc65a6125)]
+interface nsIAsyncInputStreamLength : nsISupports
+{
+  /**
+   * If the stream is non-blocking, nsIInputStreamLength::length() can return
+   * NS_BASE_STREAM_WOULD_BLOCK. The caller must then wait for the stream to
+   * know its length.
+   *
+   * If the stream implements nsIAsyncInputStreamLength, then the caller can
+   * use this interface to request an asynchronous notification when the
+   * stream's length becomes known (via the AsyncLengthWait method).
+   * If the length is already known, the aCallback will be still called
+   * asynchronously.
+   *
+   * If the stream has already been read (read()/readSegments()/close()/seek()
+   * methods has been called), length() returns NS_ERROR_NOT_AVAILABLE.
+   *
+   * @param aCallback
+   *        This object is notified when the length becomes known. This
+   *        parameter may be null to clear an existing callback.
+   * @param aEventTarget
+   *        Specify that the notification must be delivered to a specific event
+   *        target.
+   */
+  void asyncLengthWait(in nsIInputStreamLengthCallback aCallback,
+                      in nsIEventTarget aEventTarget);
+};
+
+/**
+ * This is a companion interface for
+ * nsIAsyncInputStreamLength::asyncLengthWait.
+ */
+[function, uuid(9c0c13b9-1b33-445d-8adb-a8a7866a6c06)]
+interface nsIInputStreamLengthCallback : nsISupports
+{
+  /**
+   * Called to inform what the total length of the stream is.
+   *
+   * @param aStream
+   *        The stream whose asyncLengthWait method was called.
+   * @param aLength
+   *        The stream's length. It can be -1 if the stream doesn't know its
+   *        length. For instance, this can happen for a pipe inputStream.
+   */
+  void onInputStreamLengthReady(in nsIAsyncInputStreamLength aStream,
+                                in long long aLength);
+};
diff --git a/xpcom/io/nsIInputStreamPriority.idl b/xpcom/io/nsIInputStreamPriority.idl
new file mode 100644
index 0000000000..d5938b7c27
--- /dev/null
+++ b/xpcom/io/nsIInputStreamPriority.idl
@@ -0,0 +1,17 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+#include "nsIRunnable.idl"
+
+[scriptable, uuid(daa45b24-98ee-4eb2-9cec-aad0bc023e9d)]
+interface nsIInputStreamPriority : nsISupports
+{
+    /**
+     * An input stream implementing this interface will dispatch runnable
+     * events with this priority. See nsIRunnablePriority.
+     */
+    attribute unsigned long priority;
+};
diff --git a/xpcom/io/nsIInputStreamTee.idl b/xpcom/io/nsIInputStreamTee.idl
new file mode 100644
index 0000000000..60881e0fb8
--- /dev/null
+++ b/xpcom/io/nsIInputStreamTee.idl
@@ -0,0 +1,42 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIInputStream.idl"
+
+interface nsIOutputStream;
+interface nsIEventTarget;
+
+/**
+ * A nsIInputStreamTee is a wrapper for an input stream, that when read
+ * reads the specified amount of data from its |source| and copies that
+ * data to its |sink|.  |sink| must be a blocking output stream.
+ */
+[scriptable, builtinclass, uuid(90a9d790-3bca-421e-a73b-98f68e13c917)]
+interface nsIInputStreamTee : nsIInputStream
+{
+    attribute nsIInputStream source;
+    attribute nsIOutputStream sink;
+
+    /**
+     * If |eventTarget| is set, copying to sink is done asynchronously using
+     * the event-target (e.g. a thread). If |eventTarget| is not set, copying
+     * to sink happens synchronously while reading from the source.
+     */
+    attribute nsIEventTarget eventTarget;
+};
+
+%{C++
+// factory methods
+extern nsresult
+NS_NewInputStreamTee(nsIInputStream **tee, // read from this input stream
+                     nsIInputStream *source,
+                     nsIOutputStream *sink);
+
+extern nsresult
+NS_NewInputStreamTeeAsync(nsIInputStream **tee, // read from this input stream
+                     nsIInputStream *source,
+                     nsIOutputStream *sink,
+                     nsIEventTarget *eventTarget);
+%}
diff --git a/xpcom/io/nsILineInputStream.idl b/xpcom/io/nsILineInputStream.idl
new file mode 100644
index 0000000000..34ef1e7320
--- /dev/null
+++ b/xpcom/io/nsILineInputStream.idl
@@ -0,0 +1,26 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+[scriptable, uuid(c97b466c-1e6e-4773-a4ab-2b2b3190a7a6)]
+interface nsILineInputStream : nsISupports
+{
+  /**
+   * Read a single line from the stream, where a line is a
+   * possibly zero length sequence of 8bit chars terminated by a
+   * CR, LF, CRLF, LFCR, or eof.
+   * The line terminator is not returned.
+   * @retval false
+   *         End of file. This line is the last line of the file
+   *         (aLine is valid).
+   * @retval true
+   *         The file contains further lines.
+   * @note Do not mix readLine with other read functions.
+   *       Doing so can cause various problems and is not supported.
+   */
+  boolean readLine(out ACString aLine);
+};
diff --git a/xpcom/io/nsILocalFileMac.idl b/xpcom/io/nsILocalFileMac.idl
new file mode 100644
index 0000000000..38559517e7
--- /dev/null
+++ b/xpcom/io/nsILocalFileMac.idl
@@ -0,0 +1,212 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIFile.idl"
+
+%{C++
+#include <Carbon/Carbon.h>
+#include <CoreFoundation/CoreFoundation.h>
+%}
+
+      native OSType(OSType);
+      native FSSpec(FSSpec);
+      native FSRef(FSRef);
+[ptr] native FSRefPtr(FSRef);
+      native CFURLRef(CFURLRef);
+
+[scriptable, builtinclass, uuid(623eca5b-c25d-4e27-be5a-789a66c4b2f7)]
+interface nsILocalFileMac : nsIFile
+{
+   /**
+    * initWithCFURL
+    *
+    * Init this object with a CFURLRef
+    *
+    * NOTE: Supported only for XP_MACOSX
+    * NOTE: If the path of the CFURL is /a/b/c, at least a/b must exist beforehand.
+    *
+    * @param   aCFURL         the CoreFoundation URL
+    *
+    */
+  [noscript] void initWithCFURL(in CFURLRef aCFURL);
+
+   /**
+    * initWithFSRef
+    *
+    * Init this object with an FSRef
+    *
+    * NOTE: Supported only for XP_MACOSX
+    *
+    * @param   aFSRef         the native FSRef
+    *
+    */
+  [noscript] void initWithFSRef([const] in FSRefPtr aFSRef);
+
+    /**
+    * getCFURL
+    *
+    * Returns the CFURLRef of the file object. The caller is
+    * responsible for calling CFRelease() on it.
+    *
+    * NOTE: Observes the state of the followLinks attribute.
+    * If the file object is an alias and followLinks is TRUE, returns
+    * the target of the alias. If followLinks is FALSE, returns
+    * the unresolved alias file.
+    *
+    * NOTE: Supported only for XP_MACOSX
+    *
+    * @return
+    *
+    */
+  [noscript] CFURLRef getCFURL();
+
+    /**
+    * getFSRef
+    *
+    * Returns the FSRef of the file object.
+    *
+    * NOTE: Observes the state of the followLinks attribute.
+    * If the file object is an alias and followLinks is TRUE, returns
+    * the target of the alias. If followLinks is FALSE, returns
+    * the unresolved alias file.
+    *
+    * NOTE: Supported only for XP_MACOSX
+    *
+    * @return
+    *
+    */
+  [noscript] FSRef getFSRef();
+
+   /**
+    * getFSSpec
+    *
+    * Returns the FSSpec of the file object.
+    *
+    * NOTE: Observes the state of the followLinks attribute.
+    * If the file object is an alias and followLinks is TRUE, returns
+    * the target of the alias. If followLinks is FALSE, returns
+    * the unresolved alias file.
+    *
+    * @return
+    *
+    */
+  [noscript] FSSpec getFSSpec();
+
+   /**
+    * fileSizeWithResFork
+    *
+    * Returns the combined size of both the data fork and the resource
+    * fork (if present) rather than just the size of the data fork
+    * as returned by GetFileSize()
+    *
+    */
+   readonly attribute int64_t fileSizeWithResFork;
+
+   /**
+    * fileType, creator
+    *
+    * File type and creator attributes
+    *
+    */
+   [noscript] attribute OSType fileType;
+   [noscript] attribute OSType fileCreator;
+
+   /**
+    * launchWithDoc
+    *
+    * Launch the application that this file points to with a document.
+    *
+    * @param   aDocToLoad          Must not be NULL. If no document, use nsIFile::launch
+    * @param   aLaunchInBackground TRUE if the application should not come to the front.
+    *
+    */
+   void launchWithDoc(in nsIFile aDocToLoad, in boolean aLaunchInBackground);
+
+   /**
+    * openDocWithApp
+    *
+    * Open the document that this file points to with the given application.
+    *
+    * @param   aAppToOpenWith      The application with  which to open the document.
+    *                              If NULL, the creator code of the document is used
+    *                              to determine the application.
+    * @param   aLaunchInBackground TRUE if the application should not come to the front.
+    *
+    */
+   void openDocWithApp(in nsIFile aAppToOpenWith, in boolean aLaunchInBackground);
+
+   /**
+    * isPackage
+    *
+    * returns true if a directory is determined to be a package under Mac OS 9/X
+    *
+    */
+   boolean isPackage();
+
+   /**
+    * bundleDisplayName
+    *
+    * returns the display name of the application bundle (usually the human
+    * readable name of the application)
+    */
+   readonly attribute AString bundleDisplayName;
+
+   /**
+    * bundleIdentifier
+    *
+    * returns the identifier of the bundle
+    */
+   readonly attribute AUTF8String bundleIdentifier;
+
+    /**
+     * Last modified time of a bundle's contents (as opposed to its package
+     * directory).  Our convention is to make the bundle's Info.plist file
+     * stand in for the rest of its contents -- since this file contains the
+     * bundle's version information and other identifiers.  For non-bundles
+     * this is the same as lastModifiedTime.
+     */
+    readonly attribute int64_t bundleContentsLastModifiedTime;
+
+    /**
+     * Return whether or not the file has an extended attribute.
+     *
+     * @param aAttrName The attribute name to check for.
+     *
+     * @return Whether or not the extended attribute is present.
+     */
+    bool hasXAttr(in ACString aAttrName);
+
+    /**
+     * Get the value of the extended attribute.
+     *
+     * @param aAttrName The attribute name to read.
+     *
+     * @return The extended attribute value.
+     */
+    Array<uint8_t> getXAttr(in ACString aAttrName);
+
+    /**
+     * Set an extended attribute.
+     *
+     * @param aAttrName The attribute name to set a value for.
+     * @param aAttrValue The value to set for the attribute.
+     */
+    void setXAttr(in ACString aAttrName, in Array<uint8_t> aAttrValue);
+
+    /**
+     * Delete an extended attribute.
+     *
+     * @param aAttrName The extended attribute to delete.
+     */
+    void delXAttr(in ACString aAttrName);
+};
+
+%{C++
+extern "C"
+{
+NS_EXPORT nsresult NS_NewLocalFileWithFSRef(const FSRef* aFSRef, bool aFollowSymlinks, nsILocalFileMac** result);
+NS_EXPORT nsresult NS_NewLocalFileWithCFURL(const CFURLRef aURL, bool aFollowSymlinks, nsILocalFileMac** result);
+}
+%}
diff --git a/xpcom/io/nsILocalFileWin.idl b/xpcom/io/nsILocalFileWin.idl
new file mode 100644
index 0000000000..a3f80d391b
--- /dev/null
+++ b/xpcom/io/nsILocalFileWin.idl
@@ -0,0 +1,98 @@
+/* -*- Mode: Java; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include "nsIFile.idl"
+
+%{C++
+struct PRFileDesc;
+%}
+
+[ptr] native PRFileDescStar(PRFileDesc);
+
+[scriptable, builtinclass, uuid(e7a3a954-384b-4aeb-a5f7-55626b0de9be)]
+interface nsILocalFileWin : nsIFile
+{
+    /**
+     *  initWithCommandLine
+     *
+     *  Initialize this object based on the main app path of a commandline
+     *  handler.
+     *
+     *   @param aCommandLine
+     *       the commandline to parse an app path out of.
+     */
+    void initWithCommandLine(in AString aCommandLine);
+   /**
+    * getVersionInfoValue
+    *
+    * Retrieve a metadata field from the file's VERSIONINFO block.
+    * Throws NS_ERROR_FAILURE if no value is found, or the value is empty.
+    *
+    * @param   aField         The field to look up.
+    *
+    */
+    AString getVersionInfoField(in string aField);
+
+    /**
+     * The canonical path of the file, which avoids short/long
+     * pathname inconsistencies. The nsIFile persistent
+     * descriptor is not guaranteed to be canonicalized (it may
+     * persist either the long or the short path name). The format of
+     * the canonical path will vary with the underlying file system:
+     * it will typically be the short pathname on filesystems that
+     * support both short and long path forms.
+     */
+    [noscript] readonly attribute AString canonicalPath;
+
+    /**
+     * Get or set whether this file is marked read-only.
+     *
+     * Throws NS_ERROR_FILE_INVALID_PATH for an invalid file.
+     * Throws NS_ERROR_FAILURE if the set or get fails.
+     */
+    attribute bool readOnly;
+
+    /**
+     * Setting this to true will prepend the prefix "\\?\" to all parsed file
+     * paths which match ^[A-Za-z]:\\.* (regex) syntax.
+     *
+     * There are two known issues (and potentially more) which can be resolved
+     * by the prefix:
+     * - In the Windows API, the maximum length for a path is MAX_PATH in
+     *   general. However, Windows API has many functions that also have Unicode
+     *   versions to permit an extended-length path for a maximum total path
+     *   length of 32,767 characters.
+     *
+     * - A path component which ends with a dot is not allowed for Windows
+     *   API.
+     *
+     * If either of these issues are expected to be common in your code, you
+     * should set this flag to true. (You should probably not have to set this
+     * flag to true.)
+     */
+    attribute boolean useDOSDevicePathSyntax;
+
+    /**
+     * Identical to nsIFile::openNSPRFileDesc except it also uses the
+     * FILE_SHARE_DELETE flag.
+    */
+    [noscript] PRFileDescStar openNSPRFileDescShareDelete(in long flags,
+                                                          in long mode);
+
+    /**
+     * Return the Windows-specific file attributes of this file.
+     */
+    [noscript] unsigned long getWindowsFileAttributes();
+
+    /**
+     * Set or clear the Windows specific file attributes of this file.
+     *
+     * @param aSetAttrs   Attribute to set on the file.
+     * @param aClearAttrs Attributes to clear on the file.
+     */
+    [noscript] void setWindowsFileAttributes(in unsigned long aSetAttrs,
+                                             in unsigned long aClearAttrs);
+};
diff --git a/xpcom/io/nsIMultiplexInputStream.idl b/xpcom/io/nsIMultiplexInputStream.idl
new file mode 100644
index 0000000000..3729ccf753
--- /dev/null
+++ b/xpcom/io/nsIMultiplexInputStream.idl
@@ -0,0 +1,35 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIInputStream.idl"
+
+/**
+ * The multiplex stream concatenates a list of input streams into a single
+ * stream.
+ */
+
+[scriptable, builtinclass, uuid(a076fd12-1dd1-11b2-b19a-d53b5dffaade)]
+interface nsIMultiplexInputStream : nsISupports
+{
+    /**
+     * Number of streams in this multiplex-stream
+     */
+    [infallible] readonly attribute unsigned long count;
+
+    /**
+     * Appends a stream to the end of the streams. The cursor of the stream
+     * should be located at the beginning of the stream if the implementation
+     * of this nsIMultiplexInputStream also is used as an nsISeekableStream.
+     * @param stream  stream to append
+     */
+    void appendStream(in nsIInputStream stream);
+
+    /**
+     * Get stream at specified index.
+     * @param index   return stream at this index, must be < count
+     * @return        stream at specified index
+     */
+    nsIInputStream getStream(in unsigned long index);
+};
diff --git a/xpcom/io/nsIOUtil.cpp b/xpcom/io/nsIOUtil.cpp
new file mode 100644
index 0000000000..b637e34a88
--- /dev/null
+++ b/xpcom/io/nsIOUtil.cpp
@@ -0,0 +1,30 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIOUtil.h"
+#include "nsIInputStream.h"
+#include "nsIOutputStream.h"
+#include "nsStreamUtils.h"
+
+NS_IMPL_ISUPPORTS(nsIOUtil, nsIIOUtil)
+
+NS_IMETHODIMP
+nsIOUtil::InputStreamIsBuffered(nsIInputStream* aStream, bool* aResult) {
+  if (NS_WARN_IF(!aStream)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aResult = NS_InputStreamIsBuffered(aStream);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsIOUtil::OutputStreamIsBuffered(nsIOutputStream* aStream, bool* aResult) {
+  if (NS_WARN_IF(!aStream)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aResult = NS_OutputStreamIsBuffered(aStream);
+  return NS_OK;
+}
diff --git a/xpcom/io/nsIOUtil.h b/xpcom/io/nsIOUtil.h
new file mode 100644
index 0000000000..32794433eb
--- /dev/null
+++ b/xpcom/io/nsIOUtil.h
@@ -0,0 +1,28 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsIOUtil_h__
+#define nsIOUtil_h__
+
+#define NS_IOUTIL_CID                                \
+  {                                                  \
+    0xeb833911, 0x4f49, 0x4623, {                    \
+      0x84, 0x5f, 0xe5, 0x8a, 0x8e, 0x6d, 0xe4, 0xc2 \
+    }                                                \
+  }
+
+#include "nsIIOUtil.h"
+#include "mozilla/Attributes.h"
+
+class nsIOUtil final : public nsIIOUtil {
+  ~nsIOUtil() = default;
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIIOUTIL
+};
+
+#endif /* nsIOUtil_h__ */
diff --git a/xpcom/io/nsIObjectInputStream.idl b/xpcom/io/nsIObjectInputStream.idl
new file mode 100644
index 0000000000..c00b93a99a
--- /dev/null
+++ b/xpcom/io/nsIObjectInputStream.idl
@@ -0,0 +1,56 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIBinaryInputStream.idl"
+
+/**
+ * @see nsIObjectOutputStream
+ * @see nsIBinaryInputStream
+ */
+
+[scriptable, builtinclass, uuid(6c248606-4eae-46fa-9df0-ba58502368eb)]
+interface nsIObjectInputStream : nsIBinaryInputStream
+{
+    /**
+     * Read an object from this stream to satisfy a strong or weak reference
+     * to one of its interfaces.  If the interface was not along the primary
+     * inheritance chain ending in the "root" or XPCOM-identity nsISupports,
+     * readObject will QueryInterface from the deserialized object root to the
+     * correct interface, which was specified when the object was serialized.
+     *
+     * @see nsIObjectOutputStream
+     */
+    nsISupports readObject(in boolean aIsStrongRef);
+
+    [notxpcom] nsresult readID(out nsID aID);
+
+    /**
+     * Optimized deserialization support -- see nsIStreamBufferAccess.idl.
+     */
+    [notxpcom] charPtr getBuffer(in uint32_t aLength, in uint32_t aAlignMask);
+    [notxpcom] void    putBuffer(in charPtr aBuffer, in uint32_t aLength);
+};
+
+%{C++
+
+already_AddRefed<nsIObjectInputStream>
+NS_NewObjectInputStream(nsIInputStream* aOutputStream);
+
+inline nsresult
+NS_ReadOptionalObject(nsIObjectInputStream* aStream, bool aIsStrongRef,
+                      nsISupports* *aResult)
+{
+    bool nonnull;
+    nsresult rv = aStream->ReadBoolean(&nonnull);
+    if (NS_SUCCEEDED(rv)) {
+        if (nonnull)
+            rv = aStream->ReadObject(aIsStrongRef, aResult);
+        else
+            *aResult = nullptr;
+    }
+    return rv;
+}
+
+%}
diff --git a/xpcom/io/nsIObjectOutputStream.idl b/xpcom/io/nsIObjectOutputStream.idl
new file mode 100644
index 0000000000..c5cdf27942
--- /dev/null
+++ b/xpcom/io/nsIObjectOutputStream.idl
@@ -0,0 +1,99 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIBinaryOutputStream.idl"
+
+/**
+ * @See nsIObjectInputStream
+ * @See nsIBinaryOutputStream
+ */
+
+[scriptable, builtinclass, uuid(92c898ac-5fde-4b99-87b3-5d486422094b)]
+interface nsIObjectOutputStream : nsIBinaryOutputStream
+{
+    /**
+     * Write the object whose "root" or XPCOM-identity nsISupports is aObject.
+     * The cause for writing this object is a strong or weak reference, so the
+     * aIsStrongRef argument must tell which kind of pointer is being followed
+     * here during serialization.
+     *
+     * If the object has only one strong reference in the serialization and no
+     * weak refs, use writeSingleRefObject.  This is a valuable optimization:
+     * it saves space in the stream, and cycles on both ends of the process.
+     *
+     * If the reference being serialized is a pointer to an interface not on
+     * the primary inheritance chain ending in the root nsISupports, you must
+     * call writeCompoundObject instead of this method.
+     */
+    void writeObject(in nsISupports aObject, in boolean aIsStrongRef);
+
+    /**
+     * Write an object referenced singly and strongly via its root nsISupports
+     * or a subclass of its root nsISupports.  There must not be other refs to
+     * aObject in memory, or in the serialization.
+     */
+    void writeSingleRefObject(in nsISupports aObject);
+
+    /**
+     * Write the object referenced by an interface pointer at aObject that
+     * inherits from a non-primary nsISupports, i.e., a reference to one of
+     * the multiply inherited interfaces derived from an nsISupports other
+     * than the root or XPCOM-identity nsISupports; or a reference to an
+     * inner object in the case of true XPCOM aggregation.  aIID identifies
+     * this interface.
+     */
+    void writeCompoundObject(in nsISupports aObject,
+                             in nsIIDRef aIID,
+                             in boolean aIsStrongRef);
+
+    void writeID(in nsIDRef aID);
+
+    /**
+     * Optimized serialization support -- see nsIStreamBufferAccess.idl.
+     */
+    [notxpcom] charPtr getBuffer(in uint32_t aLength, in uint32_t aAlignMask);
+    [notxpcom] void    putBuffer(in charPtr aBuffer, in uint32_t aLength);
+};
+
+%{C++
+already_AddRefed<nsIObjectOutputStream>
+NS_NewObjectOutputStream(nsIOutputStream* aOutputStream);
+
+inline nsresult
+NS_WriteOptionalObject(nsIObjectOutputStream* aStream, nsISupports* aObject,
+                       bool aIsStrongRef)
+{
+    bool nonnull = (aObject != nullptr);
+    nsresult rv = aStream->WriteBoolean(nonnull);
+    if (NS_SUCCEEDED(rv) && nonnull)
+        rv = aStream->WriteObject(aObject, aIsStrongRef);
+    return rv;
+}
+
+inline nsresult
+NS_WriteOptionalSingleRefObject(nsIObjectOutputStream* aStream,
+                                nsISupports* aObject)
+{
+    bool nonnull = (aObject != nullptr);
+    nsresult rv = aStream->WriteBoolean(nonnull);
+    if (NS_SUCCEEDED(rv) && nonnull)
+        rv = aStream->WriteSingleRefObject(aObject);
+    return rv;
+}
+
+inline nsresult
+NS_WriteOptionalCompoundObject(nsIObjectOutputStream* aStream,
+                               nsISupports* aObject,
+                               const nsIID& aIID,
+                               bool aIsStrongRef)
+{
+    bool nonnull = (aObject != nullptr);
+    nsresult rv = aStream->WriteBoolean(nonnull);
+    if (NS_SUCCEEDED(rv) && nonnull)
+        rv = aStream->WriteCompoundObject(aObject, aIID, aIsStrongRef);
+    return rv;
+}
+
+%}
diff --git a/xpcom/io/nsIOutputStream.idl b/xpcom/io/nsIOutputStream.idl
new file mode 100644
index 0000000000..ffe9a5ffed
--- /dev/null
+++ b/xpcom/io/nsIOutputStream.idl
@@ -0,0 +1,164 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsIOutputStream;
+interface nsIInputStream;
+
+%{C++
+/**
+ * The signature for the reader function passed to WriteSegments. This
+ * is the "provider" of data that gets written into the stream's buffer.
+ *
+ * @param aOutStream stream being written to
+ * @param aClosure opaque parameter passed to WriteSegments
+ * @param aToSegment pointer to memory owned by the output stream
+ * @param aFromOffset amount already written (since WriteSegments was called)
+ * @param aCount length of toSegment
+ * @param aReadCount number of bytes written
+ *
+ * Implementers should return the following:
+ *
+ * @throws <any-error> if not interested in providing any data
+ *
+ * Errors are never passed to the caller of WriteSegments.
+ */
+typedef nsresult (*nsReadSegmentFun)(nsIOutputStream *aOutStream,
+                                     void *aClosure,
+                                     char *aToSegment,
+                                     uint32_t aFromOffset,
+                                     uint32_t aCount,
+                                     uint32_t *aReadCount);
+%}
+
+native nsReadSegmentFun(nsReadSegmentFun);
+
+/**
+ * nsIOutputStream
+ *
+ * An interface describing a writable stream of data.  An output stream may be
+ * "blocking" or "non-blocking" (see the IsNonBlocking method).  A blocking
+ * output stream may suspend the calling thread in order to satisfy a call to
+ * Close, Flush, Write, WriteFrom, or WriteSegments.  A non-blocking output
+ * stream, on the other hand, must not block the calling thread of execution.
+ *
+ * NOTE: blocking output streams are often written to on a background thread to
+ * avoid locking up the main application thread.  For this reason, it is
+ * generally the case that a blocking output stream should be implemented using
+ * thread- safe AddRef and Release.
+ */
+[scriptable, builtinclass, uuid(0d0acd2a-61b4-11d4-9877-00c04fa0cf4a)]
+interface nsIOutputStream : nsISupports
+{
+    /**
+     * Close the stream. Forces the output stream to flush any buffered data.
+     * Any subsequent calls to StreamStatus should throw NS_BASE_STREAM_CLOSED.
+     * Succeeds without effect if already closed.
+     *
+     * @throws NS_BASE_STREAM_WOULD_BLOCK if unable to flush without blocking
+     *   the calling thread (non-blocking mode only)
+     */
+    void close();
+
+    /**
+     * Flush the stream.
+     *
+     * @throws NS_BASE_STREAM_WOULD_BLOCK if unable to flush without blocking
+     *   the calling thread (non-blocking mode only)
+     */
+    void flush();
+
+    /**
+     * Check the current status of the stream.  A stream that is closed will
+     * throw an exception when this method is called.  That enables the caller
+     * to know the condition of the stream before attempting to write into it.
+     *
+     * This method will not throw NS_BASE_STREAM_WOULD_BLOCK, even if the stream
+     * is a non-blocking stream with no available space. A non-blocking stream
+     * which has not been closed, but has no available room should return NS_OK.
+     *
+     * NOTE: This method should not block the calling thread (e.g. to query the
+     * state of a file descriptor), even when called on a blocking stream.
+     *
+     * @throws NS_BASE_STREAM_CLOSED if the stream closed normally
+     * @throws <other-error> if the stream closed with a different status
+     */
+    void streamStatus();
+
+    /**
+     * Write data into the stream.
+     *
+     * @param aBuf the buffer containing the data to be written
+     * @param aCount the maximum number of bytes to be written
+     *
+     * @return number of bytes written (may be less than aCount)
+     *
+     * @throws NS_BASE_STREAM_WOULD_BLOCK if writing to the output stream would
+     *   block the calling thread (non-blocking mode only)
+     * @throws <other-error> on failure
+     */
+    unsigned long write(in string aBuf, in unsigned long aCount);
+
+    /**
+     * Writes data into the stream from an input stream.
+     *
+     * @param aFromStream the stream containing the data to be written
+     * @param aCount the maximum number of bytes to be written
+     *
+     * @return number of bytes written (may be less than aCount)
+     *
+     * @throws NS_BASE_STREAM_WOULD_BLOCK if writing to the output stream would
+     *    block the calling thread (non-blocking mode only). This failure
+     *    means no bytes were transferred.
+     * @throws <other-error> on failure
+     *
+     * NOTE: This method is defined by this interface in order to allow the
+     * output stream to efficiently copy the data from the input stream into
+     * its internal buffer (if any). If this method was provided as an external
+     * facility, a separate char* buffer would need to be used in order to call
+     * the output stream's other Write method.
+     */
+    unsigned long writeFrom(in nsIInputStream aFromStream,
+                            in unsigned long aCount);
+
+    /**
+     * Low-level write method that has access to the stream's underlying buffer.
+     * The reader function may be called multiple times for segmented buffers.
+     * WriteSegments is expected to keep calling the reader until either there
+     * is nothing left to write or the reader returns an error.  WriteSegments
+     * should not call the reader with zero bytes to provide.
+     *
+     * @param aReader the "provider" of the data to be written
+     * @param aClosure opaque parameter passed to reader
+     * @param aCount the maximum number of bytes to be written
+     *
+     * @return number of bytes written (may be less than aCount)
+     *
+     * @throws NS_BASE_STREAM_WOULD_BLOCK if writing to the output stream would
+     *    block the calling thread (non-blocking mode only). This failure
+     *    means no bytes were transferred.
+     * @throws NS_ERROR_NOT_IMPLEMENTED if the stream has no underlying buffer
+     * @throws <other-error> on failure
+     *
+     * NOTE: this function may be unimplemented if a stream has no underlying
+     * buffer (e.g., socket output stream).
+     */
+    [noscript] unsigned long writeSegments(in nsReadSegmentFun aReader,
+                                           in voidPtr aClosure,
+                                           in unsigned long aCount);
+
+    /**
+     * @return true if stream is non-blocking
+     *
+     * NOTE: writing to a blocking output stream will block the calling thread
+     * until all given data can be consumed by the stream.
+     *
+     * NOTE: a non-blocking output stream may implement nsIAsyncOutputStream to
+     * provide consumers with a way to wait for the stream to accept more data
+     * once its write method is unable to accept any data without blocking.
+     */
+    boolean isNonBlocking();
+};
diff --git a/xpcom/io/nsIPipe.idl b/xpcom/io/nsIPipe.idl
new file mode 100644
index 0000000000..cb5a035a32
--- /dev/null
+++ b/xpcom/io/nsIPipe.idl
@@ -0,0 +1,171 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsIAsyncInputStream;
+interface nsIAsyncOutputStream;
+
+/**
+ * nsIPipe represents an in-process buffer that can be read using nsIInputStream
+ * and written using nsIOutputStream.  The reader and writer of a pipe do not
+ * have to be on the same thread.  As a result, the pipe is an ideal mechanism
+ * to bridge data exchange between two threads.  For example, a worker thread
+ * might write data to a pipe from which the main thread will read.
+ *
+ * Each end of the pipe can be either blocking or non-blocking.  Recall that a
+ * non-blocking stream will return NS_BASE_STREAM_WOULD_BLOCK if it cannot be
+ * read or written to without blocking the calling thread.  For example, if you
+ * try to read from an empty pipe that has not yet been closed, then if that
+ * pipe's input end is non-blocking, then the read call will fail immediately
+ * with NS_BASE_STREAM_WOULD_BLOCK as the error condition.  However, if that
+ * pipe's input end is blocking, then the read call will not return until the
+ * pipe has data or until the pipe is closed.  This example presumes that the
+ * pipe is being filled asynchronously on some background thread.
+ *
+ * The pipe supports nsIAsyncInputStream and nsIAsyncOutputStream, which give
+ * the user of a non-blocking pipe the ability to wait for the pipe to become
+ * ready again.  For example, in the case of an empty non-blocking pipe, the
+ * user can call AsyncWait on the input end of the pipe to be notified when
+ * the pipe has data to read (or when the pipe becomes closed).
+ *
+ * NS_NewPipe2 and NS_NewPipe provide convenient pipe constructors.  In most
+ * cases nsIPipe is not actually used.  It is usually enough to just get
+ * references to the pipe's input and output end.  In which case, the pipe is
+ * automatically closed when the respective pipe ends are released.
+ */
+[scriptable, uuid(25d0de93-685e-4ea4-95d3-d884e31df63c)]
+interface nsIPipe : nsISupports
+{
+    /**
+     * initialize this pipe
+     *
+     * @param nonBlockingInput
+     *        true specifies non-blocking input stream behavior
+     * @param nonBlockingOutput
+     *        true specifies non-blocking output stream behavior
+     * @param segmentSize
+     *        specifies the segment size in bytes (pass 0 to use default value)
+     * @param segmentCount
+     *        specifies the max number of segments (pass 0 to use default
+     *        value).   Passing UINT32_MAX here causes the pipe to have
+     *        "infinite" space.  This mode can be useful in some cases, but
+     *        should always be used with caution.  The default value for this
+     *        parameter is a finite value.
+     */
+    [must_use] void init(in boolean nonBlockingInput,
+                         in boolean nonBlockingOutput,
+                         in unsigned long segmentSize,
+                         in unsigned long segmentCount);
+
+    /**
+     * The pipe's input end, which also implements nsISearchableInputStream.
+     * Getting fails if the pipe hasn't been initialized.
+     */
+    [must_use] readonly attribute nsIAsyncInputStream inputStream;
+
+    /**
+     * The pipe's output end. Getting fails if the pipe hasn't been
+     * initialized.
+     */
+    [must_use] readonly attribute nsIAsyncOutputStream outputStream;
+};
+
+/**
+ * XXX this interface doesn't really belong in here.  It is here because
+ * currently nsPipeInputStream is the only implementation of this interface.
+ */
+[scriptable, uuid(8C39EF62-F7C9-11d4-98F5-001083010E9B)]
+interface nsISearchableInputStream : nsISupports
+{
+    /**
+     * Searches for a string in the input stream. Since the stream has a notion
+     * of EOF, it is possible that the string may at some time be in the
+     * buffer, but is is not currently found up to some offset. Consequently,
+     * both the found and not found cases return an offset:
+     *    if found, return offset where it was found
+     *    if not found, return offset of the first byte not searched
+     * In the case the stream is at EOF and the string is not found, the first
+     * byte not searched will correspond to the length of the buffer.
+     */
+    void search(in string forString,
+                in boolean ignoreCase,
+                out boolean found,
+                out unsigned long offsetSearchedTo);
+};
+
+%{C++
+
+class nsIInputStream;
+class nsIOutputStream;
+
+/**
+ * NS_NewPipe2
+ *
+ * This function supersedes NS_NewPipe.  It differs from NS_NewPipe in two
+ * major ways:
+ *  (1) returns nsIAsyncInputStream and nsIAsyncOutputStream, so it is
+ *      not necessary to QI in order to access these interfaces.
+ *  (2) the size of the pipe is determined by the number of segments
+ *      times the size of each segment.
+ *
+ * @param pipeIn
+ *        resulting input end of the pipe
+ * @param pipeOut
+ *        resulting output end of the pipe
+ * @param nonBlockingInput
+ *        true specifies non-blocking input stream behavior
+ * @param nonBlockingOutput
+ *        true specifies non-blocking output stream behavior
+ * @param segmentSize
+ *        specifies the segment size in bytes (pass 0 to use default value)
+ * @param segmentCount
+ *        specifies the max number of segments (pass 0 to use default value)
+ *        passing UINT32_MAX here causes the pipe to have "infinite" space.
+ *        this mode can be useful in some cases, but should always be used with
+ *        caution.  the default value for this parameter is a finite value.
+ */
+extern void
+NS_NewPipe2(nsIAsyncInputStream **pipeIn,
+            nsIAsyncOutputStream **pipeOut,
+            bool nonBlockingInput = false,
+            bool nonBlockingOutput = false,
+            uint32_t segmentSize = 0,
+            uint32_t segmentCount = 0);
+
+/**
+ * NS_NewPipe
+ *
+ * Preserved for backwards compatibility.  Plus, this interface is more
+ * amiable in certain contexts (e.g., when you don't need the pipe's async
+ * capabilities).
+ *
+ * @param pipeIn
+ *        resulting input end of the pipe
+ * @param pipeOut
+ *        resulting output end of the pipe
+ * @param segmentSize
+ *        specifies the segment size in bytes (pass 0 to use default value)
+ * @param maxSize
+ *        specifies the max size of the pipe (pass 0 to use default value)
+ *        number of segments is maxSize / segmentSize, and maxSize must be a
+ *        multiple of segmentSize.  passing UINT32_MAX here causes the
+ *        pipe to have "infinite" space.  this mode can be useful in some
+ *        cases, but should always be used with caution.  the default value
+ *        for this parameter is a finite value.
+ * @param nonBlockingInput
+ *        true specifies non-blocking input stream behavior
+ * @param nonBlockingOutput
+ *        true specifies non-blocking output stream behavior
+ */
+extern void
+NS_NewPipe(nsIInputStream **pipeIn,
+           nsIOutputStream **pipeOut,
+           uint32_t segmentSize = 0,
+           uint32_t maxSize = 0,
+           bool nonBlockingInput = false,
+           bool nonBlockingOutput = false);
+
+%}
diff --git a/xpcom/io/nsIRandomAccessStream.idl b/xpcom/io/nsIRandomAccessStream.idl
new file mode 100644
index 0000000000..20421def17
--- /dev/null
+++ b/xpcom/io/nsIRandomAccessStream.idl
@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+#include "nsISeekableStream.idl"
+
+interface nsIInputStream;
+interface nsIInterfaceRequestor;
+interface nsIOutputStream;
+
+%{C++
+namespace mozilla::ipc {
+class RandomAccessStreamParams;
+}  // namespace mozilla::ipc
+%}
+
+native RandomAccessStreamParams(mozilla::ipc::RandomAccessStreamParams);
+[ref] native RandomAccessStreamParamsRef(mozilla::ipc::RandomAccessStreamParams);
+
+/**
+ * nsIRandomAccessStream
+ *
+ * An interface which supports both reading and writing to a storage starting
+ * at the current offset. Both the input stream and the output stream share the
+ * offset in the stream. Read operations invoked on the input stream start at
+ * the offset and advance it past the bytes read. Write operations invoked on
+ * the output stream start the offset and advance it past the bytes written.
+ * The offset can be set to an arbitrary value prior reading or writting. Each
+ * call to getInputStream or getOutputStream always returns the same object,
+ * rather than creating a new stream. It's recommended for objects implementing
+ * this interface to also implement nsIInputStream and nsIOutputStream, so they
+ * can be easilly used with e.g. NS_AsyncCopy.
+ */
+[scriptable, builtinclass, uuid(9b5904a8-886a-420f-a1d8-847de8ffc133)]
+interface nsIRandomAccessStream : nsISeekableStream
+{
+  /**
+   * This method always returns the same object.
+   */
+  nsIInputStream getInputStream();
+
+  /**
+   * This method always returns the same object.
+   */
+  nsIOutputStream getOutputStream();
+
+  /**
+   * Like getInputStream but infallible.
+   */
+  [notxpcom, nostdcall] nsIInputStream inputStream();
+
+  /**
+   * Like getOutputStream but infallible.
+   */
+  [notxpcom, nostdcall] nsIOutputStream outputStream();
+
+  [notxpcom, nostdcall] RandomAccessStreamParams serialize(in nsIInterfaceRequestor aCallbacks);
+
+  [notxpcom, nostdcall] bool deserialize(inout RandomAccessStreamParamsRef params);
+};
diff --git a/xpcom/io/nsISafeOutputStream.idl b/xpcom/io/nsISafeOutputStream.idl
new file mode 100644
index 0000000000..dae78b554a
--- /dev/null
+++ b/xpcom/io/nsISafeOutputStream.idl
@@ -0,0 +1,39 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+/**
+ * This interface provides a mechanism to control an output stream
+ * that takes care not to overwrite an existing target until it is known
+ * that all writes to the destination succeeded.
+ *
+ * An object that supports this interface is intended to also support
+ * nsIOutputStream.
+ *
+ * For example, a file output stream that supports this interface writes to
+ * a temporary file, and moves it over the original file when |finish| is
+ * called only if the stream can be successfully closed and all writes
+ * succeeded.  If |finish| is called but something went wrong during
+ * writing, it will delete the temporary file and not touch the original.
+ * If the stream is closed by calling |close| directly, or the stream
+ * goes away, the original file will not be overwritten, and the temporary
+ * file will be deleted.
+ *
+ * Currently, this interface is implemented only for file output streams.
+ */
+[scriptable, uuid(5f914307-5c34-4e1f-8e32-ec749d25b27a)]
+interface nsISafeOutputStream : nsISupports
+{
+    /**
+     * Call this method to close the stream and cause the original target
+     * to be overwritten. Note: if any call to |write| failed to write out
+     * all of the data given to it, then calling this method will |close| the
+     * stream and return failure. Further, if closing the stream fails, this
+     * method will return failure. The original target will be overwritten only
+     * if all calls to |write| succeeded and the stream was successfully closed.
+     */
+    void finish();
+};
diff --git a/xpcom/io/nsIScriptableBase64Encoder.idl b/xpcom/io/nsIScriptableBase64Encoder.idl
new file mode 100644
index 0000000000..6414518056
--- /dev/null
+++ b/xpcom/io/nsIScriptableBase64Encoder.idl
@@ -0,0 +1,32 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsIInputStream;
+
+/**
+ * nsIScriptableBase64Encoder efficiently encodes the contents
+ * of a nsIInputStream to a Base64 string.  This avoids the need
+ * to read the entire stream into a buffer, and only then do the
+ * Base64 encoding.
+ *
+ *  If you already have a buffer full of data, you should use
+ *  btoa instead!
+ */
+[scriptable, uuid(9479c864-d1f9-45ab-b7b9-28b907bd2ba9)]
+interface nsIScriptableBase64Encoder : nsISupports
+{
+  /**
+   *  These methods take an nsIInputStream and return a narrow or wide
+   *  string with the contents of the nsIInputStream base64 encoded.
+   *
+   *  The stream passed in must support ReadSegments and must not be
+   *  a non-blocking stream that will return NS_BASE_STREAM_WOULD_BLOCK.
+   *  If either of these restrictions are violated we will abort.
+   */
+  ACString encodeToCString(in nsIInputStream stream, in unsigned long length);
+  AString encodeToString(in nsIInputStream stream, in unsigned long length);
+};
diff --git a/xpcom/io/nsIScriptableInputStream.idl b/xpcom/io/nsIScriptableInputStream.idl
new file mode 100644
index 0000000000..7c18274055
--- /dev/null
+++ b/xpcom/io/nsIScriptableInputStream.idl
@@ -0,0 +1,67 @@
+/* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsIInputStream;
+
+/**
+ * nsIScriptableInputStream provides scriptable access to an nsIInputStream
+ * instance.
+ */
+[scriptable, uuid(3fce9015-472a-4080-ac3e-cd875dbe361e)]
+interface nsIScriptableInputStream : nsISupports
+{
+    /**
+     * Closes the stream.
+     */
+    void close();
+
+    /**
+     * Wrap the given nsIInputStream with this nsIScriptableInputStream.
+     *
+     * @param aInputStream parameter providing the stream to wrap
+     */
+    void init(in nsIInputStream aInputStream);
+
+    /**
+     * Return the number of bytes currently available in the stream
+     *
+     * @return the number of bytes
+     *
+     * @throws NS_BASE_STREAM_CLOSED if called after the stream has been closed
+     */
+    unsigned long long available();
+
+    /**
+     * Read data from the stream.
+     *
+     * WARNING: If the data contains a null byte, then this method will return
+     * a truncated string.
+     *
+     * @param aCount the maximum number of bytes to read
+     *
+     * @return the data, which will be an empty string if the stream is at EOF.
+     *
+     * @throws NS_BASE_STREAM_CLOSED if called after the stream has been closed
+     * @throws NS_ERROR_NOT_INITIALIZED if init was not called
+     */
+    string read(in unsigned long aCount);
+
+    /**
+     * Read data from the stream, including NULL bytes.
+     *
+     * @param aCount the maximum number of bytes to read.
+     *
+     * @return the data from the stream, which will be an empty string if EOF
+     *         has been reached.
+     *
+     * @throws NS_BASE_STREAM_WOULD_BLOCK if reading from the input stream
+     *         would block the calling thread (non-blocking mode only).
+     * @throws NS_ERROR_FAILURE if there are not enough bytes available to read
+     *         aCount amount of data.
+     */
+    ACString readBytes(in unsigned long aCount);
+};
diff --git a/xpcom/io/nsISeekableStream.idl b/xpcom/io/nsISeekableStream.idl
new file mode 100644
index 0000000000..b12a7f9baf
--- /dev/null
+++ b/xpcom/io/nsISeekableStream.idl
@@ -0,0 +1,65 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+
+#include "nsITellableStream.idl"
+
+/*
+ * nsISeekableStream
+ *
+ * Note that a stream might not implement all methods (e.g., a readonly stream
+ * won't implement setEOF)
+ */
+
+#include "nsISupports.idl"
+
+[scriptable, uuid(8429d350-1040-4661-8b71-f2a6ba455980)]
+interface nsISeekableStream : nsITellableStream
+{
+    /*
+     * Sets the stream pointer to the value of the 'offset' parameter
+     */
+    const int32_t NS_SEEK_SET = 0;
+
+    /*
+     * Sets the stream pointer to its current location plus the value
+     * of the offset parameter.
+     */
+    const int32_t NS_SEEK_CUR = 1;
+
+    /*
+     * Sets the stream pointer to the size of the stream plus the value
+     * of the offset parameter.
+     */
+    const int32_t NS_SEEK_END = 2;
+
+    /**
+     *  seek
+     *
+     *  This method moves the stream offset of the steam implementing this
+     *  interface.
+     *
+     *   @param whence specifies how to interpret the 'offset' parameter in
+     *                 setting the stream offset associated with the implementing
+     *                 stream.
+     *
+     *   @param offset specifies a value, in bytes, that is used in conjunction
+     *                 with the 'whence' parameter to set the stream offset of the
+     *                 implementing stream.  A negative value causes seeking in
+     *                 the reverse direction.
+     *
+     *   @throws NS_BASE_STREAM_CLOSED if called on a closed stream.
+     */
+    void seek(in long whence, in long long offset);
+
+    /**
+     *  setEOF
+     *
+     *  This method truncates the stream at the current offset.
+     *
+     *   @throws NS_BASE_STREAM_CLOSED if called on a closed stream.
+     */
+    void setEOF();
+};
diff --git a/xpcom/io/nsIStorageStream.idl b/xpcom/io/nsIStorageStream.idl
new file mode 100644
index 0000000000..c2792f5002
--- /dev/null
+++ b/xpcom/io/nsIStorageStream.idl
@@ -0,0 +1,69 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsIInputStream;
+interface nsIOutputStream;
+
+/**
+ * The nsIStorageStream interface maintains an internal data buffer that can be
+ * filled using a single output stream.  One or more independent input streams
+ * can be created to read the data from the buffer non-destructively.
+ */
+
+[scriptable, uuid(44a200fe-6c2b-4b41-b4e3-63e8c14e7c0d)]
+interface nsIStorageStream : nsISupports
+{
+    /**
+     *
+     * Initialize the stream, setting up the amount of space that will be
+     * allocated for the stream's backing-store.
+     *
+     * @param segmentSize
+     *        Size of each segment. Must be a power of two.
+     * @param maxSize
+     *        Maximum total size of this stream. length will always be less
+     *        than or equal to this value. Passing UINT32_MAX is safe.
+     */
+    void init(in uint32_t segmentSize, in uint32_t maxSize);
+
+    /**
+     * Get a reference to the one and only output stream for this instance.
+     * The zero-based startPosition argument is used is used to set the initial
+     * write cursor position.  The startPosition cannot be set larger than the
+     * current buffer length.  Calling this method has the side-effect of
+     * truncating the internal buffer to startPosition bytes.
+     */
+    nsIOutputStream getOutputStream(in int32_t startPosition);
+
+    /**
+     * Create a new input stream to read data (written by the singleton output
+     * stream) from the internal buffer.  Multiple, independent input streams
+     * can be created.
+     */
+    nsIInputStream newInputStream(in int32_t startPosition);
+
+    /**
+     * The length attribute indicates the total number of bytes stored in the
+     * nsIStorageStream internal buffer, regardless of any consumption by input
+     * streams.  Assigning to the length field can be used to truncate the
+     * buffer data, but can not be used when either the instance's output
+     * stream is in use.
+     *
+     * @See #writeInProgress */
+    attribute uint32_t length;
+
+    /**
+     * True, when output stream has not yet been Close'ed
+     */
+    readonly attribute boolean writeInProgress;
+};
+
+%{C++
+// Factory method
+nsresult
+NS_NewStorageStream(uint32_t segmentSize, uint32_t maxSize, nsIStorageStream **result);
+%}
diff --git a/xpcom/io/nsIStreamBufferAccess.idl b/xpcom/io/nsIStreamBufferAccess.idl
new file mode 100644
index 0000000000..c0883a439b
--- /dev/null
+++ b/xpcom/io/nsIStreamBufferAccess.idl
@@ -0,0 +1,88 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+/**
+ * An interface for access to a buffering stream implementation's underlying
+ * memory buffer.
+ *
+ * Stream implementations that QueryInterface to nsIStreamBufferAccess must
+ * ensure that all buffers are aligned on the most restrictive type size for
+ * the current architecture (e.g., sizeof(double) for RISCy CPUs).  malloc(3)
+ * satisfies this requirement.
+ */
+[scriptable, builtinclass, uuid(ac923b72-ac87-4892-ac7a-ca385d429435)]
+interface nsIStreamBufferAccess : nsISupports
+{
+    /**
+     * Get access to a contiguous, aligned run of bytes in the stream's buffer.
+     * Exactly one successful getBuffer call must occur before a putBuffer call
+     * taking the non-null pointer returned by the successful getBuffer.
+     *
+     * The run of bytes are the next bytes (modulo alignment padding) to read
+     * for an input stream, and the next bytes (modulo alignment padding) to
+     * store before (eventually) writing buffered data to an output stream.
+     * There can be space beyond this run of bytes in the buffer for further
+     * accesses before the fill or flush point is reached.
+     *
+     * @param aLength
+     *    Count of contiguous bytes requested at the address A that satisfies
+     *    (A & aAlignMask) == 0 in the buffer, starting from the current stream
+     *    position, mapped to a buffer address B.  The stream implementation
+     *    must pad from B to A by skipping bytes (if input stream) or storing
+     *    zero bytes (if output stream).
+     *
+     * @param aAlignMask
+     *    Bit-mask computed by subtracting 1 from the power-of-two alignment
+     *    modulus (e.g., 3 or sizeof(uint32_t)-1 for uint32_t alignment).
+     *
+     * @return
+     *    The aligned pointer to aLength bytes in the buffer, or null if the
+     *    buffer has no room for aLength bytes starting at the next address A
+     *    after the current position that satisfies (A & aAlignMask) == 0.
+     */
+    [notxpcom,noscript] charPtr getBuffer(in uint32_t aLength, in uint32_t aAlignMask);
+
+    /**
+     * Relinquish access to the stream's buffer, filling if at end of an input
+     * buffer, flushing if completing an output buffer.  After a getBuffer call
+     * that returns non-null, putBuffer must be called.
+     *
+     * @param aBuffer
+     *    A non-null pointer returned by getBuffer on the same stream buffer
+     *    access object.
+     *
+     * @param aLength
+     *    The same count of contiguous bytes passed to the getBuffer call that
+     *    returned aBuffer.
+     */
+    [notxpcom,noscript] void putBuffer(in charPtr aBuffer, in uint32_t aLength);
+
+    /**
+     * Disable and enable buffering on the stream implementing this interface.
+     * DisableBuffering flushes an output stream's buffer, and invalidates an
+     * input stream's buffer.
+     */
+    void disableBuffering();
+    void enableBuffering();
+
+    /**
+     * The underlying, unbuffered input or output stream.
+     */
+    readonly attribute nsISupports unbufferedStream;
+};
+
+%{C++
+
+/**
+ * These macros get and put a buffer given either an sba parameter that may
+ * point to an object implementing nsIStreamBufferAccess, nsIObjectInputStream,
+ * or nsIObjectOutputStream.
+ */
+#define NS_GET_BUFFER(sba,n,a)  ((sba)->GetBuffer(n, a))
+#define NS_PUT_BUFFER(sba,p,n)  ((sba)->PutBuffer(p, n))
+
+%}
diff --git a/xpcom/io/nsIStringStream.idl b/xpcom/io/nsIStringStream.idl
new file mode 100644
index 0000000000..3e084cbe7f
--- /dev/null
+++ b/xpcom/io/nsIStringStream.idl
@@ -0,0 +1,92 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIInputStream.idl"
+
+%{C++
+#include "mozilla/MemoryReporting.h"
+
+namespace mozilla {
+class StreamBufferSource;
+}  // namespace mozilla
+%}
+
+native MallocSizeOf(mozilla::MallocSizeOf);
+[ptr] native StreamBufferSource(mozilla::StreamBufferSource);
+
+/**
+ * nsIStringInputStream
+ *
+ * Provides scriptable and specialized C++-only methods for initializing a
+ * nsIInputStream implementation with a simple character array.
+ */
+[scriptable, builtinclass, uuid(450cd2d4-f0fd-424d-b365-b1251f80fd53)]
+interface nsIStringInputStream : nsIInputStream
+{
+    /**
+     * SetData - assign data to the input stream (copied on assignment).
+     *
+     * @param data    - stream data
+     * @param dataLen - stream data length (-1 if length should be computed)
+     *
+     * NOTE: C++ code should consider using AdoptData or ShareData to avoid
+     * making an extra copy of the stream data.
+     *
+     * NOTE: For JS callers, the given data must not contain null characters
+     * (other than a null terminator) because a null character in the middle of
+     * the data string will be seen as a terminator when the data is converted
+     * from a JS string to a C++ character array.
+     */
+    void setData(in string data, in long dataLen);
+
+    /**
+     * SetUTF8Data - encode input data to UTF-8 and assign it to the input
+     * stream.
+     *
+     * @param data    - stream data
+     *
+     * NOTE: This method is meant to be used by JS callers,
+     */
+    void setUTF8Data(in AUTF8String data);
+
+    /**
+     * NOTE: the following methods are designed to give C++ code added control
+     * over the ownership and lifetime of the stream data.  Use with care :-)
+     */
+
+    /**
+     * AdoptData - assign data to the input stream.  the input stream takes
+     * ownership of the given data buffer and will free it when
+     * the input stream is destroyed.
+     *
+     * @param data      - stream data
+     * @param dataLen   - stream data length (-1 if length should be computed)
+     */
+    [noscript] void adoptData(in charPtr data, in long dataLen);
+
+    /**
+     * ShareData - assign data to the input stream.  the input stream references
+     * the given data buffer until the input stream is destroyed.  the given
+     * data buffer must outlive the input stream.
+     *
+     * @param data      - stream data
+     * @param dataLen   - stream data length (-1 if length should be computed)
+     */
+    [noscript] void shareData(in string data, in long dataLen);
+
+    /**
+     * SetDataSource - assign data to the input stream.  the input stream holds
+     * a strong reference to the given data buffer until it is destroyed.
+     *
+     * @param source    - stream data source
+     */
+    [noscript] void setDataSource(in StreamBufferSource source);
+
+    [noscript, notxpcom]
+    size_t SizeOfIncludingThisIfUnshared(in MallocSizeOf aMallocSizeOf);
+
+    [noscript, notxpcom]
+    size_t SizeOfIncludingThisEvenIfShared(in MallocSizeOf aMallocSizeOf);
+};
diff --git a/xpcom/io/nsITellableStream.idl b/xpcom/io/nsITellableStream.idl
new file mode 100644
index 0000000000..c2cfaba0de
--- /dev/null
+++ b/xpcom/io/nsITellableStream.idl
@@ -0,0 +1,34 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+
+/*
+ * nsITellableStream
+ *
+ * This class is separate from nsISeekableStream in order to let streams to
+ * implement ::Tell() without implementing the whole nsISeekableStream
+ * interface. Callers can QI the stream to know what is implemented. This is
+ * mainly done for nsPipeInputStream.
+ *
+ *
+ * Implementing this interface, streams are able to expose the current offset
+ * via ::tell().
+ */
+
+#include "nsISupports.idl"
+
+[scriptable, uuid(ee942946-4538-45d2-bf05-ffdbf5932621)]
+interface nsITellableStream : nsISupports
+{
+    /**
+     *  tell
+     *
+     *  This method reports the current offset, in bytes, from the start of the
+     *  stream.
+     *
+     *   @throws NS_BASE_STREAM_CLOSED if called on a closed stream.
+     */
+    long long tell();
+};
diff --git a/xpcom/io/nsIUnicharInputStream.idl b/xpcom/io/nsIUnicharInputStream.idl
new file mode 100644
index 0000000000..3ae467cc83
--- /dev/null
+++ b/xpcom/io/nsIUnicharInputStream.idl
@@ -0,0 +1,97 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsIUnicharInputStream;
+interface nsIInputStream;
+
+%{C++
+/**
+ * The signature of the writer function passed to ReadSegments. This
+ * is the "consumer" of data that gets read from the stream's buffer.
+ *
+ * @param aInStream stream being read
+ * @param aClosure opaque parameter passed to ReadSegments
+ * @param aFromSegment pointer to memory owned by the input stream
+ * @param aToOffset number of UTF-16 code units already read
+ *                  (since ReadSegments was called)
+ * @param aCount length of fromSegment
+ * @param aWriteCount number of UTF-16 code units read
+ *
+ * Implementers should return the following:
+ *
+ * @throws <any-error> if not interested in consuming any data
+ *
+ * Errors are never passed to the caller of ReadSegments.
+ *
+ * NOTE: returning NS_OK and (*aWriteCount = 0) has undefined behavior.
+ */
+typedef nsresult (*nsWriteUnicharSegmentFun)(nsIUnicharInputStream *aInStream,
+                                             void *aClosure,
+                                             const char16_t *aFromSegment,
+                                             uint32_t aToOffset,
+                                             uint32_t aCount,
+                                             uint32_t *aWriteCount);
+%}
+native nsWriteUnicharSegmentFun(nsWriteUnicharSegmentFun);
+
+/**
+ * Abstract UTF-16 input stream
+ * @see nsIInputStream
+ */
+[scriptable, uuid(d5e3bd80-6723-4b92-b0c9-22f6162fd94f)]
+interface nsIUnicharInputStream : nsISupports {
+  /**
+   * Reads into a caller-provided array.
+   *
+   * @return The number of utf-16 code units that were successfully read.
+   *         May be less than aCount, even if there is more data in the input
+   *         stream. A return value of 0 means EOF.
+   *
+   * @note To read more than 2^32 code units, call this method multiple times.
+   */
+  [noscript] unsigned long read([array, size_is(aCount)] in char16_t aBuf,
+                                in unsigned long aCount);
+
+  /**
+   * Low-level read method that has access to the stream's underlying buffer.
+   * The writer function may be called multiple times for segmented buffers.
+   * ReadSegments is expected to keep calling the writer until either there is
+   * nothing left to read or the writer returns an error.  ReadSegments should
+   * not call the writer with zero UTF-16 code units to consume.
+   *
+   * @param aWriter the "consumer" of the data to be read
+   * @param aClosure opaque parameter passed to writer
+   * @param aCount the maximum number of UTF-16 code units to be read
+   *
+   * @return number of UTF-16 code units read (may be less than aCount)
+   * @return 0 if reached end of file (or if aWriter refused to consume data)
+   *
+   * @throws NS_BASE_STREAM_WOULD_BLOCK if reading from the input stream would
+   *   block the calling thread (non-blocking mode only)
+   * @throws <other-error> on failure
+   *
+   * NOTE: this function may be unimplemented if a stream has no underlying
+   * buffer
+   */
+  [noscript] unsigned long readSegments(in nsWriteUnicharSegmentFun aWriter,
+                                        in voidPtr aClosure,
+                                        in unsigned long aCount);
+
+  /**
+   * Read into a string object.
+   *
+   * @param aCount The number of UTF-16 code units that should be read
+   * @return The number of UTF-16 code units that were read.
+   */
+  unsigned long readString(in unsigned long aCount, out AString aString);
+
+  /**
+   * Close the stream and free associated resources. This also closes the
+   * underlying stream, if any.
+   */
+  void close();
+};
diff --git a/xpcom/io/nsIUnicharLineInputStream.idl b/xpcom/io/nsIUnicharLineInputStream.idl
new file mode 100644
index 0000000000..0322c6a1eb
--- /dev/null
+++ b/xpcom/io/nsIUnicharLineInputStream.idl
@@ -0,0 +1,26 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+[scriptable, uuid(67f42475-ba80-40f8-ac0b-649c89230184)]
+interface nsIUnicharLineInputStream : nsISupports
+{
+  /**
+   * Read a single line from the stream, where a line is a
+   * possibly zero length sequence of characters terminated by a
+   * CR, LF, CRLF, LFCR, or eof.
+   * The line terminator is not returned.
+   * @retval false
+   *         End of file. This line is the last line of the file
+   *         (aLine is valid).
+   * @retval true
+   *         The file contains further lines.
+   * @note Do not mix readLine with other read functions.
+   *       Doing so can cause various problems and is not supported.
+   */
+  boolean readLine(out AString aLine);
+};
diff --git a/xpcom/io/nsIUnicharOutputStream.idl b/xpcom/io/nsIUnicharOutputStream.idl
new file mode 100644
index 0000000000..743f532e03
--- /dev/null
+++ b/xpcom/io/nsIUnicharOutputStream.idl
@@ -0,0 +1,45 @@
+/* vim:set expandtab ts=4 sw=4 sts=4 cin: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+/**
+ * An interface that allows writing unicode data.
+ */
+[scriptable, uuid(2d00b1bb-8b21-4a63-bcc6-7213f513ac2e)]
+interface nsIUnicharOutputStream : nsISupports
+{
+    /**
+     * Write a single character to the stream. When writing many characters,
+     * prefer the string-taking write method.
+     *
+     * @retval true The character was written successfully
+     * @retval false Not all bytes of the character could be written.
+     */
+    boolean write(in unsigned long aCount,
+                  [const, array, size_is(aCount)] in char16_t c);
+
+    /**
+     * Write a string to the stream.
+     *
+     * @retval true The string was written successfully
+     * @retval false Not all bytes of the string could be written.
+     */
+    boolean writeString(in AString str);
+
+    /**
+     * Flush the stream. This finishes the conversion and writes any bytes that
+     * finish the current byte sequence.
+     *
+     * It does NOT flush the underlying stream.
+     */
+    void flush();
+
+    /**
+     * Close the stream and free associated resources. This also closes the
+     * underlying stream.
+     */
+    void close();
+};
diff --git a/xpcom/io/nsInputStreamTee.cpp b/xpcom/io/nsInputStreamTee.cpp
new file mode 100644
index 0000000000..5b7a651350
--- /dev/null
+++ b/xpcom/io/nsInputStreamTee.cpp
@@ -0,0 +1,341 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <stdlib.h>
+#include "mozilla/Logging.h"
+
+#include "mozilla/Maybe.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/Attributes.h"
+#include "nsIInputStreamTee.h"
+#include "nsIInputStream.h"
+#include "nsIOutputStream.h"
+#include "nsCOMPtr.h"
+#include "nsIEventTarget.h"
+#include "nsThreadUtils.h"
+
+using namespace mozilla;
+
+#ifdef LOG
+#  undef LOG
+#endif
+
+static LazyLogModule sTeeLog("nsInputStreamTee");
+#define LOG(args) MOZ_LOG(sTeeLog, mozilla::LogLevel::Debug, args)
+
+class nsInputStreamTee final : public nsIInputStreamTee {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINPUTSTREAM
+  NS_DECL_NSIINPUTSTREAMTEE
+
+  nsInputStreamTee();
+  bool SinkIsValid();
+  void InvalidateSink();
+
+ private:
+  ~nsInputStreamTee() = default;
+
+  nsresult TeeSegment(const char* aBuf, uint32_t aCount);
+
+  static nsresult WriteSegmentFun(nsIInputStream*, void*, const char*, uint32_t,
+                                  uint32_t, uint32_t*);
+
+ private:
+  nsCOMPtr<nsIInputStream> mSource;
+  nsCOMPtr<nsIOutputStream> mSink;
+  nsCOMPtr<nsIEventTarget> mEventTarget;
+  nsWriteSegmentFun mWriter;  // for implementing ReadSegments
+  void* mClosure;             // for implementing ReadSegments
+  Maybe<Mutex> mLock;         // synchronize access to mSinkIsValid
+  bool mSinkIsValid;          // False if TeeWriteEvent fails
+};
+
+class nsInputStreamTeeWriteEvent : public Runnable {
+ public:
+  // aTee's lock is held across construction of this object
+  nsInputStreamTeeWriteEvent(const char* aBuf, uint32_t aCount,
+                             nsIOutputStream* aSink, nsInputStreamTee* aTee)
+      : mozilla::Runnable("nsInputStreamTeeWriteEvent") {
+    // copy the buffer - will be free'd by dtor
+    mBuf = (char*)malloc(aCount);
+    if (mBuf) {
+      memcpy(mBuf, (char*)aBuf, aCount);
+    }
+    mCount = aCount;
+    mSink = aSink;
+    bool isNonBlocking;
+    mSink->IsNonBlocking(&isNonBlocking);
+    NS_ASSERTION(isNonBlocking == false, "mSink is nonblocking");
+    mTee = aTee;
+  }
+
+  NS_IMETHOD Run() override {
+    if (!mBuf) {
+      NS_WARNING(
+          "nsInputStreamTeeWriteEvent::Run() "
+          "memory not allocated\n");
+      return NS_OK;
+    }
+    MOZ_ASSERT(mSink, "mSink is null!");
+
+    //  The output stream could have been invalidated between when
+    //  this event was dispatched and now, so check before writing.
+    if (!mTee->SinkIsValid()) {
+      return NS_OK;
+    }
+
+    LOG(
+        ("nsInputStreamTeeWriteEvent::Run() [%p]"
+         "will write %u bytes to %p\n",
+         this, mCount, mSink.get()));
+
+    uint32_t totalBytesWritten = 0;
+    while (mCount) {
+      nsresult rv;
+      uint32_t bytesWritten = 0;
+      rv = mSink->Write(mBuf + totalBytesWritten, mCount, &bytesWritten);
+      if (NS_FAILED(rv)) {
+        LOG(("nsInputStreamTeeWriteEvent::Run[%p] error %" PRIx32 " in writing",
+             this, static_cast<uint32_t>(rv)));
+        mTee->InvalidateSink();
+        break;
+      }
+      totalBytesWritten += bytesWritten;
+      NS_ASSERTION(bytesWritten <= mCount, "wrote too much");
+      mCount -= bytesWritten;
+    }
+    return NS_OK;
+  }
+
+ protected:
+  virtual ~nsInputStreamTeeWriteEvent() {
+    if (mBuf) {
+      free(mBuf);
+    }
+    mBuf = nullptr;
+  }
+
+ private:
+  char* mBuf;
+  uint32_t mCount;
+  nsCOMPtr<nsIOutputStream> mSink;
+  // back pointer to the tee that created this runnable
+  RefPtr<nsInputStreamTee> mTee;
+};
+
+nsInputStreamTee::nsInputStreamTee()
+    : mWriter(nullptr), mClosure(nullptr), mLock(), mSinkIsValid(true) {}
+
+bool nsInputStreamTee::SinkIsValid() {
+  MutexAutoLock lock(*mLock);
+  return mSinkIsValid;
+}
+
+void nsInputStreamTee::InvalidateSink() {
+  MutexAutoLock lock(*mLock);
+  mSinkIsValid = false;
+}
+
+nsresult nsInputStreamTee::TeeSegment(const char* aBuf, uint32_t aCount) {
+  if (!mSink) {
+    return NS_OK;  // nothing to do
+  }
+  if (mLock) {  // asynchronous case
+    NS_ASSERTION(mEventTarget, "mEventTarget is null, mLock is not null.");
+    if (!SinkIsValid()) {
+      return NS_OK;  // nothing to do
+    }
+    nsCOMPtr<nsIRunnable> event =
+        new nsInputStreamTeeWriteEvent(aBuf, aCount, mSink, this);
+    LOG(("nsInputStreamTee::TeeSegment [%p] dispatching write %u bytes\n", this,
+         aCount));
+    return mEventTarget->Dispatch(event, NS_DISPATCH_NORMAL);
+  } else {  // synchronous case
+    NS_ASSERTION(!mEventTarget, "mEventTarget is not null, mLock is null.");
+    nsresult rv;
+    uint32_t totalBytesWritten = 0;
+    while (aCount) {
+      uint32_t bytesWritten = 0;
+      rv = mSink->Write(aBuf + totalBytesWritten, aCount, &bytesWritten);
+      if (NS_FAILED(rv)) {
+        // ok, this is not a fatal error... just drop our reference to mSink
+        // and continue on as if nothing happened.
+        NS_WARNING("Write failed (non-fatal)");
+        // catch possible misuse of the input stream tee
+        NS_ASSERTION(rv != NS_BASE_STREAM_WOULD_BLOCK,
+                     "sink must be a blocking stream");
+        mSink = nullptr;
+        break;
+      }
+      totalBytesWritten += bytesWritten;
+      NS_ASSERTION(bytesWritten <= aCount, "wrote too much");
+      aCount -= bytesWritten;
+    }
+    return NS_OK;
+  }
+}
+
+nsresult nsInputStreamTee::WriteSegmentFun(nsIInputStream* aIn, void* aClosure,
+                                           const char* aFromSegment,
+                                           uint32_t aOffset, uint32_t aCount,
+                                           uint32_t* aWriteCount) {
+  nsInputStreamTee* tee = reinterpret_cast<nsInputStreamTee*>(aClosure);
+  nsresult rv = tee->mWriter(aIn, tee->mClosure, aFromSegment, aOffset, aCount,
+                             aWriteCount);
+  if (NS_FAILED(rv) || (*aWriteCount == 0)) {
+    NS_ASSERTION((NS_FAILED(rv) ? (*aWriteCount == 0) : true),
+                 "writer returned an error with non-zero writeCount");
+    return rv;
+  }
+
+  return tee->TeeSegment(aFromSegment, *aWriteCount);
+}
+
+NS_IMPL_ISUPPORTS(nsInputStreamTee, nsIInputStreamTee, nsIInputStream)
+NS_IMETHODIMP
+nsInputStreamTee::Close() {
+  if (NS_WARN_IF(!mSource)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  nsresult rv = mSource->Close();
+  mSource = nullptr;
+  mSink = nullptr;
+  return rv;
+}
+
+NS_IMETHODIMP
+nsInputStreamTee::Available(uint64_t* aAvail) {
+  if (NS_WARN_IF(!mSource)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  return mSource->Available(aAvail);
+}
+
+NS_IMETHODIMP
+nsInputStreamTee::StreamStatus() {
+  if (NS_WARN_IF(!mSource)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  return mSource->StreamStatus();
+}
+
+NS_IMETHODIMP
+nsInputStreamTee::Read(char* aBuf, uint32_t aCount, uint32_t* aBytesRead) {
+  if (NS_WARN_IF(!mSource)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  nsresult rv = mSource->Read(aBuf, aCount, aBytesRead);
+  if (NS_FAILED(rv) || (*aBytesRead == 0)) {
+    return rv;
+  }
+
+  return TeeSegment(aBuf, *aBytesRead);
+}
+
+NS_IMETHODIMP
+nsInputStreamTee::ReadSegments(nsWriteSegmentFun aWriter, void* aClosure,
+                               uint32_t aCount, uint32_t* aBytesRead) {
+  if (NS_WARN_IF(!mSource)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  mWriter = aWriter;
+  mClosure = aClosure;
+
+  return mSource->ReadSegments(WriteSegmentFun, this, aCount, aBytesRead);
+}
+
+NS_IMETHODIMP
+nsInputStreamTee::IsNonBlocking(bool* aResult) {
+  if (NS_WARN_IF(!mSource)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  return mSource->IsNonBlocking(aResult);
+}
+
+NS_IMETHODIMP
+nsInputStreamTee::SetSource(nsIInputStream* aSource) {
+  mSource = aSource;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsInputStreamTee::GetSource(nsIInputStream** aSource) {
+  NS_IF_ADDREF(*aSource = mSource);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsInputStreamTee::SetSink(nsIOutputStream* aSink) {
+#ifdef DEBUG
+  if (aSink) {
+    bool nonBlocking;
+    nsresult rv = aSink->IsNonBlocking(&nonBlocking);
+    if (NS_FAILED(rv) || nonBlocking) {
+      NS_ERROR("aSink should be a blocking stream");
+    }
+  }
+#endif
+  mSink = aSink;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsInputStreamTee::GetSink(nsIOutputStream** aSink) {
+  NS_IF_ADDREF(*aSink = mSink);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsInputStreamTee::SetEventTarget(nsIEventTarget* aEventTarget) {
+  mEventTarget = aEventTarget;
+  if (mEventTarget) {
+    // Only need synchronization if this is an async tee
+    mLock.emplace("nsInputStreamTee.mLock");
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsInputStreamTee::GetEventTarget(nsIEventTarget** aEventTarget) {
+  NS_IF_ADDREF(*aEventTarget = mEventTarget);
+  return NS_OK;
+}
+
+nsresult NS_NewInputStreamTeeAsync(nsIInputStream** aResult,
+                                   nsIInputStream* aSource,
+                                   nsIOutputStream* aSink,
+                                   nsIEventTarget* aEventTarget) {
+  nsresult rv;
+
+  nsCOMPtr<nsIInputStreamTee> tee = new nsInputStreamTee();
+  rv = tee->SetSource(aSource);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  rv = tee->SetSink(aSink);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  rv = tee->SetEventTarget(aEventTarget);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  tee.forget(aResult);
+  return rv;
+}
+
+nsresult NS_NewInputStreamTee(nsIInputStream** aResult, nsIInputStream* aSource,
+                              nsIOutputStream* aSink) {
+  return NS_NewInputStreamTeeAsync(aResult, aSource, aSink, nullptr);
+}
+
+#undef LOG
diff --git a/xpcom/io/nsLinebreakConverter.cpp b/xpcom/io/nsLinebreakConverter.cpp
new file mode 100644
index 0000000000..019fc0e4ae
--- /dev/null
+++ b/xpcom/io/nsLinebreakConverter.cpp
@@ -0,0 +1,452 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsLinebreakConverter.h"
+
+#include "nsCRT.h"
+
+/*----------------------------------------------------------------------------
+  GetLinebreakString
+
+  Could make this inline
+----------------------------------------------------------------------------*/
+static const char* GetLinebreakString(
+    nsLinebreakConverter::ELinebreakType aBreakType) {
+  static const char* const sLinebreaks[] = {"",            // any
+                                            NS_LINEBREAK,  // platform
+                                            LFSTR,         // content
+                                            CRLF,          // net
+                                            CRSTR,         // Mac
+                                            LFSTR,         // Unix
+                                            CRLF,          // Windows
+                                            " ",           // space
+                                            nullptr};
+
+  return sLinebreaks[aBreakType];
+}
+
+/*----------------------------------------------------------------------------
+  AppendLinebreak
+
+  Wee inline method to append a line break. Modifies ioDest.
+----------------------------------------------------------------------------*/
+template <class T>
+void AppendLinebreak(T*& aIoDest, const char* aLineBreakStr) {
+  *aIoDest++ = *aLineBreakStr;
+
+  if (aLineBreakStr[1]) {
+    *aIoDest++ = aLineBreakStr[1];
+  }
+}
+
+/*----------------------------------------------------------------------------
+  CountChars
+
+  Counts occurrences of breakStr in aSrc
+----------------------------------------------------------------------------*/
+template <class T>
+int32_t CountLinebreaks(const T* aSrc, int32_t aInLen, const char* aBreakStr) {
+  const T* src = aSrc;
+  const T* srcEnd = aSrc + aInLen;
+  int32_t theCount = 0;
+
+  while (src < srcEnd) {
+    if (*src == *aBreakStr) {
+      src++;
+
+      if (aBreakStr[1]) {
+        if (src < srcEnd && *src == aBreakStr[1]) {
+          src++;
+          theCount++;
+        }
+      } else {
+        theCount++;
+      }
+    } else {
+      src++;
+    }
+  }
+
+  return theCount;
+}
+
+/*----------------------------------------------------------------------------
+  ConvertBreaks
+
+  ioLen *includes* a terminating null, if any
+----------------------------------------------------------------------------*/
+template <class T>
+static T* ConvertBreaks(const T* aInSrc, int32_t& aIoLen, const char* aSrcBreak,
+                        const char* aDestBreak) {
+  NS_ASSERTION(aInSrc && aSrcBreak && aDestBreak, "Got a null string");
+
+  T* resultString = nullptr;
+
+  // handle the no conversion case
+  if (nsCRT::strcmp(aSrcBreak, aDestBreak) == 0) {
+    resultString = (T*)malloc(sizeof(T) * aIoLen);
+    if (!resultString) {
+      return nullptr;
+    }
+    memcpy(resultString, aInSrc,
+           sizeof(T) * aIoLen);  // includes the null, if any
+    return resultString;
+  }
+
+  int32_t srcBreakLen = strlen(aSrcBreak);
+  int32_t destBreakLen = strlen(aDestBreak);
+
+  // handle the easy case, where the string length does not change, and the
+  // breaks are only 1 char long, i.e. CR <-> LF
+  if (srcBreakLen == destBreakLen && srcBreakLen == 1) {
+    resultString = (T*)malloc(sizeof(T) * aIoLen);
+    if (!resultString) {
+      return nullptr;
+    }
+
+    const T* src = aInSrc;
+    const T* srcEnd = aInSrc + aIoLen;  // includes null, if any
+    T* dst = resultString;
+
+    char srcBreakChar = *aSrcBreak;  // we know it's one char long already
+    char dstBreakChar = *aDestBreak;
+
+    while (src < srcEnd) {
+      if (*src == srcBreakChar) {
+        *dst++ = dstBreakChar;
+        src++;
+      } else {
+        *dst++ = *src++;
+      }
+    }
+
+    // aIoLen does not change
+  } else {
+    // src and dest termination is different length. Do it a slower way.
+
+    // count linebreaks in src. Assumes that chars in 2-char linebreaks are
+    // unique.
+    int32_t numLinebreaks = CountLinebreaks(aInSrc, aIoLen, aSrcBreak);
+
+    int32_t newBufLen =
+        aIoLen - (numLinebreaks * srcBreakLen) + (numLinebreaks * destBreakLen);
+    resultString = (T*)malloc(sizeof(T) * newBufLen);
+    if (!resultString) {
+      return nullptr;
+    }
+
+    const T* src = aInSrc;
+    const T* srcEnd = aInSrc + aIoLen;  // includes null, if any
+    T* dst = resultString;
+
+    while (src < srcEnd) {
+      if (*src == *aSrcBreak) {
+        *dst++ = *aDestBreak;
+        if (aDestBreak[1]) {
+          *dst++ = aDestBreak[1];
+        }
+
+        src++;
+        if (src < srcEnd && aSrcBreak[1] && *src == aSrcBreak[1]) {
+          src++;
+        }
+      } else {
+        *dst++ = *src++;
+      }
+    }
+
+    aIoLen = newBufLen;
+  }
+
+  return resultString;
+}
+
+/*----------------------------------------------------------------------------
+  ConvertBreaksInSitu
+
+  Convert breaks in situ. Can only do this if the linebreak length
+  does not change.
+----------------------------------------------------------------------------*/
+template <class T>
+static void ConvertBreaksInSitu(T* aInSrc, int32_t aInLen, char aSrcBreak,
+                                char aDestBreak) {
+  T* src = aInSrc;
+  T* srcEnd = aInSrc + aInLen;
+
+  while (src < srcEnd) {
+    if (*src == aSrcBreak) {
+      *src = aDestBreak;
+    }
+
+    src++;
+  }
+}
+
+/*----------------------------------------------------------------------------
+  ConvertUnknownBreaks
+
+  Convert unknown line breaks to the specified break.
+
+  This will convert CRLF pairs to one break, and single CR or LF to a break.
+----------------------------------------------------------------------------*/
+template <class T>
+static T* ConvertUnknownBreaks(const T* aInSrc, int32_t& aIoLen,
+                               const char* aDestBreak) {
+  const T* src = aInSrc;
+  const T* srcEnd = aInSrc + aIoLen;  // includes null, if any
+
+  int32_t destBreakLen = strlen(aDestBreak);
+  int32_t finalLen = 0;
+
+  while (src < srcEnd) {
+    if (*src == nsCRT::CR) {
+      if (src + 1 < srcEnd && src[1] == nsCRT::LF) {
+        // CRLF
+        finalLen += destBreakLen;
+        src++;
+      } else {
+        // Lone CR
+        finalLen += destBreakLen;
+      }
+    } else if (*src == nsCRT::LF) {
+      // Lone LF
+      finalLen += destBreakLen;
+    } else {
+      finalLen++;
+    }
+    src++;
+  }
+
+  T* resultString = (T*)malloc(sizeof(T) * finalLen);
+  if (!resultString) {
+    return nullptr;
+  }
+
+  src = aInSrc;
+  srcEnd = aInSrc + aIoLen;  // includes null, if any
+
+  T* dst = resultString;
+
+  while (src < srcEnd) {
+    if (*src == nsCRT::CR) {
+      if (src + 1 < srcEnd && src[1] == nsCRT::LF) {
+        // CRLF
+        AppendLinebreak(dst, aDestBreak);
+        src++;
+      } else {
+        // Lone CR
+        AppendLinebreak(dst, aDestBreak);
+      }
+    } else if (*src == nsCRT::LF) {
+      // Lone LF
+      AppendLinebreak(dst, aDestBreak);
+    } else {
+      *dst++ = *src;
+    }
+    src++;
+  }
+
+  aIoLen = finalLen;
+  return resultString;
+}
+
+/*----------------------------------------------------------------------------
+  ConvertLineBreaks
+
+----------------------------------------------------------------------------*/
+char* nsLinebreakConverter::ConvertLineBreaks(const char* aSrc,
+                                              ELinebreakType aSrcBreaks,
+                                              ELinebreakType aDestBreaks,
+                                              int32_t aSrcLen,
+                                              int32_t* aOutLen) {
+  NS_ASSERTION(aDestBreaks != eLinebreakAny && aSrcBreaks != eLinebreakSpace,
+               "Invalid parameter");
+  if (!aSrc) {
+    return nullptr;
+  }
+
+  int32_t sourceLen = (aSrcLen == kIgnoreLen) ? strlen(aSrc) + 1 : aSrcLen;
+
+  char* resultString;
+  if (aSrcBreaks == eLinebreakAny) {
+    resultString =
+        ConvertUnknownBreaks(aSrc, sourceLen, GetLinebreakString(aDestBreaks));
+  } else
+    resultString =
+        ConvertBreaks(aSrc, sourceLen, GetLinebreakString(aSrcBreaks),
+                      GetLinebreakString(aDestBreaks));
+
+  if (aOutLen) {
+    *aOutLen = sourceLen;
+  }
+  return resultString;
+}
+
+/*----------------------------------------------------------------------------
+  ConvertLineBreaksInSitu
+
+----------------------------------------------------------------------------*/
+nsresult nsLinebreakConverter::ConvertLineBreaksInSitu(
+    char** aIoBuffer, ELinebreakType aSrcBreaks, ELinebreakType aDestBreaks,
+    int32_t aSrcLen, int32_t* aOutLen) {
+  NS_ASSERTION(aIoBuffer && *aIoBuffer, "Null pointer passed");
+  if (!aIoBuffer || !*aIoBuffer) {
+    return NS_ERROR_NULL_POINTER;
+  }
+
+  NS_ASSERTION(aDestBreaks != eLinebreakAny && aSrcBreaks != eLinebreakSpace,
+               "Invalid parameter");
+
+  int32_t sourceLen =
+      (aSrcLen == kIgnoreLen) ? strlen(*aIoBuffer) + 1 : aSrcLen;
+
+  // can we convert in-place?
+  const char* srcBreaks = GetLinebreakString(aSrcBreaks);
+  const char* dstBreaks = GetLinebreakString(aDestBreaks);
+
+  if (aSrcBreaks != eLinebreakAny && strlen(srcBreaks) == 1 &&
+      strlen(dstBreaks) == 1) {
+    ConvertBreaksInSitu(*aIoBuffer, sourceLen, *srcBreaks, *dstBreaks);
+    if (aOutLen) {
+      *aOutLen = sourceLen;
+    }
+  } else {
+    char* destBuffer;
+
+    if (aSrcBreaks == eLinebreakAny) {
+      destBuffer = ConvertUnknownBreaks(*aIoBuffer, sourceLen, dstBreaks);
+    } else {
+      destBuffer = ConvertBreaks(*aIoBuffer, sourceLen, srcBreaks, dstBreaks);
+    }
+
+    if (!destBuffer) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    *aIoBuffer = destBuffer;
+    if (aOutLen) {
+      *aOutLen = sourceLen;
+    }
+  }
+
+  return NS_OK;
+}
+
+/*----------------------------------------------------------------------------
+  ConvertUnicharLineBreaks
+
+----------------------------------------------------------------------------*/
+char16_t* nsLinebreakConverter::ConvertUnicharLineBreaks(
+    const char16_t* aSrc, ELinebreakType aSrcBreaks, ELinebreakType aDestBreaks,
+    int32_t aSrcLen, int32_t* aOutLen) {
+  NS_ASSERTION(aDestBreaks != eLinebreakAny && aSrcBreaks != eLinebreakSpace,
+               "Invalid parameter");
+  if (!aSrc) {
+    return nullptr;
+  }
+
+  int32_t bufLen = (aSrcLen == kIgnoreLen) ? NS_strlen(aSrc) + 1 : aSrcLen;
+
+  char16_t* resultString;
+  if (aSrcBreaks == eLinebreakAny) {
+    resultString =
+        ConvertUnknownBreaks(aSrc, bufLen, GetLinebreakString(aDestBreaks));
+  } else
+    resultString = ConvertBreaks(aSrc, bufLen, GetLinebreakString(aSrcBreaks),
+                                 GetLinebreakString(aDestBreaks));
+
+  if (aOutLen) {
+    *aOutLen = bufLen;
+  }
+  return resultString;
+}
+
+/*----------------------------------------------------------------------------
+  ConvertStringLineBreaks
+
+----------------------------------------------------------------------------*/
+nsresult nsLinebreakConverter::ConvertUnicharLineBreaksInSitu(
+    char16_t** aIoBuffer, ELinebreakType aSrcBreaks, ELinebreakType aDestBreaks,
+    int32_t aSrcLen, int32_t* aOutLen) {
+  NS_ASSERTION(aIoBuffer && *aIoBuffer, "Null pointer passed");
+  if (!aIoBuffer || !*aIoBuffer) {
+    return NS_ERROR_NULL_POINTER;
+  }
+  NS_ASSERTION(aDestBreaks != eLinebreakAny && aSrcBreaks != eLinebreakSpace,
+               "Invalid parameter");
+
+  int32_t sourceLen =
+      (aSrcLen == kIgnoreLen) ? NS_strlen(*aIoBuffer) + 1 : aSrcLen;
+
+  // can we convert in-place?
+  const char* srcBreaks = GetLinebreakString(aSrcBreaks);
+  const char* dstBreaks = GetLinebreakString(aDestBreaks);
+
+  if ((aSrcBreaks != eLinebreakAny) && (strlen(srcBreaks) == 1) &&
+      (strlen(dstBreaks) == 1)) {
+    ConvertBreaksInSitu(*aIoBuffer, sourceLen, *srcBreaks, *dstBreaks);
+    if (aOutLen) {
+      *aOutLen = sourceLen;
+    }
+  } else {
+    char16_t* destBuffer;
+
+    if (aSrcBreaks == eLinebreakAny) {
+      destBuffer = ConvertUnknownBreaks(*aIoBuffer, sourceLen, dstBreaks);
+    } else {
+      destBuffer = ConvertBreaks(*aIoBuffer, sourceLen, srcBreaks, dstBreaks);
+    }
+
+    if (!destBuffer) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    *aIoBuffer = destBuffer;
+    if (aOutLen) {
+      *aOutLen = sourceLen;
+    }
+  }
+
+  return NS_OK;
+}
+
+/*----------------------------------------------------------------------------
+  ConvertStringLineBreaks
+
+----------------------------------------------------------------------------*/
+nsresult nsLinebreakConverter::ConvertStringLineBreaks(
+    nsString& aIoString, ELinebreakType aSrcBreaks,
+    ELinebreakType aDestBreaks) {
+  NS_ASSERTION(aDestBreaks != eLinebreakAny && aSrcBreaks != eLinebreakSpace,
+               "Invalid parameter");
+
+  // nothing to do
+  if (aIoString.IsEmpty()) {
+    return NS_OK;
+  }
+
+  nsresult rv;
+
+  // remember the old buffer in case
+  // we blow it away later
+  char16_t* stringBuf = aIoString.BeginWriting(mozilla::fallible);
+  if (!stringBuf) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  int32_t newLen;
+
+  rv = ConvertUnicharLineBreaksInSitu(&stringBuf, aSrcBreaks, aDestBreaks,
+                                      aIoString.Length() + 1, &newLen);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  const char16_t* currentBuf = aIoString.get();
+  if (currentBuf != stringBuf) {
+    aIoString.Adopt(stringBuf, newLen - 1);
+  }
+
+  return NS_OK;
+}
diff --git a/xpcom/io/nsLinebreakConverter.h b/xpcom/io/nsLinebreakConverter.h
new file mode 100644
index 0000000000..2ecde3beec
--- /dev/null
+++ b/xpcom/io/nsLinebreakConverter.h
@@ -0,0 +1,141 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsLinebreakConverter_h_
+#define nsLinebreakConverter_h_
+
+#include "nscore.h"
+#include "nsString.h"
+
+// utility class for converting between different line breaks.
+
+class nsLinebreakConverter {
+ public:
+  // Note: enum must match char* array in GetLinebreakString
+  typedef enum {
+    eLinebreakAny,  // any kind of linebreak (i.e. "don't care" source)
+
+    eLinebreakPlatform,  // platform linebreak
+    eLinebreakContent,   // Content model linebreak (LF)
+    eLinebreakNet,       // Form submission linebreak (CRLF)
+
+    eLinebreakMac,      // CR
+    eLinebreakUnix,     // LF
+    eLinebreakWindows,  // CRLF
+
+    eLinebreakSpace  // space characters. Only valid as destination type
+
+  } ELinebreakType;
+
+  enum { kIgnoreLen = -1 };
+
+  /* ConvertLineBreaks
+   * Convert line breaks in the supplied string, allocating and returning
+   * a new buffer. Returns nullptr on failure.
+   * @param aSrc: the source string. if aSrcLen == kIgnoreLen this string is
+   *              assumed to be null terminated, otherwise it must be at least
+   *              aSrcLen long.
+   * @param aSrcBreaks: the line breaks in the source. If unknown, pass
+   *              eLinebreakAny.  If known, pass the known value, as this may
+   *              be more efficient.
+   * @param aDestBreaks: the line breaks you want in the output.
+   * @param aSrcLen: length of the source. If -1, the source is assumed to be a
+   *              null-terminated string.
+   * @param aOutLen: used to return character length of returned buffer, if not
+   *              null.
+   */
+  static char* ConvertLineBreaks(const char* aSrc, ELinebreakType aSrcBreaks,
+                                 ELinebreakType aDestBreaks,
+                                 int32_t aSrcLen = kIgnoreLen,
+                                 int32_t* aOutLen = nullptr);
+
+  /* ConvertUnicharLineBreaks
+   * Convert line breaks in the supplied string, allocating and returning
+   * a new buffer. Returns nullptr on failure.
+   * @param aSrc: the source string. if aSrcLen == kIgnoreLen this string is
+   *              assumed to be null terminated, otherwise it must be at least
+   *              aSrcLen long.
+   * @param aSrcBreaks: the line breaks in the source. If unknown, pass
+   *              eLinebreakAny.  If known, pass the known value, as this may
+   *              be more efficient.
+   * @param aDestBreaks: the line breaks you want in the output.
+   * @param aSrcLen: length of the source, in characters. If -1, the source is
+   *              assumed to be a null-terminated string.
+   * @param aOutLen: used to return character length of returned buffer, if not
+   *              null.
+   */
+  static char16_t* ConvertUnicharLineBreaks(const char16_t* aSrc,
+                                            ELinebreakType aSrcBreaks,
+                                            ELinebreakType aDestBreaks,
+                                            int32_t aSrcLen = kIgnoreLen,
+                                            int32_t* aOutLen = nullptr);
+
+  /* ConvertStringLineBreaks
+   * Convert line breaks in the supplied string, changing the string buffer
+   * (i.e. in-place conversion)
+   * @param ioString: the string to be converted.
+   * @param aSrcBreaks: the line breaks in the source. If unknown, pass
+   *              eLinebreakAny.  If known, pass the known value, as this may
+   *              be more efficient.
+   * @param aDestBreaks: the line breaks you want in the output.
+   * @param aSrcLen: length of the source, in characters. If -1, the source is
+   *              assumed to be a null-terminated string.
+   */
+  static nsresult ConvertStringLineBreaks(nsString& aIoString,
+                                          ELinebreakType aSrcBreaks,
+                                          ELinebreakType aDestBreaks);
+
+  /* ConvertLineBreaksInSitu
+   * Convert line breaks in place if possible. NOTE: THIS MAY REALLOCATE THE
+   * BUFFER, BUT IT WON'T FREE THE OLD BUFFER (because it doesn't know how). So
+   * be prepared to keep a copy of the old pointer, and free it if this passes
+   * back a new pointer.  ALSO NOTE: DON'T PASS A STATIC STRING POINTER TO THIS
+   * FUNCTION.
+   *
+   * @param ioBuffer: the source buffer. if aSrcLen == kIgnoreLen this string
+   *              is assumed to be null terminated, otherwise it must be at
+   *              least aSrcLen long.
+   * @param aSrcBreaks: the line breaks in the source. If unknown, pass
+   *              eLinebreakAny.  If known, pass the known value, as this may
+   *              be more efficient.
+   * @param aDestBreaks: the line breaks you want in the output.
+   * @param aSrcLen: length of the source. If -1, the source is assumed to be a
+   *              null-terminated string.
+   * @param aOutLen: used to return character length of returned buffer, if not
+   *              null.
+   */
+  static nsresult ConvertLineBreaksInSitu(char** aIoBuffer,
+                                          ELinebreakType aSrcBreaks,
+                                          ELinebreakType aDestBreaks,
+                                          int32_t aSrcLen = kIgnoreLen,
+                                          int32_t* aOutLen = nullptr);
+
+  /* ConvertUnicharLineBreaksInSitu
+   * Convert line breaks in place if possible. NOTE: THIS MAY REALLOCATE THE
+   * BUFFER, BUT IT WON'T FREE THE OLD BUFFER (because it doesn't know how). So
+   * be prepared to keep a copy of the old pointer, and free it if this passes
+   * back a new pointer.
+   *
+   * @param ioBuffer: the source buffer. if aSrcLen == kIgnoreLen this string
+   *              is assumed to be null terminated, otherwise it must be at
+   *              least aSrcLen long.
+   * @param aSrcBreaks: the line breaks in the source. If unknown, pass
+   *              eLinebreakAny.  If known, pass the known value, as this may
+   *              be more efficient.
+   * @param aDestBreaks: the line breaks you want in the output.
+   * @param aSrcLen: length of the source in characters. If -1, the source is
+   *              assumed to be a null-terminated string.
+   * @param aOutLen: used to return character length of returned buffer, if not
+   *              null.
+   */
+  static nsresult ConvertUnicharLineBreaksInSitu(char16_t** aIoBuffer,
+                                                 ELinebreakType aSrcBreaks,
+                                                 ELinebreakType aDestBreaks,
+                                                 int32_t aSrcLen = kIgnoreLen,
+                                                 int32_t* aOutLen = nullptr);
+};
+
+#endif  // nsLinebreakConverter_h_
diff --git a/xpcom/io/nsLocalFile.h b/xpcom/io/nsLocalFile.h
new file mode 100644
index 0000000000..779b2e6c95
--- /dev/null
+++ b/xpcom/io/nsLocalFile.h
@@ -0,0 +1,124 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef _NS_LOCAL_FILE_H_
+#define _NS_LOCAL_FILE_H_
+
+#include "nscore.h"
+
+#define NS_LOCAL_FILE_CID                            \
+  {                                                  \
+    0x2e23e220, 0x60be, 0x11d3, {                    \
+      0x8c, 0x4a, 0x00, 0x00, 0x64, 0x65, 0x73, 0x74 \
+    }                                                \
+  }
+
+#define NS_DECL_NSLOCALFILE_UNICODE_METHODS                           \
+  nsresult AppendUnicode(const char16_t* aNode);                      \
+  nsresult GetUnicodeLeafName(char16_t** aLeafName);                  \
+  nsresult SetUnicodeLeafName(const char16_t* aLeafName);             \
+  nsresult CopyToUnicode(nsIFile* aNewParentDir,                      \
+                         const char16_t* aNewLeafName);               \
+  nsresult CopyToFollowingLinksUnicode(nsIFile* aNewParentDir,        \
+                                       const char16_t* aNewLeafName); \
+  nsresult MoveToUnicode(nsIFile* aNewParentDir,                      \
+                         const char16_t* aNewLeafName);               \
+  nsresult GetUnicodeTarget(char16_t** aTarget);                      \
+  nsresult GetUnicodePath(char16_t** aPath);                          \
+  nsresult InitWithUnicodePath(const char16_t* aPath);                \
+  nsresult AppendRelativeUnicodePath(const char16_t* aRelativePath);
+
+// XPCOMInit needs to know about how we are implemented,
+// so here we will export it.  Other users should not depend
+// on this.
+
+#include <errno.h>
+#include "nsIFile.h"
+
+#ifdef XP_WIN
+#  include "nsLocalFileWin.h"
+#elif defined(XP_UNIX)
+#  include "nsLocalFileUnix.h"
+#else
+#  error NOT_IMPLEMENTED
+#endif
+
+#define NSRESULT_FOR_RETURN(ret) (((ret) < 0) ? NSRESULT_FOR_ERRNO() : NS_OK)
+
+inline nsresult nsresultForErrno(int aErr) {
+  switch (aErr) {
+    case 0:
+      return NS_OK;
+#ifdef EDQUOT
+    case EDQUOT:        /* Quota exceeded */
+      [[fallthrough]];  // to NS_ERROR_FILE_NO_DEVICE_SPACE
+#endif
+    case ENOSPC:
+      return NS_ERROR_FILE_NO_DEVICE_SPACE;
+#ifdef EISDIR
+    case EISDIR: /*      Is a directory. */
+      return NS_ERROR_FILE_IS_DIRECTORY;
+#endif
+    case ENAMETOOLONG:
+      return NS_ERROR_FILE_NAME_TOO_LONG;
+    case ENOEXEC: /*     Executable file format error. */
+      return NS_ERROR_FILE_EXECUTION_FAILED;
+    case ENOENT:
+      return NS_ERROR_FILE_NOT_FOUND;
+    case ENOTDIR:
+      return NS_ERROR_FILE_DESTINATION_NOT_DIR;
+#ifdef ELOOP
+    case ELOOP:
+      return NS_ERROR_FILE_UNRESOLVABLE_SYMLINK;
+#endif /* ELOOP */
+#ifdef ENOLINK
+    case ENOLINK:
+      return NS_ERROR_FILE_UNRESOLVABLE_SYMLINK;
+#endif /* ENOLINK */
+    case EEXIST:
+      return NS_ERROR_FILE_ALREADY_EXISTS;
+#ifdef EPERM
+    case EPERM:
+#endif /* EPERM */
+    case EACCES:
+      return NS_ERROR_FILE_ACCESS_DENIED;
+#ifdef EROFS
+    case EROFS: /*     Read-only file system. */
+      return NS_ERROR_FILE_READ_ONLY;
+#endif
+      /*
+       * On AIX 4.3, ENOTEMPTY is defined as EEXIST,
+       * so there can't be cases for both without
+       * preprocessing.
+       */
+#if ENOTEMPTY != EEXIST
+    case ENOTEMPTY:
+      return NS_ERROR_FILE_DIR_NOT_EMPTY;
+#endif /* ENOTEMPTY != EEXIST */
+    /* Note that nsIFile.createUnique() returns
+       NS_ERROR_FILE_TOO_BIG when it cannot create a temporary
+       file with a unique filename.
+       See https://developer.mozilla.org/en-US/docs/Table_Of_Errors
+       Other usages of NS_ERROR_FILE_TOO_BIG in the source tree
+       are in line with the POSIX semantics of EFBIG.
+       So this is a reasonably good approximation.
+    */
+    case EFBIG: /*     File too large. */
+      return NS_ERROR_FILE_TOO_BIG;
+
+#ifdef ENOATTR
+    case ENOATTR:
+      return NS_ERROR_NOT_AVAILABLE;
+#endif  // ENOATTR
+
+    default:
+      return NS_ERROR_FAILURE;
+  }
+}
+
+#define NSRESULT_FOR_ERRNO() nsresultForErrno(errno)
+
+#endif
diff --git a/xpcom/io/nsLocalFileCommon.cpp b/xpcom/io/nsLocalFileCommon.cpp
new file mode 100644
index 0000000000..f6eabf2d0f
--- /dev/null
+++ b/xpcom/io/nsLocalFileCommon.cpp
@@ -0,0 +1,438 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsLocalFile.h"  // includes platform-specific headers
+
+#include "nsString.h"
+#include "nsCOMPtr.h"
+#include "nsReadableUtils.h"
+#include "nsPrintfCString.h"
+#include "nsCRT.h"
+#include "nsNativeCharsetUtils.h"
+#include "nsUTF8Utils.h"
+#include "nsArray.h"
+#include "nsLocalFileCommon.h"
+
+#ifdef XP_WIN
+#  include <string.h>
+#endif
+
+// Extensions that should be considered 'executable', ie will not allow users
+// to open immediately without first saving to disk, and potentially provoke
+// other warnings. PLEASE read the longer comment in
+// toolkit/components/reputationservice/ApplicationReputation.cpp
+// before modifying this list!
+// If you update this list, make sure to update the length of sExecutableExts
+// in nsLocalFileCommmon.h.
+/* static */
+const char* const sExecutableExts[] = {
+    // clang-format off
+  ".accda",       // MS Access database
+  ".accdb",       // MS Access database
+  ".accde",       // MS Access database
+  ".accdr",       // MS Access database
+  ".ad",
+  ".ade",         // access project extension
+  ".adp",
+  ".afploc",      // Apple Filing Protocol Location
+  ".air",         // Adobe AIR installer
+  ".app",         // executable application
+  ".application", // from bug 348763
+  ".appref-ms",   // ClickOnce link
+  ".appx",
+  ".appxbundle",
+  ".asp",
+  ".atloc",       // Appletalk Location
+  ".bas",
+  ".bat",
+  ".cer",         // Signed certificate file
+  ".chm",
+  ".cmd",
+  ".com",
+  ".cpl",
+  ".crt",
+  ".der",
+  ".diagcab",     // Windows archive
+  ".exe",
+  ".fileloc",     // Apple finder internet location data file
+  ".ftploc",      // Apple FTP Location
+  ".fxp",         // FoxPro compiled app
+  ".hlp",
+  ".hta",
+  ".inetloc",     // Apple finder internet location data file
+  ".inf",
+  ".ins",
+  ".isp",
+  ".jar",         // java application bundle
+#ifndef MOZ_ESR
+  ".jnlp",
+#endif
+  ".js",
+  ".jse",
+  ".lnk",
+  ".mad",         // Access Module Shortcut
+  ".maf",         // Access
+  ".mag",         // Access Diagram Shortcut
+  ".mam",         // Access Macro Shortcut
+  ".maq",         // Access Query Shortcut
+  ".mar",         // Access Report Shortcut
+  ".mas",         // Access Stored Procedure
+  ".mat",         // Access Table Shortcut
+  ".mau",         // Media Attachment Unit
+  ".mav",         // Access View Shortcut
+  ".maw",         // Access Data Access Page
+  ".mda",         // Access Add-in, MDA Access 2 Workgroup
+  ".mdb",
+  ".mde",
+  ".mdt",         // Access Add-in Data
+  ".mdw",         // Access Workgroup Information
+  ".mdz",         // Access Wizard Template
+  ".msc",
+  ".msh",         // Microsoft Shell
+  ".msh1",        // Microsoft Shell
+  ".msh1xml",     // Microsoft Shell
+  ".msh2",        // Microsoft Shell
+  ".msh2xml",     // Microsoft Shell
+  ".mshxml",      // Microsoft Shell
+  ".msi",
+  ".msix",
+  ".msixbundle",
+  ".msp",
+  ".mst",
+  ".ops",         // Office Profile Settings
+  ".pcd",
+  ".pif",
+  ".plg",         // Developer Studio Build Log
+  ".prf",         // windows system file
+  ".prg",
+  ".pst",
+  ".reg",
+  ".scf",         // Windows explorer command
+  ".scr",
+  ".sct",
+  ".settingcontent-ms",
+  ".shb",
+  ".shs",
+  ".url",
+  ".vb",
+  ".vbe",
+  ".vbs",
+  ".vdx",
+  ".vsd",
+  ".vsdm",
+  ".vsdx",
+  ".vsmacros",    // Visual Studio .NET Binary-based Macro Project
+  ".vss",
+  ".vssm",
+  ".vssx",
+  ".vst",
+  ".vstm",
+  ".vstx",
+  ".vsw",
+  ".vsx",
+  ".vtx",
+  ".webloc",       // MacOS website location file
+  ".ws",
+  ".wsc",
+  ".wsf",
+  ".wsh",
+  ".xll"         // MS Excel dynamic link library
+    // clang-format on
+};
+
+#if !defined(MOZ_WIDGET_COCOA) && !defined(XP_WIN)
+NS_IMETHODIMP
+nsLocalFile::InitWithFile(nsIFile* aFile) {
+  if (NS_WARN_IF(!aFile)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsAutoCString path;
+  aFile->GetNativePath(path);
+  if (path.IsEmpty()) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  return InitWithNativePath(path);
+}
+#endif
+
+#define kMaxFilenameLength 255
+#define kMaxExtensionLength 100
+#define kMaxSequenceNumberLength 5  // "-9999"
+// requirement: kMaxExtensionLength <
+//                kMaxFilenameLength - kMaxSequenceNumberLength
+
+NS_IMETHODIMP
+nsLocalFile::CreateUnique(uint32_t aType, uint32_t aAttributes) {
+  nsresult rv;
+  bool longName;
+
+#ifdef XP_WIN
+  nsAutoString pathName, leafName, rootName, suffix;
+  rv = GetPath(pathName);
+#else
+  nsAutoCString pathName, leafName, rootName, suffix;
+  rv = GetNativePath(pathName);
+#endif
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  auto FailedBecauseExists = [&](nsresult aRv) {
+    if (aRv == NS_ERROR_FILE_ACCESS_DENIED) {
+      bool exists;
+      return NS_SUCCEEDED(Exists(&exists)) && exists;
+    }
+    return aRv == NS_ERROR_FILE_ALREADY_EXISTS;
+  };
+
+  longName =
+      (pathName.Length() + kMaxSequenceNumberLength > kMaxFilenameLength);
+  if (!longName) {
+    rv = Create(aType, aAttributes);
+    if (!FailedBecauseExists(rv)) {
+      return rv;
+    }
+  }
+
+#ifdef XP_WIN
+  rv = GetLeafName(leafName);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  const int32_t lastDot = leafName.RFindChar(char16_t('.'));
+#else
+  rv = GetNativeLeafName(leafName);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  const int32_t lastDot = leafName.RFindChar('.');
+#endif
+
+  if (lastDot == kNotFound) {
+    rootName = leafName;
+  } else {
+    suffix = Substring(leafName, lastDot);       // include '.'
+    rootName = Substring(leafName, 0, lastDot);  // strip suffix and dot
+  }
+
+  if (longName) {
+    int32_t maxRootLength =
+        (kMaxFilenameLength - (pathName.Length() - leafName.Length()) -
+         suffix.Length() - kMaxSequenceNumberLength);
+
+    // We cannot create an item inside a directory whose name is too long.
+    // Also, ensure that at least one character remains after we truncate
+    // the root name, as we don't want to end up with an empty leaf name.
+    if (maxRootLength < 2) {
+      return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+    }
+
+#ifdef XP_WIN
+    // ensure that we don't cut the name in mid-UTF16-character
+    rootName.SetLength(NS_IS_LOW_SURROGATE(rootName[maxRootLength])
+                           ? maxRootLength - 1
+                           : maxRootLength);
+    SetLeafName(rootName + suffix);
+#else
+    if (NS_IsNativeUTF8()) {
+      // ensure that we don't cut the name in mid-UTF8-character
+      // (assume the name is valid UTF8 to begin with)
+      while (UTF8traits::isInSeq(rootName[maxRootLength])) {
+        --maxRootLength;
+      }
+
+      // Another check to avoid ending up with an empty leaf name.
+      if (maxRootLength == 0 && suffix.IsEmpty()) {
+        return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+      }
+    }
+
+    rootName.SetLength(maxRootLength);
+    SetNativeLeafName(rootName + suffix);
+#endif
+    nsresult rvCreate = Create(aType, aAttributes);
+    if (!FailedBecauseExists(rvCreate)) {
+      return rvCreate;
+    }
+  }
+
+  for (int indx = 1; indx < 10000; ++indx) {
+    // start with "Picture-1.jpg" after "Picture.jpg" exists
+#ifdef XP_WIN
+    SetLeafName(rootName +
+                NS_ConvertASCIItoUTF16(nsPrintfCString("-%d", indx)) + suffix);
+#else
+    SetNativeLeafName(rootName + nsPrintfCString("-%d", indx) + suffix);
+#endif
+    rv = Create(aType, aAttributes);
+    if (NS_SUCCEEDED(rv) || !FailedBecauseExists(rv)) {
+      return rv;
+    }
+  }
+
+  // The disk is full, sort of
+  return NS_ERROR_FILE_TOO_BIG;
+}
+
+#if defined(XP_WIN)
+static const char16_t kPathSeparatorChar = '\\';
+#elif defined(XP_UNIX)
+static const char16_t kPathSeparatorChar = '/';
+#else
+#  error Need to define file path separator for your platform
+#endif
+
+static void SplitPath(char16_t* aPath, nsTArray<char16_t*>& aNodeArray) {
+  if (*aPath == 0) {
+    return;
+  }
+
+  if (*aPath == kPathSeparatorChar) {
+    aPath++;
+  }
+  aNodeArray.AppendElement(aPath);
+
+  for (char16_t* cp = aPath; *cp != 0; ++cp) {
+    if (*cp == kPathSeparatorChar) {
+      *cp++ = 0;
+      if (*cp == 0) {
+        break;
+      }
+      aNodeArray.AppendElement(cp);
+    }
+  }
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetRelativeDescriptor(nsIFile* aFromFile, nsACString& aResult) {
+  if (NS_WARN_IF(!aFromFile)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  //
+  // aResult will be UTF-8 encoded
+  //
+
+  nsresult rv;
+  aResult.Truncate(0);
+
+  nsAutoString thisPath, fromPath;
+  AutoTArray<char16_t*, 32> thisNodes;
+  AutoTArray<char16_t*, 32> fromNodes;
+
+  rv = GetPath(thisPath);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  rv = aFromFile->GetPath(fromPath);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // get raw pointer to mutable string buffer
+  char16_t* thisPathPtr = thisPath.BeginWriting();
+  char16_t* fromPathPtr = fromPath.BeginWriting();
+
+  SplitPath(thisPathPtr, thisNodes);
+  SplitPath(fromPathPtr, fromNodes);
+
+  size_t nodeIndex;
+  for (nodeIndex = 0;
+       nodeIndex < thisNodes.Length() && nodeIndex < fromNodes.Length();
+       ++nodeIndex) {
+#ifdef XP_WIN
+    if (_wcsicmp(char16ptr_t(thisNodes[nodeIndex]),
+                 char16ptr_t(fromNodes[nodeIndex]))) {
+      break;
+    }
+#else
+    if (nsCRT::strcmp(thisNodes[nodeIndex], fromNodes[nodeIndex])) {
+      break;
+    }
+#endif
+  }
+
+  size_t branchIndex = nodeIndex;
+  for (nodeIndex = branchIndex; nodeIndex < fromNodes.Length(); ++nodeIndex) {
+    aResult.AppendLiteral("../");
+  }
+  StringJoinAppend(aResult, "/"_ns, mozilla::Span{thisNodes}.From(branchIndex),
+                   [](nsACString& dest, const auto& thisNode) {
+                     // XXX(Bug 1682869) We wouldn't need to reconstruct a
+                     // nsDependentString here if SplitPath already returned
+                     // nsDependentString. In fact, it seems SplitPath might be
+                     // replaced by ParseString?
+                     AppendUTF16toUTF8(nsDependentString{thisNode}, dest);
+                   });
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetRelativeDescriptor(nsIFile* aFromFile,
+                                   const nsACString& aRelativeDesc) {
+  constexpr auto kParentDirStr = "../"_ns;
+
+  nsCOMPtr<nsIFile> targetFile;
+  nsresult rv = aFromFile->Clone(getter_AddRefs(targetFile));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  //
+  // aRelativeDesc is UTF-8 encoded
+  //
+
+  nsCString::const_iterator strBegin, strEnd;
+  aRelativeDesc.BeginReading(strBegin);
+  aRelativeDesc.EndReading(strEnd);
+
+  nsCString::const_iterator nodeBegin(strBegin), nodeEnd(strEnd);
+  nsCString::const_iterator pos(strBegin);
+
+  nsCOMPtr<nsIFile> parentDir;
+  while (FindInReadable(kParentDirStr, nodeBegin, nodeEnd)) {
+    rv = targetFile->GetParent(getter_AddRefs(parentDir));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+    if (!parentDir) {
+      return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+    }
+    targetFile = parentDir;
+
+    nodeBegin = nodeEnd;
+    pos = nodeEnd;
+    nodeEnd = strEnd;
+  }
+
+  nodeBegin = nodeEnd = pos;
+  while (nodeEnd != strEnd) {
+    FindCharInReadable('/', nodeEnd, strEnd);
+    targetFile->Append(NS_ConvertUTF8toUTF16(Substring(nodeBegin, nodeEnd)));
+    if (nodeEnd != strEnd) {  // If there's more left in the string, inc over
+                              // the '/' nodeEnd is on.
+      ++nodeEnd;
+    }
+    nodeBegin = nodeEnd;
+  }
+
+  return InitWithFile(targetFile);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetRelativePath(nsIFile* aFromFile, nsACString& aResult) {
+  return GetRelativeDescriptor(aFromFile, aResult);
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetRelativePath(nsIFile* aFromFile,
+                             const nsACString& aRelativePath) {
+  return SetRelativeDescriptor(aFromFile, aRelativePath);
+}
diff --git a/xpcom/io/nsLocalFileCommon.h b/xpcom/io/nsLocalFileCommon.h
new file mode 100644
index 0000000000..3db0ac9e89
--- /dev/null
+++ b/xpcom/io/nsLocalFileCommon.h
@@ -0,0 +1,16 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef _NS_LOCAL_FILE_COMMON_H_
+#define _NS_LOCAL_FILE_COMMON_H_
+
+#ifdef MOZ_ESR
+extern const char* const sExecutableExts[107];
+#else
+extern const char* const sExecutableExts[108];
+#endif
+
+#endif
diff --git a/xpcom/io/nsLocalFileUnix.cpp b/xpcom/io/nsLocalFileUnix.cpp
new file mode 100644
index 0000000000..f841a78da5
--- /dev/null
+++ b/xpcom/io/nsLocalFileUnix.cpp
@@ -0,0 +1,2916 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Implementation of nsIFile for "unixy" systems.
+ */
+
+#include "nsLocalFile.h"
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/CheckedInt.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Sprintf.h"
+#include "mozilla/FilePreferences.h"
+#include "prtime.h"
+
+#include <sys/select.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <dirent.h>
+
+#if defined(XP_MACOSX)
+#  include <sys/xattr.h>
+#endif
+
+#if defined(USE_LINUX_QUOTACTL)
+#  include <sys/mount.h>
+#  include <sys/quota.h>
+#  include <sys/sysmacros.h>
+#  ifndef BLOCK_SIZE
+#    define BLOCK_SIZE 1024 /* kernel block size */
+#  endif
+#endif
+
+#include "nsDirectoryServiceDefs.h"
+#include "nsCOMPtr.h"
+#include "nsIFile.h"
+#include "nsString.h"
+#include "nsIDirectoryEnumerator.h"
+#include "nsSimpleEnumerator.h"
+#include "private/pprio.h"
+#include "prlink.h"
+
+#ifdef MOZ_WIDGET_GTK
+#  include "nsIGIOService.h"
+#endif
+
+#ifdef MOZ_WIDGET_COCOA
+#  include <Carbon/Carbon.h>
+#  include "CocoaFileUtils.h"
+#  include "prmem.h"
+#  include "plbase64.h"
+
+static nsresult MacErrorMapper(OSErr inErr);
+#endif
+
+#ifdef MOZ_WIDGET_ANDROID
+#  include "mozilla/java/GeckoAppShellWrappers.h"
+#  include "nsIMIMEService.h"
+#  include <linux/magic.h>
+#endif
+
+#include "nsNativeCharsetUtils.h"
+#include "nsTraceRefcnt.h"
+
+/**
+ *  we need these for statfs()
+ */
+#ifdef HAVE_SYS_STATVFS_H
+#  if defined(__osf__) && defined(__DECCXX)
+extern "C" int statvfs(const char*, struct statvfs*);
+#  endif
+#  include <sys/statvfs.h>
+#endif
+
+#ifdef HAVE_SYS_STATFS_H
+#  include <sys/statfs.h>
+#endif
+
+#ifdef HAVE_SYS_VFS_H
+#  include <sys/vfs.h>
+#endif
+
+#if defined(HAVE_STATVFS64) && (!defined(LINUX) && !defined(__osf__))
+#  define STATFS statvfs64
+#  define F_BSIZE f_frsize
+#elif defined(HAVE_STATVFS) && (!defined(LINUX) && !defined(__osf__))
+#  define STATFS statvfs
+#  define F_BSIZE f_frsize
+#elif defined(HAVE_STATFS64)
+#  define STATFS statfs64
+#  define F_BSIZE f_bsize
+#elif defined(HAVE_STATFS)
+#  define STATFS statfs
+#  define F_BSIZE f_bsize
+#endif
+
+using namespace mozilla;
+
+#define ENSURE_STAT_CACHE()                            \
+  do {                                                 \
+    if (!FillStatCache()) return NSRESULT_FOR_ERRNO(); \
+  } while (0)
+
+#define CHECK_mPath()                                     \
+  do {                                                    \
+    if (mPath.IsEmpty()) return NS_ERROR_NOT_INITIALIZED; \
+    if (!FilePreferences::IsAllowedPath(mPath))           \
+      return NS_ERROR_FILE_ACCESS_DENIED;                 \
+  } while (0)
+
+static PRTime TimespecToMillis(const struct timespec& aTimeSpec) {
+  return PRTime(aTimeSpec.tv_sec) * PR_MSEC_PER_SEC +
+         PRTime(aTimeSpec.tv_nsec) / PR_NSEC_PER_MSEC;
+}
+
+/* directory enumerator */
+class nsDirEnumeratorUnix final : public nsSimpleEnumerator,
+                                  public nsIDirectoryEnumerator {
+ public:
+  nsDirEnumeratorUnix();
+
+  // nsISupports interface
+  NS_DECL_ISUPPORTS_INHERITED
+
+  // nsISimpleEnumerator interface
+  NS_DECL_NSISIMPLEENUMERATOR
+
+  // nsIDirectoryEnumerator interface
+  NS_DECL_NSIDIRECTORYENUMERATOR
+
+  NS_IMETHOD Init(nsLocalFile* aParent, bool aIgnored);
+
+  NS_FORWARD_NSISIMPLEENUMERATORBASE(nsSimpleEnumerator::)
+
+  const nsID& DefaultInterface() override { return NS_GET_IID(nsIFile); }
+
+ private:
+  ~nsDirEnumeratorUnix() override;
+
+ protected:
+  NS_IMETHOD GetNextEntry();
+
+  DIR* mDir;
+  struct dirent* mEntry;
+  nsCString mParentPath;
+};
+
+nsDirEnumeratorUnix::nsDirEnumeratorUnix() : mDir(nullptr), mEntry(nullptr) {}
+
+nsDirEnumeratorUnix::~nsDirEnumeratorUnix() { Close(); }
+
+NS_IMPL_ISUPPORTS_INHERITED(nsDirEnumeratorUnix, nsSimpleEnumerator,
+                            nsIDirectoryEnumerator)
+
+NS_IMETHODIMP
+nsDirEnumeratorUnix::Init(nsLocalFile* aParent,
+                          bool aResolveSymlinks /*ignored*/) {
+  nsAutoCString dirPath;
+  if (NS_FAILED(aParent->GetNativePath(dirPath)) || dirPath.IsEmpty()) {
+    return NS_ERROR_FILE_INVALID_PATH;
+  }
+
+  // When enumerating the directory, the paths must have a slash at the end.
+  nsAutoCString dirPathWithSlash(dirPath);
+  dirPathWithSlash.Append('/');
+  if (!FilePreferences::IsAllowedPath(dirPathWithSlash)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+
+  if (NS_FAILED(aParent->GetNativePath(mParentPath))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  mDir = opendir(dirPath.get());
+  if (!mDir) {
+    return NSRESULT_FOR_ERRNO();
+  }
+  return GetNextEntry();
+}
+
+NS_IMETHODIMP
+nsDirEnumeratorUnix::HasMoreElements(bool* aResult) {
+  *aResult = mDir && mEntry;
+  if (!*aResult) {
+    Close();
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDirEnumeratorUnix::GetNext(nsISupports** aResult) {
+  nsCOMPtr<nsIFile> file;
+  nsresult rv = GetNextFile(getter_AddRefs(file));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (!file) {
+    return NS_ERROR_FAILURE;
+  }
+  file.forget(aResult);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDirEnumeratorUnix::GetNextEntry() {
+  do {
+    errno = 0;
+    mEntry = readdir(mDir);
+
+    // end of dir or error
+    if (!mEntry) {
+      return NSRESULT_FOR_ERRNO();
+    }
+
+    // keep going past "." and ".."
+  } while (mEntry->d_name[0] == '.' &&
+           (mEntry->d_name[1] == '\0' ||                                // .\0
+            (mEntry->d_name[1] == '.' && mEntry->d_name[2] == '\0')));  // ..\0
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDirEnumeratorUnix::GetNextFile(nsIFile** aResult) {
+  nsresult rv;
+  if (!mDir || !mEntry) {
+    *aResult = nullptr;
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIFile> file = new nsLocalFile();
+
+  if (NS_FAILED(rv = file->InitWithNativePath(mParentPath)) ||
+      NS_FAILED(rv = file->AppendNative(nsDependentCString(mEntry->d_name)))) {
+    return rv;
+  }
+
+  file.forget(aResult);
+  return GetNextEntry();
+}
+
+NS_IMETHODIMP
+nsDirEnumeratorUnix::Close() {
+  if (mDir) {
+    closedir(mDir);
+    mDir = nullptr;
+  }
+  return NS_OK;
+}
+
+nsLocalFile::nsLocalFile() : mCachedStat() {}
+
+nsLocalFile::nsLocalFile(const nsACString& aFilePath) : mCachedStat() {
+  InitWithNativePath(aFilePath);
+}
+
+nsLocalFile::nsLocalFile(const nsLocalFile& aOther) : mPath(aOther.mPath) {}
+
+#ifdef MOZ_WIDGET_COCOA
+NS_IMPL_ISUPPORTS(nsLocalFile, nsILocalFileMac, nsIFile)
+#else
+NS_IMPL_ISUPPORTS(nsLocalFile, nsIFile)
+#endif
+
+nsresult nsLocalFile::nsLocalFileConstructor(const nsIID& aIID,
+                                             void** aInstancePtr) {
+  if (NS_WARN_IF(!aInstancePtr)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  *aInstancePtr = nullptr;
+
+  nsCOMPtr<nsIFile> inst = new nsLocalFile();
+  return inst->QueryInterface(aIID, aInstancePtr);
+}
+
+bool nsLocalFile::FillStatCache() {
+  if (!FilePreferences::IsAllowedPath(mPath)) {
+    errno = EACCES;
+    return false;
+  }
+
+  if (STAT(mPath.get(), &mCachedStat) == -1) {
+    // try lstat it may be a symlink
+    if (LSTAT(mPath.get(), &mCachedStat) == -1) {
+      return false;
+    }
+  }
+  return true;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Clone(nsIFile** aFile) {
+  // Just copy-construct ourselves
+  RefPtr<nsLocalFile> copy = new nsLocalFile(*this);
+  copy.forget(aFile);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::InitWithNativePath(const nsACString& aFilePath) {
+  if (aFilePath.EqualsLiteral("~") ||
+      Substring(aFilePath, 0, 2).EqualsLiteral("~/")) {
+    nsCOMPtr<nsIFile> homeDir;
+    nsAutoCString homePath;
+    if (NS_FAILED(
+            NS_GetSpecialDirectory(NS_OS_HOME_DIR, getter_AddRefs(homeDir))) ||
+        NS_FAILED(homeDir->GetNativePath(homePath))) {
+      return NS_ERROR_FAILURE;
+    }
+
+    mPath = homePath;
+    if (aFilePath.Length() > 2) {
+      mPath.Append(Substring(aFilePath, 1, aFilePath.Length() - 1));
+    }
+  } else {
+    if (aFilePath.IsEmpty() || aFilePath.First() != '/') {
+      return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+    }
+    mPath = aFilePath;
+  }
+
+  if (!FilePreferences::IsAllowedPath(mPath)) {
+    mPath.Truncate();
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+
+  // trim off trailing slashes
+  ssize_t len = mPath.Length();
+  while ((len > 1) && (mPath[len - 1] == '/')) {
+    --len;
+  }
+  mPath.SetLength(len);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::CreateAllAncestors(uint32_t aPermissions) {
+  if (!FilePreferences::IsAllowedPath(mPath)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+
+  // <jband> I promise to play nice
+  char* buffer = mPath.BeginWriting();
+  char* slashp = buffer;
+  int mkdir_result = 0;
+  int mkdir_errno;
+
+#ifdef DEBUG_NSIFILE
+  fprintf(stderr, "nsIFile: before: %s\n", buffer);
+#endif
+
+  while ((slashp = strchr(slashp + 1, '/'))) {
+    /*
+     * Sequences of '/' are equivalent to a single '/'.
+     */
+    if (slashp[1] == '/') {
+      continue;
+    }
+
+    /*
+     * If the path has a trailing slash, don't make the last component,
+     * because we'll get EEXIST in Create when we try to build the final
+     * component again, and it's easier to condition the logic here than
+     * there.
+     */
+    if (slashp[1] == '\0') {
+      break;
+    }
+
+    /* Temporarily NUL-terminate here */
+    *slashp = '\0';
+#ifdef DEBUG_NSIFILE
+    fprintf(stderr, "nsIFile: mkdir(\"%s\")\n", buffer);
+#endif
+    mkdir_result = mkdir(buffer, aPermissions);
+    if (mkdir_result == -1) {
+      mkdir_errno = errno;
+      /*
+       * Always set |errno| to EEXIST if the dir already exists
+       * (we have to do this here since the errno value is not consistent
+       * in all cases - various reasons like different platform,
+       * automounter-controlled dir, etc. can affect it (see bug 125489
+       * for details)).
+       */
+      if (mkdir_errno != EEXIST && access(buffer, F_OK) == 0) {
+        mkdir_errno = EEXIST;
+      }
+#ifdef DEBUG_NSIFILE
+      fprintf(stderr, "nsIFile: errno: %d\n", mkdir_errno);
+#endif
+    }
+
+    /* Put the / back */
+    *slashp = '/';
+  }
+
+  /*
+   * We could get EEXIST for an existing file -- not directory --
+   * but that's OK: we'll get ENOTDIR when we try to make the final
+   * component of the path back in Create and error out appropriately.
+   */
+  if (mkdir_result == -1 && mkdir_errno != EEXIST) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::OpenNSPRFileDesc(int32_t aFlags, int32_t aMode,
+                              PRFileDesc** aResult) {
+  if (!FilePreferences::IsAllowedPath(mPath)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+  *aResult = PR_Open(mPath.get(), aFlags, aMode);
+  if (!*aResult) {
+    return NS_ErrorAccordingToNSPR();
+  }
+
+  if (aFlags & DELETE_ON_CLOSE) {
+    PR_Delete(mPath.get());
+  }
+
+#if defined(HAVE_POSIX_FADVISE)
+  if (aFlags & OS_READAHEAD) {
+    posix_fadvise(PR_FileDesc2NativeHandle(*aResult), 0, 0,
+                  POSIX_FADV_SEQUENTIAL);
+  }
+#endif
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::OpenANSIFileDesc(const char* aMode, FILE** aResult) {
+  if (!FilePreferences::IsAllowedPath(mPath)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+  *aResult = fopen(mPath.get(), aMode);
+  if (!*aResult) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+static int do_create(const char* aPath, int aFlags, mode_t aMode,
+                     PRFileDesc** aResult) {
+  *aResult = PR_Open(aPath, aFlags, aMode);
+  return *aResult ? 0 : -1;
+}
+
+static int do_mkdir(const char* aPath, int aFlags, mode_t aMode,
+                    PRFileDesc** aResult) {
+  *aResult = nullptr;
+  return mkdir(aPath, aMode);
+}
+
+nsresult nsLocalFile::CreateAndKeepOpen(uint32_t aType, int aFlags,
+                                        uint32_t aPermissions,
+                                        bool aSkipAncestors,
+                                        PRFileDesc** aResult) {
+  if (!FilePreferences::IsAllowedPath(mPath)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+
+  if (aType != NORMAL_FILE_TYPE && aType != DIRECTORY_TYPE) {
+    return NS_ERROR_FILE_UNKNOWN_TYPE;
+  }
+
+  int (*createFunc)(const char*, int, mode_t, PRFileDesc**) =
+      (aType == NORMAL_FILE_TYPE) ? do_create : do_mkdir;
+
+  int result = createFunc(mPath.get(), aFlags, aPermissions, aResult);
+  if (result == -1 && errno == ENOENT && !aSkipAncestors) {
+    /*
+     * If we failed because of missing ancestor components, try to create
+     * them and then retry the original creation.
+     *
+     * Ancestor directories get the same permissions as the file we're
+     * creating, with the X bit set for each of (user,group,other) with
+     * an R bit in the original permissions.    If you want to do anything
+     * fancy like setgid or sticky bits, do it by hand.
+     */
+    int dirperm = aPermissions;
+    if (aPermissions & S_IRUSR) {
+      dirperm |= S_IXUSR;
+    }
+    if (aPermissions & S_IRGRP) {
+      dirperm |= S_IXGRP;
+    }
+    if (aPermissions & S_IROTH) {
+      dirperm |= S_IXOTH;
+    }
+
+#ifdef DEBUG_NSIFILE
+    fprintf(stderr, "nsIFile: perm = %o, dirperm = %o\n", aPermissions,
+            dirperm);
+#endif
+
+    if (NS_FAILED(CreateAllAncestors(dirperm))) {
+      return NS_ERROR_FAILURE;
+    }
+
+#ifdef DEBUG_NSIFILE
+    fprintf(stderr, "nsIFile: Create(\"%s\") again\n", mPath.get());
+#endif
+    result = createFunc(mPath.get(), aFlags, aPermissions, aResult);
+  }
+  return NSRESULT_FOR_RETURN(result);
+}
+
+NS_IMETHODIMP
+nsLocalFile::Create(uint32_t aType, uint32_t aPermissions,
+                    bool aSkipAncestors) {
+  if (!FilePreferences::IsAllowedPath(mPath)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+
+  PRFileDesc* junk = nullptr;
+  nsresult rv = CreateAndKeepOpen(
+      aType, PR_WRONLY | PR_CREATE_FILE | PR_TRUNCATE | PR_EXCL, aPermissions,
+      aSkipAncestors, &junk);
+  if (junk) {
+    PR_Close(junk);
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::AppendNative(const nsACString& aFragment) {
+  if (aFragment.IsEmpty()) {
+    return NS_OK;
+  }
+
+  // only one component of path can be appended and cannot append ".."
+  nsACString::const_iterator begin, end;
+  if (aFragment.EqualsASCII("..") ||
+      FindCharInReadable('/', aFragment.BeginReading(begin),
+                         aFragment.EndReading(end))) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+
+  return AppendRelativeNativePath(aFragment);
+}
+
+NS_IMETHODIMP
+nsLocalFile::AppendRelativeNativePath(const nsACString& aFragment) {
+  if (aFragment.IsEmpty()) {
+    return NS_OK;
+  }
+
+  // No leading '/' and cannot be ".."
+  if (aFragment.First() == '/' || aFragment.EqualsASCII("..")) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+
+  if (aFragment.Contains('/')) {
+    // can't contain .. as a path component. Ensure that the valid components
+    // "foo..foo", "..foo", and "foo.." are not falsely detected,
+    // but the invalid paths "../", "foo/..", "foo/../foo",
+    // "../foo", etc are.
+    constexpr auto doubleDot = "/.."_ns;
+    nsACString::const_iterator start, end, offset;
+    aFragment.BeginReading(start);
+    aFragment.EndReading(end);
+    offset = end;
+    while (FindInReadable(doubleDot, start, offset)) {
+      if (offset == end || *offset == '/') {
+        return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+      }
+      start = offset;
+      offset = end;
+    }
+
+    // catches the remaining cases of prefixes
+    if (StringBeginsWith(aFragment, "../"_ns)) {
+      return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+    }
+  }
+
+  if (!mPath.EqualsLiteral("/")) {
+    mPath.Append('/');
+  }
+  mPath.Append(aFragment);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Normalize() {
+  char resolved_path[PATH_MAX] = "";
+  char* resolved_path_ptr = nullptr;
+
+  if (!FilePreferences::IsAllowedPath(mPath)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+
+  resolved_path_ptr = realpath(mPath.get(), resolved_path);
+
+  // if there is an error, the return is null.
+  if (!resolved_path_ptr) {
+    return NSRESULT_FOR_ERRNO();
+  }
+
+  mPath = resolved_path;
+  return NS_OK;
+}
+
+void nsLocalFile::LocateNativeLeafName(nsACString::const_iterator& aBegin,
+                                       nsACString::const_iterator& aEnd) {
+  // XXX perhaps we should cache this??
+
+  mPath.BeginReading(aBegin);
+  mPath.EndReading(aEnd);
+
+  nsACString::const_iterator it = aEnd;
+  nsACString::const_iterator stop = aBegin;
+  --stop;
+  while (--it != stop) {
+    if (*it == '/') {
+      aBegin = ++it;
+      return;
+    }
+  }
+  // else, the entire path is the leaf name (which means this
+  // isn't an absolute path... unexpected??)
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetNativeLeafName(nsACString& aLeafName) {
+  nsACString::const_iterator begin, end;
+  LocateNativeLeafName(begin, end);
+  aLeafName = Substring(begin, end);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetNativeLeafName(const nsACString& aLeafName) {
+  nsACString::const_iterator begin, end;
+  LocateNativeLeafName(begin, end);
+  mPath.Replace(begin.get() - mPath.get(), Distance(begin, end), aLeafName);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetDisplayName(nsAString& aLeafName) {
+  return GetLeafName(aLeafName);
+}
+
+nsCString nsLocalFile::NativePath() { return mPath; }
+
+nsresult nsIFile::GetNativePath(nsACString& aResult) {
+  aResult = NativePath();
+  return NS_OK;
+}
+
+nsCString nsIFile::HumanReadablePath() {
+  nsCString path;
+  DebugOnly<nsresult> rv = GetNativePath(path);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+  return path;
+}
+
+nsresult nsLocalFile::GetNativeTargetPathName(nsIFile* aNewParent,
+                                              const nsACString& aNewName,
+                                              nsACString& aResult) {
+  nsresult rv;
+  nsCOMPtr<nsIFile> oldParent;
+
+  if (!aNewParent) {
+    if (NS_FAILED(rv = GetParent(getter_AddRefs(oldParent)))) {
+      return rv;
+    }
+    aNewParent = oldParent.get();
+  } else {
+    // check to see if our target directory exists
+    bool targetExists;
+    if (NS_FAILED(rv = aNewParent->Exists(&targetExists))) {
+      return rv;
+    }
+
+    if (!targetExists) {
+      // XXX create the new directory with some permissions
+      rv = aNewParent->Create(DIRECTORY_TYPE, 0755);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    } else {
+      // make sure that the target is actually a directory
+      bool targetIsDirectory;
+      if (NS_FAILED(rv = aNewParent->IsDirectory(&targetIsDirectory))) {
+        return rv;
+      }
+      if (!targetIsDirectory) {
+        return NS_ERROR_FILE_DESTINATION_NOT_DIR;
+      }
+    }
+  }
+
+  nsACString::const_iterator nameBegin, nameEnd;
+  if (!aNewName.IsEmpty()) {
+    aNewName.BeginReading(nameBegin);
+    aNewName.EndReading(nameEnd);
+  } else {
+    LocateNativeLeafName(nameBegin, nameEnd);
+  }
+
+  nsAutoCString dirName;
+  if (NS_FAILED(rv = aNewParent->GetNativePath(dirName))) {
+    return rv;
+  }
+
+  aResult = dirName + "/"_ns + Substring(nameBegin, nameEnd);
+  return NS_OK;
+}
+
+nsresult nsLocalFile::CopyDirectoryTo(nsIFile* aNewParent) {
+  nsresult rv;
+  /*
+   * dirCheck is used for various boolean test results such as from Equals,
+   * Exists, isDir, etc.
+   */
+  bool dirCheck, isSymlink;
+  uint32_t oldPerms;
+
+  if (NS_FAILED(rv = IsDirectory(&dirCheck))) {
+    return rv;
+  }
+  if (!dirCheck) {
+    return CopyToNative(aNewParent, ""_ns);
+  }
+
+  if (NS_FAILED(rv = Equals(aNewParent, &dirCheck))) {
+    return rv;
+  }
+  if (dirCheck) {
+    // can't copy dir to itself
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  if (NS_FAILED(rv = aNewParent->Exists(&dirCheck))) {
+    return rv;
+  }
+  // get the dirs old permissions
+  if (NS_FAILED(rv = GetPermissions(&oldPerms))) {
+    return rv;
+  }
+  if (!dirCheck) {
+    if (NS_FAILED(rv = aNewParent->Create(DIRECTORY_TYPE, oldPerms))) {
+      return rv;
+    }
+  } else {  // dir exists lets try to use leaf
+    nsAutoCString leafName;
+    if (NS_FAILED(rv = GetNativeLeafName(leafName))) {
+      return rv;
+    }
+    if (NS_FAILED(rv = aNewParent->AppendNative(leafName))) {
+      return rv;
+    }
+    if (NS_FAILED(rv = aNewParent->Exists(&dirCheck))) {
+      return rv;
+    }
+    if (dirCheck) {
+      return NS_ERROR_FILE_ALREADY_EXISTS;  // dest exists
+    }
+    if (NS_FAILED(rv = aNewParent->Create(DIRECTORY_TYPE, oldPerms))) {
+      return rv;
+    }
+  }
+
+  nsCOMPtr<nsIDirectoryEnumerator> dirIterator;
+  if (NS_FAILED(rv = GetDirectoryEntries(getter_AddRefs(dirIterator)))) {
+    return rv;
+  }
+
+  nsCOMPtr<nsIFile> entry;
+  while (NS_SUCCEEDED(dirIterator->GetNextFile(getter_AddRefs(entry))) &&
+         entry) {
+    if (NS_FAILED(rv = entry->IsSymlink(&isSymlink))) {
+      return rv;
+    }
+    if (NS_FAILED(rv = entry->IsDirectory(&dirCheck))) {
+      return rv;
+    }
+    if (dirCheck && !isSymlink) {
+      nsCOMPtr<nsIFile> destClone;
+      rv = aNewParent->Clone(getter_AddRefs(destClone));
+      if (NS_SUCCEEDED(rv)) {
+        if (NS_FAILED(rv = entry->CopyToNative(destClone, ""_ns))) {
+#ifdef DEBUG
+          nsresult rv2;
+          nsAutoCString pathName;
+          if (NS_FAILED(rv2 = entry->GetNativePath(pathName))) {
+            return rv2;
+          }
+          printf("Operation not supported: %s\n", pathName.get());
+#endif
+          if (rv == NS_ERROR_OUT_OF_MEMORY) {
+            return rv;
+          }
+          continue;
+        }
+      }
+    } else {
+      if (NS_FAILED(rv = entry->CopyToNative(aNewParent, ""_ns))) {
+#ifdef DEBUG
+        nsresult rv2;
+        nsAutoCString pathName;
+        if (NS_FAILED(rv2 = entry->GetNativePath(pathName))) {
+          return rv2;
+        }
+        printf("Operation not supported: %s\n", pathName.get());
+#endif
+        if (rv == NS_ERROR_OUT_OF_MEMORY) {
+          return rv;
+        }
+        continue;
+      }
+    }
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::CopyToNative(nsIFile* aNewParent, const nsACString& aNewName) {
+  nsresult rv;
+  // check to make sure that this has been initialized properly
+  CHECK_mPath();
+
+  // we copy the parent here so 'aNewParent' remains immutable
+  nsCOMPtr<nsIFile> workParent;
+  if (aNewParent) {
+    if (NS_FAILED(rv = aNewParent->Clone(getter_AddRefs(workParent)))) {
+      return rv;
+    }
+  } else {
+    if (NS_FAILED(rv = GetParent(getter_AddRefs(workParent)))) {
+      return rv;
+    }
+  }
+
+  // check to see if we are a directory or if we are a file
+  bool isDirectory;
+  if (NS_FAILED(rv = IsDirectory(&isDirectory))) {
+    return rv;
+  }
+
+  nsAutoCString newPathName;
+  if (isDirectory) {
+    if (!aNewName.IsEmpty()) {
+      if (NS_FAILED(rv = workParent->AppendNative(aNewName))) {
+        return rv;
+      }
+    } else {
+      if (NS_FAILED(rv = GetNativeLeafName(newPathName))) {
+        return rv;
+      }
+      if (NS_FAILED(rv = workParent->AppendNative(newPathName))) {
+        return rv;
+      }
+    }
+    if (NS_FAILED(rv = CopyDirectoryTo(workParent))) {
+      return rv;
+    }
+  } else {
+    rv = GetNativeTargetPathName(workParent, aNewName, newPathName);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+#ifdef DEBUG_blizzard
+    printf("nsLocalFile::CopyTo() %s -> %s\n", mPath.get(), newPathName.get());
+#endif
+
+    // actually create the file.
+    auto* newFile = new nsLocalFile();
+    nsCOMPtr<nsIFile> fileRef(newFile);  // release on exit
+
+    rv = newFile->InitWithNativePath(newPathName);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // get the old permissions
+    uint32_t myPerms = 0;
+    rv = GetPermissions(&myPerms);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // Create the new file with the old file's permissions, even if write
+    // permission is missing.  We can't create with write permission and
+    // then change back to myPerm on all filesystems (FAT on Linux, e.g.).
+    // But we can write to a read-only file on all Unix filesystems if we
+    // open it successfully for writing.
+
+    PRFileDesc* newFD;
+    rv = newFile->CreateAndKeepOpen(
+        NORMAL_FILE_TYPE, PR_WRONLY | PR_CREATE_FILE | PR_TRUNCATE, myPerms,
+        /* aSkipAncestors = */ false, &newFD);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // open the old file, too
+    bool specialFile;
+    if (NS_FAILED(rv = IsSpecial(&specialFile))) {
+      PR_Close(newFD);
+      return rv;
+    }
+    if (specialFile) {
+#ifdef DEBUG
+      printf("Operation not supported: %s\n", mPath.get());
+#endif
+      // make sure to clean up properly
+      PR_Close(newFD);
+      return NS_OK;
+    }
+
+#if defined(XP_MACOSX)
+    bool quarantined = true;
+    (void)HasXAttr("com.apple.quarantine"_ns, &quarantined);
+#endif
+
+    PRFileDesc* oldFD;
+    rv = OpenNSPRFileDesc(PR_RDONLY, myPerms, &oldFD);
+    if (NS_FAILED(rv)) {
+      // make sure to clean up properly
+      PR_Close(newFD);
+      return rv;
+    }
+
+#ifdef DEBUG_blizzard
+    int32_t totalRead = 0;
+    int32_t totalWritten = 0;
+#endif
+    char buf[BUFSIZ];
+    int32_t bytesRead;
+
+    // record PR_Write() error for better error message later.
+    nsresult saved_write_error = NS_OK;
+    nsresult saved_read_error = NS_OK;
+    nsresult saved_read_close_error = NS_OK;
+    nsresult saved_write_close_error = NS_OK;
+
+    // DONE: Does PR_Read() return bytesRead < 0 for error?
+    // Yes., The errors from PR_Read are not so common and
+    // the value may not have correspondence in NS_ERROR_*, but
+    // we do catch it still, immediately after while() loop.
+    // We can differentiate errors pf PR_Read and PR_Write by
+    // looking at saved_write_error value. If PR_Write error occurs (and not
+    // PR_Read() error), save_write_error is not NS_OK.
+
+    while ((bytesRead = PR_Read(oldFD, buf, BUFSIZ)) > 0) {
+#ifdef DEBUG_blizzard
+      totalRead += bytesRead;
+#endif
+
+      // PR_Write promises never to do a short write
+      int32_t bytesWritten = PR_Write(newFD, buf, bytesRead);
+      if (bytesWritten < 0) {
+        saved_write_error = NSRESULT_FOR_ERRNO();
+        bytesRead = -1;
+        break;
+      }
+      NS_ASSERTION(bytesWritten == bytesRead, "short PR_Write?");
+
+#ifdef DEBUG_blizzard
+      totalWritten += bytesWritten;
+#endif
+    }
+
+    // TODO/FIXME: If CIFS (and NFS?) may force read/write to return EINTR,
+    // we are better off to prepare for retrying. But we need confirmation if
+    // EINTR is returned.
+
+    // Record error if PR_Read() failed.
+    // Must be done before any other I/O which may reset errno.
+    if (bytesRead < 0 && saved_write_error == NS_OK) {
+      saved_read_error = NSRESULT_FOR_ERRNO();
+    }
+
+#ifdef DEBUG_blizzard
+    printf("read %d bytes, wrote %d bytes\n", totalRead, totalWritten);
+#endif
+
+    // DONE: Errors of close can occur.  Read man page of
+    // close(2);
+    // This is likely to happen if the file system is remote file
+    // system (NFS, CIFS, etc.) and network outage occurs.
+    // At least, we should tell the user that filesystem/disk is
+    // hosed (possibly due to network error, hard disk failure,
+    // etc.) so that users can take remedial action.
+
+    // close the files
+    if (PR_Close(newFD) < 0) {
+      saved_write_close_error = NSRESULT_FOR_ERRNO();
+#if DEBUG
+      // This error merits printing.
+      fprintf(stderr, "ERROR: PR_Close(newFD) returned error. errno = %d\n",
+              errno);
+#endif
+    }
+#if defined(XP_MACOSX)
+    else if (!quarantined) {
+      // If the original file was not in quarantine, lift the quarantine that
+      // file creation added because of LSFileQuarantineEnabled.
+      (void)newFile->DelXAttr("com.apple.quarantine"_ns);
+    }
+#endif  // defined(XP_MACOSX)
+
+    if (PR_Close(oldFD) < 0) {
+      saved_read_close_error = NSRESULT_FOR_ERRNO();
+#if DEBUG
+      fprintf(stderr, "ERROR: PR_Close(oldFD) returned error. errno = %d\n",
+              errno);
+#endif
+    }
+
+    // Let us report the failure to write and read.
+    // check for write/read error after cleaning up
+    if (bytesRead < 0) {
+      if (saved_write_error != NS_OK) {
+        return saved_write_error;
+      }
+      if (saved_read_error != NS_OK) {
+        return saved_read_error;
+      }
+#if DEBUG
+      MOZ_ASSERT(0);
+#endif
+    }
+
+    if (saved_write_close_error != NS_OK) {
+      return saved_write_close_error;
+    }
+    if (saved_read_close_error != NS_OK) {
+      return saved_read_close_error;
+    }
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::CopyToFollowingLinksNative(nsIFile* aNewParent,
+                                        const nsACString& aNewName) {
+  return CopyToNative(aNewParent, aNewName);
+}
+
+NS_IMETHODIMP
+nsLocalFile::MoveToNative(nsIFile* aNewParent, const nsACString& aNewName) {
+  nsresult rv;
+
+  // check to make sure that this has been initialized properly
+  CHECK_mPath();
+
+  // check to make sure that we have a new parent
+  nsAutoCString newPathName;
+  rv = GetNativeTargetPathName(aNewParent, aNewName, newPathName);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (!FilePreferences::IsAllowedPath(newPathName)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+
+  // try for atomic rename, falling back to copy/delete
+  if (rename(mPath.get(), newPathName.get()) < 0) {
+    if (errno == EXDEV) {
+      rv = CopyToNative(aNewParent, aNewName);
+      if (NS_SUCCEEDED(rv)) {
+        rv = Remove(true);
+      }
+    } else {
+      rv = NSRESULT_FOR_ERRNO();
+    }
+  }
+
+  if (NS_SUCCEEDED(rv)) {
+    // Adjust this
+    mPath = newPathName;
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::MoveToFollowingLinksNative(nsIFile* aNewParent,
+                                        const nsACString& aNewName) {
+  return MoveToNative(aNewParent, aNewName);
+}
+
+NS_IMETHODIMP
+nsLocalFile::Remove(bool aRecursive, uint32_t* aRemoveCount) {
+  CHECK_mPath();
+  ENSURE_STAT_CACHE();
+
+  bool isSymLink;
+
+  nsresult rv = IsSymlink(&isSymLink);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (isSymLink || !S_ISDIR(mCachedStat.st_mode)) {
+    rv = NSRESULT_FOR_RETURN(unlink(mPath.get()));
+    if (NS_SUCCEEDED(rv) && aRemoveCount) {
+      *aRemoveCount += 1;
+    }
+    return rv;
+  }
+
+  if (aRecursive) {
+    auto* dir = new nsDirEnumeratorUnix();
+
+    RefPtr<nsSimpleEnumerator> dirRef(dir);  // release on exit
+
+    rv = dir->Init(this, false);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    bool more;
+    while (NS_SUCCEEDED(dir->HasMoreElements(&more)) && more) {
+      nsCOMPtr<nsISupports> item;
+      rv = dir->GetNext(getter_AddRefs(item));
+      if (NS_FAILED(rv)) {
+        return NS_ERROR_FAILURE;
+      }
+
+      nsCOMPtr<nsIFile> file = do_QueryInterface(item, &rv);
+      if (NS_FAILED(rv)) {
+        return NS_ERROR_FAILURE;
+      }
+      // XXX: We care the result of the removal here while
+      // nsLocalFileWin does not. We should align the behavior. (bug 1779696)
+      rv = file->Remove(aRecursive, aRemoveCount);
+
+#ifdef ANDROID
+      // See bug 580434 - Bionic gives us just deleted files
+      if (rv == NS_ERROR_FILE_NOT_FOUND) {
+        continue;
+      }
+#endif
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    }
+  }
+
+  rv = NSRESULT_FOR_RETURN(rmdir(mPath.get()));
+  if (NS_SUCCEEDED(rv) && aRemoveCount) {
+    *aRemoveCount += 1;
+  }
+  return rv;
+}
+
+nsresult nsLocalFile::GetTimeImpl(PRTime* aTime,
+                                  nsLocalFile::TimeField aTimeField,
+                                  bool aFollowLinks) {
+  CHECK_mPath();
+  if (NS_WARN_IF(!aTime)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  using StatFn = int (*)(const char*, struct STAT*);
+  StatFn statFn = aFollowLinks ? &STAT : &LSTAT;
+
+  struct STAT fileStats {};
+  if (statFn(mPath.get(), &fileStats) < 0) {
+    return NSRESULT_FOR_ERRNO();
+  }
+
+  struct timespec* timespec;
+  switch (aTimeField) {
+    case TimeField::AccessedTime:
+#if (defined(__APPLE__) && defined(__MACH__))
+      timespec = &fileStats.st_atimespec;
+#else
+      timespec = &fileStats.st_atim;
+#endif
+      break;
+
+    case TimeField::ModifiedTime:
+#if (defined(__APPLE__) && defined(__MACH__))
+      timespec = &fileStats.st_mtimespec;
+#else
+      timespec = &fileStats.st_mtim;
+#endif
+      break;
+
+    default:
+      MOZ_CRASH("Unknown TimeField");
+  }
+
+  *aTime = TimespecToMillis(*timespec);
+
+  return NS_OK;
+}
+
+nsresult nsLocalFile::SetTimeImpl(PRTime aTime,
+                                  nsLocalFile::TimeField aTimeField,
+                                  bool aFollowLinks) {
+  CHECK_mPath();
+
+  using UtimesFn = int (*)(const char*, const timeval*);
+  UtimesFn utimesFn = &utimes;
+
+#if HAVE_LUTIMES
+  if (!aFollowLinks) {
+    utimesFn = &lutimes;
+  }
+#endif
+
+  ENSURE_STAT_CACHE();
+
+  if (aTime == 0) {
+    aTime = PR_Now();
+  }
+
+  // We only want to write to a single field (accessed time or modified time),
+  // but utimes() doesn't let you omit one. If you do, it will set that field to
+  // the current time, which is not what we want.
+  //
+  // So what we do is write to both fields, but copy one of the fields from our
+  // cached stat structure.
+  //
+  // If we are writing to the accessed time field, then we want to copy the
+  // modified time and vice versa.
+
+  timeval times[2];
+
+  const size_t writeIndex = aTimeField == TimeField::AccessedTime ? 0 : 1;
+  const size_t copyIndex = aTimeField == TimeField::AccessedTime ? 1 : 0;
+
+#if (defined(__APPLE__) && defined(__MACH__))
+  auto* copyFrom = aTimeField == TimeField::AccessedTime
+                       ? &mCachedStat.st_mtimespec
+                       : &mCachedStat.st_atimespec;
+#else
+  auto* copyFrom = aTimeField == TimeField::AccessedTime ? &mCachedStat.st_mtim
+                                                         : &mCachedStat.st_atim;
+#endif
+
+  times[copyIndex].tv_sec = copyFrom->tv_sec;
+  times[copyIndex].tv_usec = copyFrom->tv_nsec / 1000;
+
+  times[writeIndex].tv_sec = aTime / PR_MSEC_PER_SEC;
+  times[writeIndex].tv_usec = (aTime % PR_MSEC_PER_SEC) * PR_USEC_PER_MSEC;
+
+  int result = utimesFn(mPath.get(), times);
+  return NSRESULT_FOR_RETURN(result);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetLastAccessedTime(PRTime* aLastAccessedTime) {
+  return GetTimeImpl(aLastAccessedTime, TimeField::AccessedTime,
+                     /* follow links? */ true);
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetLastAccessedTime(PRTime aLastAccessedTime) {
+  return SetTimeImpl(aLastAccessedTime, TimeField::AccessedTime,
+                     /* follow links? */ true);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetLastAccessedTimeOfLink(PRTime* aLastAccessedTime) {
+  return GetTimeImpl(aLastAccessedTime, TimeField::AccessedTime,
+                     /* follow links? */ false);
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetLastAccessedTimeOfLink(PRTime aLastAccessedTime) {
+  return SetTimeImpl(aLastAccessedTime, TimeField::AccessedTime,
+                     /* follow links? */ false);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetLastModifiedTime(PRTime* aLastModTime) {
+  return GetTimeImpl(aLastModTime, TimeField::ModifiedTime,
+                     /* follow links? */ true);
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetLastModifiedTime(PRTime aLastModTime) {
+  return SetTimeImpl(aLastModTime, TimeField::ModifiedTime,
+                     /* follow links ? */ true);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetLastModifiedTimeOfLink(PRTime* aLastModTimeOfLink) {
+  return GetTimeImpl(aLastModTimeOfLink, TimeField::ModifiedTime,
+                     /* follow link? */ false);
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetLastModifiedTimeOfLink(PRTime aLastModTimeOfLink) {
+  return SetTimeImpl(aLastModTimeOfLink, TimeField::ModifiedTime,
+                     /* follow links? */ false);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetCreationTime(PRTime* aCreationTime) {
+  return GetCreationTimeImpl(aCreationTime, false);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetCreationTimeOfLink(PRTime* aCreationTimeOfLink) {
+  return GetCreationTimeImpl(aCreationTimeOfLink, /* aFollowLinks = */ true);
+}
+
+nsresult nsLocalFile::GetCreationTimeImpl(PRTime* aCreationTime,
+                                          bool aFollowLinks) {
+  CHECK_mPath();
+  if (NS_WARN_IF(!aCreationTime)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+#if defined(_DARWIN_FEATURE_64_BIT_INODE)
+  using StatFn = int (*)(const char*, struct STAT*);
+  StatFn statFn = aFollowLinks ? &STAT : &LSTAT;
+
+  struct STAT fileStats {};
+  if (statFn(mPath.get(), &fileStats) < 0) {
+    return NSRESULT_FOR_ERRNO();
+  }
+
+  *aCreationTime = TimespecToMillis(fileStats.st_birthtimespec);
+  return NS_OK;
+#else
+  return NS_ERROR_NOT_IMPLEMENTED;
+#endif
+}
+
+/*
+ * Only send back permissions bits: maybe we want to send back the whole
+ * mode_t to permit checks against other file types?
+ */
+
+#define NORMALIZE_PERMS(mode) ((mode) & (S_IRWXU | S_IRWXG | S_IRWXO))
+
+NS_IMETHODIMP
+nsLocalFile::GetPermissions(uint32_t* aPermissions) {
+  if (NS_WARN_IF(!aPermissions)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  ENSURE_STAT_CACHE();
+  *aPermissions = NORMALIZE_PERMS(mCachedStat.st_mode);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetPermissionsOfLink(uint32_t* aPermissionsOfLink) {
+  CHECK_mPath();
+  if (NS_WARN_IF(!aPermissionsOfLink)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  struct STAT sbuf;
+  if (LSTAT(mPath.get(), &sbuf) == -1) {
+    return NSRESULT_FOR_ERRNO();
+  }
+  *aPermissionsOfLink = NORMALIZE_PERMS(sbuf.st_mode);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetPermissions(uint32_t aPermissions) {
+  CHECK_mPath();
+
+  /*
+   * Race condition here: we should use fchmod instead, there's no way to
+   * guarantee the name still refers to the same file.
+   */
+  if (chmod(mPath.get(), aPermissions) >= 0) {
+    return NS_OK;
+  }
+#if defined(ANDROID) && defined(STATFS)
+  // For the time being, this is restricted for use by Android, but we
+  // will figure out what to do for all platforms in bug 638503
+  struct STATFS sfs;
+  if (STATFS(mPath.get(), &sfs) < 0) {
+    return NSRESULT_FOR_ERRNO();
+  }
+
+  // if this is a FAT file system we can't set file permissions
+  if (sfs.f_type == MSDOS_SUPER_MAGIC) {
+    return NS_OK;
+  }
+#endif
+  return NSRESULT_FOR_ERRNO();
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetPermissionsOfLink(uint32_t aPermissions) {
+  // There isn't a consistent mechanism for doing this on UNIX platforms. We
+  // might want to carefully implement this in the future though.
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetFileSize(int64_t* aFileSize) {
+  if (NS_WARN_IF(!aFileSize)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aFileSize = 0;
+  ENSURE_STAT_CACHE();
+
+  if (!S_ISDIR(mCachedStat.st_mode)) {
+    *aFileSize = (int64_t)mCachedStat.st_size;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetFileSize(int64_t aFileSize) {
+  CHECK_mPath();
+
+#if defined(ANDROID)
+  /* no truncate on bionic */
+  int fd = open(mPath.get(), O_WRONLY);
+  if (fd == -1) {
+    return NSRESULT_FOR_ERRNO();
+  }
+
+  int ret = ftruncate(fd, (off_t)aFileSize);
+  close(fd);
+
+  if (ret == -1) {
+    return NSRESULT_FOR_ERRNO();
+  }
+#elif defined(HAVE_TRUNCATE64)
+  if (truncate64(mPath.get(), (off64_t)aFileSize) == -1) {
+    return NSRESULT_FOR_ERRNO();
+  }
+#else
+  off_t size = (off_t)aFileSize;
+  if (truncate(mPath.get(), size) == -1) {
+    return NSRESULT_FOR_ERRNO();
+  }
+#endif
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetFileSizeOfLink(int64_t* aFileSize) {
+  CHECK_mPath();
+  if (NS_WARN_IF(!aFileSize)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  struct STAT sbuf;
+  if (LSTAT(mPath.get(), &sbuf) == -1) {
+    return NSRESULT_FOR_ERRNO();
+  }
+
+  *aFileSize = (int64_t)sbuf.st_size;
+  return NS_OK;
+}
+
+#if defined(USE_LINUX_QUOTACTL)
+/*
+ * Searches /proc/self/mountinfo for given device (Major:Minor),
+ * returns exported name from /dev
+ *
+ * Fails when /proc/self/mountinfo or diven device don't exist.
+ */
+static bool GetDeviceName(unsigned int aDeviceMajor, unsigned int aDeviceMinor,
+                          nsACString& aDeviceName) {
+  bool ret = false;
+
+  const int kMountInfoLineLength = 200;
+  const int kMountInfoDevPosition = 6;
+
+  char mountinfoLine[kMountInfoLineLength];
+  char deviceNum[kMountInfoLineLength];
+
+  SprintfLiteral(deviceNum, "%u:%u", aDeviceMajor, aDeviceMinor);
+
+  FILE* f = fopen("/proc/self/mountinfo", "rt");
+  if (!f) {
+    return ret;
+  }
+
+  // Expects /proc/self/mountinfo in format:
+  // 'ID ID major:minor root mountpoint flags - type devicename flags'
+  while (fgets(mountinfoLine, kMountInfoLineLength, f)) {
+    char* p_dev = strstr(mountinfoLine, deviceNum);
+
+    for (int i = 0; i < kMountInfoDevPosition && p_dev; ++i) {
+      p_dev = strchr(p_dev, ' ');
+      if (p_dev) {
+        p_dev++;
+      }
+    }
+
+    if (p_dev) {
+      char* p_dev_end = strchr(p_dev, ' ');
+      if (p_dev_end) {
+        *p_dev_end = '\0';
+        aDeviceName.Assign(p_dev);
+        ret = true;
+        break;
+      }
+    }
+  }
+
+  fclose(f);
+  return ret;
+}
+#endif
+
+#if defined(USE_LINUX_QUOTACTL)
+template <typename StatInfoFunc, typename QuotaInfoFunc>
+nsresult nsLocalFile::GetDiskInfo(StatInfoFunc&& aStatInfoFunc,
+                                  QuotaInfoFunc&& aQuotaInfoFunc,
+                                  int64_t* aResult)
+#else
+template <typename StatInfoFunc>
+nsresult nsLocalFile::GetDiskInfo(StatInfoFunc&& aStatInfoFunc,
+                                  int64_t* aResult)
+#endif
+{
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // These systems have the operations necessary to check disk space.
+
+#ifdef STATFS
+
+  // check to make sure that mPath is properly initialized
+  CHECK_mPath();
+
+  struct STATFS fs_buf;
+
+  /*
+   * Members of the STATFS struct that you should know about:
+   * F_BSIZE = block size on disk.
+   * f_bavail = number of free blocks available to a non-superuser.
+   * f_bfree = number of total free blocks in file system.
+   * f_blocks = number of total used or free blocks in file system.
+   */
+
+  if (STATFS(mPath.get(), &fs_buf) < 0) {
+    // The call to STATFS failed.
+#  ifdef DEBUG
+    printf("ERROR: GetDiskInfo: STATFS call FAILED. \n");
+#  endif
+    return NS_ERROR_FAILURE;
+  }
+
+  CheckedInt64 statfsResult = std::forward<StatInfoFunc>(aStatInfoFunc)(fs_buf);
+  if (!statfsResult.isValid()) {
+    return NS_ERROR_CANNOT_CONVERT_DATA;
+  }
+
+  // Assign statfsResult to *aResult in case one of the quota calls fails.
+  *aResult = statfsResult.value();
+
+#  if defined(USE_LINUX_QUOTACTL)
+
+  if (!FillStatCache()) {
+    // Returns info from statfs
+    return NS_OK;
+  }
+
+  nsAutoCString deviceName;
+  if (!GetDeviceName(major(mCachedStat.st_dev), minor(mCachedStat.st_dev),
+                     deviceName)) {
+    // Returns info from statfs
+    return NS_OK;
+  }
+
+  struct dqblk dq;
+  if (!quotactl(QCMD(Q_GETQUOTA, USRQUOTA), deviceName.get(), getuid(),
+                (caddr_t)&dq)
+#    ifdef QIF_BLIMITS
+      && dq.dqb_valid & QIF_BLIMITS
+#    endif
+      && dq.dqb_bhardlimit) {
+    CheckedInt64 quotaResult = std::forward<QuotaInfoFunc>(aQuotaInfoFunc)(dq);
+    if (!quotaResult.isValid()) {
+      // Returns info from statfs
+      return NS_OK;
+    }
+
+    if (quotaResult.value() < *aResult) {
+      *aResult = quotaResult.value();
+    }
+  }
+#  endif  // defined(USE_LINUX_QUOTACTL)
+
+#  ifdef DEBUG_DISK_SPACE
+  printf("DiskInfo: %lu bytes\n", *aResult);
+#  endif
+
+  return NS_OK;
+
+#else  // STATFS
+  /*
+   * This platform doesn't have statfs or statvfs.  I'm sure that there's
+   * a way to check for free disk space and disk capacity on platforms that
+   * don't have statfs (I'm SURE they have df, for example).
+   *
+   * Until we figure out how to do that, lets be honest and say that this
+   * command isn't implemented properly for these platforms yet.
+   */
+#  ifdef DEBUG
+  printf("ERROR: GetDiskInfo: Not implemented for plaforms without statfs.\n");
+#  endif
+  return NS_ERROR_NOT_IMPLEMENTED;
+
+#endif  // STATFS
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetDiskSpaceAvailable(int64_t* aDiskSpaceAvailable) {
+  return GetDiskInfo(
+      [](const struct STATFS& aStatInfo) {
+        return aStatInfo.f_bavail * static_cast<uint64_t>(aStatInfo.F_BSIZE);
+      },
+#if defined(USE_LINUX_QUOTACTL)
+      [](const struct dqblk& aQuotaInfo) -> uint64_t {
+        // dqb_bhardlimit is count of BLOCK_SIZE blocks, dqb_curspace is bytes
+        const uint64_t hardlimit = aQuotaInfo.dqb_bhardlimit * BLOCK_SIZE;
+        if (hardlimit > aQuotaInfo.dqb_curspace) {
+          return hardlimit - aQuotaInfo.dqb_curspace;
+        }
+        return 0;
+      },
+#endif
+      aDiskSpaceAvailable);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetDiskCapacity(int64_t* aDiskCapacity) {
+  return GetDiskInfo(
+      [](const struct STATFS& aStatInfo) {
+        return aStatInfo.f_blocks * static_cast<uint64_t>(aStatInfo.F_BSIZE);
+      },
+#if defined(USE_LINUX_QUOTACTL)
+      [](const struct dqblk& aQuotaInfo) {
+        // dqb_bhardlimit is count of BLOCK_SIZE blocks
+        return aQuotaInfo.dqb_bhardlimit * BLOCK_SIZE;
+      },
+#endif
+      aDiskCapacity);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetParent(nsIFile** aParent) {
+  CHECK_mPath();
+  if (NS_WARN_IF(!aParent)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aParent = nullptr;
+
+  // if '/' we are at the top of the volume, return null
+  if (mPath.EqualsLiteral("/")) {
+    return NS_OK;
+  }
+
+  // <brendan, after jband> I promise to play nice
+  char* buffer = mPath.BeginWriting();
+  // find the last significant slash in buffer
+  char* slashp = strrchr(buffer, '/');
+  NS_ASSERTION(slashp, "non-canonical path?");
+  if (!slashp) {
+    return NS_ERROR_FILE_INVALID_PATH;
+  }
+
+  // for the case where we are at '/'
+  if (slashp == buffer) {
+    slashp++;
+  }
+
+  // temporarily terminate buffer at the last significant slash
+  char c = *slashp;
+  *slashp = '\0';
+
+  nsCOMPtr<nsIFile> localFile;
+  nsresult rv = NS_NewNativeLocalFile(nsDependentCString(buffer), true,
+                                      getter_AddRefs(localFile));
+
+  // make buffer whole again
+  *slashp = c;
+
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  localFile.forget(aParent);
+  return NS_OK;
+}
+
+/*
+ * The results of Exists, isWritable and isReadable are not cached.
+ */
+
+NS_IMETHODIMP
+nsLocalFile::Exists(bool* aResult) {
+  CHECK_mPath();
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  *aResult = (access(mPath.get(), F_OK) == 0);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsWritable(bool* aResult) {
+  CHECK_mPath();
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  *aResult = (access(mPath.get(), W_OK) == 0);
+  if (*aResult || errno == EACCES) {
+    return NS_OK;
+  }
+  return NSRESULT_FOR_ERRNO();
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsReadable(bool* aResult) {
+  CHECK_mPath();
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  *aResult = (access(mPath.get(), R_OK) == 0);
+  if (*aResult || errno == EACCES) {
+    return NS_OK;
+  }
+  return NSRESULT_FOR_ERRNO();
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsExecutable(bool* aResult) {
+  CHECK_mPath();
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // Check extension (bug 663899). On certain platforms, the file
+  // extension may cause the OS to treat it as executable regardless of
+  // the execute bit, such as .jar on Mac OS X. We borrow the code from
+  // nsLocalFileWin, slightly modified.
+
+  // Don't be fooled by symlinks.
+  bool symLink;
+  nsresult rv = IsSymlink(&symLink);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  nsAutoString path;
+  if (symLink) {
+    GetTarget(path);
+  } else {
+    GetPath(path);
+  }
+
+  int32_t dotIdx = path.RFindChar(char16_t('.'));
+  if (dotIdx != kNotFound) {
+    // Convert extension to lower case.
+    char16_t* p = path.BeginWriting();
+    for (p += dotIdx + 1; *p; ++p) {
+      *p += (*p >= L'A' && *p <= L'Z') ? 'a' - 'A' : 0;
+    }
+
+    // Search for any of the set of executable extensions.
+    static const char* const executableExts[] = {
+#ifdef MOZ_WIDGET_COCOA
+        "afploc",  // Can point to other files.
+#endif
+        "air",  // Adobe AIR installer
+#ifdef MOZ_WIDGET_COCOA
+        "atloc",    // Can point to other files.
+        "fileloc",  // File location files can be used to point to other
+                    // files.
+        "ftploc",   // Can point to other files.
+        "inetloc",  // Shouldn't be able to do the same, but can, due to
+                    // macOS vulnerabilities.
+#endif
+        "jar"  // java application bundle
+    };
+    nsDependentSubstring ext = Substring(path, dotIdx + 1);
+    for (auto executableExt : executableExts) {
+      if (ext.EqualsASCII(executableExt)) {
+        // Found a match.  Set result and quit.
+        *aResult = true;
+        return NS_OK;
+      }
+    }
+  }
+
+  // On OS X, then query Launch Services.
+#ifdef MOZ_WIDGET_COCOA
+  // Certain Mac applications, such as Classic applications, which
+  // run under Rosetta, might not have the +x mode bit but are still
+  // considered to be executable by Launch Services (bug 646748).
+  CFURLRef url;
+  if (NS_FAILED(GetCFURL(&url))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  LSRequestedInfo theInfoRequest = kLSRequestAllInfo;
+  LSItemInfoRecord theInfo;
+  OSStatus result = ::LSCopyItemInfoForURL(url, theInfoRequest, &theInfo);
+  ::CFRelease(url);
+  if (result == noErr) {
+    if ((theInfo.flags & kLSItemInfoIsApplication) != 0) {
+      *aResult = true;
+      return NS_OK;
+    }
+  }
+#endif
+
+  // Then check the execute bit.
+  *aResult = (access(mPath.get(), X_OK) == 0);
+#ifdef SOLARIS
+  // On Solaris, access will always return 0 for root user, however
+  // the file is only executable if S_IXUSR | S_IXGRP | S_IXOTH is set.
+  // See bug 351950, https://bugzilla.mozilla.org/show_bug.cgi?id=351950
+  if (*aResult) {
+    struct STAT buf;
+
+    *aResult = (STAT(mPath.get(), &buf) == 0);
+    if (*aResult || errno == EACCES) {
+      *aResult = *aResult && (buf.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH));
+      return NS_OK;
+    }
+
+    return NSRESULT_FOR_ERRNO();
+  }
+#endif
+  if (*aResult || errno == EACCES) {
+    return NS_OK;
+  }
+  return NSRESULT_FOR_ERRNO();
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsDirectory(bool* aResult) {
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aResult = false;
+  ENSURE_STAT_CACHE();
+  *aResult = S_ISDIR(mCachedStat.st_mode);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsFile(bool* aResult) {
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aResult = false;
+  ENSURE_STAT_CACHE();
+  *aResult = S_ISREG(mCachedStat.st_mode);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsHidden(bool* aResult) {
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  nsACString::const_iterator begin, end;
+  LocateNativeLeafName(begin, end);
+  *aResult = (*begin == '.');
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsSymlink(bool* aResult) {
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  CHECK_mPath();
+
+  struct STAT symStat;
+  if (LSTAT(mPath.get(), &symStat) == -1) {
+    return NSRESULT_FOR_ERRNO();
+  }
+  *aResult = S_ISLNK(symStat.st_mode);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsSpecial(bool* aResult) {
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  ENSURE_STAT_CACHE();
+  *aResult = S_ISCHR(mCachedStat.st_mode) || S_ISBLK(mCachedStat.st_mode) ||
+#ifdef S_ISSOCK
+             S_ISSOCK(mCachedStat.st_mode) ||
+#endif
+             S_ISFIFO(mCachedStat.st_mode);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Equals(nsIFile* aInFile, bool* aResult) {
+  if (NS_WARN_IF(!aInFile)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aResult = false;
+
+  nsAutoCString inPath;
+  nsresult rv = aInFile->GetNativePath(inPath);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // We don't need to worry about "/foo/" vs. "/foo" here
+  // because trailing slashes are stripped on init.
+  *aResult = !strcmp(inPath.get(), mPath.get());
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Contains(nsIFile* aInFile, bool* aResult) {
+  CHECK_mPath();
+  if (NS_WARN_IF(!aInFile)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsAutoCString inPath;
+  nsresult rv;
+
+  if (NS_FAILED(rv = aInFile->GetNativePath(inPath))) {
+    return rv;
+  }
+
+  *aResult = false;
+
+  ssize_t len = mPath.Length();
+  if (strncmp(mPath.get(), inPath.get(), len) == 0) {
+    // Now make sure that the |aInFile|'s path has a separator at len,
+    // which implies that it has more components after len.
+    if (inPath[len] == '/') {
+      *aResult = true;
+    }
+  }
+
+  return NS_OK;
+}
+
+static nsresult ReadLinkSafe(const nsCString& aTarget, int32_t aExpectedSize,
+                             nsACString& aOutBuffer) {
+  // If we call readlink with a buffer size S it returns S, then we cannot tell
+  // if the buffer was big enough to hold the entire path. We allocate an
+  // additional byte so we can check if the buffer was large enough.
+  const auto allocSize = CheckedInt<size_t>(aExpectedSize) + 1;
+  if (!allocSize.isValid()) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  auto result = aOutBuffer.BulkWrite(allocSize.value(), 0, false);
+  if (result.isErr()) {
+    return result.unwrapErr();
+  }
+
+  auto handle = result.unwrap();
+
+  while (true) {
+    ssize_t bytesWritten =
+        readlink(aTarget.get(), handle.Elements(), handle.Length());
+    if (bytesWritten < 0) {
+      return NSRESULT_FOR_ERRNO();
+    }
+
+    // written >= 0 so it is safe to cast to size_t.
+    if ((size_t)bytesWritten < handle.Length()) {
+      // Target might have changed since the lstat call, or lstat might lie, see
+      // bug 1791029.
+      handle.Finish(bytesWritten, false);
+      return NS_OK;
+    }
+
+    // The buffer was not large enough, so double it and try again.
+    auto restartResult = handle.RestartBulkWrite(handle.Length() * 2, 0, false);
+    if (restartResult.isErr()) {
+      return restartResult.unwrapErr();
+    }
+  }
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetNativeTarget(nsACString& aResult) {
+  CHECK_mPath();
+  aResult.Truncate();
+
+  struct STAT symStat;
+  if (LSTAT(mPath.get(), &symStat) == -1) {
+    return NSRESULT_FOR_ERRNO();
+  }
+
+  if (!S_ISLNK(symStat.st_mode)) {
+    return NS_ERROR_FILE_INVALID_PATH;
+  }
+
+  nsAutoCString target;
+  nsresult rv = ReadLinkSafe(mPath, symStat.st_size, target);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  nsCOMPtr<nsIFile> self(this);
+  int32_t maxLinks = 40;
+  while (true) {
+    if (maxLinks-- == 0) {
+      rv = NS_ERROR_FILE_UNRESOLVABLE_SYMLINK;
+      break;
+    }
+
+    if (target[0] != '/') {
+      nsCOMPtr<nsIFile> parent;
+      if (NS_FAILED(rv = self->GetParent(getter_AddRefs(parent)))) {
+        break;
+      }
+      if (NS_FAILED(rv = parent->AppendRelativeNativePath(target))) {
+        break;
+      }
+      if (NS_FAILED(rv = parent->GetNativePath(aResult))) {
+        break;
+      }
+      self = parent;
+    } else {
+      aResult = target;
+    }
+
+    const nsPromiseFlatCString& flatRetval = PromiseFlatCString(aResult);
+
+    // Any failure in testing the current target we'll just interpret
+    // as having reached our destiny.
+    if (LSTAT(flatRetval.get(), &symStat) == -1) {
+      break;
+    }
+
+    // And of course we're done if it isn't a symlink.
+    if (!S_ISLNK(symStat.st_mode)) {
+      break;
+    }
+
+    nsAutoCString newTarget;
+    rv = ReadLinkSafe(flatRetval, symStat.st_size, newTarget);
+    if (NS_FAILED(rv)) {
+      break;
+    }
+
+    target = newTarget;
+  }
+
+  if (NS_FAILED(rv)) {
+    aResult.Truncate();
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetDirectoryEntriesImpl(nsIDirectoryEnumerator** aEntries) {
+  RefPtr<nsDirEnumeratorUnix> dir = new nsDirEnumeratorUnix();
+
+  nsresult rv = dir->Init(this, false);
+  if (NS_FAILED(rv)) {
+    *aEntries = nullptr;
+  } else {
+    dir.forget(aEntries);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Load(PRLibrary** aResult) {
+  CHECK_mPath();
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+  nsTraceRefcnt::SetActivityIsLegal(false);
+#endif
+
+  *aResult = PR_LoadLibrary(mPath.get());
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+  nsTraceRefcnt::SetActivityIsLegal(true);
+#endif
+
+  if (!*aResult) {
+    return NS_ERROR_FAILURE;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetPersistentDescriptor(nsACString& aPersistentDescriptor) {
+  return GetNativePath(aPersistentDescriptor);
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetPersistentDescriptor(const nsACString& aPersistentDescriptor) {
+#ifdef MOZ_WIDGET_COCOA
+  if (aPersistentDescriptor.IsEmpty()) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // Support pathnames as user-supplied descriptors if they begin with '/'
+  // or '~'.  These characters do not collide with the base64 set used for
+  // encoding alias records.
+  char first = aPersistentDescriptor.First();
+  if (first == '/' || first == '~') {
+    return InitWithNativePath(aPersistentDescriptor);
+  }
+
+  uint32_t dataSize = aPersistentDescriptor.Length();
+  char* decodedData = PL_Base64Decode(
+      PromiseFlatCString(aPersistentDescriptor).get(), dataSize, nullptr);
+  if (!decodedData) {
+    NS_ERROR("SetPersistentDescriptor was given bad data");
+    return NS_ERROR_FAILURE;
+  }
+
+  // Cast to an alias record and resolve.
+  AliasRecord aliasHeader = *(AliasPtr)decodedData;
+  int32_t aliasSize = ::GetAliasSizeFromPtr(&aliasHeader);
+  if (aliasSize >
+      ((int32_t)dataSize * 3) / 4) {  // be paranoid about having too few data
+    PR_Free(decodedData);             // PL_Base64Decode() uses PR_Malloc().
+    return NS_ERROR_FAILURE;
+  }
+
+  nsresult rv = NS_OK;
+
+  // Move the now-decoded data into the Handle.
+  // The size of the decoded data is 3/4 the size of the encoded data. See
+  // plbase64.h
+  Handle newHandle = nullptr;
+  if (::PtrToHand(decodedData, &newHandle, aliasSize) != noErr) {
+    rv = NS_ERROR_OUT_OF_MEMORY;
+  }
+  PR_Free(decodedData);  // PL_Base64Decode() uses PR_Malloc().
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  Boolean changed;
+  FSRef resolvedFSRef;
+  OSErr err = ::FSResolveAlias(nullptr, (AliasHandle)newHandle, &resolvedFSRef,
+                               &changed);
+
+  rv = MacErrorMapper(err);
+  DisposeHandle(newHandle);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  return InitWithFSRef(&resolvedFSRef);
+#else
+  return InitWithNativePath(aPersistentDescriptor);
+#endif
+}
+
+NS_IMETHODIMP
+nsLocalFile::Reveal() {
+  if (!FilePreferences::IsAllowedPath(mPath)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+
+#ifdef MOZ_WIDGET_GTK
+  nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
+  if (!giovfs) {
+    return NS_ERROR_FAILURE;
+  }
+  return giovfs->RevealFile(this);
+#elif defined(MOZ_WIDGET_COCOA)
+  CFURLRef url;
+  if (NS_SUCCEEDED(GetCFURL(&url))) {
+    nsresult rv = CocoaFileUtils::RevealFileInFinder(url);
+    ::CFRelease(url);
+    return rv;
+  }
+  return NS_ERROR_FAILURE;
+#else
+  return NS_ERROR_FAILURE;
+#endif
+}
+
+NS_IMETHODIMP
+nsLocalFile::Launch() {
+  if (!FilePreferences::IsAllowedPath(mPath)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+
+#ifdef MOZ_WIDGET_GTK
+  nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
+  if (!giovfs) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return giovfs->LaunchFile(mPath);
+#elif defined(MOZ_WIDGET_ANDROID)
+  // Not supported on GeckoView
+  return NS_ERROR_NOT_IMPLEMENTED;
+#elif defined(MOZ_WIDGET_COCOA)
+  CFURLRef url;
+  if (NS_SUCCEEDED(GetCFURL(&url))) {
+    nsresult rv = CocoaFileUtils::OpenURL(url);
+    ::CFRelease(url);
+    return rv;
+  }
+  return NS_ERROR_FAILURE;
+#else
+  return NS_ERROR_FAILURE;
+#endif
+}
+
+nsresult NS_NewNativeLocalFile(const nsACString& aPath, bool aFollowSymlinks,
+                               nsIFile** aResult) {
+  RefPtr<nsLocalFile> file = new nsLocalFile();
+
+  if (!aPath.IsEmpty()) {
+    nsresult rv = file->InitWithNativePath(aPath);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+  file.forget(aResult);
+  return NS_OK;
+}
+
+//-----------------------------------------------------------------------------
+// unicode support
+//-----------------------------------------------------------------------------
+
+#define SET_UCS(func, ucsArg)                          \
+  {                                                    \
+    nsAutoCString buf;                                 \
+    nsresult rv = NS_CopyUnicodeToNative(ucsArg, buf); \
+    if (NS_FAILED(rv)) return rv;                      \
+    return (func)(buf);                                \
+  }
+
+#define GET_UCS(func, ucsArg)                   \
+  {                                             \
+    nsAutoCString buf;                          \
+    nsresult rv = (func)(buf);                  \
+    if (NS_FAILED(rv)) return rv;               \
+    return NS_CopyNativeToUnicode(buf, ucsArg); \
+  }
+
+#define SET_UCS_2ARGS_2(func, opaqueArg, ucsArg)       \
+  {                                                    \
+    nsAutoCString buf;                                 \
+    nsresult rv = NS_CopyUnicodeToNative(ucsArg, buf); \
+    if (NS_FAILED(rv)) return rv;                      \
+    return (func)(opaqueArg, buf);                     \
+  }
+
+// Unicode interface Wrapper
+nsresult nsLocalFile::InitWithPath(const nsAString& aFilePath) {
+  SET_UCS(InitWithNativePath, aFilePath);
+}
+nsresult nsLocalFile::Append(const nsAString& aNode) {
+  SET_UCS(AppendNative, aNode);
+}
+nsresult nsLocalFile::AppendRelativePath(const nsAString& aNode) {
+  SET_UCS(AppendRelativeNativePath, aNode);
+}
+nsresult nsLocalFile::GetLeafName(nsAString& aLeafName) {
+  GET_UCS(GetNativeLeafName, aLeafName);
+}
+nsresult nsLocalFile::SetLeafName(const nsAString& aLeafName) {
+  SET_UCS(SetNativeLeafName, aLeafName);
+}
+nsresult nsLocalFile::GetPath(nsAString& aResult) {
+  return NS_CopyNativeToUnicode(mPath, aResult);
+}
+nsresult nsLocalFile::CopyTo(nsIFile* aNewParentDir,
+                             const nsAString& aNewName) {
+  SET_UCS_2ARGS_2(CopyToNative, aNewParentDir, aNewName);
+}
+nsresult nsLocalFile::CopyToFollowingLinks(nsIFile* aNewParentDir,
+                                           const nsAString& aNewName) {
+  SET_UCS_2ARGS_2(CopyToFollowingLinksNative, aNewParentDir, aNewName);
+}
+nsresult nsLocalFile::MoveTo(nsIFile* aNewParentDir,
+                             const nsAString& aNewName) {
+  SET_UCS_2ARGS_2(MoveToNative, aNewParentDir, aNewName);
+}
+NS_IMETHODIMP
+nsLocalFile::MoveToFollowingLinks(nsIFile* aNewParentDir,
+                                  const nsAString& aNewName) {
+  SET_UCS_2ARGS_2(MoveToFollowingLinksNative, aNewParentDir, aNewName);
+}
+
+NS_IMETHODIMP
+nsLocalFile::RenameTo(nsIFile* aNewParentDir, const nsAString& aNewName) {
+  SET_UCS_2ARGS_2(RenameToNative, aNewParentDir, aNewName);
+}
+
+NS_IMETHODIMP
+nsLocalFile::RenameToNative(nsIFile* aNewParentDir,
+                            const nsACString& aNewName) {
+  nsresult rv;
+
+  // check to make sure that this has been initialized properly
+  CHECK_mPath();
+
+  // check to make sure that we have a new parent
+  nsAutoCString newPathName;
+  rv = GetNativeTargetPathName(aNewParentDir, aNewName, newPathName);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (!FilePreferences::IsAllowedPath(newPathName)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+
+  // try for atomic rename
+  if (rename(mPath.get(), newPathName.get()) < 0) {
+    if (errno == EXDEV) {
+      rv = NS_ERROR_FILE_ACCESS_DENIED;
+    } else {
+      rv = NSRESULT_FOR_ERRNO();
+    }
+  }
+
+  return rv;
+}
+
+nsresult nsLocalFile::GetTarget(nsAString& aResult) {
+  GET_UCS(GetNativeTarget, aResult);
+}
+
+nsresult NS_NewLocalFile(const nsAString& aPath, bool aFollowLinks,
+                         nsIFile** aResult) {
+  nsAutoCString buf;
+  nsresult rv = NS_CopyUnicodeToNative(aPath, buf);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  return NS_NewNativeLocalFile(buf, aFollowLinks, aResult);
+}
+
+// nsILocalFileMac
+
+#ifdef MOZ_WIDGET_COCOA
+
+NS_IMETHODIMP
+nsLocalFile::HasXAttr(const nsACString& aAttrName, bool* aHasAttr) {
+  NS_ENSURE_ARG_POINTER(aHasAttr);
+
+  nsAutoCString attrName{aAttrName};
+
+  ssize_t size = getxattr(mPath.get(), attrName.get(), nullptr, 0, 0, 0);
+  if (size == -1) {
+    if (errno == ENOATTR) {
+      *aHasAttr = false;
+    } else {
+      return NSRESULT_FOR_ERRNO();
+    }
+  } else {
+    *aHasAttr = true;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetXAttr(const nsACString& aAttrName,
+                      nsTArray<uint8_t>& aAttrValue) {
+  aAttrValue.Clear();
+
+  nsAutoCString attrName{aAttrName};
+
+  ssize_t size = getxattr(mPath.get(), attrName.get(), nullptr, 0, 0, 0);
+
+  if (size == -1) {
+    return NSRESULT_FOR_ERRNO();
+  }
+
+  for (;;) {
+    aAttrValue.SetCapacity(size);
+
+    // The attribute can change between our first call and this call, so we need
+    // to re-check the size and possibly call with a larger buffer.
+    ssize_t newSize = getxattr(mPath.get(), attrName.get(),
+                               aAttrValue.Elements(), size, 0, 0);
+    if (newSize == -1) {
+      return NSRESULT_FOR_ERRNO();
+    }
+
+    if (newSize <= size) {
+      aAttrValue.SetLength(newSize);
+      break;
+    } else {
+      size = newSize;
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetXAttr(const nsACString& aAttrName,
+                      const nsTArray<uint8_t>& aAttrValue) {
+  nsAutoCString attrName{aAttrName};
+
+  if (setxattr(mPath.get(), attrName.get(), aAttrValue.Elements(),
+               aAttrValue.Length(), 0, 0) == -1) {
+    return NSRESULT_FOR_ERRNO();
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::DelXAttr(const nsACString& aAttrName) {
+  nsAutoCString attrName{aAttrName};
+
+  // Ignore removing an attribute that does not exist.
+  if (removexattr(mPath.get(), attrName.get(), 0) == -1) {
+    return NSRESULT_FOR_ERRNO();
+  }
+
+  return NS_OK;
+}
+
+static nsresult MacErrorMapper(OSErr inErr) {
+  nsresult outErr;
+
+  switch (inErr) {
+    case noErr:
+      outErr = NS_OK;
+      break;
+
+    case fnfErr:
+    case afpObjectNotFound:
+    case afpDirNotFound:
+      outErr = NS_ERROR_FILE_NOT_FOUND;
+      break;
+
+    case dupFNErr:
+    case afpObjectExists:
+      outErr = NS_ERROR_FILE_ALREADY_EXISTS;
+      break;
+
+    case dskFulErr:
+    case afpDiskFull:
+      outErr = NS_ERROR_FILE_NO_DEVICE_SPACE;
+      break;
+
+    case fLckdErr:
+    case afpVolLocked:
+      outErr = NS_ERROR_FILE_IS_LOCKED;
+      break;
+
+    case afpAccessDenied:
+      outErr = NS_ERROR_FILE_ACCESS_DENIED;
+      break;
+
+    case afpDirNotEmpty:
+      outErr = NS_ERROR_FILE_DIR_NOT_EMPTY;
+      break;
+
+    // Can't find good map for some
+    case bdNamErr:
+      outErr = NS_ERROR_FAILURE;
+      break;
+
+    default:
+      outErr = NS_ERROR_FAILURE;
+      break;
+  }
+
+  return outErr;
+}
+
+static nsresult CFStringReftoUTF8(CFStringRef aInStrRef, nsACString& aOutStr) {
+  // first see if the conversion would succeed and find the length of the
+  // result
+  CFIndex usedBufLen, inStrLen = ::CFStringGetLength(aInStrRef);
+  CFIndex charsConverted = ::CFStringGetBytes(
+      aInStrRef, CFRangeMake(0, inStrLen), kCFStringEncodingUTF8, 0, false,
+      nullptr, 0, &usedBufLen);
+  if (charsConverted == inStrLen) {
+    // all characters converted, do the actual conversion
+    aOutStr.SetLength(usedBufLen);
+    if (aOutStr.Length() != (unsigned int)usedBufLen) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    UInt8* buffer = (UInt8*)aOutStr.BeginWriting();
+    ::CFStringGetBytes(aInStrRef, CFRangeMake(0, inStrLen),
+                       kCFStringEncodingUTF8, 0, false, buffer, usedBufLen,
+                       &usedBufLen);
+    return NS_OK;
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsLocalFile::InitWithCFURL(CFURLRef aCFURL) {
+  UInt8 path[PATH_MAX];
+  if (::CFURLGetFileSystemRepresentation(aCFURL, true, path, PATH_MAX)) {
+    nsDependentCString nativePath((char*)path);
+    return InitWithNativePath(nativePath);
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsLocalFile::InitWithFSRef(const FSRef* aFSRef) {
+  if (NS_WARN_IF(!aFSRef)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  CFURLRef newURLRef = ::CFURLCreateFromFSRef(kCFAllocatorDefault, aFSRef);
+  if (newURLRef) {
+    nsresult rv = InitWithCFURL(newURLRef);
+    ::CFRelease(newURLRef);
+    return rv;
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetCFURL(CFURLRef* aResult) {
+  CHECK_mPath();
+
+  bool isDir;
+  IsDirectory(&isDir);
+  *aResult = ::CFURLCreateFromFileSystemRepresentation(
+      kCFAllocatorDefault, (UInt8*)mPath.get(), mPath.Length(), isDir);
+
+  return (*aResult ? NS_OK : NS_ERROR_FAILURE);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetFSRef(FSRef* aResult) {
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsresult rv = NS_ERROR_FAILURE;
+
+  CFURLRef url = nullptr;
+  if (NS_SUCCEEDED(GetCFURL(&url))) {
+    if (::CFURLGetFSRef(url, aResult)) {
+      rv = NS_OK;
+    }
+    ::CFRelease(url);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetFSSpec(FSSpec* aResult) {
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  FSRef fsRef;
+  nsresult rv = GetFSRef(&fsRef);
+  if (NS_SUCCEEDED(rv)) {
+    OSErr err = ::FSGetCatalogInfo(&fsRef, kFSCatInfoNone, nullptr, nullptr,
+                                   aResult, nullptr);
+    return MacErrorMapper(err);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetFileSizeWithResFork(int64_t* aFileSizeWithResFork) {
+  if (NS_WARN_IF(!aFileSizeWithResFork)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  FSRef fsRef;
+  nsresult rv = GetFSRef(&fsRef);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  FSCatalogInfo catalogInfo;
+  OSErr err =
+      ::FSGetCatalogInfo(&fsRef, kFSCatInfoDataSizes + kFSCatInfoRsrcSizes,
+                         &catalogInfo, nullptr, nullptr, nullptr);
+  if (err != noErr) {
+    return MacErrorMapper(err);
+  }
+
+  *aFileSizeWithResFork =
+      catalogInfo.dataLogicalSize + catalogInfo.rsrcLogicalSize;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetFileType(OSType* aFileType) {
+  CFURLRef url;
+  if (NS_SUCCEEDED(GetCFURL(&url))) {
+    nsresult rv = CocoaFileUtils::GetFileTypeCode(url, aFileType);
+    ::CFRelease(url);
+    return rv;
+  }
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetFileType(OSType aFileType) {
+  CFURLRef url;
+  if (NS_SUCCEEDED(GetCFURL(&url))) {
+    nsresult rv = CocoaFileUtils::SetFileTypeCode(url, aFileType);
+    ::CFRelease(url);
+    return rv;
+  }
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetFileCreator(OSType* aFileCreator) {
+  CFURLRef url;
+  if (NS_SUCCEEDED(GetCFURL(&url))) {
+    nsresult rv = CocoaFileUtils::GetFileCreatorCode(url, aFileCreator);
+    ::CFRelease(url);
+    return rv;
+  }
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetFileCreator(OSType aFileCreator) {
+  CFURLRef url;
+  if (NS_SUCCEEDED(GetCFURL(&url))) {
+    nsresult rv = CocoaFileUtils::SetFileCreatorCode(url, aFileCreator);
+    ::CFRelease(url);
+    return rv;
+  }
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsLocalFile::LaunchWithDoc(nsIFile* aDocToLoad, bool aLaunchInBackground) {
+  bool isExecutable;
+  nsresult rv = IsExecutable(&isExecutable);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (!isExecutable) {
+    return NS_ERROR_FILE_EXECUTION_FAILED;
+  }
+
+  FSRef appFSRef, docFSRef;
+  rv = GetFSRef(&appFSRef);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (aDocToLoad) {
+    nsCOMPtr<nsILocalFileMac> macDoc = do_QueryInterface(aDocToLoad);
+    rv = macDoc->GetFSRef(&docFSRef);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  LSLaunchFlags theLaunchFlags = kLSLaunchDefaults;
+  LSLaunchFSRefSpec thelaunchSpec;
+
+  if (aLaunchInBackground) {
+    theLaunchFlags |= kLSLaunchDontSwitch;
+  }
+  memset(&thelaunchSpec, 0, sizeof(LSLaunchFSRefSpec));
+
+  thelaunchSpec.appRef = &appFSRef;
+  if (aDocToLoad) {
+    thelaunchSpec.numDocs = 1;
+    thelaunchSpec.itemRefs = &docFSRef;
+  }
+  thelaunchSpec.launchFlags = theLaunchFlags;
+
+  OSErr err = ::LSOpenFromRefSpec(&thelaunchSpec, nullptr);
+  if (err != noErr) {
+    return MacErrorMapper(err);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::OpenDocWithApp(nsIFile* aAppToOpenWith, bool aLaunchInBackground) {
+  FSRef docFSRef;
+  nsresult rv = GetFSRef(&docFSRef);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (!aAppToOpenWith) {
+    OSErr err = ::LSOpenFSRef(&docFSRef, nullptr);
+    return MacErrorMapper(err);
+  }
+
+  nsCOMPtr<nsILocalFileMac> appFileMac = do_QueryInterface(aAppToOpenWith, &rv);
+  if (!appFileMac) {
+    return rv;
+  }
+
+  bool isExecutable;
+  rv = appFileMac->IsExecutable(&isExecutable);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (!isExecutable) {
+    return NS_ERROR_FILE_EXECUTION_FAILED;
+  }
+
+  FSRef appFSRef;
+  rv = appFileMac->GetFSRef(&appFSRef);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  LSLaunchFlags theLaunchFlags = kLSLaunchDefaults;
+  LSLaunchFSRefSpec thelaunchSpec;
+
+  if (aLaunchInBackground) {
+    theLaunchFlags |= kLSLaunchDontSwitch;
+  }
+  memset(&thelaunchSpec, 0, sizeof(LSLaunchFSRefSpec));
+
+  thelaunchSpec.appRef = &appFSRef;
+  thelaunchSpec.numDocs = 1;
+  thelaunchSpec.itemRefs = &docFSRef;
+  thelaunchSpec.launchFlags = theLaunchFlags;
+
+  OSErr err = ::LSOpenFromRefSpec(&thelaunchSpec, nullptr);
+  if (err != noErr) {
+    return MacErrorMapper(err);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsPackage(bool* aResult) {
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aResult = false;
+
+  CFURLRef url;
+  nsresult rv = GetCFURL(&url);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  LSItemInfoRecord info;
+  OSStatus status =
+      ::LSCopyItemInfoForURL(url, kLSRequestBasicFlagsOnly, &info);
+
+  ::CFRelease(url);
+
+  if (status != noErr) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *aResult = !!(info.flags & kLSItemInfoIsPackage);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetBundleDisplayName(nsAString& aOutBundleName) {
+  bool isPackage = false;
+  nsresult rv = IsPackage(&isPackage);
+  if (NS_FAILED(rv) || !isPackage) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsAutoString name;
+  rv = GetLeafName(name);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  int32_t length = name.Length();
+  if (Substring(name, length - 4, length).EqualsLiteral(".app")) {
+    // 4 characters in ".app"
+    aOutBundleName = Substring(name, 0, length - 4);
+  } else {
+    aOutBundleName = name;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetBundleIdentifier(nsACString& aOutBundleIdentifier) {
+  nsresult rv = NS_ERROR_FAILURE;
+
+  CFURLRef urlRef;
+  if (NS_SUCCEEDED(GetCFURL(&urlRef))) {
+    CFBundleRef bundle = ::CFBundleCreate(nullptr, urlRef);
+    if (bundle) {
+      CFStringRef bundleIdentifier = ::CFBundleGetIdentifier(bundle);
+      if (bundleIdentifier) {
+        rv = CFStringReftoUTF8(bundleIdentifier, aOutBundleIdentifier);
+      }
+      ::CFRelease(bundle);
+    }
+    ::CFRelease(urlRef);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetBundleContentsLastModifiedTime(int64_t* aLastModTime) {
+  CHECK_mPath();
+  if (NS_WARN_IF(!aLastModTime)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  bool isPackage = false;
+  nsresult rv = IsPackage(&isPackage);
+  if (NS_FAILED(rv) || !isPackage) {
+    return GetLastModifiedTime(aLastModTime);
+  }
+
+  nsAutoCString infoPlistPath(mPath);
+  infoPlistPath.AppendLiteral("/Contents/Info.plist");
+  PRFileInfo64 info;
+  if (PR_GetFileInfo64(infoPlistPath.get(), &info) != PR_SUCCESS) {
+    return GetLastModifiedTime(aLastModTime);
+  }
+  int64_t modTime = int64_t(info.modifyTime);
+  if (modTime == 0) {
+    *aLastModTime = 0;
+  } else {
+    *aLastModTime = modTime / int64_t(PR_USEC_PER_MSEC);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsLocalFile::InitWithFile(nsIFile* aFile) {
+  if (NS_WARN_IF(!aFile)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsAutoCString nativePath;
+  nsresult rv = aFile->GetNativePath(nativePath);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  return InitWithNativePath(nativePath);
+}
+
+nsresult NS_NewLocalFileWithFSRef(const FSRef* aFSRef, bool aFollowLinks,
+                                  nsILocalFileMac** aResult) {
+  RefPtr<nsLocalFile> file = new nsLocalFile();
+
+  nsresult rv = file->InitWithFSRef(aFSRef);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  file.forget(aResult);
+  return NS_OK;
+}
+
+nsresult NS_NewLocalFileWithCFURL(const CFURLRef aURL, bool aFollowLinks,
+                                  nsILocalFileMac** aResult) {
+  RefPtr<nsLocalFile> file = new nsLocalFile();
+
+  nsresult rv = file->InitWithCFURL(aURL);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  file.forget(aResult);
+  return NS_OK;
+}
+
+#endif
diff --git a/xpcom/io/nsLocalFileUnix.h b/xpcom/io/nsLocalFileUnix.h
new file mode 100644
index 0000000000..eb37e3effd
--- /dev/null
+++ b/xpcom/io/nsLocalFileUnix.h
@@ -0,0 +1,104 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * Implementation of nsIFile for ``Unixy'' systems.
+ */
+
+#ifndef _nsLocalFileUNIX_H_
+#define _nsLocalFileUNIX_H_
+
+#include <sys/stat.h>
+
+#include "nscore.h"
+#include "nsString.h"
+#ifdef MOZ_WIDGET_COCOA
+#  include "nsILocalFileMac.h"
+#endif
+
+// stat64 and lstat64 are deprecated on OS X. Normal stat and lstat are
+// 64-bit by default on OS X 10.6+.
+#if defined(HAVE_STAT64) && defined(HAVE_LSTAT64) && !defined(XP_DARWIN)
+#  if defined(AIX)
+#    if defined STAT
+#      undef STAT
+#    endif
+#  endif
+#  define STAT stat64
+#  define LSTAT lstat64
+#  define HAVE_STATS64 1
+#else
+#  define STAT stat
+#  define LSTAT lstat
+#endif
+
+#if defined(HAVE_SYS_QUOTA_H) && defined(HAVE_LINUX_QUOTA_H)
+#  define USE_LINUX_QUOTACTL
+#endif
+
+class nsLocalFile final
+#ifdef MOZ_WIDGET_COCOA
+    : public nsILocalFileMac
+#else
+    : public nsIFile
+#endif
+{
+ public:
+  NS_DEFINE_STATIC_CID_ACCESSOR(NS_LOCAL_FILE_CID)
+
+  nsLocalFile();
+  explicit nsLocalFile(const nsACString& aFilePath);
+
+  static nsresult nsLocalFileConstructor(const nsIID& aIID,
+                                         void** aInstancePtr);
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIFILE
+#ifdef MOZ_WIDGET_COCOA
+  NS_DECL_NSILOCALFILEMAC
+#endif
+
+ private:
+  nsLocalFile(const nsLocalFile& aOther);
+  ~nsLocalFile() = default;
+
+ protected:
+  // This stat cache holds the *last stat* - it does not invalidate.
+  // Call "FillStatCache" whenever you want to stat our file.
+  struct STAT mCachedStat;
+  nsCString mPath;
+
+  void LocateNativeLeafName(nsACString::const_iterator&,
+                            nsACString::const_iterator&);
+
+  nsresult CopyDirectoryTo(nsIFile* aNewParent);
+  nsresult CreateAllAncestors(uint32_t aPermissions);
+  nsresult GetNativeTargetPathName(nsIFile* aNewParent,
+                                   const nsACString& aNewName,
+                                   nsACString& aResult);
+
+  bool FillStatCache();
+
+  nsresult CreateAndKeepOpen(uint32_t aType, int aFlags, uint32_t aPermissions,
+                             bool aSkipAncestors, PRFileDesc** aResult);
+
+  enum class TimeField { AccessedTime, ModifiedTime };
+  nsresult SetTimeImpl(PRTime aTime, TimeField aTimeField, bool aFollowLinks);
+  nsresult GetTimeImpl(PRTime* aTime, TimeField aTimeField, bool aFollowLinks);
+
+  nsresult GetCreationTimeImpl(PRTime* aCreationTime, bool aFollowLinks);
+
+#if defined(USE_LINUX_QUOTACTL)
+  template <typename StatInfoFunc, typename QuotaInfoFunc>
+  nsresult GetDiskInfo(StatInfoFunc&& aStatInfoFunc,
+                       QuotaInfoFunc&& aQuotaInfoFunc, int64_t* aResult);
+#else
+  template <typename StatInfoFunc>
+  nsresult GetDiskInfo(StatInfoFunc&& aStatInfoFunc, int64_t* aResult);
+#endif
+};
+
+#endif /* _nsLocalFileUNIX_H_ */
diff --git a/xpcom/io/nsLocalFileWin.cpp b/xpcom/io/nsLocalFileWin.cpp
new file mode 100644
index 0000000000..13fea1d2ca
--- /dev/null
+++ b/xpcom/io/nsLocalFileWin.cpp
@@ -0,0 +1,3697 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/ProfilerLabels.h"
+#include "mozilla/TextUtils.h"
+#include "mozilla/UniquePtrExtensions.h"
+#include "mozilla/Utf8.h"
+#include "mozilla/WinHeaderOnlyUtils.h"
+
+#include "nsCOMPtr.h"
+
+#include "nsLocalFile.h"
+#include "nsLocalFileCommon.h"
+#include "nsIDirectoryEnumerator.h"
+#include "nsNativeCharsetUtils.h"
+
+#include "nsSimpleEnumerator.h"
+#include "prio.h"
+#include "private/pprio.h"  // To get PR_ImportFile
+#include "nsHashKeys.h"
+
+#include "nsString.h"
+#include "nsReadableUtils.h"
+
+#include <direct.h>
+#include <fileapi.h>
+#include <windows.h>
+#include <shlwapi.h>
+#include <aclapi.h>
+
+#include "shellapi.h"
+#include "shlguid.h"
+
+#include <io.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <mbstring.h>
+
+#include "prproces.h"
+#include "prlink.h"
+
+#include "mozilla/FilePreferences.h"
+#include "mozilla/Mutex.h"
+#include "SpecialSystemDirectory.h"
+
+#include "nsTraceRefcnt.h"
+#include "nsXPCOMCIDInternal.h"
+#include "nsThreadUtils.h"
+#include "nsXULAppAPI.h"
+#include "nsIWindowMediator.h"
+
+#include "mozIDOMWindow.h"
+#include "nsPIDOMWindow.h"
+#include "nsIWidget.h"
+#include "mozilla/ShellHeaderOnlyUtils.h"
+#include "mozilla/WidgetUtils.h"
+#include "WinUtils.h"
+
+using namespace mozilla;
+using mozilla::FilePreferences::kDevicePathSpecifier;
+using mozilla::FilePreferences::kPathSeparator;
+
+#define CHECK_mWorkingPath()                                     \
+  do {                                                           \
+    if (mWorkingPath.IsEmpty()) return NS_ERROR_NOT_INITIALIZED; \
+  } while (0)
+
+#ifndef FILE_ATTRIBUTE_NOT_CONTENT_INDEXED
+#  define FILE_ATTRIBUTE_NOT_CONTENT_INDEXED 0x00002000
+#endif
+
+#ifndef DRIVE_REMOTE
+#  define DRIVE_REMOTE 4
+#endif
+
+namespace {
+
+nsresult NewLocalFile(const nsAString& aPath, bool aUseDOSDevicePathSyntax,
+                      nsIFile** aResult) {
+  RefPtr<nsLocalFile> file = new nsLocalFile();
+
+  file->SetUseDOSDevicePathSyntax(aUseDOSDevicePathSyntax);
+
+  if (!aPath.IsEmpty()) {
+    nsresult rv = file->InitWithPath(aPath);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  file.forget(aResult);
+  return NS_OK;
+}
+
+}  // anonymous namespace
+
+static HWND GetMostRecentNavigatorHWND() {
+  nsresult rv;
+  nsCOMPtr<nsIWindowMediator> winMediator(
+      do_GetService(NS_WINDOWMEDIATOR_CONTRACTID, &rv));
+  if (NS_FAILED(rv)) {
+    return nullptr;
+  }
+
+  nsCOMPtr<mozIDOMWindowProxy> navWin;
+  rv = winMediator->GetMostRecentWindow(u"navigator:browser",
+                                        getter_AddRefs(navWin));
+  if (NS_FAILED(rv) || !navWin) {
+    return nullptr;
+  }
+
+  nsPIDOMWindowOuter* win = nsPIDOMWindowOuter::From(navWin);
+  nsCOMPtr<nsIWidget> widget = widget::WidgetUtils::DOMWindowToWidget(win);
+  if (!widget) {
+    return nullptr;
+  }
+
+  return reinterpret_cast<HWND>(widget->GetNativeData(NS_NATIVE_WINDOW));
+}
+
+nsresult nsLocalFile::RevealFile(const nsString& aResolvedPath) {
+  MOZ_ASSERT(!NS_IsMainThread(), "Don't run on the main thread");
+
+  DWORD attributes = GetFileAttributesW(aResolvedPath.get());
+  if (INVALID_FILE_ATTRIBUTES == attributes) {
+    return NS_ERROR_FILE_INVALID_PATH;
+  }
+
+  HRESULT hr;
+  if (attributes & FILE_ATTRIBUTE_DIRECTORY) {
+    // We have a directory so we should open the directory itself.
+    LPITEMIDLIST dir = ILCreateFromPathW(aResolvedPath.get());
+    if (!dir) {
+      return NS_ERROR_FAILURE;
+    }
+
+    LPCITEMIDLIST selection[] = {dir};
+    UINT count = ArrayLength(selection);
+
+    // Perform the open of the directory.
+    hr = SHOpenFolderAndSelectItems(dir, count, selection, 0);
+    CoTaskMemFree(dir);
+  } else {
+    int32_t len = aResolvedPath.Length();
+    // We don't currently handle UNC long paths of the form \\?\ anywhere so
+    // this should be fine.
+    if (len > MAX_PATH) {
+      return NS_ERROR_FILE_INVALID_PATH;
+    }
+    WCHAR parentDirectoryPath[MAX_PATH + 1] = {0};
+    wcsncpy(parentDirectoryPath, aResolvedPath.get(), MAX_PATH);
+    PathRemoveFileSpecW(parentDirectoryPath);
+
+    // We have a file so we should open the parent directory.
+    LPITEMIDLIST dir = ILCreateFromPathW(parentDirectoryPath);
+    if (!dir) {
+      return NS_ERROR_FAILURE;
+    }
+
+    // Set the item in the directory to select to the file we want to reveal.
+    LPITEMIDLIST item = ILCreateFromPathW(aResolvedPath.get());
+    if (!item) {
+      CoTaskMemFree(dir);
+      return NS_ERROR_FAILURE;
+    }
+
+    LPCITEMIDLIST selection[] = {item};
+    UINT count = ArrayLength(selection);
+
+    // Perform the selection of the file.
+    hr = SHOpenFolderAndSelectItems(dir, count, selection, 0);
+
+    CoTaskMemFree(dir);
+    CoTaskMemFree(item);
+  }
+
+  return SUCCEEDED(hr) ? NS_OK : NS_ERROR_FAILURE;
+}
+
+// static
+bool nsLocalFile::CheckForReservedFileName(const nsString& aFileName) {
+  static const nsLiteralString forbiddenNames[] = {
+      u"COM1"_ns, u"COM2"_ns, u"COM3"_ns, u"COM4"_ns, u"COM5"_ns,  u"COM6"_ns,
+      u"COM7"_ns, u"COM8"_ns, u"COM9"_ns, u"LPT1"_ns, u"LPT2"_ns,  u"LPT3"_ns,
+      u"LPT4"_ns, u"LPT5"_ns, u"LPT6"_ns, u"LPT7"_ns, u"LPT8"_ns,  u"LPT9"_ns,
+      u"CON"_ns,  u"PRN"_ns,  u"AUX"_ns,  u"NUL"_ns,  u"CLOCK$"_ns};
+
+  for (const nsLiteralString& forbiddenName : forbiddenNames) {
+    if (StringBeginsWith(aFileName, forbiddenName,
+                         nsASCIICaseInsensitiveStringComparator)) {
+      // invalid name is either the entire string, or a prefix with a period
+      if (aFileName.Length() == forbiddenName.Length() ||
+          aFileName.CharAt(forbiddenName.Length()) == char16_t('.')) {
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+class nsDriveEnumerator : public nsSimpleEnumerator,
+                          public nsIDirectoryEnumerator {
+ public:
+  explicit nsDriveEnumerator(bool aUseDOSDevicePathSyntax);
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_NSISIMPLEENUMERATOR
+  NS_FORWARD_NSISIMPLEENUMERATORBASE(nsSimpleEnumerator::)
+  nsresult Init();
+
+  const nsID& DefaultInterface() override { return NS_GET_IID(nsIFile); }
+
+  NS_IMETHOD GetNextFile(nsIFile** aResult) override {
+    bool hasMore = false;
+    nsresult rv = HasMoreElements(&hasMore);
+    if (NS_FAILED(rv) || !hasMore) {
+      return rv;
+    }
+    nsCOMPtr<nsISupports> next;
+    rv = GetNext(getter_AddRefs(next));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCOMPtr<nsIFile> result = do_QueryInterface(next);
+    result.forget(aResult);
+    return NS_OK;
+  }
+
+  NS_IMETHOD Close() override { return NS_OK; }
+
+ private:
+  virtual ~nsDriveEnumerator();
+
+  /* mDrives stores the null-separated drive names.
+   * Init sets them.
+   * HasMoreElements checks mStartOfCurrentDrive.
+   * GetNext advances mStartOfCurrentDrive.
+   */
+  nsString mDrives;
+  nsAString::const_iterator mStartOfCurrentDrive;
+  nsAString::const_iterator mEndOfDrivesString;
+  const bool mUseDOSDevicePathSyntax;
+};
+
+//-----------------------------------------------------------------------------
+// static helper functions
+//-----------------------------------------------------------------------------
+
+/**
+ * While not comprehensive, this will map many common Windows error codes to a
+ * corresponding nsresult. If an unmapped error is encountered, the hex error
+ * code will be logged to stderr. Error codes, names, and descriptions can be
+ * found at the following MSDN page:
+ * https://docs.microsoft.com/en-us/windows/win32/debug/system-error-codes
+ *
+ * \note When adding more mappings here, it must be checked if there's code that
+ * depends on the current generic NS_ERROR_MODULE_WIN32 mapping for such error
+ * codes.
+ */
+static nsresult ConvertWinError(DWORD aWinErr) {
+  nsresult rv;
+
+  switch (aWinErr) {
+    case ERROR_FILE_NOT_FOUND:
+      [[fallthrough]];  // to NS_ERROR_FILE_NOT_FOUND
+    case ERROR_PATH_NOT_FOUND:
+      [[fallthrough]];  // to NS_ERROR_FILE_NOT_FOUND
+    case ERROR_INVALID_DRIVE:
+      rv = NS_ERROR_FILE_NOT_FOUND;
+      break;
+    case ERROR_ACCESS_DENIED:
+      [[fallthrough]];  // to NS_ERROR_FILE_ACCESS_DENIED
+    case ERROR_NOT_SAME_DEVICE:
+      [[fallthrough]];  // to NS_ERROR_FILE_ACCESS_DENIED
+    case ERROR_CANNOT_MAKE:
+      [[fallthrough]];  // to NS_ERROR_FILE_ACCESS_DENIED
+    case ERROR_CONTENT_BLOCKED:
+      rv = NS_ERROR_FILE_ACCESS_DENIED;
+      break;
+    case ERROR_SHARING_VIOLATION:  // CreateFile without sharing flags
+      [[fallthrough]];             // to NS_ERROR_FILE_IS_LOCKED
+    case ERROR_LOCK_VIOLATION:     // LockFile, LockFileEx
+      rv = NS_ERROR_FILE_IS_LOCKED;
+      break;
+    case ERROR_NOT_ENOUGH_MEMORY:
+      [[fallthrough]];  // to NS_ERROR_OUT_OF_MEMORY
+    case ERROR_NO_SYSTEM_RESOURCES:
+      rv = NS_ERROR_OUT_OF_MEMORY;
+      break;
+    case ERROR_DIR_NOT_EMPTY:
+      [[fallthrough]];  // to NS_ERROR_FILE_DIR_NOT_EMPTY
+    case ERROR_CURRENT_DIRECTORY:
+      rv = NS_ERROR_FILE_DIR_NOT_EMPTY;
+      break;
+    case ERROR_WRITE_PROTECT:
+      rv = NS_ERROR_FILE_READ_ONLY;
+      break;
+    case ERROR_HANDLE_DISK_FULL:
+      [[fallthrough]];  // to NS_ERROR_FILE_NO_DEVICE_SPACE
+    case ERROR_DISK_FULL:
+      rv = NS_ERROR_FILE_NO_DEVICE_SPACE;
+      break;
+    case ERROR_FILE_EXISTS:
+      [[fallthrough]];  // to NS_ERROR_FILE_ALREADY_EXISTS
+    case ERROR_ALREADY_EXISTS:
+      rv = NS_ERROR_FILE_ALREADY_EXISTS;
+      break;
+    case ERROR_FILENAME_EXCED_RANGE:
+      rv = NS_ERROR_FILE_NAME_TOO_LONG;
+      break;
+    case ERROR_DIRECTORY:
+      rv = NS_ERROR_FILE_NOT_DIRECTORY;
+      break;
+    case ERROR_FILE_CORRUPT:
+      [[fallthrough]];  // to NS_ERROR_FILE_FS_CORRUPTED
+    case ERROR_DISK_CORRUPT:
+      rv = NS_ERROR_FILE_FS_CORRUPTED;
+      break;
+    case ERROR_DEVICE_HARDWARE_ERROR:
+      [[fallthrough]];  // to NS_ERROR_FILE_DEVICE_FAILURE
+    case ERROR_DEVICE_NOT_CONNECTED:
+      [[fallthrough]];  // to NS_ERROR_FILE_DEVICE_FAILURE
+    case ERROR_DEV_NOT_EXIST:
+      [[fallthrough]];  // to NS_ERROR_FILE_DEVICE_FAILURE
+    case ERROR_IO_DEVICE:
+      rv = NS_ERROR_FILE_DEVICE_FAILURE;
+      break;
+    case ERROR_NOT_READY:
+      rv = NS_ERROR_FILE_DEVICE_TEMPORARY_FAILURE;
+      break;
+    case ERROR_INVALID_NAME:
+      rv = NS_ERROR_FILE_INVALID_PATH;
+      break;
+    case ERROR_INVALID_BLOCK:
+      [[fallthrough]];  // to NS_ERROR_FILE_INVALID_HANDLE
+    case ERROR_INVALID_HANDLE:
+      [[fallthrough]];  // to NS_ERROR_FILE_INVALID_HANDLE
+    case ERROR_ARENA_TRASHED:
+      rv = NS_ERROR_FILE_INVALID_HANDLE;
+      break;
+    case 0:
+      rv = NS_OK;
+      break;
+    default:
+      printf_stderr(
+          "ConvertWinError received an unrecognized WinError: 0x%" PRIx32 "\n",
+          static_cast<uint32_t>(aWinErr));
+      MOZ_ASSERT((aWinErr & 0xFFFF) == aWinErr);
+      rv = NS_ERROR_GENERATE_FAILURE(NS_ERROR_MODULE_WIN32, aWinErr & 0xFFFF);
+      break;
+  }
+  return rv;
+}
+
+// Check whether a path is a volume root. Expects paths to be \-terminated.
+static bool IsRootPath(const nsAString& aPath) {
+  // Easy cases first:
+  if (aPath.Last() != L'\\') {
+    return false;
+  }
+  if (StringEndsWith(aPath, u":\\"_ns)) {
+    return true;
+  }
+
+  nsAString::const_iterator begin, end;
+  aPath.BeginReading(begin);
+  aPath.EndReading(end);
+  // We know we've got a trailing slash, skip that:
+  end--;
+  // Find the next last slash:
+  if (RFindInReadable(u"\\"_ns, begin, end)) {
+    // Reset iterator:
+    aPath.EndReading(end);
+    end--;
+    auto lastSegment = Substring(++begin, end);
+    if (lastSegment.IsEmpty()) {
+      return false;
+    }
+
+    // Check if we end with e.g. "c$", a drive letter in UNC or network shares
+    if (lastSegment.Last() == L'$' && lastSegment.Length() == 2 &&
+        IsAsciiAlpha(lastSegment.First())) {
+      return true;
+    }
+    // Volume GUID paths:
+    if (StringBeginsWith(lastSegment, u"Volume{"_ns) &&
+        lastSegment.Last() == L'}') {
+      return true;
+    }
+  }
+  return false;
+}
+
+static auto kSpecialNTFSFilesInRoot = {
+    u"$MFT"_ns,     u"$MFTMirr"_ns, u"$LogFile"_ns, u"$Volume"_ns,
+    u"$AttrDef"_ns, u"$Bitmap"_ns,  u"$Boot"_ns,    u"$BadClus"_ns,
+    u"$Secure"_ns,  u"$UpCase"_ns,  u"$Extend"_ns};
+static bool IsSpecialNTFSPath(const nsAString& aFilePath) {
+  nsAString::const_iterator begin, end;
+  aFilePath.BeginReading(begin);
+  aFilePath.EndReading(end);
+  auto iter = begin;
+  // Early exit if there's no '$' (common case)
+  if (!FindCharInReadable(L'$', iter, end)) {
+    return false;
+  }
+
+  iter = begin;
+  // Any use of ':$' is illegal in filenames anyway; while we support some
+  // ADS stuff (ie ":Zone.Identifier"), none of them use the ':$' syntax:
+  if (FindInReadable(u":$"_ns, iter, end)) {
+    return true;
+  }
+
+  auto normalized = mozilla::MakeUniqueFallible<wchar_t[]>(MAX_PATH);
+  if (!normalized) {
+    return true;
+  }
+  auto flatPath = PromiseFlatString(aFilePath);
+  auto fullPathRV =
+      GetFullPathNameW(flatPath.get(), MAX_PATH - 1, normalized.get(), nullptr);
+  if (fullPathRV == 0 || fullPathRV > MAX_PATH - 1) {
+    return false;
+  }
+
+  nsString normalizedPath(normalized.get());
+  normalizedPath.BeginReading(begin);
+  normalizedPath.EndReading(end);
+  iter = begin;
+  auto kDelimiters = u"\\:"_ns;
+  while (iter != end && FindCharInReadable(L'$', iter, end)) {
+    for (auto str : kSpecialNTFSFilesInRoot) {
+      if (StringBeginsWith(Substring(iter, end), str,
+                           nsCaseInsensitiveStringComparator)) {
+        // If we're enclosed by separators or the beginning/end of the string,
+        // this is one of the special files. Check if we're on a volume root.
+        auto iterCopy = iter;
+        iterCopy.advance(str.Length());
+        // We check for both \ and : here because the filename could be
+        // followd by a colon and a stream name/type, which shouldn't affect
+        // our check:
+        if (iterCopy == end || kDelimiters.Contains(*iterCopy)) {
+          iterCopy = iter;
+          // At the start of this path component, we don't need to care about
+          // colons: we would have caught those in the check for `:$` above.
+          if (iterCopy == begin || *(--iterCopy) == L'\\') {
+            return IsRootPath(Substring(begin, iter));
+          }
+        }
+      }
+    }
+    iter++;
+  }
+
+  return false;
+}
+
+//-----------------------------------------------------------------------------
+// We need the following three definitions to make |OpenFile| convert a file
+// handle to an NSPR file descriptor correctly when |O_APPEND| flag is
+// specified. It is defined in a private header of NSPR (primpl.h) we can't
+// include. As a temporary workaround until we decide how to extend
+// |PR_ImportFile|, we define it here. Currently, |_PR_HAVE_PEEK_BUFFER|
+// and |PR_STRICT_ADDR_LEN| are not defined for the 'w95'-dependent portion
+// of NSPR so that fields of |PRFilePrivate| #ifdef'd by them are not copied.
+// Similarly, |_MDFileDesc| is taken from nsprpub/pr/include/md/_win95.h.
+// In an unlikely case we switch to 'NT'-dependent NSPR AND this temporary
+// workaround last beyond the switch, |PRFilePrivate| and |_MDFileDesc|
+// need to be changed to match the definitions for WinNT.
+//-----------------------------------------------------------------------------
+typedef enum {
+  _PR_TRI_TRUE = 1,
+  _PR_TRI_FALSE = 0,
+  _PR_TRI_UNKNOWN = -1
+} _PRTriStateBool;
+
+struct _MDFileDesc {
+  PROsfd osfd;
+};
+
+struct PRFilePrivate {
+  int32_t state;
+  bool nonblocking;
+  _PRTriStateBool inheritable;
+  PRFileDesc* next;
+  int lockCount; /*   0: not locked
+                  *  -1: a native lockfile call is in progress
+                  * > 0: # times the file is locked */
+  bool appendMode;
+  _MDFileDesc md;
+};
+
+//-----------------------------------------------------------------------------
+// Six static methods defined below (OpenFile,  FileTimeToPRTime, GetFileInfo,
+// OpenDir, CloseDir, ReadDir) should go away once the corresponding
+// UTF-16 APIs are implemented on all the supported platforms (or at least
+// Windows 9x/ME) in NSPR. Currently, they're only implemented on
+// Windows NT4 or later. (bug 330665)
+//-----------------------------------------------------------------------------
+
+// copied from nsprpub/pr/src/{io/prfile.c | md/windows/w95io.c} :
+// PR_Open and _PR_MD_OPEN
+nsresult OpenFile(const nsString& aName, int aOsflags, int aMode,
+                  bool aShareDelete, PRFileDesc** aFd) {
+  int32_t access = 0;
+
+  int32_t shareMode = FILE_SHARE_READ | FILE_SHARE_WRITE;
+  int32_t disposition = 0;
+  int32_t attributes = 0;
+
+  if (aShareDelete) {
+    shareMode |= FILE_SHARE_DELETE;
+  }
+
+  if (aOsflags & PR_SYNC) {
+    attributes = FILE_FLAG_WRITE_THROUGH;
+  }
+  if (aOsflags & PR_RDONLY || aOsflags & PR_RDWR) {
+    access |= GENERIC_READ;
+  }
+  if (aOsflags & PR_WRONLY || aOsflags & PR_RDWR) {
+    access |= GENERIC_WRITE;
+  }
+
+  if (aOsflags & PR_CREATE_FILE && aOsflags & PR_EXCL) {
+    disposition = CREATE_NEW;
+  } else if (aOsflags & PR_CREATE_FILE) {
+    if (aOsflags & PR_TRUNCATE) {
+      disposition = CREATE_ALWAYS;
+    } else {
+      disposition = OPEN_ALWAYS;
+    }
+  } else {
+    if (aOsflags & PR_TRUNCATE) {
+      disposition = TRUNCATE_EXISTING;
+    } else {
+      disposition = OPEN_EXISTING;
+    }
+  }
+
+  if (aOsflags & nsIFile::DELETE_ON_CLOSE) {
+    attributes |= FILE_FLAG_DELETE_ON_CLOSE;
+  }
+
+  if (aOsflags & nsIFile::OS_READAHEAD) {
+    attributes |= FILE_FLAG_SEQUENTIAL_SCAN;
+  }
+
+  // If no write permissions are requested, and if we are possibly creating
+  // the file, then set the new file as read only.
+  // The flag has no effect if we happen to open the file.
+  if (!(aMode & (PR_IWUSR | PR_IWGRP | PR_IWOTH)) &&
+      disposition != OPEN_EXISTING) {
+    attributes |= FILE_ATTRIBUTE_READONLY;
+  }
+
+  HANDLE file = ::CreateFileW(aName.get(), access, shareMode, nullptr,
+                              disposition, attributes, nullptr);
+
+  if (file == INVALID_HANDLE_VALUE) {
+    *aFd = nullptr;
+    return ConvertWinError(GetLastError());
+  }
+
+  *aFd = PR_ImportFile((PROsfd)file);
+  if (*aFd) {
+    // On Windows, _PR_HAVE_O_APPEND is not defined so that we have to
+    // add it manually. (see |PR_Open| in nsprpub/pr/src/io/prfile.c)
+    (*aFd)->secret->appendMode = (PR_APPEND & aOsflags) ? true : false;
+    return NS_OK;
+  }
+
+  nsresult rv = NS_ErrorAccordingToNSPR();
+
+  CloseHandle(file);
+
+  return rv;
+}
+
+// copied from nsprpub/pr/src/{io/prfile.c | md/windows/w95io.c} :
+// PR_FileTimeToPRTime and _PR_FileTimeToPRTime
+static void FileTimeToPRTime(const FILETIME* aFiletime, PRTime* aPrtm) {
+#ifdef __GNUC__
+  const PRTime _pr_filetime_offset = 116444736000000000LL;
+#else
+  const PRTime _pr_filetime_offset = 116444736000000000i64;
+#endif
+
+  MOZ_ASSERT(sizeof(FILETIME) == sizeof(PRTime));
+  ::CopyMemory(aPrtm, aFiletime, sizeof(PRTime));
+#ifdef __GNUC__
+  *aPrtm = (*aPrtm - _pr_filetime_offset) / 10LL;
+#else
+  *aPrtm = (*aPrtm - _pr_filetime_offset) / 10i64;
+#endif
+}
+
+// copied from nsprpub/pr/src/{io/prfile.c | md/windows/w95io.c} with some
+// changes : PR_GetFileInfo64, _PR_MD_GETFILEINFO64
+static nsresult GetFileInfo(const nsString& aName,
+                            nsLocalFile::FileInfo* aInfo) {
+  if (aName.IsEmpty()) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // Checking u"?*" for the file path excluding the kDevicePathSpecifier.
+  // ToDo: Check if checking "?" for the file path is still needed.
+  const int32_t offset = StringBeginsWith(aName, kDevicePathSpecifier)
+                             ? kDevicePathSpecifier.Length()
+                             : 0;
+
+  if (aName.FindCharInSet(u"?*", offset) != kNotFound) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  WIN32_FILE_ATTRIBUTE_DATA fileData;
+  if (!::GetFileAttributesExW(aName.get(), GetFileExInfoStandard, &fileData)) {
+    return ConvertWinError(GetLastError());
+  }
+
+  if (fileData.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) {
+    aInfo->type = PR_FILE_OTHER;
+  } else if (fileData.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) {
+    aInfo->type = PR_FILE_DIRECTORY;
+  } else {
+    aInfo->type = PR_FILE_FILE;
+  }
+
+  aInfo->size = fileData.nFileSizeHigh;
+  aInfo->size = (aInfo->size << 32) + fileData.nFileSizeLow;
+
+  if (0 == fileData.ftCreationTime.dwLowDateTime &&
+      0 == fileData.ftCreationTime.dwHighDateTime) {
+    aInfo->creationTime = aInfo->modifyTime;
+  } else {
+    FileTimeToPRTime(&fileData.ftCreationTime, &aInfo->creationTime);
+  }
+
+  FileTimeToPRTime(&fileData.ftLastAccessTime, &aInfo->accessTime);
+  FileTimeToPRTime(&fileData.ftLastWriteTime, &aInfo->modifyTime);
+
+  return NS_OK;
+}
+
+struct nsDir {
+  HANDLE handle;
+  WIN32_FIND_DATAW data;
+  bool firstEntry;
+};
+
+static nsresult OpenDir(const nsString& aName, nsDir** aDir) {
+  if (NS_WARN_IF(!aDir)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  *aDir = nullptr;
+
+  nsDir* d = new nsDir();
+  nsAutoString filename(aName);
+
+  // If |aName| ends in a slash or backslash, do not append another backslash.
+  if (filename.Last() == L'/' || filename.Last() == L'\\') {
+    filename.Append('*');
+  } else {
+    filename.AppendLiteral("\\*");
+  }
+
+  filename.ReplaceChar(L'/', L'\\');
+
+  // FindFirstFileW Will have a last error of ERROR_DIRECTORY if
+  // <file_path>\* is passed in.  If <unknown_path>\* is passed in then
+  // ERROR_PATH_NOT_FOUND will be the last error.
+  d->handle = ::FindFirstFileW(filename.get(), &(d->data));
+
+  if (d->handle == INVALID_HANDLE_VALUE) {
+    delete d;
+    return ConvertWinError(GetLastError());
+  }
+  d->firstEntry = true;
+
+  *aDir = d;
+  return NS_OK;
+}
+
+static nsresult ReadDir(nsDir* aDir, PRDirFlags aFlags, nsString& aName) {
+  aName.Truncate();
+  if (NS_WARN_IF(!aDir)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  while (1) {
+    BOOL rv;
+    if (aDir->firstEntry) {
+      aDir->firstEntry = false;
+      rv = 1;
+    } else {
+      rv = ::FindNextFileW(aDir->handle, &(aDir->data));
+    }
+
+    if (rv == 0) {
+      break;
+    }
+
+    const wchar_t* fileName;
+    fileName = (aDir)->data.cFileName;
+
+    if ((aFlags & PR_SKIP_DOT) && (fileName[0] == L'.') &&
+        (fileName[1] == L'\0')) {
+      continue;
+    }
+    if ((aFlags & PR_SKIP_DOT_DOT) && (fileName[0] == L'.') &&
+        (fileName[1] == L'.') && (fileName[2] == L'\0')) {
+      continue;
+    }
+
+    DWORD attrib = aDir->data.dwFileAttributes;
+    if ((aFlags & PR_SKIP_HIDDEN) && (attrib & FILE_ATTRIBUTE_HIDDEN)) {
+      continue;
+    }
+
+    aName = fileName;
+    return NS_OK;
+  }
+
+  DWORD err = GetLastError();
+  return err == ERROR_NO_MORE_FILES ? NS_OK : ConvertWinError(err);
+}
+
+static nsresult CloseDir(nsDir*& aDir) {
+  if (NS_WARN_IF(!aDir)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  BOOL isOk = FindClose(aDir->handle);
+  delete aDir;
+  aDir = nullptr;
+  return isOk ? NS_OK : ConvertWinError(GetLastError());
+}
+
+//-----------------------------------------------------------------------------
+// nsDirEnumerator
+//-----------------------------------------------------------------------------
+
+class nsDirEnumerator final : public nsSimpleEnumerator,
+                              public nsIDirectoryEnumerator {
+ private:
+  ~nsDirEnumerator() { Close(); }
+
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+
+  NS_FORWARD_NSISIMPLEENUMERATORBASE(nsSimpleEnumerator::)
+
+  nsDirEnumerator() : mDir(nullptr) {}
+
+  const nsID& DefaultInterface() override { return NS_GET_IID(nsIFile); }
+
+  nsresult Init(nsIFile* aParent) {
+    nsAutoString filepath;
+    aParent->GetTarget(filepath);
+
+    if (filepath.IsEmpty()) {
+      aParent->GetPath(filepath);
+    }
+
+    if (filepath.IsEmpty()) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    // IsDirectory is not needed here because OpenDir will return
+    // NS_ERROR_FILE_NOT_DIRECTORY if the passed in path is a file.
+    nsresult rv = OpenDir(filepath, &mDir);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    mParent = aParent;
+    return NS_OK;
+  }
+
+  NS_IMETHOD HasMoreElements(bool* aResult) override {
+    nsresult rv;
+    if (!mNext && mDir) {
+      nsString name;
+      rv = ReadDir(mDir, PR_SKIP_BOTH, name);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+      if (name.IsEmpty()) {
+        // end of dir entries
+        rv = CloseDir(mDir);
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+
+        *aResult = false;
+        return NS_OK;
+      }
+
+      nsCOMPtr<nsIFile> file;
+      rv = mParent->Clone(getter_AddRefs(file));
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      rv = file->Append(name);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      mNext = file.forget();
+    }
+    *aResult = mNext != nullptr;
+    if (!*aResult) {
+      Close();
+    }
+    return NS_OK;
+  }
+
+  NS_IMETHOD GetNext(nsISupports** aResult) override {
+    nsresult rv;
+    bool hasMore;
+    rv = HasMoreElements(&hasMore);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+    if (!hasMore) {
+      return NS_ERROR_FAILURE;
+    }
+
+    mNext.forget(aResult);
+    return NS_OK;
+  }
+
+  NS_IMETHOD GetNextFile(nsIFile** aResult) override {
+    *aResult = nullptr;
+    bool hasMore = false;
+    nsresult rv = HasMoreElements(&hasMore);
+    if (NS_FAILED(rv) || !hasMore) {
+      return rv;
+    }
+    mNext.forget(aResult);
+    return NS_OK;
+  }
+
+  NS_IMETHOD Close() override {
+    if (mDir) {
+      nsresult rv = CloseDir(mDir);
+      NS_ASSERTION(NS_SUCCEEDED(rv), "close failed");
+      if (NS_FAILED(rv)) {
+        return NS_ERROR_FAILURE;
+      }
+    }
+    return NS_OK;
+  }
+
+ protected:
+  nsDir* mDir;
+  nsCOMPtr<nsIFile> mParent;
+  nsCOMPtr<nsIFile> mNext;
+};
+
+NS_IMPL_ISUPPORTS_INHERITED(nsDirEnumerator, nsSimpleEnumerator,
+                            nsIDirectoryEnumerator)
+
+//-----------------------------------------------------------------------------
+// nsLocalFile <public>
+//-----------------------------------------------------------------------------
+
+nsLocalFile::nsLocalFile()
+    : mDirty(true), mResolveDirty(true), mUseDOSDevicePathSyntax(false) {}
+
+nsLocalFile::nsLocalFile(const nsAString& aFilePath)
+    : mUseDOSDevicePathSyntax(false) {
+  InitWithPath(aFilePath);
+}
+
+nsresult nsLocalFile::nsLocalFileConstructor(const nsIID& aIID,
+                                             void** aInstancePtr) {
+  if (NS_WARN_IF(!aInstancePtr)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsLocalFile* inst = new nsLocalFile();
+  nsresult rv = inst->QueryInterface(aIID, aInstancePtr);
+  if (NS_FAILED(rv)) {
+    delete inst;
+    return rv;
+  }
+  return NS_OK;
+}
+
+//-----------------------------------------------------------------------------
+// nsLocalFile::nsISupports
+//-----------------------------------------------------------------------------
+
+NS_IMPL_ISUPPORTS(nsLocalFile, nsIFile, nsILocalFileWin)
+
+//-----------------------------------------------------------------------------
+// nsLocalFile <private>
+//-----------------------------------------------------------------------------
+
+nsLocalFile::nsLocalFile(const nsLocalFile& aOther)
+    : mDirty(true),
+      mResolveDirty(true),
+      mUseDOSDevicePathSyntax(aOther.mUseDOSDevicePathSyntax),
+      mWorkingPath(aOther.mWorkingPath) {}
+
+nsresult nsLocalFile::ResolveSymlink() {
+  std::wstring workingPath(mWorkingPath.Data());
+  if (!widget::WinUtils::ResolveJunctionPointsAndSymLinks(workingPath)) {
+    return NS_ERROR_FAILURE;
+  }
+  mResolvedPath.Assign(workingPath.c_str(), workingPath.length());
+  return NS_OK;
+}
+
+// Resolve any shortcuts and stat the resolved path. After a successful return
+// the path is guaranteed valid and the members of mFileInfo can be used.
+nsresult nsLocalFile::ResolveAndStat() {
+  // if we aren't dirty then we are already done
+  if (!mDirty) {
+    return NS_OK;
+  }
+
+  AUTO_PROFILER_LABEL("nsLocalFile::ResolveAndStat", OTHER);
+  // we can't resolve/stat anything that isn't a valid NSPR addressable path
+  if (mWorkingPath.IsEmpty()) {
+    return NS_ERROR_FILE_INVALID_PATH;
+  }
+
+  // this is usually correct
+  mResolvedPath.Assign(mWorkingPath);
+
+  // Make sure root paths have a trailing slash.
+  nsAutoString nsprPath(mWorkingPath);
+  if (mWorkingPath.Length() == 2 && mWorkingPath.CharAt(1) == u':') {
+    nsprPath.Append('\\');
+  }
+
+  // first we will see if the working path exists. If it doesn't then
+  // there is nothing more that can be done
+  nsresult rv = GetFileInfo(nsprPath, &mFileInfo);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (mFileInfo.type != PR_FILE_OTHER) {
+    mResolveDirty = false;
+    mDirty = false;
+    return NS_OK;
+  }
+
+  // OTHER from GetFileInfo currently means a symlink
+  rv = ResolveSymlink();
+  // Even if it fails we need to have the resolved path equal to working path
+  // for those functions that always use the resolved path.
+  if (NS_FAILED(rv)) {
+    mResolvedPath.Assign(mWorkingPath);
+    return rv;
+  }
+
+  mResolveDirty = false;
+  // get the details of the resolved path
+  rv = GetFileInfo(mResolvedPath, &mFileInfo);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  mDirty = false;
+  return NS_OK;
+}
+
+/**
+ * Fills the mResolvedPath member variable with the file or symlink target
+ * if follow symlinks is on.  This is a copy of the Resolve parts from
+ * ResolveAndStat. ResolveAndStat is much slower though because of the stat.
+ *
+ * @return NS_OK on success.
+ */
+nsresult nsLocalFile::Resolve() {
+  // if we aren't dirty then we are already done
+  if (!mResolveDirty) {
+    return NS_OK;
+  }
+
+  // we can't resolve/stat anything that isn't a valid NSPR addressable path
+  if (mWorkingPath.IsEmpty()) {
+    return NS_ERROR_FILE_INVALID_PATH;
+  }
+
+  // this is usually correct
+  mResolvedPath.Assign(mWorkingPath);
+
+  // TODO: Implement symlink support
+
+  mResolveDirty = false;
+  return NS_OK;
+}
+
+//-----------------------------------------------------------------------------
+// nsLocalFile::nsIFile
+//-----------------------------------------------------------------------------
+
+NS_IMETHODIMP
+nsLocalFile::Clone(nsIFile** aFile) {
+  // Just copy-construct ourselves
+  RefPtr<nsLocalFile> file = new nsLocalFile(*this);
+  file.forget(aFile);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::InitWithFile(nsIFile* aFile) {
+  if (NS_WARN_IF(!aFile)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsAutoString path;
+  aFile->GetPath(path);
+  if (path.IsEmpty()) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  return InitWithPath(path);
+}
+
+NS_IMETHODIMP
+nsLocalFile::InitWithPath(const nsAString& aFilePath) {
+  MakeDirty();
+
+  nsAString::const_iterator begin, end;
+  aFilePath.BeginReading(begin);
+  aFilePath.EndReading(end);
+
+  // input string must not be empty
+  if (begin == end) {
+    return NS_ERROR_FAILURE;
+  }
+
+  char16_t firstChar = *begin;
+  char16_t secondChar = *(++begin);
+
+  // just do a sanity check.  if it has any forward slashes, it is not a Native
+  // path on windows.  Also, it must have a colon at after the first char.
+  if (FindCharInReadable(L'/', begin, end)) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+
+  if (FilePreferences::IsBlockedUNCPath(aFilePath)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+
+  if (secondChar != L':' && (secondChar != L'\\' || firstChar != L'\\')) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+
+  if (secondChar == L':') {
+    // Make sure we have a valid drive, later code assumes the drive letter
+    // is a single char a-z or A-Z.
+    if (MozPathGetDriveNumber<wchar_t>(aFilePath.Data()) == -1) {
+      return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+    }
+  }
+
+  if (IsSpecialNTFSPath(aFilePath)) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+
+  mWorkingPath = aFilePath;
+  // kill any trailing '\'
+  if (mWorkingPath.Last() == L'\\') {
+    mWorkingPath.Truncate(mWorkingPath.Length() - 1);
+  }
+
+  // Bug 1626514: make sure that we don't end up with multiple prefixes.
+
+  // Prepend the "\\?\" prefix if the useDOSDevicePathSyntax is set and the path
+  // starts with a disk designator and backslash.
+  if (mUseDOSDevicePathSyntax &&
+      FilePreferences::StartsWithDiskDesignatorAndBackslash(mWorkingPath)) {
+    mWorkingPath = kDevicePathSpecifier + mWorkingPath;
+  }
+
+  return NS_OK;
+}
+
+// Strip a handler command string of its quotes and parameters.
+static void CleanupHandlerPath(nsString& aPath) {
+  // Example command strings passed into this routine:
+
+  // 1) C:\Program Files\Company\some.exe -foo -bar
+  // 2) C:\Program Files\Company\some.dll
+  // 3) C:\Windows\some.dll,-foo -bar
+  // 4) C:\Windows\some.cpl,-foo -bar
+
+  int32_t lastCommaPos = aPath.RFindChar(',');
+  if (lastCommaPos != kNotFound) aPath.Truncate(lastCommaPos);
+
+  aPath.Append(' ');
+
+  // case insensitive
+  int32_t index = aPath.LowerCaseFindASCII(".exe ");
+  if (index == kNotFound) index = aPath.LowerCaseFindASCII(".dll ");
+  if (index == kNotFound) index = aPath.LowerCaseFindASCII(".cpl ");
+
+  if (index != kNotFound) aPath.Truncate(index + 4);
+  aPath.Trim(" ", true, true);
+}
+
+// Strip the windows host process bootstrap executable rundll32.exe
+// from a handler's command string if it exists.
+static void StripRundll32(nsString& aCommandString) {
+  // Example rundll formats:
+  // C:\Windows\System32\rundll32.exe "path to dll"
+  // rundll32.exe "path to dll"
+  // C:\Windows\System32\rundll32.exe "path to dll", var var
+  // rundll32.exe "path to dll", var var
+
+  constexpr auto rundllSegment = "rundll32.exe "_ns;
+  constexpr auto rundllSegmentShort = "rundll32 "_ns;
+
+  // case insensitive
+  int32_t strLen = rundllSegment.Length();
+  int32_t index = aCommandString.LowerCaseFindASCII(rundllSegment);
+  if (index == kNotFound) {
+    strLen = rundllSegmentShort.Length();
+    index = aCommandString.LowerCaseFindASCII(rundllSegmentShort);
+  }
+
+  if (index != kNotFound) {
+    uint32_t rundllSegmentLength = index + strLen;
+    aCommandString.Cut(0, rundllSegmentLength);
+  }
+}
+
+// Returns the fully qualified path to an application handler based on
+// a parameterized command string. Note this routine should not be used
+// to launch the associated application as it strips parameters and
+// rundll.exe from the string. Designed for retrieving display information
+// on a particular handler.
+/* static */
+bool nsLocalFile::CleanupCmdHandlerPath(nsAString& aCommandHandler) {
+  nsAutoString handlerCommand(aCommandHandler);
+
+  // Straight command path:
+  //
+  // %SystemRoot%\system32\NOTEPAD.EXE var
+  // "C:\Program Files\iTunes\iTunes.exe" var var
+  // C:\Program Files\iTunes\iTunes.exe var var
+  //
+  // Example rundll handlers:
+  //
+  // rundll32.exe "%ProgramFiles%\Win...ery\PhotoViewer.dll", var var
+  // rundll32.exe "%ProgramFiles%\Windows Photo Gallery\PhotoViewer.dll"
+  // C:\Windows\System32\rundll32.exe "path to dll", var var
+  // %SystemRoot%\System32\rundll32.exe "%ProgramFiles%\Win...ery\Photo
+  //    Viewer.dll", var var
+
+  // Expand environment variables so we have full path strings.
+  uint32_t bufLength =
+      ::ExpandEnvironmentStringsW(handlerCommand.get(), nullptr, 0);
+  if (bufLength == 0)  // Error
+    return false;
+
+  auto destination = mozilla::MakeUniqueFallible<wchar_t[]>(bufLength);
+  if (!destination) return false;
+  if (!::ExpandEnvironmentStringsW(handlerCommand.get(), destination.get(),
+                                   bufLength))
+    return false;
+
+  handlerCommand.Assign(destination.get());
+
+  // Remove quotes around paths
+  handlerCommand.StripChars(u"\"");
+
+  // Strip windows host process bootstrap so we can get to the actual
+  // handler.
+  StripRundll32(handlerCommand);
+
+  // Trim any command parameters so that we have a native path we can
+  // initialize a local file with.
+  CleanupHandlerPath(handlerCommand);
+
+  aCommandHandler.Assign(handlerCommand);
+  return true;
+}
+
+NS_IMETHODIMP
+nsLocalFile::InitWithCommandLine(const nsAString& aCommandLine) {
+  nsAutoString commandLine(aCommandLine);
+  if (!CleanupCmdHandlerPath(commandLine)) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+  return InitWithPath(commandLine);
+}
+
+NS_IMETHODIMP
+nsLocalFile::OpenNSPRFileDesc(int32_t aFlags, int32_t aMode,
+                              PRFileDesc** aResult) {
+  nsresult rv = OpenNSPRFileDescMaybeShareDelete(aFlags, aMode, false, aResult);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::OpenANSIFileDesc(const char* aMode, FILE** aResult) {
+  *aResult = _wfopen(mWorkingPath.get(), NS_ConvertASCIItoUTF16(aMode).get());
+  if (*aResult) {
+    return NS_OK;
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+static nsresult do_create(nsIFile* aFile, const nsString& aPath,
+                          uint32_t aAttributes) {
+  PRFileDesc* file;
+  nsresult rv =
+      OpenFile(aPath, PR_RDONLY | PR_CREATE_FILE | PR_APPEND | PR_EXCL,
+               aAttributes, false, &file);
+  if (file) {
+    PR_Close(file);
+  }
+
+  if (rv == NS_ERROR_FILE_ACCESS_DENIED) {
+    // need to return already-exists for directories (bug 452217)
+    bool isdir;
+    if (NS_SUCCEEDED(aFile->IsDirectory(&isdir)) && isdir) {
+      rv = NS_ERROR_FILE_ALREADY_EXISTS;
+    }
+  }
+  return rv;
+}
+
+static nsresult do_mkdir(nsIFile*, const nsString& aPath, uint32_t) {
+  if (!::CreateDirectoryW(aPath.get(), nullptr)) {
+    return ConvertWinError(GetLastError());
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Create(uint32_t aType, uint32_t aAttributes, bool aSkipAncestors) {
+  if (aType != NORMAL_FILE_TYPE && aType != DIRECTORY_TYPE) {
+    return NS_ERROR_FILE_UNKNOWN_TYPE;
+  }
+
+  auto* createFunc = (aType == NORMAL_FILE_TYPE ? do_create : do_mkdir);
+
+  nsresult rv = createFunc(this, mWorkingPath, aAttributes);
+
+  if (NS_SUCCEEDED(rv) || NS_ERROR_FILE_ALREADY_EXISTS == rv ||
+      aSkipAncestors) {
+    return rv;
+  }
+
+  // create directories to target
+  //
+  // A given local file can be either one of these forms:
+  //
+  //   - normal:    X:\some\path\on\this\drive
+  //                       ^--- start here
+  //
+  //   - UNC path:  \\machine\volume\some\path\on\this\drive
+  //                                     ^--- start here
+  //
+  // Skip the first 'X:\' for the first form, and skip the first full
+  // '\\machine\volume\' segment for the second form.
+
+  wchar_t* path = char16ptr_t(mWorkingPath.BeginWriting());
+
+  if (path[0] == L'\\' && path[1] == L'\\') {
+    // dealing with a UNC path here; skip past '\\machine\'
+    path = wcschr(path + 2, L'\\');
+    if (!path) {
+      return NS_ERROR_FILE_INVALID_PATH;
+    }
+    ++path;
+  }
+
+  // search for first slash after the drive (or volume) name
+  wchar_t* slash = wcschr(path, L'\\');
+
+  nsresult directoryCreateError = NS_OK;
+  if (slash) {
+    // skip the first '\\'
+    ++slash;
+    slash = wcschr(slash, L'\\');
+
+    while (slash) {
+      *slash = L'\0';
+
+      if (!::CreateDirectoryW(mWorkingPath.get(), nullptr)) {
+        rv = ConvertWinError(GetLastError());
+        if (NS_ERROR_FILE_NOT_FOUND == rv &&
+            NS_ERROR_FILE_ACCESS_DENIED == directoryCreateError) {
+          // If a previous CreateDirectory failed due to access, return that.
+          return NS_ERROR_FILE_ACCESS_DENIED;
+        }
+        // perhaps the base path already exists, or perhaps we don't have
+        // permissions to create the directory.  NOTE: access denied could
+        // occur on a parent directory even though it exists.
+        else if (rv != NS_ERROR_FILE_ALREADY_EXISTS &&
+                 rv != NS_ERROR_FILE_ACCESS_DENIED) {
+          return rv;
+        }
+
+        directoryCreateError = rv;
+      }
+      *slash = L'\\';
+      ++slash;
+      slash = wcschr(slash, L'\\');
+    }
+  }
+
+  // If our last CreateDirectory failed due to access, return that.
+  if (NS_ERROR_FILE_ACCESS_DENIED == directoryCreateError) {
+    return directoryCreateError;
+  }
+
+  return createFunc(this, mWorkingPath, aAttributes);
+}
+
+NS_IMETHODIMP
+nsLocalFile::Append(const nsAString& aNode) {
+  // append this path, multiple components are not permitted
+  return AppendInternal(PromiseFlatString(aNode), false);
+}
+
+NS_IMETHODIMP
+nsLocalFile::AppendRelativePath(const nsAString& aNode) {
+  // append this path, multiple components are permitted
+  return AppendInternal(PromiseFlatString(aNode), true);
+}
+
+nsresult nsLocalFile::AppendInternal(const nsString& aNode,
+                                     bool aMultipleComponents) {
+  if (aNode.IsEmpty()) {
+    return NS_OK;
+  }
+
+  // check the relative path for validity
+  if (aNode.First() == L'\\' ||   // can't start with an '\'
+      aNode.Contains(L'/') ||     // can't contain /
+      aNode.EqualsASCII("..")) {  // can't be ..
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+
+  if (aMultipleComponents) {
+    // can't contain .. as a path component. Ensure that the valid components
+    // "foo..foo", "..foo", and "foo.." are not falsely detected,
+    // but the invalid paths "..\", "foo\..", "foo\..\foo",
+    // "..\foo", etc are.
+    constexpr auto doubleDot = u"\\.."_ns;
+    nsAString::const_iterator start, end, offset;
+    aNode.BeginReading(start);
+    aNode.EndReading(end);
+    offset = end;
+    while (FindInReadable(doubleDot, start, offset)) {
+      if (offset == end || *offset == L'\\') {
+        return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+      }
+      start = offset;
+      offset = end;
+    }
+
+    // catches the remaining cases of prefixes
+    if (StringBeginsWith(aNode, u"..\\"_ns)) {
+      return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+    }
+  }
+  // single components can't contain '\'
+  else if (aNode.Contains(L'\\')) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+
+  MakeDirty();
+
+  mWorkingPath.Append('\\');
+  mWorkingPath.Append(aNode);
+
+  if (IsSpecialNTFSPath(mWorkingPath)) {
+    // Revert changes to mWorkingPath:
+    mWorkingPath.SetLength(mWorkingPath.Length() - aNode.Length() - 1);
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+
+  return NS_OK;
+}
+
+nsresult nsLocalFile::OpenNSPRFileDescMaybeShareDelete(int32_t aFlags,
+                                                       int32_t aMode,
+                                                       bool aShareDelete,
+                                                       PRFileDesc** aResult) {
+  return OpenFile(mWorkingPath, aFlags, aMode, aShareDelete, aResult);
+}
+
+#define TOUPPER(u) (((u) >= L'a' && (u) <= L'z') ? (u) - (L'a' - L'A') : (u))
+
+NS_IMETHODIMP
+nsLocalFile::Normalize() {
+  // XXX See bug 187957 comment 18 for possible problems with this
+  // implementation.
+
+  if (mWorkingPath.IsEmpty()) {
+    return NS_OK;
+  }
+
+  nsAutoString path(mWorkingPath);
+
+  // find the index of the root backslash for the path. Everything before
+  // this is considered fully normalized and cannot be ascended beyond
+  // using ".."  For a local drive this is the first slash (e.g. "c:\").
+  // For a UNC path it is the slash following the share name
+  // (e.g. "\\server\share\").
+  int32_t rootIdx = 2;                  // default to local drive
+  if (path.First() == L'\\') {          // if a share then calculate the rootIdx
+    rootIdx = path.FindChar(L'\\', 2);  // skip \\ in front of the server
+    if (rootIdx == kNotFound) {
+      return NS_OK;  // already normalized
+    }
+    rootIdx = path.FindChar(L'\\', rootIdx + 1);
+    if (rootIdx == kNotFound) {
+      return NS_OK;  // already normalized
+    }
+  } else if (path.CharAt(rootIdx) != L'\\') {
+    // The path has been specified relative to the current working directory
+    // for that drive. To normalize it, the current working directory for
+    // that drive needs to be inserted before the supplied relative path
+    // which will provide an absolute path (and the rootIdx will still be 2).
+    WCHAR cwd[MAX_PATH];
+    WCHAR* pcwd = cwd;
+    int drive = TOUPPER(path.First()) - 'A' + 1;
+    /* We need to worry about IPH, for details read bug 419326.
+     * _getdrives - http://msdn2.microsoft.com/en-us/library/xdhk0xd2.aspx
+     * uses a bitmask, bit 0 is 'a:'
+     * _chdrive - http://msdn2.microsoft.com/en-us/library/0d1409hb.aspx
+     * _getdcwd - http://msdn2.microsoft.com/en-us/library/7t2zk3s4.aspx
+     * take an int, 1 is 'a:'.
+     *
+     * Because of this, we need to do some math. Subtract 1 to convert from
+     * _chdrive/_getdcwd format to _getdrives drive numbering.
+     * Shift left x bits to convert from integer indexing to bitfield indexing.
+     * And of course, we need to find out if the drive is in the bitmask.
+     *
+     * If we're really unlucky, we can still lose, but only if the user
+     * manages to eject the drive between our call to _getdrives() and
+     * our *calls* to _wgetdcwd.
+     */
+    if (!((1 << (drive - 1)) & _getdrives())) {
+      return NS_ERROR_FILE_INVALID_PATH;
+    }
+    if (!_wgetdcwd(drive, pcwd, MAX_PATH)) {
+      pcwd = _wgetdcwd(drive, 0, 0);
+    }
+    if (!pcwd) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    nsAutoString currentDir(pcwd);
+    if (pcwd != cwd) {
+      free(pcwd);
+    }
+
+    if (currentDir.Last() == '\\') {
+      path.Replace(0, 2, currentDir);
+    } else {
+      path.Replace(0, 2, currentDir + u"\\"_ns);
+    }
+  }
+
+  MOZ_ASSERT(0 < rootIdx && rootIdx < (int32_t)path.Length(),
+             "rootIdx is invalid");
+  MOZ_ASSERT(path.CharAt(rootIdx) == '\\', "rootIdx is invalid");
+
+  // if there is nothing following the root path then it is already normalized
+  if (rootIdx + 1 == (int32_t)path.Length()) {
+    return NS_OK;
+  }
+
+  // assign the root
+  const char16_t* pathBuffer = path.get();  // simplify access to the buffer
+  mWorkingPath.SetCapacity(path.Length());  // it won't ever grow longer
+  mWorkingPath.Assign(pathBuffer, rootIdx);
+
+  // Normalize the path components. The actions taken are:
+  //
+  //  "\\"    condense to single backslash
+  //  "."     remove from path
+  //  ".."    up a directory
+  //  "..."   remove from path (any number of dots > 2)
+  //
+  // The last form is something that Windows 95 and 98 supported and
+  // is a shortcut for changing up multiple directories. Windows XP
+  // and ilk ignore it in a path, as is done here.
+  int32_t len, begin, end = rootIdx;
+  while (end < (int32_t)path.Length()) {
+    // find the current segment (text between the backslashes) to
+    // be examined, this will set the following variables:
+    //  begin == index of first char in segment
+    //  end   == index 1 char after last char in segment
+    //  len   == length of segment
+    begin = end + 1;
+    end = path.FindChar('\\', begin);
+    if (end == kNotFound) {
+      end = path.Length();
+    }
+    len = end - begin;
+
+    // ignore double backslashes
+    if (len == 0) {
+      continue;
+    }
+
+    // len != 0, and interesting paths always begin with a dot
+    if (pathBuffer[begin] == '.') {
+      // ignore single dots
+      if (len == 1) {
+        continue;
+      }
+
+      // handle multiple dots
+      if (len >= 2 && pathBuffer[begin + 1] == L'.') {
+        // back up a path component on double dot
+        if (len == 2) {
+          int32_t prev = mWorkingPath.RFindChar('\\');
+          if (prev >= rootIdx) {
+            mWorkingPath.Truncate(prev);
+          }
+          continue;
+        }
+
+        // length is > 2 and the first two characters are dots.
+        // if the rest of the string is dots, then ignore it.
+        int idx = len - 1;
+        for (; idx >= 2; --idx) {
+          if (pathBuffer[begin + idx] != L'.') {
+            break;
+          }
+        }
+
+        // this is true if the loop above didn't break
+        // and all characters in this segment are dots.
+        if (idx < 2) {
+          continue;
+        }
+      }
+    }
+
+    // add the current component to the path, including the preceding backslash
+    mWorkingPath.Append(pathBuffer + begin - 1, len + 1);
+  }
+
+  // kill trailing dots and spaces.
+  int32_t filePathLen = mWorkingPath.Length() - 1;
+  while (filePathLen > 0 && (mWorkingPath[filePathLen] == L' ' ||
+                             mWorkingPath[filePathLen] == L'.')) {
+    mWorkingPath.Truncate(filePathLen--);
+  }
+
+  MakeDirty();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetLeafName(nsAString& aLeafName) {
+  aLeafName.Truncate();
+
+  if (mWorkingPath.IsEmpty()) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+
+  int32_t offset = mWorkingPath.RFindChar(L'\\');
+
+  // if the working path is just a node without any lashes.
+  if (offset == kNotFound) {
+    aLeafName = mWorkingPath;
+  } else {
+    aLeafName = Substring(mWorkingPath, offset + 1);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetLeafName(const nsAString& aLeafName) {
+  MakeDirty();
+
+  if (mWorkingPath.IsEmpty()) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+
+  // cannot use nsCString::RFindChar() due to 0x5c problem
+  int32_t offset = mWorkingPath.RFindChar(L'\\');
+  nsString newDir;
+  if (offset) {
+    newDir = Substring(mWorkingPath, 0, offset + 1) + aLeafName;
+  } else {
+    newDir = mWorkingPath + aLeafName;
+  }
+  if (IsSpecialNTFSPath(newDir)) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+
+  mWorkingPath.Assign(newDir);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetDisplayName(nsAString& aLeafName) {
+  aLeafName.Truncate();
+
+  if (mWorkingPath.IsEmpty()) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+  SHFILEINFOW sfi = {};
+  DWORD_PTR result = ::SHGetFileInfoW(mWorkingPath.get(), 0, &sfi, sizeof(sfi),
+                                      SHGFI_DISPLAYNAME);
+  // If we found a display name, return that:
+  if (result) {
+    aLeafName.Assign(sfi.szDisplayName);
+    return NS_OK;
+  }
+  // Nope - fall back to the regular leaf name.
+  return GetLeafName(aLeafName);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetPath(nsAString& aResult) {
+  MOZ_ASSERT_IF(
+      mUseDOSDevicePathSyntax,
+      !FilePreferences::StartsWithDiskDesignatorAndBackslash(mWorkingPath));
+  aResult = mWorkingPath;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetCanonicalPath(nsAString& aResult) {
+  EnsureShortPath();
+  aResult.Assign(mShortWorkingPath);
+  return NS_OK;
+}
+
+typedef struct {
+  WORD wLanguage;
+  WORD wCodePage;
+} LANGANDCODEPAGE;
+
+NS_IMETHODIMP
+nsLocalFile::GetVersionInfoField(const char* aField, nsAString& aResult) {
+  nsresult rv = NS_ERROR_FAILURE;
+
+  const WCHAR* path = mWorkingPath.get();
+
+  DWORD dummy;
+  DWORD size = ::GetFileVersionInfoSizeW(path, &dummy);
+  if (!size) {
+    return rv;
+  }
+
+  void* ver = moz_xcalloc(size, 1);
+  if (::GetFileVersionInfoW(path, 0, size, ver)) {
+    LANGANDCODEPAGE* translate = nullptr;
+    UINT pageCount;
+    BOOL queryResult = ::VerQueryValueW(ver, L"\\VarFileInfo\\Translation",
+                                        (void**)&translate, &pageCount);
+    if (queryResult && translate) {
+      for (int32_t i = 0; i < 2; ++i) {
+        wchar_t subBlock[MAX_PATH];
+        _snwprintf(subBlock, MAX_PATH, L"\\StringFileInfo\\%04x%04x\\%S",
+                   (i == 0 ? translate[0].wLanguage : ::GetUserDefaultLangID()),
+                   translate[0].wCodePage, aField);
+        subBlock[MAX_PATH - 1] = 0;
+        LPVOID value = nullptr;
+        UINT size;
+        queryResult = ::VerQueryValueW(ver, subBlock, &value, &size);
+        if (queryResult && value) {
+          aResult.Assign(static_cast<char16_t*>(value));
+          if (!aResult.IsEmpty()) {
+            rv = NS_OK;
+            break;
+          }
+        }
+      }
+    }
+  }
+  free(ver);
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::OpenNSPRFileDescShareDelete(int32_t aFlags, int32_t aMode,
+                                         PRFileDesc** aResult) {
+  nsresult rv = OpenNSPRFileDescMaybeShareDelete(aFlags, aMode, true, aResult);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+/**
+ * Determines if the drive type for the specified file is rmeote or local.
+ *
+ * @param path   The path of the file to check
+ * @param remote Out parameter, on function success holds true if the specified
+ *               file path is remote, or false if the file path is local.
+ * @return true  on success. The return value implies absolutely nothing about
+ *               wether the file is local or remote.
+ */
+static bool IsRemoteFilePath(LPCWSTR aPath, bool& aRemote) {
+  // Obtain the parent directory path and make sure it ends with
+  // a trailing backslash.
+  WCHAR dirPath[MAX_PATH + 1] = {0};
+  wcsncpy(dirPath, aPath, MAX_PATH);
+  if (!PathRemoveFileSpecW(dirPath)) {
+    return false;
+  }
+  size_t len = wcslen(dirPath);
+  // In case the dirPath holds exaclty MAX_PATH and remains unchanged, we
+  // recheck the required length here since we need to terminate it with
+  // a backslash.
+  if (len >= MAX_PATH) {
+    return false;
+  }
+
+  dirPath[len] = L'\\';
+  dirPath[len + 1] = L'\0';
+  UINT driveType = GetDriveTypeW(dirPath);
+  aRemote = driveType == DRIVE_REMOTE;
+  return true;
+}
+
+nsresult nsLocalFile::CopySingleFile(nsIFile* aSourceFile, nsIFile* aDestParent,
+                                     const nsAString& aNewName,
+                                     uint32_t aOptions) {
+  nsresult rv = NS_OK;
+  nsAutoString filePath;
+
+  bool move = aOptions & (Move | Rename);
+
+  // get the path that we are going to copy to.
+  // Since windows does not know how to auto
+  // resolve shortcuts, we must work with the
+  // target.
+  nsAutoString destPath;
+  rv = aDestParent->GetTarget(destPath);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  destPath.Append('\\');
+
+  if (aNewName.IsEmpty()) {
+    nsAutoString aFileName;
+    aSourceFile->GetLeafName(aFileName);
+    destPath.Append(aFileName);
+  } else {
+    destPath.Append(aNewName);
+  }
+
+  if (aOptions & FollowSymlinks) {
+    rv = aSourceFile->GetTarget(filePath);
+    if (filePath.IsEmpty()) {
+      rv = aSourceFile->GetPath(filePath);
+    }
+  } else {
+    rv = aSourceFile->GetPath(filePath);
+  }
+
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+#ifdef DEBUG
+  nsCOMPtr<nsILocalFileWin> srcWinFile = do_QueryInterface(aSourceFile);
+  MOZ_ASSERT(srcWinFile);
+
+  bool srcUseDOSDevicePathSyntax;
+  srcWinFile->GetUseDOSDevicePathSyntax(&srcUseDOSDevicePathSyntax);
+
+  nsCOMPtr<nsILocalFileWin> destWinFile = do_QueryInterface(aDestParent);
+  MOZ_ASSERT(destWinFile);
+
+  bool destUseDOSDevicePathSyntax;
+  destWinFile->GetUseDOSDevicePathSyntax(&destUseDOSDevicePathSyntax);
+
+  MOZ_ASSERT(srcUseDOSDevicePathSyntax == destUseDOSDevicePathSyntax,
+             "Copy or Move files with different values for "
+             "useDOSDevicePathSyntax would fail");
+#endif
+
+  if (FilePreferences::IsBlockedUNCPath(destPath)) {
+    return NS_ERROR_FILE_ACCESS_DENIED;
+  }
+
+  int copyOK = 0;
+  if (move) {
+    copyOK = ::MoveFileExW(filePath.get(), destPath.get(),
+                           MOVEFILE_REPLACE_EXISTING);
+  }
+
+  // If we either failed to move the file, or this is a copy, try copying:
+  if (!copyOK && (!move || GetLastError() == ERROR_NOT_SAME_DEVICE)) {
+    // Failed renames here should just return access denied.
+    if (move && (aOptions & Rename)) {
+      return NS_ERROR_FILE_ACCESS_DENIED;
+    }
+
+    // Pass the flag COPY_FILE_NO_BUFFERING to CopyFileEx as we may be copying
+    // to a SMBV2 remote drive. Without this parameter subsequent append mode
+    // file writes can cause the resultant file to become corrupt. We only need
+    // to do this if the major version of Windows is > 5(Only Windows Vista and
+    // above can support SMBV2).  With a 7200RPM hard drive: Copying a 1KB file
+    // with COPY_FILE_NO_BUFFERING takes about 30-60ms. Copying a 1KB file
+    // without COPY_FILE_NO_BUFFERING takes < 1ms. So we only use
+    // COPY_FILE_NO_BUFFERING when we have a remote drive.
+    DWORD dwCopyFlags = COPY_FILE_ALLOW_DECRYPTED_DESTINATION;
+    bool path1Remote, path2Remote;
+    if (!IsRemoteFilePath(filePath.get(), path1Remote) ||
+        !IsRemoteFilePath(destPath.get(), path2Remote) || path1Remote ||
+        path2Remote) {
+      dwCopyFlags |= COPY_FILE_NO_BUFFERING;
+    }
+
+    copyOK = ::CopyFileExW(filePath.get(), destPath.get(), nullptr, nullptr,
+                           nullptr, dwCopyFlags);
+    // On Windows 10, copying without buffering has started failing, so try
+    // with buffering...
+    if (!copyOK && (dwCopyFlags & COPY_FILE_NO_BUFFERING) &&
+        GetLastError() == ERROR_INVALID_PARAMETER) {
+      dwCopyFlags &= ~COPY_FILE_NO_BUFFERING;
+      copyOK = ::CopyFileExW(filePath.get(), destPath.get(), nullptr, nullptr,
+                             nullptr, dwCopyFlags);
+    }
+
+    if (move && copyOK) {
+      DeleteFileW(filePath.get());
+    }
+  }
+
+  if (!copyOK) {  // CopyFileEx and MoveFileEx return zero at failure.
+    rv = ConvertWinError(GetLastError());
+  } else if (move && !(aOptions & SkipNtfsAclReset)) {
+    // Set security permissions to inherit from parent.
+    // Note: propagates to all children: slow for big file trees
+    PACL pOldDACL = nullptr;
+    PSECURITY_DESCRIPTOR pSD = nullptr;
+    ::GetNamedSecurityInfoW((LPWSTR)destPath.get(), SE_FILE_OBJECT,
+                            DACL_SECURITY_INFORMATION, nullptr, nullptr,
+                            &pOldDACL, nullptr, &pSD);
+    UniquePtr<VOID, LocalFreeDeleter> autoFreeSecDesc(pSD);
+    if (pOldDACL) {
+      // Test the current DACL, if we find one that is inherited then we can
+      // skip the reset. This avoids a request for SeTcbPrivilege, which can
+      // cause a lot of audit events if enabled (Bug 1816694).
+      bool inherited = false;
+      for (DWORD i = 0; i < pOldDACL->AceCount; ++i) {
+        VOID* pAce = nullptr;
+        if (::GetAce(pOldDACL, i, &pAce) &&
+            static_cast<PACE_HEADER>(pAce)->AceFlags & INHERITED_ACE) {
+          inherited = true;
+          break;
+        }
+      }
+
+      if (!inherited) {
+        ::SetNamedSecurityInfoW(
+            (LPWSTR)destPath.get(), SE_FILE_OBJECT,
+            DACL_SECURITY_INFORMATION | UNPROTECTED_DACL_SECURITY_INFORMATION,
+            nullptr, nullptr, pOldDACL, nullptr);
+      }
+    }
+  }
+
+  return rv;
+}
+
+nsresult nsLocalFile::CopyMove(nsIFile* aParentDir, const nsAString& aNewName,
+                               uint32_t aOptions) {
+  bool move = aOptions & (Move | Rename);
+  bool followSymlinks = aOptions & FollowSymlinks;
+  // If we're not provided with a new parent, we're copying or moving to
+  // another file in the same directory and can safely skip checking if the
+  // destination directory exists:
+  bool targetInSameDirectory = !aParentDir;
+
+  nsCOMPtr<nsIFile> newParentDir = aParentDir;
+  // check to see if this exists, otherwise return an error.
+  // we will check this by resolving.  If the user wants us
+  // to follow links, then we are talking about the target,
+  // hence we can use the |FollowSymlinks| option.
+  nsresult rv = ResolveAndStat();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (!newParentDir) {
+    // no parent was specified.  We must rename.
+    if (aNewName.IsEmpty()) {
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    rv = GetParent(getter_AddRefs(newParentDir));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  if (!newParentDir) {
+    return NS_ERROR_FILE_DESTINATION_NOT_DIR;
+  }
+
+  if (!targetInSameDirectory) {
+    // make sure it exists and is a directory.  Create it if not there.
+    bool exists = false;
+    rv = newParentDir->Exists(&exists);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    if (!exists) {
+      rv = newParentDir->Create(DIRECTORY_TYPE,
+                                0644);  // TODO, what permissions should we use
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    } else {
+      bool isDir = false;
+      rv = newParentDir->IsDirectory(&isDir);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      if (!isDir) {
+        if (followSymlinks) {
+          bool isLink = false;
+          rv = newParentDir->IsSymlink(&isLink);
+          if (NS_FAILED(rv)) {
+            return rv;
+          }
+
+          if (isLink) {
+            nsAutoString target;
+            rv = newParentDir->GetTarget(target);
+            if (NS_FAILED(rv)) {
+              return rv;
+            }
+
+            nsCOMPtr<nsIFile> realDest = new nsLocalFile();
+            rv = realDest->InitWithPath(target);
+            if (NS_FAILED(rv)) {
+              return rv;
+            }
+
+            return CopyMove(realDest, aNewName, aOptions);
+          }
+        } else {
+          return NS_ERROR_FILE_DESTINATION_NOT_DIR;
+        }
+      }
+    }
+  }
+
+  // Try different ways to move/copy files/directories
+  bool done = false;
+
+  bool isDir = false;
+  rv = IsDirectory(&isDir);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  bool isSymlink = false;
+  rv = IsSymlink(&isSymlink);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // Try to move the file or directory, or try to copy a single file (or
+  // non-followed symlink)
+  if (move || !isDir || (isSymlink && !followSymlinks)) {
+    // Copy/Move single file, or move a directory
+    if (!aParentDir) {
+      aOptions |= SkipNtfsAclReset;
+    }
+    rv = CopySingleFile(this, newParentDir, aNewName, aOptions);
+    done = NS_SUCCEEDED(rv);
+    // If we are moving a directory and that fails, fallback on directory
+    // enumeration.  See bug 231300 for details.
+    if (!done && !(move && isDir)) {
+      return rv;
+    }
+  }
+
+  // Not able to copy or move directly, so enumerate it
+  if (!done) {
+    // create a new target destination in the new parentDir;
+    nsCOMPtr<nsIFile> target;
+    rv = newParentDir->Clone(getter_AddRefs(target));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    nsAutoString allocatedNewName;
+    if (aNewName.IsEmpty()) {
+      bool isLink = false;
+      rv = IsSymlink(&isLink);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      if (isLink) {
+        nsAutoString temp;
+        rv = GetTarget(temp);
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+
+        int32_t offset = temp.RFindChar(L'\\');
+        if (offset == kNotFound) {
+          allocatedNewName = temp;
+        } else {
+          allocatedNewName = Substring(temp, offset + 1);
+        }
+      } else {
+        GetLeafName(allocatedNewName);  // this should be the leaf name of the
+      }
+    } else {
+      allocatedNewName = aNewName;
+    }
+
+    rv = target->Append(allocatedNewName);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    allocatedNewName.Truncate();
+
+    bool exists = false;
+    // check if the destination directory already exists
+    rv = target->Exists(&exists);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    if (!exists) {
+      // if the destination directory cannot be created, return an error
+      rv = target->Create(DIRECTORY_TYPE,
+                          0644);  // TODO, what permissions should we use
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    } else {
+      // check if the destination directory is writable and empty
+      bool isWritable = false;
+      rv = target->IsWritable(&isWritable);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      if (!isWritable) {
+        return NS_ERROR_FILE_ACCESS_DENIED;
+      }
+
+      nsCOMPtr<nsIDirectoryEnumerator> targetIterator;
+      rv = target->GetDirectoryEntries(getter_AddRefs(targetIterator));
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      bool more;
+      targetIterator->HasMoreElements(&more);
+      // return error if target directory is not empty
+      if (more) {
+        return NS_ERROR_FILE_DIR_NOT_EMPTY;
+      }
+    }
+
+    RefPtr<nsDirEnumerator> dirEnum = new nsDirEnumerator();
+
+    rv = dirEnum->Init(this);
+    if (NS_FAILED(rv)) {
+      NS_WARNING("dirEnum initialization failed");
+      return rv;
+    }
+
+    nsCOMPtr<nsIFile> file;
+    while (NS_SUCCEEDED(dirEnum->GetNextFile(getter_AddRefs(file))) && file) {
+      bool isDir = false;
+      rv = file->IsDirectory(&isDir);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      bool isLink = false;
+      rv = file->IsSymlink(&isLink);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      if (move) {
+        if (followSymlinks) {
+          return NS_ERROR_FAILURE;
+        }
+
+        rv = file->MoveTo(target, u""_ns);
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+      } else {
+        if (followSymlinks) {
+          rv = file->CopyToFollowingLinks(target, u""_ns);
+        } else {
+          rv = file->CopyTo(target, u""_ns);
+        }
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+      }
+    }
+    // we've finished moving all the children of this directory
+    // in the new directory.  so now delete the directory
+    // note, we don't need to do a recursive delete.
+    // MoveTo() is recursive.  At this point,
+    // we've already moved the children of the current folder
+    // to the new location.  nothing should be left in the folder.
+    if (move) {
+      rv = Remove(false /* recursive */);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    }
+  }
+
+  // If we moved, we want to adjust this.
+  if (move) {
+    MakeDirty();
+
+    nsAutoString newParentPath;
+    newParentDir->GetPath(newParentPath);
+
+    if (newParentPath.IsEmpty()) {
+      return NS_ERROR_FAILURE;
+    }
+
+    if (aNewName.IsEmpty()) {
+      nsAutoString aFileName;
+      GetLeafName(aFileName);
+
+      InitWithPath(newParentPath);
+      Append(aFileName);
+    } else {
+      InitWithPath(newParentPath);
+      Append(aNewName);
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::CopyTo(nsIFile* aNewParentDir, const nsAString& aNewName) {
+  return CopyMove(aNewParentDir, aNewName, 0);
+}
+
+NS_IMETHODIMP
+nsLocalFile::CopyToFollowingLinks(nsIFile* aNewParentDir,
+                                  const nsAString& aNewName) {
+  return CopyMove(aNewParentDir, aNewName, FollowSymlinks);
+}
+
+NS_IMETHODIMP
+nsLocalFile::MoveTo(nsIFile* aNewParentDir, const nsAString& aNewName) {
+  return CopyMove(aNewParentDir, aNewName, Move);
+}
+
+NS_IMETHODIMP
+nsLocalFile::MoveToFollowingLinks(nsIFile* aNewParentDir,
+                                  const nsAString& aNewName) {
+  return CopyMove(aNewParentDir, aNewName, Move | FollowSymlinks);
+}
+
+NS_IMETHODIMP
+nsLocalFile::RenameTo(nsIFile* aNewParentDir, const nsAString& aNewName) {
+  // If we're not provided with a new parent, we're renaming inside one and
+  // the same directory and can safely skip checking if the destination
+  // directory exists:
+  bool targetInSameDirectory = !aNewParentDir;
+
+  nsCOMPtr<nsIFile> targetParentDir = aNewParentDir;
+  // check to see if this exists, otherwise return an error.
+  // we will check this by resolving.  If the user wants us
+  // to follow links, then we are talking about the target,
+  // hence we can use the |followSymlinks| parameter.
+  nsresult rv = ResolveAndStat();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (!targetParentDir) {
+    // no parent was specified.  We must rename.
+    if (aNewName.IsEmpty()) {
+      return NS_ERROR_INVALID_ARG;
+    }
+    rv = GetParent(getter_AddRefs(targetParentDir));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  if (!targetParentDir) {
+    return NS_ERROR_FILE_DESTINATION_NOT_DIR;
+  }
+
+  if (!targetInSameDirectory) {
+    // make sure it exists and is a directory.  Create it if not there.
+    bool exists = false;
+    rv = targetParentDir->Exists(&exists);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    if (!exists) {
+      rv = targetParentDir->Create(DIRECTORY_TYPE, 0644);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    } else {
+      bool isDir = false;
+      rv = targetParentDir->IsDirectory(&isDir);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+      if (!isDir) {
+        return NS_ERROR_FILE_DESTINATION_NOT_DIR;
+      }
+    }
+  }
+
+  uint32_t options = Rename;
+  if (!aNewParentDir) {
+    options |= SkipNtfsAclReset;
+  }
+  // Move single file, or move a directory
+  return CopySingleFile(this, targetParentDir, aNewName, options);
+}
+
+NS_IMETHODIMP
+nsLocalFile::RenameToNative(nsIFile* aNewParentDir,
+                            const nsACString& aNewName) {
+  nsAutoString tmp;
+  nsresult rv = NS_CopyNativeToUnicode(aNewName, tmp);
+  if (NS_SUCCEEDED(rv)) {
+    return RenameTo(aNewParentDir, tmp);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Load(PRLibrary** aResult) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+  nsTraceRefcnt::SetActivityIsLegal(false);
+#endif
+
+  PRLibSpec libSpec;
+  libSpec.value.pathname_u = mWorkingPath.get();
+  libSpec.type = PR_LibSpec_PathnameU;
+  *aResult = PR_LoadLibraryWithFlags(libSpec, 0);
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+  nsTraceRefcnt::SetActivityIsLegal(true);
+#endif
+
+  if (*aResult) {
+    return NS_OK;
+  }
+  return NS_ERROR_NULL_POINTER;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Remove(bool aRecursive, uint32_t* aRemoveCount) {
+  // NOTE:
+  //
+  // if the working path points to a shortcut, then we will only
+  // delete the shortcut itself.  even if the shortcut points to
+  // a directory, we will not recurse into that directory or
+  // delete that directory itself.  likewise, if the shortcut
+  // points to a normal file, we will not delete the real file.
+  // this is done to be consistent with the other platforms that
+  // behave this way.  we do this even if the followLinks attribute
+  // is set to true.  this helps protect against misuse that could
+  // lead to security bugs (e.g., bug 210588).
+  //
+  // Since shortcut files are no longer permitted to be used as unix-like
+  // symlinks interspersed in the path (e.g. "c:/file.lnk/foo/bar.txt")
+  // this processing is a lot simpler. Even if the shortcut file is
+  // pointing to a directory, only the mWorkingPath value is used and so
+  // only the shortcut file will be deleted.
+
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  nsresult rv = NS_OK;
+
+  bool isLink = false;
+  rv = IsSymlink(&isLink);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // only check to see if we have a directory if it isn't a link
+  bool isDir = false;
+  if (!isLink) {
+    rv = IsDirectory(&isDir);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  if (isDir) {
+    if (aRecursive) {
+      // WARNING: neither the `SHFileOperation` nor `IFileOperation` APIs are
+      // appropriate here as neither handle long path names, i.e. paths prefixed
+      // with `\\?\` or longer than 260 characters on Windows 10+ system with
+      // long paths enabled.
+
+      RefPtr<nsDirEnumerator> dirEnum = new nsDirEnumerator();
+
+      rv = dirEnum->Init(this);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      // XXX: We are ignoring the result of the removal here while
+      // nsLocalFileUnix does not. We should align the behavior. (bug 1779696)
+      nsCOMPtr<nsIFile> file;
+      while (NS_SUCCEEDED(dirEnum->GetNextFile(getter_AddRefs(file))) && file) {
+        file->Remove(aRecursive, aRemoveCount);
+      }
+    }
+    if (RemoveDirectoryW(mWorkingPath.get()) == 0) {
+      return ConvertWinError(GetLastError());
+    }
+  } else {
+    if (DeleteFileW(mWorkingPath.get()) == 0) {
+      return ConvertWinError(GetLastError());
+    }
+  }
+
+  if (aRemoveCount) {
+    *aRemoveCount += 1;
+  }
+
+  MakeDirty();
+  return rv;
+}
+
+nsresult nsLocalFile::GetDateImpl(PRTime* aTime,
+                                  nsLocalFile::TimeField aTimeField,
+                                  bool aFollowLinks) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (NS_WARN_IF(!aTime)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  FileInfo symlinkInfo{};
+  FileInfo* pInfo;
+
+  if (aFollowLinks) {
+    if (nsresult rv = GetFileInfo(mWorkingPath, &symlinkInfo); NS_FAILED(rv)) {
+      return rv;
+    }
+
+    pInfo = &symlinkInfo;
+  } else {
+    if (nsresult rv = ResolveAndStat(); NS_FAILED(rv)) {
+      return rv;
+    }
+
+    pInfo = &mFileInfo;
+  }
+
+  switch (aTimeField) {
+    case TimeField::AccessedTime:
+      *aTime = pInfo->accessTime / PR_USEC_PER_MSEC;
+      break;
+
+    case TimeField::ModifiedTime:
+      *aTime = pInfo->modifyTime / PR_USEC_PER_MSEC;
+      break;
+
+    default:
+      MOZ_CRASH("Unknown time field");
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetLastAccessedTime(PRTime* aLastAccessedTime) {
+  return GetDateImpl(aLastAccessedTime, TimeField::AccessedTime,
+                     /* aFollowSymlinks = */ true);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetLastAccessedTimeOfLink(PRTime* aLastAccessedTime) {
+  return GetDateImpl(aLastAccessedTime, TimeField::AccessedTime,
+                     /* aFollowSymlinks = */ false);
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetLastAccessedTime(PRTime aLastAccessedTime) {
+  return SetDateImpl(aLastAccessedTime, TimeField::AccessedTime);
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetLastAccessedTimeOfLink(PRTime aLastAccessedTime) {
+  return SetLastAccessedTime(aLastAccessedTime);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetLastModifiedTime(PRTime* aLastModifiedTime) {
+  return GetDateImpl(aLastModifiedTime, TimeField::ModifiedTime,
+                     /* aFollowSymlinks = */ true);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetLastModifiedTimeOfLink(PRTime* aLastModifiedTime) {
+  return GetDateImpl(aLastModifiedTime, TimeField::ModifiedTime,
+                     /* aFollowSymlinks = */ false);
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetLastModifiedTime(PRTime aLastModifiedTime) {
+  return SetDateImpl(aLastModifiedTime, TimeField::ModifiedTime);
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetLastModifiedTimeOfLink(PRTime aLastModifiedTime) {
+  return SetLastModifiedTime(aLastModifiedTime);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetCreationTime(PRTime* aCreationTime) {
+  CHECK_mWorkingPath();
+
+  if (NS_WARN_IF(!aCreationTime)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsresult rv = ResolveAndStat();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  *aCreationTime = mFileInfo.creationTime / PR_USEC_PER_MSEC;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetCreationTimeOfLink(PRTime* aCreationTime) {
+  CHECK_mWorkingPath();
+
+  if (NS_WARN_IF(!aCreationTime)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  FileInfo info;
+  nsresult rv = GetFileInfo(mWorkingPath, &info);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  *aCreationTime = info.creationTime / PR_USEC_PER_MSEC;
+
+  return NS_OK;
+}
+
+nsresult nsLocalFile::SetDateImpl(PRTime aTime,
+                                  nsLocalFile::TimeField aTimeField) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  // The FILE_FLAG_BACKUP_SEMANTICS is required in order to change the
+  // modification time for directories.
+  HANDLE file =
+      ::CreateFileW(mWorkingPath.get(),  // pointer to name of the file
+                    GENERIC_WRITE,       // access (write) mode
+                    0,                   // share mode
+                    nullptr,             // pointer to security attributes
+                    OPEN_EXISTING,       // how to create
+                    FILE_FLAG_BACKUP_SEMANTICS,  // file attributes
+                    nullptr);
+
+  if (file == INVALID_HANDLE_VALUE) {
+    return ConvertWinError(GetLastError());
+  }
+
+  FILETIME ft;
+  SYSTEMTIME st;
+  PRExplodedTime pret;
+
+  if (aTime == 0) {
+    aTime = PR_Now() / PR_USEC_PER_MSEC;
+  }
+
+  // PR_ExplodeTime expects usecs...
+  PR_ExplodeTime(aTime * PR_USEC_PER_MSEC, PR_GMTParameters, &pret);
+  st.wYear = pret.tm_year;
+  st.wMonth =
+      pret.tm_month + 1;  // Convert start offset -- Win32: Jan=1; NSPR: Jan=0
+  st.wDayOfWeek = pret.tm_wday;
+  st.wDay = pret.tm_mday;
+  st.wHour = pret.tm_hour;
+  st.wMinute = pret.tm_min;
+  st.wSecond = pret.tm_sec;
+  st.wMilliseconds = pret.tm_usec / 1000;
+
+  const FILETIME* accessTime = nullptr;
+  const FILETIME* modifiedTime = nullptr;
+
+  if (aTimeField == TimeField::AccessedTime) {
+    accessTime = &ft;
+  } else {
+    modifiedTime = &ft;
+  }
+
+  nsresult rv = NS_OK;
+
+  // if at least one of these fails...
+  if (!(SystemTimeToFileTime(&st, &ft) != 0 &&
+        SetFileTime(file, nullptr, accessTime, modifiedTime) != 0)) {
+    rv = ConvertWinError(GetLastError());
+  }
+
+  CloseHandle(file);
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetPermissions(uint32_t* aPermissions) {
+  if (NS_WARN_IF(!aPermissions)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // get the permissions of the target as determined by mFollowSymlinks
+  // If true, then this will be for the target of the shortcut file,
+  // otherwise it will be for the shortcut file itself (i.e. the same
+  // results as GetPermissionsOfLink)
+  nsresult rv = ResolveAndStat();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  bool isWritable = false;
+  rv = IsWritable(&isWritable);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  bool isExecutable = false;
+  rv = IsExecutable(&isExecutable);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  *aPermissions = PR_IRUSR | PR_IRGRP | PR_IROTH;  // all read
+  if (isWritable) {
+    *aPermissions |= PR_IWUSR | PR_IWGRP | PR_IWOTH;  // all write
+  }
+  if (isExecutable) {
+    *aPermissions |= PR_IXUSR | PR_IXGRP | PR_IXOTH;  // all execute
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetPermissionsOfLink(uint32_t* aPermissions) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (NS_WARN_IF(!aPermissions)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // The caller is assumed to have already called IsSymlink
+  // and to have found that this file is a link. It is not
+  // possible for a link file to be executable.
+
+  DWORD word = ::GetFileAttributesW(mWorkingPath.get());
+  if (word == INVALID_FILE_ATTRIBUTES) {
+    return NS_ERROR_FILE_INVALID_PATH;
+  }
+
+  bool isWritable = !(word & FILE_ATTRIBUTE_READONLY);
+  *aPermissions = PR_IRUSR | PR_IRGRP | PR_IROTH;  // all read
+  if (isWritable) {
+    *aPermissions |= PR_IWUSR | PR_IWGRP | PR_IWOTH;  // all write
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetPermissions(uint32_t aPermissions) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  // set the permissions of the target as determined by mFollowSymlinks
+  // If true, then this will be for the target of the shortcut file,
+  // otherwise it will be for the shortcut file itself (i.e. the same
+  // results as SetPermissionsOfLink)
+  nsresult rv = Resolve();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // windows only knows about the following permissions
+  int mode = 0;
+  if (aPermissions & (PR_IRUSR | PR_IRGRP | PR_IROTH)) {  // any read
+    mode |= _S_IREAD;
+  }
+  if (aPermissions & (PR_IWUSR | PR_IWGRP | PR_IWOTH)) {  // any write
+    mode |= _S_IWRITE;
+  }
+
+  if (_wchmod(mResolvedPath.get(), mode) == -1) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetPermissionsOfLink(uint32_t aPermissions) {
+  // The caller is assumed to have already called IsSymlink
+  // and to have found that this file is a link.
+
+  // windows only knows about the following permissions
+  int mode = 0;
+  if (aPermissions & (PR_IRUSR | PR_IRGRP | PR_IROTH)) {  // any read
+    mode |= _S_IREAD;
+  }
+  if (aPermissions & (PR_IWUSR | PR_IWGRP | PR_IWOTH)) {  // any write
+    mode |= _S_IWRITE;
+  }
+
+  if (_wchmod(mWorkingPath.get(), mode) == -1) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetFileSize(int64_t* aFileSize) {
+  if (NS_WARN_IF(!aFileSize)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsresult rv = ResolveAndStat();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  *aFileSize = mFileInfo.size;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetFileSizeOfLink(int64_t* aFileSize) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (NS_WARN_IF(!aFileSize)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // The caller is assumed to have already called IsSymlink
+  // and to have found that this file is a link.
+
+  FileInfo info{};
+  if (NS_FAILED(GetFileInfo(mWorkingPath, &info))) {
+    return NS_ERROR_FILE_INVALID_PATH;
+  }
+
+  *aFileSize = info.size;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetFileSize(int64_t aFileSize) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  HANDLE hFile =
+      ::CreateFileW(mWorkingPath.get(),     // pointer to name of the file
+                    GENERIC_WRITE,          // access (write) mode
+                    FILE_SHARE_READ,        // share mode
+                    nullptr,                // pointer to security attributes
+                    OPEN_EXISTING,          // how to create
+                    FILE_ATTRIBUTE_NORMAL,  // file attributes
+                    nullptr);
+  if (hFile == INVALID_HANDLE_VALUE) {
+    return ConvertWinError(GetLastError());
+  }
+
+  // seek the file pointer to the new, desired end of file
+  // and then truncate the file at that position
+  nsresult rv = NS_ERROR_FAILURE;
+  LARGE_INTEGER distance;
+  distance.QuadPart = aFileSize;
+  if (SetFilePointerEx(hFile, distance, nullptr, FILE_BEGIN) &&
+      SetEndOfFile(hFile)) {
+    MakeDirty();
+    rv = NS_OK;
+  }
+
+  CloseHandle(hFile);
+  return rv;
+}
+
+static nsresult GetDiskSpaceAttributes(const nsString& aResolvedPath,
+                                       int64_t* aFreeBytesAvailable,
+                                       int64_t* aTotalBytes) {
+  ULARGE_INTEGER liFreeBytesAvailableToCaller;
+  ULARGE_INTEGER liTotalNumberOfBytes;
+  if (::GetDiskFreeSpaceExW(aResolvedPath.get(), &liFreeBytesAvailableToCaller,
+                            &liTotalNumberOfBytes, nullptr)) {
+    *aFreeBytesAvailable = liFreeBytesAvailableToCaller.QuadPart;
+    *aTotalBytes = liTotalNumberOfBytes.QuadPart;
+
+    return NS_OK;
+  }
+
+  return ConvertWinError(::GetLastError());
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetDiskSpaceAvailable(int64_t* aDiskSpaceAvailable) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (NS_WARN_IF(!aDiskSpaceAvailable)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  *aDiskSpaceAvailable = 0;
+
+  nsresult rv = ResolveAndStat();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (mFileInfo.type == PR_FILE_FILE) {
+    // Since GetDiskFreeSpaceExW works only on directories, use the parent.
+    nsCOMPtr<nsIFile> parent;
+    if (NS_SUCCEEDED(GetParent(getter_AddRefs(parent))) && parent) {
+      return parent->GetDiskSpaceAvailable(aDiskSpaceAvailable);
+    }
+  }
+
+  int64_t dummy = 0;
+  return GetDiskSpaceAttributes(mResolvedPath, aDiskSpaceAvailable, &dummy);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetDiskCapacity(int64_t* aDiskCapacity) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (NS_WARN_IF(!aDiskCapacity)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsresult rv = ResolveAndStat();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (mFileInfo.type == PR_FILE_FILE) {
+    // Since GetDiskFreeSpaceExW works only on directories, use the parent.
+    nsCOMPtr<nsIFile> parent;
+    if (NS_SUCCEEDED(GetParent(getter_AddRefs(parent))) && parent) {
+      return parent->GetDiskCapacity(aDiskCapacity);
+    }
+  }
+
+  int64_t dummy = 0;
+  return GetDiskSpaceAttributes(mResolvedPath, &dummy, aDiskCapacity);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetParent(nsIFile** aParent) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (NS_WARN_IF(!aParent)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // A two-character path must be a drive such as C:, so it has no parent
+  if (mWorkingPath.Length() == 2) {
+    *aParent = nullptr;
+    return NS_OK;
+  }
+
+  int32_t offset = mWorkingPath.RFindChar(char16_t('\\'));
+  // adding this offset check that was removed in bug 241708 fixes mail
+  // directories that aren't relative to/underneath the profile dir.
+  // e.g., on a different drive. Before you remove them, please make
+  // sure local mail directories that aren't underneath the profile dir work.
+  if (offset == kNotFound) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+
+  // A path of the form \\NAME is a top-level path and has no parent
+  if (offset == 1 && mWorkingPath[0] == L'\\') {
+    *aParent = nullptr;
+    return NS_OK;
+  }
+
+  nsAutoString parentPath(mWorkingPath);
+
+  if (offset > 0) {
+    parentPath.Truncate(offset);
+  } else {
+    parentPath.AssignLiteral("\\\\.");
+  }
+
+  nsCOMPtr<nsIFile> localFile;
+  nsresult rv = NewLocalFile(parentPath, mUseDOSDevicePathSyntax,
+                             getter_AddRefs(localFile));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  localFile.forget(aParent);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Exists(bool* aResult) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aResult = false;
+
+  MakeDirty();
+  nsresult rv = ResolveAndStat();
+  *aResult = NS_SUCCEEDED(rv) || rv == NS_ERROR_FILE_IS_LOCKED;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsWritable(bool* aIsWritable) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  // The read-only attribute on a FAT directory only means that it can't
+  // be deleted. It is still possible to modify the contents of the directory.
+  nsresult rv = IsDirectory(aIsWritable);
+  if (rv == NS_ERROR_FILE_ACCESS_DENIED) {
+    *aIsWritable = true;
+    return NS_OK;
+  } else if (rv == NS_ERROR_FILE_IS_LOCKED) {
+    // If the file is normally allowed write access
+    // we should still return that the file is writable.
+  } else if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (*aIsWritable) {
+    return NS_OK;
+  }
+
+  // writable if the file doesn't have the readonly attribute
+  rv = HasFileAttribute(FILE_ATTRIBUTE_READONLY, aIsWritable);
+  if (rv == NS_ERROR_FILE_ACCESS_DENIED) {
+    *aIsWritable = false;
+    return NS_OK;
+  } else if (rv == NS_ERROR_FILE_IS_LOCKED) {
+    // If the file is normally allowed write access
+    // we should still return that the file is writable.
+  } else if (NS_FAILED(rv)) {
+    return rv;
+  }
+  *aIsWritable = !*aIsWritable;
+
+  // If the read only attribute is not set, check to make sure
+  // we can open the file with write access.
+  if (*aIsWritable) {
+    PRFileDesc* file;
+    rv = OpenFile(mResolvedPath, PR_WRONLY, 0, false, &file);
+    if (NS_SUCCEEDED(rv)) {
+      PR_Close(file);
+    } else if (rv == NS_ERROR_FILE_ACCESS_DENIED) {
+      *aIsWritable = false;
+    } else if (rv == NS_ERROR_FILE_IS_LOCKED) {
+      // If it is locked and read only we would have
+      // gotten access denied
+      *aIsWritable = true;
+    } else {
+      return rv;
+    }
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsReadable(bool* aResult) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aResult = false;
+
+  nsresult rv = ResolveAndStat();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  *aResult = true;
+  return NS_OK;
+}
+
+nsresult nsLocalFile::LookupExtensionIn(const char* const* aExtensionsArray,
+                                        size_t aArrayLength, bool* aResult) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aResult = false;
+
+  nsresult rv;
+
+  // only files can be executables
+  bool isFile;
+  rv = IsFile(&isFile);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (!isFile) {
+    return NS_OK;
+  }
+
+  // TODO: shouldn't we be checking mFollowSymlinks here?
+  bool symLink = false;
+  rv = IsSymlink(&symLink);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  nsAutoString path;
+  if (symLink) {
+    GetTarget(path);
+  } else {
+    GetPath(path);
+  }
+
+  // kill trailing dots and spaces.
+  int32_t filePathLen = path.Length() - 1;
+  while (filePathLen > 0 &&
+         (path[filePathLen] == L' ' || path[filePathLen] == L'.')) {
+    path.Truncate(filePathLen--);
+  }
+
+  // Get extension.
+  int32_t dotIdx = path.RFindChar(char16_t('.'));
+  if (dotIdx != kNotFound) {
+    // Convert extension to lower case.
+    char16_t* p = path.BeginWriting();
+    for (p += dotIdx + 1; *p; ++p) {
+      *p += (*p >= L'A' && *p <= L'Z') ? 'a' - 'A' : 0;
+    }
+
+    nsDependentSubstring ext = Substring(path, dotIdx);
+    for (size_t i = 0; i < aArrayLength; ++i) {
+      if (ext.EqualsASCII(aExtensionsArray[i])) {
+        // Found a match.  Set result and quit.
+        *aResult = true;
+        break;
+      }
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsExecutable(bool* aResult) {
+  return LookupExtensionIn(sExecutableExts, ArrayLength(sExecutableExts),
+                           aResult);
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsDirectory(bool* aResult) {
+  return HasFileAttribute(FILE_ATTRIBUTE_DIRECTORY, aResult);
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsFile(bool* aResult) {
+  nsresult rv = HasFileAttribute(FILE_ATTRIBUTE_DIRECTORY, aResult);
+  if (NS_SUCCEEDED(rv)) {
+    *aResult = !*aResult;
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsHidden(bool* aResult) {
+  return HasFileAttribute(FILE_ATTRIBUTE_HIDDEN, aResult);
+}
+
+nsresult nsLocalFile::HasFileAttribute(DWORD aFileAttrib, bool* aResult) {
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsresult rv = Resolve();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  DWORD attributes = GetFileAttributesW(mResolvedPath.get());
+  if (INVALID_FILE_ATTRIBUTES == attributes) {
+    return ConvertWinError(GetLastError());
+  }
+
+  *aResult = ((attributes & aFileAttrib) != 0);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsSymlink(bool* aResult) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // TODO: Implement symlink support
+  *aResult = false;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::IsSpecial(bool* aResult) {
+  return HasFileAttribute(FILE_ATTRIBUTE_SYSTEM, aResult);
+}
+
+NS_IMETHODIMP
+nsLocalFile::Equals(nsIFile* aInFile, bool* aResult) {
+  if (NS_WARN_IF(!aInFile)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  if (NS_WARN_IF(!aResult)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsCOMPtr<nsILocalFileWin> lf(do_QueryInterface(aInFile));
+  if (!lf) {
+    *aResult = false;
+    return NS_OK;
+  }
+
+  bool inUseDOSDevicePathSyntax;
+  lf->GetUseDOSDevicePathSyntax(&inUseDOSDevicePathSyntax);
+
+  // If useDOSDevicePathSyntax are different remove the prefix from the one that
+  // might have it. This is added because of Omnijar. It compares files from
+  // different modules with itself.
+  bool removePathPrefix, removeInPathPrefix;
+  if (inUseDOSDevicePathSyntax != mUseDOSDevicePathSyntax) {
+    removeInPathPrefix = inUseDOSDevicePathSyntax;
+    removePathPrefix = mUseDOSDevicePathSyntax;
+  } else {
+    removePathPrefix = removeInPathPrefix = false;
+  }
+
+  nsAutoString inFilePath, workingPath;
+  aInFile->GetPath(inFilePath);
+  workingPath = mWorkingPath;
+
+  constexpr static auto equalPath =
+      [](nsAutoString& workingPath, nsAutoString& inFilePath,
+         bool removePathPrefix, bool removeInPathPrefix) {
+        if (removeInPathPrefix &&
+            StringBeginsWith(inFilePath, kDevicePathSpecifier)) {
+          MOZ_ASSERT(!StringBeginsWith(workingPath, kDevicePathSpecifier));
+
+          inFilePath = Substring(inFilePath, kDevicePathSpecifier.Length());
+        } else if (removePathPrefix &&
+                   StringBeginsWith(workingPath, kDevicePathSpecifier)) {
+          MOZ_ASSERT(!StringBeginsWith(inFilePath, kDevicePathSpecifier));
+
+          workingPath = Substring(workingPath, kDevicePathSpecifier.Length());
+        }
+
+        return _wcsicmp(workingPath.get(), inFilePath.get()) == 0;
+      };
+
+  if (equalPath(workingPath, inFilePath, removePathPrefix,
+                removeInPathPrefix)) {
+    *aResult = true;
+    return NS_OK;
+  }
+
+  EnsureShortPath();
+  lf->GetCanonicalPath(inFilePath);
+  workingPath = mShortWorkingPath;
+  *aResult =
+      equalPath(workingPath, inFilePath, removePathPrefix, removeInPathPrefix);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Contains(nsIFile* aInFile, bool* aResult) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  *aResult = false;
+
+  nsAutoString myFilePath;
+  if (NS_FAILED(GetTarget(myFilePath))) {
+    GetPath(myFilePath);
+  }
+
+  uint32_t myFilePathLen = myFilePath.Length();
+
+  nsAutoString inFilePath;
+  if (NS_FAILED(aInFile->GetTarget(inFilePath))) {
+    aInFile->GetPath(inFilePath);
+  }
+
+  // Make sure that the |aInFile|'s path has a trailing separator.
+  if (inFilePath.Length() > myFilePathLen &&
+      inFilePath[myFilePathLen] == L'\\') {
+    if (_wcsnicmp(myFilePath.get(), inFilePath.get(), myFilePathLen) == 0) {
+      *aResult = true;
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetTarget(nsAString& aResult) {
+  aResult.Truncate();
+  Resolve();
+
+  MOZ_ASSERT_IF(
+      mUseDOSDevicePathSyntax,
+      !FilePreferences::StartsWithDiskDesignatorAndBackslash(mResolvedPath));
+
+  aResult = mResolvedPath;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetDirectoryEntriesImpl(nsIDirectoryEnumerator** aEntries) {
+  nsresult rv;
+
+  *aEntries = nullptr;
+  if (mWorkingPath.EqualsLiteral("\\\\.")) {
+    RefPtr<nsDriveEnumerator> drives =
+        new nsDriveEnumerator(mUseDOSDevicePathSyntax);
+    rv = drives->Init();
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+    drives.forget(aEntries);
+    return NS_OK;
+  }
+
+  RefPtr<nsDirEnumerator> dirEnum = new nsDirEnumerator();
+  rv = dirEnum->Init(this);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  dirEnum.forget(aEntries);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetPersistentDescriptor(nsACString& aPersistentDescriptor) {
+  CopyUTF16toUTF8(mWorkingPath, aPersistentDescriptor);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetPersistentDescriptor(const nsACString& aPersistentDescriptor) {
+  if (IsUtf8(aPersistentDescriptor)) {
+    return InitWithPath(NS_ConvertUTF8toUTF16(aPersistentDescriptor));
+  } else {
+    return InitWithNativePath(aPersistentDescriptor);
+  }
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetReadOnly(bool* aReadOnly) {
+  NS_ENSURE_ARG_POINTER(aReadOnly);
+
+  DWORD dwAttrs = GetFileAttributesW(mWorkingPath.get());
+  if (dwAttrs == INVALID_FILE_ATTRIBUTES) {
+    return NS_ERROR_FILE_INVALID_PATH;
+  }
+
+  *aReadOnly = dwAttrs & FILE_ATTRIBUTE_READONLY;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetReadOnly(bool aReadOnly) {
+  DWORD dwAttrs = GetFileAttributesW(mWorkingPath.get());
+  if (dwAttrs == INVALID_FILE_ATTRIBUTES) {
+    return NS_ERROR_FILE_INVALID_PATH;
+  }
+
+  if (aReadOnly) {
+    dwAttrs |= FILE_ATTRIBUTE_READONLY;
+  } else {
+    dwAttrs &= ~FILE_ATTRIBUTE_READONLY;
+  }
+
+  if (SetFileAttributesW(mWorkingPath.get(), dwAttrs) == 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetUseDOSDevicePathSyntax(bool* aUseDOSDevicePathSyntax) {
+  MOZ_ASSERT(aUseDOSDevicePathSyntax);
+
+  *aUseDOSDevicePathSyntax = mUseDOSDevicePathSyntax;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetUseDOSDevicePathSyntax(bool aUseDOSDevicePathSyntax) {
+  if (mUseDOSDevicePathSyntax == aUseDOSDevicePathSyntax) {
+    return NS_OK;
+  }
+
+  if (mUseDOSDevicePathSyntax) {
+    if (StringBeginsWith(mWorkingPath, kDevicePathSpecifier)) {
+      MakeDirty();
+      // Remove the prefix
+      mWorkingPath = Substring(mWorkingPath, kDevicePathSpecifier.Length());
+    }
+  } else {
+    if (FilePreferences::StartsWithDiskDesignatorAndBackslash(mWorkingPath)) {
+      MakeDirty();
+      // Prepend the prefix
+      mWorkingPath = kDevicePathSpecifier + mWorkingPath;
+    }
+  }
+
+  mUseDOSDevicePathSyntax = aUseDOSDevicePathSyntax;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Reveal() {
+  // This API should be main thread only
+  MOZ_ASSERT(NS_IsMainThread());
+
+  // make sure mResolvedPath is set
+  nsresult rv = Resolve();
+  if (NS_FAILED(rv) && rv != NS_ERROR_FILE_NOT_FOUND) {
+    return rv;
+  }
+
+  nsCOMPtr<nsIRunnable> task =
+      NS_NewRunnableFunction("nsLocalFile::Reveal", [path = mResolvedPath]() {
+        MOZ_ASSERT(!NS_IsMainThread(), "Don't run on the main thread");
+
+        bool doCoUninitialize = SUCCEEDED(CoInitializeEx(
+            nullptr, COINIT_APARTMENTTHREADED | COINIT_DISABLE_OLE1DDE));
+        RevealFile(path);
+        if (doCoUninitialize) {
+          CoUninitialize();
+        }
+      });
+
+  return NS_DispatchBackgroundTask(task,
+                                   nsIEventTarget::DISPATCH_EVENT_MAY_BLOCK);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetWindowsFileAttributes(uint32_t* aAttrs) {
+  NS_ENSURE_ARG_POINTER(aAttrs);
+
+  DWORD dwAttrs = ::GetFileAttributesW(mWorkingPath.get());
+  if (dwAttrs == INVALID_FILE_ATTRIBUTES) {
+    return ConvertWinError(GetLastError());
+  }
+
+  *aAttrs = dwAttrs;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetWindowsFileAttributes(uint32_t aSetAttrs,
+                                      uint32_t aClearAttrs) {
+  DWORD dwAttrs = ::GetFileAttributesW(mWorkingPath.get());
+  if (dwAttrs == INVALID_FILE_ATTRIBUTES) {
+    return ConvertWinError(GetLastError());
+  }
+
+  dwAttrs = (dwAttrs & ~aClearAttrs) | aSetAttrs;
+
+  if (::SetFileAttributesW(mWorkingPath.get(), dwAttrs) == 0) {
+    return ConvertWinError(GetLastError());
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Launch() {
+  // This API should be main thread only
+  MOZ_ASSERT(NS_IsMainThread());
+
+  // use the app registry name to launch a shell execute....
+  _bstr_t execPath(mWorkingPath.get());
+
+  _variant_t args;
+  // Pass VT_ERROR/DISP_E_PARAMNOTFOUND to omit an optional RPC parameter
+  // to execute a file with the default verb.
+  _variant_t verbDefault(DISP_E_PARAMNOTFOUND, VT_ERROR);
+  _variant_t showCmd(SW_SHOWNORMAL);
+
+  // Use the directory of the file we're launching as the working
+  // directory. That way if we have a self extracting EXE it won't
+  // suggest to extract to the install directory.
+  wchar_t* workingDirectoryPtr = nullptr;
+  WCHAR workingDirectory[MAX_PATH + 1] = {L'\0'};
+  wcsncpy(workingDirectory, mWorkingPath.get(), MAX_PATH);
+  if (PathRemoveFileSpecW(workingDirectory)) {
+    workingDirectoryPtr = workingDirectory;
+  } else {
+    NS_WARNING("Could not set working directory for launched file.");
+  }
+
+  // We have two methods to launch a file: ShellExecuteExW and
+  // ShellExecuteByExplorer.  ShellExecuteExW starts a new process as a child
+  // of the current process, while ShellExecuteByExplorer starts a new process
+  // as a child of explorer.exe.
+  //
+  // We prefer launching a process via ShellExecuteByExplorer because
+  // applications may not support the mitigation policies inherited from our
+  // process.  For example, Skype for Business does not start correctly with
+  // the PreferSystem32Images policy which is one of the policies we use.
+  //
+  // If ShellExecuteByExplorer fails for some reason e.g. a system without
+  // running explorer.exe or VDI environment like Citrix, we fall back to
+  // ShellExecuteExW which still works in those special environments.
+  //
+  // There is an exception where we go straight to ShellExecuteExW without
+  // trying ShellExecuteByExplorer.  When the extension of a downloaded file is
+  // "exe", we prefer security rather than compatibility.
+  //
+  // When a user launches a downloaded executable, the directory containing
+  // the downloaded file may contain a malicious DLL with a common name, which
+  // may have been downloaded before.  If the downloaded executable is launched
+  // without the PreferSystem32Images policy, the process can be tricked into
+  // loading the malicious DLL in the same directory if its name is in the
+  // executable's dependent modules.  Therefore, we always launch ".exe"
+  // executables via ShellExecuteExW so they inherit our process's mitigation
+  // policies including PreferSystem32Images.
+  //
+  // If the extension is not "exe", then we assume that we are launching an
+  // installed application, and therefore the security risk described above
+  // is lessened, as a malicious DLL is less likely to be installed in the
+  // application's directory.  In that case, we attempt to preserve
+  // compatibility and try ShellExecuteByExplorer first.
+
+  static const char* const onlyExeExt[] = {".exe"};
+  bool isExecutable;
+  nsresult rv =
+      LookupExtensionIn(onlyExeExt, ArrayLength(onlyExeExt), &isExecutable);
+  if (NS_FAILED(rv)) {
+    isExecutable = false;
+  }
+
+  // If the file is an executable, go straight to ShellExecuteExW.
+  // Otherwise try ShellExecuteByExplorer first, and if it fails,
+  // run ShellExecuteExW.
+  if (!isExecutable) {
+    mozilla::LauncherVoidResult shellExecuteOk =
+        mozilla::ShellExecuteByExplorer(execPath, args, verbDefault,
+                                        workingDirectoryPtr, showCmd);
+    if (shellExecuteOk.isOk()) {
+      return NS_OK;
+    }
+  }
+
+  SHELLEXECUTEINFOW seinfo = {sizeof(SHELLEXECUTEINFOW)};
+  seinfo.fMask = SEE_MASK_ASYNCOK;
+  seinfo.hwnd = GetMostRecentNavigatorHWND();
+  seinfo.lpVerb = nullptr;
+  seinfo.lpFile = mWorkingPath.get();
+  seinfo.lpParameters = nullptr;
+  seinfo.lpDirectory = workingDirectoryPtr;
+  seinfo.nShow = SW_SHOWNORMAL;
+
+  if (!ShellExecuteExW(&seinfo)) {
+    return NS_ERROR_FILE_EXECUTION_FAILED;
+  }
+
+  return NS_OK;
+}
+
+nsresult NS_NewLocalFile(const nsAString& aPath, bool aFollowLinks,
+                         nsIFile** aResult) {
+  RefPtr<nsLocalFile> file = new nsLocalFile();
+
+  if (!aPath.IsEmpty()) {
+    nsresult rv = file->InitWithPath(aPath);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  file.forget(aResult);
+  return NS_OK;
+}
+
+//-----------------------------------------------------------------------------
+// Native (lossy) interface
+//-----------------------------------------------------------------------------
+
+NS_IMETHODIMP
+nsLocalFile::InitWithNativePath(const nsACString& aFilePath) {
+  nsAutoString tmp;
+  nsresult rv = NS_CopyNativeToUnicode(aFilePath, tmp);
+  if (NS_SUCCEEDED(rv)) {
+    return InitWithPath(tmp);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::AppendNative(const nsACString& aNode) {
+  nsAutoString tmp;
+  nsresult rv = NS_CopyNativeToUnicode(aNode, tmp);
+  if (NS_SUCCEEDED(rv)) {
+    return Append(tmp);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::AppendRelativeNativePath(const nsACString& aNode) {
+  nsAutoString tmp;
+  nsresult rv = NS_CopyNativeToUnicode(aNode, tmp);
+  if (NS_SUCCEEDED(rv)) {
+    return AppendRelativePath(tmp);
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetNativeLeafName(nsACString& aLeafName) {
+  // NS_WARNING("This API is lossy. Use GetLeafName !");
+  nsAutoString tmp;
+  nsresult rv = GetLeafName(tmp);
+  if (NS_SUCCEEDED(rv)) {
+    rv = NS_CopyUnicodeToNative(tmp, aLeafName);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetNativeLeafName(const nsACString& aLeafName) {
+  nsAutoString tmp;
+  nsresult rv = NS_CopyNativeToUnicode(aLeafName, tmp);
+  if (NS_SUCCEEDED(rv)) {
+    return SetLeafName(tmp);
+  }
+
+  return rv;
+}
+
+nsString nsLocalFile::NativePath() { return mWorkingPath; }
+
+nsCString nsIFile::HumanReadablePath() {
+  nsString path;
+  DebugOnly<nsresult> rv = GetPath(path);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+  return NS_ConvertUTF16toUTF8(path);
+}
+
+NS_IMETHODIMP
+nsLocalFile::CopyToNative(nsIFile* aNewParentDir, const nsACString& aNewName) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (aNewName.IsEmpty()) {
+    return CopyTo(aNewParentDir, u""_ns);
+  }
+
+  nsAutoString tmp;
+  nsresult rv = NS_CopyNativeToUnicode(aNewName, tmp);
+  if (NS_SUCCEEDED(rv)) {
+    return CopyTo(aNewParentDir, tmp);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::CopyToFollowingLinksNative(nsIFile* aNewParentDir,
+                                        const nsACString& aNewName) {
+  if (aNewName.IsEmpty()) {
+    return CopyToFollowingLinks(aNewParentDir, u""_ns);
+  }
+
+  nsAutoString tmp;
+  nsresult rv = NS_CopyNativeToUnicode(aNewName, tmp);
+  if (NS_SUCCEEDED(rv)) {
+    return CopyToFollowingLinks(aNewParentDir, tmp);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::MoveToNative(nsIFile* aNewParentDir, const nsACString& aNewName) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (aNewName.IsEmpty()) {
+    return MoveTo(aNewParentDir, u""_ns);
+  }
+
+  nsAutoString tmp;
+  nsresult rv = NS_CopyNativeToUnicode(aNewName, tmp);
+  if (NS_SUCCEEDED(rv)) {
+    return MoveTo(aNewParentDir, tmp);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::MoveToFollowingLinksNative(nsIFile* aNewParentDir,
+                                        const nsACString& aNewName) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  if (aNewName.IsEmpty()) {
+    return MoveToFollowingLinks(aNewParentDir, u""_ns);
+  }
+
+  nsAutoString tmp;
+  nsresult rv = NS_CopyNativeToUnicode(aNewName, tmp);
+  if (NS_SUCCEEDED(rv)) {
+    return MoveToFollowingLinks(aNewParentDir, tmp);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetNativeTarget(nsACString& aResult) {
+  // Check we are correctly initialized.
+  CHECK_mWorkingPath();
+
+  NS_WARNING("This API is lossy. Use GetTarget !");
+  nsAutoString tmp;
+  nsresult rv = GetTarget(tmp);
+  if (NS_SUCCEEDED(rv)) {
+    rv = NS_CopyUnicodeToNative(tmp, aResult);
+  }
+
+  return rv;
+}
+
+nsresult NS_NewNativeLocalFile(const nsACString& aPath, bool aFollowLinks,
+                               nsIFile** aResult) {
+  nsAutoString buf;
+  nsresult rv = NS_CopyNativeToUnicode(aPath, buf);
+  if (NS_FAILED(rv)) {
+    *aResult = nullptr;
+    return rv;
+  }
+  return NS_NewLocalFile(buf, aFollowLinks, aResult);
+}
+
+void nsLocalFile::EnsureShortPath() {
+  if (!mShortWorkingPath.IsEmpty()) {
+    return;
+  }
+
+  WCHAR shortPath[MAX_PATH + 1];
+  DWORD lengthNeeded = ::GetShortPathNameW(mWorkingPath.get(), shortPath,
+                                           ArrayLength(shortPath));
+  // If an error occurred then lengthNeeded is set to 0 or the length of the
+  // needed buffer including null termination.  If it succeeds the number of
+  // wide characters not including null termination is returned.
+  if (lengthNeeded != 0 && lengthNeeded < ArrayLength(shortPath)) {
+    mShortWorkingPath.Assign(shortPath);
+  } else {
+    mShortWorkingPath.Assign(mWorkingPath);
+  }
+}
+
+NS_IMPL_ISUPPORTS_INHERITED(nsDriveEnumerator, nsSimpleEnumerator,
+                            nsIDirectoryEnumerator)
+
+nsDriveEnumerator::nsDriveEnumerator(bool aUseDOSDevicePathSyntax)
+    : mUseDOSDevicePathSyntax(aUseDOSDevicePathSyntax) {}
+
+nsDriveEnumerator::~nsDriveEnumerator() {}
+
+nsresult nsDriveEnumerator::Init() {
+  /* If the length passed to GetLogicalDriveStrings is smaller
+   * than the length of the string it would return, it returns
+   * the length required for the string. */
+  DWORD length = GetLogicalDriveStringsW(0, 0);
+  /* The string is null terminated */
+  if (!mDrives.SetLength(length + 1, fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  if (!GetLogicalDriveStringsW(length, mDrives.get())) {
+    return NS_ERROR_FAILURE;
+  }
+  mDrives.BeginReading(mStartOfCurrentDrive);
+  mDrives.EndReading(mEndOfDrivesString);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDriveEnumerator::HasMoreElements(bool* aHasMore) {
+  *aHasMore = *mStartOfCurrentDrive != L'\0';
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDriveEnumerator::GetNext(nsISupports** aNext) {
+  /* GetLogicalDrives stored in mDrives is a concatenation
+   * of null terminated strings, followed by a null terminator.
+   * mStartOfCurrentDrive is an iterator pointing at the first
+   * character of the current drive. */
+  if (*mStartOfCurrentDrive == L'\0') {
+    *aNext = nullptr;
+    return NS_ERROR_FAILURE;
+  }
+
+  nsAString::const_iterator driveEnd = mStartOfCurrentDrive;
+  FindCharInReadable(L'\0', driveEnd, mEndOfDrivesString);
+  nsString drive(Substring(mStartOfCurrentDrive, driveEnd));
+  mStartOfCurrentDrive = ++driveEnd;
+
+  nsIFile* file;
+  nsresult rv = NewLocalFile(drive, mUseDOSDevicePathSyntax, &file);
+
+  *aNext = file;
+  return rv;
+}
diff --git a/xpcom/io/nsLocalFileWin.h b/xpcom/io/nsLocalFileWin.h
new file mode 100644
index 0000000000..a3ea03a666
--- /dev/null
+++ b/xpcom/io/nsLocalFileWin.h
@@ -0,0 +1,127 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef _nsLocalFileWIN_H_
+#define _nsLocalFileWIN_H_
+
+#include "nscore.h"
+#include "nsError.h"
+#include "nsString.h"
+#include "nsCRT.h"
+#include "nsIFile.h"
+#include "nsILocalFileWin.h"
+#include "nsIClassInfoImpl.h"
+#include "prio.h"
+
+#include "mozilla/Attributes.h"
+
+#include <windows.h>
+#include <shlobj.h>
+
+#include <sys/stat.h>
+
+class nsLocalFile final : public nsILocalFileWin {
+ public:
+  NS_DEFINE_STATIC_CID_ACCESSOR(NS_LOCAL_FILE_CID)
+
+  nsLocalFile();
+  explicit nsLocalFile(const nsAString& aFilePath);
+
+  static nsresult nsLocalFileConstructor(const nsIID& aIID,
+                                         void** aInstancePtr);
+
+  // nsISupports interface
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  // nsIFile interface
+  NS_DECL_NSIFILE
+
+  // nsILocalFileWin interface
+  NS_DECL_NSILOCALFILEWIN
+
+ public:
+  // Removes registry command handler parameters, quotes, and expands
+  // environment strings.
+  static bool CleanupCmdHandlerPath(nsAString& aCommandHandler);
+  // Called off the main thread to open the window revealing the file
+  static nsresult RevealFile(const nsString& aResolvedPath);
+
+  // Checks if the filename is one of the windows reserved filenames
+  // (com1, com2, etc...) and returns true if so.
+  static bool CheckForReservedFileName(const nsString& aFileName);
+
+  // PRFileInfo64 does not hvae an accessTime field;
+  struct FileInfo {
+    PRFileType type;
+    PROffset64 size;
+    PRTime creationTime;
+    PRTime accessTime;
+    PRTime modifyTime;
+  };
+
+ private:
+  // CopyMove and CopySingleFile constants for |options| parameter:
+  enum CopyFileOption {
+    FollowSymlinks = 1u << 0,
+    Move = 1u << 1,
+    SkipNtfsAclReset = 1u << 2,
+    Rename = 1u << 3
+  };
+
+  nsLocalFile(const nsLocalFile& aOther);
+  ~nsLocalFile() {}
+
+  bool mDirty;  // cached information can only be used when this is false
+  bool mResolveDirty;
+
+  bool mUseDOSDevicePathSyntax;
+
+  // this string will always be in native format!
+  nsString mWorkingPath;
+
+  // this will be the resolved path of shortcuts, it will *NEVER*
+  // be returned to the user
+  nsString mResolvedPath;
+
+  // this string, if not empty, is the *short* pathname that represents
+  // mWorkingPath
+  nsString mShortWorkingPath;
+
+  FileInfo mFileInfo;
+
+  void MakeDirty() {
+    mDirty = true;
+    mResolveDirty = true;
+    mShortWorkingPath.Truncate();
+  }
+
+  nsresult LookupExtensionIn(const char* const* aExtensionsArray,
+                             size_t aArrayLength, bool* aResult);
+
+  nsresult ResolveAndStat();
+  nsresult Resolve();
+  nsresult ResolveSymlink();
+
+  void EnsureShortPath();
+
+  nsresult CopyMove(nsIFile* aNewParentDir, const nsAString& aNewName,
+                    uint32_t aOptions);
+  nsresult CopySingleFile(nsIFile* aSource, nsIFile* aDest,
+                          const nsAString& aNewName, uint32_t aOptions);
+
+  enum class TimeField { AccessedTime, ModifiedTime };
+
+  nsresult SetDateImpl(int64_t aTime, TimeField aTimeField);
+  nsresult GetDateImpl(PRTime* aTime, TimeField aTimeField, bool aFollowLinks);
+  nsresult HasFileAttribute(DWORD aFileAttrib, bool* aResult);
+  nsresult AppendInternal(const nsString& aNode, bool aMultipleComponents);
+
+  nsresult OpenNSPRFileDescMaybeShareDelete(int32_t aFlags, int32_t aMode,
+                                            bool aShareDelete,
+                                            PRFileDesc** aResult);
+};
+
+#endif
diff --git a/xpcom/io/nsMultiplexInputStream.cpp b/xpcom/io/nsMultiplexInputStream.cpp
new file mode 100644
index 0000000000..bc8a67ed23
--- /dev/null
+++ b/xpcom/io/nsMultiplexInputStream.cpp
@@ -0,0 +1,1557 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * The multiplex stream concatenates a list of input streams into a single
+ * stream.
+ */
+
+#include "mozilla/Attributes.h"
+#include "mozilla/CheckedInt.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/Mutex.h"
+
+#include "base/basictypes.h"
+
+#include "nsMultiplexInputStream.h"
+#include "nsIBufferedStreams.h"
+#include "nsICloneableInputStream.h"
+#include "nsIMultiplexInputStream.h"
+#include "nsISeekableStream.h"
+#include "nsCOMPtr.h"
+#include "nsCOMArray.h"
+#include "nsIClassInfoImpl.h"
+#include "nsIIPCSerializableInputStream.h"
+#include "mozilla/ipc/InputStreamUtils.h"
+#include "nsIAsyncInputStream.h"
+#include "nsIInputStreamLength.h"
+#include "nsNetUtil.h"
+#include "nsStreamUtils.h"
+
+using namespace mozilla;
+using namespace mozilla::ipc;
+
+using mozilla::DeprecatedAbs;
+
+class nsMultiplexInputStream final : public nsIMultiplexInputStream,
+                                     public nsISeekableStream,
+                                     public nsIIPCSerializableInputStream,
+                                     public nsICloneableInputStream,
+                                     public nsIAsyncInputStream,
+                                     public nsIInputStreamCallback,
+                                     public nsIInputStreamLength,
+                                     public nsIAsyncInputStreamLength {
+ public:
+  nsMultiplexInputStream();
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINPUTSTREAM
+  NS_DECL_NSIMULTIPLEXINPUTSTREAM
+  NS_DECL_NSISEEKABLESTREAM
+  NS_DECL_NSITELLABLESTREAM
+  NS_DECL_NSIIPCSERIALIZABLEINPUTSTREAM
+  NS_DECL_NSICLONEABLEINPUTSTREAM
+  NS_DECL_NSIASYNCINPUTSTREAM
+  NS_DECL_NSIINPUTSTREAMCALLBACK
+  NS_DECL_NSIINPUTSTREAMLENGTH
+  NS_DECL_NSIASYNCINPUTSTREAMLENGTH
+
+  // This is used for nsIAsyncInputStream::AsyncWait
+  void AsyncWaitCompleted();
+
+  // This is used for nsIAsyncInputStreamLength::AsyncLengthWait
+  void AsyncWaitCompleted(int64_t aLength, const MutexAutoLock& aProofOfLock)
+      MOZ_REQUIRES(mLock);
+
+  struct StreamData {
+    nsresult Initialize(nsIInputStream* aOriginalStream) {
+      mCurrentPos = 0;
+
+      mOriginalStream = aOriginalStream;
+
+      mBufferedStream = aOriginalStream;
+      if (!NS_InputStreamIsBuffered(mBufferedStream)) {
+        nsCOMPtr<nsIInputStream> bufferedStream;
+        nsresult rv = NS_NewBufferedInputStream(getter_AddRefs(bufferedStream),
+                                                mBufferedStream.forget(), 4096);
+        NS_ENSURE_SUCCESS(rv, rv);
+        mBufferedStream = bufferedStream;
+      }
+
+      mAsyncStream = do_QueryInterface(mBufferedStream);
+      mSeekableStream = do_QueryInterface(mBufferedStream);
+
+      return NS_OK;
+    }
+
+    nsCOMPtr<nsIInputStream> mOriginalStream;
+
+    // Equal to mOriginalStream or a wrap around the original stream to make it
+    // buffered.
+    nsCOMPtr<nsIInputStream> mBufferedStream;
+
+    // This can be null.
+    nsCOMPtr<nsIAsyncInputStream> mAsyncStream;
+    // This can be null.
+    nsCOMPtr<nsISeekableStream> mSeekableStream;
+
+    uint64_t mCurrentPos;
+  };
+
+  Mutex& GetLock() MOZ_RETURN_CAPABILITY(mLock) { return mLock; }
+
+ private:
+  ~nsMultiplexInputStream() = default;
+
+  void NextStream() MOZ_REQUIRES(mLock) {
+    ++mCurrentStream;
+    mStartedReadingCurrent = false;
+  }
+
+  nsresult AsyncWaitInternal();
+
+  // This method updates mSeekableStreams, mTellableStreams,
+  // mIPCSerializableStreams and mCloneableStreams values.
+  void UpdateQIMap(StreamData& aStream) MOZ_REQUIRES(mLock);
+
+  struct MOZ_STACK_CLASS ReadSegmentsState {
+    nsCOMPtr<nsIInputStream> mThisStream;
+    uint32_t mOffset;
+    nsWriteSegmentFun mWriter;
+    void* mClosure;
+    bool mDone;
+  };
+
+  void SerializedComplexityInternal(uint32_t aMaxSize, uint32_t* aSizeUsed,
+                                    uint32_t* aPipes, uint32_t* aTransferables,
+                                    bool* aSerializeAsPipe);
+
+  static nsresult ReadSegCb(nsIInputStream* aIn, void* aClosure,
+                            const char* aFromRawSegment, uint32_t aToOffset,
+                            uint32_t aCount, uint32_t* aWriteCount);
+
+  bool IsSeekable() const;
+  bool IsIPCSerializable() const;
+  bool IsCloneable() const;
+  bool IsAsyncInputStream() const;
+  bool IsInputStreamLength() const;
+  bool IsAsyncInputStreamLength() const;
+
+  Mutex mLock;  // Protects access to all data members.
+
+  nsTArray<StreamData> mStreams MOZ_GUARDED_BY(mLock);
+
+  uint32_t mCurrentStream MOZ_GUARDED_BY(mLock);
+  bool mStartedReadingCurrent MOZ_GUARDED_BY(mLock);
+  nsresult mStatus MOZ_GUARDED_BY(mLock);
+  nsCOMPtr<nsIInputStreamCallback> mAsyncWaitCallback MOZ_GUARDED_BY(mLock);
+  uint32_t mAsyncWaitFlags MOZ_GUARDED_BY(mLock);
+  uint32_t mAsyncWaitRequestedCount MOZ_GUARDED_BY(mLock);
+  nsCOMPtr<nsIEventTarget> mAsyncWaitEventTarget MOZ_GUARDED_BY(mLock);
+  nsCOMPtr<nsIInputStreamLengthCallback> mAsyncWaitLengthCallback
+      MOZ_GUARDED_BY(mLock);
+
+  class AsyncWaitLengthHelper;
+  RefPtr<AsyncWaitLengthHelper> mAsyncWaitLengthHelper MOZ_GUARDED_BY(mLock);
+
+  uint32_t mSeekableStreams MOZ_GUARDED_BY(mLock);
+  uint32_t mIPCSerializableStreams MOZ_GUARDED_BY(mLock);
+  uint32_t mCloneableStreams MOZ_GUARDED_BY(mLock);
+
+  // These are Atomics so that we can check them in QueryInterface without
+  // taking a lock (to look at mStreams.Length() and the numbers above)
+  // With no streams added yet, all of these are possible
+  Atomic<bool, Relaxed> mIsSeekableStream{true};
+  Atomic<bool, Relaxed> mIsIPCSerializableStream{true};
+  Atomic<bool, Relaxed> mIsCloneableStream{true};
+
+  Atomic<bool, Relaxed> mIsAsyncInputStream{false};
+  Atomic<bool, Relaxed> mIsInputStreamLength{false};
+  Atomic<bool, Relaxed> mIsAsyncInputStreamLength{false};
+};
+
+NS_IMPL_ADDREF(nsMultiplexInputStream)
+NS_IMPL_RELEASE(nsMultiplexInputStream)
+
+NS_IMPL_CLASSINFO(nsMultiplexInputStream, nullptr, nsIClassInfo::THREADSAFE,
+                  NS_MULTIPLEXINPUTSTREAM_CID)
+
+NS_INTERFACE_MAP_BEGIN(nsMultiplexInputStream)
+  NS_INTERFACE_MAP_ENTRY(nsIMultiplexInputStream)
+  NS_INTERFACE_MAP_ENTRY(nsIInputStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsISeekableStream, IsSeekable())
+  NS_INTERFACE_MAP_ENTRY(nsITellableStream)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIIPCSerializableInputStream,
+                                     IsIPCSerializable())
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsICloneableInputStream, IsCloneable())
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIAsyncInputStream, IsAsyncInputStream())
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIInputStreamCallback,
+                                     IsAsyncInputStream())
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIInputStreamLength,
+                                     IsInputStreamLength())
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIAsyncInputStreamLength,
+                                     IsAsyncInputStreamLength())
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIMultiplexInputStream)
+  NS_IMPL_QUERY_CLASSINFO(nsMultiplexInputStream)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CI_INTERFACE_GETTER(nsMultiplexInputStream, nsIMultiplexInputStream,
+                            nsIInputStream, nsISeekableStream,
+                            nsITellableStream)
+
+static nsresult AvailableMaybeSeek(nsMultiplexInputStream::StreamData& aStream,
+                                   uint64_t* aResult) {
+  nsresult rv = aStream.mBufferedStream->Available(aResult);
+  if (rv == NS_BASE_STREAM_CLOSED) {
+    // Blindly seek to the current position if Available() returns
+    // NS_BASE_STREAM_CLOSED.
+    // If nsIFileInputStream is closed in Read() due to CLOSE_ON_EOF flag,
+    // Seek() could reopen the file if REOPEN_ON_REWIND flag is set.
+    if (aStream.mSeekableStream) {
+      nsresult rvSeek =
+          aStream.mSeekableStream->Seek(nsISeekableStream::NS_SEEK_CUR, 0);
+      if (NS_SUCCEEDED(rvSeek)) {
+        rv = aStream.mBufferedStream->Available(aResult);
+      }
+    }
+  }
+  return rv;
+}
+
+nsMultiplexInputStream::nsMultiplexInputStream()
+    : mLock("nsMultiplexInputStream lock"),
+      mCurrentStream(0),
+      mStartedReadingCurrent(false),
+      mStatus(NS_OK),
+      mAsyncWaitFlags(0),
+      mAsyncWaitRequestedCount(0),
+      mSeekableStreams(0),
+      mIPCSerializableStreams(0),
+      mCloneableStreams(0) {}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::GetCount(uint32_t* aCount) {
+  MutexAutoLock lock(mLock);
+  *aCount = mStreams.Length();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::AppendStream(nsIInputStream* aStream) {
+  MutexAutoLock lock(mLock);
+
+  StreamData* streamData = mStreams.AppendElement(fallible);
+  if (NS_WARN_IF(!streamData)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  nsresult rv = streamData->Initialize(aStream);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  UpdateQIMap(*streamData);
+
+  if (mStatus == NS_BASE_STREAM_CLOSED) {
+    // We were closed, but now we have more data to read.
+    mStatus = NS_OK;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::GetStream(uint32_t aIndex, nsIInputStream** aResult) {
+  MutexAutoLock lock(mLock);
+
+  if (aIndex >= mStreams.Length()) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  StreamData& streamData = mStreams.ElementAt(aIndex);
+  nsCOMPtr<nsIInputStream> stream = streamData.mOriginalStream;
+  stream.forget(aResult);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::Close() {
+  nsTArray<nsCOMPtr<nsIInputStream>> streams;
+
+  // Let's take a copy of the streams becuase, calling close() it could trigger
+  // a nsIInputStreamCallback immediately and we don't want to create a deadlock
+  // with mutex.
+  {
+    MutexAutoLock lock(mLock);
+    uint32_t len = mStreams.Length();
+    for (uint32_t i = 0; i < len; ++i) {
+      if (NS_WARN_IF(
+              !streams.AppendElement(mStreams[i].mBufferedStream, fallible))) {
+        mStatus = NS_BASE_STREAM_CLOSED;
+        return NS_ERROR_OUT_OF_MEMORY;
+      }
+    }
+    mStatus = NS_BASE_STREAM_CLOSED;
+  }
+
+  nsresult rv = NS_OK;
+
+  uint32_t len = streams.Length();
+  for (uint32_t i = 0; i < len; ++i) {
+    nsresult rv2 = streams[i]->Close();
+    // We still want to close all streams, but we should return an error
+    if (NS_FAILED(rv2)) {
+      rv = rv2;
+    }
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::Available(uint64_t* aResult) {
+  *aResult = 0;
+
+  MutexAutoLock lock(mLock);
+  if (NS_FAILED(mStatus)) {
+    return mStatus;
+  }
+
+  uint64_t avail = 0;
+  nsresult rv = NS_BASE_STREAM_CLOSED;
+
+  uint32_t len = mStreams.Length();
+  for (uint32_t i = mCurrentStream; i < len; i++) {
+    uint64_t streamAvail;
+    rv = AvailableMaybeSeek(mStreams[i], &streamAvail);
+    if (rv == NS_BASE_STREAM_CLOSED) {
+      // If a stream is closed, we continue with the next one.
+      // If this is the current stream we move to the following stream.
+      if (mCurrentStream == i) {
+        NextStream();
+      }
+
+      // If this is the last stream, we want to return this error code.
+      continue;
+    }
+
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      mStatus = rv;
+      return mStatus;
+    }
+
+    // If the current stream is async, we have to return what we have so far
+    // without processing the following streams. This is needed because
+    // ::Available should return only what is currently available. In case of an
+    // nsIAsyncInputStream, we have to call AsyncWait() in order to read more.
+    if (mStreams[i].mAsyncStream) {
+      avail += streamAvail;
+      break;
+    }
+
+    if (streamAvail == 0) {
+      // Nothing to read for this stream. Let's move to the next one.
+      continue;
+    }
+
+    avail += streamAvail;
+  }
+
+  // We still have something to read. We don't want to return an error code yet.
+  if (avail) {
+    *aResult = avail;
+    return NS_OK;
+  }
+
+  // Let's propagate the last error message.
+  mStatus = rv;
+  return rv;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::StreamStatus() {
+  MutexAutoLock lock(mLock);
+  return mStatus;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::Read(char* aBuf, uint32_t aCount, uint32_t* aResult) {
+  MutexAutoLock lock(mLock);
+  // It is tempting to implement this method in terms of ReadSegments, but
+  // that would prevent this class from being used with streams that only
+  // implement Read (e.g., file streams).
+
+  *aResult = 0;
+
+  if (mStatus == NS_BASE_STREAM_CLOSED) {
+    return NS_OK;
+  }
+  if (NS_FAILED(mStatus)) {
+    return mStatus;
+  }
+
+  nsresult rv = NS_OK;
+
+  uint32_t len = mStreams.Length();
+  while (mCurrentStream < len && aCount) {
+    uint32_t read;
+    rv = mStreams[mCurrentStream].mBufferedStream->Read(aBuf, aCount, &read);
+
+    // XXX some streams return NS_BASE_STREAM_CLOSED to indicate EOF.
+    // (This is a bug in those stream implementations)
+    if (rv == NS_BASE_STREAM_CLOSED) {
+      MOZ_ASSERT_UNREACHABLE(
+          "Input stream's Read method returned "
+          "NS_BASE_STREAM_CLOSED");
+      rv = NS_OK;
+      read = 0;
+    } else if (NS_FAILED(rv)) {
+      break;
+    }
+
+    if (read == 0) {
+      NextStream();
+    } else {
+      NS_ASSERTION(aCount >= read, "Read more than requested");
+      *aResult += read;
+      aCount -= read;
+      aBuf += read;
+      mStartedReadingCurrent = true;
+
+      mStreams[mCurrentStream].mCurrentPos += read;
+    }
+  }
+  return *aResult ? NS_OK : rv;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::ReadSegments(nsWriteSegmentFun aWriter, void* aClosure,
+                                     uint32_t aCount, uint32_t* aResult) {
+  MutexAutoLock lock(mLock);
+
+  if (mStatus == NS_BASE_STREAM_CLOSED) {
+    *aResult = 0;
+    return NS_OK;
+  }
+  if (NS_FAILED(mStatus)) {
+    return mStatus;
+  }
+
+  NS_ASSERTION(aWriter, "missing aWriter");
+
+  nsresult rv = NS_OK;
+  ReadSegmentsState state;
+  state.mThisStream = this;
+  state.mOffset = 0;
+  state.mWriter = aWriter;
+  state.mClosure = aClosure;
+  state.mDone = false;
+
+  uint32_t len = mStreams.Length();
+  while (mCurrentStream < len && aCount) {
+    uint32_t read;
+    rv = mStreams[mCurrentStream].mBufferedStream->ReadSegments(
+        ReadSegCb, &state, aCount, &read);
+
+    // XXX some streams return NS_BASE_STREAM_CLOSED to indicate EOF.
+    // (This is a bug in those stream implementations)
+    if (rv == NS_BASE_STREAM_CLOSED) {
+      MOZ_ASSERT_UNREACHABLE(
+          "Input stream's Read method returned "
+          "NS_BASE_STREAM_CLOSED");
+      rv = NS_OK;
+      read = 0;
+    }
+
+    // if |aWriter| decided to stop reading segments...
+    if (state.mDone || NS_FAILED(rv)) {
+      break;
+    }
+
+    // if stream is empty, then advance to the next stream.
+    if (read == 0) {
+      NextStream();
+    } else {
+      NS_ASSERTION(aCount >= read, "Read more than requested");
+      state.mOffset += read;
+      aCount -= read;
+      mStartedReadingCurrent = true;
+
+      mStreams[mCurrentStream].mCurrentPos += read;
+    }
+  }
+
+  // if we successfully read some data, then this call succeeded.
+  *aResult = state.mOffset;
+  return state.mOffset ? NS_OK : rv;
+}
+
+nsresult nsMultiplexInputStream::ReadSegCb(nsIInputStream* aIn, void* aClosure,
+                                           const char* aFromRawSegment,
+                                           uint32_t aToOffset, uint32_t aCount,
+                                           uint32_t* aWriteCount) {
+  nsresult rv;
+  ReadSegmentsState* state = (ReadSegmentsState*)aClosure;
+  rv = (state->mWriter)(state->mThisStream, state->mClosure, aFromRawSegment,
+                        aToOffset + state->mOffset, aCount, aWriteCount);
+  if (NS_FAILED(rv)) {
+    state->mDone = true;
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::IsNonBlocking(bool* aNonBlocking) {
+  MutexAutoLock lock(mLock);
+
+  uint32_t len = mStreams.Length();
+  if (len == 0) {
+    // Claim to be non-blocking, since we won't block the caller.
+    *aNonBlocking = true;
+    return NS_OK;
+  }
+
+  for (uint32_t i = 0; i < len; ++i) {
+    nsresult rv = mStreams[i].mBufferedStream->IsNonBlocking(aNonBlocking);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+    // If one is blocking the entire stream becomes blocking.
+    if (!*aNonBlocking) {
+      return NS_OK;
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::Seek(int32_t aWhence, int64_t aOffset) {
+  MutexAutoLock lock(mLock);
+
+  if (NS_FAILED(mStatus)) {
+    return mStatus;
+  }
+
+  nsresult rv;
+
+  uint32_t oldCurrentStream = mCurrentStream;
+  bool oldStartedReadingCurrent = mStartedReadingCurrent;
+
+  if (aWhence == NS_SEEK_SET) {
+    int64_t remaining = aOffset;
+    if (aOffset == 0) {
+      mCurrentStream = 0;
+    }
+    for (uint32_t i = 0; i < mStreams.Length(); ++i) {
+      nsCOMPtr<nsISeekableStream> stream = mStreams[i].mSeekableStream;
+      if (!stream) {
+        return NS_ERROR_FAILURE;
+      }
+
+      // See if all remaining streams should be rewound
+      if (remaining == 0) {
+        if (i < oldCurrentStream ||
+            (i == oldCurrentStream && oldStartedReadingCurrent)) {
+          rv = stream->Seek(NS_SEEK_SET, 0);
+          if (NS_WARN_IF(NS_FAILED(rv))) {
+            return rv;
+          }
+
+          mStreams[i].mCurrentPos = 0;
+          continue;
+        } else {
+          break;
+        }
+      }
+
+      // Get position in the current stream
+      int64_t streamPos;
+      if (i > oldCurrentStream ||
+          (i == oldCurrentStream && !oldStartedReadingCurrent)) {
+        streamPos = 0;
+      } else {
+        streamPos = mStreams[i].mCurrentPos;
+      }
+
+      // See if we need to seek the current stream forward or backward
+      if (remaining < streamPos) {
+        rv = stream->Seek(NS_SEEK_SET, remaining);
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return rv;
+        }
+
+        mStreams[i].mCurrentPos = remaining;
+        mCurrentStream = i;
+        mStartedReadingCurrent = remaining != 0;
+
+        remaining = 0;
+      } else if (remaining > streamPos) {
+        if (i < oldCurrentStream) {
+          // We're already at end so no need to seek this stream
+          remaining -= streamPos;
+          NS_ASSERTION(remaining >= 0, "Remaining invalid");
+        } else {
+          uint64_t avail;
+          rv = AvailableMaybeSeek(mStreams[i], &avail);
+          if (NS_WARN_IF(NS_FAILED(rv))) {
+            return rv;
+          }
+
+          int64_t newPos = XPCOM_MIN(remaining, streamPos + (int64_t)avail);
+
+          rv = stream->Seek(NS_SEEK_SET, newPos);
+          if (NS_WARN_IF(NS_FAILED(rv))) {
+            return rv;
+          }
+
+          mStreams[i].mCurrentPos = newPos;
+          mCurrentStream = i;
+          mStartedReadingCurrent = true;
+
+          remaining -= newPos;
+          NS_ASSERTION(remaining >= 0, "Remaining invalid");
+        }
+      } else {
+        NS_ASSERTION(remaining == streamPos, "Huh?");
+        MOZ_ASSERT(remaining != 0, "Zero remaining should be handled earlier");
+        remaining = 0;
+        mCurrentStream = i;
+        mStartedReadingCurrent = true;
+      }
+    }
+
+    return NS_OK;
+  }
+
+  if (aWhence == NS_SEEK_CUR && aOffset > 0) {
+    int64_t remaining = aOffset;
+    for (uint32_t i = mCurrentStream; remaining && i < mStreams.Length(); ++i) {
+      uint64_t avail;
+      rv = AvailableMaybeSeek(mStreams[i], &avail);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      int64_t seek = XPCOM_MIN((int64_t)avail, remaining);
+
+      rv = mStreams[i].mSeekableStream->Seek(NS_SEEK_CUR, seek);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      mStreams[i].mCurrentPos += seek;
+      mCurrentStream = i;
+      mStartedReadingCurrent = true;
+
+      remaining -= seek;
+    }
+
+    return NS_OK;
+  }
+
+  if (aWhence == NS_SEEK_CUR && aOffset < 0) {
+    int64_t remaining = -aOffset;
+    for (uint32_t i = mCurrentStream; remaining && i != (uint32_t)-1; --i) {
+      int64_t pos = mStreams[i].mCurrentPos;
+
+      int64_t seek = XPCOM_MIN(pos, remaining);
+
+      rv = mStreams[i].mSeekableStream->Seek(NS_SEEK_CUR, -seek);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      mStreams[i].mCurrentPos -= seek;
+      mCurrentStream = i;
+      mStartedReadingCurrent = seek != -pos;
+
+      remaining -= seek;
+    }
+
+    return NS_OK;
+  }
+
+  if (aWhence == NS_SEEK_CUR) {
+    NS_ASSERTION(aOffset == 0, "Should have handled all non-zero values");
+
+    return NS_OK;
+  }
+
+  if (aWhence == NS_SEEK_END) {
+    if (aOffset > 0) {
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    int64_t remaining = aOffset;
+    int32_t i;
+    for (i = mStreams.Length() - 1; i >= 0; --i) {
+      nsCOMPtr<nsISeekableStream> stream = mStreams[i].mSeekableStream;
+
+      uint64_t avail;
+      rv = AvailableMaybeSeek(mStreams[i], &avail);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      int64_t streamLength = avail + mStreams[i].mCurrentPos;
+
+      // The seek(END) can be completed in the current stream.
+      if (streamLength >= DeprecatedAbs(remaining)) {
+        rv = stream->Seek(NS_SEEK_END, remaining);
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return rv;
+        }
+
+        mStreams[i].mCurrentPos = streamLength + remaining;
+        mCurrentStream = i;
+        mStartedReadingCurrent = true;
+        break;
+      }
+
+      // We are at the beginning of this stream.
+      rv = stream->Seek(NS_SEEK_SET, 0);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      remaining += streamLength;
+      mStreams[i].mCurrentPos = 0;
+    }
+
+    // Any other stream must be set to the end.
+    for (--i; i >= 0; --i) {
+      nsCOMPtr<nsISeekableStream> stream = mStreams[i].mSeekableStream;
+
+      uint64_t avail;
+      rv = AvailableMaybeSeek(mStreams[i], &avail);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      int64_t streamLength = avail + mStreams[i].mCurrentPos;
+
+      rv = stream->Seek(NS_SEEK_END, 0);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      mStreams[i].mCurrentPos = streamLength;
+    }
+
+    return NS_OK;
+  }
+
+  // other Seeks not implemented yet
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::Tell(int64_t* aResult) {
+  MutexAutoLock lock(mLock);
+
+  if (NS_FAILED(mStatus)) {
+    return mStatus;
+  }
+
+  int64_t ret64 = 0;
+#ifdef DEBUG
+  bool zeroFound = false;
+#endif
+
+  for (uint32_t i = 0; i < mStreams.Length(); ++i) {
+    ret64 += mStreams[i].mCurrentPos;
+
+#ifdef DEBUG
+    // When we see 1 stream with currentPos = 0, all the remaining streams must
+    // be set to 0 as well.
+    MOZ_ASSERT_IF(zeroFound, mStreams[i].mCurrentPos == 0);
+    if (mStreams[i].mCurrentPos == 0) {
+      zeroFound = true;
+    }
+#endif
+  }
+  *aResult = ret64;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::SetEOF() { return NS_ERROR_NOT_IMPLEMENTED; }
+
+NS_IMETHODIMP
+nsMultiplexInputStream::CloseWithStatus(nsresult aStatus) { return Close(); }
+
+// This class is used to inform nsMultiplexInputStream that it's time to execute
+// the asyncWait callback.
+class AsyncWaitRunnable final : public DiscardableRunnable {
+  RefPtr<nsMultiplexInputStream> mStream;
+
+ public:
+  static void Create(nsMultiplexInputStream* aStream,
+                     nsIEventTarget* aEventTarget) {
+    RefPtr<AsyncWaitRunnable> runnable = new AsyncWaitRunnable(aStream);
+    if (aEventTarget) {
+      aEventTarget->Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
+    } else {
+      runnable->Run();
+    }
+  }
+
+  NS_IMETHOD
+  Run() override {
+    mStream->AsyncWaitCompleted();
+    return NS_OK;
+  }
+
+ private:
+  explicit AsyncWaitRunnable(nsMultiplexInputStream* aStream)
+      : DiscardableRunnable("AsyncWaitRunnable"), mStream(aStream) {
+    MOZ_ASSERT(aStream);
+  }
+};
+
+NS_IMETHODIMP
+nsMultiplexInputStream::AsyncWait(nsIInputStreamCallback* aCallback,
+                                  uint32_t aFlags, uint32_t aRequestedCount,
+                                  nsIEventTarget* aEventTarget) {
+  {
+    MutexAutoLock lock(mLock);
+
+    // We must execute the callback also when the stream is closed.
+    if (NS_FAILED(mStatus) && mStatus != NS_BASE_STREAM_CLOSED) {
+      return mStatus;
+    }
+
+    if (NS_WARN_IF(mAsyncWaitCallback && aCallback &&
+                   mAsyncWaitCallback != aCallback)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    mAsyncWaitCallback = aCallback;
+    mAsyncWaitFlags = aFlags;
+    mAsyncWaitRequestedCount = aRequestedCount;
+    mAsyncWaitEventTarget = aEventTarget;
+  }
+
+  return AsyncWaitInternal();
+}
+
+nsresult nsMultiplexInputStream::AsyncWaitInternal() {
+  nsCOMPtr<nsIAsyncInputStream> stream;
+  nsIInputStreamCallback* asyncWaitCallback = nullptr;
+  uint32_t asyncWaitFlags = 0;
+  uint32_t asyncWaitRequestedCount = 0;
+  nsCOMPtr<nsIEventTarget> asyncWaitEventTarget;
+
+  {
+    MutexAutoLock lock(mLock);
+
+    // Let's take the first async stream if we are not already closed, and if
+    // it has data to read or if it async.
+    if (mStatus != NS_BASE_STREAM_CLOSED) {
+      for (; mCurrentStream < mStreams.Length(); NextStream()) {
+        stream = mStreams[mCurrentStream].mAsyncStream;
+        if (stream) {
+          break;
+        }
+
+        uint64_t avail = 0;
+        nsresult rv = AvailableMaybeSeek(mStreams[mCurrentStream], &avail);
+        if (rv == NS_BASE_STREAM_CLOSED || (NS_SUCCEEDED(rv) && avail == 0)) {
+          // Nothing to read here. Let's move on.
+          continue;
+        }
+
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+
+        break;
+      }
+    }
+
+    asyncWaitCallback = mAsyncWaitCallback ? this : nullptr;
+    asyncWaitFlags = mAsyncWaitFlags;
+    asyncWaitRequestedCount = mAsyncWaitRequestedCount;
+    asyncWaitEventTarget = mAsyncWaitEventTarget;
+
+    MOZ_ASSERT_IF(stream, NS_SUCCEEDED(mStatus));
+  }
+
+  // If we are here it's because we are already closed, or if the current stream
+  // is not async. In both case we have to execute the callback.
+  if (!stream) {
+    if (asyncWaitCallback) {
+      AsyncWaitRunnable::Create(this, asyncWaitEventTarget);
+    }
+    return NS_OK;
+  }
+
+  return stream->AsyncWait(asyncWaitCallback, asyncWaitFlags,
+                           asyncWaitRequestedCount, asyncWaitEventTarget);
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::OnInputStreamReady(nsIAsyncInputStream* aStream) {
+  nsCOMPtr<nsIInputStreamCallback> callback;
+
+  // When OnInputStreamReady is called, we could be in 2 scenarios:
+  // a. there is something to read;
+  // b. the stream is closed.
+  // But if the stream is closed and it was not the last one, we must proceed
+  // with the following stream in order to have something to read by the callee.
+
+  {
+    MutexAutoLock lock(mLock);
+
+    // The callback has been nullified in the meantime.
+    if (!mAsyncWaitCallback) {
+      return NS_OK;
+    }
+
+    if (NS_SUCCEEDED(mStatus)) {
+      uint64_t avail = 0;
+      nsresult rv = NS_OK;
+      // Only check `Available()` if `aStream` is actually the current stream,
+      // otherwise we'll always want to re-poll, as we got the callback for the
+      // wrong stream.
+      if (mCurrentStream < mStreams.Length() &&
+          aStream == mStreams[mCurrentStream].mAsyncStream) {
+        rv = aStream->Available(&avail);
+      }
+      if (rv == NS_BASE_STREAM_CLOSED || (NS_SUCCEEDED(rv) && avail == 0)) {
+        // This stream is either closed, has no data available, or is not the
+        // current stream. If it is closed and current, move to the next stream,
+        // otherwise re-wait on the current stream until it has data available
+        // or becomes closed.
+        // Unlike streams not implementing nsIAsyncInputStream, async streams
+        // cannot use `Available() == 0` to indicate EOF, so we re-poll in that
+        // situation.
+        if (NS_FAILED(rv)) {
+          NextStream();
+        }
+
+        // Unlock and invoke AsyncWaitInternal to wait again.  If this succeeds,
+        // we'll be called again, otherwise fall through and notify.
+        MutexAutoUnlock unlock(mLock);
+        if (NS_SUCCEEDED(AsyncWaitInternal())) {
+          return NS_OK;
+        }
+      }
+    }
+
+    mAsyncWaitCallback.swap(callback);
+    mAsyncWaitEventTarget = nullptr;
+  }
+
+  return callback ? callback->OnInputStreamReady(this) : NS_OK;
+}
+
+void nsMultiplexInputStream::AsyncWaitCompleted() {
+  nsCOMPtr<nsIInputStreamCallback> callback;
+
+  {
+    MutexAutoLock lock(mLock);
+
+    // The callback has been nullified in the meantime.
+    if (!mAsyncWaitCallback) {
+      return;
+    }
+
+    mAsyncWaitCallback.swap(callback);
+    mAsyncWaitEventTarget = nullptr;
+  }
+
+  callback->OnInputStreamReady(this);
+}
+
+nsresult nsMultiplexInputStreamConstructor(REFNSIID aIID, void** aResult) {
+  *aResult = nullptr;
+
+  RefPtr<nsMultiplexInputStream> inst = new nsMultiplexInputStream();
+
+  return inst->QueryInterface(aIID, aResult);
+}
+
+void nsMultiplexInputStream::SerializedComplexity(uint32_t aMaxSize,
+                                                  uint32_t* aSizeUsed,
+                                                  uint32_t* aPipes,
+                                                  uint32_t* aTransferables) {
+  MutexAutoLock lock(mLock);
+  bool serializeAsPipe = false;
+  SerializedComplexityInternal(aMaxSize, aSizeUsed, aPipes, aTransferables,
+                               &serializeAsPipe);
+}
+
+void nsMultiplexInputStream::SerializedComplexityInternal(
+    uint32_t aMaxSize, uint32_t* aSizeUsed, uint32_t* aPipes,
+    uint32_t* aTransferables, bool* aSerializeAsPipe) {
+  mLock.AssertCurrentThreadOwns();
+  CheckedUint32 totalSizeUsed = 0;
+  CheckedUint32 totalPipes = 0;
+  CheckedUint32 totalTransferables = 0;
+  CheckedUint32 maxSize = aMaxSize;
+
+  uint32_t streamCount = mStreams.Length();
+
+  for (uint32_t index = 0; index < streamCount; index++) {
+    uint32_t sizeUsed = 0;
+    uint32_t pipes = 0;
+    uint32_t transferables = 0;
+    InputStreamHelper::SerializedComplexity(mStreams[index].mOriginalStream,
+                                            maxSize.value(), &sizeUsed, &pipes,
+                                            &transferables);
+
+    MOZ_ASSERT(maxSize.value() >= sizeUsed);
+
+    maxSize -= sizeUsed;
+    MOZ_DIAGNOSTIC_ASSERT(maxSize.isValid());
+    totalSizeUsed += sizeUsed;
+    MOZ_DIAGNOSTIC_ASSERT(totalSizeUsed.isValid());
+    totalPipes += pipes;
+    MOZ_DIAGNOSTIC_ASSERT(totalPipes.isValid());
+    totalTransferables += transferables;
+    MOZ_DIAGNOSTIC_ASSERT(totalTransferables.isValid());
+  }
+
+  // If the combination of all streams when serialized independently is
+  // sufficiently complex, we may choose to serialize it as a pipe to limit the
+  // complexity of the payload.
+  if (totalTransferables.value() == 0) {
+    // If there are no transferables within our serialization, and it would
+    // contain at least one pipe, serialize the entire payload as a pipe for
+    // simplicity.
+    *aSerializeAsPipe = totalSizeUsed.value() > 0 && totalPipes.value() > 0;
+  } else {
+    // Otherwise, we may want to still serialize in segments to take advantage
+    // of the efficiency of serializing transferables. We'll only serialize as a
+    // pipe if the total attachment count exceeds kMaxAttachmentThreshold.
+    static constexpr uint32_t kMaxAttachmentThreshold = 8;
+    CheckedUint32 totalAttachments = totalPipes + totalTransferables;
+    *aSerializeAsPipe = !totalAttachments.isValid() ||
+                        totalAttachments.value() > kMaxAttachmentThreshold;
+  }
+
+  if (*aSerializeAsPipe) {
+    NS_WARNING(
+        nsPrintfCString("Choosing to serialize multiplex stream as a pipe "
+                        "(would be %u bytes, %u pipes, %u transferables)",
+                        totalSizeUsed.value(), totalPipes.value(),
+                        totalTransferables.value())
+            .get());
+    *aSizeUsed = 0;
+    *aPipes = 1;
+    *aTransferables = 0;
+  } else {
+    *aSizeUsed = totalSizeUsed.value();
+    *aPipes = totalPipes.value();
+    *aTransferables = totalTransferables.value();
+  }
+}
+
+void nsMultiplexInputStream::Serialize(InputStreamParams& aParams,
+                                       uint32_t aMaxSize, uint32_t* aSizeUsed) {
+  MutexAutoLock lock(mLock);
+
+  // Check if we should serialize this stream as a pipe to reduce complexity.
+  uint32_t dummySizeUsed = 0, dummyPipes = 0, dummyTransferables = 0;
+  bool serializeAsPipe = false;
+  SerializedComplexityInternal(aMaxSize, &dummySizeUsed, &dummyPipes,
+                               &dummyTransferables, &serializeAsPipe);
+  if (serializeAsPipe) {
+    *aSizeUsed = 0;
+    MutexAutoUnlock unlock(mLock);
+    InputStreamHelper::SerializeInputStreamAsPipe(this, aParams);
+    return;
+  }
+
+  MultiplexInputStreamParams params;
+
+  CheckedUint32 totalSizeUsed = 0;
+  CheckedUint32 maxSize = aMaxSize;
+
+  uint32_t streamCount = mStreams.Length();
+  if (streamCount) {
+    nsTArray<InputStreamParams>& streams = params.streams();
+
+    streams.SetCapacity(streamCount);
+    for (uint32_t index = 0; index < streamCount; index++) {
+      uint32_t sizeUsed = 0;
+      InputStreamHelper::SerializeInputStream(mStreams[index].mOriginalStream,
+                                              *streams.AppendElement(),
+                                              maxSize.value(), &sizeUsed);
+
+      MOZ_ASSERT(maxSize.value() >= sizeUsed);
+
+      maxSize -= sizeUsed;
+      MOZ_DIAGNOSTIC_ASSERT(maxSize.isValid());
+
+      totalSizeUsed += sizeUsed;
+      MOZ_DIAGNOSTIC_ASSERT(totalSizeUsed.isValid());
+    }
+  }
+
+  params.currentStream() = mCurrentStream;
+  params.status() = mStatus;
+  params.startedReadingCurrent() = mStartedReadingCurrent;
+
+  aParams = std::move(params);
+
+  MOZ_ASSERT(aSizeUsed);
+  *aSizeUsed = totalSizeUsed.value();
+}
+
+bool nsMultiplexInputStream::Deserialize(const InputStreamParams& aParams) {
+  if (aParams.type() != InputStreamParams::TMultiplexInputStreamParams) {
+    NS_ERROR("Received unknown parameters from the other process!");
+    return false;
+  }
+
+  const MultiplexInputStreamParams& params =
+      aParams.get_MultiplexInputStreamParams();
+
+  const nsTArray<InputStreamParams>& streams = params.streams();
+
+  uint32_t streamCount = streams.Length();
+  for (uint32_t index = 0; index < streamCount; index++) {
+    nsCOMPtr<nsIInputStream> stream =
+        InputStreamHelper::DeserializeInputStream(streams[index]);
+    if (!stream) {
+      NS_WARNING("Deserialize failed!");
+      return false;
+    }
+
+    if (NS_FAILED(AppendStream(stream))) {
+      NS_WARNING("AppendStream failed!");
+      return false;
+    }
+  }
+
+  MutexAutoLock lock(mLock);
+  mCurrentStream = params.currentStream();
+  mStatus = params.status();
+  mStartedReadingCurrent = params.startedReadingCurrent();
+
+  return true;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::GetCloneable(bool* aCloneable) {
+  MutexAutoLock lock(mLock);
+  // XXXnsm Cloning a multiplex stream which has started reading is not
+  // permitted right now.
+  if (mCurrentStream > 0 || mStartedReadingCurrent) {
+    *aCloneable = false;
+    return NS_OK;
+  }
+
+  uint32_t len = mStreams.Length();
+  for (uint32_t i = 0; i < len; ++i) {
+    nsCOMPtr<nsICloneableInputStream> cis =
+        do_QueryInterface(mStreams[i].mBufferedStream);
+    if (!cis || !cis->GetCloneable()) {
+      *aCloneable = false;
+      return NS_OK;
+    }
+  }
+
+  *aCloneable = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::Clone(nsIInputStream** aClone) {
+  MutexAutoLock lock(mLock);
+
+  // XXXnsm Cloning a multiplex stream which has started reading is not
+  // permitted right now.
+  if (mCurrentStream > 0 || mStartedReadingCurrent) {
+    return NS_ERROR_FAILURE;
+  }
+
+  RefPtr<nsMultiplexInputStream> clone = new nsMultiplexInputStream();
+
+  nsresult rv;
+  uint32_t len = mStreams.Length();
+  for (uint32_t i = 0; i < len; ++i) {
+    nsCOMPtr<nsICloneableInputStream> substream =
+        do_QueryInterface(mStreams[i].mBufferedStream);
+    if (NS_WARN_IF(!substream)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    nsCOMPtr<nsIInputStream> clonedSubstream;
+    rv = substream->Clone(getter_AddRefs(clonedSubstream));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    rv = clone->AppendStream(clonedSubstream);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  clone.forget(aClone);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMultiplexInputStream::Length(int64_t* aLength) {
+  MutexAutoLock lock(mLock);
+
+  if (mCurrentStream > 0 || mStartedReadingCurrent) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  CheckedInt64 length = 0;
+  nsresult retval = NS_OK;
+
+  for (uint32_t i = 0, len = mStreams.Length(); i < len; ++i) {
+    nsCOMPtr<nsIInputStreamLength> substream =
+        do_QueryInterface(mStreams[i].mBufferedStream);
+    if (!substream) {
+      // Let's use available as fallback.
+      uint64_t streamAvail = 0;
+      nsresult rv = AvailableMaybeSeek(mStreams[i], &streamAvail);
+      if (rv == NS_BASE_STREAM_CLOSED) {
+        continue;
+      }
+
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        mStatus = rv;
+        return mStatus;
+      }
+
+      length += streamAvail;
+      if (!length.isValid()) {
+        return NS_ERROR_OUT_OF_MEMORY;
+      }
+
+      continue;
+    }
+
+    int64_t size = 0;
+    nsresult rv = substream->Length(&size);
+    if (rv == NS_BASE_STREAM_CLOSED) {
+      continue;
+    }
+
+    if (rv == NS_ERROR_NOT_AVAILABLE) {
+      return rv;
+    }
+
+    // If one stream blocks, we all block.
+    if (rv != NS_BASE_STREAM_WOULD_BLOCK && NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    // We want to return WOULD_BLOCK if there is 1 stream that blocks. But want
+    // to see if there are other streams with length = -1.
+    if (rv == NS_BASE_STREAM_WOULD_BLOCK) {
+      retval = NS_BASE_STREAM_WOULD_BLOCK;
+      continue;
+    }
+
+    // If one of the stream doesn't know the size, we all don't know the size.
+    if (size == -1) {
+      *aLength = -1;
+      return NS_OK;
+    }
+
+    length += size;
+    if (!length.isValid()) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+  }
+
+  *aLength = length.value();
+  return retval;
+}
+
+class nsMultiplexInputStream::AsyncWaitLengthHelper final
+    : public nsIInputStreamLengthCallback {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  AsyncWaitLengthHelper()
+      : mStreamNotified(false), mLength(0), mNegativeSize(false) {}
+
+  bool AddStream(nsIAsyncInputStreamLength* aStream) {
+    return mPendingStreams.AppendElement(aStream, fallible);
+  }
+
+  bool AddSize(int64_t aSize) {
+    MOZ_ASSERT(!mNegativeSize);
+
+    mLength += aSize;
+    return mLength.isValid();
+  }
+
+  void NegativeSize() {
+    MOZ_ASSERT(!mNegativeSize);
+    mNegativeSize = true;
+  }
+
+  nsresult Proceed(nsMultiplexInputStream* aParentStream,
+                   nsIEventTarget* aEventTarget,
+                   const MutexAutoLock& aProofOfLock) {
+    MOZ_ASSERT(!mStream);
+
+    // If we don't need to wait, let's inform the callback immediately.
+    if (mPendingStreams.IsEmpty() || mNegativeSize) {
+      RefPtr<nsMultiplexInputStream> parentStream = aParentStream;
+      int64_t length = -1;
+      if (!mNegativeSize && mLength.isValid()) {
+        length = mLength.value();
+      }
+      nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+          "AsyncWaitLengthHelper", [parentStream, length]() {
+            MutexAutoLock lock(parentStream->GetLock());
+            parentStream->AsyncWaitCompleted(length, lock);
+          });
+      return aEventTarget->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+    }
+
+    // Let's store the callback and the parent stream until we have
+    // notifications from the async length streams.
+
+    mStream = aParentStream;
+
+    // Let's activate all the pending streams.
+    for (nsIAsyncInputStreamLength* stream : mPendingStreams) {
+      nsresult rv = stream->AsyncLengthWait(this, aEventTarget);
+      if (rv == NS_BASE_STREAM_CLOSED) {
+        continue;
+      }
+
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+    }
+
+    return NS_OK;
+  }
+
+  NS_IMETHOD
+  OnInputStreamLengthReady(nsIAsyncInputStreamLength* aStream,
+                           int64_t aLength) override {
+    MutexAutoLock lock(mStream->GetLock());
+
+    MOZ_ASSERT(mPendingStreams.Contains(aStream));
+    mPendingStreams.RemoveElement(aStream);
+
+    // Already notified.
+    if (mStreamNotified) {
+      return NS_OK;
+    }
+
+    if (aLength == -1) {
+      mNegativeSize = true;
+    } else {
+      mLength += aLength;
+      if (!mLength.isValid()) {
+        mNegativeSize = true;
+      }
+    }
+
+    // We need to wait.
+    if (!mNegativeSize && !mPendingStreams.IsEmpty()) {
+      return NS_OK;
+    }
+
+    // Let's notify the parent stream.
+    mStreamNotified = true;
+    mStream->AsyncWaitCompleted(mNegativeSize ? -1 : mLength.value(), lock);
+    return NS_OK;
+  }
+
+ private:
+  ~AsyncWaitLengthHelper() = default;
+
+  RefPtr<nsMultiplexInputStream> mStream;
+  bool mStreamNotified;
+
+  CheckedInt64 mLength;
+  bool mNegativeSize;
+
+  nsTArray<nsCOMPtr<nsIAsyncInputStreamLength>> mPendingStreams;
+};
+
+NS_IMPL_ISUPPORTS(nsMultiplexInputStream::AsyncWaitLengthHelper,
+                  nsIInputStreamLengthCallback)
+
+NS_IMETHODIMP
+nsMultiplexInputStream::AsyncLengthWait(nsIInputStreamLengthCallback* aCallback,
+                                        nsIEventTarget* aEventTarget) {
+  if (NS_WARN_IF(!aEventTarget)) {
+    return NS_ERROR_NULL_POINTER;
+  }
+
+  MutexAutoLock lock(mLock);
+
+  if (mCurrentStream > 0 || mStartedReadingCurrent) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  if (!aCallback) {
+    mAsyncWaitLengthCallback = nullptr;
+    return NS_OK;
+  }
+
+  // We have a pending operation! Let's use this instead of creating a new one.
+  if (mAsyncWaitLengthHelper) {
+    mAsyncWaitLengthCallback = aCallback;
+    return NS_OK;
+  }
+
+  RefPtr<AsyncWaitLengthHelper> helper = new AsyncWaitLengthHelper();
+
+  for (uint32_t i = 0, len = mStreams.Length(); i < len; ++i) {
+    nsCOMPtr<nsIAsyncInputStreamLength> asyncStream =
+        do_QueryInterface(mStreams[i].mBufferedStream);
+    if (asyncStream) {
+      if (NS_WARN_IF(!helper->AddStream(asyncStream))) {
+        return NS_ERROR_OUT_OF_MEMORY;
+      }
+      continue;
+    }
+
+    nsCOMPtr<nsIInputStreamLength> stream =
+        do_QueryInterface(mStreams[i].mBufferedStream);
+    if (!stream) {
+      // Let's use available as fallback.
+      uint64_t streamAvail = 0;
+      nsresult rv = AvailableMaybeSeek(mStreams[i], &streamAvail);
+      if (rv == NS_BASE_STREAM_CLOSED) {
+        continue;
+      }
+
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        mStatus = rv;
+        return mStatus;
+      }
+
+      if (NS_WARN_IF(!helper->AddSize(streamAvail))) {
+        return NS_ERROR_OUT_OF_MEMORY;
+      }
+
+      continue;
+    }
+
+    int64_t size = 0;
+    nsresult rv = stream->Length(&size);
+    if (rv == NS_BASE_STREAM_CLOSED) {
+      continue;
+    }
+
+    MOZ_ASSERT(rv != NS_BASE_STREAM_WOULD_BLOCK,
+               "A nsILengthInutStream returns NS_BASE_STREAM_WOULD_BLOCK but "
+               "it doesn't implement nsIAsyncInputStreamLength.");
+
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    if (size == -1) {
+      helper->NegativeSize();
+      break;
+    }
+
+    if (NS_WARN_IF(!helper->AddSize(size))) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+  }
+
+  nsresult rv = helper->Proceed(this, aEventTarget, lock);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  mAsyncWaitLengthHelper = helper;
+  mAsyncWaitLengthCallback = aCallback;
+  return NS_OK;
+}
+
+void nsMultiplexInputStream::AsyncWaitCompleted(
+    int64_t aLength, const MutexAutoLock& aProofOfLock) {
+  mLock.AssertCurrentThreadOwns();
+
+  nsCOMPtr<nsIInputStreamLengthCallback> callback;
+  callback.swap(mAsyncWaitLengthCallback);
+
+  mAsyncWaitLengthHelper = nullptr;
+
+  // Already canceled.
+  if (!callback) {
+    return;
+  }
+
+  MutexAutoUnlock unlock(mLock);
+  callback->OnInputStreamLengthReady(this, aLength);
+}
+
+#define MAYBE_UPDATE_VALUE_REAL(x, y) \
+  if (y) {                            \
+    ++x;                              \
+  }
+
+#define MAYBE_UPDATE_VALUE(x, y)                                        \
+  {                                                                     \
+    nsCOMPtr<y> substream = do_QueryInterface(aStream.mBufferedStream); \
+    MAYBE_UPDATE_VALUE_REAL(x, substream)                               \
+  }
+
+#define MAYBE_UPDATE_BOOL(x, y)                                         \
+  if (!x) {                                                             \
+    nsCOMPtr<y> substream = do_QueryInterface(aStream.mBufferedStream); \
+    if (substream) {                                                    \
+      x = true;                                                         \
+    }                                                                   \
+  }
+
+void nsMultiplexInputStream::UpdateQIMap(StreamData& aStream) {
+  auto length = mStreams.Length();
+
+  MAYBE_UPDATE_VALUE_REAL(mSeekableStreams, aStream.mSeekableStream)
+  mIsSeekableStream = (mSeekableStreams == length);
+  MAYBE_UPDATE_VALUE(mIPCSerializableStreams, nsIIPCSerializableInputStream)
+  mIsIPCSerializableStream = (mIPCSerializableStreams == length);
+  MAYBE_UPDATE_VALUE(mCloneableStreams, nsICloneableInputStream)
+  mIsCloneableStream = (mCloneableStreams == length);
+  // nsMultiplexInputStream is nsIAsyncInputStream if at least 1 of the
+  // substream implements that interface
+  if (!mIsAsyncInputStream && aStream.mAsyncStream) {
+    mIsAsyncInputStream = true;
+  }
+  MAYBE_UPDATE_BOOL(mIsInputStreamLength, nsIInputStreamLength)
+  MAYBE_UPDATE_BOOL(mIsAsyncInputStreamLength, nsIAsyncInputStreamLength)
+}
+
+#undef MAYBE_UPDATE_VALUE
+#undef MAYBE_UPDATE_VALUE_REAL
+#undef MAYBE_UPDATE_BOOL
+
+bool nsMultiplexInputStream::IsSeekable() const { return mIsSeekableStream; }
+
+bool nsMultiplexInputStream::IsIPCSerializable() const {
+  return mIsIPCSerializableStream;
+}
+
+bool nsMultiplexInputStream::IsCloneable() const { return mIsCloneableStream; }
+
+bool nsMultiplexInputStream::IsAsyncInputStream() const {
+  // nsMultiplexInputStream is nsIAsyncInputStream if at least 1 of the
+  // substream implements that interface.
+  return mIsAsyncInputStream;
+}
+
+bool nsMultiplexInputStream::IsInputStreamLength() const {
+  return mIsInputStreamLength;
+}
+
+bool nsMultiplexInputStream::IsAsyncInputStreamLength() const {
+  return mIsAsyncInputStreamLength;
+}
diff --git a/xpcom/io/nsMultiplexInputStream.h b/xpcom/io/nsMultiplexInputStream.h
new file mode 100644
index 0000000000..9b84697c34
--- /dev/null
+++ b/xpcom/io/nsMultiplexInputStream.h
@@ -0,0 +1,27 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * The multiplex stream concatenates a list of input streams into a single
+ * stream.
+ */
+
+#ifndef _nsMultiplexInputStream_h_
+#define _nsMultiplexInputStream_h_
+
+#define NS_MULTIPLEXINPUTSTREAM_CONTRACTID \
+  "@mozilla.org/io/multiplex-input-stream;1"
+#define NS_MULTIPLEXINPUTSTREAM_CID                  \
+  { /* 565e3a2c-1dd2-11b2-8da1-b4cef17e568d */       \
+    0x565e3a2c, 0x1dd2, 0x11b2, {                    \
+      0x8d, 0xa1, 0xb4, 0xce, 0xf1, 0x7e, 0x56, 0x8d \
+    }                                                \
+  }
+
+extern nsresult nsMultiplexInputStreamConstructor(REFNSIID aIID,
+                                                  void** aResult);
+
+#endif  //  _nsMultiplexInputStream_h_
diff --git a/xpcom/io/nsNativeCharsetUtils.cpp b/xpcom/io/nsNativeCharsetUtils.cpp
new file mode 100644
index 0000000000..847ae3666c
--- /dev/null
+++ b/xpcom/io/nsNativeCharsetUtils.cpp
@@ -0,0 +1,98 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//-----------------------------------------------------------------------------
+// Non-Windows
+//-----------------------------------------------------------------------------
+#ifndef XP_WIN
+
+#  include "nsAString.h"
+#  include "nsReadableUtils.h"
+#  include "nsString.h"
+
+nsresult NS_CopyNativeToUnicode(const nsACString& aInput, nsAString& aOutput) {
+  CopyUTF8toUTF16(aInput, aOutput);
+  return NS_OK;
+}
+
+nsresult NS_CopyUnicodeToNative(const nsAString& aInput, nsACString& aOutput) {
+  CopyUTF16toUTF8(aInput, aOutput);
+  return NS_OK;
+}
+
+//-----------------------------------------------------------------------------
+// XP_WIN
+//-----------------------------------------------------------------------------
+#else
+
+#  include <windows.h>
+#  include "nsString.h"
+#  include "nsAString.h"
+#  include "nsReadableUtils.h"
+
+using namespace mozilla;
+
+nsresult NS_CopyNativeToUnicode(const nsACString& aInput, nsAString& aOutput) {
+  uint32_t inputLen = aInput.Length();
+
+  nsACString::const_iterator iter;
+  aInput.BeginReading(iter);
+
+  const char* buf = iter.get();
+
+  // determine length of result
+  uint32_t resultLen = 0;
+  int n = ::MultiByteToWideChar(CP_ACP, 0, buf, inputLen, nullptr, 0);
+  if (n > 0) {
+    resultLen += n;
+  }
+
+  // allocate sufficient space
+  if (!aOutput.SetLength(resultLen, fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  if (resultLen > 0) {
+    char16ptr_t result = aOutput.BeginWriting();
+    ::MultiByteToWideChar(CP_ACP, 0, buf, inputLen, result, resultLen);
+  }
+  return NS_OK;
+}
+
+nsresult NS_CopyUnicodeToNative(const nsAString& aInput, nsACString& aOutput) {
+  uint32_t inputLen = aInput.Length();
+
+  nsAString::const_iterator iter;
+  aInput.BeginReading(iter);
+
+  char16ptr_t buf = iter.get();
+
+  // determine length of result
+  uint32_t resultLen = 0;
+
+  int n = ::WideCharToMultiByte(CP_ACP, 0, buf, inputLen, nullptr, 0, nullptr,
+                                nullptr);
+  if (n > 0) {
+    resultLen += n;
+  }
+
+  // allocate sufficient space
+  if (!aOutput.SetLength(resultLen, fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  if (resultLen > 0) {
+    char* result = aOutput.BeginWriting();
+
+    // default "defaultChar" is '?', which is an illegal character on windows
+    // file system.  That will cause file uncreatable. Change it to '_'
+    const char defaultChar = '_';
+
+    ::WideCharToMultiByte(CP_ACP, 0, buf, inputLen, result, resultLen,
+                          &defaultChar, nullptr);
+  }
+  return NS_OK;
+}
+
+#endif
diff --git a/xpcom/io/nsNativeCharsetUtils.h b/xpcom/io/nsNativeCharsetUtils.h
new file mode 100644
index 0000000000..dcbf60238f
--- /dev/null
+++ b/xpcom/io/nsNativeCharsetUtils.h
@@ -0,0 +1,52 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsNativeCharsetUtils_h__
+#define nsNativeCharsetUtils_h__
+
+/*****************************************************************************\
+ *                                                                           *
+ *                             **** NOTICE ****                              *
+ *                                                                           *
+ *             *** THESE ARE NOT GENERAL PURPOSE CONVERTERS ***              *
+ *                                                                           *
+ *    NS_CopyNativeToUnicode / NS_CopyUnicodeToNative should only be used    *
+ *    for converting *FILENAMES* between bytes and UTF-16. They are not      *
+ *    designed or tested for general encoding converter use.                 *
+ *                                                                           *
+ *    On Windows, these functions convert to and from the system's legacy    *
+ *    code page, which cannot represent all of Unicode. Elsewhere, these     *
+ *    convert to and from UTF-8.                                             *
+ *                                                                           *
+\*****************************************************************************/
+
+#include "nsError.h"
+#include "nsStringFwd.h"
+
+/**
+ * thread-safe conversion routines that do not depend on uconv libraries.
+ */
+nsresult NS_CopyNativeToUnicode(const nsACString& aInput, nsAString& aOutput);
+nsresult NS_CopyUnicodeToNative(const nsAString& aInput, nsACString& aOutput);
+
+/*
+ * This function indicates whether the character encoding used in the file
+ * system (more exactly what's used for |GetNativeFoo| and |SetNativeFoo|
+ * of |nsIFile|) is UTF-8 or not. Knowing that helps us avoid an
+ * unncessary encoding conversion in some cases. For instance, to get the leaf
+ * name in UTF-8 out of nsIFile, we can just use |GetNativeLeafName| rather
+ * than using |GetLeafName| and converting the result to UTF-8 if the file
+ * system  encoding is UTF-8.
+ */
+inline constexpr bool NS_IsNativeUTF8() {
+#ifdef XP_WIN
+  return false;
+#else
+  return true;
+#endif
+}
+
+#endif  // nsNativeCharsetUtils_h__
diff --git a/xpcom/io/nsPipe.h b/xpcom/io/nsPipe.h
new file mode 100644
index 0000000000..c9e8b1dfd4
--- /dev/null
+++ b/xpcom/io/nsPipe.h
@@ -0,0 +1,21 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsPipe_h__
+#define nsPipe_h__
+
+#define NS_PIPE_CONTRACTID "@mozilla.org/pipe;1"
+#define NS_PIPE_CID                                  \
+  { /* e4a0ee4e-0775-457b-9118-b3ae97a7c758 */       \
+    0xe4a0ee4e, 0x0775, 0x457b, {                    \
+      0x91, 0x18, 0xb3, 0xae, 0x97, 0xa7, 0xc7, 0x58 \
+    }                                                \
+  }
+
+// Generic factory constructor for the nsPipe class
+nsresult nsPipeConstructor(REFNSIID iid, void** result);
+
+#endif  // !defined(nsPipe_h__)
diff --git a/xpcom/io/nsPipe3.cpp b/xpcom/io/nsPipe3.cpp
new file mode 100644
index 0000000000..3d7486e673
--- /dev/null
+++ b/xpcom/io/nsPipe3.cpp
@@ -0,0 +1,1884 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <algorithm>
+#include "mozilla/Attributes.h"
+#include "mozilla/IntegerPrintfMacros.h"
+#include "mozilla/ReentrantMonitor.h"
+#include "nsIBufferedStreams.h"
+#include "nsICloneableInputStream.h"
+#include "nsIPipe.h"
+#include "nsIEventTarget.h"
+#include "nsITellableStream.h"
+#include "mozilla/RefPtr.h"
+#include "nsSegmentedBuffer.h"
+#include "nsStreamUtils.h"
+#include "nsString.h"
+#include "nsCOMPtr.h"
+#include "nsCRT.h"
+#include "mozilla/Logging.h"
+#include "nsIClassInfoImpl.h"
+#include "nsAlgorithm.h"
+#include "nsPipe.h"
+#include "nsIAsyncInputStream.h"
+#include "nsIAsyncOutputStream.h"
+#include "nsIInputStreamPriority.h"
+#include "nsThreadUtils.h"
+
+using namespace mozilla;
+
+#ifdef LOG
+#  undef LOG
+#endif
+//
+// set MOZ_LOG=nsPipe:5
+//
+static LazyLogModule sPipeLog("nsPipe");
+#define LOG(args) MOZ_LOG(sPipeLog, mozilla::LogLevel::Debug, args)
+
+#define DEFAULT_SEGMENT_SIZE 4096
+#define DEFAULT_SEGMENT_COUNT 16
+
+class nsPipe;
+class nsPipeEvents;
+class nsPipeInputStream;
+class nsPipeOutputStream;
+class AutoReadSegment;
+
+namespace {
+
+enum MonitorAction { DoNotNotifyMonitor, NotifyMonitor };
+
+enum SegmentChangeResult { SegmentNotChanged, SegmentAdvanceBufferRead };
+
+}  // namespace
+
+//-----------------------------------------------------------------------------
+
+class CallbackHolder {
+ public:
+  CallbackHolder() = default;
+  MOZ_IMPLICIT CallbackHolder(std::nullptr_t) {}
+
+  CallbackHolder(nsIAsyncInputStream* aStream,
+                 nsIInputStreamCallback* aCallback, uint32_t aFlags,
+                 nsIEventTarget* aEventTarget)
+      : mRunnable(aCallback ? NS_NewCancelableRunnableFunction(
+                                  "nsPipeInputStream AsyncWait Callback",
+                                  [stream = nsCOMPtr{aStream},
+                                   callback = nsCOMPtr{aCallback}]() {
+                                    callback->OnInputStreamReady(stream);
+                                  })
+                            : nullptr),
+        mEventTarget(aEventTarget),
+        mFlags(aFlags) {}
+
+  CallbackHolder(nsIAsyncOutputStream* aStream,
+                 nsIOutputStreamCallback* aCallback, uint32_t aFlags,
+                 nsIEventTarget* aEventTarget)
+      : mRunnable(aCallback ? NS_NewCancelableRunnableFunction(
+                                  "nsPipeOutputStream AsyncWait Callback",
+                                  [stream = nsCOMPtr{aStream},
+                                   callback = nsCOMPtr{aCallback}]() {
+                                    callback->OnOutputStreamReady(stream);
+                                  })
+                            : nullptr),
+        mEventTarget(aEventTarget),
+        mFlags(aFlags) {}
+
+  CallbackHolder(const CallbackHolder&) = delete;
+  CallbackHolder(CallbackHolder&&) = default;
+  CallbackHolder& operator=(const CallbackHolder&) = delete;
+  CallbackHolder& operator=(CallbackHolder&&) = default;
+
+  CallbackHolder& operator=(std::nullptr_t) {
+    mRunnable = nullptr;
+    mEventTarget = nullptr;
+    mFlags = 0;
+    return *this;
+  }
+
+  MOZ_IMPLICIT operator bool() const { return mRunnable; }
+
+  uint32_t Flags() const {
+    MOZ_ASSERT(mRunnable, "Should only be called when a callback is present");
+    return mFlags;
+  }
+
+  void Notify() {
+    nsCOMPtr<nsIRunnable> runnable = mRunnable.forget();
+    nsCOMPtr<nsIEventTarget> eventTarget = mEventTarget.forget();
+    if (runnable) {
+      if (eventTarget) {
+        eventTarget->Dispatch(runnable.forget());
+      } else {
+        runnable->Run();
+      }
+    }
+  }
+
+ private:
+  nsCOMPtr<nsIRunnable> mRunnable;
+  nsCOMPtr<nsIEventTarget> mEventTarget;
+  uint32_t mFlags = 0;
+};
+
+//-----------------------------------------------------------------------------
+
+// this class is used to delay notifications until the end of a particular
+// scope.  it helps avoid the complexity of issuing callbacks while inside
+// a critical section.
+class nsPipeEvents {
+ public:
+  nsPipeEvents() = default;
+  ~nsPipeEvents();
+
+  inline void NotifyReady(CallbackHolder aCallback) {
+    mCallbacks.AppendElement(std::move(aCallback));
+  }
+
+ private:
+  nsTArray<CallbackHolder> mCallbacks;
+};
+
+//-----------------------------------------------------------------------------
+
+// This class is used to maintain input stream state.  Its broken out from the
+// nsPipeInputStream class because generally the nsPipe should be modifying
+// this state and not the input stream itself.
+struct nsPipeReadState {
+  nsPipeReadState()
+      : mReadCursor(nullptr),
+        mReadLimit(nullptr),
+        mSegment(0),
+        mAvailable(0),
+        mActiveRead(false),
+        mNeedDrain(false) {}
+
+  // All members of this type are guarded by the pipe monitor, however it cannot
+  // be named from this type, so the less-reliable MOZ_GUARDED_VAR is used
+  // instead. In the future it would be nice to avoid this, especially as
+  // MOZ_GUARDED_VAR is deprecated.
+  char* mReadCursor MOZ_GUARDED_VAR;
+  char* mReadLimit MOZ_GUARDED_VAR;
+  int32_t mSegment MOZ_GUARDED_VAR;
+  uint32_t mAvailable MOZ_GUARDED_VAR;
+
+  // This flag is managed using the AutoReadSegment RAII stack class.
+  bool mActiveRead MOZ_GUARDED_VAR;
+
+  // Set to indicate that the input stream has closed and should be drained,
+  // but that drain has been delayed due to an active read.  When the read
+  // completes, this flag indicate the drain should then be performed.
+  bool mNeedDrain MOZ_GUARDED_VAR;
+};
+
+//-----------------------------------------------------------------------------
+
+// an input end of a pipe (maintained as a list of refs within the pipe)
+class nsPipeInputStream final : public nsIAsyncInputStream,
+                                public nsITellableStream,
+                                public nsISearchableInputStream,
+                                public nsICloneableInputStream,
+                                public nsIClassInfo,
+                                public nsIBufferedInputStream,
+                                public nsIInputStreamPriority {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINPUTSTREAM
+  NS_DECL_NSIASYNCINPUTSTREAM
+  NS_DECL_NSITELLABLESTREAM
+  NS_DECL_NSISEARCHABLEINPUTSTREAM
+  NS_DECL_NSICLONEABLEINPUTSTREAM
+  NS_DECL_NSICLASSINFO
+  NS_DECL_NSIBUFFEREDINPUTSTREAM
+  NS_DECL_NSIINPUTSTREAMPRIORITY
+
+  explicit nsPipeInputStream(nsPipe* aPipe)
+      : mPipe(aPipe),
+        mLogicalOffset(0),
+        mInputStatus(NS_OK),
+        mBlocking(true),
+        mBlocked(false),
+        mPriority(nsIRunnablePriority::PRIORITY_NORMAL) {}
+
+  nsPipeInputStream(const nsPipeInputStream& aOther)
+      : mPipe(aOther.mPipe),
+        mLogicalOffset(aOther.mLogicalOffset),
+        mInputStatus(aOther.mInputStatus),
+        mBlocking(aOther.mBlocking),
+        mBlocked(false),
+        mReadState(aOther.mReadState),
+        mPriority(nsIRunnablePriority::PRIORITY_NORMAL) {}
+
+  void SetNonBlocking(bool aNonBlocking) { mBlocking = !aNonBlocking; }
+
+  uint32_t Available() MOZ_REQUIRES(Monitor());
+
+  // synchronously wait for the pipe to become readable.
+  nsresult Wait();
+
+  // These two don't acquire the monitor themselves.  Instead they
+  // expect their caller to have done so and to pass the monitor as
+  // evidence.
+  MonitorAction OnInputReadable(uint32_t aBytesWritten, nsPipeEvents&,
+                                const ReentrantMonitorAutoEnter& ev)
+      MOZ_REQUIRES(Monitor());
+  MonitorAction OnInputException(nsresult, nsPipeEvents&,
+                                 const ReentrantMonitorAutoEnter& ev)
+      MOZ_REQUIRES(Monitor());
+
+  nsPipeReadState& ReadState() { return mReadState; }
+
+  const nsPipeReadState& ReadState() const { return mReadState; }
+
+  nsresult Status() const;
+
+  // A version of Status() that doesn't acquire the monitor.
+  nsresult Status(const ReentrantMonitorAutoEnter& ev) const
+      MOZ_REQUIRES(Monitor());
+
+  // The status of this input stream, ignoring the status of the underlying
+  // monitor. If this status is errored, the input stream has either already
+  // been removed from the pipe, or will be removed from the pipe shortly.
+  nsresult InputStatus(const ReentrantMonitorAutoEnter&) const
+      MOZ_REQUIRES(Monitor()) {
+    return mInputStatus;
+  }
+
+  ReentrantMonitor& Monitor() const;
+
+ private:
+  virtual ~nsPipeInputStream();
+
+  RefPtr<nsPipe> mPipe;
+
+  int64_t mLogicalOffset;
+  // Individual input streams can be closed without effecting the rest of the
+  // pipe.  So track individual input stream status separately.  |mInputStatus|
+  // is protected by |mPipe->mReentrantMonitor|.
+  nsresult mInputStatus MOZ_GUARDED_BY(Monitor());
+  bool mBlocking;
+
+  // these variables can only be accessed while inside the pipe's monitor
+  bool mBlocked MOZ_GUARDED_BY(Monitor());
+  CallbackHolder mCallback MOZ_GUARDED_BY(Monitor());
+
+  // requires pipe's monitor to access members; usually treat as an opaque token
+  // to pass to nsPipe
+  nsPipeReadState mReadState;
+  Atomic<uint32_t, Relaxed> mPriority;
+};
+
+//-----------------------------------------------------------------------------
+
+// the output end of a pipe (allocated as a member of the pipe).
+class nsPipeOutputStream : public nsIAsyncOutputStream, public nsIClassInfo {
+ public:
+  // since this class will be allocated as a member of the pipe, we do not
+  // need our own ref count.  instead, we share the lifetime (the ref count)
+  // of the entire pipe.  this macro is just convenience since it does not
+  // declare a mRefCount variable; however, don't let the name fool you...
+  // we are not inheriting from nsPipe ;-)
+  NS_DECL_ISUPPORTS_INHERITED
+
+  NS_DECL_NSIOUTPUTSTREAM
+  NS_DECL_NSIASYNCOUTPUTSTREAM
+  NS_DECL_NSICLASSINFO
+
+  explicit nsPipeOutputStream(nsPipe* aPipe)
+      : mPipe(aPipe),
+        mWriterRefCnt(0),
+        mLogicalOffset(0),
+        mBlocking(true),
+        mBlocked(false),
+        mWritable(true) {}
+
+  void SetNonBlocking(bool aNonBlocking) { mBlocking = !aNonBlocking; }
+  void SetWritable(bool aWritable) MOZ_REQUIRES(Monitor()) {
+    mWritable = aWritable;
+  }
+
+  // synchronously wait for the pipe to become writable.
+  nsresult Wait();
+
+  MonitorAction OnOutputWritable(nsPipeEvents&) MOZ_REQUIRES(Monitor());
+  MonitorAction OnOutputException(nsresult, nsPipeEvents&)
+      MOZ_REQUIRES(Monitor());
+
+  ReentrantMonitor& Monitor() const;
+
+ private:
+  nsPipe* mPipe;
+
+  // separate refcnt so that we know when to close the producer
+  ThreadSafeAutoRefCnt mWriterRefCnt;
+  int64_t mLogicalOffset;
+  bool mBlocking;
+
+  // these variables can only be accessed while inside the pipe's monitor
+  bool mBlocked MOZ_GUARDED_BY(Monitor());
+  bool mWritable MOZ_GUARDED_BY(Monitor());
+  CallbackHolder mCallback MOZ_GUARDED_BY(Monitor());
+};
+
+//-----------------------------------------------------------------------------
+
+class nsPipe final {
+ public:
+  friend class nsPipeInputStream;
+  friend class nsPipeOutputStream;
+  friend class AutoReadSegment;
+
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(nsPipe)
+
+  // public constructor
+  friend void NS_NewPipe2(nsIAsyncInputStream**, nsIAsyncOutputStream**, bool,
+                          bool, uint32_t, uint32_t);
+
+ private:
+  nsPipe(uint32_t aSegmentSize, uint32_t aSegmentCount);
+  ~nsPipe();
+
+  //
+  // Methods below may only be called while inside the pipe's monitor.  Some
+  // of these methods require passing a ReentrantMonitorAutoEnter to prove the
+  // monitor is held.
+  //
+
+  void PeekSegment(const nsPipeReadState& aReadState, uint32_t aIndex,
+                   char*& aCursor, char*& aLimit)
+      MOZ_REQUIRES(mReentrantMonitor);
+  SegmentChangeResult AdvanceReadSegment(nsPipeReadState& aReadState,
+                                         const ReentrantMonitorAutoEnter& ev)
+      MOZ_REQUIRES(mReentrantMonitor);
+  bool ReadSegmentBeingWritten(nsPipeReadState& aReadState)
+      MOZ_REQUIRES(mReentrantMonitor);
+  uint32_t CountSegmentReferences(int32_t aSegment)
+      MOZ_REQUIRES(mReentrantMonitor);
+  void SetAllNullReadCursors() MOZ_REQUIRES(mReentrantMonitor);
+  bool AllReadCursorsMatchWriteCursor() MOZ_REQUIRES(mReentrantMonitor);
+  void RollBackAllReadCursors(char* aWriteCursor)
+      MOZ_REQUIRES(mReentrantMonitor);
+  void UpdateAllReadCursors(char* aWriteCursor) MOZ_REQUIRES(mReentrantMonitor);
+  void ValidateAllReadCursors() MOZ_REQUIRES(mReentrantMonitor);
+  uint32_t GetBufferSegmentCount(const nsPipeReadState& aReadState,
+                                 const ReentrantMonitorAutoEnter& ev) const
+      MOZ_REQUIRES(mReentrantMonitor);
+  bool IsAdvanceBufferFull(const ReentrantMonitorAutoEnter& ev) const
+      MOZ_REQUIRES(mReentrantMonitor);
+
+  //
+  // methods below may be called while outside the pipe's monitor
+  //
+
+  void DrainInputStream(nsPipeReadState& aReadState, nsPipeEvents& aEvents);
+  nsresult GetWriteSegment(char*& aSegment, uint32_t& aSegmentLen);
+  void AdvanceWriteCursor(uint32_t aCount);
+
+  void OnInputStreamException(nsPipeInputStream* aStream, nsresult aReason);
+  void OnPipeException(nsresult aReason, bool aOutputOnly = false);
+
+  nsresult CloneInputStream(nsPipeInputStream* aOriginal,
+                            nsIInputStream** aCloneOut);
+
+  // methods below should only be called by AutoReadSegment
+  nsresult GetReadSegment(nsPipeReadState& aReadState, const char*& aSegment,
+                          uint32_t& aLength);
+  void ReleaseReadSegment(nsPipeReadState& aReadState, nsPipeEvents& aEvents);
+  void AdvanceReadCursor(nsPipeReadState& aReadState, uint32_t aCount);
+
+  // We can't inherit from both nsIInputStream and nsIOutputStream
+  // because they collide on their Close method. Consequently we nest their
+  // implementations to avoid the extra object allocation.
+  nsPipeOutputStream mOutput;
+
+  // Since the input stream can be cloned, we may have more than one.  Use
+  // a weak reference as the streams will clear their entry here in their
+  // destructor.  Using a strong reference would create a reference cycle.
+  // Only usable while mReentrantMonitor is locked.
+  nsTArray<nsPipeInputStream*> mInputList MOZ_GUARDED_BY(mReentrantMonitor);
+
+  ReentrantMonitor mReentrantMonitor;
+  nsSegmentedBuffer mBuffer MOZ_GUARDED_BY(mReentrantMonitor);
+
+  // The maximum number of segments to allow to be buffered in advance
+  // of the fastest reader.  This is collection of segments is called
+  // the "advance buffer".
+  uint32_t mMaxAdvanceBufferSegmentCount MOZ_GUARDED_BY(mReentrantMonitor);
+
+  int32_t mWriteSegment MOZ_GUARDED_BY(mReentrantMonitor);
+  char* mWriteCursor MOZ_GUARDED_BY(mReentrantMonitor);
+  char* mWriteLimit MOZ_GUARDED_BY(mReentrantMonitor);
+
+  // |mStatus| is protected by |mReentrantMonitor|.
+  nsresult mStatus MOZ_GUARDED_BY(mReentrantMonitor);
+};
+
+//-----------------------------------------------------------------------------
+
+// Declarations of Monitor() methods on the streams.
+//
+// These must be placed early to provide MOZ_RETURN_CAPABILITY annotations for
+// the thread-safety analysis. This couldn't be done at the declaration due to
+// nsPipe not yet being defined.
+
+ReentrantMonitor& nsPipeOutputStream::Monitor() const
+    MOZ_RETURN_CAPABILITY(mPipe->mReentrantMonitor) {
+  return mPipe->mReentrantMonitor;
+}
+
+ReentrantMonitor& nsPipeInputStream::Monitor() const
+    MOZ_RETURN_CAPABILITY(mPipe->mReentrantMonitor) {
+  return mPipe->mReentrantMonitor;
+}
+
+//-----------------------------------------------------------------------------
+
+// RAII class representing an active read segment.  When it goes out of scope
+// it automatically updates the read cursor and releases the read segment.
+class MOZ_STACK_CLASS AutoReadSegment final {
+ public:
+  AutoReadSegment(nsPipe* aPipe, nsPipeReadState& aReadState,
+                  uint32_t aMaxLength)
+      : mPipe(aPipe),
+        mReadState(aReadState),
+        mStatus(NS_ERROR_FAILURE),
+        mSegment(nullptr),
+        mLength(0),
+        mOffset(0) {
+    MOZ_DIAGNOSTIC_ASSERT(mPipe);
+    MOZ_DIAGNOSTIC_ASSERT(!mReadState.mActiveRead);
+    mStatus = mPipe->GetReadSegment(mReadState, mSegment, mLength);
+    if (NS_SUCCEEDED(mStatus)) {
+      MOZ_DIAGNOSTIC_ASSERT(mReadState.mActiveRead);
+      MOZ_DIAGNOSTIC_ASSERT(mSegment);
+      mLength = std::min(mLength, aMaxLength);
+      MOZ_DIAGNOSTIC_ASSERT(mLength);
+    }
+  }
+
+  ~AutoReadSegment() {
+    if (NS_SUCCEEDED(mStatus)) {
+      if (mOffset) {
+        mPipe->AdvanceReadCursor(mReadState, mOffset);
+      } else {
+        nsPipeEvents events;
+        mPipe->ReleaseReadSegment(mReadState, events);
+      }
+    }
+    MOZ_DIAGNOSTIC_ASSERT(!mReadState.mActiveRead);
+  }
+
+  nsresult Status() const { return mStatus; }
+
+  const char* Data() const {
+    MOZ_DIAGNOSTIC_ASSERT(NS_SUCCEEDED(mStatus));
+    MOZ_DIAGNOSTIC_ASSERT(mSegment);
+    return mSegment + mOffset;
+  }
+
+  uint32_t Length() const {
+    MOZ_DIAGNOSTIC_ASSERT(NS_SUCCEEDED(mStatus));
+    MOZ_DIAGNOSTIC_ASSERT(mLength >= mOffset);
+    return mLength - mOffset;
+  }
+
+  void Advance(uint32_t aCount) {
+    MOZ_DIAGNOSTIC_ASSERT(NS_SUCCEEDED(mStatus));
+    MOZ_DIAGNOSTIC_ASSERT(aCount <= (mLength - mOffset));
+    mOffset += aCount;
+  }
+
+  nsPipeReadState& ReadState() const { return mReadState; }
+
+ private:
+  // guaranteed to remain alive due to limited stack lifetime of AutoReadSegment
+  nsPipe* mPipe;
+  nsPipeReadState& mReadState;
+  nsresult mStatus;
+  const char* mSegment;
+  uint32_t mLength;
+  uint32_t mOffset;
+};
+
+//
+// NOTES on buffer architecture:
+//
+//       +-----------------+ - - mBuffer.GetSegment(0)
+//       |                 |
+//       + - - - - - - - - + - - nsPipeReadState.mReadCursor
+//       |/////////////////|
+//       |/////////////////|
+//       |/////////////////|
+//       |/////////////////|
+//       +-----------------+ - - nsPipeReadState.mReadLimit
+//                |
+//       +-----------------+
+//       |/////////////////|
+//       |/////////////////|
+//       |/////////////////|
+//       |/////////////////|
+//       |/////////////////|
+//       |/////////////////|
+//       +-----------------+
+//                |
+//       +-----------------+ - - mBuffer.GetSegment(mWriteSegment)
+//       |/////////////////|
+//       |/////////////////|
+//       |/////////////////|
+//       + - - - - - - - - + - - mWriteCursor
+//       |                 |
+//       |                 |
+//       +-----------------+ - - mWriteLimit
+//
+// (shaded region contains data)
+//
+// NOTE: Each input stream produced by the nsPipe contains its own, separate
+//       nsPipeReadState.  This means there are multiple mReadCursor and
+//       mReadLimit values in play.  The pipe cannot discard old data until
+//       all mReadCursors have moved beyond that point in the stream.
+//
+//       Likewise, each input stream reader will have it's own amount of
+//       buffered data.  The pipe size threshold, however, is only applied
+//       to the input stream that is being read fastest.  We call this
+//       the "advance buffer" in that its in advance of all readers.  We
+//       allow slower input streams to buffer more data so that we don't
+//       stall processing of the faster input stream.
+//
+// NOTE: on some systems (notably OS/2), the heap allocator uses an arena for
+// small allocations (e.g., 64 byte allocations).  this means that buffers may
+// be allocated back-to-back.  in the diagram above, for example, mReadLimit
+// would actually be pointing at the beginning of the next segment.  when
+// making changes to this file, please keep this fact in mind.
+//
+
+//-----------------------------------------------------------------------------
+// nsPipe methods:
+//-----------------------------------------------------------------------------
+
+nsPipe::nsPipe(uint32_t aSegmentSize, uint32_t aSegmentCount)
+    : mOutput(this),
+      mReentrantMonitor("nsPipe.mReentrantMonitor"),
+      // protect against overflow
+      mMaxAdvanceBufferSegmentCount(
+          std::min(aSegmentCount, UINT32_MAX / aSegmentSize)),
+      mWriteSegment(-1),
+      mWriteCursor(nullptr),
+      mWriteLimit(nullptr),
+      mStatus(NS_OK) {
+  // The internal buffer is always "infinite" so that we can allow
+  // the size to expand when cloned streams are read at different
+  // rates.  We enforce a limit on how much data can be buffered
+  // ahead of the fastest reader in GetWriteSegment().
+  MOZ_ALWAYS_SUCCEEDS(mBuffer.Init(aSegmentSize));
+}
+
+nsPipe::~nsPipe() = default;
+
+void nsPipe::PeekSegment(const nsPipeReadState& aReadState, uint32_t aIndex,
+                         char*& aCursor, char*& aLimit) {
+  if (aIndex == 0) {
+    MOZ_DIAGNOSTIC_ASSERT(!aReadState.mReadCursor || mBuffer.GetSegmentCount());
+    aCursor = aReadState.mReadCursor;
+    aLimit = aReadState.mReadLimit;
+  } else {
+    uint32_t absoluteIndex = aReadState.mSegment + aIndex;
+    uint32_t numSegments = mBuffer.GetSegmentCount();
+    if (absoluteIndex >= numSegments) {
+      aCursor = aLimit = nullptr;
+    } else {
+      aCursor = mBuffer.GetSegment(absoluteIndex);
+      if (mWriteSegment == (int32_t)absoluteIndex) {
+        aLimit = mWriteCursor;
+      } else {
+        aLimit = aCursor + mBuffer.GetSegmentSize();
+      }
+    }
+  }
+}
+
+nsresult nsPipe::GetReadSegment(nsPipeReadState& aReadState,
+                                const char*& aSegment, uint32_t& aLength) {
+  ReentrantMonitorAutoEnter mon(mReentrantMonitor);
+
+  if (aReadState.mReadCursor == aReadState.mReadLimit) {
+    return NS_FAILED(mStatus) ? mStatus : NS_BASE_STREAM_WOULD_BLOCK;
+  }
+
+  // The input stream locks the pipe while getting the buffer to read from,
+  // but then unlocks while actual data copying is taking place.  In
+  // order to avoid deleting the buffer out from under this lockless read
+  // set a flag to indicate a read is active.  This flag is only modified
+  // while the lock is held.
+  MOZ_DIAGNOSTIC_ASSERT(!aReadState.mActiveRead);
+  aReadState.mActiveRead = true;
+
+  aSegment = aReadState.mReadCursor;
+  aLength = aReadState.mReadLimit - aReadState.mReadCursor;
+  MOZ_DIAGNOSTIC_ASSERT(aLength <= aReadState.mAvailable);
+
+  return NS_OK;
+}
+
+void nsPipe::ReleaseReadSegment(nsPipeReadState& aReadState,
+                                nsPipeEvents& aEvents) {
+  ReentrantMonitorAutoEnter mon(mReentrantMonitor);
+
+  MOZ_DIAGNOSTIC_ASSERT(aReadState.mActiveRead);
+  aReadState.mActiveRead = false;
+
+  // When a read completes and releases the mActiveRead flag, we may have
+  // blocked a drain from completing.  This occurs when the input stream is
+  // closed during the read.  In these cases, we need to complete the drain as
+  // soon as the active read completes.
+  if (aReadState.mNeedDrain) {
+    aReadState.mNeedDrain = false;
+    DrainInputStream(aReadState, aEvents);
+  }
+}
+
+void nsPipe::AdvanceReadCursor(nsPipeReadState& aReadState,
+                               uint32_t aBytesRead) {
+  MOZ_DIAGNOSTIC_ASSERT(aBytesRead > 0);
+
+  nsPipeEvents events;
+  {
+    ReentrantMonitorAutoEnter mon(mReentrantMonitor);
+
+    LOG(("III advancing read cursor by %u\n", aBytesRead));
+    MOZ_DIAGNOSTIC_ASSERT(aBytesRead <= mBuffer.GetSegmentSize());
+
+    aReadState.mReadCursor += aBytesRead;
+    MOZ_DIAGNOSTIC_ASSERT(aReadState.mReadCursor <= aReadState.mReadLimit);
+
+    MOZ_DIAGNOSTIC_ASSERT(aReadState.mAvailable >= aBytesRead);
+    aReadState.mAvailable -= aBytesRead;
+
+    // Check to see if we're at the end of the available read data.  If we
+    // are, and this segment is not still being written, then we can possibly
+    // free up the segment.
+    if (aReadState.mReadCursor == aReadState.mReadLimit &&
+        !ReadSegmentBeingWritten(aReadState)) {
+      // Advance the segment position.  If we have read any segments from the
+      // advance buffer then we can potentially notify blocked writers.
+      mOutput.Monitor().AssertCurrentThreadIn();
+      if (AdvanceReadSegment(aReadState, mon) == SegmentAdvanceBufferRead &&
+          mOutput.OnOutputWritable(events) == NotifyMonitor) {
+        mon.NotifyAll();
+      }
+    }
+
+    ReleaseReadSegment(aReadState, events);
+  }
+}
+
+SegmentChangeResult nsPipe::AdvanceReadSegment(
+    nsPipeReadState& aReadState, const ReentrantMonitorAutoEnter& ev) {
+  // Calculate how many segments are buffered for this stream to start.
+  uint32_t startBufferSegments = GetBufferSegmentCount(aReadState, ev);
+
+  int32_t currentSegment = aReadState.mSegment;
+
+  // Move to the next segment to read
+  aReadState.mSegment += 1;
+
+  // If this was the last reference to the first segment, then remove it.
+  if (currentSegment == 0 && CountSegmentReferences(currentSegment) == 0) {
+    // shift write and read segment index (-1 indicates an empty buffer).
+    mWriteSegment -= 1;
+
+    // Directly modify the current read state.  If the associated input
+    // stream is closed simultaneous with reading, then it may not be
+    // in the mInputList any more.
+    aReadState.mSegment -= 1;
+
+    for (uint32_t i = 0; i < mInputList.Length(); ++i) {
+      // Skip the current read state structure since we modify it manually
+      // before entering this loop.
+      if (&mInputList[i]->ReadState() == &aReadState) {
+        continue;
+      }
+      mInputList[i]->ReadState().mSegment -= 1;
+    }
+
+    // done with this segment
+    mBuffer.DeleteFirstSegment();
+    LOG(("III deleting first segment\n"));
+  }
+
+  if (mWriteSegment < aReadState.mSegment) {
+    // read cursor has hit the end of written data, so reset it
+    MOZ_DIAGNOSTIC_ASSERT(mWriteSegment == (aReadState.mSegment - 1));
+    aReadState.mReadCursor = nullptr;
+    aReadState.mReadLimit = nullptr;
+    // also, the buffer is completely empty, so reset the write cursor
+    if (mWriteSegment == -1) {
+      mWriteCursor = nullptr;
+      mWriteLimit = nullptr;
+    }
+  } else {
+    // advance read cursor and limit to next buffer segment
+    aReadState.mReadCursor = mBuffer.GetSegment(aReadState.mSegment);
+    if (mWriteSegment == aReadState.mSegment) {
+      aReadState.mReadLimit = mWriteCursor;
+    } else {
+      aReadState.mReadLimit = aReadState.mReadCursor + mBuffer.GetSegmentSize();
+    }
+  }
+
+  // Calculate how many segments are buffered for the stream after
+  // reading.
+  uint32_t endBufferSegments = GetBufferSegmentCount(aReadState, ev);
+
+  // If the stream has read a segment out of the set of advanced buffer
+  // segments, then the writer may advance.
+  if (startBufferSegments >= mMaxAdvanceBufferSegmentCount &&
+      endBufferSegments < mMaxAdvanceBufferSegmentCount) {
+    return SegmentAdvanceBufferRead;
+  }
+
+  // Otherwise there are no significant changes to the segment structure.
+  return SegmentNotChanged;
+}
+
+void nsPipe::DrainInputStream(nsPipeReadState& aReadState,
+                              nsPipeEvents& aEvents) {
+  ReentrantMonitorAutoEnter mon(mReentrantMonitor);
+
+  // If a segment is actively being read in ReadSegments() for this input
+  // stream, then we cannot drain the stream.  This can happen because
+  // ReadSegments() does not hold the lock while copying from the buffer.
+  // If we detect this condition, simply note that we need a drain once
+  // the read completes and return immediately.
+  if (aReadState.mActiveRead) {
+    MOZ_DIAGNOSTIC_ASSERT(!aReadState.mNeedDrain);
+    aReadState.mNeedDrain = true;
+    return;
+  }
+
+  while (mWriteSegment >= aReadState.mSegment) {
+    // If the last segment to free is still being written to, we're done
+    // draining.  We can't free any more.
+    if (ReadSegmentBeingWritten(aReadState)) {
+      break;
+    }
+
+    // Don't bother checking if this results in an advance buffer segment
+    // read.  Since we are draining the entire stream we will read an
+    // advance buffer segment no matter what.
+    AdvanceReadSegment(aReadState, mon);
+  }
+
+  // Force the stream into an empty state.  Make sure mAvailable, mCursor, and
+  // mReadLimit are consistent with one another.
+  aReadState.mAvailable = 0;
+  aReadState.mReadCursor = nullptr;
+  aReadState.mReadLimit = nullptr;
+
+  // Remove the input stream from the pipe's list of streams.  This will
+  // prevent the pipe from holding the stream alive or trying to update
+  // its read state any further.
+  DebugOnly<uint32_t> numRemoved = 0;
+  mInputList.RemoveElementsBy([&](nsPipeInputStream* aEntry) {
+    bool result = &aReadState == &aEntry->ReadState();
+    numRemoved += result ? 1 : 0;
+    return result;
+  });
+  MOZ_ASSERT(numRemoved == 1);
+
+  // If we have read any segments from the advance buffer then we can
+  // potentially notify blocked writers.
+  mOutput.Monitor().AssertCurrentThreadIn();
+  if (!IsAdvanceBufferFull(mon) &&
+      mOutput.OnOutputWritable(aEvents) == NotifyMonitor) {
+    mon.NotifyAll();
+  }
+}
+
+bool nsPipe::ReadSegmentBeingWritten(nsPipeReadState& aReadState) {
+  mReentrantMonitor.AssertCurrentThreadIn();
+  bool beingWritten =
+      mWriteSegment == aReadState.mSegment && mWriteLimit > mWriteCursor;
+  MOZ_DIAGNOSTIC_ASSERT(!beingWritten || aReadState.mReadLimit == mWriteCursor);
+  return beingWritten;
+}
+
+nsresult nsPipe::GetWriteSegment(char*& aSegment, uint32_t& aSegmentLen) {
+  ReentrantMonitorAutoEnter mon(mReentrantMonitor);
+
+  if (NS_FAILED(mStatus)) {
+    return mStatus;
+  }
+
+  // write cursor and limit may both be null indicating an empty buffer.
+  if (mWriteCursor == mWriteLimit) {
+    // The pipe is full if we have hit our limit on advance data buffering.
+    // This means the fastest reader is still reading slower than data is
+    // being written into the pipe.
+    if (IsAdvanceBufferFull(mon)) {
+      return NS_BASE_STREAM_WOULD_BLOCK;
+    }
+
+    // The nsSegmentedBuffer is configured to be "infinite", so this
+    // should never return nullptr here.
+    char* seg = mBuffer.AppendNewSegment();
+    if (!seg) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    LOG(("OOO appended new segment\n"));
+    mWriteCursor = seg;
+    mWriteLimit = mWriteCursor + mBuffer.GetSegmentSize();
+    ++mWriteSegment;
+  }
+
+  // make sure read cursor is initialized
+  SetAllNullReadCursors();
+
+  // check to see if we can roll-back our read and write cursors to the
+  // beginning of the current/first segment.  this is purely an optimization.
+  if (mWriteSegment == 0 && AllReadCursorsMatchWriteCursor()) {
+    char* head = mBuffer.GetSegment(0);
+    LOG(("OOO rolling back write cursor %" PRId64 " bytes\n",
+         static_cast<int64_t>(mWriteCursor - head)));
+    RollBackAllReadCursors(head);
+    mWriteCursor = head;
+  }
+
+  aSegment = mWriteCursor;
+  aSegmentLen = mWriteLimit - mWriteCursor;
+  return NS_OK;
+}
+
+void nsPipe::AdvanceWriteCursor(uint32_t aBytesWritten) {
+  MOZ_DIAGNOSTIC_ASSERT(aBytesWritten > 0);
+
+  nsPipeEvents events;
+  {
+    ReentrantMonitorAutoEnter mon(mReentrantMonitor);
+
+    LOG(("OOO advancing write cursor by %u\n", aBytesWritten));
+
+    char* newWriteCursor = mWriteCursor + aBytesWritten;
+    MOZ_DIAGNOSTIC_ASSERT(newWriteCursor <= mWriteLimit);
+
+    // update read limit if reading in the same segment
+    UpdateAllReadCursors(newWriteCursor);
+
+    mWriteCursor = newWriteCursor;
+
+    ValidateAllReadCursors();
+
+    // update the writable flag on the output stream
+    if (mWriteCursor == mWriteLimit) {
+      mOutput.Monitor().AssertCurrentThreadIn();
+      mOutput.SetWritable(!IsAdvanceBufferFull(mon));
+    }
+
+    // notify input stream that pipe now contains additional data
+    bool needNotify = false;
+    for (uint32_t i = 0; i < mInputList.Length(); ++i) {
+      mInputList[i]->Monitor().AssertCurrentThreadIn();
+      if (mInputList[i]->OnInputReadable(aBytesWritten, events, mon) ==
+          NotifyMonitor) {
+        needNotify = true;
+      }
+    }
+
+    if (needNotify) {
+      mon.NotifyAll();
+    }
+  }
+}
+
+void nsPipe::OnInputStreamException(nsPipeInputStream* aStream,
+                                    nsresult aReason) {
+  MOZ_DIAGNOSTIC_ASSERT(NS_FAILED(aReason));
+
+  nsPipeEvents events;
+  {
+    ReentrantMonitorAutoEnter mon(mReentrantMonitor);
+
+    // Its possible to re-enter this method when we call OnPipeException() or
+    // OnInputExection() below.  If there is a caller stuck in our synchronous
+    // Wait() method, then they will get woken up with a failure code which
+    // re-enters this method.  Therefore, gracefully handle unknown streams
+    // here.
+
+    // If we only have one stream open and it is the given stream, then shut
+    // down the entire pipe.
+    if (mInputList.Length() == 1) {
+      if (mInputList[0] == aStream) {
+        OnPipeException(aReason);
+      }
+      return;
+    }
+
+    // Otherwise just close the particular stream that hit an exception.
+    for (uint32_t i = 0; i < mInputList.Length(); ++i) {
+      if (mInputList[i] != aStream) {
+        continue;
+      }
+
+      mInputList[i]->Monitor().AssertCurrentThreadIn();
+      MonitorAction action =
+          mInputList[i]->OnInputException(aReason, events, mon);
+
+      // Notify after element is removed in case we re-enter as a result.
+      if (action == NotifyMonitor) {
+        mon.NotifyAll();
+      }
+
+      return;
+    }
+  }
+}
+
+void nsPipe::OnPipeException(nsresult aReason, bool aOutputOnly) {
+  LOG(("PPP nsPipe::OnPipeException [reason=%" PRIx32 " output-only=%d]\n",
+       static_cast<uint32_t>(aReason), aOutputOnly));
+
+  nsPipeEvents events;
+  {
+    ReentrantMonitorAutoEnter mon(mReentrantMonitor);
+
+    // if we've already hit an exception, then ignore this one.
+    if (NS_FAILED(mStatus)) {
+      return;
+    }
+
+    mStatus = aReason;
+
+    bool needNotify = false;
+
+    // OnInputException() can drain the stream and remove it from
+    // mInputList.  So iterate over a temp list instead.
+    nsTArray<nsPipeInputStream*> list = mInputList.Clone();
+    for (uint32_t i = 0; i < list.Length(); ++i) {
+      // an output-only exception applies to the input end if the pipe has
+      // zero bytes available.
+      list[i]->Monitor().AssertCurrentThreadIn();
+      if (aOutputOnly && list[i]->Available()) {
+        continue;
+      }
+
+      if (list[i]->OnInputException(aReason, events, mon) == NotifyMonitor) {
+        needNotify = true;
+      }
+    }
+
+    mOutput.Monitor().AssertCurrentThreadIn();
+    if (mOutput.OnOutputException(aReason, events) == NotifyMonitor) {
+      needNotify = true;
+    }
+
+    // Notify after we have removed any input streams from mInputList
+    if (needNotify) {
+      mon.NotifyAll();
+    }
+  }
+}
+
+nsresult nsPipe::CloneInputStream(nsPipeInputStream* aOriginal,
+                                  nsIInputStream** aCloneOut) {
+  ReentrantMonitorAutoEnter mon(mReentrantMonitor);
+  RefPtr<nsPipeInputStream> ref = new nsPipeInputStream(*aOriginal);
+  // don't add clones of closed pipes to mInputList.
+  ref->Monitor().AssertCurrentThreadIn();
+  if (NS_SUCCEEDED(ref->InputStatus(mon))) {
+    mInputList.AppendElement(ref);
+  }
+  nsCOMPtr<nsIAsyncInputStream> upcast = std::move(ref);
+  upcast.forget(aCloneOut);
+  return NS_OK;
+}
+
+uint32_t nsPipe::CountSegmentReferences(int32_t aSegment) {
+  mReentrantMonitor.AssertCurrentThreadIn();
+  uint32_t count = 0;
+  for (uint32_t i = 0; i < mInputList.Length(); ++i) {
+    if (aSegment >= mInputList[i]->ReadState().mSegment) {
+      count += 1;
+    }
+  }
+  return count;
+}
+
+void nsPipe::SetAllNullReadCursors() {
+  mReentrantMonitor.AssertCurrentThreadIn();
+  for (uint32_t i = 0; i < mInputList.Length(); ++i) {
+    nsPipeReadState& readState = mInputList[i]->ReadState();
+    if (!readState.mReadCursor) {
+      MOZ_DIAGNOSTIC_ASSERT(mWriteSegment == readState.mSegment);
+      readState.mReadCursor = readState.mReadLimit = mWriteCursor;
+    }
+  }
+}
+
+bool nsPipe::AllReadCursorsMatchWriteCursor() {
+  mReentrantMonitor.AssertCurrentThreadIn();
+  for (uint32_t i = 0; i < mInputList.Length(); ++i) {
+    const nsPipeReadState& readState = mInputList[i]->ReadState();
+    if (readState.mSegment != mWriteSegment ||
+        readState.mReadCursor != mWriteCursor) {
+      return false;
+    }
+  }
+  return true;
+}
+
+void nsPipe::RollBackAllReadCursors(char* aWriteCursor) {
+  mReentrantMonitor.AssertCurrentThreadIn();
+  for (uint32_t i = 0; i < mInputList.Length(); ++i) {
+    nsPipeReadState& readState = mInputList[i]->ReadState();
+    MOZ_DIAGNOSTIC_ASSERT(mWriteSegment == readState.mSegment);
+    MOZ_DIAGNOSTIC_ASSERT(mWriteCursor == readState.mReadCursor);
+    MOZ_DIAGNOSTIC_ASSERT(mWriteCursor == readState.mReadLimit);
+    readState.mReadCursor = aWriteCursor;
+    readState.mReadLimit = aWriteCursor;
+  }
+}
+
+void nsPipe::UpdateAllReadCursors(char* aWriteCursor) {
+  mReentrantMonitor.AssertCurrentThreadIn();
+  for (uint32_t i = 0; i < mInputList.Length(); ++i) {
+    nsPipeReadState& readState = mInputList[i]->ReadState();
+    if (mWriteSegment == readState.mSegment &&
+        readState.mReadLimit == mWriteCursor) {
+      readState.mReadLimit = aWriteCursor;
+    }
+  }
+}
+
+void nsPipe::ValidateAllReadCursors() {
+  mReentrantMonitor.AssertCurrentThreadIn();
+  // The only way mReadCursor == mWriteCursor is if:
+  //
+  // - mReadCursor is at the start of a segment (which, based on how
+  //   nsSegmentedBuffer works, means that this segment is the "first"
+  //   segment)
+  // - mWriteCursor points at the location past the end of the current
+  //   write segment (so the current write filled the current write
+  //   segment, so we've incremented mWriteCursor to point past the end
+  //   of it)
+  // - the segment to which data has just been written is located
+  //   exactly one segment's worth of bytes before the first segment
+  //   where mReadCursor is located
+  //
+  // Consequently, the byte immediately after the end of the current
+  // write segment is the first byte of the first segment, so
+  // mReadCursor == mWriteCursor.  (Another way to think about this is
+  // to consider the buffer architecture diagram above, but consider it
+  // with an arena allocator which allocates from the *end* of the
+  // arena to the *beginning* of the arena.)
+#ifdef DEBUG
+  for (uint32_t i = 0; i < mInputList.Length(); ++i) {
+    const nsPipeReadState& state = mInputList[i]->ReadState();
+    MOZ_ASSERT(state.mReadCursor != mWriteCursor ||
+               (mBuffer.GetSegment(state.mSegment) == state.mReadCursor &&
+                mWriteCursor == mWriteLimit));
+  }
+#endif
+}
+
+uint32_t nsPipe::GetBufferSegmentCount(
+    const nsPipeReadState& aReadState,
+    const ReentrantMonitorAutoEnter& ev) const {
+  // The write segment can be smaller than the current reader position
+  // in some cases.  For example, when the first write segment has not
+  // been allocated yet mWriteSegment is negative.  In these cases
+  // the stream is effectively using zero segments.
+  if (mWriteSegment < aReadState.mSegment) {
+    return 0;
+  }
+
+  MOZ_DIAGNOSTIC_ASSERT(mWriteSegment >= 0);
+  MOZ_DIAGNOSTIC_ASSERT(aReadState.mSegment >= 0);
+
+  // Otherwise at least one segment is being used.  We add one here
+  // since a single segment is being used when the write and read
+  // segment indices are the same.
+  return 1 + mWriteSegment - aReadState.mSegment;
+}
+
+bool nsPipe::IsAdvanceBufferFull(const ReentrantMonitorAutoEnter& ev) const {
+  // If we have fewer total segments than the limit we can immediately
+  // determine we are not full.  Note, we must add one to mWriteSegment
+  // to convert from a index to a count.
+  MOZ_DIAGNOSTIC_ASSERT(mWriteSegment >= -1);
+  MOZ_DIAGNOSTIC_ASSERT(mWriteSegment < INT32_MAX);
+  uint32_t totalWriteSegments = mWriteSegment + 1;
+  if (totalWriteSegments < mMaxAdvanceBufferSegmentCount) {
+    return false;
+  }
+
+  // Otherwise we must inspect all of our reader streams.  We need
+  // to determine the buffer depth of the fastest reader.
+  uint32_t minBufferSegments = UINT32_MAX;
+  for (uint32_t i = 0; i < mInputList.Length(); ++i) {
+    // Only count buffer segments from input streams that are open.
+    mInputList[i]->Monitor().AssertCurrentThreadIn();
+    if (NS_FAILED(mInputList[i]->Status(ev))) {
+      continue;
+    }
+    const nsPipeReadState& state = mInputList[i]->ReadState();
+    uint32_t bufferSegments = GetBufferSegmentCount(state, ev);
+    minBufferSegments = std::min(minBufferSegments, bufferSegments);
+    // We only care if any reader has fewer segments buffered than
+    // our threshold.  We can stop once we hit that threshold.
+    if (minBufferSegments < mMaxAdvanceBufferSegmentCount) {
+      return false;
+    }
+  }
+
+  // Note, its possible for minBufferSegments to exceed our
+  // mMaxAdvanceBufferSegmentCount here.  This happens when a cloned
+  // reader gets far behind, but then the fastest reader stream is
+  // closed.  This leaves us with a single stream that is buffered
+  // beyond our max.  Naturally we continue to indicate the pipe
+  // is full at this point.
+
+  return true;
+}
+
+//-----------------------------------------------------------------------------
+// nsPipeEvents methods:
+//-----------------------------------------------------------------------------
+
+nsPipeEvents::~nsPipeEvents() {
+  // dispatch any pending events
+  for (auto& callback : mCallbacks) {
+    callback.Notify();
+  }
+  mCallbacks.Clear();
+}
+
+//-----------------------------------------------------------------------------
+// nsPipeInputStream methods:
+//-----------------------------------------------------------------------------
+
+NS_IMPL_ADDREF(nsPipeInputStream);
+NS_IMPL_RELEASE(nsPipeInputStream);
+
+NS_INTERFACE_TABLE_HEAD(nsPipeInputStream)
+  NS_INTERFACE_TABLE_BEGIN
+    NS_INTERFACE_TABLE_ENTRY(nsPipeInputStream, nsIAsyncInputStream)
+    NS_INTERFACE_TABLE_ENTRY(nsPipeInputStream, nsITellableStream)
+    NS_INTERFACE_TABLE_ENTRY(nsPipeInputStream, nsISearchableInputStream)
+    NS_INTERFACE_TABLE_ENTRY(nsPipeInputStream, nsICloneableInputStream)
+    NS_INTERFACE_TABLE_ENTRY(nsPipeInputStream, nsIBufferedInputStream)
+    NS_INTERFACE_TABLE_ENTRY(nsPipeInputStream, nsIClassInfo)
+    NS_INTERFACE_TABLE_ENTRY(nsPipeInputStream, nsIInputStreamPriority)
+    NS_INTERFACE_TABLE_ENTRY_AMBIGUOUS(nsPipeInputStream, nsIInputStream,
+                                       nsIAsyncInputStream)
+    NS_INTERFACE_TABLE_ENTRY_AMBIGUOUS(nsPipeInputStream, nsISupports,
+                                       nsIAsyncInputStream)
+  NS_INTERFACE_TABLE_END
+NS_INTERFACE_TABLE_TAIL
+
+NS_IMPL_CI_INTERFACE_GETTER(nsPipeInputStream, nsIInputStream,
+                            nsIAsyncInputStream, nsITellableStream,
+                            nsISearchableInputStream, nsICloneableInputStream,
+                            nsIBufferedInputStream)
+
+NS_IMPL_THREADSAFE_CI(nsPipeInputStream)
+
+NS_IMETHODIMP
+nsPipeInputStream::Init(nsIInputStream*, uint32_t) {
+  MOZ_CRASH(
+      "nsPipeInputStream should never be initialized with "
+      "nsIBufferedInputStream::Init!\n");
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::GetData(nsIInputStream** aResult) {
+  // as this was not created with init() we are not
+  // wrapping anything
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+uint32_t nsPipeInputStream::Available() {
+  mPipe->mReentrantMonitor.AssertCurrentThreadIn();
+  return mReadState.mAvailable;
+}
+
+nsresult nsPipeInputStream::Wait() {
+  MOZ_DIAGNOSTIC_ASSERT(mBlocking);
+
+  ReentrantMonitorAutoEnter mon(mPipe->mReentrantMonitor);
+
+  while (NS_SUCCEEDED(Status(mon)) && (mReadState.mAvailable == 0)) {
+    LOG(("III pipe input: waiting for data\n"));
+
+    mBlocked = true;
+    mon.Wait();
+    mBlocked = false;
+
+    LOG(("III pipe input: woke up [status=%" PRIx32 " available=%u]\n",
+         static_cast<uint32_t>(Status(mon)), mReadState.mAvailable));
+  }
+
+  return Status(mon) == NS_BASE_STREAM_CLOSED ? NS_OK : Status(mon);
+}
+
+MonitorAction nsPipeInputStream::OnInputReadable(
+    uint32_t aBytesWritten, nsPipeEvents& aEvents,
+    const ReentrantMonitorAutoEnter& ev) {
+  MonitorAction result = DoNotNotifyMonitor;
+
+  mPipe->mReentrantMonitor.AssertCurrentThreadIn();
+  mReadState.mAvailable += aBytesWritten;
+
+  if (mCallback && !(mCallback.Flags() & WAIT_CLOSURE_ONLY)) {
+    aEvents.NotifyReady(std::move(mCallback));
+  } else if (mBlocked) {
+    result = NotifyMonitor;
+  }
+
+  return result;
+}
+
+MonitorAction nsPipeInputStream::OnInputException(
+    nsresult aReason, nsPipeEvents& aEvents,
+    const ReentrantMonitorAutoEnter& ev) {
+  LOG(("nsPipeInputStream::OnInputException [this=%p reason=%" PRIx32 "]\n",
+       this, static_cast<uint32_t>(aReason)));
+
+  MonitorAction result = DoNotNotifyMonitor;
+
+  MOZ_DIAGNOSTIC_ASSERT(NS_FAILED(aReason));
+
+  if (NS_SUCCEEDED(mInputStatus)) {
+    mInputStatus = aReason;
+  }
+
+  // force count of available bytes to zero.
+  mPipe->DrainInputStream(mReadState, aEvents);
+
+  if (mCallback) {
+    aEvents.NotifyReady(std::move(mCallback));
+  } else if (mBlocked) {
+    result = NotifyMonitor;
+  }
+
+  return result;
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::CloseWithStatus(nsresult aReason) {
+  LOG(("III CloseWithStatus [this=%p reason=%" PRIx32 "]\n", this,
+       static_cast<uint32_t>(aReason)));
+
+  ReentrantMonitorAutoEnter mon(mPipe->mReentrantMonitor);
+
+  if (NS_FAILED(mInputStatus)) {
+    return NS_OK;
+  }
+
+  if (NS_SUCCEEDED(aReason)) {
+    aReason = NS_BASE_STREAM_CLOSED;
+  }
+
+  mPipe->OnInputStreamException(this, aReason);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::SetPriority(uint32_t priority) {
+  mPriority = priority;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::GetPriority(uint32_t* priority) {
+  *priority = mPriority;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::Close() { return CloseWithStatus(NS_BASE_STREAM_CLOSED); }
+
+NS_IMETHODIMP
+nsPipeInputStream::Available(uint64_t* aResult) {
+  // nsPipeInputStream supports under 4GB stream only
+  ReentrantMonitorAutoEnter mon(mPipe->mReentrantMonitor);
+
+  // return error if closed
+  if (!mReadState.mAvailable && NS_FAILED(Status(mon))) {
+    return Status(mon);
+  }
+
+  *aResult = (uint64_t)mReadState.mAvailable;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::StreamStatus() {
+  ReentrantMonitorAutoEnter mon(mPipe->mReentrantMonitor);
+  return mReadState.mAvailable ? NS_OK : Status(mon);
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::ReadSegments(nsWriteSegmentFun aWriter, void* aClosure,
+                                uint32_t aCount, uint32_t* aReadCount) {
+  LOG(("III ReadSegments [this=%p count=%u]\n", this, aCount));
+
+  nsresult rv = NS_OK;
+
+  *aReadCount = 0;
+  while (aCount) {
+    AutoReadSegment segment(mPipe, mReadState, aCount);
+    rv = segment.Status();
+    if (NS_FAILED(rv)) {
+      // ignore this error if we've already read something.
+      if (*aReadCount > 0) {
+        rv = NS_OK;
+        break;
+      }
+      if (rv == NS_BASE_STREAM_WOULD_BLOCK) {
+        // pipe is empty
+        if (!mBlocking) {
+          break;
+        }
+        // wait for some data to be written to the pipe
+        rv = Wait();
+        if (NS_SUCCEEDED(rv)) {
+          continue;
+        }
+      }
+      // ignore this error, just return.
+      if (rv == NS_BASE_STREAM_CLOSED) {
+        rv = NS_OK;
+        break;
+      }
+      mPipe->OnInputStreamException(this, rv);
+      break;
+    }
+
+    uint32_t writeCount;
+    while (segment.Length()) {
+      writeCount = 0;
+
+      rv = aWriter(static_cast<nsIAsyncInputStream*>(this), aClosure,
+                   segment.Data(), *aReadCount, segment.Length(), &writeCount);
+
+      if (NS_FAILED(rv) || writeCount == 0) {
+        aCount = 0;
+        // any errors returned from the writer end here: do not
+        // propagate to the caller of ReadSegments.
+        rv = NS_OK;
+        break;
+      }
+
+      MOZ_DIAGNOSTIC_ASSERT(writeCount <= segment.Length());
+      segment.Advance(writeCount);
+      aCount -= writeCount;
+      *aReadCount += writeCount;
+      mLogicalOffset += writeCount;
+    }
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::Read(char* aToBuf, uint32_t aBufLen, uint32_t* aReadCount) {
+  return ReadSegments(NS_CopySegmentToBuffer, aToBuf, aBufLen, aReadCount);
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::IsNonBlocking(bool* aNonBlocking) {
+  *aNonBlocking = !mBlocking;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::AsyncWait(nsIInputStreamCallback* aCallback, uint32_t aFlags,
+                             uint32_t aRequestedCount,
+                             nsIEventTarget* aTarget) {
+  LOG(("III AsyncWait [this=%p]\n", this));
+
+  nsPipeEvents pipeEvents;
+  {
+    ReentrantMonitorAutoEnter mon(mPipe->mReentrantMonitor);
+
+    // replace a pending callback
+    mCallback = nullptr;
+
+    if (!aCallback) {
+      return NS_OK;
+    }
+
+    CallbackHolder callback(this, aCallback, aFlags, aTarget);
+
+    if (NS_FAILED(Status(mon)) ||
+        (mReadState.mAvailable && !(aFlags & WAIT_CLOSURE_ONLY))) {
+      // stream is already closed or readable; post event.
+      pipeEvents.NotifyReady(std::move(callback));
+    } else {
+      // queue up callback object to be notified when data becomes available
+      mCallback = std::move(callback);
+    }
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::Tell(int64_t* aOffset) {
+  ReentrantMonitorAutoEnter mon(mPipe->mReentrantMonitor);
+
+  // return error if closed
+  if (!mReadState.mAvailable && NS_FAILED(Status(mon))) {
+    return Status(mon);
+  }
+
+  *aOffset = mLogicalOffset;
+  return NS_OK;
+}
+
+static bool strings_equal(bool aIgnoreCase, const char* aS1, const char* aS2,
+                          uint32_t aLen) {
+  return aIgnoreCase ? !nsCRT::strncasecmp(aS1, aS2, aLen)
+                     : !strncmp(aS1, aS2, aLen);
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::Search(const char* aForString, bool aIgnoreCase,
+                          bool* aFound, uint32_t* aOffsetSearchedTo) {
+  LOG(("III Search [for=%s ic=%u]\n", aForString, aIgnoreCase));
+
+  ReentrantMonitorAutoEnter mon(mPipe->mReentrantMonitor);
+
+  char* cursor1;
+  char* limit1;
+  uint32_t index = 0, offset = 0;
+  uint32_t strLen = strlen(aForString);
+
+  mPipe->PeekSegment(mReadState, 0, cursor1, limit1);
+  if (cursor1 == limit1) {
+    *aFound = false;
+    *aOffsetSearchedTo = 0;
+    LOG(("  result [aFound=%u offset=%u]\n", *aFound, *aOffsetSearchedTo));
+    return NS_OK;
+  }
+
+  while (true) {
+    uint32_t i, len1 = limit1 - cursor1;
+
+    // check if the string is in the buffer segment
+    for (i = 0; i < len1 - strLen + 1; i++) {
+      if (strings_equal(aIgnoreCase, &cursor1[i], aForString, strLen)) {
+        *aFound = true;
+        *aOffsetSearchedTo = offset + i;
+        LOG(("  result [aFound=%u offset=%u]\n", *aFound, *aOffsetSearchedTo));
+        return NS_OK;
+      }
+    }
+
+    // get the next segment
+    char* cursor2;
+    char* limit2;
+    uint32_t len2;
+
+    index++;
+    offset += len1;
+
+    mPipe->PeekSegment(mReadState, index, cursor2, limit2);
+    if (cursor2 == limit2) {
+      *aFound = false;
+      *aOffsetSearchedTo = offset - strLen + 1;
+      LOG(("  result [aFound=%u offset=%u]\n", *aFound, *aOffsetSearchedTo));
+      return NS_OK;
+    }
+    len2 = limit2 - cursor2;
+
+    // check if the string is straddling the next buffer segment
+    uint32_t lim = XPCOM_MIN(strLen, len2 + 1);
+    for (i = 0; i < lim; ++i) {
+      uint32_t strPart1Len = strLen - i - 1;
+      uint32_t strPart2Len = strLen - strPart1Len;
+      const char* strPart2 = &aForString[strLen - strPart2Len];
+      uint32_t bufSeg1Offset = len1 - strPart1Len;
+      if (strings_equal(aIgnoreCase, &cursor1[bufSeg1Offset], aForString,
+                        strPart1Len) &&
+          strings_equal(aIgnoreCase, cursor2, strPart2, strPart2Len)) {
+        *aFound = true;
+        *aOffsetSearchedTo = offset - strPart1Len;
+        LOG(("  result [aFound=%u offset=%u]\n", *aFound, *aOffsetSearchedTo));
+        return NS_OK;
+      }
+    }
+
+    // finally continue with the next buffer
+    cursor1 = cursor2;
+    limit1 = limit2;
+  }
+
+  MOZ_ASSERT_UNREACHABLE("can't get here");
+  return NS_ERROR_UNEXPECTED;  // keep compiler happy
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::GetCloneable(bool* aCloneableOut) {
+  *aCloneableOut = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPipeInputStream::Clone(nsIInputStream** aCloneOut) {
+  return mPipe->CloneInputStream(this, aCloneOut);
+}
+
+nsresult nsPipeInputStream::Status(const ReentrantMonitorAutoEnter& ev) const {
+  if (NS_FAILED(mInputStatus)) {
+    return mInputStatus;
+  }
+
+  if (mReadState.mAvailable) {
+    // Still something to read and this input stream state is OK.
+    return NS_OK;
+  }
+
+  // Nothing to read, just fall through to the pipe's state that
+  // may reflect state of its output stream side (already closed).
+  return mPipe->mStatus;
+}
+
+nsresult nsPipeInputStream::Status() const {
+  ReentrantMonitorAutoEnter mon(mPipe->mReentrantMonitor);
+  return Status(mon);
+}
+
+nsPipeInputStream::~nsPipeInputStream() { Close(); }
+
+//-----------------------------------------------------------------------------
+// nsPipeOutputStream methods:
+//-----------------------------------------------------------------------------
+
+NS_IMPL_QUERY_INTERFACE(nsPipeOutputStream, nsIOutputStream,
+                        nsIAsyncOutputStream, nsIClassInfo)
+
+NS_IMPL_CI_INTERFACE_GETTER(nsPipeOutputStream, nsIOutputStream,
+                            nsIAsyncOutputStream)
+
+NS_IMPL_THREADSAFE_CI(nsPipeOutputStream)
+
+nsresult nsPipeOutputStream::Wait() {
+  MOZ_DIAGNOSTIC_ASSERT(mBlocking);
+
+  ReentrantMonitorAutoEnter mon(mPipe->mReentrantMonitor);
+
+  if (NS_SUCCEEDED(mPipe->mStatus) && !mWritable) {
+    LOG(("OOO pipe output: waiting for space\n"));
+    mBlocked = true;
+    mon.Wait();
+    mBlocked = false;
+    LOG(("OOO pipe output: woke up [pipe-status=%" PRIx32 " writable=%u]\n",
+         static_cast<uint32_t>(mPipe->mStatus), mWritable));
+  }
+
+  return mPipe->mStatus == NS_BASE_STREAM_CLOSED ? NS_OK : mPipe->mStatus;
+}
+
+MonitorAction nsPipeOutputStream::OnOutputWritable(nsPipeEvents& aEvents) {
+  MonitorAction result = DoNotNotifyMonitor;
+
+  mWritable = true;
+
+  if (mCallback && !(mCallback.Flags() & WAIT_CLOSURE_ONLY)) {
+    aEvents.NotifyReady(std::move(mCallback));
+  } else if (mBlocked) {
+    result = NotifyMonitor;
+  }
+
+  return result;
+}
+
+MonitorAction nsPipeOutputStream::OnOutputException(nsresult aReason,
+                                                    nsPipeEvents& aEvents) {
+  LOG(("nsPipeOutputStream::OnOutputException [this=%p reason=%" PRIx32 "]\n",
+       this, static_cast<uint32_t>(aReason)));
+
+  MonitorAction result = DoNotNotifyMonitor;
+
+  MOZ_DIAGNOSTIC_ASSERT(NS_FAILED(aReason));
+  mWritable = false;
+
+  if (mCallback) {
+    aEvents.NotifyReady(std::move(mCallback));
+  } else if (mBlocked) {
+    result = NotifyMonitor;
+  }
+
+  return result;
+}
+
+NS_IMETHODIMP_(MozExternalRefCountType)
+nsPipeOutputStream::AddRef() {
+  ++mWriterRefCnt;
+  return mPipe->AddRef();
+}
+
+NS_IMETHODIMP_(MozExternalRefCountType)
+nsPipeOutputStream::Release() {
+  if (--mWriterRefCnt == 0) {
+    Close();
+  }
+  return mPipe->Release();
+}
+
+NS_IMETHODIMP
+nsPipeOutputStream::CloseWithStatus(nsresult aReason) {
+  LOG(("OOO CloseWithStatus [this=%p reason=%" PRIx32 "]\n", this,
+       static_cast<uint32_t>(aReason)));
+
+  if (NS_SUCCEEDED(aReason)) {
+    aReason = NS_BASE_STREAM_CLOSED;
+  }
+
+  // input stream may remain open
+  mPipe->OnPipeException(aReason, true);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPipeOutputStream::Close() { return CloseWithStatus(NS_BASE_STREAM_CLOSED); }
+
+NS_IMETHODIMP
+nsPipeOutputStream::WriteSegments(nsReadSegmentFun aReader, void* aClosure,
+                                  uint32_t aCount, uint32_t* aWriteCount) {
+  LOG(("OOO WriteSegments [this=%p count=%u]\n", this, aCount));
+
+  nsresult rv = NS_OK;
+
+  char* segment;
+  uint32_t segmentLen;
+
+  *aWriteCount = 0;
+  while (aCount) {
+    rv = mPipe->GetWriteSegment(segment, segmentLen);
+    if (NS_FAILED(rv)) {
+      if (rv == NS_BASE_STREAM_WOULD_BLOCK) {
+        // pipe is full
+        if (!mBlocking) {
+          // ignore this error if we've already written something
+          if (*aWriteCount > 0) {
+            rv = NS_OK;
+          }
+          break;
+        }
+        // wait for the pipe to have an empty segment.
+        rv = Wait();
+        if (NS_SUCCEEDED(rv)) {
+          continue;
+        }
+      }
+      mPipe->OnPipeException(rv);
+      break;
+    }
+
+    // write no more than aCount
+    if (segmentLen > aCount) {
+      segmentLen = aCount;
+    }
+
+    uint32_t readCount, originalLen = segmentLen;
+    while (segmentLen) {
+      readCount = 0;
+
+      rv = aReader(this, aClosure, segment, *aWriteCount, segmentLen,
+                   &readCount);
+
+      if (NS_FAILED(rv) || readCount == 0) {
+        aCount = 0;
+        // any errors returned from the aReader end here: do not
+        // propagate to the caller of WriteSegments.
+        rv = NS_OK;
+        break;
+      }
+
+      MOZ_DIAGNOSTIC_ASSERT(readCount <= segmentLen);
+      segment += readCount;
+      segmentLen -= readCount;
+      aCount -= readCount;
+      *aWriteCount += readCount;
+      mLogicalOffset += readCount;
+    }
+
+    if (segmentLen < originalLen) {
+      mPipe->AdvanceWriteCursor(originalLen - segmentLen);
+    }
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsPipeOutputStream::Write(const char* aFromBuf, uint32_t aBufLen,
+                          uint32_t* aWriteCount) {
+  return WriteSegments(NS_CopyBufferToSegment, (void*)aFromBuf, aBufLen,
+                       aWriteCount);
+}
+
+NS_IMETHODIMP
+nsPipeOutputStream::Flush() {
+  // nothing to do
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPipeOutputStream::StreamStatus() {
+  ReentrantMonitorAutoEnter mon(mPipe->mReentrantMonitor);
+  return mPipe->mStatus;
+}
+
+NS_IMETHODIMP
+nsPipeOutputStream::WriteFrom(nsIInputStream* aFromStream, uint32_t aCount,
+                              uint32_t* aWriteCount) {
+  return WriteSegments(NS_CopyStreamToSegment, aFromStream, aCount,
+                       aWriteCount);
+}
+
+NS_IMETHODIMP
+nsPipeOutputStream::IsNonBlocking(bool* aNonBlocking) {
+  *aNonBlocking = !mBlocking;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPipeOutputStream::AsyncWait(nsIOutputStreamCallback* aCallback,
+                              uint32_t aFlags, uint32_t aRequestedCount,
+                              nsIEventTarget* aTarget) {
+  LOG(("OOO AsyncWait [this=%p]\n", this));
+
+  nsPipeEvents pipeEvents;
+  {
+    ReentrantMonitorAutoEnter mon(mPipe->mReentrantMonitor);
+
+    // replace a pending callback
+    mCallback = nullptr;
+
+    if (!aCallback) {
+      return NS_OK;
+    }
+
+    CallbackHolder callback(this, aCallback, aFlags, aTarget);
+
+    if (NS_FAILED(mPipe->mStatus) ||
+        (mWritable && !(aFlags & WAIT_CLOSURE_ONLY))) {
+      // stream is already closed or writable; post event.
+      pipeEvents.NotifyReady(std::move(callback));
+    } else {
+      // queue up callback object to be notified when data becomes available
+      mCallback = std::move(callback);
+    }
+  }
+  return NS_OK;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+void NS_NewPipe(nsIInputStream** aPipeIn, nsIOutputStream** aPipeOut,
+                uint32_t aSegmentSize, uint32_t aMaxSize,
+                bool aNonBlockingInput, bool aNonBlockingOutput) {
+  if (aSegmentSize == 0) {
+    aSegmentSize = DEFAULT_SEGMENT_SIZE;
+  }
+
+  // Handle aMaxSize of UINT32_MAX as a special case
+  uint32_t segmentCount;
+  if (aMaxSize == UINT32_MAX) {
+    segmentCount = UINT32_MAX;
+  } else {
+    segmentCount = aMaxSize / aSegmentSize;
+  }
+
+  nsIAsyncInputStream* in;
+  nsIAsyncOutputStream* out;
+  NS_NewPipe2(&in, &out, aNonBlockingInput, aNonBlockingOutput, aSegmentSize,
+              segmentCount);
+
+  *aPipeIn = in;
+  *aPipeOut = out;
+}
+
+// Disable thread safety analysis as this is logically a constructor, and no
+// additional threads can observe these objects yet.
+void NS_NewPipe2(nsIAsyncInputStream** aPipeIn, nsIAsyncOutputStream** aPipeOut,
+                 bool aNonBlockingInput, bool aNonBlockingOutput,
+                 uint32_t aSegmentSize,
+                 uint32_t aSegmentCount) MOZ_NO_THREAD_SAFETY_ANALYSIS {
+  RefPtr<nsPipe> pipe =
+      new nsPipe(aSegmentSize ? aSegmentSize : DEFAULT_SEGMENT_SIZE,
+                 aSegmentCount ? aSegmentCount : DEFAULT_SEGMENT_COUNT);
+
+  RefPtr<nsPipeInputStream> pipeIn = new nsPipeInputStream(pipe);
+  pipe->mInputList.AppendElement(pipeIn);
+  RefPtr<nsPipeOutputStream> pipeOut = &pipe->mOutput;
+
+  pipeIn->SetNonBlocking(aNonBlockingInput);
+  pipeOut->SetNonBlocking(aNonBlockingOutput);
+
+  pipeIn.forget(aPipeIn);
+  pipeOut.forget(aPipeOut);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+// Thin nsIPipe implementation for consumers of the component manager interface
+// for creating pipes. Acts as a thin wrapper around NS_NewPipe2 for JS callers.
+class nsPipeHolder final : public nsIPipe {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIPIPE
+
+ private:
+  ~nsPipeHolder() = default;
+
+  nsCOMPtr<nsIAsyncInputStream> mInput;
+  nsCOMPtr<nsIAsyncOutputStream> mOutput;
+};
+
+NS_IMPL_ISUPPORTS(nsPipeHolder, nsIPipe)
+
+NS_IMETHODIMP
+nsPipeHolder::Init(bool aNonBlockingInput, bool aNonBlockingOutput,
+                   uint32_t aSegmentSize, uint32_t aSegmentCount) {
+  if (mInput || mOutput) {
+    return NS_ERROR_ALREADY_INITIALIZED;
+  }
+  NS_NewPipe2(getter_AddRefs(mInput), getter_AddRefs(mOutput),
+              aNonBlockingInput, aNonBlockingOutput, aSegmentSize,
+              aSegmentCount);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPipeHolder::GetInputStream(nsIAsyncInputStream** aInputStream) {
+  if (mInput) {
+    *aInputStream = do_AddRef(mInput).take();
+    return NS_OK;
+  }
+  return NS_ERROR_NOT_INITIALIZED;
+}
+
+NS_IMETHODIMP
+nsPipeHolder::GetOutputStream(nsIAsyncOutputStream** aOutputStream) {
+  if (mOutput) {
+    *aOutputStream = do_AddRef(mOutput).take();
+    return NS_OK;
+  }
+  return NS_ERROR_NOT_INITIALIZED;
+}
+
+nsresult nsPipeConstructor(REFNSIID aIID, void** aResult) {
+  RefPtr<nsPipeHolder> pipe = new nsPipeHolder();
+  nsresult rv = pipe->QueryInterface(aIID, aResult);
+  return rv;
+}
+
+////////////////////////////////////////////////////////////////////////////////
diff --git a/xpcom/io/nsScriptableBase64Encoder.cpp b/xpcom/io/nsScriptableBase64Encoder.cpp
new file mode 100644
index 0000000000..8513a95380
--- /dev/null
+++ b/xpcom/io/nsScriptableBase64Encoder.cpp
@@ -0,0 +1,26 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsScriptableBase64Encoder.h"
+#include "mozilla/Base64.h"
+
+using namespace mozilla;
+
+NS_IMPL_ISUPPORTS(nsScriptableBase64Encoder, nsIScriptableBase64Encoder)
+
+NS_IMETHODIMP
+nsScriptableBase64Encoder::EncodeToCString(nsIInputStream* aStream,
+                                           uint32_t aLength,
+                                           nsACString& aResult) {
+  return Base64EncodeInputStream(aStream, aResult, aLength);
+}
+
+NS_IMETHODIMP
+nsScriptableBase64Encoder::EncodeToString(nsIInputStream* aStream,
+                                          uint32_t aLength,
+                                          nsAString& aResult) {
+  return Base64EncodeInputStream(aStream, aResult, aLength);
+}
diff --git a/xpcom/io/nsScriptableBase64Encoder.h b/xpcom/io/nsScriptableBase64Encoder.h
new file mode 100644
index 0000000000..8982657e59
--- /dev/null
+++ b/xpcom/io/nsScriptableBase64Encoder.h
@@ -0,0 +1,30 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsScriptableBase64Encoder_h__
+#define nsScriptableBase64Encoder_h__
+
+#include "nsIScriptableBase64Encoder.h"
+#include "mozilla/Attributes.h"
+
+#define NS_SCRIPTABLEBASE64ENCODER_CID               \
+  {                                                  \
+    0xaaf68860, 0xf849, 0x40ee, {                    \
+      0xbb, 0x7a, 0xb2, 0x29, 0xbc, 0xe0, 0x36, 0xa3 \
+    }                                                \
+  }
+#define NS_SCRIPTABLEBASE64ENCODER_CONTRACTID \
+  "@mozilla.org/scriptablebase64encoder;1"
+
+class nsScriptableBase64Encoder final : public nsIScriptableBase64Encoder {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSISCRIPTABLEBASE64ENCODER
+ private:
+  ~nsScriptableBase64Encoder() = default;
+};
+
+#endif
diff --git a/xpcom/io/nsScriptableInputStream.cpp b/xpcom/io/nsScriptableInputStream.cpp
new file mode 100644
index 0000000000..5f8b139c6f
--- /dev/null
+++ b/xpcom/io/nsScriptableInputStream.cpp
@@ -0,0 +1,117 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsScriptableInputStream.h"
+#include "nsString.h"
+
+NS_IMPL_ISUPPORTS(nsScriptableInputStream, nsIScriptableInputStream)
+
+// nsIScriptableInputStream methods
+NS_IMETHODIMP
+nsScriptableInputStream::Close() {
+  if (!mInputStream) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  return mInputStream->Close();
+}
+
+NS_IMETHODIMP
+nsScriptableInputStream::Init(nsIInputStream* aInputStream) {
+  if (!aInputStream) {
+    return NS_ERROR_NULL_POINTER;
+  }
+  mInputStream = aInputStream;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptableInputStream::Available(uint64_t* aResult) {
+  if (!mInputStream) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  return mInputStream->Available(aResult);
+}
+
+NS_IMETHODIMP
+nsScriptableInputStream::Read(uint32_t aCount, char** aResult) {
+  nsresult rv = NS_OK;
+  uint64_t count64 = 0;
+  char* buffer = nullptr;
+
+  if (!mInputStream) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  rv = mInputStream->Available(&count64);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // bug716556 - Ensure count+1 doesn't overflow
+  uint32_t count =
+      XPCOM_MIN((uint32_t)XPCOM_MIN<uint64_t>(count64, aCount), UINT32_MAX - 1);
+  buffer = (char*)malloc(count + 1);  // make room for '\0'
+  if (!buffer) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  rv = ReadHelper(buffer, count);
+  if (NS_FAILED(rv)) {
+    free(buffer);
+    return rv;
+  }
+
+  buffer[count] = '\0';
+  *aResult = buffer;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptableInputStream::ReadBytes(uint32_t aCount, nsACString& aResult) {
+  if (!mInputStream) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  if (!aResult.SetLength(aCount, mozilla::fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  MOZ_ASSERT(aResult.Length() == aCount);
+  char* ptr = aResult.BeginWriting();
+  nsresult rv = ReadHelper(ptr, aCount);
+  if (NS_FAILED(rv)) {
+    aResult.Truncate();
+  }
+  return rv;
+}
+
+nsresult nsScriptableInputStream::ReadHelper(char* aBuffer, uint32_t aCount) {
+  uint32_t totalBytesRead = 0;
+  while (1) {
+    uint32_t bytesRead;
+    nsresult rv = mInputStream->Read(aBuffer + totalBytesRead,
+                                     aCount - totalBytesRead, &bytesRead);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    totalBytesRead += bytesRead;
+    if (totalBytesRead == aCount) {
+      break;
+    }
+
+    // If we have read zero bytes, we have hit EOF.
+    if (bytesRead == 0) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+  return NS_OK;
+}
+
+nsresult nsScriptableInputStream::Create(REFNSIID aIID, void** aResult) {
+  RefPtr<nsScriptableInputStream> sis = new nsScriptableInputStream();
+  return sis->QueryInterface(aIID, aResult);
+}
diff --git a/xpcom/io/nsScriptableInputStream.h b/xpcom/io/nsScriptableInputStream.h
new file mode 100644
index 0000000000..1dc8a80962
--- /dev/null
+++ b/xpcom/io/nsScriptableInputStream.h
@@ -0,0 +1,46 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef ___nsscriptableinputstream___h_
+#define ___nsscriptableinputstream___h_
+
+#include "nsIScriptableInputStream.h"
+#include "nsIInputStream.h"
+#include "nsCOMPtr.h"
+#include "mozilla/Attributes.h"
+
+#define NS_SCRIPTABLEINPUTSTREAM_CID               \
+  {                                                \
+    0x7225c040, 0xa9bf, 0x11d3, {                  \
+      0xa1, 0x97, 0x0, 0x50, 0x4, 0x1c, 0xaf, 0x44 \
+    }                                              \
+  }
+
+#define NS_SCRIPTABLEINPUTSTREAM_CONTRACTID \
+  "@mozilla.org/scriptableinputstream;1"
+
+class nsScriptableInputStream final : public nsIScriptableInputStream {
+ public:
+  // nsISupports methods
+  NS_DECL_ISUPPORTS
+
+  // nsIScriptableInputStream methods
+  NS_DECL_NSISCRIPTABLEINPUTSTREAM
+
+  // nsScriptableInputStream methods
+  nsScriptableInputStream() = default;
+
+  static nsresult Create(REFNSIID aIID, void** aResult);
+
+ private:
+  ~nsScriptableInputStream() = default;
+
+  nsresult ReadHelper(char* aBuffer, uint32_t aCount);
+
+  nsCOMPtr<nsIInputStream> mInputStream;
+};
+
+#endif  // ___nsscriptableinputstream___h_
diff --git a/xpcom/io/nsSegmentedBuffer.cpp b/xpcom/io/nsSegmentedBuffer.cpp
new file mode 100644
index 0000000000..01d075368a
--- /dev/null
+++ b/xpcom/io/nsSegmentedBuffer.cpp
@@ -0,0 +1,170 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsSegmentedBuffer.h"
+#include "nsNetCID.h"
+#include "nsServiceManagerUtils.h"
+#include "nsThreadUtils.h"
+#include "mozilla/ScopeExit.h"
+
+nsresult nsSegmentedBuffer::Init(uint32_t aSegmentSize) {
+  if (mSegmentArrayCount != 0) {
+    return NS_ERROR_FAILURE;  // initialized more than once
+  }
+  mSegmentSize = aSegmentSize;
+  mSegmentArrayCount = NS_SEGMENTARRAY_INITIAL_COUNT;
+  return NS_OK;
+}
+
+char* nsSegmentedBuffer::AppendNewSegment() {
+  if (!mSegmentArray) {
+    uint32_t bytes = mSegmentArrayCount * sizeof(char*);
+    mSegmentArray = (char**)moz_xmalloc(bytes);
+    memset(mSegmentArray, 0, bytes);
+  }
+
+  if (IsFull()) {
+    mozilla::CheckedInt<uint32_t> newArraySize =
+        mozilla::CheckedInt<uint32_t>(mSegmentArrayCount) * 2;
+    mozilla::CheckedInt<uint32_t> bytes = newArraySize * sizeof(char*);
+    if (!bytes.isValid()) {
+      return nullptr;
+    }
+
+    mSegmentArray = (char**)moz_xrealloc(mSegmentArray, bytes.value());
+    // copy wrapped content to new extension
+    if (mFirstSegmentIndex > mLastSegmentIndex) {
+      // deal with wrap around case
+      memcpy(&mSegmentArray[mSegmentArrayCount], mSegmentArray,
+             mLastSegmentIndex * sizeof(char*));
+      memset(mSegmentArray, 0, mLastSegmentIndex * sizeof(char*));
+      mLastSegmentIndex += mSegmentArrayCount;
+      memset(&mSegmentArray[mLastSegmentIndex], 0,
+             (newArraySize.value() - mLastSegmentIndex) * sizeof(char*));
+    } else {
+      memset(&mSegmentArray[mLastSegmentIndex], 0,
+             (newArraySize.value() - mLastSegmentIndex) * sizeof(char*));
+    }
+    mSegmentArrayCount = newArraySize.value();
+  }
+
+  char* seg = (char*)malloc(mSegmentSize);
+  if (!seg) {
+    return nullptr;
+  }
+  mSegmentArray[mLastSegmentIndex] = seg;
+  mLastSegmentIndex = ModSegArraySize(mLastSegmentIndex + 1);
+  return seg;
+}
+
+bool nsSegmentedBuffer::DeleteFirstSegment() {
+  NS_ASSERTION(mSegmentArray[mFirstSegmentIndex] != nullptr,
+               "deleting bad segment");
+  FreeOMT(mSegmentArray[mFirstSegmentIndex]);
+  mSegmentArray[mFirstSegmentIndex] = nullptr;
+  int32_t last = ModSegArraySize(mLastSegmentIndex - 1);
+  if (mFirstSegmentIndex == last) {
+    mLastSegmentIndex = last;
+    return true;
+  } else {
+    mFirstSegmentIndex = ModSegArraySize(mFirstSegmentIndex + 1);
+    return false;
+  }
+}
+
+bool nsSegmentedBuffer::DeleteLastSegment() {
+  int32_t last = ModSegArraySize(mLastSegmentIndex - 1);
+  NS_ASSERTION(mSegmentArray[last] != nullptr, "deleting bad segment");
+  FreeOMT(mSegmentArray[last]);
+  mSegmentArray[last] = nullptr;
+  mLastSegmentIndex = last;
+  return (bool)(mLastSegmentIndex == mFirstSegmentIndex);
+}
+
+bool nsSegmentedBuffer::ReallocLastSegment(size_t aNewSize) {
+  int32_t last = ModSegArraySize(mLastSegmentIndex - 1);
+  NS_ASSERTION(mSegmentArray[last] != nullptr, "realloc'ing bad segment");
+  char* newSegment = (char*)realloc(mSegmentArray[last], aNewSize);
+  if (newSegment) {
+    mSegmentArray[last] = newSegment;
+    return true;
+  }
+  return false;
+}
+
+void nsSegmentedBuffer::Empty() {
+  auto clearMembers = mozilla::MakeScopeExit([&] {
+    mSegmentArray = nullptr;
+    mSegmentArrayCount = NS_SEGMENTARRAY_INITIAL_COUNT;
+    mFirstSegmentIndex = mLastSegmentIndex = 0;
+  });
+
+  // If mSegmentArray is null, there's no need to actually free anything
+  if (!mSegmentArray) {
+    return;
+  }
+
+  // Dispatch a task that frees up the array. This may run immediately or on
+  // a background thread.
+  FreeOMT([segmentArray = mSegmentArray, arrayCount = mSegmentArrayCount]() {
+    for (uint32_t i = 0; i < arrayCount; i++) {
+      if (segmentArray[i]) {
+        free(segmentArray[i]);
+      }
+    }
+    free(segmentArray);
+  });
+}
+
+void nsSegmentedBuffer::FreeOMT(void* aPtr) {
+  FreeOMT([aPtr]() { free(aPtr); });
+}
+
+void nsSegmentedBuffer::FreeOMT(std::function<void()>&& aTask) {
+  if (!NS_IsMainThread()) {
+    aTask();
+    return;
+  }
+
+  if (mFreeOMT) {
+    // There is a runnable pending which will handle this object
+    if (mFreeOMT->AddTask(std::move(aTask)) > 1) {
+      return;
+    }
+  } else {
+    mFreeOMT = mozilla::MakeRefPtr<FreeOMTPointers>();
+    mFreeOMT->AddTask(std::move(aTask));
+  }
+
+  if (!mIOThread) {
+    mIOThread = do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID);
+  }
+
+  // During the shutdown we are not able to obtain the IOThread and/or the
+  // dispatching of runnable fails.
+  if (!mIOThread || NS_FAILED(mIOThread->Dispatch(NS_NewRunnableFunction(
+                        "nsSegmentedBuffer::FreeOMT",
+                        [obj = mFreeOMT]() { obj->FreeAll(); })))) {
+    mFreeOMT->FreeAll();
+  }
+}
+
+void nsSegmentedBuffer::FreeOMTPointers::FreeAll() {
+  // Take all the tasks from the object. If AddTask is called after we release
+  // the lock, then another runnable will be dispatched for that task. This is
+  // necessary to avoid blocking the main thread while memory is being freed.
+  nsTArray<std::function<void()>> tasks = [this]() {
+    auto t = mTasks.Lock();
+    return std::move(*t);
+  }();
+
+  // Finally run all the tasks to free memory.
+  for (auto& task : tasks) {
+    task();
+  }
+}
+
+////////////////////////////////////////////////////////////////////////////////
diff --git a/xpcom/io/nsSegmentedBuffer.h b/xpcom/io/nsSegmentedBuffer.h
new file mode 100644
index 0000000000..c654956df9
--- /dev/null
+++ b/xpcom/io/nsSegmentedBuffer.h
@@ -0,0 +1,126 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsSegmentedBuffer_h__
+#define nsSegmentedBuffer_h__
+
+#include <stddef.h>
+#include <functional>
+
+#include "nsCOMPtr.h"
+#include "nsDebug.h"
+#include "nsError.h"
+#include "nsTArray.h"
+#include "mozilla/DataMutex.h"
+
+class nsIEventTarget;
+
+class nsSegmentedBuffer {
+ public:
+  nsSegmentedBuffer()
+      : mSegmentSize(0),
+        mSegmentArray(nullptr),
+        mSegmentArrayCount(0),
+        mFirstSegmentIndex(0),
+        mLastSegmentIndex(0) {}
+
+  ~nsSegmentedBuffer() { Empty(); }
+
+  nsresult Init(uint32_t aSegmentSize);
+
+  char* AppendNewSegment();  // pushes at end
+
+  // returns true if no more segments remain:
+  bool DeleteFirstSegment();  // pops from beginning
+
+  // returns true if no more segments remain:
+  bool DeleteLastSegment();  // pops from beginning
+
+  // Call Realloc() on last segment.  This is used to reduce memory
+  // consumption when data is not an exact multiple of segment size.
+  bool ReallocLastSegment(size_t aNewSize);
+
+  void Empty();  // frees all segments
+
+  inline uint32_t GetSegmentCount() {
+    if (mFirstSegmentIndex <= mLastSegmentIndex) {
+      return mLastSegmentIndex - mFirstSegmentIndex;
+    } else {
+      return mSegmentArrayCount + mLastSegmentIndex - mFirstSegmentIndex;
+    }
+  }
+
+  inline uint32_t GetSegmentSize() { return mSegmentSize; }
+
+  inline char* GetSegment(uint32_t aIndex) {
+    NS_ASSERTION(aIndex < GetSegmentCount(), "index out of bounds");
+    int32_t i = ModSegArraySize(mFirstSegmentIndex + (int32_t)aIndex);
+    return mSegmentArray[i];
+  }
+
+ protected:
+  inline int32_t ModSegArraySize(int32_t aIndex) {
+    uint32_t result = aIndex & (mSegmentArrayCount - 1);
+    NS_ASSERTION(result == aIndex % mSegmentArrayCount,
+                 "non-power-of-2 mSegmentArrayCount");
+    return result;
+  }
+
+  inline bool IsFull() {
+    return ModSegArraySize(mLastSegmentIndex + 1) == mFirstSegmentIndex;
+  }
+
+ protected:
+  uint32_t mSegmentSize;
+  char** mSegmentArray;
+  uint32_t mSegmentArrayCount;
+  int32_t mFirstSegmentIndex;
+  int32_t mLastSegmentIndex;
+
+ private:
+  class FreeOMTPointers {
+    NS_INLINE_DECL_THREADSAFE_REFCOUNTING(FreeOMTPointers)
+
+   public:
+    FreeOMTPointers() : mTasks("nsSegmentedBuffer::FreeOMTPointers") {}
+
+    void FreeAll();
+
+    // Adds a task to the array. Returns the size of the array.
+    size_t AddTask(std::function<void()>&& aTask) {
+      auto tasks = mTasks.Lock();
+      tasks->AppendElement(std::move(aTask));
+      return tasks->Length();
+    }
+
+   private:
+    ~FreeOMTPointers() = default;
+
+    mozilla::DataMutex<nsTArray<std::function<void()>>> mTasks;
+  };
+
+  void FreeOMT(void* aPtr);
+  void FreeOMT(std::function<void()>&& aTask);
+
+  nsCOMPtr<nsIEventTarget> mIOThread;
+
+  // This object is created the first time we need to dispatch to another thread
+  // to free segments. It is only freed when the nsSegmentedBufer is destroyed
+  // or when the runnable is finally handled and its refcount goes to 0.
+  RefPtr<FreeOMTPointers> mFreeOMT;
+};
+
+// NS_SEGMENTARRAY_INITIAL_SIZE: This number needs to start out as a
+// power of 2 given how it gets used. We double the segment array
+// when we overflow it, and use that fact that it's a power of 2
+// to compute a fast modulus operation in IsFull.
+//
+// 32 segment array entries can accommodate 128k of data if segments
+// are 4k in size. That seems like a reasonable amount that will avoid
+// needing to grow the segment array.
+#define NS_SEGMENTARRAY_INITIAL_COUNT 32
+
+#endif  // nsSegmentedBuffer_h__
diff --git a/xpcom/io/nsStorageStream.cpp b/xpcom/io/nsStorageStream.cpp
new file mode 100644
index 0000000000..cd3dfd6645
--- /dev/null
+++ b/xpcom/io/nsStorageStream.cpp
@@ -0,0 +1,680 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * The storage stream provides an internal buffer that can be filled by a
+ * client using a single output stream.  One or more independent input streams
+ * can be created to read the data out non-destructively.  The implementation
+ * uses a segmented buffer internally to avoid realloc'ing of large buffers,
+ * with the attendant performance loss and heap fragmentation.
+ */
+
+#include "mozilla/Mutex.h"
+#include "nsAlgorithm.h"
+#include "nsStorageStream.h"
+#include "nsSegmentedBuffer.h"
+#include "nsStreamUtils.h"
+#include "nsCOMPtr.h"
+#include "nsICloneableInputStream.h"
+#include "nsIInputStream.h"
+#include "nsIIPCSerializableInputStream.h"
+#include "nsISeekableStream.h"
+#include "mozilla/Logging.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Likely.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/ipc/InputStreamUtils.h"
+
+using mozilla::MutexAutoLock;
+using mozilla::ipc::InputStreamParams;
+using mozilla::ipc::StringInputStreamParams;
+
+//
+// Log module for StorageStream logging...
+//
+// To enable logging (see prlog.h for full details):
+//
+//    set MOZ_LOG=StorageStreamLog:5
+//    set MOZ_LOG_FILE=storage.log
+//
+// This enables LogLevel::Debug level information and places all output in
+// the file storage.log.
+//
+static mozilla::LazyLogModule sStorageStreamLog("nsStorageStream");
+#ifdef LOG
+#  undef LOG
+#endif
+#define LOG(args) MOZ_LOG(sStorageStreamLog, mozilla::LogLevel::Debug, args)
+
+nsStorageStream::nsStorageStream() {
+  LOG(("Creating nsStorageStream [%p].\n", this));
+}
+
+nsStorageStream::~nsStorageStream() { delete mSegmentedBuffer; }
+
+NS_IMPL_ISUPPORTS(nsStorageStream, nsIStorageStream, nsIOutputStream)
+
+NS_IMETHODIMP
+nsStorageStream::Init(uint32_t aSegmentSize, uint32_t aMaxSize) {
+  MutexAutoLock lock(mMutex);
+  mSegmentedBuffer = new nsSegmentedBuffer();
+  mSegmentSize = aSegmentSize;
+  mSegmentSizeLog2 = mozilla::FloorLog2(aSegmentSize);
+  mMaxLogicalLength = aMaxSize;
+
+  // Segment size must be a power of two
+  if (mSegmentSize != ((uint32_t)1 << mSegmentSizeLog2)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  return mSegmentedBuffer->Init(aSegmentSize);
+}
+
+NS_IMETHODIMP
+nsStorageStream::GetOutputStream(int32_t aStartingOffset,
+                                 nsIOutputStream** aOutputStream) {
+  if (NS_WARN_IF(!aOutputStream)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  MutexAutoLock lock(mMutex);
+  if (NS_WARN_IF(!mSegmentedBuffer)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  if (mWriteInProgress) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  if (mActiveSegmentBorrows > 0) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  nsresult rv = Seek(aStartingOffset);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // Enlarge the last segment in the buffer so that it is the same size as
+  // all the other segments in the buffer.  (It may have been realloc'ed
+  // smaller in the Close() method.)
+  if (mLastSegmentNum >= 0)
+    if (mSegmentedBuffer->ReallocLastSegment(mSegmentSize)) {
+      // Need to re-Seek, since realloc changed segment base pointer
+      rv = Seek(aStartingOffset);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+    }
+
+  NS_ADDREF(this);
+  *aOutputStream = static_cast<nsIOutputStream*>(this);
+  mWriteInProgress = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageStream::Close() {
+  MutexAutoLock lock(mMutex);
+  if (NS_WARN_IF(!mSegmentedBuffer)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  mWriteInProgress = false;
+
+  int32_t segmentOffset = SegOffset(mLogicalLength);
+
+  // Shrink the final segment in the segmented buffer to the minimum size
+  // needed to contain the data, so as to conserve memory.
+  if (segmentOffset && !mActiveSegmentBorrows) {
+    mSegmentedBuffer->ReallocLastSegment(segmentOffset);
+  }
+
+  mWriteCursor = 0;
+  mSegmentEnd = 0;
+
+  LOG(("nsStorageStream [%p] Close mWriteCursor=%p mSegmentEnd=%p\n", this,
+       mWriteCursor, mSegmentEnd));
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageStream::Flush() { return NS_OK; }
+
+NS_IMETHODIMP
+nsStorageStream::StreamStatus() {
+  MutexAutoLock lock(mMutex);
+  if (!mSegmentedBuffer) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageStream::Write(const char* aBuffer, uint32_t aCount,
+                       uint32_t* aNumWritten) {
+  if (NS_WARN_IF(!aNumWritten) || NS_WARN_IF(!aBuffer)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  MutexAutoLock lock(mMutex);
+  if (NS_WARN_IF(!mSegmentedBuffer)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  if (NS_WARN_IF(mLogicalLength >= mMaxLogicalLength)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  LOG(("nsStorageStream [%p] Write mWriteCursor=%p mSegmentEnd=%p aCount=%d\n",
+       this, mWriteCursor, mSegmentEnd, aCount));
+
+  uint32_t remaining = aCount;
+  const char* readCursor = aBuffer;
+
+  remaining = std::min(remaining, mMaxLogicalLength - mLogicalLength);
+
+  auto onExit = mozilla::MakeScopeExit([&] {
+    mMutex.AssertCurrentThreadOwns();
+    *aNumWritten = aCount - remaining;
+    mLogicalLength += *aNumWritten;
+
+    LOG(
+        ("nsStorageStream [%p] Wrote mWriteCursor=%p mSegmentEnd=%p "
+         "numWritten=%d\n",
+         this, mWriteCursor, mSegmentEnd, *aNumWritten));
+  });
+
+  // If no segments have been created yet, create one even if we don't have
+  // to write any data; this enables creating an input stream which reads from
+  // the very end of the data for any amount of data in the stream (i.e.
+  // this stream contains N bytes of data and newInputStream(N) is called),
+  // even for N=0 (with the caveat that we require .write("", 0) be called to
+  // initialize internal buffers).
+  bool firstTime = mSegmentedBuffer->GetSegmentCount() == 0;
+  while (remaining || MOZ_UNLIKELY(firstTime)) {
+    firstTime = false;
+    uint32_t availableInSegment = mSegmentEnd - mWriteCursor;
+    if (!availableInSegment) {
+      mWriteCursor = mSegmentedBuffer->AppendNewSegment();
+      if (!mWriteCursor) {
+        mSegmentEnd = 0;
+        return NS_ERROR_OUT_OF_MEMORY;
+      }
+      mLastSegmentNum++;
+      mSegmentEnd = mWriteCursor + mSegmentSize;
+      availableInSegment = mSegmentEnd - mWriteCursor;
+      LOG(
+          ("nsStorageStream [%p] Write (new seg) mWriteCursor=%p "
+           "mSegmentEnd=%p\n",
+           this, mWriteCursor, mSegmentEnd));
+    }
+
+    uint32_t count = XPCOM_MIN(availableInSegment, remaining);
+    memcpy(mWriteCursor, readCursor, count);
+    remaining -= count;
+    readCursor += count;
+    mWriteCursor += count;
+    LOG(
+        ("nsStorageStream [%p] Writing mWriteCursor=%p mSegmentEnd=%p "
+         "count=%d\n",
+         this, mWriteCursor, mSegmentEnd, count));
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageStream::WriteFrom(nsIInputStream* aInStr, uint32_t aCount,
+                           uint32_t* aResult) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsStorageStream::WriteSegments(nsReadSegmentFun aReader, void* aClosure,
+                               uint32_t aCount, uint32_t* aResult) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsStorageStream::IsNonBlocking(bool* aNonBlocking) {
+  *aNonBlocking = false;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageStream::GetLength(uint32_t* aLength) {
+  MutexAutoLock lock(mMutex);
+  *aLength = mLogicalLength;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageStream::SetLength(uint32_t aLength) {
+  MutexAutoLock lock(mMutex);
+  return SetLengthLocked(aLength);
+}
+
+// Truncate the buffer by deleting the end segments
+nsresult nsStorageStream::SetLengthLocked(uint32_t aLength) {
+  if (NS_WARN_IF(!mSegmentedBuffer)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  if (mWriteInProgress) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  if (mActiveSegmentBorrows) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  if (aLength > mLogicalLength) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  int32_t newLastSegmentNum = SegNum(aLength);
+  int32_t segmentOffset = SegOffset(aLength);
+  if (segmentOffset == 0) {
+    newLastSegmentNum--;
+  }
+
+  while (newLastSegmentNum < mLastSegmentNum) {
+    mSegmentedBuffer->DeleteLastSegment();
+    mLastSegmentNum--;
+  }
+
+  mLogicalLength = aLength;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageStream::GetWriteInProgress(bool* aWriteInProgress) {
+  MutexAutoLock lock(mMutex);
+  *aWriteInProgress = mWriteInProgress;
+  return NS_OK;
+}
+
+nsresult nsStorageStream::Seek(int32_t aPosition) {
+  if (NS_WARN_IF(!mSegmentedBuffer)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  // An argument of -1 means "seek to end of stream"
+  if (aPosition == -1) {
+    aPosition = mLogicalLength;
+  }
+
+  // Seeking beyond the buffer end is illegal
+  if ((uint32_t)aPosition > mLogicalLength) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // Seeking backwards in the write stream results in truncation
+  SetLengthLocked(aPosition);
+
+  // Special handling for seek to start-of-buffer
+  if (aPosition == 0) {
+    mWriteCursor = 0;
+    mSegmentEnd = 0;
+    LOG(("nsStorageStream [%p] Seek mWriteCursor=%p mSegmentEnd=%p\n", this,
+         mWriteCursor, mSegmentEnd));
+    return NS_OK;
+  }
+
+  // Segment may have changed, so reset pointers
+  mWriteCursor = mSegmentedBuffer->GetSegment(mLastSegmentNum);
+  NS_ASSERTION(mWriteCursor, "null mWriteCursor");
+  mSegmentEnd = mWriteCursor + mSegmentSize;
+
+  // Adjust write cursor for current segment offset.  This test is necessary
+  // because SegNum may reference the next-to-be-allocated segment, in which
+  // case we need to be pointing at the end of the last segment.
+  int32_t segmentOffset = SegOffset(aPosition);
+  if (segmentOffset == 0 && (SegNum(aPosition) > (uint32_t)mLastSegmentNum)) {
+    mWriteCursor = mSegmentEnd;
+  } else {
+    mWriteCursor += segmentOffset;
+  }
+
+  LOG(("nsStorageStream [%p] Seek mWriteCursor=%p mSegmentEnd=%p\n", this,
+       mWriteCursor, mSegmentEnd));
+  return NS_OK;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+// There can be many nsStorageInputStreams for a single nsStorageStream
+class nsStorageInputStream final : public nsIInputStream,
+                                   public nsISeekableStream,
+                                   public nsIIPCSerializableInputStream,
+                                   public nsICloneableInputStream {
+ public:
+  nsStorageInputStream(nsStorageStream* aStorageStream, uint32_t aSegmentSize)
+      : mStorageStream(aStorageStream),
+        mReadCursor(0),
+        mSegmentEnd(0),
+        mSegmentNum(0),
+        mSegmentSize(aSegmentSize),
+        mLogicalCursor(0),
+        mStatus(NS_OK) {}
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINPUTSTREAM
+  NS_DECL_NSISEEKABLESTREAM
+  NS_DECL_NSITELLABLESTREAM
+  NS_DECL_NSIIPCSERIALIZABLEINPUTSTREAM
+  NS_DECL_NSICLONEABLEINPUTSTREAM
+
+ private:
+  ~nsStorageInputStream() = default;
+
+ protected:
+  nsresult Seek(uint32_t aPosition) MOZ_REQUIRES(mStorageStream->mMutex);
+
+  friend class nsStorageStream;
+
+ private:
+  RefPtr<nsStorageStream> mStorageStream;
+  uint32_t mReadCursor;     // Next memory location to read byte, or 0
+  uint32_t mSegmentEnd;     // One byte past end of current buffer segment
+  uint32_t mSegmentNum;     // Segment number containing read cursor
+  uint32_t mSegmentSize;    // All segments, except the last, are of this size
+  uint32_t mLogicalCursor;  // Logical offset into stream
+  nsresult mStatus;
+
+  uint32_t SegNum(uint32_t aPosition) MOZ_REQUIRES(mStorageStream->mMutex) {
+    return aPosition >> mStorageStream->mSegmentSizeLog2;
+  }
+  uint32_t SegOffset(uint32_t aPosition) {
+    return aPosition & (mSegmentSize - 1);
+  }
+};
+
+NS_IMPL_ISUPPORTS(nsStorageInputStream, nsIInputStream, nsISeekableStream,
+                  nsITellableStream, nsIIPCSerializableInputStream,
+                  nsICloneableInputStream)
+
+NS_IMETHODIMP
+nsStorageStream::NewInputStream(int32_t aStartingOffset,
+                                nsIInputStream** aInputStream) {
+  MutexAutoLock lock(mMutex);
+  if (NS_WARN_IF(!mSegmentedBuffer)) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  RefPtr<nsStorageInputStream> inputStream =
+      new nsStorageInputStream(this, mSegmentSize);
+
+  inputStream->mStorageStream->mMutex.AssertCurrentThreadOwns();
+  nsresult rv = inputStream->Seek(aStartingOffset);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  inputStream.forget(aInputStream);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageInputStream::Close() {
+  mStatus = NS_BASE_STREAM_CLOSED;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageInputStream::Available(uint64_t* aAvailable) {
+  if (NS_FAILED(mStatus)) {
+    return mStatus;
+  }
+
+  MutexAutoLock lock(mStorageStream->mMutex);
+  *aAvailable = mStorageStream->mLogicalLength - mLogicalCursor;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageInputStream::StreamStatus() { return mStatus; }
+
+NS_IMETHODIMP
+nsStorageInputStream::Read(char* aBuffer, uint32_t aCount, uint32_t* aNumRead) {
+  return ReadSegments(NS_CopySegmentToBuffer, aBuffer, aCount, aNumRead);
+}
+
+NS_IMETHODIMP
+nsStorageInputStream::ReadSegments(nsWriteSegmentFun aWriter, void* aClosure,
+                                   uint32_t aCount, uint32_t* aNumRead) {
+  *aNumRead = 0;
+  if (mStatus == NS_BASE_STREAM_CLOSED) {
+    return NS_OK;
+  }
+  if (NS_FAILED(mStatus)) {
+    return mStatus;
+  }
+
+  uint32_t count, availableInSegment, remainingCapacity, bytesConsumed;
+  nsresult rv;
+
+  remainingCapacity = aCount;
+  while (remainingCapacity) {
+    const char* cur = nullptr;
+    {
+      MutexAutoLock lock(mStorageStream->mMutex);
+      availableInSegment = mSegmentEnd - mReadCursor;
+      if (!availableInSegment) {
+        uint32_t available = mStorageStream->mLogicalLength - mLogicalCursor;
+        if (!available) {
+          break;
+        }
+
+        // We have data in the stream, but if mSegmentEnd is zero, then we
+        // were likely constructed prior to any data being written into
+        // the stream.  Therefore, if mSegmentEnd is non-zero, we should
+        // move into the next segment; otherwise, we should stay in this
+        // segment so our input state can be updated and we can properly
+        // perform the initial read.
+        if (mSegmentEnd > 0) {
+          mSegmentNum++;
+        }
+        mReadCursor = 0;
+        mSegmentEnd = XPCOM_MIN(mSegmentSize, available);
+        availableInSegment = mSegmentEnd;
+      }
+      cur = mStorageStream->mSegmentedBuffer->GetSegment(mSegmentNum);
+      mStorageStream->mActiveSegmentBorrows++;
+    }
+    auto dropBorrow = mozilla::MakeScopeExit([&] {
+      MutexAutoLock lock(mStorageStream->mMutex);
+      mStorageStream->mActiveSegmentBorrows--;
+    });
+
+    count = XPCOM_MIN(availableInSegment, remainingCapacity);
+    rv = aWriter(this, aClosure, cur + mReadCursor, aCount - remainingCapacity,
+                 count, &bytesConsumed);
+    if (NS_FAILED(rv) || (bytesConsumed == 0)) {
+      break;
+    }
+    remainingCapacity -= bytesConsumed;
+    mReadCursor += bytesConsumed;
+    mLogicalCursor += bytesConsumed;
+  }
+
+  *aNumRead = aCount - remainingCapacity;
+
+  bool isWriteInProgress = false;
+  if (NS_FAILED(mStorageStream->GetWriteInProgress(&isWriteInProgress))) {
+    isWriteInProgress = false;
+  }
+
+  if (*aNumRead == 0 && isWriteInProgress) {
+    return NS_BASE_STREAM_WOULD_BLOCK;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageInputStream::IsNonBlocking(bool* aNonBlocking) {
+  // TODO: This class should implement nsIAsyncInputStream so that callers
+  // have some way of dealing with NS_BASE_STREAM_WOULD_BLOCK errors.
+
+  *aNonBlocking = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageInputStream::Seek(int32_t aWhence, int64_t aOffset) {
+  if (NS_FAILED(mStatus)) {
+    return mStatus;
+  }
+
+  MutexAutoLock lock(mStorageStream->mMutex);
+  int64_t pos = aOffset;
+
+  switch (aWhence) {
+    case NS_SEEK_SET:
+      break;
+    case NS_SEEK_CUR:
+      pos += mLogicalCursor;
+      break;
+    case NS_SEEK_END:
+      pos += mStorageStream->mLogicalLength;
+      break;
+    default:
+      MOZ_ASSERT_UNREACHABLE("unexpected whence value");
+      return NS_ERROR_UNEXPECTED;
+  }
+  if (pos == int64_t(mLogicalCursor)) {
+    return NS_OK;
+  }
+
+  return Seek(pos);
+}
+
+NS_IMETHODIMP
+nsStorageInputStream::Tell(int64_t* aResult) {
+  if (NS_FAILED(mStatus)) {
+    return mStatus;
+  }
+
+  *aResult = mLogicalCursor;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageInputStream::SetEOF() {
+  MOZ_ASSERT_UNREACHABLE("nsStorageInputStream::SetEOF");
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+nsresult nsStorageInputStream::Seek(uint32_t aPosition) {
+  uint32_t length = mStorageStream->mLogicalLength;
+  if (aPosition > length) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  if (length == 0) {
+    return NS_OK;
+  }
+
+  mSegmentNum = SegNum(aPosition);
+  mReadCursor = SegOffset(aPosition);
+  uint32_t available = length - aPosition;
+  mSegmentEnd = mReadCursor + XPCOM_MIN(mSegmentSize - mReadCursor, available);
+  mLogicalCursor = aPosition;
+  return NS_OK;
+}
+
+void nsStorageInputStream::SerializedComplexity(uint32_t aMaxSize,
+                                                uint32_t* aSizeUsed,
+                                                uint32_t* aPipes,
+                                                uint32_t* aTransferables) {
+  uint64_t remaining = 0;
+  mozilla::DebugOnly<nsresult> rv = Available(&remaining);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+  if (remaining >= aMaxSize) {
+    *aPipes = 1;
+  } else {
+    *aSizeUsed = remaining;
+  }
+}
+
+void nsStorageInputStream::Serialize(InputStreamParams& aParams,
+                                     uint32_t aMaxSize, uint32_t* aSizeUsed) {
+  MOZ_ASSERT(aSizeUsed);
+  *aSizeUsed = 0;
+
+  uint64_t remaining = 0;
+  mozilla::DebugOnly<nsresult> rv = Available(&remaining);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+  if (remaining >= aMaxSize) {
+    mozilla::ipc::InputStreamHelper::SerializeInputStreamAsPipe(this, aParams);
+    return;
+  }
+
+  *aSizeUsed = remaining;
+
+  nsCString combined;
+  int64_t offset;
+  rv = Tell(&offset);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+  auto handleOrErr = combined.BulkWrite(remaining, 0, false);
+  MOZ_ASSERT(!handleOrErr.isErr());
+
+  auto handle = handleOrErr.unwrap();
+
+  uint32_t numRead = 0;
+
+  rv = Read(handle.Elements(), remaining, &numRead);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+  MOZ_ASSERT(numRead == remaining);
+  handle.Finish(numRead, false);
+
+  rv = Seek(NS_SEEK_SET, offset);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+  StringInputStreamParams params;
+  params.data() = combined;
+  aParams = params;
+}
+
+bool nsStorageInputStream::Deserialize(const InputStreamParams& aParams) {
+  MOZ_ASSERT_UNREACHABLE(
+      "We should never attempt to deserialize a storage "
+      "input stream.");
+  return false;
+}
+
+NS_IMETHODIMP
+nsStorageInputStream::GetCloneable(bool* aCloneableOut) {
+  *aCloneableOut = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStorageInputStream::Clone(nsIInputStream** aCloneOut) {
+  return mStorageStream->NewInputStream(mLogicalCursor, aCloneOut);
+}
+
+nsresult NS_NewStorageStream(uint32_t aSegmentSize, uint32_t aMaxSize,
+                             nsIStorageStream** aResult) {
+  RefPtr<nsStorageStream> storageStream = new nsStorageStream();
+  nsresult rv = storageStream->Init(aSegmentSize, aMaxSize);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  storageStream.forget(aResult);
+  return NS_OK;
+}
+
+// Undefine LOG, so that other .cpp files (or their includes) won't complain
+// about it already being defined, when we build in unified mode.
+#undef LOG
diff --git a/xpcom/io/nsStorageStream.h b/xpcom/io/nsStorageStream.h
new file mode 100644
index 0000000000..78265b4c6b
--- /dev/null
+++ b/xpcom/io/nsStorageStream.h
@@ -0,0 +1,79 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * The storage stream provides an internal buffer that can be filled by a
+ * client using a single output stream.  One or more independent input streams
+ * can be created to read the data out non-destructively.  The implementation
+ * uses a segmented buffer internally to avoid realloc'ing of large buffers,
+ * with the attendant performance loss and heap fragmentation.
+ */
+
+#ifndef _nsStorageStream_h_
+#define _nsStorageStream_h_
+
+#include "nsIStorageStream.h"
+#include "nsIOutputStream.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Mutex.h"
+
+#define NS_STORAGESTREAM_CID                         \
+  { /* 669a9795-6ff7-4ed4-9150-c34ce2971b63 */       \
+    0x669a9795, 0x6ff7, 0x4ed4, {                    \
+      0x91, 0x50, 0xc3, 0x4c, 0xe2, 0x97, 0x1b, 0x63 \
+    }                                                \
+  }
+
+#define NS_STORAGESTREAM_CONTRACTID "@mozilla.org/storagestream;1"
+
+class nsSegmentedBuffer;
+
+class nsStorageStream final : public nsIStorageStream, public nsIOutputStream {
+ public:
+  nsStorageStream();
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSISTORAGESTREAM
+  NS_DECL_NSIOUTPUTSTREAM
+
+  friend class nsStorageInputStream;
+
+ private:
+  ~nsStorageStream();
+
+  mozilla::Mutex mMutex{"nsStorageStream"};
+  nsSegmentedBuffer* mSegmentedBuffer MOZ_GUARDED_BY(mMutex) = nullptr;
+  // All segments, except possibly the last, are of this size.  Must be
+  // power-of-2
+  uint32_t mSegmentSize MOZ_GUARDED_BY(mMutex) = 0;
+  // log2(mSegmentSize)
+  uint32_t mSegmentSizeLog2 MOZ_GUARDED_BY(mMutex) = 0;
+  // true, if an un-Close'ed output stream exists
+  bool mWriteInProgress MOZ_GUARDED_BY(mMutex) = false;
+  // Last segment # in use, -1 initially
+  int32_t mLastSegmentNum MOZ_GUARDED_BY(mMutex) = -1;
+  // Pointer to next byte to be written
+  char* mWriteCursor MOZ_GUARDED_BY(mMutex) = nullptr;
+  // Pointer to one byte after end of segment containing the write cursor
+  char* mSegmentEnd MOZ_GUARDED_BY(mMutex) = nullptr;
+  // Maximum number of bytes which may be written to the stream
+  uint32_t mMaxLogicalLength MOZ_GUARDED_BY(mMutex) = 0;
+  // Number of bytes written to stream
+  uint32_t mLogicalLength MOZ_GUARDED_BY(mMutex) = 0;
+  // number of input streams actively reading a segment.
+  uint32_t mActiveSegmentBorrows MOZ_GUARDED_BY(mMutex) = 0;
+
+  nsresult SetLengthLocked(uint32_t aLength) MOZ_REQUIRES(mMutex);
+  nsresult Seek(int32_t aPosition) MOZ_REQUIRES(mMutex);
+  uint32_t SegNum(uint32_t aPosition) MOZ_REQUIRES(mMutex) {
+    return aPosition >> mSegmentSizeLog2;
+  }
+  uint32_t SegOffset(uint32_t aPosition) MOZ_REQUIRES(mMutex) {
+    return aPosition & (mSegmentSize - 1);
+  }
+};
+
+#endif  //  _nsStorageStream_h_
diff --git a/xpcom/io/nsStreamUtils.cpp b/xpcom/io/nsStreamUtils.cpp
new file mode 100644
index 0000000000..94669b71dc
--- /dev/null
+++ b/xpcom/io/nsStreamUtils.cpp
@@ -0,0 +1,976 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/Mutex.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/InputStreamLengthWrapper.h"
+#include "nsIInputStreamLength.h"
+#include "nsStreamUtils.h"
+#include "nsCOMPtr.h"
+#include "nsICloneableInputStream.h"
+#include "nsIEventTarget.h"
+#include "nsICancelableRunnable.h"
+#include "nsISafeOutputStream.h"
+#include "nsString.h"
+#include "nsIAsyncInputStream.h"
+#include "nsIAsyncOutputStream.h"
+#include "nsIBufferedStreams.h"
+#include "nsIPipe.h"
+#include "nsNetCID.h"
+#include "nsServiceManagerUtils.h"
+#include "nsThreadUtils.h"
+#include "nsITransport.h"
+#include "nsIStreamTransportService.h"
+#include "NonBlockingAsyncInputStream.h"
+
+using namespace mozilla;
+
+static NS_DEFINE_CID(kStreamTransportServiceCID, NS_STREAMTRANSPORTSERVICE_CID);
+
+//-----------------------------------------------------------------------------
+
+// This is a nsICancelableRunnable because we can dispatch it to Workers and
+// those can be shut down at any time, and in these cases, Cancel() is called
+// instead of Run().
+class nsInputStreamReadyEvent final : public CancelableRunnable,
+                                      public nsIInputStreamCallback,
+                                      public nsIRunnablePriority {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+
+  nsInputStreamReadyEvent(const char* aName, nsIInputStreamCallback* aCallback,
+                          nsIEventTarget* aTarget, uint32_t aPriority)
+      : CancelableRunnable(aName),
+        mCallback(aCallback),
+        mTarget(aTarget),
+        mPriority(aPriority) {}
+
+ private:
+  ~nsInputStreamReadyEvent() {
+    if (!mCallback) {
+      return;
+    }
+    //
+    // whoa!!  looks like we never posted this event.  take care to
+    // release mCallback on the correct thread.  if mTarget lives on the
+    // calling thread, then we are ok.  otherwise, we have to try to
+    // proxy the Release over the right thread.  if that thread is dead,
+    // then there's nothing we can do... better to leak than crash.
+    //
+    bool val;
+    nsresult rv = mTarget->IsOnCurrentThread(&val);
+    if (NS_FAILED(rv) || !val) {
+      nsCOMPtr<nsIInputStreamCallback> event = NS_NewInputStreamReadyEvent(
+          "~nsInputStreamReadyEvent", mCallback, mTarget, mPriority);
+      mCallback = nullptr;
+      if (event) {
+        rv = event->OnInputStreamReady(nullptr);
+        if (NS_FAILED(rv)) {
+          MOZ_ASSERT_UNREACHABLE("leaking stream event");
+          nsISupports* sup = event;
+          NS_ADDREF(sup);
+        }
+      }
+    }
+  }
+
+ public:
+  NS_IMETHOD OnInputStreamReady(nsIAsyncInputStream* aStream) override {
+    mStream = aStream;
+
+    nsresult rv = mTarget->Dispatch(this, NS_DISPATCH_NORMAL);
+    if (NS_FAILED(rv)) {
+      NS_WARNING("Dispatch failed");
+      return NS_ERROR_FAILURE;
+    }
+
+    return NS_OK;
+  }
+
+  NS_IMETHOD Run() override {
+    if (mCallback) {
+      if (mStream) {
+        mCallback->OnInputStreamReady(mStream);
+      }
+      mCallback = nullptr;
+    }
+    return NS_OK;
+  }
+
+  nsresult Cancel() override {
+    mCallback = nullptr;
+    return NS_OK;
+  }
+
+  NS_IMETHOD GetPriority(uint32_t* aPriority) override {
+    *aPriority = mPriority;
+    return NS_OK;
+  }
+
+ private:
+  nsCOMPtr<nsIAsyncInputStream> mStream;
+  nsCOMPtr<nsIInputStreamCallback> mCallback;
+  nsCOMPtr<nsIEventTarget> mTarget;
+  uint32_t mPriority;
+};
+
+NS_IMPL_ISUPPORTS_INHERITED(nsInputStreamReadyEvent, CancelableRunnable,
+                            nsIInputStreamCallback, nsIRunnablePriority)
+
+//-----------------------------------------------------------------------------
+
+// This is a nsICancelableRunnable because we can dispatch it to Workers and
+// those can be shut down at any time, and in these cases, Cancel() is called
+// instead of Run().
+class nsOutputStreamReadyEvent final : public CancelableRunnable,
+                                       public nsIOutputStreamCallback {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+
+  nsOutputStreamReadyEvent(nsIOutputStreamCallback* aCallback,
+                           nsIEventTarget* aTarget)
+      : CancelableRunnable("nsOutputStreamReadyEvent"),
+        mCallback(aCallback),
+        mTarget(aTarget) {}
+
+ private:
+  ~nsOutputStreamReadyEvent() {
+    if (!mCallback) {
+      return;
+    }
+    //
+    // whoa!!  looks like we never posted this event.  take care to
+    // release mCallback on the correct thread.  if mTarget lives on the
+    // calling thread, then we are ok.  otherwise, we have to try to
+    // proxy the Release over the right thread.  if that thread is dead,
+    // then there's nothing we can do... better to leak than crash.
+    //
+    bool val;
+    nsresult rv = mTarget->IsOnCurrentThread(&val);
+    if (NS_FAILED(rv) || !val) {
+      nsCOMPtr<nsIOutputStreamCallback> event =
+          NS_NewOutputStreamReadyEvent(mCallback, mTarget);
+      mCallback = nullptr;
+      if (event) {
+        rv = event->OnOutputStreamReady(nullptr);
+        if (NS_FAILED(rv)) {
+          MOZ_ASSERT_UNREACHABLE("leaking stream event");
+          nsISupports* sup = event;
+          NS_ADDREF(sup);
+        }
+      }
+    }
+  }
+
+ public:
+  NS_IMETHOD OnOutputStreamReady(nsIAsyncOutputStream* aStream) override {
+    mStream = aStream;
+
+    nsresult rv = mTarget->Dispatch(this, NS_DISPATCH_NORMAL);
+    if (NS_FAILED(rv)) {
+      NS_WARNING("PostEvent failed");
+      return NS_ERROR_FAILURE;
+    }
+
+    return NS_OK;
+  }
+
+  NS_IMETHOD Run() override {
+    if (mCallback) {
+      if (mStream) {
+        mCallback->OnOutputStreamReady(mStream);
+      }
+      mCallback = nullptr;
+    }
+    return NS_OK;
+  }
+
+  nsresult Cancel() override {
+    mCallback = nullptr;
+    return NS_OK;
+  }
+
+ private:
+  nsCOMPtr<nsIAsyncOutputStream> mStream;
+  nsCOMPtr<nsIOutputStreamCallback> mCallback;
+  nsCOMPtr<nsIEventTarget> mTarget;
+};
+
+NS_IMPL_ISUPPORTS_INHERITED(nsOutputStreamReadyEvent, CancelableRunnable,
+                            nsIOutputStreamCallback)
+
+//-----------------------------------------------------------------------------
+
+already_AddRefed<nsIInputStreamCallback> NS_NewInputStreamReadyEvent(
+    const char* aName, nsIInputStreamCallback* aCallback,
+    nsIEventTarget* aTarget, uint32_t aPriority) {
+  NS_ASSERTION(aCallback, "null callback");
+  NS_ASSERTION(aTarget, "null target");
+  RefPtr<nsInputStreamReadyEvent> ev =
+      new nsInputStreamReadyEvent(aName, aCallback, aTarget, aPriority);
+  return ev.forget();
+}
+
+already_AddRefed<nsIOutputStreamCallback> NS_NewOutputStreamReadyEvent(
+    nsIOutputStreamCallback* aCallback, nsIEventTarget* aTarget) {
+  NS_ASSERTION(aCallback, "null callback");
+  NS_ASSERTION(aTarget, "null target");
+  RefPtr<nsOutputStreamReadyEvent> ev =
+      new nsOutputStreamReadyEvent(aCallback, aTarget);
+  return ev.forget();
+}
+
+//-----------------------------------------------------------------------------
+// NS_AsyncCopy implementation
+
+// abstract stream copier...
+class nsAStreamCopier : public nsIInputStreamCallback,
+                        public nsIOutputStreamCallback,
+                        public CancelableRunnable {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+
+  nsAStreamCopier()
+      : CancelableRunnable("nsAStreamCopier"),
+        mLock("nsAStreamCopier.mLock"),
+        mCallback(nullptr),
+        mProgressCallback(nullptr),
+        mClosure(nullptr),
+        mChunkSize(0),
+        mEventInProcess(false),
+        mEventIsPending(false),
+        mCloseSource(true),
+        mCloseSink(true),
+        mCanceled(false),
+        mCancelStatus(NS_OK) {}
+
+  // kick off the async copy...
+  nsresult Start(nsIInputStream* aSource, nsIOutputStream* aSink,
+                 nsIEventTarget* aTarget, nsAsyncCopyCallbackFun aCallback,
+                 void* aClosure, uint32_t aChunksize, bool aCloseSource,
+                 bool aCloseSink, nsAsyncCopyProgressFun aProgressCallback) {
+    mSource = aSource;
+    mSink = aSink;
+    mTarget = aTarget;
+    mCallback = aCallback;
+    mClosure = aClosure;
+    mChunkSize = aChunksize;
+    mCloseSource = aCloseSource;
+    mCloseSink = aCloseSink;
+    mProgressCallback = aProgressCallback;
+
+    mAsyncSource = do_QueryInterface(mSource);
+    mAsyncSink = do_QueryInterface(mSink);
+
+    return PostContinuationEvent();
+  }
+
+  // implemented by subclasses, returns number of bytes copied and
+  // sets source and sink condition before returning.
+  virtual uint32_t DoCopy(nsresult* aSourceCondition,
+                          nsresult* aSinkCondition) = 0;
+
+  void Process() {
+    if (!mSource || !mSink) {
+      return;
+    }
+
+    nsresult cancelStatus;
+    bool canceled;
+    {
+      MutexAutoLock lock(mLock);
+      canceled = mCanceled;
+      cancelStatus = mCancelStatus;
+    }
+
+    // If the copy was canceled before Process() was even called, then
+    // sourceCondition and sinkCondition should be set to error results to
+    // ensure we don't call Finish() on a canceled nsISafeOutputStream.
+    MOZ_ASSERT(NS_FAILED(cancelStatus) == canceled, "cancel needs an error");
+    nsresult sourceCondition = cancelStatus;
+    nsresult sinkCondition = cancelStatus;
+
+    // Copy data from the source to the sink until we hit failure or have
+    // copied all the data.
+    for (;;) {
+      // Note: copyFailed will be true if the source or the sink have
+      //       reported an error, or if we failed to write any bytes
+      //       because we have consumed all of our data.
+      bool copyFailed = false;
+      if (!canceled) {
+        uint32_t n = DoCopy(&sourceCondition, &sinkCondition);
+        if (n > 0 && mProgressCallback) {
+          mProgressCallback(mClosure, n);
+        }
+        copyFailed =
+            NS_FAILED(sourceCondition) || NS_FAILED(sinkCondition) || n == 0;
+
+        MutexAutoLock lock(mLock);
+        canceled = mCanceled;
+        cancelStatus = mCancelStatus;
+      }
+      if (copyFailed && !canceled) {
+        if (sourceCondition == NS_BASE_STREAM_WOULD_BLOCK && mAsyncSource) {
+          // need to wait for more data from source.  while waiting for
+          // more source data, be sure to observe failures on output end.
+          mAsyncSource->AsyncWait(this, 0, 0, nullptr);
+
+          if (mAsyncSink) {
+            mAsyncSink->AsyncWait(this, nsIAsyncOutputStream::WAIT_CLOSURE_ONLY,
+                                  0, nullptr);
+          }
+          break;
+        }
+        if (sinkCondition == NS_BASE_STREAM_WOULD_BLOCK && mAsyncSink) {
+          // need to wait for more room in the sink.  while waiting for
+          // more room in the sink, be sure to observer failures on the
+          // input end.
+          mAsyncSink->AsyncWait(this, 0, 0, nullptr);
+
+          if (mAsyncSource) {
+            mAsyncSource->AsyncWait(
+                this, nsIAsyncInputStream::WAIT_CLOSURE_ONLY, 0, nullptr);
+          }
+          break;
+        }
+      }
+      if (copyFailed || canceled) {
+        if (mAsyncSource) {
+          // cancel any previously-registered AsyncWait callbacks to avoid leaks
+          mAsyncSource->AsyncWait(nullptr, 0, 0, nullptr);
+        }
+        if (mCloseSource) {
+          // close source
+          if (mAsyncSource) {
+            mAsyncSource->CloseWithStatus(canceled ? cancelStatus
+                                                   : sinkCondition);
+          } else {
+            mSource->Close();
+          }
+        }
+        mAsyncSource = nullptr;
+        mSource = nullptr;
+
+        if (mAsyncSink) {
+          // cancel any previously-registered AsyncWait callbacks to avoid leaks
+          mAsyncSink->AsyncWait(nullptr, 0, 0, nullptr);
+        }
+        if (mCloseSink) {
+          // close sink
+          if (mAsyncSink) {
+            mAsyncSink->CloseWithStatus(canceled ? cancelStatus
+                                                 : sourceCondition);
+          } else {
+            // If we have an nsISafeOutputStream, and our
+            // sourceCondition and sinkCondition are not set to a
+            // failure state, finish writing.
+            nsCOMPtr<nsISafeOutputStream> sostream = do_QueryInterface(mSink);
+            if (sostream && NS_SUCCEEDED(sourceCondition) &&
+                NS_SUCCEEDED(sinkCondition)) {
+              sostream->Finish();
+            } else {
+              mSink->Close();
+            }
+          }
+        }
+        mAsyncSink = nullptr;
+        mSink = nullptr;
+
+        // notify state complete...
+        if (mCallback) {
+          nsresult status;
+          if (!canceled) {
+            status = sourceCondition;
+            if (NS_SUCCEEDED(status)) {
+              status = sinkCondition;
+            }
+            if (status == NS_BASE_STREAM_CLOSED) {
+              status = NS_OK;
+            }
+          } else {
+            status = cancelStatus;
+          }
+          mCallback(mClosure, status);
+        }
+        break;
+      }
+    }
+  }
+
+  nsresult Cancel(nsresult aReason) {
+    MutexAutoLock lock(mLock);
+    if (mCanceled) {
+      return NS_ERROR_FAILURE;
+    }
+
+    if (NS_SUCCEEDED(aReason)) {
+      NS_WARNING("cancel with non-failure status code");
+      aReason = NS_BASE_STREAM_CLOSED;
+    }
+
+    mCanceled = true;
+    mCancelStatus = aReason;
+    return NS_OK;
+  }
+
+  NS_IMETHOD OnInputStreamReady(nsIAsyncInputStream* aSource) override {
+    PostContinuationEvent();
+    return NS_OK;
+  }
+
+  NS_IMETHOD OnOutputStreamReady(nsIAsyncOutputStream* aSink) override {
+    PostContinuationEvent();
+    return NS_OK;
+  }
+
+  // continuation event handler
+  NS_IMETHOD Run() override {
+    Process();
+
+    // clear "in process" flag and post any pending continuation event
+    MutexAutoLock lock(mLock);
+    mEventInProcess = false;
+    if (mEventIsPending) {
+      mEventIsPending = false;
+      PostContinuationEvent_Locked();
+    }
+
+    return NS_OK;
+  }
+
+  nsresult Cancel() MOZ_MUST_OVERRIDE override = 0;
+
+  nsresult PostContinuationEvent() {
+    // we cannot post a continuation event if there is currently
+    // an event in process.  doing so could result in Process being
+    // run simultaneously on multiple threads, so we mark the event
+    // as pending, and if an event is already in process then we
+    // just let that existing event take care of posting the real
+    // continuation event.
+
+    MutexAutoLock lock(mLock);
+    return PostContinuationEvent_Locked();
+  }
+
+  nsresult PostContinuationEvent_Locked() MOZ_REQUIRES(mLock) {
+    nsresult rv = NS_OK;
+    if (mEventInProcess) {
+      mEventIsPending = true;
+    } else {
+      rv = mTarget->Dispatch(this, NS_DISPATCH_NORMAL);
+      if (NS_SUCCEEDED(rv)) {
+        mEventInProcess = true;
+      } else {
+        NS_WARNING("unable to post continuation event");
+      }
+    }
+    return rv;
+  }
+
+ protected:
+  nsCOMPtr<nsIInputStream> mSource;
+  nsCOMPtr<nsIOutputStream> mSink;
+  nsCOMPtr<nsIAsyncInputStream> mAsyncSource;
+  nsCOMPtr<nsIAsyncOutputStream> mAsyncSink;
+  nsCOMPtr<nsIEventTarget> mTarget;
+  Mutex mLock;
+  nsAsyncCopyCallbackFun mCallback;
+  nsAsyncCopyProgressFun mProgressCallback;
+  void* mClosure;
+  uint32_t mChunkSize;
+  bool mEventInProcess MOZ_GUARDED_BY(mLock);
+  bool mEventIsPending MOZ_GUARDED_BY(mLock);
+  bool mCloseSource;
+  bool mCloseSink;
+  bool mCanceled MOZ_GUARDED_BY(mLock);
+  nsresult mCancelStatus MOZ_GUARDED_BY(mLock);
+
+  // virtual since subclasses call superclass Release()
+  virtual ~nsAStreamCopier() = default;
+};
+
+NS_IMPL_ISUPPORTS_INHERITED(nsAStreamCopier, CancelableRunnable,
+                            nsIInputStreamCallback, nsIOutputStreamCallback)
+
+class nsStreamCopierIB final : public nsAStreamCopier {
+ public:
+  nsStreamCopierIB() : nsAStreamCopier() {}
+  virtual ~nsStreamCopierIB() = default;
+
+  struct MOZ_STACK_CLASS ReadSegmentsState {
+    // the nsIOutputStream will outlive the ReadSegmentsState on the stack
+    nsIOutputStream* MOZ_NON_OWNING_REF mSink;
+    nsresult mSinkCondition;
+  };
+
+  static nsresult ConsumeInputBuffer(nsIInputStream* aInStr, void* aClosure,
+                                     const char* aBuffer, uint32_t aOffset,
+                                     uint32_t aCount, uint32_t* aCountWritten) {
+    ReadSegmentsState* state = (ReadSegmentsState*)aClosure;
+
+    nsresult rv = state->mSink->Write(aBuffer, aCount, aCountWritten);
+    if (NS_FAILED(rv)) {
+      state->mSinkCondition = rv;
+    } else if (*aCountWritten == 0) {
+      state->mSinkCondition = NS_BASE_STREAM_CLOSED;
+    }
+
+    return state->mSinkCondition;
+  }
+
+  uint32_t DoCopy(nsresult* aSourceCondition,
+                  nsresult* aSinkCondition) override {
+    ReadSegmentsState state;
+    state.mSink = mSink;
+    state.mSinkCondition = NS_OK;
+
+    uint32_t n;
+    *aSourceCondition =
+        mSource->ReadSegments(ConsumeInputBuffer, &state, mChunkSize, &n);
+    *aSinkCondition = NS_SUCCEEDED(state.mSinkCondition) && n == 0
+                          ? mSink->StreamStatus()
+                          : state.mSinkCondition;
+    return n;
+  }
+
+  nsresult Cancel() override { return NS_OK; }
+};
+
+class nsStreamCopierOB final : public nsAStreamCopier {
+ public:
+  nsStreamCopierOB() : nsAStreamCopier() {}
+  virtual ~nsStreamCopierOB() = default;
+
+  struct MOZ_STACK_CLASS WriteSegmentsState {
+    // the nsIInputStream will outlive the WriteSegmentsState on the stack
+    nsIInputStream* MOZ_NON_OWNING_REF mSource;
+    nsresult mSourceCondition;
+  };
+
+  static nsresult FillOutputBuffer(nsIOutputStream* aOutStr, void* aClosure,
+                                   char* aBuffer, uint32_t aOffset,
+                                   uint32_t aCount, uint32_t* aCountRead) {
+    WriteSegmentsState* state = (WriteSegmentsState*)aClosure;
+
+    nsresult rv = state->mSource->Read(aBuffer, aCount, aCountRead);
+    if (NS_FAILED(rv)) {
+      state->mSourceCondition = rv;
+    } else if (*aCountRead == 0) {
+      state->mSourceCondition = NS_BASE_STREAM_CLOSED;
+    }
+
+    return state->mSourceCondition;
+  }
+
+  uint32_t DoCopy(nsresult* aSourceCondition,
+                  nsresult* aSinkCondition) override {
+    WriteSegmentsState state;
+    state.mSource = mSource;
+    state.mSourceCondition = NS_OK;
+
+    uint32_t n;
+    *aSinkCondition =
+        mSink->WriteSegments(FillOutputBuffer, &state, mChunkSize, &n);
+    *aSourceCondition = NS_SUCCEEDED(state.mSourceCondition) && n == 0
+                            ? mSource->StreamStatus()
+                            : state.mSourceCondition;
+    return n;
+  }
+
+  nsresult Cancel() override { return NS_OK; }
+};
+
+//-----------------------------------------------------------------------------
+
+nsresult NS_AsyncCopy(nsIInputStream* aSource, nsIOutputStream* aSink,
+                      nsIEventTarget* aTarget, nsAsyncCopyMode aMode,
+                      uint32_t aChunkSize, nsAsyncCopyCallbackFun aCallback,
+                      void* aClosure, bool aCloseSource, bool aCloseSink,
+                      nsISupports** aCopierCtx,
+                      nsAsyncCopyProgressFun aProgressCallback) {
+  NS_ASSERTION(aTarget, "non-null target required");
+
+  nsresult rv;
+  nsAStreamCopier* copier;
+
+  if (aMode == NS_ASYNCCOPY_VIA_READSEGMENTS) {
+    copier = new nsStreamCopierIB();
+  } else {
+    copier = new nsStreamCopierOB();
+  }
+
+  // Start() takes an owning ref to the copier...
+  NS_ADDREF(copier);
+  rv = copier->Start(aSource, aSink, aTarget, aCallback, aClosure, aChunkSize,
+                     aCloseSource, aCloseSink, aProgressCallback);
+
+  if (aCopierCtx) {
+    *aCopierCtx = static_cast<nsISupports*>(static_cast<nsIRunnable*>(copier));
+    NS_ADDREF(*aCopierCtx);
+  }
+  NS_RELEASE(copier);
+
+  return rv;
+}
+
+//-----------------------------------------------------------------------------
+
+nsresult NS_CancelAsyncCopy(nsISupports* aCopierCtx, nsresult aReason) {
+  nsAStreamCopier* copier =
+      static_cast<nsAStreamCopier*>(static_cast<nsIRunnable*>(aCopierCtx));
+  return copier->Cancel(aReason);
+}
+
+//-----------------------------------------------------------------------------
+
+namespace {
+template <typename T>
+struct ResultTraits {};
+
+template <>
+struct ResultTraits<nsACString> {
+  static void Clear(nsACString& aString) { aString.Truncate(); }
+
+  static char* GetStorage(nsACString& aString) {
+    return aString.BeginWriting();
+  }
+};
+
+template <>
+struct ResultTraits<nsTArray<uint8_t>> {
+  static void Clear(nsTArray<uint8_t>& aArray) { aArray.Clear(); }
+
+  static char* GetStorage(nsTArray<uint8_t>& aArray) {
+    return reinterpret_cast<char*>(aArray.Elements());
+  }
+};
+}  // namespace
+
+template <typename T>
+nsresult DoConsumeStream(nsIInputStream* aStream, uint32_t aMaxCount,
+                         T& aResult) {
+  nsresult rv = NS_OK;
+  ResultTraits<T>::Clear(aResult);
+
+  while (aMaxCount) {
+    uint64_t avail64;
+    rv = aStream->Available(&avail64);
+    if (NS_FAILED(rv)) {
+      if (rv == NS_BASE_STREAM_CLOSED) {
+        rv = NS_OK;
+      }
+      break;
+    }
+    if (avail64 == 0) {
+      break;
+    }
+
+    uint32_t avail = (uint32_t)XPCOM_MIN<uint64_t>(avail64, aMaxCount);
+
+    // resize aResult buffer
+    uint32_t length = aResult.Length();
+    CheckedInt<uint32_t> newLength = CheckedInt<uint32_t>(length) + avail;
+    if (!newLength.isValid()) {
+      return NS_ERROR_FILE_TOO_BIG;
+    }
+
+    if (!aResult.SetLength(newLength.value(), fallible)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    char* buf = ResultTraits<T>::GetStorage(aResult) + length;
+
+    uint32_t n;
+    rv = aStream->Read(buf, avail, &n);
+    if (NS_FAILED(rv)) {
+      break;
+    }
+    if (n != avail) {
+      MOZ_ASSERT(n < avail, "What happened there???");
+      aResult.SetLength(length + n);
+    }
+    if (n == 0) {
+      break;
+    }
+    aMaxCount -= n;
+  }
+
+  return rv;
+}
+
+nsresult NS_ConsumeStream(nsIInputStream* aStream, uint32_t aMaxCount,
+                          nsACString& aResult) {
+  return DoConsumeStream(aStream, aMaxCount, aResult);
+}
+
+nsresult NS_ConsumeStream(nsIInputStream* aStream, uint32_t aMaxCount,
+                          nsTArray<uint8_t>& aResult) {
+  return DoConsumeStream(aStream, aMaxCount, aResult);
+}
+
+//-----------------------------------------------------------------------------
+
+static nsresult TestInputStream(nsIInputStream* aInStr, void* aClosure,
+                                const char* aBuffer, uint32_t aOffset,
+                                uint32_t aCount, uint32_t* aCountWritten) {
+  bool* result = static_cast<bool*>(aClosure);
+  *result = true;
+  *aCountWritten = 0;
+  return NS_ERROR_ABORT;  // don't call me anymore
+}
+
+bool NS_InputStreamIsBuffered(nsIInputStream* aStream) {
+  nsCOMPtr<nsIBufferedInputStream> bufferedIn = do_QueryInterface(aStream);
+  if (bufferedIn) {
+    return true;
+  }
+
+  bool result = false;
+  uint32_t n;
+  nsresult rv = aStream->ReadSegments(TestInputStream, &result, 1, &n);
+  return result || rv != NS_ERROR_NOT_IMPLEMENTED;
+}
+
+static nsresult TestOutputStream(nsIOutputStream* aOutStr, void* aClosure,
+                                 char* aBuffer, uint32_t aOffset,
+                                 uint32_t aCount, uint32_t* aCountRead) {
+  bool* result = static_cast<bool*>(aClosure);
+  *result = true;
+  *aCountRead = 0;
+  return NS_ERROR_ABORT;  // don't call me anymore
+}
+
+bool NS_OutputStreamIsBuffered(nsIOutputStream* aStream) {
+  nsCOMPtr<nsIBufferedOutputStream> bufferedOut = do_QueryInterface(aStream);
+  if (bufferedOut) {
+    return true;
+  }
+
+  bool result = false;
+  uint32_t n;
+  aStream->WriteSegments(TestOutputStream, &result, 1, &n);
+  return result;
+}
+
+//-----------------------------------------------------------------------------
+
+nsresult NS_CopySegmentToStream(nsIInputStream* aInStr, void* aClosure,
+                                const char* aBuffer, uint32_t aOffset,
+                                uint32_t aCount, uint32_t* aCountWritten) {
+  nsIOutputStream* outStr = static_cast<nsIOutputStream*>(aClosure);
+  *aCountWritten = 0;
+  while (aCount) {
+    uint32_t n;
+    nsresult rv = outStr->Write(aBuffer, aCount, &n);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+    aBuffer += n;
+    aCount -= n;
+    *aCountWritten += n;
+  }
+  return NS_OK;
+}
+
+nsresult NS_CopySegmentToBuffer(nsIInputStream* aInStr, void* aClosure,
+                                const char* aBuffer, uint32_t aOffset,
+                                uint32_t aCount, uint32_t* aCountWritten) {
+  char* toBuf = static_cast<char*>(aClosure);
+  memcpy(&toBuf[aOffset], aBuffer, aCount);
+  *aCountWritten = aCount;
+  return NS_OK;
+}
+
+nsresult NS_CopyBufferToSegment(nsIOutputStream* aOutStr, void* aClosure,
+                                char* aBuffer, uint32_t aOffset,
+                                uint32_t aCount, uint32_t* aCountRead) {
+  const char* fromBuf = static_cast<const char*>(aClosure);
+  memcpy(aBuffer, &fromBuf[aOffset], aCount);
+  *aCountRead = aCount;
+  return NS_OK;
+}
+
+nsresult NS_CopyStreamToSegment(nsIOutputStream* aOutputStream, void* aClosure,
+                                char* aToSegment, uint32_t aFromOffset,
+                                uint32_t aCount, uint32_t* aReadCount) {
+  nsIInputStream* fromStream = static_cast<nsIInputStream*>(aClosure);
+  return fromStream->Read(aToSegment, aCount, aReadCount);
+}
+
+nsresult NS_DiscardSegment(nsIInputStream* aInStr, void* aClosure,
+                           const char* aBuffer, uint32_t aOffset,
+                           uint32_t aCount, uint32_t* aCountWritten) {
+  *aCountWritten = aCount;
+  return NS_OK;
+}
+
+//-----------------------------------------------------------------------------
+
+nsresult NS_WriteSegmentThunk(nsIInputStream* aInStr, void* aClosure,
+                              const char* aBuffer, uint32_t aOffset,
+                              uint32_t aCount, uint32_t* aCountWritten) {
+  nsWriteSegmentThunk* thunk = static_cast<nsWriteSegmentThunk*>(aClosure);
+  return thunk->mFun(thunk->mStream, thunk->mClosure, aBuffer, aOffset, aCount,
+                     aCountWritten);
+}
+
+nsresult NS_FillArray(FallibleTArray<char>& aDest, nsIInputStream* aInput,
+                      uint32_t aKeep, uint32_t* aNewBytes) {
+  MOZ_ASSERT(aInput, "null stream");
+  MOZ_ASSERT(aKeep <= aDest.Length(), "illegal keep count");
+
+  char* aBuffer = aDest.Elements();
+  int64_t keepOffset = int64_t(aDest.Length()) - aKeep;
+  if (aKeep != 0 && keepOffset > 0) {
+    memmove(aBuffer, aBuffer + keepOffset, aKeep);
+  }
+
+  nsresult rv =
+      aInput->Read(aBuffer + aKeep, aDest.Capacity() - aKeep, aNewBytes);
+  if (NS_FAILED(rv)) {
+    *aNewBytes = 0;
+  }
+  // NOTE: we rely on the fact that the new slots are NOT initialized by
+  // SetLengthAndRetainStorage here, see nsTArrayElementTraits::Construct()
+  // in nsTArray.h:
+  aDest.SetLengthAndRetainStorage(aKeep + *aNewBytes);
+
+  MOZ_ASSERT(aDest.Length() <= aDest.Capacity(), "buffer overflow");
+  return rv;
+}
+
+bool NS_InputStreamIsCloneable(nsIInputStream* aSource) {
+  if (!aSource) {
+    return false;
+  }
+
+  nsCOMPtr<nsICloneableInputStream> cloneable = do_QueryInterface(aSource);
+  return cloneable && cloneable->GetCloneable();
+}
+
+nsresult NS_CloneInputStream(nsIInputStream* aSource,
+                             nsIInputStream** aCloneOut,
+                             nsIInputStream** aReplacementOut) {
+  if (NS_WARN_IF(!aSource)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Attempt to perform the clone directly on the source stream
+  nsCOMPtr<nsICloneableInputStream> cloneable = do_QueryInterface(aSource);
+  if (cloneable && cloneable->GetCloneable()) {
+    if (aReplacementOut) {
+      *aReplacementOut = nullptr;
+    }
+    return cloneable->Clone(aCloneOut);
+  }
+
+  // If we failed the clone and the caller does not want to replace their
+  // original stream, then we are done.  Return error.
+  if (!aReplacementOut) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // The caller has opted-in to the fallback clone support that replaces
+  // the original stream.  Copy the data to a pipe and return two cloned
+  // input streams.
+
+  nsCOMPtr<nsIInputStream> reader;
+  nsCOMPtr<nsIInputStream> readerClone;
+  nsCOMPtr<nsIOutputStream> writer;
+
+  NS_NewPipe(getter_AddRefs(reader), getter_AddRefs(writer), 0,
+             0,            // default segment size and max size
+             true, true);  // non-blocking
+
+  // Propagate length information provided by nsIInputStreamLength. We don't use
+  // InputStreamLengthHelper::GetSyncLength to avoid the risk of blocking when
+  // called off-main-thread.
+  int64_t length = -1;
+  if (nsCOMPtr<nsIInputStreamLength> streamLength = do_QueryInterface(aSource);
+      streamLength && NS_SUCCEEDED(streamLength->Length(&length)) &&
+      length != -1) {
+    reader = new mozilla::InputStreamLengthWrapper(reader.forget(), length);
+  }
+
+  cloneable = do_QueryInterface(reader);
+  MOZ_ASSERT(cloneable && cloneable->GetCloneable());
+
+  nsresult rv = cloneable->Clone(getter_AddRefs(readerClone));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsCOMPtr<nsIEventTarget> target =
+      do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID, &rv);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = NS_AsyncCopy(aSource, writer, target, NS_ASYNCCOPY_VIA_WRITESEGMENTS);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  readerClone.forget(aCloneOut);
+  reader.forget(aReplacementOut);
+
+  return NS_OK;
+}
+
+nsresult NS_MakeAsyncNonBlockingInputStream(
+    already_AddRefed<nsIInputStream> aSource,
+    nsIAsyncInputStream** aAsyncInputStream, bool aCloseWhenDone,
+    uint32_t aFlags, uint32_t aSegmentSize, uint32_t aSegmentCount) {
+  nsCOMPtr<nsIInputStream> source = std::move(aSource);
+  if (NS_WARN_IF(!aAsyncInputStream)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  bool nonBlocking = false;
+  nsresult rv = source->IsNonBlocking(&nonBlocking);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsCOMPtr<nsIAsyncInputStream> asyncStream = do_QueryInterface(source);
+
+  if (nonBlocking && asyncStream) {
+    // This stream is perfect!
+    asyncStream.forget(aAsyncInputStream);
+    return NS_OK;
+  }
+
+  if (nonBlocking) {
+    // If the stream is non-blocking but not async, we wrap it.
+    return NonBlockingAsyncInputStream::Create(source.forget(),
+                                               aAsyncInputStream);
+  }
+
+  nsCOMPtr<nsIStreamTransportService> sts =
+      do_GetService(kStreamTransportServiceCID, &rv);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsCOMPtr<nsITransport> transport;
+  rv = sts->CreateInputTransport(source, aCloseWhenDone,
+                                 getter_AddRefs(transport));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsCOMPtr<nsIInputStream> wrapper;
+  rv = transport->OpenInputStream(aFlags, aSegmentSize, aSegmentCount,
+                                  getter_AddRefs(wrapper));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  asyncStream = do_QueryInterface(wrapper);
+  MOZ_ASSERT(asyncStream);
+
+  asyncStream.forget(aAsyncInputStream);
+  return NS_OK;
+}
diff --git a/xpcom/io/nsStreamUtils.h b/xpcom/io/nsStreamUtils.h
new file mode 100644
index 0000000000..f274d9134a
--- /dev/null
+++ b/xpcom/io/nsStreamUtils.h
@@ -0,0 +1,332 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsStreamUtils_h__
+#define nsStreamUtils_h__
+
+#include "nsCOMPtr.h"
+#include "nsStringFwd.h"
+#include "nsIInputStream.h"
+#include "nsTArray.h"
+#include "nsIRunnable.h"
+
+class nsIAsyncInputStream;
+class nsIOutputStream;
+class nsIInputStreamCallback;
+class nsIOutputStreamCallback;
+class nsIEventTarget;
+
+/**
+ * A "one-shot" proxy of the OnInputStreamReady callback.  The resulting
+ * proxy object's OnInputStreamReady function may only be called once!  The
+ * proxy object ensures that the real notify object will be free'd on the
+ * thread corresponding to the given event target regardless of what thread
+ * the proxy object is destroyed on.
+ *
+ * This function is designed to be used to implement AsyncWait when the
+ * aTarget parameter is non-null.
+ *
+ * The optional aPriority parameter allows the input stream runnable events
+ * to be dispatched with a different priority than normal.
+ */
+extern already_AddRefed<nsIInputStreamCallback> NS_NewInputStreamReadyEvent(
+    const char* aName, nsIInputStreamCallback* aNotify, nsIEventTarget* aTarget,
+    uint32_t aPriority = nsIRunnablePriority::PRIORITY_NORMAL);
+
+/**
+ * A "one-shot" proxy of the OnOutputStreamReady callback.  The resulting
+ * proxy object's OnOutputStreamReady function may only be called once!  The
+ * proxy object ensures that the real notify object will be free'd on the
+ * thread corresponding to the given event target regardless of what thread
+ * the proxy object is destroyed on.
+ *
+ * This function is designed to be used to implement AsyncWait when the
+ * aTarget parameter is non-null.
+ */
+extern already_AddRefed<nsIOutputStreamCallback> NS_NewOutputStreamReadyEvent(
+    nsIOutputStreamCallback* aNotify, nsIEventTarget* aTarget);
+
+/* ------------------------------------------------------------------------- */
+
+enum nsAsyncCopyMode {
+  NS_ASYNCCOPY_VIA_READSEGMENTS,
+  NS_ASYNCCOPY_VIA_WRITESEGMENTS
+};
+
+/**
+ * This function is called when a new chunk of data has been copied.  The
+ * reported count is the size of the current chunk.
+ */
+typedef void (*nsAsyncCopyProgressFun)(void* closure, uint32_t count);
+
+/**
+ * This function is called when the async copy process completes.  The reported
+ * status is NS_OK on success and some error code on failure.
+ */
+typedef void (*nsAsyncCopyCallbackFun)(void* closure, nsresult status);
+
+/**
+ * This function asynchronously copies data from the source to the sink. All
+ * data transfer occurs on the thread corresponding to the given event target.
+ * A null event target is not permitted.
+ *
+ * The copier handles blocking or non-blocking streams transparently.  If a
+ * stream operation returns NS_BASE_STREAM_WOULD_BLOCK, then the stream will
+ * be QI'd to nsIAsync{In,Out}putStream and its AsyncWait method will be used
+ * to determine when to resume copying.
+ *
+ * Source and sink are closed by default when copying finishes or when error
+ * occurs. Caller can prevent closing source or sink by setting aCloseSource
+ * or aCloseSink to false.
+ *
+ * Caller can obtain aCopierCtx to be able to cancel copying.
+ */
+extern nsresult NS_AsyncCopy(
+    nsIInputStream* aSource, nsIOutputStream* aSink, nsIEventTarget* aTarget,
+    nsAsyncCopyMode aMode = NS_ASYNCCOPY_VIA_READSEGMENTS,
+    uint32_t aChunkSize = 4096, nsAsyncCopyCallbackFun aCallbackFun = nullptr,
+    void* aCallbackClosure = nullptr, bool aCloseSource = true,
+    bool aCloseSink = true, nsISupports** aCopierCtx = nullptr,
+    nsAsyncCopyProgressFun aProgressCallbackFun = nullptr);
+
+/**
+ * This function cancels copying started by function NS_AsyncCopy.
+ *
+ * @param aCopierCtx
+ *        Copier context returned by NS_AsyncCopy.
+ * @param aReason
+ *        A failure code indicating why the operation is being canceled.
+ *        It is an error to pass a success code.
+ */
+extern nsresult NS_CancelAsyncCopy(nsISupports* aCopierCtx, nsresult aReason);
+
+/**
+ * This function copies all of the available data from the stream (up to at
+ * most aMaxCount bytes) into the given buffer.  The buffer is truncated at
+ * the start of the function.
+ *
+ * If an error occurs while reading from the stream or while attempting to
+ * resize the buffer, then the corresponding error code is returned from this
+ * function, and any data that has already been read will be returned in the
+ * output buffer.  This allows one to use this function with a non-blocking
+ * input stream that may return NS_BASE_STREAM_WOULD_BLOCK if it only has
+ * partial data available.
+ *
+ * @param aSource
+ *        The input stream to read.
+ * @param aMaxCount
+ *        The maximum number of bytes to consume from the stream.  Pass the
+ *        value UINT32_MAX to consume the entire stream.  The number of
+ *        bytes actually read is given by the length of aBuffer upon return.
+ * @param aBuffer
+ *        The string object that will contain the stream data upon return.
+ *        Note: The data copied to the string may contain null bytes and may
+ *        contain non-ASCII values.
+ */
+extern nsresult NS_ConsumeStream(nsIInputStream* aSource, uint32_t aMaxCount,
+                                 nsACString& aBuffer);
+
+/**
+ * Just like the above, but consumes into an nsTArray<uint8_t>.
+ */
+extern nsresult NS_ConsumeStream(nsIInputStream* aSource, uint32_t aMaxCount,
+                                 nsTArray<uint8_t>& aBuffer);
+
+/**
+ * This function tests whether or not the input stream is buffered. A buffered
+ * input stream is one that implements readSegments.  The test for this is to
+ * 1/ check whether the input stream implements nsIBufferedInputStream;
+ * 2/ if not, call readSegments, without actually consuming any data from the
+ * stream, to verify that it functions.
+ *
+ * NOTE: If the stream is non-blocking and has no data available yet, then this
+ * test will fail.  In that case, we return false even though the test is not
+ * really conclusive.
+ *
+ * PERFORMANCE NOTE: If the stream does not implement nsIBufferedInputStream,
+ * calling readSegments may cause I/O. Therefore, you should avoid calling
+ * this function from the main thread.
+ *
+ * @param aInputStream
+ *        The input stream to test.
+ */
+extern bool NS_InputStreamIsBuffered(nsIInputStream* aInputStream);
+
+/**
+ * This function tests whether or not the output stream is buffered.  A
+ * buffered output stream is one that implements writeSegments.  The test for
+ * this is to:
+ * 1/ check whether the output stream implements nsIBufferedOutputStream;
+ * 2/ if not, call writeSegments, without actually writing any data into
+ * the stream, to verify that it functions.
+ *
+ * NOTE: If the stream is non-blocking and has no available space yet, then
+ * this test will fail.  In that case, we return false even though the test is
+ * not really conclusive.
+ *
+ * PERFORMANCE NOTE: If the stream does not implement nsIBufferedOutputStream,
+ * calling writeSegments may cause I/O. Therefore, you should avoid calling
+ * this function from the main thread.
+ *
+ * @param aOutputStream
+ *        The output stream to test.
+ */
+extern bool NS_OutputStreamIsBuffered(nsIOutputStream* aOutputStream);
+
+/**
+ * This function is intended to be passed to nsIInputStream::ReadSegments to
+ * copy data from the nsIInputStream into a nsIOutputStream passed as the
+ * aClosure parameter to the ReadSegments function.
+ *
+ * @see nsIInputStream.idl for a description of this function's parameters.
+ */
+extern nsresult NS_CopySegmentToStream(nsIInputStream* aInputStream,
+                                       void* aClosure, const char* aFromSegment,
+                                       uint32_t aToOffset, uint32_t aCount,
+                                       uint32_t* aWriteCount);
+
+/**
+ * This function is intended to be passed to nsIInputStream::ReadSegments to
+ * copy data from the nsIInputStream into a character buffer passed as the
+ * aClosure parameter to the ReadSegments function.  The character buffer
+ * must be at least as large as the aCount parameter passed to ReadSegments.
+ *
+ * @see nsIInputStream.idl for a description of this function's parameters.
+ */
+extern nsresult NS_CopySegmentToBuffer(nsIInputStream* aInputStream,
+                                       void* aClosure, const char* aFromSegment,
+                                       uint32_t aToOffset, uint32_t aCount,
+                                       uint32_t* aWriteCount);
+
+/**
+ * This function is intended to be passed to nsIOutputStream::WriteSegments to
+ * copy data into the nsIOutputStream from a character buffer passed as the
+ * aClosure parameter to the WriteSegments function.
+ *
+ * @see nsIOutputStream.idl for a description of this function's parameters.
+ */
+extern nsresult NS_CopyBufferToSegment(nsIOutputStream* aOutputStream,
+                                       void* aClosure, char* aToSegment,
+                                       uint32_t aFromOffset, uint32_t aCount,
+                                       uint32_t* aReadCount);
+
+/**
+ * This function is intended to be passed to nsIOutputStream::WriteSegments to
+ * copy data into the nsIOutputStream from a nsIInputStream passed as the
+ * aClosure parameter to the WriteSegments function.
+ *
+ * @see nsIOutputStream.idl for a description of this function's parameters.
+ */
+extern nsresult NS_CopyStreamToSegment(nsIOutputStream* aOutputStream,
+                                       void* aClosure, char* aToSegment,
+                                       uint32_t aFromOffset, uint32_t aCount,
+                                       uint32_t* aReadCount);
+
+/**
+ * This function is intended to be passed to nsIInputStream::ReadSegments to
+ * discard data from the nsIInputStream.  This can be used to efficiently read
+ * data from the stream without actually copying any bytes.
+ *
+ * @see nsIInputStream.idl for a description of this function's parameters.
+ */
+extern nsresult NS_DiscardSegment(nsIInputStream* aInputStream, void* aClosure,
+                                  const char* aFromSegment, uint32_t aToOffset,
+                                  uint32_t aCount, uint32_t* aWriteCount);
+
+/**
+ * This function is intended to be passed to nsIInputStream::ReadSegments to
+ * adjust the aInputStream parameter passed to a consumer's WriteSegmentFun.
+ * The aClosure parameter must be a pointer to a nsWriteSegmentThunk object.
+ * The mStream and mClosure members of that object will be passed to the mFun
+ * function, with the remainder of the parameters being what are passed to
+ * NS_WriteSegmentThunk.
+ *
+ * This function comes in handy when implementing ReadSegments in terms of an
+ * inner stream's ReadSegments.
+ */
+extern nsresult NS_WriteSegmentThunk(nsIInputStream* aInputStream,
+                                     void* aClosure, const char* aFromSegment,
+                                     uint32_t aToOffset, uint32_t aCount,
+                                     uint32_t* aWriteCount);
+
+struct MOZ_STACK_CLASS nsWriteSegmentThunk {
+  nsCOMPtr<nsIInputStream> mStream;
+  nsWriteSegmentFun mFun;
+  void* mClosure;
+};
+
+/**
+ * Read data from aInput and store in aDest.  A non-zero aKeep will keep that
+ * many bytes from aDest (from the end).  New data is appended after the kept
+ * bytes (if any).  aDest's new length on returning from this function is
+ * aKeep + aNewBytes and is guaranteed to be less than or equal to aDest's
+ * current capacity.
+ * @param aDest the array to fill
+ * @param aInput the stream to read from
+ * @param aKeep number of bytes to keep (0 <= aKeep <= aDest.Length())
+ * @param aNewBytes (out) number of bytes read from aInput or zero if Read()
+ *        failed
+ * @return the result from aInput->Read(...)
+ */
+extern nsresult NS_FillArray(FallibleTArray<char>& aDest,
+                             nsIInputStream* aInput, uint32_t aKeep,
+                             uint32_t* aNewBytes);
+
+/**
+ * Return true if the given stream can be directly cloned.
+ */
+extern bool NS_InputStreamIsCloneable(nsIInputStream* aSource);
+
+/**
+ * Clone the provided source stream in the most efficient way possible.  This
+ * first attempts to QI to nsICloneableInputStream to use Clone().  If that is
+ * not supported or its cloneable attribute is false, then a fallback clone is
+ * provided by copying the source to a pipe.  In this case the caller must
+ * replace the source stream with the resulting replacement stream.  The clone
+ * and the replacement stream are then cloneable using nsICloneableInputStream
+ * without duplicating memory.  This fallback clone using the pipe is only
+ * performed if a replacement stream parameter is also passed in.
+ * @param aSource         The input stream to clone.
+ * @param aCloneOut       Required out parameter to hold resulting clone.
+ * @param aReplacementOut Optional out parameter to hold stream to replace
+ *                        original source stream after clone.  If not
+ *                        provided then the fallback clone process is not
+ *                        supported and a non-cloneable source will result
+ *                        in failure.  Replacement streams are non-blocking.
+ * @return NS_OK on successful clone.  Error otherwise.
+ */
+extern nsresult NS_CloneInputStream(nsIInputStream* aSource,
+                                    nsIInputStream** aCloneOut,
+                                    nsIInputStream** aReplacementOut = nullptr);
+
+/*
+ * This function returns a non-blocking nsIAsyncInputStream. Internally,
+ * different approaches are used based on what |aSource| is and what it
+ * implements.
+ *
+ * Note that this component takes the owninship of aSource.
+ *
+ * If the |aSource| is already a non-blocking and async stream,
+ * |aAsyncInputStream| will be equal to |aSource|.
+ *
+ * Otherwise, if |aSource| is just non-blocking, NonBlockingAsyncInputStream
+ * class is used in order to make it async.
+ *
+ * The last step is to use nsIStreamTransportService and create a pipe in order
+ * to expose a non-blocking async inputStream and read |aSource| data from
+ * a separate thread.
+ *
+ * In case we need to create a pipe, |aCloseWhenDone| will be used to create the
+ * inputTransport, |aFlags|, |aSegmentSize|, |asegmentCount| will be used to
+ * open the inputStream. If true, the input stream will be closed after it has
+ * been read. Read more in nsITransport.idl.
+ */
+extern nsresult NS_MakeAsyncNonBlockingInputStream(
+    already_AddRefed<nsIInputStream> aSource,
+    nsIAsyncInputStream** aAsyncInputStream, bool aCloseWhenDone = true,
+    uint32_t aFlags = 0, uint32_t aSegmentSize = 0, uint32_t aSegmentCount = 0);
+
+#endif  // !nsStreamUtils_h__
diff --git a/xpcom/io/nsStringStream.cpp b/xpcom/io/nsStringStream.cpp
new file mode 100644
index 0000000000..b3e83a58ba
--- /dev/null
+++ b/xpcom/io/nsStringStream.cpp
@@ -0,0 +1,591 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Based on original code from nsIStringStream.cpp
+ */
+
+#include "ipc/IPCMessageUtils.h"
+
+#include "nsStringStream.h"
+#include "nsStreamUtils.h"
+#include "nsReadableUtils.h"
+#include "nsICloneableInputStream.h"
+#include "nsISeekableStream.h"
+#include "nsISupportsPrimitives.h"
+#include "nsCRT.h"
+#include "prerror.h"
+#include "nsIClassInfoImpl.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/ipc/InputStreamUtils.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/ReentrantMonitor.h"
+#include "mozilla/StreamBufferSourceImpl.h"
+#include "nsIIPCSerializableInputStream.h"
+#include "XPCOMModule.h"
+
+using namespace mozilla::ipc;
+using mozilla::fallible;
+using mozilla::MakeRefPtr;
+using mozilla::MallocSizeOf;
+using mozilla::nsBorrowedSource;
+using mozilla::nsCStringSource;
+using mozilla::nsTArraySource;
+using mozilla::ReentrantMonitorAutoEnter;
+using mozilla::Span;
+using mozilla::StreamBufferSource;
+
+//-----------------------------------------------------------------------------
+// nsIStringInputStream implementation
+//-----------------------------------------------------------------------------
+
+class nsStringInputStream final : public nsIStringInputStream,
+                                  public nsISeekableStream,
+                                  public nsISupportsCString,
+                                  public nsIIPCSerializableInputStream,
+                                  public nsICloneableInputStream {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINPUTSTREAM
+  NS_DECL_NSISTRINGINPUTSTREAM
+  NS_DECL_NSISEEKABLESTREAM
+  NS_DECL_NSITELLABLESTREAM
+  NS_DECL_NSISUPPORTSPRIMITIVE
+  NS_DECL_NSISUPPORTSCSTRING
+  NS_DECL_NSIIPCSERIALIZABLEINPUTSTREAM
+  NS_DECL_NSICLONEABLEINPUTSTREAM
+
+  nsStringInputStream() = default;
+
+  nsresult Init(nsCString&& aString);
+
+  nsresult Init(nsTArray<uint8_t>&& aArray);
+
+ private:
+  ~nsStringInputStream() = default;
+
+  size_t Length() const MOZ_REQUIRES(mMon) {
+    return mSource ? mSource->Data().Length() : 0;
+  }
+
+  size_t LengthRemaining() const MOZ_REQUIRES(mMon) {
+    return Length() - mOffset;
+  }
+
+  void Clear() MOZ_REQUIRES(mMon) { mSource = nullptr; }
+
+  bool Closed() MOZ_REQUIRES(mMon) { return !mSource; }
+
+  RefPtr<StreamBufferSource> mSource MOZ_GUARDED_BY(mMon);
+  size_t mOffset MOZ_GUARDED_BY(mMon) = 0;
+
+  mutable mozilla::ReentrantMonitor mMon{"nsStringInputStream"};
+};
+
+nsresult nsStringInputStream::Init(nsCString&& aString) {
+  nsCString string;
+  if (!string.Assign(std::move(aString), fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  auto source = MakeRefPtr<nsCStringSource>(std::move(string));
+  return SetDataSource(source);
+}
+
+nsresult nsStringInputStream::Init(nsTArray<uint8_t>&& aArray) {
+  auto source = MakeRefPtr<nsTArraySource>(std::move(aArray));
+  return SetDataSource(source);
+}
+
+// This class needs to support threadsafe refcounting since people often
+// allocate a string stream, and then read it from a background thread.
+NS_IMPL_ADDREF(nsStringInputStream)
+NS_IMPL_RELEASE(nsStringInputStream)
+
+NS_IMPL_CLASSINFO(nsStringInputStream, nullptr, nsIClassInfo::THREADSAFE,
+                  NS_STRINGINPUTSTREAM_CID)
+NS_IMPL_QUERY_INTERFACE_CI(nsStringInputStream, nsIStringInputStream,
+                           nsIInputStream, nsISupportsCString,
+                           nsISeekableStream, nsITellableStream,
+                           nsIIPCSerializableInputStream,
+                           nsICloneableInputStream)
+NS_IMPL_CI_INTERFACE_GETTER(nsStringInputStream, nsIStringInputStream,
+                            nsIInputStream, nsISupportsCString,
+                            nsISeekableStream, nsITellableStream,
+                            nsICloneableInputStream)
+
+/////////
+// nsISupportsCString implementation
+/////////
+
+NS_IMETHODIMP
+nsStringInputStream::GetType(uint16_t* aType) {
+  *aType = TYPE_CSTRING;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStringInputStream::GetData(nsACString& data) {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  // The stream doesn't have any data when it is closed.  We could fake it
+  // and return an empty string here, but it seems better to keep this return
+  // value consistent with the behavior of the other 'getter' methods.
+  if (NS_WARN_IF(Closed())) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  return mSource->GetData(data);
+}
+
+NS_IMETHODIMP
+nsStringInputStream::SetData(const nsACString& aData) {
+  nsCString string;
+  if (!string.Assign(aData, fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  auto source = MakeRefPtr<nsCStringSource>(std::move(string));
+  return SetDataSource(source);
+}
+
+NS_IMETHODIMP
+nsStringInputStream::ToString(char** aResult) {
+  // NOTE: This method may result in data loss, so we do not implement it.
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+/////////
+// nsIStringInputStream implementation
+/////////
+
+NS_IMETHODIMP
+nsStringInputStream::SetData(const char* aData, int32_t aDataLen) {
+  if (NS_WARN_IF(!aData)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsCString string;
+  if (NS_WARN_IF(!string.Assign(aData, aDataLen, fallible))) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  auto source = MakeRefPtr<nsCStringSource>(std::move(string));
+  return SetDataSource(source);
+}
+
+NS_IMETHODIMP
+nsStringInputStream::SetUTF8Data(const nsACString& aData) {
+  return nsStringInputStream::SetData(aData);
+}
+
+NS_IMETHODIMP
+nsStringInputStream::AdoptData(char* aData, int32_t aDataLen) {
+  if (NS_WARN_IF(!aData)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  nsCString string;
+  string.Adopt(aData, aDataLen);
+  auto source = MakeRefPtr<nsCStringSource>(std::move(string));
+  return SetDataSource(source);
+}
+
+NS_IMETHODIMP
+nsStringInputStream::ShareData(const char* aData, int32_t aDataLen) {
+  if (NS_WARN_IF(!aData)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  size_t length = aDataLen < 0 ? strlen(aData) : size_t(aDataLen);
+  auto source = MakeRefPtr<nsBorrowedSource>(Span{aData, length});
+  return SetDataSource(source);
+}
+
+NS_IMETHODIMP
+nsStringInputStream::SetDataSource(StreamBufferSource* aSource) {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  if (NS_WARN_IF(!aSource)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  mSource = aSource;
+  mOffset = 0;
+  return NS_OK;
+}
+
+NS_IMETHODIMP_(size_t)
+nsStringInputStream::SizeOfIncludingThisIfUnshared(MallocSizeOf aMallocSizeOf) {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  size_t n = aMallocSizeOf(this);
+  if (mSource) {
+    n += mSource->SizeOfIncludingThisIfUnshared(aMallocSizeOf);
+  }
+  return n;
+}
+
+NS_IMETHODIMP_(size_t)
+nsStringInputStream::SizeOfIncludingThisEvenIfShared(
+    MallocSizeOf aMallocSizeOf) {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  size_t n = aMallocSizeOf(this);
+  if (mSource) {
+    n += mSource->SizeOfIncludingThisEvenIfShared(aMallocSizeOf);
+  }
+  return n;
+}
+
+/////////
+// nsIInputStream implementation
+/////////
+
+NS_IMETHODIMP
+nsStringInputStream::Close() {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  Clear();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStringInputStream::Available(uint64_t* aLength) {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  NS_ASSERTION(aLength, "null ptr");
+
+  if (Closed()) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  *aLength = LengthRemaining();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStringInputStream::StreamStatus() {
+  ReentrantMonitorAutoEnter lock(mMon);
+  return Closed() ? NS_BASE_STREAM_CLOSED : NS_OK;
+}
+
+NS_IMETHODIMP
+nsStringInputStream::Read(char* aBuf, uint32_t aCount, uint32_t* aReadCount) {
+  NS_ASSERTION(aBuf, "null ptr");
+  return ReadSegments(NS_CopySegmentToBuffer, aBuf, aCount, aReadCount);
+}
+
+NS_IMETHODIMP
+nsStringInputStream::ReadSegments(nsWriteSegmentFun aWriter, void* aClosure,
+                                  uint32_t aCount, uint32_t* aResult) {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  NS_ASSERTION(aResult, "null ptr");
+  NS_ASSERTION(Length() >= mOffset, "bad stream state");
+
+  if (Closed()) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  // We may be at end-of-file
+  size_t maxCount = LengthRemaining();
+  if (maxCount == 0) {
+    *aResult = 0;
+    return NS_OK;
+  }
+
+  if (aCount > maxCount) {
+    aCount = maxCount;
+  }
+
+  RefPtr<StreamBufferSource> source = mSource;
+  size_t offset = mOffset;
+
+  nsresult rv = aWriter(this, aClosure, source->Data().Elements() + offset, 0,
+                        aCount, aResult);
+
+  if (Closed()) {
+    NS_WARNING("nsStringInputStream was closed during ReadSegments");
+    return NS_OK;
+  }
+
+  MOZ_RELEASE_ASSERT(mSource == source, "String was replaced!");
+  MOZ_RELEASE_ASSERT(mOffset == offset, "Nested read operation!");
+
+  if (NS_SUCCEEDED(rv)) {
+    NS_ASSERTION(*aResult <= aCount,
+                 "writer should not write more than we asked it to write");
+    mOffset = offset + *aResult;
+  }
+
+  // errors returned from the writer end here!
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStringInputStream::IsNonBlocking(bool* aNonBlocking) {
+  *aNonBlocking = true;
+  return NS_OK;
+}
+
+/////////
+// nsISeekableStream implementation
+/////////
+
+NS_IMETHODIMP
+nsStringInputStream::Seek(int32_t aWhence, int64_t aOffset) {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  if (Closed()) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  // Compute new stream position.  The given offset may be a negative value.
+
+  int64_t newPos = aOffset;
+  switch (aWhence) {
+    case NS_SEEK_SET:
+      break;
+    case NS_SEEK_CUR:
+      newPos += (int64_t)mOffset;
+      break;
+    case NS_SEEK_END:
+      newPos += (int64_t)Length();
+      break;
+    default:
+      NS_ERROR("invalid aWhence");
+      return NS_ERROR_INVALID_ARG;
+  }
+
+  if (NS_WARN_IF(newPos < 0) || NS_WARN_IF(newPos > (int64_t)Length())) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  mOffset = (size_t)newPos;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStringInputStream::SetEOF() {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  if (Closed()) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  mOffset = Length();
+  return NS_OK;
+}
+
+/////////
+// nsITellableStream implementation
+/////////
+
+NS_IMETHODIMP
+nsStringInputStream::Tell(int64_t* aOutWhere) {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  if (Closed()) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  *aOutWhere = (int64_t)mOffset;
+  return NS_OK;
+}
+
+/////////
+// nsIIPCSerializableInputStream implementation
+/////////
+
+void nsStringInputStream::SerializedComplexity(uint32_t aMaxSize,
+                                               uint32_t* aSizeUsed,
+                                               uint32_t* aPipes,
+                                               uint32_t* aTransferables) {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  if (Length() >= aMaxSize) {
+    *aPipes = 1;
+  } else {
+    *aSizeUsed = Length();
+  }
+}
+
+void nsStringInputStream::Serialize(InputStreamParams& aParams,
+                                    uint32_t aMaxSize, uint32_t* aSizeUsed) {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  MOZ_DIAGNOSTIC_ASSERT(!Closed(), "cannot send a closed stream!");
+  MOZ_ASSERT(aSizeUsed);
+  *aSizeUsed = 0;
+
+  if (Length() >= aMaxSize) {
+    // If the input stream is non-owning (i.e. it was initialized with
+    // `ShareData`), create a new owning source so that it doesn't go away while
+    // async copying.
+    if (!mSource->Owning()) {
+      auto source =
+          MakeRefPtr<nsCStringSource>(nsDependentCSubstring(mSource->Data()));
+      mSource = source;
+    }
+
+    InputStreamHelper::SerializeInputStreamAsPipe(this, aParams);
+    return;
+  }
+
+  *aSizeUsed = Length();
+
+  StringInputStreamParams params;
+  mSource->GetData(params.data());
+  aParams = params;
+}
+
+bool nsStringInputStream::Deserialize(const InputStreamParams& aParams) {
+  if (aParams.type() != InputStreamParams::TStringInputStreamParams) {
+    NS_ERROR("Received unknown parameters from the other process!");
+    return false;
+  }
+
+  const StringInputStreamParams& params = aParams.get_StringInputStreamParams();
+
+  if (NS_FAILED(SetData(params.data()))) {
+    NS_WARNING("SetData failed!");
+    return false;
+  }
+
+  return true;
+}
+
+/////////
+// nsICloneableInputStream implementation
+/////////
+
+NS_IMETHODIMP
+nsStringInputStream::GetCloneable(bool* aCloneableOut) {
+  *aCloneableOut = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsStringInputStream::Clone(nsIInputStream** aCloneOut) {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  RefPtr<nsStringInputStream> ref = new nsStringInputStream();
+  // Nothing else can access this yet, but suppress static analysis warnings
+  ReentrantMonitorAutoEnter reflock(ref->mMon);
+  if (mSource && !mSource->Owning()) {
+    auto data = mSource->Data();
+    nsresult rv = ref->SetData(data.Elements(), data.Length());
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  } else {
+    ref->mSource = mSource;
+  }
+
+  // mOffset is overwritten by SetData().
+  ref->mOffset = mOffset;
+
+  ref.forget(aCloneOut);
+  return NS_OK;
+}
+
+nsresult NS_NewByteInputStream(nsIInputStream** aStreamResult,
+                               mozilla::Span<const char> aStringToRead,
+                               nsAssignmentType aAssignment) {
+  MOZ_ASSERT(aStreamResult, "null out ptr");
+
+  RefPtr<nsStringInputStream> stream = new nsStringInputStream();
+
+  nsresult rv;
+  switch (aAssignment) {
+    case NS_ASSIGNMENT_COPY:
+      rv = stream->SetData(aStringToRead.Elements(), aStringToRead.Length());
+      break;
+    case NS_ASSIGNMENT_DEPEND:
+      rv = stream->ShareData(aStringToRead.Elements(), aStringToRead.Length());
+      break;
+    case NS_ASSIGNMENT_ADOPT:
+      rv = stream->AdoptData(const_cast<char*>(aStringToRead.Elements()),
+                             aStringToRead.Length());
+      break;
+    default:
+      NS_ERROR("invalid assignment type");
+      rv = NS_ERROR_INVALID_ARG;
+  }
+
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  stream.forget(aStreamResult);
+  return NS_OK;
+}
+
+nsresult NS_NewByteInputStream(nsIInputStream** aStreamResult,
+                               nsTArray<uint8_t>&& aArray) {
+  MOZ_ASSERT(aStreamResult, "null out ptr");
+
+  RefPtr<nsStringInputStream> stream = new nsStringInputStream();
+
+  nsresult rv = stream->Init(std::move(aArray));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  stream.forget(aStreamResult);
+  return NS_OK;
+}
+
+extern nsresult NS_NewByteInputStream(nsIInputStream** aStreamResult,
+                                      mozilla::StreamBufferSource* aSource) {
+  MOZ_ASSERT(aStreamResult, "null out ptr");
+
+  RefPtr<nsStringInputStream> stream = new nsStringInputStream();
+
+  nsresult rv = stream->SetDataSource(aSource);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  stream.forget(aStreamResult);
+  return NS_OK;
+}
+
+nsresult NS_NewCStringInputStream(nsIInputStream** aStreamResult,
+                                  const nsACString& aStringToRead) {
+  MOZ_ASSERT(aStreamResult, "null out ptr");
+
+  RefPtr<nsStringInputStream> stream = new nsStringInputStream();
+
+  nsresult rv = stream->SetData(aStringToRead);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  stream.forget(aStreamResult);
+  return NS_OK;
+}
+
+nsresult NS_NewCStringInputStream(nsIInputStream** aStreamResult,
+                                  nsCString&& aStringToRead) {
+  MOZ_ASSERT(aStreamResult, "null out ptr");
+
+  RefPtr<nsStringInputStream> stream = new nsStringInputStream();
+
+  nsresult rv = stream->Init(std::move(aStringToRead));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  stream.forget(aStreamResult);
+  return NS_OK;
+}
+
+// factory method for constructing a nsStringInputStream object
+nsresult nsStringInputStreamConstructor(REFNSIID aIID, void** aResult) {
+  *aResult = nullptr;
+
+  RefPtr<nsStringInputStream> inst = new nsStringInputStream();
+  return inst->QueryInterface(aIID, aResult);
+}
diff --git a/xpcom/io/nsStringStream.h b/xpcom/io/nsStringStream.h
new file mode 100644
index 0000000000..8568cc33f8
--- /dev/null
+++ b/xpcom/io/nsStringStream.h
@@ -0,0 +1,89 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsStringStream_h__
+#define nsStringStream_h__
+
+#include "nsIStringStream.h"
+#include "nsString.h"
+#include "nsTArray.h"
+
+/**
+ * Implements:
+ *   nsIStringInputStream
+ *   nsIInputStream
+ *   nsISeekableStream
+ *   nsITellableStream
+ *   nsISupportsCString
+ */
+#define NS_STRINGINPUTSTREAM_CONTRACTID "@mozilla.org/io/string-input-stream;1"
+#define NS_STRINGINPUTSTREAM_CID                     \
+  { /* 0abb0835-5000-4790-af28-61b3ba17c295 */       \
+    0x0abb0835, 0x5000, 0x4790, {                    \
+      0xaf, 0x28, 0x61, 0xb3, 0xba, 0x17, 0xc2, 0x95 \
+    }                                                \
+  }
+
+/**
+ * An enumeration type used to represent a method of assignment.
+ */
+enum nsAssignmentType {
+  NS_ASSIGNMENT_COPY,    // copy by value
+  NS_ASSIGNMENT_DEPEND,  // copy by reference
+  NS_ASSIGNMENT_ADOPT    // copy by reference (take ownership of resource)
+};
+
+/**
+ * Factory method to get an nsInputStream from a byte buffer.  Result will
+ * implement nsIStringInputStream, nsITellableStream and nsISeekableStream.
+ *
+ * If aAssignment is NS_ASSIGNMENT_COPY, then the resulting stream holds a copy
+ * of the given buffer (aStringToRead), and the caller is free to discard
+ * aStringToRead after this function returns.
+ *
+ * If aAssignment is NS_ASSIGNMENT_DEPEND, then the resulting stream refers
+ * directly to the given buffer (aStringToRead), so the caller must ensure that
+ * the buffer remains valid for the lifetime of the stream object.  Use with
+ * care!!
+ *
+ * If aAssignment is NS_ASSIGNMENT_ADOPT, then the resulting stream refers
+ * directly to the given buffer (aStringToRead) and will free aStringToRead
+ * once the stream is closed.
+ */
+extern nsresult NS_NewByteInputStream(nsIInputStream** aStreamResult,
+                                      mozilla::Span<const char> aStringToRead,
+                                      nsAssignmentType aAssignment);
+
+/**
+ * Factory method to get an nsIInputStream from an nsTArray representing a byte
+ * buffer.  This will take ownership of the data and empty out the nsTArray.
+ *
+ * Result will implement nsIStringInputStream, nsITellableStream and
+ * nsISeekableStream.
+ */
+extern nsresult NS_NewByteInputStream(nsIInputStream** aStreamResult,
+                                      nsTArray<uint8_t>&& aArray);
+
+/**
+ * Factory method to get an nsIInputStream from an arbitrary StreamBufferSource.
+ * This will take a strong reference to the source.
+ *
+ * Result will implement nsIStringInputStream, nsITellableStream and
+ * nsISeekableStream.
+ */
+extern nsresult NS_NewByteInputStream(nsIInputStream** aStreamResult,
+                                      mozilla::StreamBufferSource* aSource);
+
+/**
+ * Factory method to get an nsInputStream from an nsACString.  Result will
+ * implement nsIStringInputStream, nsTellableStream and nsISeekableStream.
+ */
+extern nsresult NS_NewCStringInputStream(nsIInputStream** aStreamResult,
+                                         const nsACString& aStringToRead);
+extern nsresult NS_NewCStringInputStream(nsIInputStream** aStreamResult,
+                                         nsCString&& aStringToRead);
+
+#endif  // nsStringStream_h__
diff --git a/xpcom/io/nsUnicharInputStream.cpp b/xpcom/io/nsUnicharInputStream.cpp
new file mode 100644
index 0000000000..1366ab1e34
--- /dev/null
+++ b/xpcom/io/nsUnicharInputStream.cpp
@@ -0,0 +1,132 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsUnicharInputStream.h"
+#include "nsIInputStream.h"
+#include "nsString.h"
+#include "nsTArray.h"
+#include "nsCRT.h"
+#include "nsStreamUtils.h"
+#include "nsConverterInputStream.h"
+#include "mozilla/Attributes.h"
+#include <fcntl.h>
+#if defined(XP_WIN)
+#  include <io.h>
+#else
+#  include <unistd.h>
+#endif
+
+#define STRING_BUFFER_SIZE 8192
+
+class StringUnicharInputStream final : public nsIUnicharInputStream {
+ public:
+  explicit StringUnicharInputStream(const nsAString& aString)
+      : mString(aString), mPos(0), mLen(aString.Length()) {}
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIUNICHARINPUTSTREAM
+
+  nsString mString;
+  uint32_t mPos;
+  uint32_t mLen;
+
+ private:
+  ~StringUnicharInputStream() = default;
+};
+
+NS_IMETHODIMP
+StringUnicharInputStream::Read(char16_t* aBuf, uint32_t aCount,
+                               uint32_t* aReadCount) {
+  if (mPos >= mLen) {
+    *aReadCount = 0;
+    return NS_OK;
+  }
+  nsAString::const_iterator iter;
+  mString.BeginReading(iter);
+  const char16_t* us = iter.get();
+  uint32_t amount = mLen - mPos;
+  if (amount > aCount) {
+    amount = aCount;
+  }
+  memcpy(aBuf, us + mPos, sizeof(char16_t) * amount);
+  mPos += amount;
+  *aReadCount = amount;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StringUnicharInputStream::ReadSegments(nsWriteUnicharSegmentFun aWriter,
+                                       void* aClosure, uint32_t aCount,
+                                       uint32_t* aReadCount) {
+  uint32_t bytesWritten;
+  uint32_t totalBytesWritten = 0;
+
+  nsresult rv;
+  aCount = XPCOM_MIN<uint32_t>(mString.Length() - mPos, aCount);
+
+  nsAString::const_iterator iter;
+  mString.BeginReading(iter);
+
+  while (aCount) {
+    rv = aWriter(this, aClosure, iter.get() + mPos, totalBytesWritten, aCount,
+                 &bytesWritten);
+
+    if (NS_FAILED(rv)) {
+      // don't propagate errors to the caller
+      break;
+    }
+
+    aCount -= bytesWritten;
+    totalBytesWritten += bytesWritten;
+    mPos += bytesWritten;
+  }
+
+  *aReadCount = totalBytesWritten;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StringUnicharInputStream::ReadString(uint32_t aCount, nsAString& aString,
+                                     uint32_t* aReadCount) {
+  if (mPos >= mLen) {
+    *aReadCount = 0;
+    return NS_OK;
+  }
+  uint32_t amount = mLen - mPos;
+  if (amount > aCount) {
+    amount = aCount;
+  }
+  aString = Substring(mString, mPos, amount);
+  mPos += amount;
+  *aReadCount = amount;
+  return NS_OK;
+}
+
+nsresult StringUnicharInputStream::Close() {
+  mPos = mLen;
+  return NS_OK;
+}
+
+NS_IMPL_ISUPPORTS(StringUnicharInputStream, nsIUnicharInputStream)
+
+//----------------------------------------------------------------------
+
+nsresult NS_NewUnicharInputStream(nsIInputStream* aStreamToWrap,
+                                  nsIUnicharInputStream** aResult) {
+  *aResult = nullptr;
+
+  // Create converter input stream
+  RefPtr<nsConverterInputStream> it = new nsConverterInputStream();
+  nsresult rv = it->Init(aStreamToWrap, "UTF-8", STRING_BUFFER_SIZE,
+                         nsIConverterInputStream::ERRORS_ARE_FATAL);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  it.forget(aResult);
+  return NS_OK;
+}
diff --git a/xpcom/io/nsUnicharInputStream.h b/xpcom/io/nsUnicharInputStream.h
new file mode 100644
index 0000000000..de0534f01c
--- /dev/null
+++ b/xpcom/io/nsUnicharInputStream.h
@@ -0,0 +1,15 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsUnicharInputStream_h__
+#define nsUnicharInputStream_h__
+
+#include "nsIUnicharInputStream.h"
+
+nsresult NS_NewUnicharInputStream(nsIInputStream* aStreamToWrap,
+                                  nsIUnicharInputStream** aResult);
+
+#endif  // nsUnicharInputStream_h__
diff --git a/xpcom/io/nsWildCard.cpp b/xpcom/io/nsWildCard.cpp
new file mode 100644
index 0000000000..64546ca676
--- /dev/null
+++ b/xpcom/io/nsWildCard.cpp
@@ -0,0 +1,435 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* *
+ *
+ *
+ * nsWildCard.cpp: shell-like wildcard match routines
+ *
+ * See nsIZipReader.findEntries documentation in nsIZipReader.idl for
+ * a description of the syntax supported by the routines in this file.
+ *
+ * Rob McCool
+ *
+ */
+
+#include "nsWildCard.h"
+#include "nsXPCOM.h"
+#include "nsCRTGlue.h"
+#include "nsCharTraits.h"
+
+/* -------------------- ASCII-specific character methods ------------------- */
+
+typedef int static_assert_character_code_arrangement['a' > 'A' ? 1 : -1];
+
+template <class T>
+static int alpha(T aChar) {
+  return ('a' <= aChar && aChar <= 'z') || ('A' <= aChar && aChar <= 'Z');
+}
+
+template <class T>
+static int alphanumeric(T aChar) {
+  return ('0' <= aChar && aChar <= '9') || ::alpha(aChar);
+}
+
+template <class T>
+static int lower(T aChar) {
+  return ('A' <= aChar && aChar <= 'Z') ? aChar + ('a' - 'A') : aChar;
+}
+
+template <class T>
+static int upper(T aChar) {
+  return ('a' <= aChar && aChar <= 'z') ? aChar - ('a' - 'A') : aChar;
+}
+
+/* ----------------------------- _valid_subexp ---------------------------- */
+
+template <class T>
+static int _valid_subexp(const T* aExpr, T aStop1, T aStop2) {
+  int x;
+  int nsc = 0; /* Number of special characters */
+  int np;      /* Number of pipe characters in union */
+  int tld = 0; /* Number of tilde characters */
+
+  for (x = 0; aExpr[x] && (aExpr[x] != aStop1) && (aExpr[x] != aStop2); ++x) {
+    switch (aExpr[x]) {
+      case '~':
+        if (tld) { /* at most one exclusion */
+          return INVALID_SXP;
+        }
+        if (aStop1) { /* no exclusions within unions */
+          return INVALID_SXP;
+        }
+        if (!aExpr[x + 1]) { /* exclusion cannot be last character */
+          return INVALID_SXP;
+        }
+        if (!x) { /* exclusion cannot be first character */
+          return INVALID_SXP;
+        }
+        ++tld;
+        [[fallthrough]];
+      case '*':
+      case '?':
+      case '$':
+        ++nsc;
+        break;
+      case '[':
+        ++nsc;
+        if ((!aExpr[++x]) || (aExpr[x] == ']')) {
+          return INVALID_SXP;
+        }
+        for (; aExpr[x] && (aExpr[x] != ']'); ++x) {
+          if (aExpr[x] == '\\' && !aExpr[++x]) {
+            return INVALID_SXP;
+          }
+        }
+        if (!aExpr[x]) {
+          return INVALID_SXP;
+        }
+        break;
+      case '(':
+        ++nsc;
+        if (aStop1) { /* no nested unions */
+          return INVALID_SXP;
+        }
+        np = -1;
+        do {
+          int t = ::_valid_subexp(&aExpr[++x], T(')'), T('|'));
+          if (t == 0 || t == INVALID_SXP) {
+            return INVALID_SXP;
+          }
+          x += t;
+          if (!aExpr[x]) {
+            return INVALID_SXP;
+          }
+          ++np;
+        } while (aExpr[x] == '|');
+        if (np < 1) { /* must be at least one pipe */
+          return INVALID_SXP;
+        }
+        break;
+      case ')':
+      case ']':
+      case '|':
+        return INVALID_SXP;
+      case '\\':
+        ++nsc;
+        if (!aExpr[++x]) {
+          return INVALID_SXP;
+        }
+        break;
+      default:
+        break;
+    }
+  }
+  if (!aStop1 && !nsc) { /* must be at least one special character */
+    return NON_SXP;
+  }
+  return ((aExpr[x] == aStop1 || aExpr[x] == aStop2) ? x : INVALID_SXP);
+}
+
+template <class T>
+int NS_WildCardValid_(const T* aExpr) {
+  int x = ::_valid_subexp(aExpr, T('\0'), T('\0'));
+  return (x < 0 ? x : VALID_SXP);
+}
+
+int NS_WildCardValid(const char* aExpr) { return NS_WildCardValid_(aExpr); }
+
+int NS_WildCardValid(const char16_t* aExpr) { return NS_WildCardValid_(aExpr); }
+
+/* ----------------------------- _shexp_match ----------------------------- */
+
+#define MATCH 0
+#define NOMATCH 1
+#define ABORTED -1
+
+template <class T>
+static int _shexp_match(const T* aStr, const T* aExpr, bool aCaseInsensitive,
+                        unsigned int aLevel);
+
+/**
+ * Count characters until we reach a NUL character or either of the
+ * two delimiter characters, stop1 or stop2.  If we encounter a bracketed
+ * expression, look only for NUL or ']' inside it.  Do not look for stop1
+ * or stop2 inside it. Return ABORTED if bracketed expression is unterminated.
+ * Handle all escaping.
+ * Return index in input string of first stop found, or ABORTED if not found.
+ * If "dest" is non-nullptr, copy counted characters to it and null terminate.
+ */
+template <class T>
+static int _scan_and_copy(const T* aExpr, T aStop1, T aStop2, T* aDest) {
+  int sx; /* source index */
+  T cc;
+
+  for (sx = 0; (cc = aExpr[sx]) && cc != aStop1 && cc != aStop2; ++sx) {
+    if (cc == '\\') {
+      if (!aExpr[++sx]) {
+        return ABORTED; /* should be impossible */
+      }
+    } else if (cc == '[') {
+      while ((cc = aExpr[++sx]) && cc != ']') {
+        if (cc == '\\' && !aExpr[++sx]) {
+          return ABORTED;
+        }
+      }
+      if (!cc) {
+        return ABORTED; /* should be impossible */
+      }
+    }
+  }
+  if (aDest && sx) {
+    /* Copy all but the closing delimiter. */
+    memcpy(aDest, aExpr, sx * sizeof(T));
+    aDest[sx] = 0;
+  }
+  return cc ? sx : ABORTED; /* index of closing delimiter */
+}
+
+/* On input, expr[0] is the opening parenthesis of a union.
+ * See if any of the alternatives in the union matches as a pattern.
+ * The strategy is to take each of the alternatives, in turn, and append
+ * the rest of the expression (after the closing ')' that marks the end of
+ * this union) to that alternative, and then see if the resultant expression
+ * matches the input string.  Repeat this until some alternative matches,
+ * or we have an abort.
+ */
+template <class T>
+static int _handle_union(const T* aStr, const T* aExpr, bool aCaseInsensitive,
+                         unsigned int aLevel) {
+  int sx; /* source index */
+  int cp; /* source index of closing parenthesis */
+  int count;
+  int ret = NOMATCH;
+  T* e2;
+
+  /* Find the closing parenthesis that ends this union in the expression */
+  cp = ::_scan_and_copy(aExpr, T(')'), T('\0'), static_cast<T*>(nullptr));
+  if (cp == ABORTED || cp < 4) { /* must be at least "(a|b" before ')' */
+    return ABORTED;
+  }
+  ++cp; /* now index of char after closing parenthesis */
+  e2 = (T*)moz_xmalloc((1 + nsCharTraits<T>::length(aExpr)) * sizeof(T));
+  for (sx = 1;; ++sx) {
+    /* Here, aExpr[sx] is one character past the preceding '(' or '|'. */
+    /* Copy everything up to the next delimiter to e2 */
+    count = ::_scan_and_copy(aExpr + sx, T(')'), T('|'), e2);
+    if (count == ABORTED || !count) {
+      ret = ABORTED;
+      break;
+    }
+    sx += count;
+    /* Append everything after closing parenthesis to e2. This is safe. */
+    nsCharTraits<T>::copy(e2 + count, aExpr + cp,
+                          nsCharTraits<T>::length(aExpr + cp) + 1);
+    ret = ::_shexp_match(aStr, e2, aCaseInsensitive, aLevel + 1);
+    if (ret != NOMATCH || !aExpr[sx] || aExpr[sx] == ')') {
+      break;
+    }
+  }
+  free(e2);
+  if (sx < 2) {
+    ret = ABORTED;
+  }
+  return ret;
+}
+
+/* returns 1 if val is in range from start..end, case insensitive. */
+static int _is_char_in_range(unsigned char aStart, unsigned char aEnd,
+                             unsigned char aVal) {
+  char map[256];
+  memset(map, 0, sizeof(map));
+  while (aStart <= aEnd) {
+    map[lower(aStart++)] = 1;
+  }
+  return map[lower(aVal)];
+}
+
+template <class T>
+static int _shexp_match(const T* aStr, const T* aExpr, bool aCaseInsensitive,
+                        unsigned int aLevel) {
+  int x; /* input string index */
+  int y; /* expression index */
+  int ret, neg;
+
+  if (aLevel > 20) { /* Don't let the stack get too deep. */
+    return ABORTED;
+  }
+  for (x = 0, y = 0; aExpr[y]; ++y, ++x) {
+    if (!aStr[x] && aExpr[y] != '$' && aExpr[y] != '*') {
+      return NOMATCH;
+    }
+    switch (aExpr[y]) {
+      case '$':
+        if (aStr[x]) {
+          return NOMATCH;
+        }
+        --x; /* we don't want loop to increment x */
+        break;
+      case '*':
+        while (aExpr[++y] == '*') {
+        }
+        if (!aExpr[y]) {
+          return MATCH;
+        }
+        while (aStr[x]) {
+          ret = ::_shexp_match(&aStr[x++], &aExpr[y], aCaseInsensitive,
+                               aLevel + 1);
+          switch (ret) {
+            case NOMATCH:
+              continue;
+            case ABORTED:
+              return ABORTED;
+            default:
+              return MATCH;
+          }
+        }
+        if (aExpr[y] == '$' && aExpr[y + 1] == '\0' && !aStr[x]) {
+          return MATCH;
+        } else {
+          return NOMATCH;
+        }
+      case '[': {
+        T start, end = 0;
+        int i;
+        ++y;
+        neg = (aExpr[y] == '^' && aExpr[y + 1] != ']');
+        if (neg) {
+          ++y;
+        }
+        i = y;
+        start = aExpr[i++];
+        if (start == '\\') {
+          start = aExpr[i++];
+        }
+        if (::alphanumeric(start) && aExpr[i++] == '-') {
+          end = aExpr[i++];
+          if (end == '\\') {
+            end = aExpr[i++];
+          }
+        }
+        if (::alphanumeric(end) && aExpr[i] == ']') {
+          /* This is a range form: a-b */
+          T val = aStr[x];
+          if (end < start) { /* swap them */
+            T tmp = end;
+            end = start;
+            start = tmp;
+          }
+          if (aCaseInsensitive && ::alpha(val)) {
+            val = ::_is_char_in_range((unsigned char)start, (unsigned char)end,
+                                      (unsigned char)val);
+            if (neg == val) {
+              return NOMATCH;
+            }
+          } else if (neg != (val < start || val > end)) {
+            return NOMATCH;
+          }
+          y = i;
+        } else {
+          /* Not range form */
+          int matched = 0;
+          for (; aExpr[y] != ']'; ++y) {
+            if (aExpr[y] == '\\') {
+              ++y;
+            }
+            if (aCaseInsensitive) {
+              matched |= (::upper(aStr[x]) == ::upper(aExpr[y]));
+            } else {
+              matched |= (aStr[x] == aExpr[y]);
+            }
+          }
+          if (neg == matched) {
+            return NOMATCH;
+          }
+        }
+      } break;
+      case '(':
+        if (!aExpr[y + 1]) {
+          return ABORTED;
+        }
+        return ::_handle_union(&aStr[x], &aExpr[y], aCaseInsensitive,
+                               aLevel + 1);
+      case '?':
+        break;
+      case ')':
+      case ']':
+      case '|':
+        return ABORTED;
+      case '\\':
+        ++y;
+        [[fallthrough]];
+      default:
+        if (aCaseInsensitive) {
+          if (::upper(aStr[x]) != ::upper(aExpr[y])) {
+            return NOMATCH;
+          }
+        } else {
+          if (aStr[x] != aExpr[y]) {
+            return NOMATCH;
+          }
+        }
+        break;
+    }
+  }
+  return (aStr[x] ? NOMATCH : MATCH);
+}
+
+template <class T>
+static int ns_WildCardMatch(const T* aStr, const T* aXp,
+                            bool aCaseInsensitive) {
+  T* expr = nullptr;
+  int ret = MATCH;
+
+  if (!nsCharTraits<T>::find(aXp, nsCharTraits<T>::length(aXp), T('~'))) {
+    return ::_shexp_match(aStr, aXp, aCaseInsensitive, 0);
+  }
+
+  expr = (T*)moz_xmalloc((nsCharTraits<T>::length(aXp) + 1) * sizeof(T));
+  memcpy(expr, aXp, (nsCharTraits<T>::length(aXp) + 1) * sizeof(T));
+
+  int x = ::_scan_and_copy(expr, T('~'), T('\0'), static_cast<T*>(nullptr));
+  if (x != ABORTED && expr[x] == '~') {
+    expr[x++] = '\0';
+    ret = ::_shexp_match(aStr, &expr[x], aCaseInsensitive, 0);
+    switch (ret) {
+      case NOMATCH:
+        ret = MATCH;
+        break;
+      case MATCH:
+        ret = NOMATCH;
+        break;
+      default:
+        break;
+    }
+  }
+  if (ret == MATCH) {
+    ret = ::_shexp_match(aStr, expr, aCaseInsensitive, 0);
+  }
+
+  free(expr);
+  return ret;
+}
+
+template <class T>
+int NS_WildCardMatch_(const T* aStr, const T* aExpr, bool aCaseInsensitive) {
+  int is_valid = NS_WildCardValid(aExpr);
+  switch (is_valid) {
+    case INVALID_SXP:
+      return -1;
+    default:
+      return ::ns_WildCardMatch(aStr, aExpr, aCaseInsensitive);
+  }
+}
+
+int NS_WildCardMatch(const char* aStr, const char* aXp, bool aCaseInsensitive) {
+  return NS_WildCardMatch_(aStr, aXp, aCaseInsensitive);
+}
+
+int NS_WildCardMatch(const char16_t* aStr, const char16_t* aXp,
+                     bool aCaseInsensitive) {
+  return NS_WildCardMatch_(aStr, aXp, aCaseInsensitive);
+}
diff --git a/xpcom/io/nsWildCard.h b/xpcom/io/nsWildCard.h
new file mode 100644
index 0000000000..e3205fa7a1
--- /dev/null
+++ b/xpcom/io/nsWildCard.h
@@ -0,0 +1,63 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * nsWildCard.h: Defines and prototypes for shell exp. match routines
+ *
+ * See nsIZipReader.findEntries docs in nsIZipReader.idl for a description of
+ * the supported expression syntax.
+ *
+ * Note that the syntax documentation explicitly says the results of certain
+ * expressions are undefined.  This is intentional to require less robustness
+ * in the code.  Regular expression parsing is hard; the smaller the set of
+ * features and interactions this code must support, the easier it is to
+ * ensure it works.
+ *
+ */
+
+#ifndef nsWildCard_h__
+#define nsWildCard_h__
+
+#include "nscore.h"
+
+/* --------------------------- Public routines ---------------------------- */
+
+/*
+ * NS_WildCardValid takes a shell expression exp as input. It returns:
+ *
+ *  NON_SXP      if exp is a standard string
+ *  INVALID_SXP  if exp is a shell expression, but invalid
+ *  VALID_SXP    if exp is a valid shell expression
+ */
+
+#define NON_SXP -1
+#define INVALID_SXP -2
+#define VALID_SXP 1
+
+int NS_WildCardValid(const char* aExpr);
+
+int NS_WildCardValid(const char16_t* aExpr);
+
+/* return values for the search routines */
+#define MATCH 0
+#define NOMATCH 1
+#define ABORTED -1
+
+/*
+ * NS_WildCardMatch
+ *
+ * Takes a prevalidated shell expression exp, and a string str.
+ *
+ * Returns 0 on match and 1 on non-match.
+ */
+
+int NS_WildCardMatch(const char* aStr, const char* aExpr,
+                     bool aCaseInsensitive);
+
+int NS_WildCardMatch(const char16_t* aStr, const char16_t* aExpr,
+                     bool aCaseInsensitive);
+
+#endif /* nsWildCard_h__ */