Adding upstream version 86.0.1.upstream/86.0.1upstream

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

1 files changed, 768 insertions, 0 deletions

diff --git a/xpcom/io/Base64.cpp b/xpcom/io/Base64.cpp
new file mode 100644
index 0000000000..d7a07a1029
--- /dev/null
+++ b/xpcom/io/Base64.cpp
@@ -0,0 +1,768 @@
+/* -*- 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;
+  }
+
+  if (!aDest.SetLength(base64LenOrErr.inspect(), mozilla::fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  EncodeInputStream_State<T> state;
+  state.charsOnStack = 0;
+  state.c[2] = '\0';
+  state.buffer = aOffset + aDest.BeginWriting();
+
+  while (true) {
+    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;
+    }
+  }
+
+  // Finish encoding if anything is left
+  if (state.charsOnStack) {
+    Encode(state.c, state.charsOnStack, state.buffer);
+  }
+
+  if (aDest.Length()) {
+    // May belong to an nsCString with an unallocated buffer, so only null
+    // terminate if there is a need to.
+    *aDest.EndWriting() = '\0';
+  }
+
+  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,
+};
+// clang-format on
+
+template <typename T>
+[[nodiscard]] bool Base64CharToValue(T aChar, uint8_t* aValue) {
+  static const size_t mask = 0x7f;
+  static_assert(
+      (mask + 1) == sizeof(kBase64DecodeTable) / sizeof(kBase64DecodeTable[0]),
+      "wrong mask");
+  size_t index = static_cast<uint8_t>(aChar);
+
+  if (index & ~mask) {
+    return false;
+  }
+  *aValue = kBase64DecodeTable[index & mask];
+
+  return *aValue != 255;
+}
+
+static const char kBase64URLAlphabet[] =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
+// 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,
+};
+// clang-format on
+
+bool Base64URLCharToValue(char aChar, uint8_t* aValue) {
+  uint8_t index = static_cast<uint8_t>(aChar);
+  *aValue = kBase64URLDecodeTable[index & 0x7f];
+  return (*aValue != 255) && !(index & ~0x7f);
+}
+
+}  // 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>
+static nsresult Base64DecodeString(const T& aBase64, T& 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 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