Adding upstream version 115.7.0esr.upstream/115.7.0esr

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

1 files changed, 1706 insertions, 0 deletions

diff --git a/xpcom/string/nsTSubstring.cpp b/xpcom/string/nsTSubstring.cpp
new file mode 100644
index 0000000000..b81b845fee
--- /dev/null
+++ b/xpcom/string/nsTSubstring.cpp
@@ -0,0 +1,1706 @@
+/* -*- 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 "double-conversion/double-conversion.h"
+#include "mozilla/CheckedInt.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/Printf.h"
+#include "mozilla/ResultExtensions.h"
+
+#include "nsASCIIMask.h"
+#include "nsCharTraits.h"
+#include "nsISupports.h"
+#include "nsString.h"
+#include "nsTArray.h"
+
+#ifdef DEBUG
+#  include "nsStringStats.h"
+#else
+#  define STRING_STAT_INCREMENT(_s)
+#endif
+
+// It's not worthwhile to reallocate the buffer and memcpy the
+// contents over when the size difference isn't large. With
+// power-of-two allocation buckets and 64 as the typical inline
+// capacity, considering that above 1000 there performance aspects
+// of realloc and memcpy seem to be absorbed, relative to the old
+// code, by the performance benefits of the new code being exact,
+// we need to choose which transitions of 256 to 128, 512 to 256
+// and 1024 to 512 to allow. As a guess, let's pick the middle
+// one as the the largest potential transition that we forgo. So
+// we'll shrink from 1024 bucket to 512 bucket but not from 512
+// bucket to 256 bucket. We'll decide by comparing the difference
+// of capacities. As bucket differences, the differences are 256
+// and 512. Since the capacities have various overheads, we
+// can't compare with 256 or 512 exactly but it's easier to
+// compare to some number that's between the two, so it's
+// far away from either to ignore the overheads.
+const uint32_t kNsStringBufferShrinkingThreshold = 384;
+
+using double_conversion::DoubleToStringConverter;
+
+// ---------------------------------------------------------------------------
+
+static const char16_t gNullChar = 0;
+
+char* const nsCharTraits<char>::sEmptyBuffer =
+    (char*)const_cast<char16_t*>(&gNullChar);
+char16_t* const nsCharTraits<char16_t>::sEmptyBuffer =
+    const_cast<char16_t*>(&gNullChar);
+
+// ---------------------------------------------------------------------------
+
+static void ReleaseData(void* aData, nsAString::DataFlags aFlags) {
+  if (aFlags & nsAString::DataFlags::REFCOUNTED) {
+    nsStringBuffer::FromData(aData)->Release();
+  } else if (aFlags & nsAString::DataFlags::OWNED) {
+    free(aData);
+    STRING_STAT_INCREMENT(AdoptFree);
+    // Treat this as destruction of a "StringAdopt" object for leak
+    // tracking purposes.
+    MOZ_LOG_DTOR(aData, "StringAdopt", 1);
+  }
+  // otherwise, nothing to do.
+}
+
+// ---------------------------------------------------------------------------
+
+#ifdef XPCOM_STRING_CONSTRUCTOR_OUT_OF_LINE
+template <typename T>
+nsTSubstring<T>::nsTSubstring(char_type* aData, size_type aLength,
+                              DataFlags aDataFlags, ClassFlags aClassFlags)
+    : ::mozilla::detail::nsTStringRepr<T>(aData, aLength, aDataFlags,
+                                          aClassFlags) {
+  AssertValid();
+
+  if (aDataFlags & DataFlags::OWNED) {
+    STRING_STAT_INCREMENT(Adopt);
+    MOZ_LOG_CTOR(this->mData, "StringAdopt", 1);
+  }
+}
+#endif /* XPCOM_STRING_CONSTRUCTOR_OUT_OF_LINE */
+
+/**
+ * helper function for down-casting a nsTSubstring to an nsTAutoString.
+ */
+template <typename T>
+inline const nsTAutoString<T>* AsAutoString(const nsTSubstring<T>* aStr) {
+  return static_cast<const nsTAutoString<T>*>(aStr);
+}
+
+template <typename T>
+mozilla::Result<mozilla::BulkWriteHandle<T>, nsresult>
+nsTSubstring<T>::BulkWrite(size_type aCapacity, size_type aPrefixToPreserve,
+                           bool aAllowShrinking) {
+  auto r = StartBulkWriteImpl(aCapacity, aPrefixToPreserve, aAllowShrinking);
+  if (MOZ_UNLIKELY(r.isErr())) {
+    return r.propagateErr();
+  }
+  return mozilla::BulkWriteHandle<T>(this, r.unwrap());
+}
+
+template <typename T>
+auto nsTSubstring<T>::StartBulkWriteImpl(size_type aCapacity,
+                                         size_type aPrefixToPreserve,
+                                         bool aAllowShrinking,
+                                         size_type aSuffixLength,
+                                         size_type aOldSuffixStart,
+                                         size_type aNewSuffixStart)
+    -> mozilla::Result<size_type, nsresult> {
+  // Note! Capacity does not include room for the terminating null char.
+
+  MOZ_ASSERT(aPrefixToPreserve <= aCapacity,
+             "Requested preservation of an overlong prefix.");
+  MOZ_ASSERT(aNewSuffixStart + aSuffixLength <= aCapacity,
+             "Requesed move of suffix to out-of-bounds location.");
+  // Can't assert aOldSuffixStart, because mLength may not be valid anymore,
+  // since this method allows itself to be called more than once.
+
+  // If zero capacity is requested, set the string to the special empty
+  // string.
+  if (MOZ_UNLIKELY(!aCapacity)) {
+    ReleaseData(this->mData, this->mDataFlags);
+    SetToEmptyBuffer();
+    return 0;
+  }
+
+  // Note! Capacity() returns 0 when the string is immutable.
+  const size_type curCapacity = Capacity();
+
+  bool shrinking = false;
+
+  // We've established that aCapacity > 0.
+  // |curCapacity == 0| means that the buffer is immutable or 0-sized, so we
+  // need to allocate a new buffer. We cannot use the existing buffer even
+  // though it might be large enough.
+
+  if (aCapacity <= curCapacity) {
+    if (aAllowShrinking) {
+      shrinking = true;
+    } else {
+      char_traits::move(this->mData + aNewSuffixStart,
+                        this->mData + aOldSuffixStart, aSuffixLength);
+      if (aSuffixLength) {
+        char_traits::uninitialize(this->mData + aPrefixToPreserve,
+                                  XPCOM_MIN(aNewSuffixStart - aPrefixToPreserve,
+                                            kNsStringBufferMaxPoison));
+        char_traits::uninitialize(
+            this->mData + aNewSuffixStart + aSuffixLength,
+            XPCOM_MIN(curCapacity + 1 - aNewSuffixStart - aSuffixLength,
+                      kNsStringBufferMaxPoison));
+      } else {
+        char_traits::uninitialize(this->mData + aPrefixToPreserve,
+                                  XPCOM_MIN(curCapacity + 1 - aPrefixToPreserve,
+                                            kNsStringBufferMaxPoison));
+      }
+      return curCapacity;
+    }
+  }
+
+  char_type* oldData = this->mData;
+  DataFlags oldFlags = this->mDataFlags;
+
+  char_type* newData;
+  DataFlags newDataFlags;
+  size_type newCapacity;
+
+  // If this is an nsTAutoStringN, it's possible that we can use the inline
+  // buffer.
+  if ((this->mClassFlags & ClassFlags::INLINE) &&
+      (aCapacity <= AsAutoString(this)->mInlineCapacity)) {
+    newCapacity = AsAutoString(this)->mInlineCapacity;
+    newData = (char_type*)AsAutoString(this)->mStorage;
+    newDataFlags = DataFlags::TERMINATED | DataFlags::INLINE;
+  } else {
+    // If |aCapacity > kMaxCapacity|, then our doubling algorithm may not be
+    // able to allocate it.  Just bail out in cases like that.  We don't want
+    // to be allocating 2GB+ strings anyway.
+    static_assert((sizeof(nsStringBuffer) & 0x1) == 0,
+                  "bad size for nsStringBuffer");
+    if (MOZ_UNLIKELY(!this->CheckCapacity(aCapacity))) {
+      return mozilla::Err(NS_ERROR_OUT_OF_MEMORY);
+    }
+
+    // We increase our capacity so that the allocated buffer grows
+    // exponentially, which gives us amortized O(1) appending. Below the
+    // threshold, we use powers-of-two. Above the threshold, we grow by at
+    // least 1.125, rounding up to the nearest MiB.
+    const size_type slowGrowthThreshold = 8 * 1024 * 1024;
+
+    // nsStringBuffer allocates sizeof(nsStringBuffer) + passed size, and
+    // storageSize below wants extra 1 * sizeof(char_type).
+    const size_type neededExtraSpace =
+        sizeof(nsStringBuffer) / sizeof(char_type) + 1;
+
+    size_type temp;
+    if (aCapacity >= slowGrowthThreshold) {
+      size_type minNewCapacity =
+          curCapacity + (curCapacity >> 3);  // multiply by 1.125
+      temp = XPCOM_MAX(aCapacity, minNewCapacity) + neededExtraSpace;
+
+      // Round up to the next multiple of MiB, but ensure the expected
+      // capacity doesn't include the extra space required by nsStringBuffer
+      // and null-termination.
+      const size_t MiB = 1 << 20;
+      temp = (MiB * ((temp + MiB - 1) / MiB)) - neededExtraSpace;
+    } else {
+      // Round up to the next power of two.
+      temp =
+          mozilla::RoundUpPow2(aCapacity + neededExtraSpace) - neededExtraSpace;
+    }
+
+    newCapacity = XPCOM_MIN(temp, base_string_type::kMaxCapacity);
+    MOZ_ASSERT(newCapacity >= aCapacity,
+               "should have hit the early return at the top");
+    // Avoid shrinking if the new buffer size is close to the old. Note that
+    // unsigned underflow is defined behavior.
+    if ((curCapacity - newCapacity) <= kNsStringBufferShrinkingThreshold &&
+        (this->mDataFlags & DataFlags::REFCOUNTED)) {
+      MOZ_ASSERT(aAllowShrinking, "How come we didn't return earlier?");
+      // We're already close enough to the right size.
+      newData = oldData;
+      newCapacity = curCapacity;
+    } else {
+      size_type storageSize = (newCapacity + 1) * sizeof(char_type);
+      // Since we allocate only by powers of 2 we always fit into a full
+      // mozjemalloc bucket, it's not useful to use realloc, which may spend
+      // time uselessly copying too much.
+      nsStringBuffer* newHdr = nsStringBuffer::Alloc(storageSize).take();
+      if (newHdr) {
+        newData = (char_type*)newHdr->Data();
+      } else if (shrinking) {
+        // We're still in a consistent state.
+        //
+        // Since shrinking is just a memory footprint optimization, we
+        // don't propagate OOM if we tried to shrink in order to avoid
+        // OOM crashes from infallible callers. If we're lucky, soon enough
+        // a fallible caller reaches OOM and is able to deal or we end up
+        // disposing of this string before reaching OOM again.
+        newData = oldData;
+        newCapacity = curCapacity;
+      } else {
+        return mozilla::Err(NS_ERROR_OUT_OF_MEMORY);
+      }
+    }
+    newDataFlags = DataFlags::TERMINATED | DataFlags::REFCOUNTED;
+  }
+
+  this->mData = newData;
+  this->mDataFlags = newDataFlags;
+
+  if (oldData == newData) {
+    char_traits::move(newData + aNewSuffixStart, oldData + aOldSuffixStart,
+                      aSuffixLength);
+    if (aSuffixLength) {
+      char_traits::uninitialize(this->mData + aPrefixToPreserve,
+                                XPCOM_MIN(aNewSuffixStart - aPrefixToPreserve,
+                                          kNsStringBufferMaxPoison));
+      char_traits::uninitialize(
+          this->mData + aNewSuffixStart + aSuffixLength,
+          XPCOM_MIN(newCapacity + 1 - aNewSuffixStart - aSuffixLength,
+                    kNsStringBufferMaxPoison));
+    } else {
+      char_traits::uninitialize(this->mData + aPrefixToPreserve,
+                                XPCOM_MIN(newCapacity + 1 - aPrefixToPreserve,
+                                          kNsStringBufferMaxPoison));
+    }
+  } else {
+    char_traits::copy(newData, oldData, aPrefixToPreserve);
+    char_traits::copy(newData + aNewSuffixStart, oldData + aOldSuffixStart,
+                      aSuffixLength);
+    ReleaseData(oldData, oldFlags);
+  }
+
+  return newCapacity;
+}
+
+template <typename T>
+void nsTSubstring<T>::FinishBulkWriteImpl(size_type aLength) {
+  if (aLength) {
+    FinishBulkWriteImplImpl(aLength);
+  } else {
+    ReleaseData(this->mData, this->mDataFlags);
+    SetToEmptyBuffer();
+  }
+  AssertValid();
+}
+
+template <typename T>
+void nsTSubstring<T>::Finalize() {
+  ReleaseData(this->mData, this->mDataFlags);
+  // this->mData, this->mLength, and this->mDataFlags are purposefully left
+  // dangling
+}
+
+template <typename T>
+bool nsTSubstring<T>::ReplacePrep(index_type aCutStart, size_type aCutLength,
+                                  size_type aNewLength) {
+  aCutLength = XPCOM_MIN(aCutLength, this->mLength - aCutStart);
+
+  mozilla::CheckedInt<size_type> newTotalLen = this->Length();
+  newTotalLen += aNewLength;
+  newTotalLen -= aCutLength;
+  if (!newTotalLen.isValid()) {
+    return false;
+  }
+
+  if (aCutStart == this->mLength && Capacity() > newTotalLen.value()) {
+    this->mDataFlags &= ~DataFlags::VOIDED;
+    this->mData[newTotalLen.value()] = char_type(0);
+    this->mLength = newTotalLen.value();
+    return true;
+  }
+
+  return ReplacePrepInternal(aCutStart, aCutLength, aNewLength,
+                             newTotalLen.value());
+}
+
+template <typename T>
+bool nsTSubstring<T>::ReplacePrepInternal(index_type aCutStart,
+                                          size_type aCutLen, size_type aFragLen,
+                                          size_type aNewLen) {
+  size_type newSuffixStart = aCutStart + aFragLen;
+  size_type oldSuffixStart = aCutStart + aCutLen;
+  size_type suffixLength = this->mLength - oldSuffixStart;
+
+  mozilla::Result<size_type, nsresult> r = StartBulkWriteImpl(
+      aNewLen, aCutStart, false, suffixLength, oldSuffixStart, newSuffixStart);
+  if (r.isErr()) {
+    return false;
+  }
+  FinishBulkWriteImpl(aNewLen);
+  return true;
+}
+
+template <typename T>
+typename nsTSubstring<T>::size_type nsTSubstring<T>::Capacity() const {
+  // return 0 to indicate an immutable or 0-sized buffer
+
+  size_type capacity;
+  if (this->mDataFlags & DataFlags::REFCOUNTED) {
+    // if the string is readonly, then we pretend that it has no capacity.
+    nsStringBuffer* hdr = nsStringBuffer::FromData(this->mData);
+    if (hdr->IsReadonly()) {
+      capacity = 0;
+    } else {
+      capacity = (size_t(hdr->StorageSize()) / sizeof(char_type)) - 1;
+    }
+  } else if (this->mDataFlags & DataFlags::INLINE) {
+    MOZ_ASSERT(this->mClassFlags & ClassFlags::INLINE);
+    capacity = AsAutoString(this)->mInlineCapacity;
+  } else if (this->mDataFlags & DataFlags::OWNED) {
+    // we don't store the capacity of an adopted buffer because that would
+    // require an additional member field.  the best we can do is base the
+    // capacity on our length.  remains to be seen if this is the right
+    // trade-off.
+    capacity = this->mLength;
+  } else {
+    capacity = 0;
+  }
+
+  return capacity;
+}
+
+template <typename T>
+bool nsTSubstring<T>::EnsureMutable(size_type aNewLen) {
+  if (aNewLen == size_type(-1) || aNewLen == this->mLength) {
+    if (this->mDataFlags & (DataFlags::INLINE | DataFlags::OWNED)) {
+      return true;
+    }
+    if ((this->mDataFlags & DataFlags::REFCOUNTED) &&
+        !nsStringBuffer::FromData(this->mData)->IsReadonly()) {
+      return true;
+    }
+
+    aNewLen = this->mLength;
+  }
+  return SetLength(aNewLen, mozilla::fallible);
+}
+
+// ---------------------------------------------------------------------------
+
+// This version of Assign is optimized for single-character assignment.
+template <typename T>
+void nsTSubstring<T>::Assign(char_type aChar) {
+  if (MOZ_UNLIKELY(!Assign(aChar, mozilla::fallible))) {
+    AllocFailed(1);
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::Assign(char_type aChar, const fallible_t&) {
+  auto r = StartBulkWriteImpl(1, 0, true);
+  if (MOZ_UNLIKELY(r.isErr())) {
+    return false;
+  }
+  *this->mData = aChar;
+  FinishBulkWriteImpl(1);
+  return true;
+}
+
+template <typename T>
+void nsTSubstring<T>::Assign(const char_type* aData, size_type aLength) {
+  if (MOZ_UNLIKELY(!Assign(aData, aLength, mozilla::fallible))) {
+    AllocFailed(aLength == size_type(-1) ? char_traits::length(aData)
+                                         : aLength);
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::Assign(const char_type* aData,
+                             const fallible_t& aFallible) {
+  return Assign(aData, size_type(-1), aFallible);
+}
+
+template <typename T>
+bool nsTSubstring<T>::Assign(const char_type* aData, size_type aLength,
+                             const fallible_t& aFallible) {
+  if (!aData || aLength == 0) {
+    Truncate();
+    return true;
+  }
+
+  if (MOZ_UNLIKELY(aLength == size_type(-1))) {
+    aLength = char_traits::length(aData);
+  }
+
+  if (MOZ_UNLIKELY(this->IsDependentOn(aData, aData + aLength))) {
+    return Assign(string_type(aData, aLength), aFallible);
+  }
+
+  auto r = StartBulkWriteImpl(aLength, 0, true);
+  if (MOZ_UNLIKELY(r.isErr())) {
+    return false;
+  }
+  char_traits::copy(this->mData, aData, aLength);
+  FinishBulkWriteImpl(aLength);
+  return true;
+}
+
+template <typename T>
+void nsTSubstring<T>::AssignASCII(const char* aData, size_type aLength) {
+  if (MOZ_UNLIKELY(!AssignASCII(aData, aLength, mozilla::fallible))) {
+    AllocFailed(aLength);
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::AssignASCII(const char* aData, size_type aLength,
+                                  const fallible_t& aFallible) {
+  MOZ_ASSERT(aLength != size_type(-1));
+
+  // A Unicode string can't depend on an ASCII string buffer,
+  // so this dependence check only applies to CStrings.
+  if constexpr (std::is_same_v<T, char>) {
+    if (this->IsDependentOn(aData, aData + aLength)) {
+      return Assign(string_type(aData, aLength), aFallible);
+    }
+  }
+
+  auto r = StartBulkWriteImpl(aLength, 0, true);
+  if (MOZ_UNLIKELY(r.isErr())) {
+    return false;
+  }
+  char_traits::copyASCII(this->mData, aData, aLength);
+  FinishBulkWriteImpl(aLength);
+  return true;
+}
+
+template <typename T>
+void nsTSubstring<T>::AssignLiteral(const char_type* aData, size_type aLength) {
+  ReleaseData(this->mData, this->mDataFlags);
+  SetData(const_cast<char_type*>(aData), aLength,
+          DataFlags::TERMINATED | DataFlags::LITERAL);
+}
+
+template <typename T>
+void nsTSubstring<T>::Assign(const self_type& aStr) {
+  if (!Assign(aStr, mozilla::fallible)) {
+    AllocFailed(aStr.Length());
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::Assign(const self_type& aStr,
+                             const fallible_t& aFallible) {
+  // |aStr| could be sharable. We need to check its flags to know how to
+  // deal with it.
+
+  if (&aStr == this) {
+    return true;
+  }
+
+  if (!aStr.mLength) {
+    Truncate();
+    this->mDataFlags |= aStr.mDataFlags & DataFlags::VOIDED;
+    return true;
+  }
+
+  if (aStr.mDataFlags & DataFlags::REFCOUNTED) {
+    // nice! we can avoid a string copy :-)
+
+    // |aStr| should be null-terminated
+    NS_ASSERTION(aStr.mDataFlags & DataFlags::TERMINATED,
+                 "shared, but not terminated");
+
+    ReleaseData(this->mData, this->mDataFlags);
+
+    SetData(aStr.mData, aStr.mLength,
+            DataFlags::TERMINATED | DataFlags::REFCOUNTED);
+
+    // get an owning reference to the this->mData
+    nsStringBuffer::FromData(this->mData)->AddRef();
+    return true;
+  } else if (aStr.mDataFlags & DataFlags::LITERAL) {
+    MOZ_ASSERT(aStr.mDataFlags & DataFlags::TERMINATED, "Unterminated literal");
+
+    AssignLiteral(aStr.mData, aStr.mLength);
+    return true;
+  }
+
+  // else, treat this like an ordinary assignment.
+  return Assign(aStr.Data(), aStr.Length(), aFallible);
+}
+
+template <typename T>
+void nsTSubstring<T>::Assign(self_type&& aStr) {
+  if (!Assign(std::move(aStr), mozilla::fallible)) {
+    AllocFailed(aStr.Length());
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::AssignOwned(self_type&& aStr) {
+  MOZ_ASSERT(aStr.mDataFlags & (DataFlags::REFCOUNTED | DataFlags::OWNED),
+             "neither shared nor owned");
+
+  // If they have a REFCOUNTED or OWNED buffer, we can avoid a copy - so steal
+  // their buffer and reset them to the empty string.
+
+  // |aStr| should be null-terminated
+  MOZ_ASSERT(aStr.mDataFlags & DataFlags::TERMINATED,
+             "shared or owned, but not terminated");
+
+  ReleaseData(this->mData, this->mDataFlags);
+
+  SetData(aStr.mData, aStr.mLength, aStr.mDataFlags);
+  aStr.SetToEmptyBuffer();
+}
+
+template <typename T>
+bool nsTSubstring<T>::Assign(self_type&& aStr, const fallible_t& aFallible) {
+  // We're moving |aStr| in this method, so we need to try to steal the data,
+  // and in the fallback perform a copy-assignment followed by a truncation of
+  // the original string.
+
+  if (&aStr == this) {
+    NS_WARNING("Move assigning a string to itself?");
+    return true;
+  }
+
+  if (aStr.mDataFlags & (DataFlags::REFCOUNTED | DataFlags::OWNED)) {
+    AssignOwned(std::move(aStr));
+    return true;
+  }
+
+  // Otherwise treat this as a normal assignment, and truncate the moved string.
+  // We don't truncate the source string if the allocation failed.
+  if (!Assign(aStr, aFallible)) {
+    return false;
+  }
+  aStr.Truncate();
+  return true;
+}
+
+template <typename T>
+void nsTSubstring<T>::Assign(const substring_tuple_type& aTuple) {
+  if (!Assign(aTuple, mozilla::fallible)) {
+    AllocFailed(aTuple.Length());
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::AssignNonDependent(const substring_tuple_type& aTuple,
+                                         size_type aTupleLength,
+                                         const mozilla::fallible_t& aFallible) {
+  NS_ASSERTION(aTuple.Length() == aTupleLength, "wrong length passed");
+
+  auto r = StartBulkWriteImpl(aTupleLength);
+  if (r.isErr()) {
+    return false;
+  }
+
+  aTuple.WriteTo(this->mData, aTupleLength);
+
+  FinishBulkWriteImpl(aTupleLength);
+  return true;
+}
+
+template <typename T>
+bool nsTSubstring<T>::Assign(const substring_tuple_type& aTuple,
+                             const fallible_t& aFallible) {
+  const auto [isDependentOnThis, tupleLength] =
+      aTuple.IsDependentOnWithLength(this->mData, this->mData + this->mLength);
+  if (isDependentOnThis) {
+    string_type temp;
+    self_type& tempSubstring = temp;
+    if (!tempSubstring.AssignNonDependent(aTuple, tupleLength, aFallible)) {
+      return false;
+    }
+    AssignOwned(std::move(temp));
+    return true;
+  }
+
+  return AssignNonDependent(aTuple, tupleLength, aFallible);
+}
+
+template <typename T>
+void nsTSubstring<T>::Adopt(char_type* aData, size_type aLength) {
+  if (aData) {
+    ReleaseData(this->mData, this->mDataFlags);
+
+    if (aLength == size_type(-1)) {
+      aLength = char_traits::length(aData);
+    }
+
+    SetData(aData, aLength, DataFlags::TERMINATED | DataFlags::OWNED);
+
+    STRING_STAT_INCREMENT(Adopt);
+    // Treat this as construction of a "StringAdopt" object for leak
+    // tracking purposes.
+    MOZ_LOG_CTOR(this->mData, "StringAdopt", 1);
+  } else {
+    SetIsVoid(true);
+  }
+}
+
+// This version of Replace is optimized for single-character replacement.
+template <typename T>
+void nsTSubstring<T>::Replace(index_type aCutStart, size_type aCutLength,
+                              char_type aChar) {
+  aCutStart = XPCOM_MIN(aCutStart, this->Length());
+
+  if (ReplacePrep(aCutStart, aCutLength, 1)) {
+    this->mData[aCutStart] = aChar;
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::Replace(index_type aCutStart, size_type aCutLength,
+                              char_type aChar, const fallible_t&) {
+  aCutStart = XPCOM_MIN(aCutStart, this->Length());
+
+  if (!ReplacePrep(aCutStart, aCutLength, 1)) {
+    return false;
+  }
+
+  this->mData[aCutStart] = aChar;
+
+  return true;
+}
+
+template <typename T>
+void nsTSubstring<T>::Replace(index_type aCutStart, size_type aCutLength,
+                              const char_type* aData, size_type aLength) {
+  if (!Replace(aCutStart, aCutLength, aData, aLength, mozilla::fallible)) {
+    AllocFailed(this->Length() - aCutLength + 1);
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::Replace(index_type aCutStart, size_type aCutLength,
+                              const char_type* aData, size_type aLength,
+                              const fallible_t& aFallible) {
+  // unfortunately, some callers pass null :-(
+  if (!aData) {
+    aLength = 0;
+  } else {
+    if (aLength == size_type(-1)) {
+      aLength = char_traits::length(aData);
+    }
+
+    if (this->IsDependentOn(aData, aData + aLength)) {
+      nsTAutoString<T> temp(aData, aLength);
+      return Replace(aCutStart, aCutLength, temp, aFallible);
+    }
+  }
+
+  aCutStart = XPCOM_MIN(aCutStart, this->Length());
+
+  bool ok = ReplacePrep(aCutStart, aCutLength, aLength);
+  if (!ok) {
+    return false;
+  }
+
+  if (aLength > 0) {
+    char_traits::copy(this->mData + aCutStart, aData, aLength);
+  }
+
+  return true;
+}
+
+template <typename T>
+void nsTSubstring<T>::Replace(index_type aCutStart, size_type aCutLength,
+                              const substring_tuple_type& aTuple) {
+  const auto [isDependentOnThis, tupleLength] =
+      aTuple.IsDependentOnWithLength(this->mData, this->mData + this->mLength);
+
+  if (isDependentOnThis) {
+    nsTAutoString<T> temp;
+    if (!temp.AssignNonDependent(aTuple, tupleLength, mozilla::fallible)) {
+      AllocFailed(tupleLength);
+    }
+    Replace(aCutStart, aCutLength, temp);
+    return;
+  }
+
+  aCutStart = XPCOM_MIN(aCutStart, this->Length());
+
+  if (ReplacePrep(aCutStart, aCutLength, tupleLength) && tupleLength > 0) {
+    aTuple.WriteTo(this->mData + aCutStart, tupleLength);
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::ReplaceLiteral(index_type aCutStart, size_type aCutLength,
+                                     const char_type* aData,
+                                     size_type aLength) {
+  aCutStart = XPCOM_MIN(aCutStart, this->Length());
+
+  if (!aCutStart && aCutLength == this->Length() &&
+      !(this->mDataFlags & DataFlags::REFCOUNTED)) {
+    // Check for REFCOUNTED above to avoid undoing the effect of
+    // SetCapacity().
+    AssignLiteral(aData, aLength);
+  } else if (ReplacePrep(aCutStart, aCutLength, aLength) && aLength > 0) {
+    char_traits::copy(this->mData + aCutStart, aData, aLength);
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::Append(char_type aChar) {
+  if (MOZ_UNLIKELY(!Append(aChar, mozilla::fallible))) {
+    AllocFailed(this->mLength + 1);
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::Append(char_type aChar, const fallible_t& aFallible) {
+  size_type oldLen = this->mLength;
+  size_type newLen = oldLen + 1;  // Can't overflow
+  auto r = StartBulkWriteImpl(newLen, oldLen, false);
+  if (MOZ_UNLIKELY(r.isErr())) {
+    return false;
+  }
+  this->mData[oldLen] = aChar;
+  FinishBulkWriteImpl(newLen);
+  return true;
+}
+
+template <typename T>
+void nsTSubstring<T>::Append(const char_type* aData, size_type aLength) {
+  if (MOZ_UNLIKELY(!Append(aData, aLength, mozilla::fallible))) {
+    AllocFailed(this->mLength + (aLength == size_type(-1)
+                                     ? char_traits::length(aData)
+                                     : aLength));
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::Append(const char_type* aData, size_type aLength,
+                             const fallible_t& aFallible) {
+  if (MOZ_UNLIKELY(aLength == size_type(-1))) {
+    aLength = char_traits::length(aData);
+  }
+
+  if (MOZ_UNLIKELY(!aLength)) {
+    // Avoid undoing the effect of SetCapacity() if both
+    // mLength and aLength are zero.
+    return true;
+  }
+
+  if (MOZ_UNLIKELY(this->IsDependentOn(aData, aData + aLength))) {
+    return Append(string_type(aData, aLength), mozilla::fallible);
+  }
+  size_type oldLen = this->mLength;
+  mozilla::CheckedInt<size_type> newLen(oldLen);
+  newLen += aLength;
+  if (MOZ_UNLIKELY(!newLen.isValid())) {
+    return false;
+  }
+  auto r = StartBulkWriteImpl(newLen.value(), oldLen, false);
+  if (MOZ_UNLIKELY(r.isErr())) {
+    return false;
+  }
+  char_traits::copy(this->mData + oldLen, aData, aLength);
+  FinishBulkWriteImpl(newLen.value());
+  return true;
+}
+
+template <typename T>
+void nsTSubstring<T>::AppendASCII(const char* aData, size_type aLength) {
+  if (MOZ_UNLIKELY(!AppendASCII(aData, aLength, mozilla::fallible))) {
+    AllocFailed(this->mLength +
+                (aLength == size_type(-1) ? strlen(aData) : aLength));
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::AppendASCII(const char* aData,
+                                  const fallible_t& aFallible) {
+  return AppendASCII(aData, size_type(-1), aFallible);
+}
+
+template <typename T>
+bool nsTSubstring<T>::AppendASCII(const char* aData, size_type aLength,
+                                  const fallible_t& aFallible) {
+  if (MOZ_UNLIKELY(aLength == size_type(-1))) {
+    aLength = strlen(aData);
+  }
+
+  if (MOZ_UNLIKELY(!aLength)) {
+    // Avoid undoing the effect of SetCapacity() if both
+    // mLength and aLength are zero.
+    return true;
+  }
+
+  if constexpr (std::is_same_v<T, char>) {
+    // 16-bit string can't depend on an 8-bit buffer
+    if (MOZ_UNLIKELY(this->IsDependentOn(aData, aData + aLength))) {
+      return Append(string_type(aData, aLength), mozilla::fallible);
+    }
+  }
+
+  size_type oldLen = this->mLength;
+  mozilla::CheckedInt<size_type> newLen(oldLen);
+  newLen += aLength;
+  if (MOZ_UNLIKELY(!newLen.isValid())) {
+    return false;
+  }
+  auto r = StartBulkWriteImpl(newLen.value(), oldLen, false);
+  if (MOZ_UNLIKELY(r.isErr())) {
+    return false;
+  }
+  char_traits::copyASCII(this->mData + oldLen, aData, aLength);
+  FinishBulkWriteImpl(newLen.value());
+  return true;
+}
+
+template <typename T>
+void nsTSubstring<T>::Append(const self_type& aStr) {
+  if (MOZ_UNLIKELY(!Append(aStr, mozilla::fallible))) {
+    AllocFailed(this->mLength + aStr.Length());
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::Append(const self_type& aStr,
+                             const fallible_t& aFallible) {
+  // Check refcounted to avoid undoing the effects of SetCapacity().
+  if (MOZ_UNLIKELY(!this->mLength &&
+                   !(this->mDataFlags & DataFlags::REFCOUNTED))) {
+    return Assign(aStr, mozilla::fallible);
+  }
+  return Append(aStr.BeginReading(), aStr.Length(), mozilla::fallible);
+}
+
+template <typename T>
+void nsTSubstring<T>::Append(const substring_tuple_type& aTuple) {
+  if (MOZ_UNLIKELY(!Append(aTuple, mozilla::fallible))) {
+    AllocFailed(this->mLength + aTuple.Length());
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::Append(const substring_tuple_type& aTuple,
+                             const fallible_t& aFallible) {
+  const auto [isDependentOnThis, tupleLength] =
+      aTuple.IsDependentOnWithLength(this->mData, this->mData + this->mLength);
+
+  if (MOZ_UNLIKELY(!tupleLength)) {
+    // Avoid undoing the effect of SetCapacity() if both
+    // mLength and tupleLength are zero.
+    return true;
+  }
+
+  if (MOZ_UNLIKELY(isDependentOnThis)) {
+    return Append(string_type(aTuple), aFallible);
+  }
+
+  size_type oldLen = this->mLength;
+  mozilla::CheckedInt<size_type> newLen(oldLen);
+  newLen += tupleLength;
+  if (MOZ_UNLIKELY(!newLen.isValid())) {
+    return false;
+  }
+  auto r = StartBulkWriteImpl(newLen.value(), oldLen, false);
+  if (MOZ_UNLIKELY(r.isErr())) {
+    return false;
+  }
+  aTuple.WriteTo(this->mData + oldLen, tupleLength);
+  FinishBulkWriteImpl(newLen.value());
+  return true;
+}
+
+template <typename T>
+void nsTSubstring<T>::SetCapacity(size_type aCapacity) {
+  if (!SetCapacity(aCapacity, mozilla::fallible)) {
+    AllocFailed(aCapacity);
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::SetCapacity(size_type aCapacity, const fallible_t&) {
+  size_type length = this->mLength;
+  // This method can no longer be used to shorten the
+  // logical length.
+  size_type capacity = XPCOM_MAX(aCapacity, length);
+
+  auto r = StartBulkWriteImpl(capacity, length, true);
+  if (r.isErr()) {
+    return false;
+  }
+
+  if (MOZ_UNLIKELY(!capacity)) {
+    // Zero capacity was requested on a zero-length
+    // string. In this special case, we are pointing
+    // to the special empty buffer, which is already
+    // zero-terminated and not writable, so we must
+    // not attempt to zero-terminate it.
+    AssertValid();
+    return true;
+  }
+
+  // FinishBulkWriteImpl with argument zero releases
+  // the heap-allocated buffer. However, SetCapacity()
+  // is a special case that allows mLength to be zero
+  // while a heap-allocated buffer exists.
+  // By calling FinishBulkWriteImplImpl, we skip the
+  // zero case handling that's inappropriate in the
+  // SetCapacity() case.
+  FinishBulkWriteImplImpl(length);
+  return true;
+}
+
+template <typename T>
+void nsTSubstring<T>::SetLength(size_type aLength) {
+  if (!SetLength(aLength, mozilla::fallible)) {
+    AllocFailed(aLength);
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::SetLength(size_type aLength,
+                                const fallible_t& aFallible) {
+  size_type preserve = XPCOM_MIN(aLength, this->Length());
+  auto r = StartBulkWriteImpl(aLength, preserve, true);
+  if (r.isErr()) {
+    return false;
+  }
+
+  FinishBulkWriteImpl(aLength);
+
+  return true;
+}
+
+template <typename T>
+void nsTSubstring<T>::Truncate() {
+  ReleaseData(this->mData, this->mDataFlags);
+  SetToEmptyBuffer();
+  AssertValid();
+}
+
+template <typename T>
+void nsTSubstring<T>::SetIsVoid(bool aVal) {
+  if (aVal) {
+    Truncate();
+    this->mDataFlags |= DataFlags::VOIDED;
+  } else {
+    this->mDataFlags &= ~DataFlags::VOIDED;
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::StripChar(char_type aChar) {
+  if (this->mLength == 0) {
+    return;
+  }
+
+  if (!EnsureMutable()) {  // XXX do this lazily?
+    AllocFailed(this->mLength);
+  }
+
+  // XXX(darin): this code should defer writing until necessary.
+
+  char_type* to = this->mData;
+  char_type* from = this->mData;
+  char_type* end = this->mData + this->mLength;
+
+  while (from < end) {
+    char_type theChar = *from++;
+    if (aChar != theChar) {
+      *to++ = theChar;
+    }
+  }
+  *to = char_type(0);  // add the null
+  this->mLength = to - this->mData;
+}
+
+template <typename T>
+void nsTSubstring<T>::StripChars(const char_type* aChars) {
+  if (this->mLength == 0) {
+    return;
+  }
+
+  if (!EnsureMutable()) {  // XXX do this lazily?
+    AllocFailed(this->mLength);
+  }
+
+  // XXX(darin): this code should defer writing until necessary.
+
+  char_type* to = this->mData;
+  char_type* from = this->mData;
+  char_type* end = this->mData + this->mLength;
+
+  while (from < end) {
+    char_type theChar = *from++;
+    const char_type* test = aChars;
+
+    for (; *test && *test != theChar; ++test)
+      ;
+
+    if (!*test) {
+      // Not stripped, copy this char.
+      *to++ = theChar;
+    }
+  }
+  *to = char_type(0);  // add the null
+  this->mLength = to - this->mData;
+}
+
+template <typename T>
+void nsTSubstring<T>::StripTaggedASCII(const ASCIIMaskArray& aToStrip) {
+  if (this->mLength == 0) {
+    return;
+  }
+
+  size_t untaggedPrefixLength = 0;
+  for (; untaggedPrefixLength < this->mLength; ++untaggedPrefixLength) {
+    uint32_t theChar = (uint32_t)this->mData[untaggedPrefixLength];
+    if (mozilla::ASCIIMask::IsMasked(aToStrip, theChar)) {
+      break;
+    }
+  }
+
+  if (untaggedPrefixLength == this->mLength) {
+    return;
+  }
+
+  if (!EnsureMutable()) {
+    AllocFailed(this->mLength);
+  }
+
+  char_type* to = this->mData + untaggedPrefixLength;
+  char_type* from = to;
+  char_type* end = this->mData + this->mLength;
+
+  while (from < end) {
+    uint32_t theChar = (uint32_t)*from++;
+    // Replacing this with a call to ASCIIMask::IsMasked
+    // regresses performance somewhat, so leaving it inlined.
+    if (!mozilla::ASCIIMask::IsMasked(aToStrip, theChar)) {
+      // Not stripped, copy this char.
+      *to++ = (char_type)theChar;
+    }
+  }
+  *to = char_type(0);  // add the null
+  this->mLength = to - this->mData;
+}
+
+template <typename T>
+void nsTSubstring<T>::StripCRLF() {
+  // Expanding this call to copy the code from StripTaggedASCII
+  // instead of just calling it does somewhat help with performance
+  // but it is not worth it given the duplicated code.
+  StripTaggedASCII(mozilla::ASCIIMask::MaskCRLF());
+}
+
+template <typename T>
+struct MOZ_STACK_CLASS PrintfAppend : public mozilla::PrintfTarget {
+  explicit PrintfAppend(nsTSubstring<T>* aString) : mString(aString) {}
+
+  bool append(const char* aStr, size_t aLen) override {
+    if (aLen == 0) {
+      return true;
+    }
+
+    mString->AppendASCII(aStr, aLen);
+    return true;
+  }
+
+ private:
+  nsTSubstring<T>* mString;
+};
+
+template <typename T>
+void nsTSubstring<T>::AppendPrintf(const char* aFormat, ...) {
+  PrintfAppend<T> appender(this);
+  va_list ap;
+  va_start(ap, aFormat);
+  bool r = appender.vprint(aFormat, ap);
+  if (!r) {
+    MOZ_CRASH("Allocation or other failure in PrintfTarget::print");
+  }
+  va_end(ap);
+}
+
+template <typename T>
+void nsTSubstring<T>::AppendVprintf(const char* aFormat, va_list aAp) {
+  PrintfAppend<T> appender(this);
+  bool r = appender.vprint(aFormat, aAp);
+  if (!r) {
+    MOZ_CRASH("Allocation or other failure in PrintfTarget::print");
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::AppendIntDec(int32_t aInteger) {
+  PrintfAppend<T> appender(this);
+  bool r = appender.appendIntDec(aInteger);
+  if (MOZ_UNLIKELY(!r)) {
+    MOZ_CRASH("Allocation or other failure while appending integers");
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::AppendIntDec(uint32_t aInteger) {
+  PrintfAppend<T> appender(this);
+  bool r = appender.appendIntDec(aInteger);
+  if (MOZ_UNLIKELY(!r)) {
+    MOZ_CRASH("Allocation or other failure while appending integers");
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::AppendIntOct(uint32_t aInteger) {
+  PrintfAppend<T> appender(this);
+  bool r = appender.appendIntOct(aInteger);
+  if (MOZ_UNLIKELY(!r)) {
+    MOZ_CRASH("Allocation or other failure while appending integers");
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::AppendIntHex(uint32_t aInteger) {
+  PrintfAppend<T> appender(this);
+  bool r = appender.appendIntHex(aInteger);
+  if (MOZ_UNLIKELY(!r)) {
+    MOZ_CRASH("Allocation or other failure while appending integers");
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::AppendIntDec(int64_t aInteger) {
+  PrintfAppend<T> appender(this);
+  bool r = appender.appendIntDec(aInteger);
+  if (MOZ_UNLIKELY(!r)) {
+    MOZ_CRASH("Allocation or other failure while appending integers");
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::AppendIntDec(uint64_t aInteger) {
+  PrintfAppend<T> appender(this);
+  bool r = appender.appendIntDec(aInteger);
+  if (MOZ_UNLIKELY(!r)) {
+    MOZ_CRASH("Allocation or other failure while appending integers");
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::AppendIntOct(uint64_t aInteger) {
+  PrintfAppend<T> appender(this);
+  bool r = appender.appendIntOct(aInteger);
+  if (MOZ_UNLIKELY(!r)) {
+    MOZ_CRASH("Allocation or other failure while appending integers");
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::AppendIntHex(uint64_t aInteger) {
+  PrintfAppend<T> appender(this);
+  bool r = appender.appendIntHex(aInteger);
+  if (MOZ_UNLIKELY(!r)) {
+    MOZ_CRASH("Allocation or other failure while appending integers");
+  }
+}
+
+// Returns the length of the formatted aDouble in aBuf.
+static int FormatWithoutTrailingZeros(char (&aBuf)[40], double aDouble,
+                                      int aPrecision) {
+  static const DoubleToStringConverter converter(
+      DoubleToStringConverter::UNIQUE_ZERO |
+          DoubleToStringConverter::NO_TRAILING_ZERO |
+          DoubleToStringConverter::EMIT_POSITIVE_EXPONENT_SIGN,
+      "Infinity", "NaN", 'e', -6, 21, 6, 1);
+  double_conversion::StringBuilder builder(aBuf, sizeof(aBuf));
+  converter.ToPrecision(aDouble, aPrecision, &builder);
+  int length = builder.position();
+  builder.Finalize();
+  return length;
+}
+
+template <typename T>
+void nsTSubstring<T>::AppendFloat(float aFloat) {
+  char buf[40];
+  int length = FormatWithoutTrailingZeros(buf, aFloat, 6);
+  AppendASCII(buf, length);
+}
+
+template <typename T>
+void nsTSubstring<T>::AppendFloat(double aFloat) {
+  char buf[40];
+  int length = FormatWithoutTrailingZeros(buf, aFloat, 15);
+  AppendASCII(buf, length);
+}
+
+template <typename T>
+size_t nsTSubstring<T>::SizeOfExcludingThisIfUnshared(
+    mozilla::MallocSizeOf aMallocSizeOf) const {
+  if (this->mDataFlags & DataFlags::REFCOUNTED) {
+    return nsStringBuffer::FromData(this->mData)
+        ->SizeOfIncludingThisIfUnshared(aMallocSizeOf);
+  }
+  if (this->mDataFlags & DataFlags::OWNED) {
+    return aMallocSizeOf(this->mData);
+  }
+
+  // If we reach here, exactly one of the following must be true:
+  // - DataFlags::VOIDED is set, and this->mData points to sEmptyBuffer;
+  // - DataFlags::INLINE is set, and this->mData points to a buffer within a
+  //   string object (e.g. nsAutoString);
+  // - None of DataFlags::REFCOUNTED, DataFlags::OWNED, DataFlags::INLINE is
+  //   set, and this->mData points to a buffer owned by something else.
+  //
+  // In all three cases, we don't measure it.
+  return 0;
+}
+
+template <typename T>
+size_t nsTSubstring<T>::SizeOfExcludingThisEvenIfShared(
+    mozilla::MallocSizeOf aMallocSizeOf) const {
+  // This is identical to SizeOfExcludingThisIfUnshared except for the
+  // DataFlags::REFCOUNTED case.
+  if (this->mDataFlags & DataFlags::REFCOUNTED) {
+    return nsStringBuffer::FromData(this->mData)
+        ->SizeOfIncludingThisEvenIfShared(aMallocSizeOf);
+  }
+  if (this->mDataFlags & DataFlags::OWNED) {
+    return aMallocSizeOf(this->mData);
+  }
+  return 0;
+}
+
+template <typename T>
+size_t nsTSubstring<T>::SizeOfIncludingThisIfUnshared(
+    mozilla::MallocSizeOf aMallocSizeOf) const {
+  return aMallocSizeOf(this) + SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+}
+
+template <typename T>
+size_t nsTSubstring<T>::SizeOfIncludingThisEvenIfShared(
+    mozilla::MallocSizeOf aMallocSizeOf) const {
+  return aMallocSizeOf(this) + SizeOfExcludingThisEvenIfShared(aMallocSizeOf);
+}
+
+template <typename T>
+nsTSubstringSplitter<T> nsTSubstring<T>::Split(const char_type aChar) const {
+  return nsTSubstringSplitter<T>(
+      nsTCharSeparatedTokenizerTemplate<
+          NS_TokenizerIgnoreNothing, T,
+          nsTokenizerFlags::IncludeEmptyTokenAtEnd>(*this, aChar));
+}
+
+// Common logic for nsTSubstring<T>::ToInteger and nsTSubstring<T>::ToInteger64.
+template <typename T, typename int_type>
+int_type ToIntegerCommon(const nsTSubstring<T>& aSrc, nsresult* aErrorCode,
+                         uint32_t aRadix) {
+  MOZ_ASSERT(aRadix == 10 || aRadix == 16);
+
+  // Initial value, override if we find an integer.
+  *aErrorCode = NS_ERROR_ILLEGAL_VALUE;
+
+  // Begin by skipping over leading chars that shouldn't be part of the number.
+  auto cp = aSrc.BeginReading();
+  auto endcp = aSrc.EndReading();
+  bool negate = false;
+  bool done = false;
+
+  // NB: For backwards compatibility I'm not going to change this logic but
+  //     it seems really odd. Previously there was logic to auto-detect the
+  //     radix if kAutoDetect was passed in. In practice this value was never
+  //     used, so it pretended to auto detect and skipped some preceding
+  //     letters (excluding valid hex digits) but never used the result.
+  //
+  //     For example if you pass in "Get the number: 10", aRadix = 10 we'd
+  //     skip the 'G', and then fail to parse "et the number: 10". If aRadix =
+  //     16 we'd skip the 'G', and parse just 'e' returning 14.
+  while ((cp < endcp) && (!done)) {
+    switch (*cp++) {
+      // clang-format off
+      case 'a': case 'b': case 'c': case 'd': case 'e': case 'f':
+      case 'A': case 'B': case 'C': case 'D': case 'E': case 'F':
+      case '0': case '1': case '2': case '3': case '4':
+      case '5': case '6': case '7': case '8': case '9':
+        done = true;
+        break;
+      // clang-format on
+      case '-':
+        negate = true;
+        break;
+      default:
+        break;
+    }
+  }
+
+  if (!done) {
+    // No base 16 or base 10 digits were found.
+    return 0;
+  }
+
+  // Step back.
+  cp--;
+
+  mozilla::CheckedInt<int_type> result;
+
+  // Now iterate the numeric chars and build our result.
+  while (cp < endcp) {
+    auto theChar = *cp++;
+    if (('0' <= theChar) && (theChar <= '9')) {
+      result = (aRadix * result) + (theChar - '0');
+    } else if ((theChar >= 'A') && (theChar <= 'F')) {
+      if (10 == aRadix) {
+        // Invalid base 10 digit, error out.
+        return 0;
+      } else {
+        result = (aRadix * result) + ((theChar - 'A') + 10);
+      }
+    } else if ((theChar >= 'a') && (theChar <= 'f')) {
+      if (10 == aRadix) {
+        // Invalid base 10 digit, error out.
+        return 0;
+      } else {
+        result = (aRadix * result) + ((theChar - 'a') + 10);
+      }
+    } else if ((('X' == theChar) || ('x' == theChar)) && result == 0) {
+      // For some reason we support a leading 'x' regardless of radix. For
+      // example: "000000x500", aRadix = 10 would be parsed as 500 rather
+      // than 0.
+      continue;
+    } else {
+      // We've encountered a char that's not a legal number or sign and we can
+      // terminate processing.
+      break;
+    }
+
+    if (!result.isValid()) {
+      // Overflow!
+      return 0;
+    }
+  }
+
+  // Integer found.
+  *aErrorCode = NS_OK;
+
+  if (negate) {
+    result = -result;
+  }
+
+  return result.value();
+}
+
+template <typename T>
+int32_t nsTSubstring<T>::ToInteger(nsresult* aErrorCode,
+                                   uint32_t aRadix) const {
+  return ToIntegerCommon<T, int32_t>(*this, aErrorCode, aRadix);
+}
+
+/**
+ * nsTSubstring::ToInteger64
+ */
+template <typename T>
+int64_t nsTSubstring<T>::ToInteger64(nsresult* aErrorCode,
+                                     uint32_t aRadix) const {
+  return ToIntegerCommon<T, int64_t>(*this, aErrorCode, aRadix);
+}
+
+/**
+ * nsTSubstring::Mid
+ */
+template <typename T>
+typename nsTSubstring<T>::size_type nsTSubstring<T>::Mid(
+    self_type& aResult, index_type aStartPos, size_type aLengthToCopy) const {
+  if (aStartPos == 0 && aLengthToCopy >= this->mLength) {
+    aResult = *this;
+  } else {
+    aResult = Substring(*this, aStartPos, aLengthToCopy);
+  }
+
+  return aResult.mLength;
+}
+
+/**
+ * nsTSubstring::StripWhitespace
+ */
+
+template <typename T>
+void nsTSubstring<T>::StripWhitespace() {
+  if (!StripWhitespace(mozilla::fallible)) {
+    this->AllocFailed(this->mLength);
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::StripWhitespace(const fallible_t&) {
+  if (!this->EnsureMutable()) {
+    return false;
+  }
+
+  this->StripTaggedASCII(mozilla::ASCIIMask::MaskWhitespace());
+  return true;
+}
+
+/**
+ * nsTSubstring::ReplaceChar,ReplaceSubstring
+ */
+
+template <typename T>
+void nsTSubstring<T>::ReplaceChar(char_type aOldChar, char_type aNewChar) {
+  int32_t i = this->FindChar(aOldChar);
+  if (i == kNotFound) {
+    return;
+  }
+
+  if (!this->EnsureMutable()) {
+    this->AllocFailed(this->mLength);
+  }
+  for (; i != kNotFound; i = this->FindChar(aOldChar, i + 1)) {
+    this->mData[i] = aNewChar;
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::ReplaceChar(const string_view& aSet, char_type aNewChar) {
+  int32_t i = this->FindCharInSet(aSet);
+  if (i == kNotFound) {
+    return;
+  }
+
+  if (!this->EnsureMutable()) {
+    this->AllocFailed(this->mLength);
+  }
+  for (; i != kNotFound; i = this->FindCharInSet(aSet, i + 1)) {
+    this->mData[i] = aNewChar;
+  }
+}
+
+template <typename T>
+void nsTSubstring<T>::ReplaceSubstring(const char_type* aTarget,
+                                       const char_type* aNewValue) {
+  ReplaceSubstring(nsTDependentString<T>(aTarget),
+                   nsTDependentString<T>(aNewValue));
+}
+
+template <typename T>
+bool nsTSubstring<T>::ReplaceSubstring(const char_type* aTarget,
+                                       const char_type* aNewValue,
+                                       const fallible_t& aFallible) {
+  return ReplaceSubstring(nsTDependentString<T>(aTarget),
+                          nsTDependentString<T>(aNewValue), aFallible);
+}
+
+template <typename T>
+void nsTSubstring<T>::ReplaceSubstring(const self_type& aTarget,
+                                       const self_type& aNewValue) {
+  if (!ReplaceSubstring(aTarget, aNewValue, mozilla::fallible)) {
+    // Note that this may wildly underestimate the allocation that failed, as
+    // we could have been replacing multiple copies of aTarget.
+    this->AllocFailed(this->mLength + (aNewValue.Length() - aTarget.Length()));
+  }
+}
+
+template <typename T>
+bool nsTSubstring<T>::ReplaceSubstring(const self_type& aTarget,
+                                       const self_type& aNewValue,
+                                       const fallible_t&) {
+  struct Segment {
+    uint32_t mBegin, mLength;
+    Segment(uint32_t aBegin, uint32_t aLength)
+        : mBegin(aBegin), mLength(aLength) {}
+  };
+
+  if (aTarget.Length() == 0) {
+    return true;
+  }
+
+  // Remember all of the non-matching parts.
+  AutoTArray<Segment, 16> nonMatching;
+  uint32_t i = 0;
+  mozilla::CheckedUint32 newLength;
+  while (true) {
+    int32_t r = this->Find(aTarget, i);
+    int32_t until = (r == kNotFound) ? this->Length() - i : r - i;
+    nonMatching.AppendElement(Segment(i, until));
+    newLength += until;
+    if (r == kNotFound) {
+      break;
+    }
+
+    newLength += aNewValue.Length();
+    i = r + aTarget.Length();
+    if (i >= this->Length()) {
+      // Add an auxiliary entry at the end of the list to help as an edge case
+      // for the algorithms below.
+      nonMatching.AppendElement(Segment(this->Length(), 0));
+      break;
+    }
+  }
+
+  if (!newLength.isValid()) {
+    return false;
+  }
+
+  // If there's only one non-matching segment, then the target string was not
+  // found, and there's nothing to do.
+  if (nonMatching.Length() == 1) {
+    MOZ_ASSERT(
+        nonMatching[0].mBegin == 0 && nonMatching[0].mLength == this->Length(),
+        "We should have the correct non-matching segment.");
+    return true;
+  }
+
+  // Make sure that we can mutate our buffer.
+  // Note that we always allocate at least an this->mLength sized buffer,
+  // because the rest of the algorithm relies on having access to all of the
+  // original string.  In other words, we over-allocate in the shrinking case.
+  uint32_t oldLen = this->Length();
+  auto r =
+      this->StartBulkWriteImpl(XPCOM_MAX(oldLen, newLength.value()), oldLen);
+  if (r.isErr()) {
+    return false;
+  }
+
+  if (aTarget.Length() >= aNewValue.Length()) {
+    // In the shrinking case, start filling the buffer from the beginning.
+    const uint32_t delta = (aTarget.Length() - aNewValue.Length());
+    for (i = 1; i < nonMatching.Length(); ++i) {
+      // When we move the i'th non-matching segment into position, we need to
+      // account for the characters deleted by the previous |i| replacements by
+      // subtracting |i * delta|.
+      const char_type* sourceSegmentPtr = this->mData + nonMatching[i].mBegin;
+      char_type* destinationSegmentPtr =
+          this->mData + nonMatching[i].mBegin - i * delta;
+      // Write the i'th replacement immediately before the new i'th non-matching
+      // segment.
+      char_traits::copy(destinationSegmentPtr - aNewValue.Length(),
+                        aNewValue.Data(), aNewValue.Length());
+      char_traits::move(destinationSegmentPtr, sourceSegmentPtr,
+                        nonMatching[i].mLength);
+    }
+  } else {
+    // In the growing case, start filling the buffer from the end.
+    const uint32_t delta = (aNewValue.Length() - aTarget.Length());
+    for (i = nonMatching.Length() - 1; i > 0; --i) {
+      // When we move the i'th non-matching segment into position, we need to
+      // account for the characters added by the previous |i| replacements by
+      // adding |i * delta|.
+      const char_type* sourceSegmentPtr = this->mData + nonMatching[i].mBegin;
+      char_type* destinationSegmentPtr =
+          this->mData + nonMatching[i].mBegin + i * delta;
+      char_traits::move(destinationSegmentPtr, sourceSegmentPtr,
+                        nonMatching[i].mLength);
+      // Write the i'th replacement immediately before the new i'th non-matching
+      // segment.
+      char_traits::copy(destinationSegmentPtr - aNewValue.Length(),
+                        aNewValue.Data(), aNewValue.Length());
+    }
+  }
+
+  // Adjust the length and make sure the string is null terminated.
+  this->FinishBulkWriteImpl(newLength.value());
+
+  return true;
+}
+
+/**
+ * nsTSubstring::Trim
+ */
+
+template <typename T>
+void nsTSubstring<T>::Trim(const std::string_view& aSet, bool aTrimLeading,
+                           bool aTrimTrailing, bool aIgnoreQuotes) {
+  char_type* start = this->mData;
+  char_type* end = this->mData + this->mLength;
+
+  // skip over quotes if requested
+  if (aIgnoreQuotes && this->mLength > 2 &&
+      this->mData[0] == this->mData[this->mLength - 1] &&
+      (this->mData[0] == '\'' || this->mData[0] == '"')) {
+    ++start;
+    --end;
+  }
+
+  if (aTrimLeading) {
+    uint32_t cutStart = start - this->mData;
+    uint32_t cutLength = 0;
+
+    // walk forward from start to end
+    for (; start != end; ++start, ++cutLength) {
+      if ((*start & ~0x7F) ||  // non-ascii
+          aSet.find(char(*start)) == std::string_view::npos) {
+        break;
+      }
+    }
+
+    if (cutLength) {
+      this->Cut(cutStart, cutLength);
+
+      // reset iterators
+      start = this->mData + cutStart;
+      end = this->mData + this->mLength - cutStart;
+    }
+  }
+
+  if (aTrimTrailing) {
+    uint32_t cutEnd = end - this->mData;
+    uint32_t cutLength = 0;
+
+    // walk backward from end to start
+    --end;
+    for (; end >= start; --end, ++cutLength) {
+      if ((*end & ~0x7F) ||  // non-ascii
+          aSet.find(char(*end)) == std::string_view::npos) {
+        break;
+      }
+    }
+
+    if (cutLength) {
+      this->Cut(cutEnd - cutLength, cutLength);
+    }
+  }
+}
+
+/**
+ * nsTSubstring::CompressWhitespace.
+ */
+
+template <typename T>
+void nsTSubstring<T>::CompressWhitespace(bool aTrimLeading,
+                                         bool aTrimTrailing) {
+  // Quick exit
+  if (this->mLength == 0) {
+    return;
+  }
+
+  if (!this->EnsureMutable()) {
+    this->AllocFailed(this->mLength);
+  }
+
+  const ASCIIMaskArray& mask = mozilla::ASCIIMask::MaskWhitespace();
+
+  char_type* to = this->mData;
+  char_type* from = this->mData;
+  char_type* end = this->mData + this->mLength;
+
+  // Compresses runs of whitespace down to a normal space ' ' and convert
+  // any whitespace to a normal space.  This assumes that whitespace is
+  // all standard 7-bit ASCII.
+  bool skipWS = aTrimLeading;
+  while (from < end) {
+    uint32_t theChar = *from++;
+    if (mozilla::ASCIIMask::IsMasked(mask, theChar)) {
+      if (!skipWS) {
+        *to++ = ' ';
+        skipWS = true;
+      }
+    } else {
+      *to++ = theChar;
+      skipWS = false;
+    }
+  }
+
+  // If we need to trim the trailing whitespace, back up one character.
+  if (aTrimTrailing && skipWS && to > this->mData) {
+    to--;
+  }
+
+  *to = char_type(0);  // add the null
+  this->mLength = to - this->mData;
+}
+
+template class nsTSubstring<char>;
+template class nsTSubstring<char16_t>;