fune/parser/htmlparser/nsScannerString.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* 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 "nsScannerString.h"
#include "mozilla/CheckedInt.h"

/**
 * nsScannerBufferList
 */

#define MAX_CAPACITY \
  ((UINT32_MAX / sizeof(char16_t)) - (sizeof(Buffer) + sizeof(char16_t)))

nsScannerBufferList::Buffer* nsScannerBufferList::AllocBufferFromString(
    const nsAString& aString) {
  uint32_t len = aString.Length();
  Buffer* buf = AllocBuffer(len);

  if (buf) {
    nsAString::const_iterator source;
    aString.BeginReading(source);
    nsCharTraits<char16_t>::copy(buf->DataStart(), source.get(), len);
  }
  return buf;
}

nsScannerBufferList::Buffer* nsScannerBufferList::AllocBuffer(
    uint32_t capacity) {
  if (capacity > MAX_CAPACITY) return nullptr;

  void* ptr = malloc(sizeof(Buffer) + (capacity + 1) * sizeof(char16_t));
  if (!ptr) return nullptr;

  Buffer* buf = new (ptr) Buffer();

  buf->mUsageCount = 0;
  buf->mDataEnd = buf->DataStart() + capacity;

  // XXX null terminate.  this shouldn't be required, but we do it because
  // nsScanner erroneously thinks it can dereference DataEnd :-(
  *buf->mDataEnd = char16_t(0);
  return buf;
}

void nsScannerBufferList::ReleaseAll() {
  while (!mBuffers.isEmpty()) {
    Buffer* node = mBuffers.popFirst();
    // printf(">>> freeing buffer @%p\n", node);
    free(node);
  }
}

void nsScannerBufferList::SplitBuffer(const Position& pos) {
  // splitting to the right keeps the work string and any extant token
  // pointing to and holding a reference count on the same buffer.

  Buffer* bufferToSplit = pos.mBuffer;
  NS_ASSERTION(bufferToSplit, "null pointer");

  uint32_t splitOffset = pos.mPosition - bufferToSplit->DataStart();
  NS_ASSERTION(pos.mPosition >= bufferToSplit->DataStart() &&
                   splitOffset <= bufferToSplit->DataLength(),
               "split offset is outside buffer");

  uint32_t len = bufferToSplit->DataLength() - splitOffset;
  Buffer* new_buffer = AllocBuffer(len);
  if (new_buffer) {
    nsCharTraits<char16_t>::copy(new_buffer->DataStart(),
                                 bufferToSplit->DataStart() + splitOffset, len);
    InsertAfter(new_buffer, bufferToSplit);
    bufferToSplit->SetDataLength(splitOffset);
  }
}

void nsScannerBufferList::DiscardUnreferencedPrefix(Buffer* aBuf) {
  if (aBuf == Head()) {
    while (!mBuffers.isEmpty() && !Head()->IsInUse()) {
      Buffer* buffer = Head();
      buffer->remove();
      free(buffer);
    }
  }
}

size_t nsScannerBufferList::Position::Distance(const Position& aStart,
                                               const Position& aEnd) {
  size_t result = 0;
  if (aStart.mBuffer == aEnd.mBuffer) {
    result = aEnd.mPosition - aStart.mPosition;
  } else {
    result = aStart.mBuffer->DataEnd() - aStart.mPosition;
    for (Buffer* b = aStart.mBuffer->Next(); b != aEnd.mBuffer; b = b->Next())
      result += b->DataLength();
    result += aEnd.mPosition - aEnd.mBuffer->DataStart();
  }
  return result;
}

/**
 * nsScannerSubstring
 */

nsScannerSubstring::nsScannerSubstring()
    : mStart(nullptr, nullptr),
      mEnd(nullptr, nullptr),
      mBufferList(nullptr),
      mLength(0) {}

nsScannerSubstring::nsScannerSubstring(const nsAString& s)
    : mBufferList(nullptr) {
  Rebind(s);
}

nsScannerSubstring::~nsScannerSubstring() {
  release_ownership_of_buffer_list();
}

void nsScannerSubstring::Rebind(const nsScannerSubstring& aString,
                                const nsScannerIterator& aStart,
                                const nsScannerIterator& aEnd) {
  // allow for the case where &aString == this

  aString.acquire_ownership_of_buffer_list();
  release_ownership_of_buffer_list();

  mStart = aStart;
  mEnd = aEnd;
  mBufferList = aString.mBufferList;
  mLength = Distance(aStart, aEnd);
}

void nsScannerSubstring::Rebind(const nsAString& aString) {
  release_ownership_of_buffer_list();

  mBufferList = new nsScannerBufferList(AllocBufferFromString(aString));

  init_range_from_buffer_list();
  acquire_ownership_of_buffer_list();
}

nsScannerIterator& nsScannerSubstring::BeginReading(
    nsScannerIterator& iter) const {
  iter.mOwner = this;

  iter.mFragment.mBuffer = mStart.mBuffer;
  iter.mFragment.mFragmentStart = mStart.mPosition;
  if (mStart.mBuffer == mEnd.mBuffer)
    iter.mFragment.mFragmentEnd = mEnd.mPosition;
  else
    iter.mFragment.mFragmentEnd = mStart.mBuffer->DataEnd();

  iter.mPosition = mStart.mPosition;
  iter.normalize_forward();
  return iter;
}

nsScannerIterator& nsScannerSubstring::EndReading(
    nsScannerIterator& iter) const {
  iter.mOwner = this;

  iter.mFragment.mBuffer = mEnd.mBuffer;
  iter.mFragment.mFragmentEnd = mEnd.mPosition;
  if (mStart.mBuffer == mEnd.mBuffer)
    iter.mFragment.mFragmentStart = mStart.mPosition;
  else
    iter.mFragment.mFragmentStart = mEnd.mBuffer->DataStart();

  iter.mPosition = mEnd.mPosition;
  // must not |normalize_backward| as that would likely invalidate tests like
  // |while ( first != last )|
  return iter;
}

bool nsScannerSubstring::GetNextFragment(nsScannerFragment& frag) const {
  // check to see if we are at the end of the buffer list
  if (frag.mBuffer == mEnd.mBuffer) return false;

  frag.mBuffer = frag.mBuffer->getNext();

  if (frag.mBuffer == mStart.mBuffer)
    frag.mFragmentStart = mStart.mPosition;
  else
    frag.mFragmentStart = frag.mBuffer->DataStart();

  if (frag.mBuffer == mEnd.mBuffer)
    frag.mFragmentEnd = mEnd.mPosition;
  else
    frag.mFragmentEnd = frag.mBuffer->DataEnd();

  return true;
}

bool nsScannerSubstring::GetPrevFragment(nsScannerFragment& frag) const {
  // check to see if we are at the beginning of the buffer list
  if (frag.mBuffer == mStart.mBuffer) return false;

  frag.mBuffer = frag.mBuffer->getPrevious();

  if (frag.mBuffer == mStart.mBuffer)
    frag.mFragmentStart = mStart.mPosition;
  else
    frag.mFragmentStart = frag.mBuffer->DataStart();

  if (frag.mBuffer == mEnd.mBuffer)
    frag.mFragmentEnd = mEnd.mPosition;
  else
    frag.mFragmentEnd = frag.mBuffer->DataEnd();

  return true;
}

/**
 * nsScannerString
 */

nsScannerString::nsScannerString(Buffer* aBuf) {
  mBufferList = new nsScannerBufferList(aBuf);

  init_range_from_buffer_list();
  acquire_ownership_of_buffer_list();
}

void nsScannerString::AppendBuffer(Buffer* aBuf) {
  mBufferList->Append(aBuf);
  mLength += aBuf->DataLength();

  mEnd.mBuffer = aBuf;
  mEnd.mPosition = aBuf->DataEnd();
}

void nsScannerString::DiscardPrefix(const nsScannerIterator& aIter) {
  Position old_start(mStart);
  mStart = aIter;
  mLength -= Position::Distance(old_start, mStart);

  mStart.mBuffer->IncrementUsageCount();
  old_start.mBuffer->DecrementUsageCount();

  mBufferList->DiscardUnreferencedPrefix(old_start.mBuffer);
}

void nsScannerString::UngetReadable(const nsAString& aReadable,
                                    const nsScannerIterator& aInsertPoint)
/*
 * Warning: this routine manipulates the shared buffer list in an
 * unexpected way.  The original design did not really allow for
 * insertions, but this call promises that if called for a point after the
 * end of all extant token strings, that no token string or the work string
 * will be invalidated.
 *
 * This routine is protected because it is the responsibility of the
 * derived class to keep those promises.
 */
{
  Position insertPos(aInsertPoint);

  mBufferList->SplitBuffer(insertPos);
  // splitting to the right keeps the work string and any extant token
  // pointing to and holding a reference count on the same buffer

  Buffer* new_buffer = AllocBufferFromString(aReadable);
  // make a new buffer with all the data to insert...
  // ALERT: we may have empty space to re-use in the split buffer,
  // measure the cost of this and decide if we should do the work to fill
  // it

  Buffer* buffer_to_split = insertPos.mBuffer;
  mBufferList->InsertAfter(new_buffer, buffer_to_split);
  mLength += aReadable.Length();

  mEnd.mBuffer = mBufferList->Tail();
  mEnd.mPosition = mEnd.mBuffer->DataEnd();
}

/**
 * nsScannerSharedSubstring
 */

void nsScannerSharedSubstring::Rebind(const nsScannerIterator& aStart,
                                      const nsScannerIterator& aEnd) {
  // If the start and end positions are inside the same buffer, we must
  // acquire ownership of the buffer.  If not, we can optimize by not holding
  // onto it.

  Buffer* buffer = const_cast<Buffer*>(aStart.buffer());
  bool sameBuffer = buffer == aEnd.buffer();

  nsScannerBufferList* bufferList;

  if (sameBuffer) {
    bufferList = aStart.mOwner->mBufferList;
    bufferList->AddRef();
    buffer->IncrementUsageCount();
  }

  if (mBufferList) ReleaseBuffer();

  if (sameBuffer) {
    mBuffer = buffer;
    mBufferList = bufferList;
    mString.Rebind(aStart.mPosition, aEnd.mPosition);
  } else {
    mBuffer = nullptr;
    mBufferList = nullptr;
    CopyUnicodeTo(aStart, aEnd, mString);
  }
}

void nsScannerSharedSubstring::ReleaseBuffer() {
  NS_ASSERTION(mBufferList, "Should only be called with non-null mBufferList");
  mBuffer->DecrementUsageCount();
  mBufferList->DiscardUnreferencedPrefix(mBuffer);
  mBufferList->Release();
}

/**
 * utils -- based on code from nsReadableUtils.cpp
 */

// private helper function
static inline nsAString::iterator& copy_multifragment_string(
    nsScannerIterator& first, const nsScannerIterator& last,
    nsAString::iterator& result) {
  typedef nsCharSourceTraits<nsScannerIterator> source_traits;
  typedef nsCharSinkTraits<nsAString::iterator> sink_traits;

  while (first != last) {
    uint32_t distance = source_traits::readable_distance(first, last);
    sink_traits::write(result, source_traits::read(first), distance);
    NS_ASSERTION(distance > 0,
                 "|copy_multifragment_string| will never terminate");
    source_traits::advance(first, distance);
  }

  return result;
}

bool CopyUnicodeTo(const nsScannerIterator& aSrcStart,
                   const nsScannerIterator& aSrcEnd, nsAString& aDest) {
  mozilla::CheckedInt<nsAString::size_type> distance(
      Distance(aSrcStart, aSrcEnd));
  if (!distance.isValid()) {
    return false;  // overflow detected
  }

  if (!aDest.SetLength(distance.value(), mozilla::fallible)) {
    aDest.Truncate();
    return false;  // out of memory
  }
  auto writer = aDest.BeginWriting();
  nsScannerIterator fromBegin(aSrcStart);

  copy_multifragment_string(fromBegin, aSrcEnd, writer);
  return true;
}

bool AppendUnicodeTo(const nsScannerIterator& aSrcStart,
                     const nsScannerIterator& aSrcEnd, nsAString& aDest) {
  const nsAString::size_type oldLength = aDest.Length();
  mozilla::CheckedInt<nsAString::size_type> newLen(
      Distance(aSrcStart, aSrcEnd));
  newLen += oldLength;
  if (!newLen.isValid()) {
    return false;  // overflow detected
  }

  if (!aDest.SetLength(newLen.value(), mozilla::fallible))
    return false;  // out of memory
  auto writer = aDest.BeginWriting();
  std::advance(writer, oldLength);
  nsScannerIterator fromBegin(aSrcStart);

  copy_multifragment_string(fromBegin, aSrcEnd, writer);
  return true;
}