gecko-dev/dom/media/mp4/Box.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 "Box.h"
#include "ByteStream.h"
#include "mozilla/EndianUtils.h"
#include "mozilla/Unused.h"
#include <algorithm>

namespace mozilla {

// Limit reads to 32MiB max.
// static
const uint64_t Box::kMAX_BOX_READ = 32 * 1024 * 1024;

// Returns the offset from the start of the body of a box of type |aType|
// to the start of its first child.
static uint32_t BoxOffset(AtomType aType) {
  const uint32_t FULLBOX_OFFSET = 4;

  if (aType == AtomType("mp4a") || aType == AtomType("enca")) {
    // AudioSampleEntry; ISO 14496-12, section 8.16
    return 28;
  } else if (aType == AtomType("mp4v") || aType == AtomType("encv")) {
    // VideoSampleEntry; ISO 14496-12, section 8.16
    return 78;
  } else if (aType == AtomType("stsd")) {
    // SampleDescriptionBox; ISO 14496-12, section 8.16
    // This is a FullBox, and contains a |count| member before its child
    // boxes.
    return FULLBOX_OFFSET + 4;
  }

  return 0;
}

Box::Box(BoxContext* aContext, uint64_t aOffset, const Box* aParent)
    : mContext(aContext), mParent(aParent) {
  uint8_t header[8];

  if (aOffset > INT64_MAX - sizeof(header)) {
    return;
  }

  MediaByteRange headerRange(aOffset, aOffset + sizeof(header));
  if (mParent && !mParent->mRange.Contains(headerRange)) {
    return;
  }

  const MediaByteRange* byteRange;
  for (int i = 0;; i++) {
    if (i == mContext->mByteRanges.Length()) {
      return;
    }

    byteRange = static_cast<const MediaByteRange*>(&mContext->mByteRanges[i]);
    if (byteRange->Contains(headerRange)) {
      break;
    }
  }

  size_t bytes;
  if (!mContext->mSource->CachedReadAt(aOffset, header, sizeof(header),
                                       &bytes) ||
      bytes != sizeof(header)) {
    return;
  }

  uint64_t size = BigEndian::readUint32(header);
  if (size == 1) {
    uint8_t bigLength[8];
    if (aOffset > INT64_MAX - sizeof(header) - sizeof(bigLength)) {
      return;
    }
    MediaByteRange bigLengthRange(headerRange.mEnd,
                                  headerRange.mEnd + sizeof(bigLength));
    if ((mParent && !mParent->mRange.Contains(bigLengthRange)) ||
        !byteRange->Contains(bigLengthRange) ||
        !mContext->mSource->CachedReadAt(aOffset + sizeof(header), bigLength,
                                         sizeof(bigLength), &bytes) ||
        bytes != sizeof(bigLength)) {
      return;
    }
    size = BigEndian::readUint64(bigLength);
    mBodyOffset = bigLengthRange.mEnd;
  } else if (size == 0) {
    // box extends to end of file.
    size = mContext->mByteRanges.LastInterval().mEnd - aOffset;
    mBodyOffset = headerRange.mEnd;
  } else {
    mBodyOffset = headerRange.mEnd;
  }

  if (size > INT64_MAX) {
    return;
  }
  int64_t end = static_cast<int64_t>(aOffset) + static_cast<int64_t>(size);
  if (end < static_cast<int64_t>(aOffset)) {
    // Overflowed.
    return;
  }

  mType = BigEndian::readUint32(&header[4]);
  mChildOffset = mBodyOffset + BoxOffset(mType);

  MediaByteRange boxRange(aOffset, end);
  if (mChildOffset > boxRange.mEnd ||
      (mParent && !mParent->mRange.Contains(boxRange)) ||
      !byteRange->Contains(boxRange)) {
    return;
  }

  mRange = boxRange;
}

Box::Box()
    : mContext(nullptr), mBodyOffset(0), mChildOffset(0), mParent(nullptr) {}

Box Box::Next() const {
  MOZ_ASSERT(IsAvailable());
  return Box(mContext, mRange.mEnd, mParent);
}

Box Box::FirstChild() const {
  MOZ_ASSERT(IsAvailable());
  if (mChildOffset == mRange.mEnd) {
    return Box();
  }
  return Box(mContext, mChildOffset, this);
}

nsTArray<uint8_t> Box::ReadCompleteBox() const {
  const size_t length = mRange.mEnd - mRange.mStart;
  nsTArray<uint8_t> out(length);
  out.SetLength(length);
  size_t bytesRead = 0;
  if (!mContext->mSource->CachedReadAt(mRange.mStart, out.Elements(), length,
                                       &bytesRead) ||
      bytesRead != length) {
    // Byte ranges are being reported incorrectly
    NS_WARNING("Read failed in mozilla::Box::ReadCompleteBox()");
    return nsTArray<uint8_t>(0);
  }
  return out;
}

nsTArray<uint8_t> Box::Read() const {
  nsTArray<uint8_t> out;
  Unused << Read(&out, mRange);
  return out;
}

bool Box::Read(nsTArray<uint8_t>* aDest, const MediaByteRange& aRange) const {
  int64_t length;
  if (!mContext->mSource->Length(&length)) {
    // The HTTP server didn't give us a length to work with.
    // Limit the read to kMAX_BOX_READ max.
    length = std::min(aRange.mEnd - mChildOffset, kMAX_BOX_READ);
  } else {
    length = aRange.mEnd - mChildOffset;
  }
  aDest->SetLength(length);
  size_t bytes;
  if (!mContext->mSource->CachedReadAt(mChildOffset, aDest->Elements(),
                                       aDest->Length(), &bytes) ||
      bytes != aDest->Length()) {
    // Byte ranges are being reported incorrectly
    NS_WARNING("Read failed in mozilla::Box::Read()");
    aDest->Clear();
    return false;
  }
  return true;
}

ByteSlice Box::ReadAsSlice() {
  if (!mContext || mRange.IsEmpty()) {
    return ByteSlice{nullptr, 0};
  }

  int64_t length;
  if (!mContext->mSource->Length(&length)) {
    // The HTTP server didn't give us a length to work with.
    // Limit the read to kMAX_BOX_READ max.
    length = std::min(mRange.mEnd - mChildOffset, kMAX_BOX_READ);
  } else {
    length = mRange.mEnd - mChildOffset;
  }

  const uint8_t* data =
      mContext->mSource->GetContiguousAccess(mChildOffset, length);
  if (data) {
    // We can direct access the underlying storage of the ByteStream.
    return ByteSlice{data, size_t(length)};
  }

  uint8_t* p = mContext->mAllocator.Allocate(size_t(length));
  size_t bytes;
  if (!mContext->mSource->CachedReadAt(mChildOffset, p, length, &bytes) ||
      bytes != length) {
    // Byte ranges are being reported incorrectly
    NS_WARNING("Read failed in mozilla::Box::ReadAsSlice()");
    return ByteSlice{nullptr, 0};
  }
  return ByteSlice{p, size_t(length)};
}

const size_t BLOCK_CAPACITY = 16 * 1024;

uint8_t* BumpAllocator::Allocate(size_t aNumBytes) {
  if (aNumBytes > BLOCK_CAPACITY) {
    mBuffers.AppendElement(nsTArray<uint8_t>(aNumBytes));
    mBuffers.LastElement().SetLength(aNumBytes);
    return mBuffers.LastElement().Elements();
  }
  for (nsTArray<uint8_t>& buffer : mBuffers) {
    if (buffer.Length() + aNumBytes < BLOCK_CAPACITY) {
      size_t offset = buffer.Length();
      buffer.SetLength(buffer.Length() + aNumBytes);
      return buffer.Elements() + offset;
    }
  }
  mBuffers.AppendElement(nsTArray<uint8_t>(BLOCK_CAPACITY));
  mBuffers.LastElement().SetLength(aNumBytes);
  return mBuffers.LastElement().Elements();
}

}  // namespace mozilla