The Tor Browser / file revision

 /* -*- 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 "nsAlgorithm.h"

 #include "WebMBufferedParser.h"

 #include "mozilla/dom/TimeRanges.h"

 #include "nsThreadUtils.h"

 #include <algorithm>

 namespace mozilla {

 static uint32_t

 VIntLength(unsigned char aFirstByte, uint32_t* aMask)

 {

   uint32_t count = 1;

   uint32_t mask = 1 << 7;

   while (count < 8) {

     if ((aFirstByte & mask) != 0) {

       break;

     }

     mask >>= 1;

     count += 1;

   }

   if (aMask) {

     *aMask = mask;

   }

   NS_ASSERTION(count >= 1 && count <= 8, "Insane VInt length.");

   return count;

 }

 void WebMBufferedParser::Append(const unsigned char* aBuffer, uint32_t aLength,

                                   nsTArray<WebMTimeDataOffset>& aMapping,

                                   ReentrantMonitor& aReentrantMonitor)

 {

   static const unsigned char CLUSTER_ID[] = { 0x1f, 0x43, 0xb6, 0x75 };

   static const unsigned char TIMECODE_ID = 0xe7;

   static const unsigned char BLOCKGROUP_ID = 0xa0;

   static const unsigned char BLOCK_ID = 0xa1;

   static const unsigned char SIMPLEBLOCK_ID = 0xa3;

   const unsigned char* p = aBuffer;

   // Parse each byte in aBuffer one-by-one, producing timecodes and updating

   // aMapping as we go.  Parser pauses at end of stream (which may be at any

   // point within the parse) and resumes parsing the next time Append is

   // called with new data.

   while (p < aBuffer + aLength) {

     switch (mState) {

     case CLUSTER_SYNC:

       if (*p++ == CLUSTER_ID[mClusterIDPos]) {

         mClusterIDPos += 1;

       } else {

         mClusterIDPos = 0;

       }

       // Cluster ID found, it's likely this is a valid sync point.  If this

       // is a spurious match, the later parse steps will encounter an error

       // and return to CLUSTER_SYNC.

       if (mClusterIDPos == sizeof(CLUSTER_ID)) {

         mClusterIDPos = 0;

         mState = READ_VINT;

         mNextState = TIMECODE_SYNC;

       }

       break;

     case READ_VINT: {

       unsigned char c = *p++;

       uint32_t mask;

       mVIntLength = VIntLength(c, &mask);

       mVIntLeft = mVIntLength - 1;

       mVInt = c & ~mask;

       mState = READ_VINT_REST;

       break;

     }

     case READ_VINT_REST:

       if (mVIntLeft) {

         mVInt <<= 8;

         mVInt |= *p++;

         mVIntLeft -= 1;

       } else {

         mState = mNextState;

       }

       break;

     case TIMECODE_SYNC:

       if (*p++ != TIMECODE_ID) {

         p -= 1;

         mState = CLUSTER_SYNC;

         break;

       }

       mClusterTimecode = 0;

       mState = READ_VINT;

       mNextState = READ_CLUSTER_TIMECODE;

       break;

     case READ_CLUSTER_TIMECODE:

       if (mVInt) {

         mClusterTimecode <<= 8;

         mClusterTimecode |= *p++;

         mVInt -= 1;

       } else {

         mState = ANY_BLOCK_SYNC;

       }

       break;

     case ANY_BLOCK_SYNC: {

       unsigned char c = *p++;

       if (c == BLOCKGROUP_ID) {

         mState = READ_VINT;

         mNextState = ANY_BLOCK_SYNC;

       } else if (c == SIMPLEBLOCK_ID || c == BLOCK_ID) {

         mBlockOffset = mCurrentOffset + (p - aBuffer) - 1;

         mState = READ_VINT;

         mNextState = READ_BLOCK;

       } else {

         uint32_t length = VIntLength(c, nullptr);

         if (length == 4) {

           p -= 1;

           mState = CLUSTER_SYNC;

         } else {

           mState = READ_VINT;

           mNextState = SKIP_ELEMENT;

         }

       }

       break;

     }

     case READ_BLOCK:

       mBlockSize = mVInt;

       mBlockTimecode = 0;

       mBlockTimecodeLength = 2;

       mState = READ_VINT;

       mNextState = READ_BLOCK_TIMECODE;

       break;

     case READ_BLOCK_TIMECODE:

       if (mBlockTimecodeLength) {

         mBlockTimecode <<= 8;

         mBlockTimecode |= *p++;

         mBlockTimecodeLength -= 1;

       } else {

         // It's possible we've parsed this data before, so avoid inserting

         // duplicate WebMTimeDataOffset entries.

         {

           ReentrantMonitorAutoEnter mon(aReentrantMonitor);

           uint32_t idx = aMapping.IndexOfFirstElementGt(mBlockOffset);

           if (idx == 0 || !(aMapping[idx-1] == mBlockOffset)) {

             WebMTimeDataOffset entry(mBlockOffset, mClusterTimecode + mBlockTimecode);

             aMapping.InsertElementAt(idx, entry);

           }

         }

         // Skip rest of block header and the block's payload.

         mBlockSize -= mVIntLength;

         mBlockSize -= 2;

         mSkipBytes = uint32_t(mBlockSize);

         mState = SKIP_DATA;

         mNextState = ANY_BLOCK_SYNC;

       }

       break;

     case SKIP_DATA:

       if (mSkipBytes) {

         uint32_t left = aLength - (p - aBuffer);

         left = std::min(left, mSkipBytes);

         p += left;

         mSkipBytes -= left;

       } else {

         mState = mNextState;

       }

       break;

     case SKIP_ELEMENT:

       mSkipBytes = uint32_t(mVInt);

       mState = SKIP_DATA;

       mNextState = ANY_BLOCK_SYNC;

       break;

     }

   }

   NS_ASSERTION(p == aBuffer + aLength, "Must have parsed to end of data.");

   mCurrentOffset += aLength;

 }

 bool WebMBufferedState::CalculateBufferedForRange(int64_t aStartOffset, int64_t aEndOffset,

                                                     uint64_t* aStartTime, uint64_t* aEndTime)

 {

   ReentrantMonitorAutoEnter mon(mReentrantMonitor);

   // Find the first WebMTimeDataOffset at or after aStartOffset.

   uint32_t start = mTimeMapping.IndexOfFirstElementGt(aStartOffset-1);

   if (start == mTimeMapping.Length()) {

     return false;

   }

   // Find the first WebMTimeDataOffset at or before aEndOffset.

   uint32_t end = mTimeMapping.IndexOfFirstElementGt(aEndOffset-1);

   if (end > 0) {

     end -= 1;

   }

   // Range is empty.

   if (end <= start) {

     return false;

   }

   NS_ASSERTION(mTimeMapping[start].mOffset >= aStartOffset &&

                mTimeMapping[end].mOffset <= aEndOffset,

                "Computed time range must lie within data range.");

   if (start > 0) {

     NS_ASSERTION(mTimeMapping[start - 1].mOffset <= aStartOffset,

                  "Must have found least WebMTimeDataOffset for start");

   }

   if (end < mTimeMapping.Length() - 1) {

     NS_ASSERTION(mTimeMapping[end + 1].mOffset >= aEndOffset,

                  "Must have found greatest WebMTimeDataOffset for end");

   }

   // The timestamp of the first media sample, in ns. We must subtract this

   // from the ranges' start and end timestamps, so that those timestamps are

   // normalized in the range [0,duration].

   *aStartTime = mTimeMapping[start].mTimecode;

   *aEndTime = mTimeMapping[end].mTimecode;

   return true;

 }

 bool WebMBufferedState::GetOffsetForTime(uint64_t aTime, int64_t* aOffset)

 {

   ReentrantMonitorAutoEnter mon(mReentrantMonitor);

   WebMTimeDataOffset result(0,0);

   for (uint32_t i = 0; i < mTimeMapping.Length(); ++i) {

     WebMTimeDataOffset o = mTimeMapping[i];

     if (o.mTimecode < aTime && o.mTimecode > result.mTimecode) {

       result = o;

     }

   }

   *aOffset = result.mOffset;

   return true;

 }

 void WebMBufferedState::NotifyDataArrived(const char* aBuffer, uint32_t aLength, int64_t aOffset)

 {

   NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");

   uint32_t idx = mRangeParsers.IndexOfFirstElementGt(aOffset - 1);

   if (idx == 0 || !(mRangeParsers[idx-1] == aOffset)) {

     // If the incoming data overlaps an already parsed range, adjust the

     // buffer so that we only reparse the new data.  It's also possible to

     // have an overlap where the end of the incoming data is within an

     // already parsed range, but we don't bother handling that other than by

     // avoiding storing duplicate timecodes when the parser runs.

     if (idx != mRangeParsers.Length() && mRangeParsers[idx].mStartOffset <= aOffset) {

       // Complete overlap, skip parsing.

       if (aOffset + aLength <= mRangeParsers[idx].mCurrentOffset) {

         return;

       }

       // Partial overlap, adjust the buffer to parse only the new data.

       int64_t adjust = mRangeParsers[idx].mCurrentOffset - aOffset;

       NS_ASSERTION(adjust >= 0, "Overlap detection bug.");

       aBuffer += adjust;

       aLength -= uint32_t(adjust);

     } else {

       mRangeParsers.InsertElementAt(idx, WebMBufferedParser(aOffset));

     }

   }

   mRangeParsers[idx].Append(reinterpret_cast<const unsigned char*>(aBuffer),

                             aLength,

                             mTimeMapping,

                             mReentrantMonitor);

   // Merge parsers with overlapping regions and clean up the remnants.

   uint32_t i = 0;

   while (i + 1 < mRangeParsers.Length()) {

     if (mRangeParsers[i].mCurrentOffset >= mRangeParsers[i + 1].mStartOffset) {

       mRangeParsers[i + 1].mStartOffset = mRangeParsers[i].mStartOffset;

       mRangeParsers.RemoveElementAt(i);

     } else {

       i += 1;

     }

   }

 }

 } // namespace mozilla