The Tor Browser: content/media/webm/WebMBufferedParser.cpp@44a2da4a2ab2 (annotated)

content/media/webm/WebMBufferedParser.cpp@44a2da4a2ab2 (annotated)

content/media/webm/WebMBufferedParser.cpp

Fri, 16 Jan 2015 04:50:19 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Fri, 16 Jan 2015 04:50:19 +0100
branch: TOR_BUG_9701
changeset 13: 44a2da4a2ab2
permissions: -rw-r--r--

Replace accessor implementation with direct member state manipulation, by
request https://trac.torproject.org/projects/tor/ticket/9701#comment:32

 /* -*- 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

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content/media/webm/WebMBufferedParser.cpp@44a2da4a2ab2 (annotated)

content/media/webm/WebMBufferedParser.cpp