The Tor Browser: content/media/MP3FrameParser.h@97036ab72558 (annotated)

content/media/MP3FrameParser.h@97036ab72558 (annotated)

content/media/MP3FrameParser.h

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- 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/. */
 #ifndef MP3FrameParser_h
 #define MP3FrameParser_h
 #include <stdint.h>
 #include "mozilla/Mutex.h"
 #include "nsString.h"
 namespace mozilla {
 // Simple parser to tell whether we've found an ID3 header and how long it is,
 // so that we can skip it.
 // XXX maybe actually parse this stuff?
 class ID3Parser
 {
 public:
   ID3Parser();
   void Reset();
   bool ParseChar(char ch);
   bool IsParsed() const;
   uint32_t GetHeaderLength() const;
 private:
   uint32_t mCurrentChar;
   uint32_t mHeaderLength;
 };
 struct MP3Frame {
   uint16_t mSync1 : 8;      // Always all set
   uint16_t mProtected : 1;  // Ignored
   uint16_t mLayer : 2;
   uint16_t mVersion : 2;
   uint16_t mSync2 : 3;      // Always all set
   uint16_t mPrivate : 1;    // Ignored
   uint16_t mPad : 1;
   uint16_t mSampleRate : 2; // Index into mpeg_srates above
   uint16_t mBitrate : 4;    // Index into mpeg_bitrates above
   uint16_t CalculateLength();
 };
 // Buffering parser for MP3 frames.
 class MP3Parser
 {
 public:
   MP3Parser();
   // Forget all data the parser has seen so far.
   void Reset();
   // Parse the given byte. If we have found a frame header, return the length of
   // the frame.
   uint16_t ParseFrameLength(uint8_t ch);
   // Get the sample rate from the current header.
   uint32_t GetSampleRate();
   // Get the number of samples per frame.
   uint32_t GetSamplesPerFrame();
 private:
   uint32_t mCurrentChar;
   union {
     uint8_t mRaw[3];
     MP3Frame mFrame;
   } mData;
 };
 // A description of the MP3 format and its extensions is available at
 //
 //  http://www.codeproject.com/Articles/8295/MPEG-Audio-Frame-Header
 //
 // The data in MP3 streams is split into small frames, with each frame
 // containing a fixed number of samples. The duration of a frame depends
 // on the frame's bit rate and sample rate. Both values can vary among
 // frames, so it is necessary to examine each individual frame of an MP3
 // stream to calculate the stream's overall duration.
 //
 // The MP3 frame parser extracts information from an MP3 data stream. It
 // accepts a range of frames of an MP3 stream as input, and parses all
 // frames for their duration. Callers can query the stream's overall
 // duration from the parser.
 //
 // Call the methods NotifyDataArrived or Parse to add new data. If you added
 // information for a certain stream position, you cannot go back to previous
 // positions. The parser will simply ignore the input. If you skip stream
 // positions, the duration of the related MP3 frames will be estimated from
 // the stream's average.
 //
 // The method GetDuration returns calculated duration of the stream, including
 // estimates for skipped ranges.
 //
 // All public methods are thread-safe.
 class MP3FrameParser
 {
 public:
   MP3FrameParser(int64_t aLength=-1);
   bool IsMP3() {
     MutexAutoLock mon(mLock);
     return mIsMP3 != NOT_MP3;
   }
   void Parse(const char* aBuffer, uint32_t aLength, uint64_t aStreamOffset);
   // Returns the duration, in microseconds. If the entire stream has not
   // been parsed yet, this is an estimate based on the bitrate of the
   // frames parsed so far.
   int64_t GetDuration();
   // Returns the offset of the first MP3 frame in the stream, or -1 of
   // no MP3 frame has been detected yet.
   int64_t GetMP3Offset();
   // Returns true if we've seen the whole first frame of the MP3 stream, and
   // therefore can make an estimate on the stream duration.
   // Otherwise, returns false.
   bool ParsedHeaders();
   // Returns true if we know the exact duration of the MP3 stream;
   // false otherwise.
   bool HasExactDuration();
   // Returns true if the parser needs more data for duration estimation.
   bool NeedsData();
 private:
   // Parses aBuffer, starting at offset 0. Returns the number of bytes
   // parsed, relative to the start of the buffer. Note this may be
   // greater than aLength if the headers in the buffer indicate that
   // the frame or ID3 tag extends outside of aBuffer. Returns failure
   // if too many non-MP3 bytes are parsed.
   nsresult ParseBuffer(const uint8_t* aBuffer,
                        uint32_t aLength,
                        int64_t aStreamOffset,
                        uint32_t* aOutBytesRead);
   // A low-contention lock for protecting the parser results
   Mutex mLock;
   // ID3 header parser. Keeps state between reads in case the header falls
   // in between.
   ID3Parser mID3Parser;
   // MP3 frame header parser.
   MP3Parser mMP3Parser;
   // If we read |MAX_SKIPPED_BYTES| from the stream without finding any MP3
   // frames, we give up and report |NOT_MP3|. Here we track the cumulative size
   // of any ID3 headers we've seen so big ID3 sections aren't counted towards
   // skipped bytes.
   uint32_t mTotalID3Size;
   // All fields below are protected by mLock
   // We keep stats on the size of all the frames we've seen, as well as how many
   // so that we can estimate the duration of the rest of the stream.
   uint64_t mTotalFrameSize;
   uint64_t mFrameCount;
   // Offset of the last data parsed. This is the end offset of the last data
   // block parsed, so it's the start offset we expect to get on the next
   // call to Parse().
   uint64_t mOffset;
   // Total length of the stream in bytes.
   int64_t mLength;
   // Offset of first MP3 frame in the bitstream. Has value -1 until the
   // first MP3 frame is found.
   int64_t mMP3Offset;
   // The exact number of frames in this stream, if we know it. -1 otherwise.
   int64_t mNumFrames;
   // Number of audio samples per second and per frame. Fixed through the whole
   // file. If we know these variables as well as the number of frames in the
   // file, we can get an exact duration for the stream.
   uint16_t mSamplesPerSecond;
   uint16_t mSamplesPerFrame;
   // If the MP3 has a variable bitrate, then there *should* be metadata about
   // the encoding in the first frame. We buffer the first frame here.
   nsAutoCString mFirstFrame;
   // While we are reading the first frame, this is the stream offset of the
   // last byte of that frame. -1 at all other times.
   int64_t mFirstFrameEnd;
   enum eIsMP3 {
     MAYBE_MP3, // We're giving the stream the benefit of the doubt...
     DEFINITELY_MP3, // We've hit at least one ID3 tag or MP3 frame.
     NOT_MP3 // Not found any evidence of the stream being MP3.
   };
   eIsMP3 mIsMP3;
 };
 }
 #endif

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content/media/MP3FrameParser.h@97036ab72558 (annotated)

content/media/MP3FrameParser.h