tor-browser

MP3FrameParser.h (13091B)

---

/* 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 MP3_FRAME_PARSER_H_
#define MP3_FRAME_PARSER_H_

#include <vector>

#include "BufferReader.h"
#include "mozilla/Maybe.h"
#include "mozilla/Result.h"

namespace mozilla {

// ID3 header parser state machine used by FrameParser.
// The header contains the following format (one byte per term):
// 'I' 'D' '3' MajorVersion MinorVersion Flags Size1 Size2 Size3 Size4
// For more details see https://id3.org/id3v2.4.0-structure
class ID3Parser {
public:
 // Holds the ID3 header and its parsing state.
 class ID3Header {
  public:
   // The header size is static, see class comment.
   static const int SIZE = 10;
   static const int ID3v1_SIZE = 128;

   // Constructor.
   ID3Header();

   // Resets the state to allow for a new parsing session.
   void Reset();

   // The ID3 tags are versioned like this: ID3vMajorVersion.MinorVersion.
   uint8_t MajorVersion() const;
   uint8_t MinorVersion() const;

   // The ID3 flags field.
   uint8_t Flags() const;

   // The derived size based on the provided size fields.
   uint32_t Size() const;

   // To see whether we have parsed the value of the size from header.
   bool HasSizeBeenSet() const;

   // Returns the size of an ID3v2.4 footer if present and zero otherwise.
   uint8_t FooterSize() const;

   // The total size of the ID3 tag including header/footer, or zero if
   // none has been found.
   uint32_t TotalTagSize() const;

   // Returns whether the parsed data is a valid ID3 header up to the given
   // byte position.
   bool IsValid(int aPos) const;

   // Returns whether the parsed data is a complete and valid ID3 header.
   bool IsValid() const;

   // Parses the next provided byte.
   // Returns whether the byte creates a valid sequence up to this point.
   bool ParseNext(uint8_t c);

  private:
   // Updates the parser state machine with the provided next byte.
   // Returns whether the provided byte is a valid next byte in the sequence.
   bool Update(uint8_t c);

   // The currently parsed byte sequence.
   uint8_t mRaw[SIZE] = {};

   // The derived size as provided by the size fields.
   // The header size fields holds a 4 byte sequence with each MSB set to 0,
   // this bits need to be ignored when deriving the actual size.
   Maybe<uint32_t> mSize;

   // The current byte position in the parsed sequence. Reset via Reset and
   // incremented via Update.
   int mPos = 0;
 };

 // Check if the buffer is starting with ID3v2 tag.
 static bool IsBufferStartingWithID3Tag(BufferReader* aReader);
 // Similarly, if the buffer is starting with ID3v1 tag.
 static bool IsBufferStartingWithID3v1Tag(BufferReader* aReader);

 // Returns the parsed ID3 header. Note: check for validity.
 const ID3Header& Header() const;

 // Returns the size of all parsed ID3 headers.
 uint32_t TotalHeadersSize() const;

 // Parses contents of given BufferReader for a valid ID3v2 header.
 // Returns the parsed ID3v2 tag size if successful and zero otherwise.
 uint32_t Parse(BufferReader* aReader);

 // Resets the state to allow for a new parsing session.
 void Reset();

private:
 uint32_t ParseInternal(BufferReader* aReader);

 // The currently parsed ID3 header. Reset via Reset, updated via Parse.
 ID3Header mHeader;
 // If a file contains multiple ID3 headers, then we would only select the
 // latest one, but keep the size of former abandoned in order to return the
 // correct size offset.
 uint32_t mFormerID3Size = 0;
};

// MPEG audio frame parser.
// The MPEG frame header has the following format (one bit per character):
// 11111111 111VVLLC BBBBSSPR MMEETOHH
// {   sync   } - 11 sync bits
//   VV         - MPEG audio version ID (0->2.5, 1->reserved, 2->2, 3->1)
//   LL         - Layer description (0->reserved, 1->III, 2->II, 3->I)
//   C          - CRC protection bit (0->protected, 1->not protected)
//   BBBB       - Bitrate index (see table in implementation)
//   SS         - Sampling rate index (see table in implementation)
//   P          - Padding bit (0->not padded, 1->padded by 1 slot size)
//   R          - Private bit (ignored)
//   MM         - Channel mode (0->stereo, 1->joint stereo, 2->dual channel,
//                3->single channel)
//   EE         - Mode extension for joint stereo (ignored)
//   T          - Copyright (0->disabled, 1->enabled)
//   O          - Original (0->copy, 1->original)
//   HH         - Emphasis (0->none, 1->50/15 ms, 2->reserved, 3->CCIT J.17)
class FrameParser {
public:
 // Holds the frame header and its parsing state.
 class FrameHeader {
  public:
   // The header size is static, see class comments.
   static const int SIZE = 4;

   // Constructor.
   FrameHeader();

   // Raw field access, see class comments for details.
   uint8_t Sync1() const;
   uint8_t Sync2() const;
   uint8_t RawVersion() const;
   uint8_t RawLayer() const;
   uint8_t RawProtection() const;
   uint8_t RawBitrate() const;
   uint8_t RawSampleRate() const;
   uint8_t Padding() const;
   uint8_t Private() const;
   uint8_t RawChannelMode() const;

   // Sampling rate frequency in Hz.
   uint32_t SampleRate() const;

   // Number of audio channels.
   uint32_t Channels() const;

   // Samples per frames, static depending on MPEG version and layer.
   uint32_t SamplesPerFrame() const;

   // Slot size used for padding, static depending on MPEG layer.
   uint32_t SlotSize() const;

   // Bitrate in kbps, can vary between frames.
   uint32_t Bitrate() const;

   // MPEG layer (0->invalid, 1->I, 2->II, 3->III).
   uint32_t Layer() const;

   // Returns whether the parsed data is a valid frame header up to the given
   // byte position.
   bool IsValid(const int aPos) const;

   // Returns whether the parsed data is a complete and valid frame header.
   bool IsValid() const;

   // Resets the state to allow for a new parsing session.
   void Reset();

   // Parses the next provided byte.
   // Returns whether the byte creates a valid sequence up to this point.
   bool ParseNext(const uint8_t c);

  private:
   // Updates the parser state machine with the provided next byte.
   // Returns whether the provided byte is a valid next byte in the sequence.
   bool Update(const uint8_t c);

   // The currently parsed byte sequence.
   uint8_t mRaw[SIZE] = {};

   // The current byte position in the parsed sequence. Reset via Reset and
   // incremented via Update.
   int mPos = 0;
 };

 // VBR frames may contain Xing or VBRI headers for additional info, we use
 // this class to parse them and access this info.
 class VBRHeader {
  public:
   // Synchronize with vbr_header TYPE_STR on change.
   enum VBRHeaderType { NONE = 0, XING, VBRI };

   // Constructor.
   VBRHeader();

   // Returns the parsed VBR header type, or NONE if no valid header found.
   VBRHeaderType Type() const;

   // Returns the total number of audio frames (excluding the VBR header frame)
   // expected in the stream/file.
   const Maybe<uint32_t>& NumAudioFrames() const;

   // Returns the expected size of the stream.
   const Maybe<uint32_t>& NumBytes() const;

   // Returns the VBR scale factor (0: best quality, 100: lowest quality).
   const Maybe<uint32_t>& Scale() const;

   // Returns true iff Xing/Info TOC (table of contents) is present.
   bool IsTOCPresent() const;

   // Returns whether the header is valid (type XING or VBRI).
   bool IsValid() const;

   // Returns whether the header is valid and contains reasonable non-zero
   // field values.
   bool IsComplete() const;

   // Returns the byte offset for the given duration percentage as a factor
   // (0: begin, 1.0: end).
   int64_t Offset(media::TimeUnit aTime, media::TimeUnit aDuration) const;

   // Parses contents of given ByteReader for a valid VBR header.
   // The offset of the passed ByteReader needs to point to an MPEG frame
   // begin, as a VBRI-style header is searched at a fixed offset relative to
   // frame begin. Returns whether a valid VBR header was found in the range.
   bool Parse(BufferReader* aReader, size_t aFrameSize);

   uint32_t EncoderDelay() const { return mEncoderDelay; }
   uint32_t EncoderPadding() const { return mEncoderPadding; }

  private:
   // Parses contents of given ByteReader for a valid Xing header.
   // The initial ByteReader offset will be preserved.
   // Returns whether a valid Xing header was found in the range.
   Result<bool, nsresult> ParseXing(BufferReader* aReader, size_t aFrameSize);

   // Parses contents of given ByteReader for a valid VBRI header.
   // The initial ByteReader offset will be preserved. It also needs to point
   // to the beginning of a valid MPEG frame, as VBRI headers are searched
   // at a fixed offset relative to frame begin.
   // Returns whether a valid VBRI header was found in the range.
   Result<bool, nsresult> ParseVBRI(BufferReader* aReader);

   // The total number of frames expected as parsed from a VBR header.
   Maybe<uint32_t> mNumAudioFrames;

   // The total number of bytes expected in the stream.
   Maybe<uint32_t> mNumBytes;

   // The VBR scale factor.
   Maybe<uint32_t> mScale;

   // The TOC table mapping duration percentage to byte offset.
   std::vector<int64_t> mTOC;

   // The detected VBR header type.
   VBRHeaderType mType;

   uint16_t mVBRISeekOffsetsFramesPerEntry = 0;

   // Delay and padding values found in the LAME header. The encoder delay is a
   // number of frames that has to be skipped at the beginning of the stream,
   // encoder padding is a number of frames that needs to be ignored in the
   // last packet.
   uint16_t mEncoderDelay = 0;
   uint16_t mEncoderPadding = 0;
 };

 // Frame meta container used to parse and hold a frame header and side info.
 class Frame {
  public:
   // Returns the length of the frame excluding the header in bytes.
   uint32_t Length() const;

   // Returns the parsed frame header.
   const FrameHeader& Header() const;

   // Resets the frame header and data.
   void Reset();

   // Parses the next provided byte.
   // Returns whether the byte creates a valid sequence up to this point.
   bool ParseNext(uint8_t c);

  private:
   // The currently parsed frame header.
   FrameHeader mHeader;
 };

 // Constructor.
 FrameParser();

 // Returns the currently parsed frame. Reset via Reset or EndFrameSession.
 const Frame& CurrentFrame() const;

 // Returns the previously parsed frame. Reset via Reset.
 const Frame& PrevFrame() const;

 // Returns the first parsed frame. Reset via Reset.
 const Frame& FirstFrame() const;

 // Returns the parsed ID3 header. Note: check for validity.
 const ID3Parser::ID3Header& ID3Header() const;

 // Returns whether ID3 metadata have been found, at the end of the file.
 bool ID3v1MetadataFound() const;

 // Returns the size of all parsed ID3 headers.
 uint32_t TotalID3HeaderSize() const;

 // Returns the parsed VBR header info. Note: check for validity by type.
 const VBRHeader& VBRInfo() const;

 // Resets the parser.
 void Reset();

 // Resets all frame data, but not the ID3Header.
 // Don't use between frames as first frame data is reset.
 void ResetFrameData();

 // Clear the last parsed frame to allow for next frame parsing, i.e.:
 // - sets PrevFrame to CurrentFrame
 // - resets the CurrentFrame
 // - resets ID3Header if no valid header was parsed yet
 void EndFrameSession();

 // Parses contents of given BufferReader for a valid frame header and returns
 // true if one was found. After returning, the variable passed to
 // 'aBytesToSkip' holds the amount of bytes to be skipped (if any) in order to
 // jump across a large ID3v2 tag spanning multiple buffers.
 Result<bool, nsresult> Parse(BufferReader* aReader, uint32_t* aBytesToSkip);

 // Parses contents of given BufferReader for a valid VBR header.
 // The offset of the passed BufferReader needs to point to an MPEG frame
 // begin, as a VBRI-style header is searched at a fixed offset relative to
 // frame begin. Returns whether a valid VBR header was found.
 bool ParseVBRHeader(BufferReader* aReader);

private:
 // ID3 header parser.
 ID3Parser mID3Parser;

 // VBR header parser.
 VBRHeader mVBRHeader;

 // We keep the first parsed frame around for static info access, the
 // previously parsed frame for debugging and the currently parsed frame.
 Frame mFirstFrame;
 Frame mFrame;
 Frame mPrevFrame;
 // If this is true, ID3v1 metadata have been found at the end of the file, and
 // must be sustracted from the stream size in order to compute the stream
 // duration, when computing the duration of a CBR file based on its length in
 // bytes. This means that the duration can change at the moment we reach the
 // end of the file.
 bool mID3v1MetadataFound = false;
};

}  // namespace mozilla

#endif