Tag Parser  7.0.0
C++ library for reading and writing MP4 (iTunes), ID3, Vorbis, Opus, FLAC and Matroska tags
oggpage.cpp
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1 #include "./oggpage.h"
2 
3 #include "../exceptions.h"
4 
5 #include <c++utilities/conversion/binaryconversion.h>
6 #include <c++utilities/io/binaryreader.h>
7 
8 using namespace std;
9 using namespace IoUtilities;
10 using namespace ConversionUtilities;
11 
12 namespace TagParser {
13 
25 void OggPage::parseHeader(istream &stream, uint64 startOffset, int32 maxSize)
26 {
27  // prepare reading
28  stream.seekg(startOffset);
29  BinaryReader reader(&stream);
30  if (maxSize < 27) {
31  throw TruncatedDataException();
32  } else {
33  maxSize -= 27;
34  }
35  // read header values
36  if (reader.readUInt32LE() != 0x5367674f) {
37  throw InvalidDataException();
38  }
39  m_startOffset = startOffset;
40  m_streamStructureVersion = reader.readByte();
41  m_headerTypeFlag = reader.readByte();
42  m_absoluteGranulePosition = reader.readUInt64LE();
43  m_streamSerialNumber = reader.readUInt32LE();
44  m_sequenceNumber = reader.readUInt32LE();
45  m_checksum = reader.readUInt32LE();
46  m_segmentCount = reader.readByte();
47  m_segmentSizes.clear();
48  if (m_segmentCount > 0) {
49  if (maxSize < m_segmentCount) {
50  throw TruncatedDataException();
51  } else {
52  maxSize -= m_segmentCount;
53  }
54  // read segment size tabe
55  m_segmentSizes.push_back(0);
56  for (byte i = 0; i < m_segmentCount;) {
57  byte entry = reader.readByte();
58  maxSize -= entry;
59  m_segmentSizes.back() += entry;
60  if (++i < m_segmentCount && entry < 0xff) {
61  m_segmentSizes.push_back(0);
62  }
63  }
64  // check whether the maximum size is exceeded
65  if (maxSize < 0) {
66  throw TruncatedDataException();
67  }
68  }
69 }
70 
75 uint32 OggPage::computeChecksum(istream &stream, uint64 startOffset)
76 {
77  stream.seekg(startOffset);
78  uint32 crc = 0x0;
79  byte value, segmentTableSize = 0, segmentTableIndex = 0;
80  for (uint32 i = 0, segmentLength = 27; i != segmentLength; ++i) {
81  switch (i) {
82  case 22:
83  // bytes 22, 23, 24, 25 hold denoted checksum and must be set to zero
84  stream.seekg(4, ios_base::cur);
85  case 23:
86  case 24:
87  case 25:
88  value = 0;
89  break;
90  case 26:
91  // byte 26 holds the number of segment sizes
92  segmentLength += (segmentTableSize = (value = stream.get()));
93  break;
94  default:
95  value = stream.get();
96  if (i > 26 && segmentTableIndex < segmentTableSize) {
97  // bytes 27 to (27 + segment size count) hold page size
98  segmentLength += value;
99  ++segmentTableIndex;
100  }
101  }
102  crc = (crc << 8) ^ BinaryReader::crc32Table[((crc >> 24) & 0xFF) ^ value];
103  }
104  return crc;
105 }
106 
111 void OggPage::updateChecksum(iostream &stream, uint64 startOffset)
112 {
113  char buff[4];
114  LE::getBytes(computeChecksum(stream, startOffset), buff);
115  stream.seekp(startOffset + 22);
116  stream.write(buff, sizeof(buff));
117 }
118 
123 uint32 OggPage::makeSegmentSizeDenotation(ostream &stream, uint32 size)
124 {
125  uint32 bytesWritten = 1;
126  while (size >= 0xff) {
127  stream.put(0xff);
128  size -= 0xff;
129  ++bytesWritten;
130  }
131  stream.put(size);
132  return bytesWritten;
133 }
134 
135 } // namespace TagParser
STL namespace.
Contains utility classes helping to read and write streams.