public PageHeader ReadPageHeader(long position)
{
_stream.Seek(position, SeekOrigin.Begin);
if (_stream.Read(_readBuffer, 0, 27) != 27)
{
return(null);
}
if (_readBuffer[0] != 79 || _readBuffer[1] != 103 || _readBuffer[2] != 103 || _readBuffer[3] != 83)
{
return(null);
}
if (_readBuffer[4] != 0)
{
return(null);
}
PageHeader pageHeader = new PageHeader();
pageHeader.Flags = (PageFlags)_readBuffer[5];
long num = BitConverter.ToInt32(_readBuffer, 6);
long num2 = BitConverter.ToInt32(_readBuffer, 10);
pageHeader.GranulePosition = num + (num2 << 32);
pageHeader.StreamSerial = BitConverter.ToInt32(_readBuffer, 14);
pageHeader.SequenceNumber = BitConverter.ToInt32(_readBuffer, 18);
uint checkCrc = BitConverter.ToUInt32(_readBuffer, 22);
_crc.Reset();
for (int i = 0; i < 22; i++)
{
_crc.Update(_readBuffer[i]);
}
_crc.Update(0);
_crc.Update(0);
_crc.Update(0);
_crc.Update(0);
_crc.Update(_readBuffer[26]);
int num3 = _readBuffer[26];
if (_stream.Read(_readBuffer, 0, num3) != num3)
{
return(null);
}
List <int> list = new List <int>(num3);
int num4 = 0;
int num5 = 0;
for (int j = 0; j < num3; j++)
{
byte b = _readBuffer[j];
_crc.Update(b);
if (num5 == list.Count)
{
list.Add(0);
}
list[num5] += b;
if (b < byte.MaxValue)
{
num5++;
pageHeader.LastPacketContinues = false;
}
else
{
pageHeader.LastPacketContinues = true;
}
num4 += b;
}
pageHeader.PacketSizes = list.ToArray();
pageHeader.DataOffset = position + 27 + num3;
if (_stream.Read(_readBuffer, 0, num4) != num4)
{
return(null);
}
for (int k = 0; k < num4; k++)
{
_crc.Update(_readBuffer[k]);
}
if (_crc.Test(checkCrc))
{
_containerBits += 8 * (27 + num3);
_pageCount++;
return(pageHeader);
}
return(null);
}
PageHeader ReadPageHeader(long position)
{
// set the stream's position
_stream.Seek(position, SeekOrigin.Begin);
// header
// NB: if the stream didn't have an EOS flag, this is the most likely spot for the EOF to be found...
if (_stream.Read(_readBuffer, 0, 27) != 27)
{
return(null);
}
// capture signature
if (_readBuffer[0] != 0x4f || _readBuffer[1] != 0x67 || _readBuffer[2] != 0x67 || _readBuffer[3] != 0x53)
{
return(null);
}
// check the stream version
if (_readBuffer[4] != 0)
{
return(null);
}
// start populating the header
var hdr = new PageHeader();
// bit flags
hdr.Flags = (PageFlags)_readBuffer[5];
// granulePosition
hdr.GranulePosition = BitConverter.ToInt64(_readBuffer, 6);
// stream serial
hdr.StreamSerial = BitConverter.ToInt32(_readBuffer, 14);
// sequence number
hdr.SequenceNumber = BitConverter.ToInt32(_readBuffer, 18);
// save off the CRC
var crc = BitConverter.ToUInt32(_readBuffer, 22);
// start calculating the CRC value for this page
_crc.Reset();
for (int i = 0; i < 22; i++)
{
_crc.Update(_readBuffer[i]);
}
_crc.Update(0);
_crc.Update(0);
_crc.Update(0);
_crc.Update(0);
_crc.Update(_readBuffer[26]);
// figure out the length of the page
var segCnt = (int)_readBuffer[26];
if (_stream.Read(_readBuffer, 0, segCnt) != segCnt)
{
return(null);
}
var packetSizes = new List <int>(segCnt);
int size = 0, idx = 0;
for (int i = 0; i < segCnt; i++)
{
var temp = _readBuffer[i];
_crc.Update(temp);
if (idx == packetSizes.Count)
{
packetSizes.Add(0);
}
packetSizes[idx] += temp;
if (temp < 255)
{
++idx;
hdr.LastPacketContinues = false;
}
else
{
hdr.LastPacketContinues = true;
}
size += temp;
}
hdr.PacketSizes = packetSizes.ToArray();
hdr.DataOffset = position + 27 + segCnt;
// now we have to go through every byte in the page
if (_stream.Read(_readBuffer, 0, size) != size)
{
return(null);
}
for (int i = 0; i < size; i++)
{
_crc.Update(_readBuffer[i]);
}
if (_crc.Test(crc))
{
_containerBits += 8 * (27 + segCnt);
++_pageCount;
return(hdr);
}
return(null);
}
private bool CheckPage(long pageOffset, out short packetCount, out long nextPageOffset)
{
if (DecodeHeader())
{
// we have a potentially good page... check the CRC
var crc = BitConverter.ToUInt32(_headerBuf, 22);
var segCount = _headerBuf[26];
_crc.Reset();
for (var j = 0; j < 22; j++)
{
_crc.Update(_headerBuf[j]);
}
_crc.Update(0);
_crc.Update(0);
_crc.Update(0);
_crc.Update(0);
_crc.Update(segCount);
// while we're here, count up the number of packets in the page
var dataLen = 0;
var pktLen = 0;
short pktCnt = 0;
for (var j = 0; j < segCount; j++)
{
var segLen = _headerBuf[27 + j];
_crc.Update(segLen);
pktLen += segLen;
dataLen += segLen;
if (segLen < 255 || j == segCount - 1)
{
if (pktLen > 0)
{
++pktCnt;
pktLen = 0;
}
}
}
packetCount = pktCnt;
// finish calculating the CRC
_stream.Position = pageOffset + 27 + segCount;
if (_stream.Read(_dataBuf, 0, dataLen) < dataLen)
{
// we're going to assume this means the stream has ended
nextPageOffset = 0;
return(false);
}
for (var j = 0; j < dataLen; j++)
{
_crc.Update(_dataBuf[j]);
}
if (_crc.Test(crc))
{
// cool, we have a valid page!
nextPageOffset = _stream.Position;
PageOffset = pageOffset;
PageCount++;
ContainerBits += 8 * (27 + segCount);
return(true);
}
}
packetCount = 0;
nextPageOffset = 0;
return(false);
}
