protected override StreamExtent MapGrain(long grainStart, int grainOffset, int numToRead)
{
if ((_hostedHeader.Flags & HostedSparseExtentFlags.CompressedGrains) != 0)
{
_fileStream.Position = grainStart;
byte[] readBuffer = Utilities.ReadFully(_fileStream, CompressedGrainHeader.Size);
CompressedGrainHeader hdr = new CompressedGrainHeader();
hdr.Read(readBuffer, 0);
return(new StreamExtent(grainStart + grainOffset, CompressedGrainHeader.Size + hdr.DataSize));
}
else
{
return(base.MapGrain(grainStart, grainOffset, numToRead));
}
}
protected override int ReadGrain(byte[] buffer, int bufferOffset, long grainStart, int grainOffset, int numToRead)
{
if ((_hostedHeader.Flags & HostedSparseExtentFlags.CompressedGrains) != 0)
{
_fileStream.Position = grainStart;
byte[] readBuffer = Utilities.ReadFully(_fileStream, CompressedGrainHeader.Size);
CompressedGrainHeader hdr = new CompressedGrainHeader();
hdr.Read(readBuffer, 0);
readBuffer = Utilities.ReadFully(_fileStream, hdr.DataSize);
// This is really a zlib stream, so has header and footer. We ignore this right now, but we sanity
// check against expected header values...
ushort header = Utilities.ToUInt16BigEndian(readBuffer, 0);
if ((header % 31) != 0)
{
throw new IOException("Invalid ZLib header found");
}
if ((header & 0x0F00) != (8 << 8))
{
throw new NotSupportedException("ZLib compression not using DEFLATE algorithm");
}
if ((header & 0x0020) != 0)
{
throw new NotSupportedException("ZLib compression using preset dictionary");
}
Stream readStream = new MemoryStream(readBuffer, 2, hdr.DataSize - 2, false);
DeflateStream deflateStream = new DeflateStream(readStream, CompressionMode.Decompress);
// Need to skip some bytes, but DefaultStream doesn't support seeking...
Utilities.ReadFully(deflateStream, grainOffset);
return(deflateStream.Read(buffer, bufferOffset, numToRead));
}
else
{
return(base.ReadGrain(buffer, bufferOffset, grainStart, grainOffset, numToRead));
}
}