private static DeflateStream CreateDeflateStreamForReading(Stream stream, bool leaveOpen)
{
if (!stream.CanRead)
{
throw new ArgumentException("The stream must support reading", "stream");
}
int compressionMethodAndFlags = stream.ReadByte();
int flags = stream.ReadByte();
if (compressionMethodAndFlags == -1 || flags == -1)
{
throw new EndOfStreamException();
}
if (((compressionMethodAndFlags << 8) + flags) % 31 != 0)
{
throw new System.FormatException("stream is not a valid zlib stream");
}
int compressionMethod = compressionMethodAndFlags & 0xF;
if (compressionMethod != 8)
{
throw new NotSupportedException("Compression method " + compressionMethod + " is not supported");
}
if ((flags & 0x10) != 0)
{
// skip DICTID
byte[] buffer = new byte[4];
if (stream.Read(buffer, 0, 4) < 4)
{
throw new EndOfStreamException();
}
}
long offset = stream.Position;
long length = stream.Length - offset - 4; // - 4 for ADLER-32 checksum
SubStream subStream = new SubStream(stream, offset, length, leaveOpen);
try {
return(new DeflateStream(subStream, CompressionMode.Decompress, false));
} catch {
subStream.Dispose();
throw;
}
}
