/// <summary>
/// Check if the stream is in ZLib format
/// </summary>
/// <param name="stream">Stream to check</param>
/// <returns>Returns <see langword="true"/> in case the stream is in ZLib format,
/// otherwise returns <see langword="true"/> or error.</returns>
public static bool IsZLibStream(Stream stream)
{
bool bResult = false;
int CMF = 0;
int Flag = 0;
ZLibHeader header;
// We check if the sequence is in position 0, if not, we throw an exception
if (stream.Position != 0)
{
throw new ArgumentOutOfRangeException("Sequence must be at position 0");
}
// We check if we can read the two bytes that make up the header
if (stream.CanRead == true)
{
CMF = stream.ReadByte();
Flag = stream.ReadByte();
try
{
header = ZLibHeader.DecodeHeader(CMF, Flag);
bResult = header.IsZLibSupported;
}
catch
{
//Nada
}
}
return(bResult);
}
public static ZLibHeader DecodeHeader(int pCMF, int pFlag)
{
ZLibHeader result = new ZLibHeader();
//Ensure that parameters are bytes
pCMF = pCMF & 0x0FF;
pFlag = pFlag & 0x0FF;
//Decode bytes
result.CompressionInfo = Convert.ToByte((pCMF & 0xF0) >> 4);
result.CompressionMethod = Convert.ToByte(pCMF & 0x0F);
result.CheckFlag = Convert.ToByte(pFlag & 0x1F);
result.DictFlag = Convert.ToBoolean(Convert.ToByte((pFlag & 0x20) >> 5));
result.CompressionLevel = (ZLibCompressionLevel)Convert.ToByte((pFlag & 0xC0) >> 6);
result.IsZLibSupported = (result.CompressionMethod == 8) &&
(result.CompressionInfo == 7) && (((pCMF * 256 + pFlag) % 31 == 0)) && (result.DictFlag == false);
return(result);
}
/// <summary>
/// Initialize the stream header in ZLib format
/// </summary>
private void InitializeZLibHeader()
{
byte[] bytesHeader;
// We set the header configuration
ZLibHeader header = new ZLibHeader();
header.CompressionMethod = 8; //Deflate
header.CompressionInfo = 7;
header.DictFlag = false; // No dictionary
header.CompressionLevel = _compressionLevel;
//switch (_compressionLevel)
//{
// case CompressionLevel.NoCompression:
// {
// header.FLevel = ZLibCompressionLevel.Faster;
// break;
// }
// case CompressionLevel.Fastest:
// {
// header.FLevel = ZLibCompressionLevel.Default;
// break;
// }
// case CompressionLevel.Optimal:
// {
// header.FLevel = ZLibCompressionLevel.Optimal;
// break;
// }
//}
bytesHeader = header.EncodeZlibHeader();
_rawStream.WriteByte(bytesHeader[0]);
_rawStream.WriteByte(bytesHeader[1]);
}