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