private int AddContentLength(long len, int offset)
{
Buffer.BlockCopy(ContentLength, 0, OutputTemp, offset, ContentLength.Length);
offset += ContentLength.Length;
offset = Serialize(len, OutputTemp, offset);
OutputTemp[offset] = 13;
OutputTemp[offset + 1] = 10;
OutputTemp[offset + 2] = 13;
OutputTemp[offset + 3] = 10;
return offset + 4;
}