// Read the gzip header from the base stream.
private void ReadHeader()
{
Crc32 headerCrc = new Crc32();
int magic1, magic2, flags, temp;
// Validate the magic number.
magic1 = ReadByte(headerCrc);
if (magic1 < 0)
{
// The stream is empty, so just report EOF and exit.
endOfStream = true;
return;
}
magic2 = ReadByte(headerCrc);
if (magic2 < 0 ||
((magic1 << 8) + magic2) != GZipConstants.GZIP_MAGIC)
{
// The magic number does not match.
throw new IOException(S._("IO_Decompress_GzipHeader"));
}
// Check the compression type, which must be 8.
if (ReadByte(headerCrc) != 0x08)
{
throw new IOException(S._("IO_Decompress_GzipHeader"));
}
// Read the flags.
flags = ReadByte(headerCrc);
if ((flags & 0xE0) != 0)
{
throw new IOException(S._("IO_Decompress_GzipHeader"));
}
// Skip the modification time, extra flags, and OS type.
for (temp = 0; temp < 6; ++temp)
{
ReadByteThrow(headerCrc);
}
// Skip the "extra" field.
if ((flags & GZipConstants.FEXTRA) != 0)
{
// Get the length of the extra field.
temp = ReadByteThrow(headerCrc);
temp += (ReadByteThrow(headerCrc) << 8);
// Skip the extra field.
while (temp > 0)
{
ReadByteThrow(headerCrc);
--temp;
}
}
// Skip the "filename" field.
if ((flags & GZipConstants.FNAME) != 0)
{
do
{
temp = ReadByteThrow(headerCrc);
}while(temp != 0);
}
// Skip the "comment" field.
if ((flags & GZipConstants.FCOMMENT) != 0)
{
do
{
temp = ReadByteThrow(headerCrc);
}while(temp != 0);
}
// Read the header checksum.
if ((flags & GZipConstants.FHCRC) != 0)
{
magic1 = stream.ReadByte();
if (magic1 < 0)
{
throw new IOException(S._("IO_Decompress_GzipHeader"));
}
temp = stream.ReadByte();
if (temp < 0)
{
throw new IOException(S._("IO_Decompress_GzipHeader"));
}
temp = magic1 + (temp << 8);
if (temp != (((int)(headerCrc.Value)) & 0xFFFF))
{
throw new IOException(S._("IO_Decompress_GzipHeader"));
}
}
// The header has been read, and we are ready to go.
headerDone = true;
}
