Using go1.6

Example code:

b, _ := hex.DecodeString("" +
    "1f8b081200096e8800ff48656c6c6f00" + // GZIP header
    "99d6" + // header.FHCRC (should cover entire header)
    "010000ffff0000000000000000", // GZIP data
)

r, err := gzip.NewReader(bytes.NewReader(b))
if err != nil {
    panic(err)
}
_ = r

This currently errors with gzip.ErrHeader, but should in fact create a gzip.Reader without issue.

Currently, Go only performs the CRC over the first 10 bytes of the header. However, RFC 1952, section 3.2.3 says:

If FHCRC is set, a CRC16 for the gzip header is present, immediately before the compressed data. The CRC16 consists of the two least significant bytes of the CRC32 for all bytes of the gzip header up to and not including the CRC16.

Instead, we should compute the CRC over the whole header.