in openwhisk/filetype.go [70:77]
func IsGz(buf []byte) bool {
// Magic number: The first two bytes are fixed (0x1f and 0x8b), which represent the magic number of a gzip file.
// Compression method: The third byte indicates the compression method used. For gzip files, this is always (deflate).
return len(buf) > 3 &&
buf[0] == 0x1f &&
buf[1] == 0x8b &&
buf[2] == 0x08
}