class Mixlib::Archive::Tar

def is_gzip_file?(path)
  # You cannot write "\x1F\x8B" because the default encoding of
  # ruby >= 1.9.3 is UTF-8 and 8B is an invalid in UTF-8.
  IO.binread(path, 2) == [0x1F, 0x8B].pack("C*")
end