distribution.go

func checkDistribution(pkgPath string) (bool, error) {
	const (
		xarHeaderMagic = 0x78617221
		xarHeaderSize  = 28
	)

	f, err := os.Open(pkgPath)
	if err != nil {
		return false, err
	}
	defer f.Close()

	hdr := make([]byte, xarHeaderSize)
	_, err = f.ReadAt(hdr, 0)
	if err != nil {
		return false, err
	}
	tocLenZlib := binary.BigEndian.Uint64(hdr[8:16])
	ztoc := make([]byte, tocLenZlib)
	_, err = f.ReadAt(ztoc, xarHeaderSize)
	if err != nil {
		return false, err
	}

	br := bytes.NewBuffer(ztoc)
	zr, err := zlib.NewReader(br)
	if err != nil {
		return false, err
	}
	toc, err := ioutil.ReadAll(zr)
	if err != nil {
		return false, err
	}
	return bytes.Contains(toc, []byte(`<name>Distribution</name>`)), nil
}