func hasTarHeader()

in pkg/3p/archiver/tar.go [48:80]

• 27 lines of code
• 9 McCabe index (conditional complexity)

func hasTarHeader(buf []byte) bool {
	if len(buf) < tarBlockSize {
		return false
	}

	b := buf[148:156]
	b = bytes.Trim(b, " \x00") // clean up all spaces and null bytes
	if len(b) == 0 {
		return false // unknown format
	}
	hdrSum, err := strconv.ParseUint(string(b), 8, 64)
	if err != nil {
		return false
	}

	// According to the go official archive/tar, Sun tar uses signed byte
	// values so this calcs both signed and unsigned
	var usum uint64
	var sum int64
	for i, c := range buf {
		if 148 <= i && i < 156 {
			c = ' ' // checksum field itself is counted as branks
		}
		usum += uint64(uint8(c))
		sum += int64(int8(c))
	}

	if hdrSum != usum && int64(hdrSum) != sum {
		return false // invalid checksum
	}

	return true
}