func unescape()

in proto/text_decode.go [707:771]

• 65 lines of code
• 24 McCabe index (conditional complexity)

func unescape(s string) (ch string, tail string, err error) {
	r, n := utf8.DecodeRuneInString(s)
	if r == utf8.RuneError && n == 1 {
		return "", "", errBadUTF8
	}
	s = s[n:]
	switch r {
	case 'a':
		return "\a", s, nil
	case 'b':
		return "\b", s, nil
	case 'f':
		return "\f", s, nil
	case 'n':
		return "\n", s, nil
	case 'r':
		return "\r", s, nil
	case 't':
		return "\t", s, nil
	case 'v':
		return "\v", s, nil
	case '?':
		return "?", s, nil // trigraph workaround
	case '\'', '"', '\\':
		return string(r), s, nil
	case '0', '1', '2', '3', '4', '5', '6', '7':
		if len(s) < 2 {
			return "", "", fmt.Errorf(`\%c requires 2 following digits`, r)
		}
		ss := string(r) + s[:2]
		s = s[2:]
		i, err := strconv.ParseUint(ss, 8, 8)
		if err != nil {
			return "", "", fmt.Errorf(`\%s contains non-octal digits`, ss)
		}
		return string([]byte{byte(i)}), s, nil
	case 'x', 'X', 'u', 'U':
		var n int
		switch r {
		case 'x', 'X':
			n = 2
		case 'u':
			n = 4
		case 'U':
			n = 8
		}
		if len(s) < n {
			return "", "", fmt.Errorf(`\%c requires %d following digits`, r, n)
		}
		ss := s[:n]
		s = s[n:]
		i, err := strconv.ParseUint(ss, 16, 64)
		if err != nil {
			return "", "", fmt.Errorf(`\%c%s contains non-hexadecimal digits`, r, ss)
		}
		if r == 'x' || r == 'X' {
			return string([]byte{byte(i)}), s, nil
		}
		if i > utf8.MaxRune {
			return "", "", fmt.Errorf(`\%c%s is not a valid Unicode code point`, r, ss)
		}
		return string(rune(i)), s, nil
	}
	return "", "", fmt.Errorf(`unknown escape \%c`, r)
}