Function unescapeToUTF8Config

escape.go:185–223

SYS-REQ-115

(config Config, in, out []byte)

// SYS-REQ-115
func unescapeToUTF8Config(config Config, in, out []byte) (inLen int, outLen int) {
	if len(in) < 2 || in[0] != '\\' {
		// Invalid escape due to insufficient characters for any escape or no initial backslash
		return -1, -1
	}

	// https://tools.ietf.org/html/rfc7159#section-7
	switch e := in[1]; e {
	case '"', '\\', '/', 'b', 'f', 'n', 'r', 't':
		// Valid basic 2-character escapes (use lookup table)
		out[0] = backslashCharEscapeTable[e]
		return 2, 1
	case '\'':
		if config.AllowSingleQuotes {
			out[0] = e
			return 2, 1
		}
	case 'u':
		// Unicode escape
		if r, inLen := decodeUnicodeEscape(in); inLen == -1 {
			// Invalid Unicode escape
			return -1, -1
		} else {
			// Valid Unicode escape; re-encode as UTF8
			outLen := utf8.EncodeRune(out, r)
			return inLen, outLen
		}
	}

	if config.AllowUnknownEscapes {
		// Lenient mode treats the escaped byte as a literal and discards the
		// escape marker. A trailing '\' and malformed \u escape remain errors:
		// they are truncated/invalid encodings, not unknown escape names.
		out[0] = in[1]
		return 2, 1
	}

	return -1, -1
}

const lowerHex = "0123456789abcdef"