// that permits any lines.
func noValidation(_ []byte) error { return nil }

// mustHaveFieldNameColon ensures that, per RFC 7230, the
// field-name is on a single line, so the first line must
// contain a colon.
func mustHaveFieldNameColon(line []byte) error {
	if bytes.IndexByte(line, ':') < 0 {
		return ProtocolError(fmt.Sprintf("malformed MIME header: missing colon: %q", line))
	}