for _, c := range s {
		if c >= 0x80 || c == 0x00 {
			return false
		}
	}
	return true
}

// toASCII converts the input to an ASCII C-style string.
// This is a best effort conversion, so invalid characters are dropped.
func toASCII(s string) string {
	if isASCII(s) {
		return s
	}
	b := make([]byte, 0, len(s))
	for _, c := range s {
		if c < 0x80 && c != 0x00 {
			b = append(b, byte(c))
		}
	}