func isASCII(s string) bool {
	for i := 0; i < len(s); i++ {
		if s[i] >= utf8.RuneSelf {
			return false
		}
	}
	return true
}

// PunycodeHostPort returns the IDNA Punycode version
// of the provided "host" or "host:port" string.
func PunycodeHostPort(v string) (string, error) {
	if isASCII(v) {
		return v, nil
	}

	host, port, err := net.SplitHostPort(v)
	if err != nil {

	// Clean the host, in case it arrives with unexpected stuff in it.
	host := r.Host
	if host == "" {
		if r.URL == nil {
			return errMissingHost
		}
		host = r.URL.Host
	}
	host, err = httpguts.PunycodeHostPort(host)
	if err != nil {
		return err
	}
	// Validate that the Host header is a valid header in general,
	// but don't validate the host itself. This is sufficient to avoid

	cc.hbuf.Reset()
	if req.URL == nil {
		return nil, http2errNilRequestURL
	}

	host := req.Host
	if host == "" {
		host = req.URL.Host
	}
	host, err := httpguts.PunycodeHostPort(host)
	if err != nil {
		return nil, err
	}
	if !httpguts.ValidHostHeader(host) {
		return nil, errors.New("http2: invalid Host header")
	}

	var path string