func idnaASCIIFromURL(url *url.URL) string {
	addr := url.Hostname()
	if v, err := idnaASCII(addr); err == nil {
		addr = v
	}
	return addr
}

// canonicalAddr returns url.Host but always with a ":port" suffix.
func canonicalAddr(url *url.URL) string {
	port := url.Port()
	if port == "" {
		port = portMap[url.Scheme]
	}
	return net.JoinHostPort(idnaASCIIFromURL(url), port)
}