code: func splitUrl(url *url.URL) (parts []string, port string) {
  	host, port, err := net.SplitHostPort(url.Host)
  	if err != nil {
  		// could not parse port
  		host, port = url.Host, ""
  	}
  	return strings.Split(host, "."), port
  }
docs: // split the host name into parts, as well as the port