code: func parse(addr string) (string, error) {
  	proxyurl, err := url.Parse(addr)
  	if err != nil || !strings.HasPrefix(proxyurl.Scheme, "http") {
  		proxyurl, err = url.Parse("http://" + addr)
  		if err != nil {
  			return "", trace.Wrap(err)
  		}
  	}
  
  	return proxyurl.Host, nil
  }
docs: // parse will extract the host:port of the proxy to dial to. If the
  // value is not prefixed by "http", then it will prepend "http" and try.