code: func Transport(s string) string {
  	switch {
  	case strings.HasPrefix(s, TransportTLS+"://"):
  		return TransportTLS
  	case strings.HasPrefix(s, TransportDNS+"://"):
  		return TransportDNS
  	case strings.HasPrefix(s, TransportGRPC+"://"):
  		return TransportGRPC
  	}
  	return TransportDNS
  }
docs: // Transport returns the protocol of the string s