code: func (t *NetTransport) WriteTo(b []byte, addr string) (time.Time, error) {
  	udpAddr, err := net.ResolveUDPAddr("udp", addr)
  	if err != nil {
  		return time.Time{}, err
  	}
  
  	// We made sure there's at least one UDP listener, so just use the
  	// packet sending interface on the first one. Take the time after the
  	// write call comes back, which will underestimate the time a little,
  	// but help account for any delays before the write occurs.
  	_, err = t.udpListeners[0].WriteTo(b, udpAddr)
  	return time.Now(), err
  }
docs: // See Transport.