code: func (l *Listener) monitor() {
  	addr, _ := net.ResolveUDPAddr("udp", l.conn.LocalAddr().String())
  	if addr.IP.To4() != nil {
  		l.monitorIPv4()
  	} else {
  		l.monitorIPv6()
  	}
  }
docs: // monitor incoming data for all connections of server