code: func (s *Server) ListenPacket() (net.PacketConn, error) {
  	p, err := net.ListenPacket("udp", s.Addr[len(TransportDNS+"://"):])
  	if err != nil {
  		return nil, err
  	}
  
  	return p, nil
  }
docs: // ListenPacket implements caddy.UDPServer interface.