code: func (s *UDPSession) readLoop() {
  	addr, _ := net.ResolveUDPAddr("udp", s.conn.LocalAddr().String())
  	if addr.IP.To4() != nil {
  		s.readLoopIPv4()
  	} else {
  		s.readLoopIPv6()
  	}
  }
docs: // the read loop for a client session