code: func (kcp *KCP) WndSize(sndwnd, rcvwnd int) int {
  	if sndwnd > 0 {
  		kcp.snd_wnd = uint32(sndwnd)
  	}
  	if rcvwnd > 0 {
  		kcp.rcv_wnd = uint32(rcvwnd)
  	}
  	return 0
  }
docs: // WndSize sets maximum window size: sndwnd=32, rcvwnd=32 by default