参考资料：
https://github.com/tewuapple/UDPNAT
https://github.com/dwoz/python-nat-hole-punching
https://github.com/7wingfly/P2Pchat
https://gist.github.com/darkguy2008/413a6fea3a5b4e67e5e0d96f750088a9
https://www.ryanxin.cn/archives/475