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