todo
长连接和短连接
http://www.cnblogs.com/0201zcr/p/4694945.html
websocket 常链接
https://www.cnblogs.com/carl10086/p/6188808.html
推送demo
https://blog.csdn.net/z69183787/article/details/52505186
ref
http://m.elecfans.com/article/665867.html
原文：https://www.cnblogs.com/huilei/p/9676522.html