https://my.oschina.net/u/2307114/blog/628504

http://mysuperbaby.iteye.com/blog/2345365

https://github.com/koajs/koa/wiki#middleware

http://www.jb51.net/article/55598.htm

http://ourjs.com/detail/5490db1c8a34fa320400000e

http://cnodejs.org/topic/56e688a983cbb63b6d120300

http://www.jdon.com/idea/nodejs/promise.html nodejs的promise用法

http://www.jdon.com/idea/nodejs/generators.html 在Node.js中使用Javascript Generators

http://www.cnblogs.com/Leo_wl/p/4684633.html Koa框架实践与中间件原理剖析

http://blog.csdn.net/zhangfei8625/article/details/48344405 koa文件上传