通过koajs的cookies方法设置cookie时，写了中文的cookie值，一直失败。代码如下:
this.cookies.set('test', '我是koajs')
报错如下：
sent error argument value is invalid to the cloud
TypeError: argument value is invalid
at new Cookie (/Users/zyy/github/fete/node_modules/cookies/lib/cookies.js:110:11)
at Cookies.set (/Users/zyy/github/fete/node_modules/cookies/lib/cookies.js:73:16)
at Object.<anonymous> (/Users/zyy/github/fete/app.js:54:18)
at next (native)
at onFulfilled (/Users/zyy/github/fete/node_modules/co/index.js:65:19)
at /Users/zyy/github/fete/node_modules/co/index.js:54:5
at Object.co (/Users/zyy/github/fete/node_modules/co/index.js:50:10)
at converted (/Users/zyy/github/fete/node_modules/koa-convert/index.js:17:15)
at dispatch (/Users/zyy/github/fete/node_modules/koa-compose/index.js:43:32)
at next (/Users/zyy/github/fete/node_modules/koa-compose/index.js:44:18)
at createGenerator (/Users/zyy/github/fete/node_modules/koa-convert/index.js:24:16)
at next (native)
at onFulfilled (/Users/zyy/github/fete/node_modules/co/index.js:65:19)
at /Users/zyy/github/fete/node_modules/co/index.js:54:5
at Object.co (/Users/zyy/github/fete/node_modules/co/index.js:50:10)
at Object.toPromise (/Users/zyy/github/fete/node_modules/co/index.js:118:63)
倒腾了半夜也没找到方案，其实是http协议的Header头有字符限制，下图是stackoverflow的解答，http的header字符集支持US-ASCII子集的字符集，故设置中文是'utf8'时就会报上面错误。
Paste_Image.png
问题链接如下：
http://stackoverflow.com/questions/4400678/http-header-should-use-what-character-encoding
故解决方案：
把字符串转成base64即可
this.cookies.set('test', new Buffer('我是koajs').toString('base64'))
base64转到字符串
new Buffer(str, 'base64').toString();//str是base64编码的字符串
