confusing accessors in koa

koa-confusing-accessors.js

// See https://github.com/koajs/koa/issues/215
// start: nvm run 0.11 --harmony koa-confusing-accessors
// test: curl -d '{"test":"ok"}' -H 'Content-Type: application/json' http://localhost:3000/

var koa = require('koa');
var app = module.exports = koa();

app.use(function *(next){
	if (this.method === 'POST') {
		this.body = '<?xml version="1.0">'
		this.type = 'application/xml'  // set this.type => set this.response.type
		switch (this.type) {	      // get this.type => get this.request.type
			case 'application/json':
				this.body += '<type>json</type>'
				break
			case 'application/xml':
				this.body += '<type>xml</type>'
				break
			default: 
				this.set(400)
				this.body += '<error>Unsupported media type</error>'
		}
	} else yield next
});

if (!module.parent) app.listen(3000);