var sha1 = require('sha1');

module.exports = function(opts){
  return function *(next){
    var token = opts.token;
    var signature = this.query.signature;
    var nonce = this.query.nonce;
    var timestamp = this.query.timestamp;
    var echostr = this.query.echostr;
    var str = [token,timestamp,nonce].sort().join('');
    var sha = sha1(str);
    this.body = (sha === signature) ? echostr + '' : 'failed';
  };
}

'use strict'

var Koa = require('koa');
var wechat = require('./wechat/generator');

var config = {
  wechat:{
    appID:'...',
    appSecret:'...',
    token:'...'
  }
};

var app = new Koa();
app.use(wechat(config.wechat));
app.listen(8080);
console.log('Listening 8080...')

function Wechat(opts){   //构造函数，用以生成实例，完成初始化工作，读写票据
  var that = this;
  this.appID = opts.appID;
  this.appSecret = opts.appSecret;
  this.getAccessToken = opts.getAccessToken;
  this.saveAccessToken = opts.saveAccessToken;

  this.getAccessToken().then(function(data){
    try{
      data = JSON.parse(data);
    }catch(e){
      return that.updateAccessToken();
    }
    if(that.isvalidAccessToken(data)){
      Promise.resolve(data);
    }else{
      return that.updateAccessToken();
    }
  }).then(function(data){
    that.access_token = data.access_token;
    that.expires_in = data.expires_in;
    that.saveAccessToken(JSON.stringify(data));
  });
}

var wechat = new Wechat(opts);

var data = yield rawBody(this.req,{
        length:this.length,
        limit:'1mb',
        encoding:this.charset
      });
console.log('data:'+data);

var content = yield util.parseXMLAsync(data);
util中的parseXMLAsync方法：

exports.parseXMLAsync = function(xml){
  return new Promise(function(resolve,reject){
    xml2js.parseString(xml,{trim:true},function(err,content){
      err ? reject(err) : resolve(content);
    })
  });
}

var message = util.formatMessage(content.xml);

function formatMessage(result){
  var message = {};
  if(typeof result === 'object'){
    var keys = Object.keys(result);
    for(var i=0;i<keys.length;i++){
      var key = keys[i];
      var item = result[key];
      if(!(item instanceof Array) || item.length === 0) continue;
      if (item.length === 1){
        var val = item[0];
        if (typeof val === 'object') message[key] = formatMessage(val);
        else message[key] = (val || '').trim();
      }else{
        message[key] = [];
        for(var j=0,k=item.length;j<k;j++) message[key].push(formatMessage(item[j]));
      }
    }
  }
  return message;
}

if(message.MsgType === 'event'){
  if(message.Event === 'subscribe'){
    var createTime = new Date().getTime();
    that.status = 200;
    that.type = 'application/xml';
    that.body = '<xml>'+
          '<ToUserName><![CDATA['+ message.FromUserName +']]></ToUserName>'+
          '<FromUserName><![CDATA['+ message.ToUserName +']]></FromUserName>'+
          '<CreateTime>'+createTime+'</CreateTime>'+
          '<MsgType><![CDATA[text]]></MsgType>'+
          '<Content><![CDATA[终于等到你，还好我没放弃]]></Content>'+
          '</xml>'
    return;
  }
}