上篇说到微信开发配置，接下来着手开发，我们先来看看文本消息的接收与自动回复：
接收普通消息–当普通微信用户向公众账号发消息时，微信服务器将POST消息的XML数据包到开发者填写的URL上，当服务器接收到消息，服务器如果没有做出回应，会断开连接并重新发起请求，重复三次操作，若还未作出回应便回复xxx直接看图：
实现思路，通过构建构造函数，将实例方法绑定在原型对象上，然后将方法导出，微信返回和接收的数据格式都是xml，所以我们要对xml进行转换。所以在今天我们会引入几个新的模块。代码如下（wechat.js）：
var sha1 = require("sha1");var parseString = require('xml2js').parseString;var msg = require("../common/msg");var request = require("request");var path = require("path");var fs = require("fs");var util = require("util");var accessTokenJson = require("../config/access_token.json");function Wechat(config) {this.config = config;this.token = config.wechat.token;this.appID = config.wechat.appID;this.appScrect = config.wechat.appSecret;this.prefix = config.wechat.prefix;this.diyApi = config.wechat.diyApi;}Wechat.prototype.autoMsg = function (req, res, next) {var buffer = [];var that = this;req.on('data', function (data) {buffer.push(data);});req.on('end', function () {var msgXml = Buffer.concat(buffer).toString('utf-8');parseString(msgXml, {explicitArray: false }, function (err, result) {if (err) throw err;result = result.xml;// console.log(result);var toUser = result.ToUserName;var fromUser = result.FromUserName;//回复普通消息if (result.MsgType === "text") {res.send(msg.textMsg(toUser, fromUser, msg.message(result.Content)));} else if (result.MsgType === "image") {//回复图片//在这里图片相当于素材，用户发送的素材只是临时素材，只能在微信服务器保存三天，回复思路：//先上传素材---先封装一个post请求，然后通过素材接口获取media_id来获取素材//上传素材就需要封装post get以及素材上传的api//注意在上传素材时需要access_token所以也需要封装获取access_token的apivar urlPath = path.join(__dirname, "../material/timg.jpg");that.uploadFile(urlPath, "image").then(function (mdeia_id) {resultXml = msg.imgMsg(fromUser, toUser, mdeia_id);res.send(resultXml);})}})})};//获取access_token//为什么要保存access_token，原因请查看文档Wechat.prototype.getAccessToken = function () {var that = this;return new Promise(function (resolve, reject) {var currentTime = new Date().getTime();//格式化请求地址,把刚才的%s按顺序替换var url = util.format(that.diyApi.getAccessToken, that.prefix, that.appID, that.appScrect);//判断本地存储的 access_token 是否有效if (accessTokenJson.access_token === "" || accessTokenJson.expires_time < currentTime) {that.requestGet(url).then(function (data) {var result = JSON.parse(data);// console.log(result);if (data.indexOf("errcode") < 0) {accessTokenJson.access_token = result.access_token;accessTokenJson.expires_time = new Date().getTime() + (parseInt(result.expires_in) - 200) * 1000;// console.log(accessTokenJson);//更新本地存储的fs.writeFile('./../config/access_token.json', JSON.stringify(accessTokenJson),function(err){if(err){throw err;}else{console.log("access_token失效,重新写入成功!");}});resolve(accessTokenJson.access_token);} else {resolve(result);}});} else {//将本地存储的 access_token 返回resolve(accessTokenJson.access_token);}});}//封装一个get方法Wechat.prototype.requestGet = function (url) {return new Promise(function (resolve, reject) {request(url, (error, response, body) => {resolve(body);})})}//封装一个post方法Wechat.prototype.requestPost = function (url, data) {return new Promise(function (resolve, reject) {request.post({url: url, formData: data }, function (err, httpResponse, body) {resolve(body);});});}//上传素材Wechat.prototype.uploadFile = function (urlPath, type) {var that = this;return new Promise(function (resolve, reject) {that.getAccessToken().then(function (data) {//data=== access_tokenvar form = {//构造表单media: fs.createReadStream(urlPath)}var url = util.format(that.diyApi.uploadFile, that.prefix, data, type);that.requestPost(url, form).then(function (result) {resolve(JSON.parse(result).media_id);})})})}
代码优化部分：msg.js
将文字回复和图片恢复的api都抽出来放于一个新的js文件，代码如下：
//回复文字消息exports.textMsg = function (toUser, fromUser, content) {var resultXml = "<xml><ToUserName><![CDATA[" + fromUser + "]]></ToUserName>";resultXml += "<FromUserName><![CDATA[" + toUser + "]]></FromUserName>";resultXml += "<CreateTime>" + new Date().getTime() + "</CreateTime>";resultXml += "<MsgType><![CDATA[text]]></MsgType>";resultXml += "<Content><![CDATA[" + content + "]]></Content></xml>";return resultXml;}//设置自动回复内容exports.message = function (data) {console.log(data)var content;if (data === "你好" || data === "hello" || data === "hi") {content = "欢迎光临小许客栈!"} else {content = "公众号还在升级，敬请期待!";}return content;}//回复图片消息exports.imgMsg = function(toUser, fromUser, media_id) {var xmlContent = "<xml><ToUserName><![CDATA["+ toUser +"]]></ToUserName>";xmlContent += "<FromUserName><![CDATA["+ fromUser +"]]></FromUserName>";xmlContent += "<CreateTime>"+ new Date().getTime() +"</CreateTime>";xmlContent += "<MsgType><![CDATA[image]]></MsgType>";xmlContent += "<Image><MediaId><![CDATA["+ media_id +"]]></MediaId></Image></xml>";return xmlContent; }
app.js
var Wechat = require('./routes/wechat');var wechat = new Wechat(config); //实例化一个WeChat对象app.get('/', (req,res,next)=>{wechat.auth(req,res,next);});app.post("/",(req,res,next)=>{wechat.autoMsg(req,res,next);});
注意看代码注释，比较重要！！！
接下来看下效果：
