Implement code analysis of online payment function of WeChat applet

Recently I needed to use the online payment function in the WeChat mini program, so I took a look at the official documentation and found that it is very convenient to implement WeChat payment in the mini program. If you have developed WeChat payment under a service account before, Then you will find that the development process of WeChat payment in the mini program is exactly the same as that in the service account. Now I will talk about the development process and points of attention of WeChat payment in the mini program in detail.

1. Open WeChat payment and WeChat merchant account
This process is the same as the WeChat payment process of opening a service account, no What can be said.

2. Get the user’s openid
Home page We need to get the current user in the client js of the mini program The user's openid can be obtained by calling the wx.login method, and then the developer server uses the login credential code to obtain the openid.

wx.login({
      success: function(res) {
        if (res.code) {
          //发起网络请求
          wx.request({
            url: 'https://yourwebsit/onLogin',
            method: 'POST',
            data: {
              code: res.code
            },
            success: function(res) {
                var openid = res.data.openid;
            },
            fail: function(err) {
                console.log(err)
            }
          })
        } else {
          console.log('获取用户登录态失败！' + res.errMsg)
        }
      }
    });

var code = req.param("code");
        request({
            url: "https://api.weixin.qq.com/sns/jscode2session?appid="+appid+"&secret="+secret+"&js_code="+code+"&grant_type=authorization_code",
            method: 'GET'
        }, function(err, response, body) {
            if (!err && response.statusCode == 200) {
                res.json(JSON.parse(body));
            }
        });

3. Obtain prepay_id and payment signature verification paySign
The process of this step is the same as the WeChat payment process in the service account, which is divided into client and server side
First, let’s take a look at the client js
In the service account, we activate the payment function through the following code

function jsApiCall()
        {
            WeixinJSBridge.invoke(
                'getBrandWCPayRequest',
                {
                   "appId":"",     //公众号名称，由商户传入     
                   "timeStamp":"",         //时间戳，自1970年以来的秒数     
                   "nonceStr":"", //随机串     
                   "package":"prepay_id=",     
                   "signType":"MD5",         //微信签名方式：     
                   "paySign":"" //微信签名
                },
                function(res){
                    WeixinJSBridge.log(res.err_msg);
                    if( res.err_msg =="get_brand_wcpay_request:ok"){
                        alert("支付成功!");
                    }else{
                        alert("支付失败!");
                    }
                }
            );
        }

In the mini program, we activate the payment function through the wx.requestPayment method , of course, before that, we first need to get the prepay_id.

              wx.request({
                    url: 'https://yourwebsit/service/getPay', 
                    method: 'POST',
                    data: {
                      bookingNo:bookingNo,  /*订单号*/
                      total_fee:total_fee,   /*订单金额*/
                      openid:openid
                    },
                    header: {
                        'content-type': 'application/json'
                    },
                    success: function(res) {
                        wx.requestPayment({
                          'timeStamp':timeStamp,
                          'nonceStr': nonceStr,
                          'package': 'prepay_id='+res.data.prepay_id,
                          'signType': 'MD5',
                          'paySign': res.data._paySignjs,
                          'success':function(res){
                              console.log(res);
                          },
                          'fail':function(res){
                              console.log('fail:'+JSON.stringify(res));
                          }
                        })
                    },
                    fail: function(err) {
                        console.log(err)
                    }
                })

The main thing to be implemented on the server side is to obtain prepay_id and sign paySign

        var bookingNo = req.param("bookingNo");
        var total_fee = req.param("total_fee");
        var openid = req.param("openid");
        var body = "费用说明";
        var url = "https://api.mch.weixin.qq.com/pay/unifiedorder";
        var formData = "<xml>";
        formData += "<appid>appid</appid>"; //appid
        formData += "<attach>test</attach>";
        formData += "" + body + "";
        formData += "<mch_id>mch_id</mch_id>"; //商户号
        formData += "<nonce_str>nonce_str</nonce_str>";
        formData += "<notify_url>notify_url</notify_url>";
        formData += "<openid>" + openid + "</openid>";
        formData += "<out_trade_no>" + bookingNo + "</out_trade_no>";
        formData += "<spbill_create_ip>spbill_create_ip</spbill_create_ip>";
        formData += "<total_fee>" + total_fee + "</total_fee>";
        formData += "<trade_type>JSAPI</trade_type>";
        formData += "<sign>" + paysignjsapi(appid, attach, body, mch_id, nonce_str, notify_url, openid, bookingNo, spbill_create_ip, total_fee, 'JSAPI') + "</sign>";
        formData += "</xml>";
        request({
            url: url,
            method: 'POST',
            body: formData
        }, function(err, response, body) {
            if(!err && response.statusCode == 200) {
                var prepay_id = getXMLNodeValue('prepay_id', body.toString("utf-8"));
                var tmp = prepay_id.split('[');
                var tmp1 = tmp[2].split(']');
                //签名
                var _paySignjs = paysignjs(appid, mch_id, 'prepay_id=' + tmp1[0], 'MD5',timeStamp);
                var o = {
                    prepay_id: tmp1[0],
                    _paySignjs: _paySignjs
                }
                res.send(o);
            }
        });

The following are the functions used

function paysignjs(appid, nonceStr, package, signType, timeStamp) {
    var ret = {
        appId: appid,
        nonceStr: nonceStr,
        package: package,
        signType: signType,
        timeStamp: timeStamp
    };
    var string = raw1(ret);
    string = string + '&key='+key;
    console.log(string);
    var crypto = require('crypto');
    return crypto.createHash('md5').update(string, 'utf8').digest('hex');
};

function raw1(args) {
    var keys = Object.keys(args);
    keys = keys.sort()
    var newArgs = {};
    keys.forEach(function(key) {
        newArgs[key] = args[key];
    });

    var string = '';
    for(var k in newArgs) {
        string += '&' + k + '=' + newArgs[k];
    }
    string = string.substr(1);
    return string;
};

function paysignjsapi(appid, attach, body, mch_id, nonce_str, notify_url, openid, out_trade_no, spbill_create_ip, total_fee, trade_type) {
    var ret = {
        appid: appid,
        attach: attach,
        body: body,
        mch_id: mch_id,
        nonce_str: nonce_str,
        notify_url: notify_url,
        openid: openid,
        out_trade_no: out_trade_no,
        spbill_create_ip: spbill_create_ip,
        total_fee: total_fee,
        trade_type: trade_type
    };
    var string = raw(ret);
    string = string + '&key='+key;
    var crypto = require('crypto');
    return crypto.createHash('md5').update(string, 'utf8').digest('hex');
};

function raw(args) {
    var keys = Object.keys(args);
    keys = keys.sort()
    var newArgs = {};
    keys.forEach(function(key) {
        newArgs[key.toLowerCase()] = args[key];
    });

    var string = '';
    for(var k in newArgs) {
        string += '&' + k + '=' + newArgs[k];
    }
    string = string.substr(1);
    return string;
};

function getXMLNodeValue(node_name, xml) {
    var tmp = xml.split("");
    var _tmp = tmp[1].split("" + node_name + ">");
    return _tmp[0];
}

This is a simple 3-step, small program The WeChat payment function has been connected. Below is the test payment rendering

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