MEAN stack: associating a socket with a user

mean-stack

I’m using the MEAN stack for an application I’m working on. The project was seeded using the Angular fullstack yeoman generator (https://github.com/DaftMonk/generator-angular-fullstack/).

Out of the box the project has support for websockets (using socket.io), and users (using passportjs). However, sockets on the server side in express running on node are not tied to users, out of the box.

For several reasons the application likely needs to know what user a socket belongs to. For example, if there’s a change made to a model that needs to be emitted, you may need to emit it to only users with a certain role.

To get around this, I made a bunch of modifications which I’ll detail below. Essentially, the user object will get saved within the socket object. So when a socket is being processed, say through a model level trigger (i.e. “save” or “delete”) using mongoose for example, the user object will be in the socket and can be used in whatever processing logic.

The MEAN project seeded from the angular fullstack generator uses a token generated through jwt, which is stored in a cookie, to authenticate a user. So when a user login occurs, an event can be emitted with the jwt token over the socket to register the user with the socket. Furthermore, in your socketio.on(‘connection’,…) function in express, you can read the cookie to get the jwt token, then get the user and put it in the socket. This is essential so that if a user is already logged in, and returns to your web application (or opens a new tab to your application) and a new websocket is created, the cookie can be used to associate the socket with the user, since a new login event will not be emitted at that point.

First, let’s define a function that can take a token either directly as a parameter, or read it from the cookie in a socket, and get the user. This same function can be called from a login emit event with a jwt token as the payload over the socket, or from socketio.on(‘connection’,…).

var auth = require('../auth/auth.service');
function setupUserInSocket(socket, inputToken)
{
  var tokenToCheck = inputToken;
  if(!tokenToCheck && socket && socket.handshake && socket.handshake.headers && socket.handshake.headers.cookie)
  {
    socket.handshake.headers.cookie.split(';').forEach(function(x) {
      var arr = x.split('=');
      if(arr[0] && arr[0].trim()=='token') {
        tokenToCheck = arr[1];
      }
    });
  }
  if(tokenToCheck)
  {
    auth.getUserFromToken(tokenToCheck, function (err, user) {
      if(user) {
        console.info('[%s] socket belongs to %s (%s)', socket.address, user.email, user._id);
        socket.user = user;
      }
    });
  }
}

Note that the cookie is in socket.handshake.headers.cookie. Also note that I call auth.getUserFromToken, which is another function I created that decrypts the user ID from the jwt token, queries the user from the model, and returns it. The function looks like this:

var User = require('../api/user/user.model');
var async = require('async');
var config = require('../config/environment');
function getUserFromToken(token, next)
{
  async.waterfall
  (
    [
      function(callback)
      {
        jwt.verify(token, config.secrets.session, function(err, decoded) {
          callback(err, decoded);
        });
      },
      function(decoded, callback)
      {
        if(!decoded || !decoded._id)
          callback(null, null);
        else {
          User.findById(decoded._id, function (err, user) {
            callback(null, user);
          });
        }
      },
    ],
    function(err, user)
    {
      next(err, user);
    }
  );
}

Next, let’s use socketio.on(‘connection’,…) to call the function with the socket. If the jwt token is already in the cookies, meaning the user already logged in previously, the user will be associated with the socket:

socketio.on('connection', function (socket) {
  setupUserInSocket(socket);
  //...
});

And that’s it for that particular scenario! Next, let’s worry about when a user actually logs in. Within socketio.on(‘connection’, …) we can listen for login emits from the client over the socket like so:

socket.on("login", function(token,next) {
  setupUserInSocket(socket,token);
  next({data: "registered"});
});

And on the client side, we emit the login event over the socket when a successful login occurs. This can be done in a number of ways, but I decided to do it in login.controller.js. After Auth.login() is called, I call socket.login():

angular.module('classActApp')
  .controller('LoginCtrl', function ($scope, Auth, socket, ...) {
    //...
        Auth.login({
          email: $scope.user.email,
          password: $scope.user.password
        })
        .then( function() {
                  //...
                  socket.login();
//...

And in the client side socket.service.js, the login() function does the following:

angular.module('classActApp')
  .factory('socket', function(socketFactory, $location, CONSTANTS, Auth) {
return {
login: function () {
  socket.emit("login", Auth.getToken(), function(data) {
  });
},

Note that you also need to worry about logouts. If the user logs out from your web application, but sticks around on your web application, the socket for that session will remain associated to the user they were logged in as previously. This could be undesirable for several reasons. So in your express side of things (server side), you want to listen for logout events and clear out the user from the socket like so (note, this is added within socketio.on(‘connection’,…)):

socket.on("logout", function(next) {
  if(socket && socket.user) {
    console.info('[%s] socket being disassociated from %s (%s)', socket.address, socket.user.email, socket.user._id);
    socket.user = null;
  }
  next({data: "un-registered"});
});

And in your angular side of things (client side), when the user logs out, you want to emit a logout event over the socket. In the angular fullstack seeded project I’m using, this happens in navbar.controller.js which has the logout function.

angular.module('classActApp')
  .controller('NavbarCtrl', function ($scope, $location, socket, ...) {
    //...
    $scope.logout = function() {
      //...
            socket.logout();

And in socket.service.js:

angular.module('classActApp')
  .factory('socket', function(socketFactory, $location, CONSTANTS, Auth) {
    //...
    return {
      //...
      logout: function () {
        socket.emit("logout", function(data) {
        });
      },

And that’s it! Now all your sockets have the user they belong to (if any) associated to them (accessible from socket.user on the server side). And when emitting events from the server side from the socket, or when reading events emitted from the client side over the socket, we can now know the user the socket belongs to!

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