How to track the number of anonymous users server-side in Meteor?

Question

I'm writing a data-sensitive application in Meteor, and am trying to limit the client access to as much information as possible. Therefore, I want to implement server side a way of counting the number of logged-in, and anonymous, users.

I have tried a variety of methods. The first was as outlined in this question Server cleanup after a client disconnects, which suggests hooking into:

this.session.socket.on("close")

However when I did, and tried to change a collection, it threw a "Meteor code must always run within a Fiber" error. I assume this problem is because once the socket is closed, that Fiber is killed, and so accessing the database is impossible. The OP pointed to this "Meteor code must always run within a Fiber" when calling Collection.insert on server as a possible solution, but I wasn't sure if that's the best method, based on the comments to the answer.

I then tried to autorun on the variable:

Meteor.default_server.stream_server.all_sockets().length

but the autorun never seemed to be called, so I'm assuming that variable is not a reactive context, and I wasn't sure how to make it one.

The last idea was to do a keepalive style thing, but that seems to completely go against the grain of the Meteor philosophy, and I think I'll only use as an absolute last resort.

I did a console.log of the functions on this.session.socket, and the only other function possible was .on("data"), but this isn't called when the socket is closed.

I'm at a bit of a loss here, so any help would be great, Thanks.

Answer 1

For the sake of completeness, it's probably best to combine the two answers above. In other words, do the following:

• Keep the online status in Meteor.users, as opposed to a separate collection, as in https://github.com/erundook/meteor-profile-online
• Keep track of disconnections via callback, instead of a heartbeat, as in https://github.com/murilopolese/howmanypeoplearelooking

This would probably be the canonical way to implement this in Meteor. I've created this as a smart package that you can install with Meteorite: https://github.com/mizzao/meteor-user-status

Answer 2

Thanks to Sorhus' tip, I managed to solve this. His answer contains a heartbeat, which I was keen to avoid. However, it contained the trick of using Meteor's "bindEnvironment". This allows access to a collection, which otherwise would not be accessible.

Meteor.publish("whatever", function() {
  userId = this.userId;
  if(userId) Stats.update({}, {$addToSet: {users: userId}});
  else Stats.update({}, {$inc: {users_anon: 1}});

  // This is required, because otherwise each time the publish function is called,
  // the events re-bind and the counts will start becoming ridiculous as the functions
  // are called multiple times!
  if(this.session.socket._events.data.length === 1) {

    this.session.socket.on("data", Meteor.bindEnvironment(function(data) {
      var method = JSON.parse(data).method;

      // If a user is logging in, dec anon. Don't need to add user to set,
      // because when a user logs in, they are re-subscribed to the collection,
      // so the publish function will be called again.
      // Similarly, if they logout, they re-subscribe, and so the anon count
      // will be handled when the publish function is called again - need only
      // to take out the user ID from the users array.
      if(method === 'login')
        Stats.update({}, {$inc: {users_anon: -1}});

      // If a user is logging out, remove from set
      else if(method === 'logout')
        Stats.update({}, {$pull: {users: userId}});

    }, function(e) {
      console.log(e);
    }));

    this.session.socket.on("close", Meteor.bindEnvironment(function() {
      if(userId === null || userId === undefined) 
        Stats.update({}, {$inc: {users_anon: -1}});
      else
        Stats.update({}, {$pull: {users: userId}});
    }, function(e) {
      console.log("close error", e);
    }));
  }
}

Answer 3

Checkout the GitHub project howmanypeoplearelooking

Meteor application test to show how many users are online right now.