rails: how to detect other clients browsing the same url

Question

What want to be accomplished is: I want to "synchronize web browsers". my site has a "wait URL" where when browser gets there it will be kept waiting till another browser also go there and then both will be presented with a quiz-like game.

Right now the wait url will call each second to Rails to check if other player came to the game. How can in the Rails framework detect a different client connecting to the same URL?

As the controller is recreated per request looks like is not the place, not the view for sure and storing this in the model looks really clumsy.

Also, after the pairing I need to check and compare every answer of the paired users so somehow that information must be retained

Answer 1

I'm not a rails expert, but since all the state resides in your database that would be the place to keep this information.

You could keep a "waiting users" table, and in the "wait URL" view check if the user is already in the table. If not, add him to the table. Then, check if there is another user waiting (maybe there's more than one?) and if so, match them up and delete them from the table.

Another improvement would be to keep a timestamp for each user in the "waiting users" table, which gets updated in the view - this would serve as a keep-alive that will enable you to detect users that left the "wait URL" page or closed the browser.

Answer 2

Assuming these users are not registered with the site so don't have some kind of user id you could store I would suggest using the session. It is a per user data store. By default the session is stored in an encrypted cookie on the users machine. However you can use ActiveRecord as the session store and could maybe query that table directly?

Store the URL in the session and do a search for it at a later time. You can normally only access the current users session using the Rails 'session' hash but maybe (untested) if you created a model called Session (or maybe something more specific like 'WaitingGamers') which used the sessions table you could lookup the information you need.

I would guess when using ActiveRecord as the session store the session data is stored as a serialised hash. Use Marshall to turn it back in to a regular hash and find the data you stored in there.

Answer 3

What you're trying to do is share information between users. So the database or memcached are the most sensible.

Simplest: I'd create an ActiveRecord object, perhaps called Quiz, instances of which people join by virtue of going to a URL, e.g using default routes:

http://yoursite.com/quizes/join/3434

You'd need an ajax poller poller to notify the others; use periodically_call_remote for this -- you could use render :nothing => true by default and render something else if there was an error to keep it efficient. You can also use the frequency method as a basis to determine whether people leave the quiz as well (e.g. if frequency is 1s, then assume someone has left if they didn't ping after 5-10s).