If you follow our UserVoice forums, you might know that my latest directive, by popular vote, is to add some kind of collaboration to Mockingbird. Though I haven't really decided on how this is going to look, I couldn't help but check out the variety of real-time-push-comet-right-here-right-now-web frameworks. Since I knew nothing (and now know next to nothing) about what's out there, the first step was, well, to see what's out there. I ended up deciding to play around with Node.js + WebSockets (specifically, using Socket.IO - a nifty little framework on top of Node.js that will use WebSockets when possible and fall back to other Comet methods otherwise).
Instead of making the usual sample chat client, I decided to try to make a very simple collaborative drawing application by integrating Socket.IO with Cappuccino so that I can also try to play around with various ways to synchronize user data (see my Hacker News thread about it). I haven't actually put in any kind of sophisticated data synchronization yet, but the code for what I do have so far is here: http://github.com/saikat/drawtogether.
And here it is in action:
Check out the README at the Github repo to get it up and running. The code itself is fairly simple. All the backend work is in server.js, and in there, the actual interesting parts that are doing anything other than serving static files start with the line "var listener = io.listen...". On the client-side, I made a very simple Objective-J class that wraps the Socket.IO client called SCSocket (located in client/SCSocket.j). It's up to you to simply set a delegate on this class and implement any of four methods (see setDelegate: on SCSocket) to handle notifications from the backend. To send notifications to the Node server, simple call [[SCSocket sharedSocket] sendMessage:].
