Neutronium update – Dec 12, 2011

I’ve continued working on Neutronium daily, but for the past week or so I’ve been focusing on refactoring some of the code I wrote earlier to facilitate actual new features. The biggest change has been putting most of the room-related logic in the STM monad, instead of having parts of it in STM and other parts using IO-based synchronization, particularly MVars. By putting all if it in STM, I avoid having the room directory MVar acting like a global mutual exclusion lock, and let room-related operations behave atomically, which could save some headaches down the time. I’ve also cleaned up various other bits of the code to simplify things and make things more easily testable, but nothing that warrants much discussion here.

Now I’m working on fixing how joining and leaving rooms work. Before, a member of a room was identified by the session identifier of the user’s session, but that’s very problematic. First, it means that opening the same room up in multiple tabs would result in confusing behavior, since the server wouldn’t have any way of distinguishing each tab. Second, it makes distinguishing one member from another difficult on the client side, since session IDs are sensitive information and can’t be shared, lest session hijacking result.

My solution is to assign yet another unique identifier to represent each member joining a room. Since member IDs aren’t sensitive, they can be freely communicated to everyone else in the room. Since it’s decoupled from the session cookie, each tab can be given its own member ID, should someone open the same room up multiple times for some reason. On the server side, each member ID is still bound to a particular session ID, preventing one member from trying to impersonate someone else; if the member ID sent in the request doesn’t match the session ID the request is made under, the request is ignored.

At least, that’s how it will work when I’m finished making those changes.

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