Sunday, November 10, 2013

Briefly, Custom Server Redux

So you already know I'm building a custom HTTP server for Deal. A question has arisen in my mind: how customized do I want it?

My initial assumption was that I'd just make it the usual general purpose HTTP server, with a few pieces focused on my end goal, but now that I'm waist deep in the guts of this thing, it occurs that I could take it further if I wanted to. For my current purposes, a relatively small subset of HTTP would do just fine. Here are the points I've noticed:

  • Deal never runs into the situation where both a GET and a POST parameter have the same name. As a result, I can do the Hunchentoot-standard thing and mangle parameters so that get-params and post-params are actually kept in the same associative structure. That simplifies the structure of both request objects and of handler functions, at the cost of differentiating between parameter types.
  • Because there's never an ambiguity between GET and POST parameters, I don't even really need to differentiate between GET and POST requests. That'll simplify the class tree of incoming requests. Specifically, it'll cap its depth at 1.
  • There are only two handlers that allow session-less requests, the rest require that the requester have a session[1], so what I could do is just make each request start up a session if a valid session token isn't passed in. That'll occasionally burn a few milliseconds of extra work[2], but it'll remove the need to assert session presence at the application level.
  • Because Deal is already targeting recent browsers[3], there's no need to support any older version of HTTP.
  • Finally, because there's only one handler that's going to need to handle extended connections, and the rest will always return immediately, I can more or less ignore request headers. In particular, I never care about Connection[4], Accept[5] or Cache-Control[6].

Acting on each of these assumptions is going to narrow the usefulness of the server, but also significantly simplify it. The optimum is eluding me, though I suspect it might be "as simple as possible" given my end goal for this particular project. Interestingly, even if I decide to do the simple thing for each of the choices outlined above, the end result will still probably be a useful general-purpose game server.

The only really funny part is that, now that I've thought it through, implementing this system as a websocket server[7] seems like it would yield an even simpler architecture. I'll save that one for later though. Step one: simple SSE+session based engine, make sure it works, then rip out its guts again and see what the other way looks like.


1 - [back] - And most of those require that the session be associated with a particular, already-instantiated game table, but optimizing for that seems like it would be going too far.

2 - [back] - When someone who just wants to watch rather than play first checks out a table.

3 - [back] - We're using quite a few features of HTML5 to make the whole thing playable.

4 - [back] - That one that I mentioned will be assumed keep-alive, while the rest assume the reverse.

5 - [back] - You're expecting text/html on the main request, text/event-stream on the subscription and application/json on the rest. If you can't handle those, you won't be able to play in any case.

6 - [back] - Everything other than the static file handlers always re-generates content; the static handlers don't need to change unless the files themselves have actually changed.

7 - [back] - Which multiple people have already recommended to me, so I'm not taking credit for that particular insight.

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