Catalyst and elementalClinic

Part of my job involves development on elementalClinic (emC). emC is a few years old, and has undergone a lot of architectural change; it started as a collection of CGI scripts, grew into a collection of scripts, templates, and modules, and made the transition to a mod_perl application in late 2006.

Now, mod_perl is fine for writing Apache modules; but I have a web application, and I don't need most of the power that mod_perl exposes. Being tied so tightly to Apache has caused some problems and inconveniences along the way. For example, any tool to deal with Perl module dependencies becomes much more complicated when one of them is mod_perl, and running tests through Apache has made certain kinds of test failures much more difficult to debug.

We'd talked internally about moving emC to Catalyst at some unspecified point in the future. Catalyst is mature, well-tested, and very powerful, and while I don't love everything about it, there are a lot of people working on it (besides, I have a commit bit, so if I don't like how things work it's partly my own fault anyway). I've been using Catalyst for another project recently after being away from it for a while, and decided that maybe it wouldn't take as much effort to start moving emC over as I thought.

So, on Thursday, I told Randall that I was going to take a few hours from the next couple of weeks, and see how far I got in just replacing the dispatch mechanism from emC -- converting the controllers and the session and so on is something we can do incrementally, but getting Catalyst in "underneath" everything is a big first step.

It turns out that the answer to "how far can I get" is "all tests passing"; with just over 5 hours' work, Catalyst is now sitting between the outside world and emC's controllers. The immediate benefit is that emC can run on any of Catalyst's engines: mod_perl, standalone, prefork, FastCGI, etc. The long-term benefits are no more maintenance of hand-rolled dispatching code and the ability to incrementally replace even more hand-rolled code with modules from CPAN.

A huge factor in this is that Matt Trout had already written Catalyst::Controller::WrapCGI, a controller for running existing CGI scripts seamlessly inside a Catalyst application. A shout out to Rafael Kitover, too, for helping me find and fix a problem with it under mod_perl, and then releasing a new version with my patch included.

My first target for Catalyzing emC's code is probably going to be the functional tests, which use WWW::Mechanize and currently each have to spin up their own Apache process -- Catalyst's test module can fake up HTTP requests in-process, which is really nice for speed during the test-edit-test cycle, and it already has a WWW::Mechanize-based wrapper, so I shouldn't need to change too much code to make use of it.

This morning I merged the Catalyst branch into emC trunk. I'm excited about how easy it was to slip Catalyst in underneath the existing emC code, and I'm looking forward to the changes it'll make possible in the future.