Friday, June 5, 2009

Week 2: Ghosts, Deeper Bugs, First Feature...

Another week gone by. This week I learned two important, though obvious, lessons. The first lesson is: if a test case fails, do not touch the test case. The second lesson is: if a test case fails, do not touch the test case. At the beginning of the week I thought there were still problems with requests using chunked transfer-encoding with trailing headers. I was able to create a failing test case and proceeded to launch another (lengthy!) bug-hunt expedition. But by the time I found a fix, I'd modified the test case ever so slightly - where I should have created other, new cases instead. When I reported my "fix" to Sebastian Riedel, the first thing he did was try my test case, and promptly tell me that it was passing on his latest master! He prefaced this news by saying "You're not going to like this..." Indeed. Had I spent hours chasing and fixing a non-existent bug? I spent some time thinking I'd gone mad, before realizing what I'd thought was a trivial change in the test-case actually prevented the bug from being triggered. Once I realized this, Sebastian found a fix that was much more elegant that what I'd proposed. Tough start to the week, but hey, that's how you learn, right? I hope so...

I was able to redeem myself by tracking down and fixing a very difficult transient bug having to do with requests expecting a 100-Continue followed by other pipelined requests. Isolating the problem took two full days, and Sebastian commented over IRC that it doesn't get much more complicated than this, protocol-wise. Anyway, so my tally for the week is:
  • always reach trailing_headers state for chunked messages
    (not my fix, but my catch);
  • problem with duplicate start line on 100-continued request with a
    following pipeline;
  • 5-second delay problem when pipelining two requests, the second
    of which includes an Expect 100-Continue;
  • allow applications to override the default continue handler.
The last of these is my first feature(tte). It has allowed me to start testing what happens client-side when a server doesn't reply with a 100 Continue to a client that requests one. This has in turn led me to start thinking about how I will implement Mojo::UserAgent... I've also discovered some issues with the deamon tests on my version of Ubuntu which I've not been able to hunt down just yet. All in all, a more intense week than the first...

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