Saturday, November 28, 2015

VerySillyMUD: Continuous Integration

This post is part of my "VerySillyMUD" series, chronicling an attempt to refactor an old MUD into working condition[1].


In our last episode, we got an autotools-driven build set up, which gets us going along the path towards being able to use a continuous integration tool like Travis CI. In this episode, we'll see if we can get it the rest of the way there. I'll be referencing the getting started guide, the custom build instructions, and the C project instructions.


It seems like the easiest way to proceed is to try to just use the default C build, which I expect not to work, but then to massage it into shape by looking at the build errors. It seems like this minimal .travis.yml is a good starting point:




As an editorial comment, the autotools toolchain uses "make check" to run tests, but Travis CI expects you to have autotools and that the default way to run tests is..."make test". I kind of wonder how this happened; my suspicion is that most projects use make test (and so that's what Travis CI assumes) but that GNU autotools defined an opinionated standard of make check that ignored existing practice.


Anyway, back to the build. As expected, this failed because there wasn't a configure script to run! This is interesting--I had not checked in any of the files generated by autoconf or automake under the general principle of "don't check in files that get generated". Ok, we should be able to just run autoreconf to get those going:




This one fails too, with the following error from autoreconf:




Hmm, very mysterious. This seems to be due to missing the AC_CHECK_HEADER_STDBOOL macro, and at least on this mailing list post, it was suggested it could be removed, so let's try that.


Ok, that build got further, and in fact built the main executable, which is great; we just failed when trying to find the Criterion header files. Since we haven't done anything to provide that dependency, this isn't surprising. I also notice that there are a lot more compiler warnings being generated now (this would appear to be based on having a different compiler, gcc vs. clang). Now we just need to decide how to provide this library dependency. The build container is an Ubuntu system, which means it uses apt-get for its package management, but there doesn't seem to be a .deb package for it provided. The options would seem to be:

  • vendor the source code for it into our repository
  • figure out how to build a .deb for it and host it somewhere we can install it via apt-get
  • download a Linux binary distribution of Criterion
  • download the source code on the fly and build it locally

I'm not crazy about vendoring, as that makes it harder to get updates from the upstream project; I'm not crazy about the binary download either, as that may or may not work in a particular environment. My preference would be to build a .deb, although I haven't done that before. I assume it would be similar to building RPMs, which I have done. Downloading and building from source is perhaps a good initial method, as I know I could get that working quickly (I have built the Criterion library from source before). If I ever get tired of waiting for it, I can always revisit and do the .deb.


According to the Travis CI docs, the usual way to install dependencies is to customize the install step with a shell script. We'll try this one to start, based on the instructions for installing Criterion from source:




Ok, this does pretty good as far as starting some of the compilation process, but it still fails with this error:




Hmm, seems to be looking for some copyright information; we'll try copying Criterion's LICENSE file into the debian.copyright file it seems to be looking for. Ok, that build succeeded in building and installing the library, and in fact, the later ./configure found it, but wasn't able to load the shared library libcriterion.so. We need to add an invocation of ldconfig after installing the library, I think. Wow, that did it! We have a passing build!


Let's record our success by linking to the build status from README.md so that people visiting the repo on GitHub know we have our act together!


Now, while debugging this build process, I got several notices that the project was running on Travis CI's legacy infrastructure instead of their newer container-based one, which purports to have faster build start times and more resources, according to their migration guide. It seems like for us the main restriction is not being able to use sudo; we use this in exactly three places at the moment:

  1. to install the check package via apt-get
  2. to run make install after building the Criterion library
  3. to run ldconfig after installing the Criterion library

It seems like there are built-in ways to install standard packages via apt, so then the question is whether we can directly compile and link against the Criterion library from the subdirectory where we downloaded and built it; if we can then we don't need sudo for that either. Ok, it looks like we just need to find the include files in the right place, by adding an appropriate -I flag to CFLAGS and then to find the built shared library by pointing the LD_LIBRARY_PATH environment variable to the right place. Nope. Nope. Nope. Nope. Ok, this answer on StackOverflow suggests we need to pass arguments through to the linker via -W options in LDFLAGS. Still nope. Maybe if we pass the Criterion build directory to the compiler via -L and to the runtime linker via -R? Bingo!


Ok, now we just need to see if we can install the check submodule via the apt configuration directives in .travis.yml. That works, and here's the final working CI configuration:




It seems that by setting CFLAGS explicitly here, we "fixed" the compiler warnings; I suspect we need to come back around and add -Wall to CFLAGS and then fix all those warnings too. But that can wait for the next episode...



[1] SillyMUD was a derivative of DikuMUD, which was originally created by Sebastian Hammer, Michael Seifert, Hans Henrik Stærfeldt, Tom Madsen, and Katja Nyboe.

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