Debsources got swag and continous integration

Posted: May 07, 2015
Categories: debian, debsources, python

Debsources (http://sources.debian.net) is still under active development. We recently had a Gnome Outreachy intern, Jingjie Jiang, and we're about to work with 2 GSoC students, Clément Schreiner and Orestis Ioannou.

I will present here the GitHub mirror we've set up, in order to allow external pull requests to be submitted, and to use the continous integration service provided by Travis-CI.

GitHub and Travis-CI

Debsources' source code is hosted on Debian's git servers, and from there is mirrored to GitHub. Every time a commit is pushed (to master or other branches) or a pull request is open, the test suite will be automatically run on Travis-CI, and the result (tests pass or don't) is displayed on GitHub. This allows us to quickly filter external contributions (when they are submitted on GitHub), and be sure everything works with our setup, before reviewing work.

Travis-CI runs the tests on OpenVZ containers. The complete infrastructure was a bit challenging to setup, but as we now have a Docker recipe to quicly begin to hack on Debsources, most of the work could be done using the Dockerfile instructions.

In average, a run on Travis-CI (which includes git cloning the code and test data, setup the server, and run the tests suite) takes 7 minutes, which is an ok amount of time to wait for before submitting a pull request, in my opinion.

Bugs discovered in the process

Setting up this continuous integration infrastructure made me discover a few bugs.

Python magic does black magic

Debsources runs fine on Debian (not surprisingly), but I got tricked by black magic when I tried to run it on Ubuntu (which is the OS run in Travis-CI's containers).

We use the magic library to guess the type of files we're dealing with, for instance when we need to decide between rendering a file (for text files) or downloading it (for binary files).

Here comes the tricky part: the Python bindings for libmagic are not the same in Debian and Pypi. Debsources uses Debian package python-magic, which is not in Ubuntu 12.04. Moreover, there's no Python egg for it on Pypi, which has however another package (called magic) which provides a different API.

I solved this with a dirty hack, using the fact python-magic lies in a single file:

mkdir /tmp/python-magic && wget https://raw.githubusercontent.com/file/file/master/python/magic.py -O /tmp/python-magic/magic.py && export PYTHONPATH=/tmp/python-magic/:$PYTHONPATH

It simply downloads the library, saves it in a temporary folder and includes it in the Python path. Let's see for how long it works before everything breaks!

Edit: Thanks to Clément Schreiner, python-magic is now installed by cloning it's Github repository and pip install'ing into it.

Size of a directory

One test in the suite was ensuring the information returned by ls -l on a directory and stored in the DB was the right information. Inode metadata was tested, such as name, permissions, type, or size.

Interestingly enough, the size of a directory was tested, and expected to be 4096 bytes. The size of a directory actually depends on the filesystem in use, and on the number of files this directory contains. We often see 4096 because it's the size of a not-too-big directory on ext4.

Travis-CI doesn't use ext4:

$ df -T
Filesystem            Type     1K-blocks      Used Available Use%
Mounted on
/vz/private/209140041 simfs    125829120 103460612  22368508  83% /
none                  devtmpfs   1572864         8   1572856   1% /dev
none                  tmpfs       314576        56    314520   1% /run
none                  tmpfs         5120         4      5116   1%
/run/lock
none                  tmpfs      1572864         0   1572864   0%
/run/shm
/dev/null             tmpfs       786432    171584    614848  22%
/var/ramfs

Simfs is a container filesystem for OpenVZ, on which directories have different sizes than on ext4:

$ ls -al /
total 0
drwxr-xr-x 23 root     root      480 Feb  4 18:08 .
drwxr-xr-x 23 root     root      480 Feb  4 18:08 ..
drwxr-xr-x  2 root     root     2480 Feb  4 18:20 bin
drwxr-xr-x  2 root     root       40 Apr 19  2012 boot
drwxr-xr-x  5 root     root      660 Apr 30 13:56 dev
drwxr-xr-x 99 root     root     3560 Apr 30 13:56 etc
-rw-r--r--  1 root     root        0 Feb  4 17:56 fastboot
drwxr-xr-x  3 root     root       80 Feb  4 17:57 home
[...]

Directory sizes are not even powers of 2.

Hence I changed the test to not check directory sizes. Hopefully this will help to make Debsources work on more filesystems!

An empty file is hiding

Last but not least, because this bug is still open in the wild. A file, which appears to be empty, is not taken into account by Debsources' updater. This file is sources/non-free/m/make-doc-non-dfsg/4.0-2/.pc/applied-patches. It is present in the filesystem in the container, is not the only empty file over there, but still doesn't appear in the database, and make fail the test which counts files.

The test has been commented out (booooooh), so that we still can use Travis-CI's platform for our GSoC students, before it's fixed.

Conclusion

Making Debsources run automatically on a different platform as the one we usually use permitted us to spot bugs, write dirty hacks, and expand the filesystems it's supposed to run on.

Now, let's hope the continuous integration will help our GSoC students, and let's wish them good luck!