Contributing to open source - a success story and advice for newbies
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:date: 2011-06-23 21:45
:tags: Subversion, OpenSource
:slug: contributing-to-open-source-a-success-story-and-advice-for-newbies
:author: Brian Neal

Recently, my team at work found a `bug in Subversion`_, I submitted a patch, and it
was accepted!  This was very exciting for me so I thought I would share this
story in the hopes of inspiring others to contribute to open source projects.
It may not be as hard as you might think!

The Bug
=======

We use Subversion_ at work for revision control. My colleague and I were trying
to merge a branch back to trunk when we ran into some strange behavior. We make
use of Subversion properties, which allow you to attach arbitrary metadata to
files and directories. Our project has to deliver our source code and
documentation to the customer in a required directory format (can you guess who
our customer is?). However not all files need to be sent to the customer. To
solve this problem we use a simple "yes/no" delivery property on each file to
control whether it is delivered or not. Before making a delivery, a script is
run that prunes out the files that have the delivery flag set to "no". 

When our merge was completed, many files were marked with having merge conflicts
on the delivery property. Looking through the logs it was discovered that after
we had made our branch, someone had changed the delivery property on some files
to "yes" on the trunk. Someone else had also changed the delivery property
independently to "yes" on the branch. When we attempted to merge the branch back
to trunk, we were getting merge conflicts, even though we were trying to change
the delivery property value to "yes" on both the trunk and branch. Why was this
a conflict? This didn't seem quite right.

I signed up for the Subversion user's mailing list and made a short post
summarizing our issue. I later learned that it is proper etiquette to attach a
bash script that can demonstrate the problem. Despite this, a Subversion developer
took interest in my post and created a test script in an attempt to reproduce our
issue. At first it looked like he could not reproduce the problem. However another
helpful user pointed out a bug in his script. Once this was fixed, the developer 
declared our problem a genuine bug and created a ticket for it in the issue tracker.

The Patch
=========

Impressed by all of this, I thanked him for his efforts and tentatively asked if
I could help. The developer told me which file and function he thought the
problem might be in. I downloaded the Subversion source and began looking at the
code. I was fairly impressed with the code quality, so I decided I would try to
create a patch for the bug over the weekend. We really wanted that bug fixed,
and I was genuinely curious to see if I would be able to figure something out.
It would be an interesting challenge and a test of my novice open source skills.

When the weekend came I began a more thorough examination of the Subversion
website. The Subversion team has done a great job in providing documentation on
their development process. This includes a contributing guide and patch
submittal process. I also discovered they had recently added a makefile that
downloaded the Subversion source code and the source for all of Subversion's
dependencies. The makefile then builds everything with debug turned on. Wow! It
took me a few tries to get this working, but the problems were because I did not
have all the development tools installed on my Ubuntu box.  Once this was
sorted, everything went smoothly, and in a matter of minutes I had a Subversion
executable I could run under the gdb debugger. Nice!

I studied the code for about an hour, peeking and poking at a few things in the
debugger. I used the script the developer wrote to recreate the problem. I
wasn't quite sure what I was doing, as I was brand new to this code base. But
the code was clearly written and commented well. My goal was to get a patch that
was in the 80-100% complete range. I wanted to do enough work that a core
developer would be able to see what I was doing and either commit it outright or
easily fill in the parts that I missed. After a while I thought I had a solution
and generated a patch. I sent it to the Subversion developer's mailing list as
per the contributing guide.

The Wait
========

Next I began probably the worst part for a contributor. I had to wait and see if
I got any feedback. On some open source projects a patch may languish for months.
It all depends on the number of developers and how busy they are. My chances
didn't look good as the developers were in the initial stages of getting a
beta version of 1.7 out the door. It was also not clear to me who "owned" the
issue tracker. On some projects, the issue tracker is wide open to the
community. Was I supposed to update the ticket? I wasn't quite sure, and the
contributing guide was silent on this issue. I eventually concluded I was not;
it looked like only committers were using the tracker. Patches were being
discussed on the mailing list instead of in the tracker. This is a bit different
than some projects I am familiar with.

I didn't have to wait long. After a few days, the original developer who
confirmed my bug took interest again. He looked at my patch, and thought I had
missed something. He suggested a change and asked for my opinion. I looked at
the code again; it seemed like a good change and I told him I agreed. I also
warned him I was brand new to the code, and to take my opinion with a grain a
salt. After running my change against the tests, he then committed my patch!
One small victory for open source!

Final Thoughts
==============

So what went right here? I have to hand it to the Subversion team. They have
been in business a long time, and they have excellent documentation for people
who want to contribute. The makefile they created that sets up a complete
development environment most definitely tipped the scale for me and enabled me
to create my patch. Without that I'm not sure I would have had the time or
patience to get all that unfamiliar source code built. The Subversion team has
really worked hard at lowering the barrier for new contributors.

My advice to people who want to contribute to open source but aren't quite sure
how to go about doing it:

- Spend some time reading the documentation. This includes any FAQ's and
  contributor guides (if any).
- Monitor the user and developer mailing lists to get a feel for how the
  community operates. Each project has different customs and traditions.
- You may also wish to hang out on the project's IRC channel for the same
  reason.
- When writing on the mailing lists, be extremely concise and polite.
  You don't want to waste anyone's time, and you don't want to
  be seen as someone who thinks they are entitled to a fix. Just remember you
  are the new guy. You can't just barge in and make demands.
- Ask how you can help. Nothing makes a developer happier when someone asks how
  they can help. Remember, most of the people in the community are volunteers.
- Open source can sometimes be "noisy". There will be people who
  won't quite understand your issue and may hurriedly suggest an incorrect solution or give
  incomplete advice. Study their responses and be polite. You may also wish to resist the temptation
  to reply right away. This is especially hard when you are new and you don't
  know who the "real" developers are. However you should assume everyone is trying to
  help.
- Finally, be patient. Again, most folks are volunteers. They have real jobs,
  families and lives. The project may also be preoccupied with other tasks, like
  getting a beta out the door. Now may not be a good time for a brand new
  feature, or your bug may not be considered a show stopper to the majority of
  the community.

A big thank-you to Stefan Sperling from the Subversion team who shepherded my
bug report and patch through their process. 

I hope this story encourages you to contribute to open source software!

.. _bug in Subversion: http://subversion.tigris.org/issues/show_bug.cgi?id=3919
.. _Subversion: http://subversion.apache.org/