[Git/Gerrit] Git and Gerrit server hooks

What are git/gerrit hooks?

Hook is user’s custom action fired, when git-specific event occurred. Git offers a set of hooks available both on client and server side. In this post, we will focus on server-side hooks for git and gerrit. Unfortunately, gerrit does not accept built-in git hooks. Luckily, it offers reach documentation with description of custom gerrit events.

Git server hooks

Git offers three types of hooks on server side:

• pre-receive: operations prepared before actual push is made.

• post-receive: operations prepared after actual push is made.

• update: similar to pre-receive. The main difference is way of hook execution. While pre-receive is executed just once (no matter how many branches you want push to), update is executed per branch.

As an example, we are going to create post-receive hook. The role of our hook is to notify jenkins server about new push. We retrieve branch name and use CURL to pass url with specific parameters.

First of all, we go to hooks directory in our git server repository. If there’s file called post-receive.sample we change it’s name to post-receive and set proper access mode, if needed:

sudo rename post-receive.sample post-receive
sudo chmod a+rx post-receive

Let’s edit it. Type sudo nano post-receive in terminal (fell free to use another text editor), and add following lines:

# Trigger jenkins with info about new git change
while read oldrev newrev refname
do
    	branch=$(git rev-parse --symbolic --abbrev-ref $refname)
    	curl http://192.168.1.109:8002/git/notifyCommit?url=git@192.168.1.109:repo.git&branches=$branch
done

After save, we can test our hook in action. On our client machine, I’ve changed one file in my repository:

git status
git add --all
git commit -m “testing post-receive hook”
git push -u origin master

After push operation, I’m checking build queue on jenkins

It works! Right after push, new build was triggered.

Gerrit server hooks

Gerrit offers a range of hooks, connected with code review server operations, like: change merged, comment added, or change abandoned. As an example we will take a look at change-merged and ref-updated hooks.

• change-merged is used in case of submitting path set into git repository.
• ref-updated is executed in case of any push changes to git repository (if git push is used directly, instead of git review).

First of all, we have to find place where hooks are stored. According to gerrit documentation, it’s in $site_path/hooks dir. Of course, we can store it in another location. To do so, we edit gerrit config file. In my case, it’s /home/mody/gerrit/etc/gerrit.config. At the end of the file, I add:

[hooks]
    	path = /var/git/repo.git/hooks

Let’s go to our hooks dir and create change-merged and ref-updates files.

• ref-updated

ref-updated --oldrev <old rev> --newrev <new rev> --refname <ref name> --project <project name> --submitter <submitter>

#!/bin/sh
curl http://192.168.1.109:8002/git/notifyCommit?url=git@192.168.1.109:repo.git&branch=$3

• change-merged

change-merged --change <change id> --change-url <change url> --project <project name> --branch <branch> --submitter <submitter> --commit <sha1>

#!/bin/sh	
curl http://192.168.1.109:8002/git/notifyCommit?url=git@192.168.1.109:repo.git&branch=$4

The first snippet for each of files is gerrit documentation for specific hook. Second one is file content. In case of ref-updated, --refname variable is used ($3), in case of change-merged --branch variable is used ($4)

Remember to save file with correct access rights:

sudo chmod a+rx ref-updated
sudo chmod a+rx change-merged

After work is completed, I restart my gerrit server:

sudo ./gerrit.sh restart

Let’s test it. If no errors occurred, our gerrit will send notifications properly. Any errors will be collected in error_log file in <YOUR_GERRIT_HOME>/logs folder.