Gerrit at Eclipse Foundation have really long history. Initially only EGit and JGit projects could use this tool, but starting from February 2012 Gerrit become fist class citizen in Eclipse ecosystem. Every Eclipse Foundation's project can immediately start using its powerful code review capabilities. Capabilities that together with TDD and CI create safety net against bugs for software development. For quite long time Gerrit features set was pretty closed and adding new functionality required upstream code base changes. That means either you ended up in port and rebase nightmare or contributed your changes back to community... where they could not have been accepted because they solve your domain's problem not something that is vital for the community edition. Plugin support in Gerrit was initially introduced in version 2.5. Since then amount of available extension points substantially increased. In this presentation we will understand Gerrit plugins architecture. We will discuss extensions and plugins especially differences between them and which one to choose when. We will see how to combine everything together (including WEB UI) to get your first full blown Gerrit plugin.

1. Your own full blown
Gerrit plugin.
2014 Dariusz Łuksza
Dariusz Łuksza, CollabNet
dariusz@luksza.org
@dluksza

2. 2014 Dariusz Łuksza
Preconditions
● Basic concept of Dependeny Injection (or have
open mind to grasp it during presentation)
● POSIX compatibe operating system (Linux or
Mac... or Windows with cygwin, sshd is
required)
● Being familiar with JavaScript
● Maven

3. 2014 Dariusz Łuksza
How Gerrit and Jenkins Gerrit
Trigger plugin works?
Trigger buld
Push
Retrigger build
Post comments
Send email
developer

4. 2014 Dariusz Łuksza
What we will build?1
2
3
Plus maven configuration to build and
deploy plugin in running Gerrit instance.

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What it requires?
● REST endpoint – to schedule a build and
receive confirmation
● UI Action – part of Gerrit Web UI that will show
button on change screen and popups
● Capabilities – so that only members of given
groups can retrigger builds
● Two HTTP calls from Gerrit to CI server – this
is implementation detail, how we actually
retrigger build

6. Initialize project
2014 Dariusz Łuksza

7. 2014 Dariusz Łuksza
Add archetype catalog
Window → Preferences → Maven → Archetypes
First of all you need to add remote archetype
catalog to Eclipse... don't know why
repo1.maven.org is not on the default list.

8. 2014 Dariusz Łuksza
Create project from archetype
Ctrl + n → Maven → Maven Project → Next x2
Fill out those addional
archetype properties

9. 2014 Dariusz Łuksza
Default project structure
You can also provide
documentation for plugin ;)

10. Automated plugin
deployment
2014 Dariusz Łuksza

11. 2014 Dariusz Łuksza
How to intall plugin in gerrit?
● Copy jar file to $gerrit_home/plugins directory
– Works fine in local development environment but could
be not compatible with integration tests
or
● Use Gerrit ssh command to install it remotley
– Plugin jar file must be on server file system
– Use scp command to copy plugin jar file, then gerrit ssh
command to install it
– Requires additional setting in $gerrit_site/etc/gerrit.config:
[plugins]
allowRemoteAdmin = true

12. 2014 Dariusz Łuksza
How to deploy plugin from
command line?
$ scp username@gerrit.host /path/to/plugin/file.jar /tmp/
$ ssh -p 4918 gerrit_username@gerrit.host gerrit plugin
install /tmp/jar.file
First operation require SSHD running on the server
and system account.
Second, require account in Gerrit (this is different
then one used in first step) and membership in Gerrit
Administrators group*.
* or Administrate Server capability

13. 2014 Dariusz Łuksza
Deploy from Maven? Yes, we can!
Those lines goes on and on... On last
slide you will find link to repository
that contains this pom.xml file

14. 2014 Dariusz Łuksza
And missing Maven profile setting
systemUser name is used
in scp command
deployUser should be
member of Gerrit
Administrators group*.
Plus have SSH public
key in Gerrit of local
system user.
* or have Administrate Server capability

15. 2014 Dariusz Łuksza
And we are good to go!
Now you can simply type `mvn verify` to
deploy newest plugin version in running Gerrit
Our two commands
being executed

16. Configure your plugin
2014 Dariusz Łuksza

17. 2014 Dariusz Łuksza
Configure plugin in gerrit.config
● Add:
[plugin "RetriggerMe"]
jenkinsUrl = http://localhost:9090/
selfName = localhost 8080
to $gerrit_site/etc/gerrit.config and restart Gerrit
● From now on, our plugin must be installed
under `RetriggerMe` name. Otherwise it will not
see this configuration.

18. 2014 Dariusz Łuksza
Let's start from plugin configuration!
pluginName will contain name
under which our plugin was
installed in Gerrit, annotation
here is very important. That
value is dynamically bound in
plugin context during
installation process.
Extract `jenkinsUrl` and `selfName` from
$gerrit_site/etc/gerrit.config file
Don't forget about @Inject

19. Communicate with
outside world via REST
endpoints
2014 Dariusz Łuksza

20. 2014 Dariusz Łuksza
Let's communicate with outside
world! - REST end points
Will be automatically
serialized to JSON
before sending to client.
Inject our configuration provider
Implement proper interface

21. 2014 Dariusz Łuksza
Let's communicate with outside
world! - REST end points
Inform Gerrit that we want to have our REST
enpoint to be registered in `change` context,
with name `retrigger`. This is another part of
Gerrit's Guice magic ;)

22. 2014 Dariusz Łuksza
Let's communicate with outside
world! - REST end points
Install our child Guice module in
main plugin module.

23. 2014 Dariusz Łuksza
Let's communicate with outside
world! - REST end points
Let's test it:
$ mvn verify
$ curl -X POST –digest
http://admin:tJESZhrTpZGm@localhost:8080/a/changes/2/RetriggerMe~retrigger
)]}'
{
"jenkins_url": "http://localhost:9090/"
}
Generated HTTP
password for admin user
Name under which
plugin was installed
REST endpoint name
Response
Context name
Response always starts with magic “)]}'” prefix. This is preventing
from JavaScript injection, this is a security feature of Gerrit.

24. Extend Web UI
2014 Dariusz Łuksza

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Add button on Web UI
Add UiAction interface

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Add button on Web UI
Handle button
`onclick` action
Gerrit's
JavaScript
magic ;)
Context
name
Our REST
endpoint
name

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Communicate back to server
Callback function
Call associated
REST endpoint
Note object fields naming
convention (underscores)

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Handle data from client and trigger
build
Input datastructure, remember
about name convention,
camelCase in Java,
underscores_in_java_script
Gerrit will automatically deserialize JSON to Java object

29. Extend Gerrit
permission system
2014 Dariusz Łuksza

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Protect retrigger button with plugin
own capability
Extend
CapabilityDefinition
class

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Protect retrigger button with plugin
own capability
Grant our plugin
capability to users group
Configuring capabilities requires changes in All-Projects access rights.

32. 2014 Dariusz Łuksza
Protect retrigger button with plugin
own capability
Bind it in plugin
main module

33. 2014 Dariusz Łuksza
Protect retrigger button with plugin
own capability
Anotate our UiAction with
@RequiresCapability
And that is it! Only members of groups with `retrigger` capability will
see `Retrigger Me!` button in Web UI.

34. Debugging?
2014 Dariusz Łuksza

35. 2014 Dariusz Łuksza
How to debug?
● Modify $gerrit_site/etc/gerrit.config:
[container]
javaOptions = -Xdebug
-Xrunjdwp:transport=dt_socket,address=8998,server=y,suspend=n
● Use 'Remote debug' from Eclipse :)

36. 2014 Dariusz Łuksza
Dariusz Łuksza, CollabNet
dariusz@luksza.org
@dluksza
Thank you!
Questions?
Links:
● Gerrit documentation:
https://gerrit-documentation.storage.googleapis.com/Documentation/2.9/index.html
Plugins development part:
https://gerrit-documentation.storage.googleapis.com/Documentation/2.9/dev-plugins.html
JavaScript API part:
https://gerrit-documentation.storage.googleapis.com/Documentation/2.9/js-api.html
● RetriggerMe source:
https://github.com/dluksza/gerrit-retriggerme
● Presentation:
http://www.slideshare.net/dluksza/gerrit-plugins
● Create Gerrit Web UI plugins using AngularJS:
https://github.com/dluksza/angular-gerrit