How to extend Gerrit Code Review using Scala and Groovy scripting plugins

1. Luca Milanesio
GerritForge
Luca@gerritforge.com
http://www.gerritforge.com
Twitter: @gitenterprise
How to script a Plugin

2. 2
About Luca
• Luca Milanesio
Co-founder of GerritForge
• over 20 years of experience
in Agile Development
SCM, CI and ALM worldwide
• Contributor to Jenkins
since 2007 (and previously Hudson)
• Git SCM mentor
for the Enterprise since 2009
• Contributor to Gerrit Code Review community since 2011

3. 3
About GerritForge
Founded in 2009 in London UK
Mission: Agile Enterprise
Products:

4. 4
Agenda
 Where we come from ?
 2 years ago: Gerrit plugins
 We want more plugins
 Create a plugin in 60 seconds
 What, how and when are coming?
 Plugins showcase

5. 5
WHO REMEMBERS
THIS ?
GitTogether 2011
Gerrit 2.2.x

6. 6
Why don’t we
introduce plugins ?
They have been so
successful with
Jenkins

7. 7
Gerrit Hackathon
7th of May 2012
The first “helloworld”
plugin was born

8. 8
WHO REMEMBERS THIS ?
Gerrit Summit 2012
Ver. 2.5.x

9. 9
Gerrit Plugins
Growth
in 2 years
50

10. 10
Can we do more ?
Let's ask Jenkins 

11. 11
PLUGINS SUCCESS
=
COMMUNITY
ENGAGEMENT

12. 12
COMMUNITY
=
BRIDGING
DIFFERENCES

13. 13
That would be very useful for
Gerrit Administrators to be
able to write quick automation
scripts for their daily tasks. I
would prioritize groovy plugin
more for the popularity of
groovy scripting.
I think adding a "scripting
language plugin" to support
plugins written in scripting
languages is a very good idea
Hi all,
I was thinking about extending
Gerrit capabilities to load
plugins / extensions by
providing "wrapper" for other
JVM languages.
So … we asked the Community
I would prefer scala, because
I've already written my plugins
with it. imho the builld process is
the main impediment.

14. 14
CHALLENGE
for building a
Gerrit Plugin

15. 15
NO STEPS, NO BUILD … just do it !
$ cat - > ~/gerrit/plugins/hello-1.0.groovy
import com.google.gerrit.sshd.*
import com.google.gerrit.extensions.annotations.*
@Export("groovy")
class GroovyCommand extends SshCommand {
public void run() { stdout.println "Hi from Groovy" }
}
^D
This sample has 190 chars: you need to type
at least 3.2 chars/sec to complete the sample
in only one minute 
https://gist.github.com/lucamilanesio/9687053

16. 16
IS THAT TRUE ? Let’s check on Gerrit
$ ssh –p 29418 user@localhost gerrit plugin ls
Name Version Status File
----------------------------------------------------------------------
hello 1.0 ENABLED hello-1.0.groovy
Gerrit auto-detects the new Groovy file under
$GERRIT_SITE/plugins, invoke the interpreter
and auto-wrap the class into a self-contained Gerrit
plugin.
Groovy class is compiled into byte-code BUT is
slower than native Java plugin.

17. 17
DOES IT REALLY WORK ?
$ ssh –p 29418 user@localhost hello groovy
Hi from Groovy
No magic … IT IS ALL REAL !
Plugin name (hello) comes from the
script filename.
A new SSH command (groovy) has
been defined in Gerrit associated to
the Groovy script loaded.

18. 18
What about Scala ? Just do it again !
$ cat - > ~/gerrit/plugins/hi-1.0.scala
import com.google.gerrit.sshd._
import com.google.gerrit.extensions.annotations._
@Export("scala")
class ScalaCommand extends SshCommand {
override def run = stdout println "Hi from Scala"
}
^D
Scala is more concise with just 178 chars :
you can take it easy with 2.9 chars/sec to type
it a minute 
https://gist.github.com/lucamilanesio/9687092

19. 19
You have now two plugins loaded
$ ssh –p 29418 user@localhost gerrit plugin ls
Name Version Status File
----------------------------------------------------------------------
hello 1.0 ENABLED hello-1.0.groovy
hi 1.0 ENABLED hi-1.0.scala
There are no differences for Gerrit between
Java, Groovy or Scala plugins: they have the same
dignity and power.
Scala compiler takes longer but byte-code runs at
the same speed as a native Java plugin!

20. 20
Reactions from the Gerrit mailing list …
So i checked it out and tried it, and
what should i say ...
Wow, it rocks! ;-)
Combined with new and shiny
Plugin API the code is really short.
So i started new repo
on gh [1] and created two working
plugins [2], [3], and sure would add
more, so to say,
cookbook-groovy-plugin:
$>ssh gerrit review approve
I59302cbb
$>Approve change: I59302cbb.
What do
YOU think
? 

21. 21
WHAT can scripting plugins do now ?
1. Define new SSH commands
2. Define new REST APIs
3. Listen to Gerrit events

22. 22
HOW can I get Gerrit with scripting plugins ?
Download the Gerrit master with scripting extensions from:
http://ci.gerritforge.com/job/Gerrit-master-scripting/lastSuccessfulBuild/artifact/buck-
out/gen/gerrit-scripting.war
Run Gerrit init and say Y for installing the Scala and Groovy scripting plugins
providers:
*** Plugins
***
Install plugin groovy-provider version v2.9-rc1-325-g96d0d43 [y/N]? Y
Install plugin scala-provider version v2.9-rc1-325-g96d0d43 [y/N]? y
You may want to increase the JVM PermGen on gerrit.config when
loading/unloading scripting plugins
[container]
javaOptions = -XX:MaxPermSize=1024m

23. 23
Scripting plugins
showcase

24. 24
Create a branch through Gerrit API
$ cat - > ~/gerrit/plugins/branch-1.0.groovy
import com.google.gerrit.sshd.*
import com.google.gerrit.extensions.annotations.*
import com.google.gerrit.extensions.api.*
import com.google.gerrit.extensions.api.projects.*
import com.google.inject.*
import org.kohsuke.args4j.*
@Export("create")
@CommandMetaData(name = "create-branch", description = "Create branch")
class CreateBranch extends SshCommand {
@Inject GerritApi api
@Argument(index = 0, usage = "Project name", metaVar = "PROJECT")
String projectName
@Argument(index = 1, usage = "Branch name", metaVar = "BRANCH")
String branchName
@Argument(index = 2, usage = "Branch point sha1", metaVar = "SHA1")
String sha1
void run() {
BranchInput branch = new BranchInput()
branch.revision = sha1
api.projects().name(projectName).branch(branchName).create(branch)
stdout.println("Branch created: " + branchName)
}
}
^D
https://gist.github.com/lucamilanesio/9687118

25. 25
Script classes get
Plugins Guice
Injections
(but cannot add Guice Modules)

26. 26
List projects via REST API
$ cat - > ~/gerrit/plugins/projects-1.0.scala
import com.google.inject._
import com.google.gerrit.extensions.annotations._
import com.google.gerrit.server.project._
import javax.servlet.http._
import scala.collection.JavaConversions._
@Singleton @Export("/")
class Projects @Inject() (val pc: ProjectCache) extends HttpServlet {
override def doGet(req: HttpServletRequest, resp: HttpServletResponse) =
resp.getWriter print
"[" +
(pc.all map ( """ + _.get + """ ) mkString ",") +
"]"
}
^D
https://gist.github.com/lucamilanesio/9687133

27. 27
Scala is
COMPACT + FUNCTIONAL
NOTE: for Guice injection
@Inject() before constructor vals

28. 28
FUNCTIONAL
IS PERFECT
FOR …

29. 29
Scalable in-process hooks
$ cat - > ~/gerrit/plugins/inprochook-1.0.scala
import org.slf4j.LoggerFactory._
import com.google.inject._
import com.google.gerrit.common._
import com.google.gerrit.server.events._
import com.google.gerrit.extensions.registration.DynamicSet
@Singleton
class ListenToChanges extends ChangeListener {
val log = getLogger(classOf[ListenToChanges])
override def onChangeEvent(e: ChangeEvent) = e match {
case comm: CommentAddedEvent =>
log info s"${comm.author.name} said '${comm.comment}' " +
s"on ${comm.change.project}/${comm.change.number}'"
case _ =>
}
}
class HooksModule extends AbstractModule {
override def configure =
DynamicSet bind(binder, classOf[ChangeListener]) to classOf[ListenToChanges]
}
^D
 Less CPU overhead (no exec/fork)  faster and scalable
 Works on behalf of user thread identity
 Access Gerrit injected objects (Cache, ReviewDb, JGit)
https://gist.github.com/lucamilanesio/9687154

30. 30
Commit message validation
$ cat - > ~/gerrit/plugins/commitheadline-1.0.scala
import scala.collection.JavaConversions._
import com.google.inject._
import com.google.gerrit.extensions.annotations._
import com.google.gerrit.server.git.validators._
import com.google.gerrit.server.events._
@Singleton
@Listen
class HasIssueInCommitHeadline extends CommitValidationListener {
override def onCommitReceived(e: CommitReceivedEvent) =
"[A-Z]+-[0-9]+".r findFirstIn e.commit.getShortMessage map {
issue => Seq(new CommitValidationMessage(s"Issue: $issue", false))
} getOrElse {
throw new CommitValidationException("Missing JIRA-ID in commit headline")
}
}
^D
 Native pattern-matching support
 Java regex available out-of-the box
 Support for Optional values (map/getOrElse)
https://gist.github.com/lucamilanesio/9687174

31. 31
And there is more …
audit events
download commands
project and group events
message of the day
Prolog predicates
auth backends
avatars

32. 32
WHEN scripting plugins will be included in Gerrit ?
Hackathon #6
24-26th March we will keep
on hacking on Gerrit
MISSION:
improve, stabilise and
merge scripting plugins into
Gerrit master !
TARGET VERSION:
Gerrit Ver. 2.10 (?)

33. 33

34. Try it on-line (with scripting): http://gerrithub.io/login
Read the Gerrit book: http://gerrithub.io/book
Keep in touch: http://gitenterprise.me
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