GitHub plugin
=============
This plugin allows existing GitHub repositories to be integrated
as Gerrit projects.

Why using GitHub and Gerrit together ?
--------------------------------------

Many people see Gerrit and GitHub as opposites: the pull-request
model adopted by GitHub is often used as "easy shortcut" to the
more comprehensive and structured code-review process in Gerrit.

There are many discussion threads on this:
- http://programmers.stackexchange.com/questions/173262/gerrit-code-review-or-githubs-fork-and-pull-model
- http://stackoverflow.com/questions/2451644/gerrit-with-github
- http://julien.danjou.info/blog/2013/rant-about-github-pull-request-workflow-implementation

In reality there are already OpenSource projects that have started
using the two tools together:
- OpenStack (https://wiki.openstack.org/wiki/GerritJenkinsGithub)
- MediaWiki (http://www.mediawiki.org/wiki/Gerrit)

The reason for using GitHub and Gerrit together are:
a) GitHub is widely recognised and accessible by lots of world-wide sites.
b) Using a public GitHub repo allows to "off-load" a lot of git pull traffic.
c) Pull-request allows novice users to start getting involved.
d) Gerrit code-review define the quality gates for avoiding "noise" of unstructured
   contributions.

Why a Gerrit plugin ?
---------------------

When using GitHub and Gerrit together, the "master of truth" has to be
Gerrit: this is because it is the place where more control in terms of
security and workflow can be defined.

A Gerrit plugin can help controlling the GitHub replica and importing
the pull requests as Gerrit changes.


Integration points
------------------

### Authentication. (DONE - Change-Id: I7291a90014e51316af3cb07fd03785c1ef33acd0)

Users can login to Gerrit using the same username and credentials
in GitHub. Gerrit login points to GitHub for generating the OAuth token
to be used for the code-review authenticated session.

The initial Gerrit registration page can be customised to import
GitHub SSH Keys directly into Gerrit.

### Push-Pull replication. (WIP - Change-Id: I596b2e80b4d9519668a1ab289d6c950139d6a922)

Existing GitHub repositories are automatically replicated to Gerrit
for the purpose of performing code-review and pushing back changes
once approved. Additionally to the standard Gerrit push replication,
supports as well the ability to pull branches from remote GitHub
repositories.

### Pull-request to Change. (DONE - Change-Id: d669e351a03798cc2ec966d028458f083c232564)

Hooks into the GitHub pull-request mechanism to automatically create
a Change in Gerrit submitted for review.

How to build this plugin
------------------------

### Gerrit 2.8 build

GitHub plugin is designed to work with Gerrit 2.8 (currently in development).
In order to build the GitHub plugin you need to have a working Gerrit 2.8
build in place.

See https://gerrit-review.googlesource.com/Documentation/dev-buck.html for a
reference on how to build Gerrit 2.8 (master branch) using BUCK.

### GitHub API

In order to access GitHub API, we have used the lucamilanesio fork of Kohsuke API 
layer hosted on GitHub at https://github.com/lucamilanesio/github-api.

You need to clone and build the GitHub API as pre-requisite for building the
GitHub plugin for Gerrit.

Example:
  git clone https://github.com/lucamilanesio/github-api.git
  cd github-api
  mvn install

### singleusergroup plugin

You need to clone, build and install the singleusergroup plugin for Gerrit
(see https://gerrit-review.googlesource.com/#/admin/projects/plugins/singleusergroup).

This plugin is needed to allow Gerrit to use individual users as Groups for being
used in Gerrit ACLs.

Example:
  git clone https://gerrit.googlesource.com/plugins/singleusergroup
  cd singleusergroup
  mvn install
  cp target/singleusergroup-*.jar $GERRIT_SITE/plugins/.

### Building GitHub integration for Gerrit

Just clone the Git repository (see https://gerrit-review.googlesource.com/#/admin/projects/plugins/github)
and do a `mvn install` from the root directory.
This will create two JARs under github-oauth/target and github-plugin/target: the oauth is a JAR library
to be copied to $GERRIT_SITE/lib whilst the plugin JAR has to be installed as usual under $GERRIT_SITE/plugins.

Example:
  git clone https://gerrit.googlesource.com/plugins/github
  cd github
  mvn install
  cp target/github-oauth/target/github-oauth-*.jar $GERRIT_SITE/lib
  cp target/github-plugin/target/github-plugin-*.jar $GERRIT_SITE/plugins