Document how to use ikiwiki with Gerrit Code Review

[ikiwiki] / doc / rcs / git.mdwn

[[!meta title="Git"]]

[Git][git] is a distributed revison control system originally developed for
the Linux kernel. Ikiwiki supports storing a wiki in git.

[git]: http://git.or.cz/

Ikiwiki can run as a git `post-update` hook to update a wiki
whenever commits come in. When running as a [[cgi]],
ikiwiki automatically commits edited pages, and uses the
git history to generate the [[RecentChanges]] page.

Normally you can just follow the instructions in [[setup]] to create
the git repositories and get started. To understand the details, read on.

## git repository setup

[[!img wiki_edit_flow.svg size=490x align=right]]

The suggested setup for git has a bare repository, and various
working clones (with working directories). The bare
repository is pushed to and pulled from the various working clones.

One of the clones is special; it is the srcdir
which is used to compile the wiki, and is also used by the
[[cgi]] to commit changes made via the web interface. It is special
since the `post-update` hook for the bare root repository is used to
trigger an update of this repository, and then an ikiwiki refresh
updates the published wiki itself.

The other (optional) clones are meant for you to work
on, and commit to, changes should then be pushed to the bare root
repository.

Using three or more repositories isn't the most obvious set up, but
it works the best for typical ikiwiki use. [[ikiwiki-makerepo]] can
automate setting this up for the common case where there is no
pre-existing wiki. [[tips/Laptop_wiki_with_git]] describes a different
way to set up ikiwiki and git.

## git repository with multiple committers

It can be tricky to get the permissions right to allow multiple people to
commit to an ikiwiki git repository. As the [[security]] page mentions,
for a secure ikiwiki installation, only one person should be able to write
to ikiwiki's srcdir. When other committers make commits, their commits
should be pushed to the bare repository, which has a `post-update` hook
that uses ikiwiki to pull the changes to the srcdir.

One setup that will work is to put all committers in a group (say,
"ikiwiki"), and use permissions to allow that group to commit to the bare git
repository. Make both the post-update hook and ikiwiki.cgi be setgid
to the group, as well as suid to the user who admins the wiki. The
`wrappergroup` [[setup_file_option|usage]] can be used to make the wrappers
be setgid to the right group. Then the srcdir, including its git
repository, should only be writable by the wiki's admin, and *not* by the
group. Take care that ikiwiki uses a umask that does not cause files in
the srcdir to become group writable. (umask 022 will work.)

## git repository with untrusted committers

By default, anyone who can commit to the git repository can modify any file
on the wiki however they like. A `pre-receive` hook can be set up to limit
incoming commits from untrusted users. Then the same limits that are placed
on edits via the web will be in effect for commits to git for the users.
They will not be allowed to edit locked pages, they will only be able to
delete pages that the [[plugins/remove]] configuration allows them to
remove, and they will only be allowed to add non-page attachments that the
[[plugins/attachment]] configuration allows.

To enable this, you need to set up the git repository to have multiple
committers. Trusted committers, including the user that ikiwiki runs as, 
will not have their commits checked by the `pre-receive` hook. Untrusted
committers will have their commits checked. The configuration settings to
enable are `git_test_receive_wrapper`, which enables generation of a
`pre-receive` hook, and `untrusted_committers`, which is a list of
usernames of the untrusted committers.

Note that when the `pre-receive` hook is checking incoming changes, it
ignores the git authorship information, and uses the username of the unix
user who made the commit. Then tests including the `locked_pages`
[[ikiwiki/PageSpec]]
are checked to see if that user can edit the pages in the commit.

You can even set up an [[anonymous_user|tips/untrusted_git_push]], to allow
anyone to push changes in via git rather than using the web interface.

## Optionally using a local wiki to preview changes

When working on your wiki,
it is common (but optional) practice to preview your changes using a
private wiki on the local host before publishing the updates by
sending it to the root repository. If you do want to setup a private
wiki, you will have to have another setup file and and an ikiwiki
installation on your local machine. You will need all the packages
this implies -- a web server, git, ikiwiki, etc.  However, there is a
_caveat_: by default, ikiwiki pulls and pushes from `origin`. This is
not ideal for the working clones on the local machine, since you might
go through several iterations of a page before pushing to the bare
root of the repository tree (and thus publishing it on your public wiki).
You do not want the action of refreshing the local wiki in order to
review your work to accidentally publish the
contents before you are ready. In order to prevent the git push that
is the normal behaviour of ikiwiki, set the configuration of the local wiki:

      gitorigin_branch => "",
      ## git post-commit wrapper
      git_wrapper => "/working/dir/.git/hooks/post-commit",

Then just committing should refresh the private ikiwiki on the local
host.  Now just run `ikiwiki -setup localwiki.setup -gettime` and
you should be good to go. (You only need the slow `-gettime` option
the first time you run setup.)  Use standard git commands to handle
pulling from and pushing to the server.  **Note**: After
pulling changes from the bare root repository, you will need to
manually update the local wiki, with a command such as `ikiwiki
-setup localwiki.setup -refresh`. You could use git's `post-merge` hook
to automate that command.

## Using ikiwiki with Gerrit

[Gerrit Code Review](https://code.google.com/p/gerrit/) manages a set of Git
repositories and provides a web interface to review and merge commits.  You can
configure ikiwiki to work with a Gerrit-managed repository, allowing you to
review and merge commits to your wiki.

First, create your initial wiki repository with Gerrit.  On the server, as the
user that will own the wiki, clone that repository to create a working
directory for ikiwiki, such as /srv/wiki/ikiwiki-checkout.  Create a setup file
and target directory as usual, referencing that working directory path, and
creating a post-update hook in Gerrit's repository.  You'll need to set
appropriate permissions on the hook directory for the repository so that the
user running ikiwiki can compile and install the post-update hook.  Also note
that you must disable web editing by disabling the editpage plugin, and you
must not enable any other plugin that commits to the repository, since ikiwiki
will not have permission to push to the repository.  (Allowing web edits to
have such permission would bypass Gerrit's code review, defeating the purpose.)

Gerrit does not run per-repository hooks, such as the post-update hook ikiwiki
installs to update the wiki after pushes.  However, Gerrit has site-wide hooks,
including a ref-updated hook that runs whenever a ref changes.  You can use
that hook to trigger ikiwiki's post-update hook.  The following script,
installed as Gerrit's ref-updated hook, will run the post-update hook on any
repository that has a "gerrit-run-post-update-hook" file in it:

    #!/bin/sh
    if [ -e "$GIT_DIR/gerrit-run-post-update-hook" ] ; then
        exec "$GIT_DIR/hooks/post-update"
    fi

Then just create gerrit-run-post-update-hook in the wiki repository, run
ikiwiki --setup on the setup file, add your wiki to /etc/ikiwiki/wikilist, and
start reviewing and committing wiki changes via Gerrit.