gitlab-org--gitlab-foss/doc/administration/file_hooks.md

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File hooks (FREE SELF)

Renamed feature from Plugins to File hooks in GitLab 12.8.

With custom file hooks, GitLab administrators can introduce custom integrations without modifying the GitLab source code.

A file hook runs on each event. You can filter events or projects in a file hook's code, and create many file hooks as you need. Each file hook is triggered by GitLab asynchronously in case of an event. For a list of events see the system hooks documentation.

NOTE: File hooks must be configured on the file system of the GitLab server. Only GitLab server administrators can complete these tasks. Explore system hooks or webhooks as an option if you do not have file system access.

Instead of writing and supporting your own file hook, you can also make changes directly to the GitLab source code and contribute back upstream. In this way, we can ensure functionality is preserved across versions and covered by tests.

Setup

The file hooks must be placed directly into the file_hooks directory, subdirectories are ignored. There is an example directory inside file_hooks where you can find some basic examples.

Follow the steps below to set up a custom hook:

1. On the GitLab server, navigate to the plugin directory. For an installation from source the path is usually /home/git/gitlab/file_hooks/. For Omnibus installs the path is usually /opt/gitlab/embedded/service/gitlab-rails/file_hooks.

   For configurations with multiple servers, your hook file should exist on each application server.

2. Inside the file_hooks directory, create a file with a name of your choice, without spaces or special characters.

3. Make the hook file executable and make sure it's owned by the Git user.

4. Write the code to make the file hook function as expected. That can be in any language, and ensure the 'shebang' at the top properly reflects the language type. For example, if the script is in Ruby the shebang will probably be #!/usr/bin/env ruby.

5. The data to the file hook is provided as JSON on STDIN. It is exactly the same as for system hooks.

That's it! Assuming the file hook code is properly implemented, the hook fires as appropriate. The file hooks file list is updated for each event, there is no need to restart GitLab to apply a new file hook.

If a file hook executes with non-zero exit code or GitLab fails to execute it, a message is logged to:

• gitlab-rails/file_hook.log in an Omnibus installation.
• log/file_hook.log in a source installation.

NOTE: In GitLab 13.12 and earlier, the filename was plugin.log

Creating file hooks

This example responds only on the event project_create, and the GitLab instance informs the administrators that a new project has been created.

#!/opt/gitlab/embedded/bin/ruby
# By using the embedded ruby version we eliminate the possibility that our chosen language
# would be unavailable from
require 'json'
require 'mail'

# The incoming variables are in JSON format so we need to parse it first.
ARGS = JSON.parse($stdin.read)

# We only want to trigger this file hook on the event project_create
return unless ARGS['event_name'] == 'project_create'

# We will inform our admins of our gitlab instance that a new project is created
Mail.deliver do
  from    'info@gitlab_instance.com'
  to      'admin@gitlab_instance.com'
  subject "new project " + ARGS['name']
  body    ARGS['owner_name'] + 'created project ' + ARGS['name']
end

Validation

Writing your own file hook can be tricky and it's easier if you can check it without altering the system. A Rake task is provided so that you can use it in a staging environment to test your file hook before using it in production. The Rake task uses a sample data and execute each of file hook. The output should be enough to determine if the system sees your file hook and if it was executed without errors.

# Omnibus installations
sudo gitlab-rake file_hooks:validate

# Installations from source
cd /home/git/gitlab
bundle exec rake file_hooks:validate RAILS_ENV=production

Example of output:

Validating file hooks from /file_hooks directory
* /home/git/gitlab/file_hooks/save_to_file.clj succeed (zero exit code)
* /home/git/gitlab/file_hooks/save_to_file.rb failure (non-zero exit code)