In the mediagoblin repository, there's a sample plugin under mediagoblin/plugins/sampleplugin that you can use to get started with plugin creation. The simplest way to get up and running is to
- Follow HackingHowto#How_to_set_up_and_maintain_an_environment_for_hacking_with_virtualenv to set up a local virtualenv mediagoblin instance
- run it with ./lazyserver.sh so you get debug output (if you run celeryd separately, you won't see logging.info from stuff run in celery tasks)
- cp -r mediagoblin/plugins/sampleplugin mediagoblin/plugins/myplugin (where "myplugin" is your plugin name)
- cp mediagoblin.ini mediagoblin_local.ini
- edit mediagoblin_local.ini and add [[mediagoblin.plugins.myplugin]] under the [plugins] section to enable your plugin
Now you can look at e.g. other core or non-core plugins for inspiration. See Available Plugins for non-core plugins.
The way you change things in plugins is by use of hooks. At certain points in the mediagoblin code, a function will say "run all hooks with name XYZ", and if you've defined a hook with such a name in a plugin you've enabled, it'll get run there. The documentation on Plugin API is your friend for defining hooks. The sample plugin shows a use of the 'setup' hook.
Note: templates are hooked with a call to pluginapi.register_template_hooks, instead of adding to the hooks variable.
Making an installable plugin
If you followed the steps above, you can use your plugin by copying it into the plugins folder; however, to get a plugin that is easily installable by users (e.g. with pip install myplugin), it should have a certain folder layout.
A good example is the RDFa plugin. This uses a setup.py file to install the files under the mediagoblin_rdfa folder into the lib/ folder of your mediagoblin installation. If you've checked out both mediagoblin and mg-rdfa in the same folder, e.g. ~/src/, you can do
cd ~/src/mg-rdfa/ ../mediagoblin/bin/python setup.py build ../mediagoblin/bin/python setup.py install
to install it to your mediagoblin instance.
The file layout of the repo is:
setup.py MANIFEST.in README.md mediagoblin_rdfa/ __init.py__ templates/ mediagoblin/ plugins/ rdfa/ metadata.html
The setup.py file defines an option include_package_data=True, which makes it read the file MANIFEST.in; MANIFEST.in contains rules for which files to include when installing. In this case, rule recursive-include mediagoblin_rdfa *.html makes it include the HTML template file (and any other you put under mediagoblin_rdfa), retaining the folder layout.