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Plugins
=======
Aptdaemon provides a plugin mechanism by making use of setuptools' entry points.
The group name is ``aptdaemon.plugins``.
Cache modifiers
---------------
Currently there are two types of plugins available which allow you to modify
the marked changes of a transaction. Each plugin can be a function which
accepts the resolver (apt.cache.ProblemResolver) and the cache (apt.cache.Cache)
as arguments:
* *modify_cache_before*
The plugged-in function is called after the intentional changes of the
transaction have been marked, but before the dependencies have been resolved.
* *modify_cache_after*
The plugged-in function is called after the dependency resolution of the
transaction. The resolver will be called again afterwards.
A short overview of the steps required to process a transaction:
1. Mark intentional changes (e.g. the to be installed packages of a
InstallPackages transaction)
2. Call all modify_cache_before plugins
3. Run the dependency resolver
4. Call all modify_cache_after_plugins and re-run the resolver
5. Commit changes
External helpers
----------------
There is also the *get_license_key* plugin which allows to retrieve the license
key content and path to store. License keys are required by propriatary
software. The plugged-in function gets called with uid of the user who started
the transaction, the package name, a JSON OAuth tocken and the name of a
server to query.
Example
-------
Here is an example which would install language packages :file:`./plugins/aptd.py`:
>>> def install_language_packs(resolver, cache):
>>> """Marks the required language packs for installation."""
>>> #... do the magic here ...
>>> language_pack.mark_install(False, True)
>>> # Only protect your changes if they are mantadory. If they cannot be
>>> # be installed the transaction will fail.
>>> resolver.clear(language_pack)
>>> resolver.protect(language_pack)
Finally you would have to register your function as entry point in :file:`setup.py`:
>>> setup(
>>> ...
>>> entry_points="""[aptdaemon.plugins]
>>> modify_cache_after=plugins.aptd:install_language_packs
>>> """,
>>> ...
>>> )
.. note::
Keep in mind that you can only register one entry point per name/plugin per
distribution.
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