mediagoblin/tools/pluginapi.py

   1 # GNU MediaGoblin -- federated, autonomous media hosting
   2 # Copyright (C) 2011, 2012 MediaGoblin contributors.  See AUTHORS.
   3 #
   4 # This program is free software: you can redistribute it and/or modify
   5 # it under the terms of the GNU Affero General Public License as published by
   6 # the Free Software Foundation, either version 3 of the License, or
   7 # (at your option) any later version.
   8 #
   9 # This program is distributed in the hope that it will be useful,
  10 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 # GNU Affero General Public License for more details.
  13 #
  14 # You should have received a copy of the GNU Affero General Public License
  15 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
  16
  17 """
  18 This module implements the plugin api bits and provides the plugin
  19 base.
  20
  21 Two things about things in this module:
  22
  23 1. they should be excessively well documented because we should pull
  24    from this file for the docs
  25
  26 2. they should be well tested
  27
  28
  29 How do plugins work?
  30 ====================
  31
  32 Plugins are structured like any Python project. You create a Python package.
  33 In that package, you define a high-level ``__init__.py`` that either defines
  34 or imports modules that define classes that inherit from the ``Plugin`` class.
  35
  36 Additionally, you want a LICENSE file that specifies the license and a
  37 ``setup.py`` that specifies the metadata for packaging your plugin. A rough
  38 file structure could look like this::
  39
  40     myplugin/
  41      |- setup.py         # plugin project packaging metadata
  42      |- README           # holds plugin project information
  43      |- LICENSE          # holds license information
  44      |- myplugin/        # plugin package directory
  45         |- __init__.py   # imports myplugin.main
  46         |- main.py       # code for plugin
  47
  48
  49 Lifecycle
  50 =========
  51
  52 1. All the modules listed as subsections of the ``plugins`` section in
  53    the config file are imported. This causes any ``Plugin`` subclasses in
  54    those modules to be defined and when the classes are defined they get
  55    automatically registered with the ``PluginCache``.
  56
  57 2. After all plugin modules are imported, registered plugin classes are
  58    instantiated and ``setup_plugin`` is called for each plugin object.
  59
  60    Plugins can do any setup they need to do in their ``setup_plugin``
  61    method.
  62 """
  63
  64 import logging
  65
  66 from mediagoblin import mg_globals
  67
  68
  69 _log = logging.getLogger(__name__)
  70
  71
  72 class PluginCache(object):
  73     """Cache of plugin things"""
  74     __state = {
  75         # list of plugin classes
  76         "plugin_classes": [],
  77
  78         # list of plugin objects
  79         "plugin_objects": []
  80         }
  81
  82     def clear(self):
  83         """This is only useful for testing."""
  84         del self.plugin_classes[:]
  85         del self.plugin_objects[:]
  86
  87     def __init__(self):
  88         self.__dict__ = self.__state
  89
  90     def register_plugin_class(self, plugin_class):
  91         """Registers a plugin class"""
  92         self.plugin_classes.append(plugin_class)
  93
  94     def register_plugin_object(self, plugin_obj):
  95         """Registers a plugin object"""
  96         self.plugin_objects.append(plugin_obj)
  97
  98
  99 class MetaPluginClass(type):
 100     """Metaclass for PluginBase derivatives"""
 101     def __new__(cls, name, bases, attrs):
 102         new_class = super(MetaPluginClass, cls).__new__(cls, name, bases, attrs)
 103         parents = [b for b in bases if isinstance(b, MetaPluginClass)]
 104         if not parents:
 105             return new_class
 106         PluginCache().register_plugin_class(new_class)
 107         return new_class
 108
 109
 110 class Plugin(object):
 111     """Exttend this class for plugins.
 112
 113     Example::
 114
 115         from mediagoblin.tools.pluginapi import Plugin
 116
 117         class MyPlugin(Plugin):
 118             ...
 119
 120             def setup_plugin(self):
 121                 ....
 122
 123     """
 124
 125     __metaclass__ = MetaPluginClass
 126
 127     def setup_plugin(self):
 128         pass
 129
 130
 131 def get_config(key):
 132     """Retrieves the configuration for a specified plugin by key
 133
 134     Example:
 135
 136     >>> get_config('mediagoblin.plugins.sampleplugin')
 137     {'foo': 'bar'}
 138     >>> get_config('myplugin')
 139     {}
 140     >>> get_config('flatpages')
 141     {'directory': '/srv/mediagoblin/pages', 'nesting': 1}}
 142
 143     """
 144
 145     global_config = mg_globals.global_config
 146     plugin_section = global_config.get('plugins', {})
 147     return plugin_section.get(key, {})