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<a name="implementing-server-plugins-full-example"></a>Implementing Server Plugins: Full Example</h2></div></div></div>
<p>In addition, the external <a class="ulink" href="http://git.gnome.org/browse/rygel-gst-0-10-plugins" target="_top">rygel-gst-0-10-plugins</a> project provides a Rygel Server plugin that uses an older GStreamer version and is an example of an external Rygel Server plugin implemented in C. Its <a class="ulink" href="http://git.gnome.org/browse/rygel-gst-0-10-plugins/tree/src/media-export" target="_top">media-export</a> plugin exposes the contents of a directory via UPnP.</p>
<p>The <code class="function">module_init</code> function first checks that the plugin has not been disabled and then creates an instance of its <code class="classname">RygelMediaExportPlugin</code>, which it adds to the provided <code class="classname">RygelPluginLoader</code> instance.</p>
<p>The <code class="classname">RygelMediaExportPlugin</code> class, derived from <a class="link" href="RygelMediaServerPlugin.html" title="RygelMediaServerPlugin">RygelMediaServerPlugin</a>, simply instantiates its <code class="classname">RygelMediaExportRootContainer</code> class, derived from <a class="link" href="RygelMediaContainer.html" title="RygelMediaContainer">RygelMediaContainer</a>, providing it to the base class as the root container.</p>
<p>The <code class="classname">RygelMediaExportRootContainer</code> creates an instance of a <code class="classname">RygelMediaExportMediaCache</code> class and a <code class="classname">RygelMediaExportHarvester</code> class. The harvester finds files on the filesystem, and stores them in the media cache, which uses SQLite to keep track of them.</p>
<p><code class="classname">RygelMediaExportRootContainer</code> informs the media cache that it should have a child container for the media content as organised on the filesystem, and additionally some virtual folders for Music, Pictures, Video and Playlists, with further sub-divisions under these, for instance by publication year. These containers are added to the media cache via instances of the <code class="classname">RygelMediaExportNullContainer</code> class, but that is just to simplify the media cache API and these instances then serve no further purpose. The virtual folders are re-added whenever the filesystem's container is updated, so that they can show the updated
content, though that is not particularly efficient.</p>
<p><code class="classname">RygelMediaExportRootContainer</code> then delegates its <code class="classname">RygelMediaContainer</code> virtual function implementations to this media cache, which in turn uses the <code class="classname">RygelMediaExportObjectFactory</code> to instantiate new containers for each request based on their ID. For instance, it returns a <code class="classname">RygelMediaExportDBContainer</code> if the requested ID indicates a virtual container, using the definition in the rest of the ID to build a suitable SQL query.</p>
<p>The root container derives from <code class="classname">TrackableDbContainer</code>, which in turn implements the <a class="link" href="RygelTrackableContainer.html" title="RygelTrackableContainer">RygelTrackableContainer</a> interface, to implement the change tracking profile of the UPnP ContentDirectory:3 specification. Therefore, whenever the root container, or its child items, have changed, we call the <code class="function">rygel_trackable_container_updated()</code> function.</p>
<p>Any filesystem folders are implemented as UPnP containers via the <code class="classname">RygelMediaExportWritableDbContainer</code> class, which implements the <a class="link" href="RygelWritableContainer.html" title="RygelWritableContainer">RygelWritableContainer</a> interface to allow new files to be uploaded to the filesystem via UPnP.</p>
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