Writing Functions for Specific Directives

You should write each function for a particular stage in the filtering process, (setup, metadata, data, enumeration, generation, and shutdown.) The function should only use the data sources that are available at the relevant stage. See the section Sources and Destinations (in the Administration Guide) for a list of the data sources available at each stage.

At the Setup stage, the filter is preparing for setup and cannot get information about the resource’s URL or content.

At the MetaData stage, the robot has encountered a URL for a resource but has not downloaded the resource’s content. Consequently, information is available about the URL and the data that is derived from other sources such as the filter.conf file. At this stage, information is not available about the content of the resource.

At the Data stage, the robot has downloaded the content of the URL, so information is available about the content, such as the description, the author, and so on.

At the Enumeration and Generation stages, the same data sources are available as for the Data stage.

At the Shutdown stage, the filter has completed its processes and shuts down. Although functions written for this stage can use the same data sources as those available at the Data stage, shutdown functions typically restrict their operations to shutdown and clean up activities.