Catalyst::Manual::Internals - Catalyst Internals
This document provides a brief overview of the internals of Catalyst. As Catalyst is still developing rapidly, details may become out of date: please treat this as a guide, and look at the source for the last word.
The coverage is split into initialization and request lifecycle.
Catalyst initializes itself in two stages:
When the Catalyst module is imported in the main application module it evaluates any options (
-Engine=XXX) and loads any specified plugins, making the application module inherit from the plugin classes. It also sets up a default log object and ensures that the application module inherits from
Catalystand from the selected specialized Engine module.
When the application module makes the first call to
Catalyst::Engine), Catalyst automatically loads all components it finds in the
Module::Pluggable). A table of actions is built up and added to on subsequent calls to
For each request Catalyst builds a context object, which includes information about the request, and then searches the action table for matching actions.
The handling of a request can be divided into three stages: preparation of the context, processing of the request, and finalization of the response. These are the steps of a Catalyst request in detail; every step can be overloaded to extend Catalyst.
handle_request prepare prepare_request prepare_connection prepare_query_parameters prepare_headers prepare_cookies prepare_path prepare_body (unless parse_on_demand) prepare_body_parameters prepare_parameters prepare_uploads prepare_action dispatch finalize finalize_uploads finalize_error (if one happened) finalize_headers finalize_cookies finalize_body
These steps are normally overloaded from engine classes, and may also be extended by plugins. For more on extending Catalyst, see Catalyst::Manual::ExtendingCatalyst.
The specialized engine classes populate the Catalyst request object with information from the underlying layer (
CGI::Simple) during the prepare phase, then push the generated response information down to the underlying layer during the finalize phase.
This program is free software, you can redistribute it and/or modify it under the same terms as Perl itself.