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Catalyst::Manual::Internals.3pm

NAME

Catalyst::Manual::Internals - Catalyst Internals

DESCRIPTION

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 As Catalyst is still developing rapidly, details may become out of date: please treat this as a guide, and look at the source for the last word.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.

Initialization

Catalyst initializes itself in two stages:

1.

When the Catalyst module is imported in the main application module it evaluates any options ("-Debug", "-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 "Catalyst" and from the selected specialized Engine module.

2.

When the application module makes the first call to "__PACKAGE__->action()" (implemented in "Catalyst::Engine"), Catalyst automatically loads all components it finds in the $class::Controller, $class::C, $class::Model, $class::M, $class::View and $class::V namespaces (using "Module::Pluggable"). A table of actions is built up and added to on subsequent calls to "action()".

Request Lifecycle

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 ("Apache::Request" or "CGI::Simple") during the prepare phase, then push the generated response information down to the underlying layer during the finalize phase.

AUTHOR

Sebastian Riedel, "sri@oook.de"

COPYRIGHT

This program is free software, you can redistribute it and/or modify it under the same terms as Perl itself.