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 As Catalyst is still developing rapidly, details may become out of date: please treat this as a guide, and look at the source for the last word.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