man Catalyst::Manual::Internals () - Catalyst Internals

NAME

Catalyst::Manual::Internals - Catalyst Internals

DESCRIPTION

This document provides an 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 As Catalyst is still developing rapidly, details may become out of date: please treat this as a guide, and look at the source for the last word.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 (I may be wrong in some of the details here - AF):

1
When the Catalyst module is imported in the main application module it evaluates any options (CW-Debug, CW-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 CWCatalyst and from the selected specialized Engine module.
2
When the application module makes the first call to CW__PACKAGE__->action() (implemented in CWCatalyst::Engine), Catalyst automatically loads all components it finds in the CW$class::Controller, CW$class::C, CW$class::Model, CW$class::M, CW$class::View and CW$class::V namespaces (using CWModule::Pluggable::Fast). A table of actions is built up and added to on subsequent calls to CWaction().

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. Extending means using multiple inheritance with NEXT.

The specialized engine classes populate the Catalyst request object with information from the underlying layer (CWApache::Request or CWCGI::Simple) during the prepare phase, then push the generated response information down to the underlying layer during the finalize phase.

AUTHOR

Sebastian Riedel, CWsri@oook.de

COPYRIGHT

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