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# NAME

Catalyst - The Elegant MVC Web Application Framework

<div>

    <a href="https://badge.fury.io/pl/Catalyst-Runtime"><img src="https://badge.fury.io/pl/Catalyst-Runtime.svg" alt="CPAN version" height="18"></a>
    <a href="https://travis-ci.org/perl-catalyst/catalyst-runtime/"><img src="https://api.travis-ci.org/perl-catalyst/catalyst-runtime.png" alt="Catalyst></a>
    <a href="http://cpants.cpanauthors.org/dist/Catalyst-Runtime"><img src="http://cpants.cpanauthors.org/dist/Catalyst-Runtime.png" alt='Kwalitee Score' /></a>
</div>

# SYNOPSIS

See the [Catalyst::Manual](https://metacpan.org/pod/Catalyst::Manual) distribution for comprehensive
documentation and tutorials.

    # Install Catalyst::Devel for helpers and other development tools
    # use the helper to create a new application
    catalyst.pl MyApp

    # add models, views, controllers
    script/myapp_create.pl model MyDatabase DBIC::Schema create=static dbi:SQLite:/path/to/db
    script/myapp_create.pl view MyTemplate TT
    script/myapp_create.pl controller Search

    # built in testserver -- use -r to restart automatically on changes
    # --help to see all available options
    script/myapp_server.pl

    # command line testing interface
    script/myapp_test.pl /yada

    ### in lib/MyApp.pm
    use Catalyst qw/-Debug/; # include plugins here as well

    ### In lib/MyApp/Controller/Root.pm (autocreated)
    sub foo : Chained('/') Args() { # called for /foo, /foo/1, /foo/1/2, etc.
        my ( $self, $c, @args ) = @_; # args are qw/1 2/ for /foo/1/2
        $c->stash->{template} = 'foo.tt'; # set the template
        # lookup something from db -- stash vars are passed to TT
        $c->stash->{data} =
          $c->model('Database::Foo')->search( { country => $args[0] } );
        if ( $c->req->params->{bar} ) { # access GET or POST parameters
            $c->forward( 'bar' ); # process another action
            # do something else after forward returns
        }
    }

    # The foo.tt TT template can use the stash data from the database
    [% WHILE (item = data.next) %]
        [% item.foo %]
    [% END %]

    # called for /bar/of/soap, /bar/of/soap/10, etc.
    sub bar : Chained('/') PathPart('/bar/of/soap') Args() { ... }

    # called after all actions are finished
    sub end : Action {
        my ( $self, $c ) = @_;
        if ( scalar @{ $c->error } ) { ... } # handle errors
        return if $c->res->body; # already have a response
        $c->forward( 'MyApp::View::TT' ); # render template
    }

See [Catalyst::Manual::Intro](https://metacpan.org/pod/Catalyst::Manual::Intro) for additional information.

# DESCRIPTION

Catalyst is a modern framework for making web applications without the
pain usually associated with this process. This document is a reference
to the main Catalyst application. If you are a new user, we suggest you
start with [Catalyst::Manual::Tutorial](https://metacpan.org/pod/Catalyst::Manual::Tutorial) or [Catalyst::Manual::Intro](https://metacpan.org/pod/Catalyst::Manual::Intro).

See [Catalyst::Manual](https://metacpan.org/pod/Catalyst::Manual) for more documentation.

Catalyst plugins can be loaded by naming them as arguments to the "use
Catalyst" statement. Omit the `Catalyst::Plugin::` prefix from the
plugin name, i.e., `Catalyst::Plugin::My::Module` becomes
`My::Module`.

    use Catalyst qw/My::Module/;

If your plugin starts with a name other than `Catalyst::Plugin::`, you can
fully qualify the name by using a unary plus:

    use Catalyst qw/
        My::Module
        +Fully::Qualified::Plugin::Name
    /;

Special flags like `-Debug` can also be specified as
arguments when Catalyst is loaded:

    use Catalyst qw/-Debug My::Module/;

The position of plugins and flags in the chain is important, because
they are loaded in the order in which they appear.

The following flags are supported:

## -Debug

Enables debug output. You can also force this setting from the system
environment with CATALYST\_DEBUG or <MYAPP>\_DEBUG. The environment
settings override the application, with <MYAPP>\_DEBUG having the highest
priority.

This sets the log level to 'debug' and enables full debug output on the
error screen. If you only want the latter, see [$c->debug](https://metacpan.org/pod/$c->debug).

## -Home

Forces Catalyst to use a specific home directory, e.g.:

    use Catalyst qw[-Home=/usr/mst];

This can also be done in the shell environment by setting either the
`CATALYST_HOME` environment variable or `MYAPP_HOME`; where `MYAPP`
is replaced with the uppercased name of your application, any "::" in
the name will be replaced with underscores, e.g. MyApp::Web should use
MYAPP\_WEB\_HOME. If both variables are set, the MYAPP\_HOME one will be used.

If none of these are set, Catalyst will attempt to automatically detect the
home directory. If you are working in a development environment, Catalyst
will try and find the directory containing either Makefile.PL, Build.PL,
dist.ini, or cpanfile. If the application has been installed into the system
(i.e. you have done `make install`), then Catalyst will use the path to your
application module, without the .pm extension (e.g., /foo/MyApp if your
application was installed at /foo/MyApp.pm)

## -Log

    use Catalyst '-Log=warn,fatal,error';

Specifies a comma-delimited list of log levels.

## -Stats

Enables statistics collection and reporting.

    use Catalyst qw/-Stats=1/;

You can also force this setting from the system environment with CATALYST\_STATS
or <MYAPP>\_STATS. The environment settings override the application, with
<MYAPP>\_STATS having the highest priority.

Stats are also enabled if [debugging ](#debug) is enabled.

# METHODS

## INFORMATION ABOUT THE CURRENT REQUEST

## $c->action

Returns a [Catalyst::Action](https://metacpan.org/pod/Catalyst::Action) object for the current action, which
stringifies to the action name. See [Catalyst::Action](https://metacpan.org/pod/Catalyst::Action).

## $c->namespace

Returns the namespace of the current action, i.e., the URI prefix
corresponding to the controller of the current action. For example:

    # in Controller::Foo::Bar
    $c->namespace; # returns 'foo/bar';

## $c->request

## $c->req

Returns the current [Catalyst::Request](https://metacpan.org/pod/Catalyst::Request) object, giving access to
information about the current client request (including parameters,
cookies, HTTP headers, etc.). See [Catalyst::Request](https://metacpan.org/pod/Catalyst::Request).

## REQUEST FLOW HANDLING

## $c->forward( $action \[, \\@arguments \] )

## $c->forward( $class, $method, \[, \\@arguments \] )

This is one way of calling another action (method) in the same or
a different controller. You can also use `$self->my_method($c, @args)`
in the same controller or `$c->controller('MyController')->my_method($c, @args)`
in a different controller.
The main difference is that 'forward' uses some of the Catalyst request
cycle overhead, including debugging, which may be useful to you. On the
other hand, there are some complications to using 'forward', restrictions
on values returned from 'forward', and it may not handle errors as you prefer.
Whether you use 'forward' or not is up to you; it is not considered superior to
the other ways to call a method.

'forward' calls  another action, by its private name. If you give a
class name but no method, `process()` is called. You may also optionally
pass arguments in an arrayref. The action will receive the arguments in
`@_` and `$c->req->args`. Upon returning from the function,
`$c->req->args` will be restored to the previous values.

Any data `return`ed from the action forwarded to, will be returned by the
call to forward.

    my $foodata = $c->forward('/foo');
    $c->forward('index');
    $c->forward(qw/Model::DBIC::Foo do_stuff/);
    $c->forward('View::TT');

Note that [forward](#c-forward-action-arguments) implies
an `eval { }` around the call (actually
[execute](#c-execute-class-coderef) does), thus rendering all
exceptions thrown by the called action non-fatal and pushing them onto
$c->error instead. If you want `die` to propagate you need to do something
like:

    $c->forward('foo');
    die join "\n", @{ $c->error } if @{ $c->error };

Or make sure to always return true values from your actions and write
your code like this:

    $c->forward('foo') || return;

Another note is that `$c->forward` always returns a scalar because it
actually returns $c->state which operates in a scalar context.
Thus, something like:

    return @array;

in an action that is forwarded to is going to return a scalar,
i.e. how many items are in that array, which is probably not what you want.
If you need to return an array then return a reference to it,
or stash it like so:

    $c->stash->{array} = \@array;

and access it from the stash.

Keep in mind that the `end` method used is that of the caller action. So a `$c->detach` inside a forwarded action would run the `end` method from the original action requested.

## $c->detach( $action \[, \\@arguments \] )

## $c->detach( $class, $method, \[, \\@arguments \] )

## $c->detach()

The same as [forward](#c-forward-action-arguments), but
doesn't return to the previous action when processing is finished.

When called with no arguments it escapes the processing chain entirely.

## $c->visit( $action \[, \\@arguments \] )

## $c->visit( $action \[, \\@captures, \\@arguments \] )

## $c->visit( $class, $method, \[, \\@arguments \] )

## $c->visit( $class, $method, \[, \\@captures, \\@arguments \] )

Almost the same as [forward](#c-forward-action-arguments),
but does a full dispatch, instead of just calling the new `$action` /
`$class->$method`. This means that `begin`, `auto` and the method
you go to are called, just like a new request.

In addition both `$c->action` and `$c->namespace` are localized.
This means, for example, that `$c->action` methods such as
[name](https://metacpan.org/pod/Catalyst::Action#name), [class](https://metacpan.org/pod/Catalyst::Action#class) and
[reverse](https://metacpan.org/pod/Catalyst::Action#reverse) return information for the visited action
when they are invoked within the visited action.  This is different from the
behavior of [forward](#c-forward-action-arguments), which
continues to use the $c->action object from the caller action even when
invoked from the called action.

`$c->stash` is kept unchanged.

In effect, [visit](#c-visit-action-captures-arguments)
allows you to "wrap" another action, just as it would have been called by
dispatching from a URL, while the analogous
[go](#c-go-action-captures-arguments) allows you to
transfer control to another action as if it had been reached directly from a URL.

## $c->go( $action \[, \\@arguments \] )

## $c->go( $action \[, \\@captures, \\@arguments \] )

## $c->go( $class, $method, \[, \\@arguments \] )

## $c->go( $class, $method, \[, \\@captures, \\@arguments \] )

The relationship between `go` and
[visit](#c-visit-action-captures-arguments) is the same as
the relationship between
[forward](#c-forward-class-method-arguments) and
[detach](#c-detach-action-arguments). Like `$c->visit`,
`$c->go` will perform a full dispatch on the specified action or method,
with localized `$c->action` and `$c->namespace`. Like `detach`,
`go` escapes the processing of the current request chain on completion, and
does not return to its cunless blessed $cunless blessed $caller.

@arguments are arguments to the final destination of $action. @captures are
arguments to the intermediate steps, if any, on the way to the final sub of
$action.

## $c->response

## $c->res

Returns the current [Catalyst::Response](https://metacpan.org/pod/Catalyst::Response) object, see there for details.

## $c->stash

Returns a hashref to the stash, which may be used to store data and pass
it between components during a request. You can also set hash keys by
passing arguments. The stash is automatically sent to the view. The
stash is cleared at the end of a request; it cannot be used for
persistent storage (for this you must use a session; see
[Catalyst::Plugin::Session](https://metacpan.org/pod/Catalyst::Plugin::Session) for a complete system integrated with
Catalyst).

    $c->stash->{foo} = $bar;
    $c->stash( { moose => 'majestic', qux => 0 } );
    $c->stash( bar => 1, gorch => 2 ); # equivalent to passing a hashref

    # stash is automatically passed to the view for use in a template
    $c->forward( 'MyApp::View::TT' );

The stash hash is currently stored in the PSGI `$env` and is managed by
[Catalyst::Middleware::Stash](https://metacpan.org/pod/Catalyst::Middleware::Stash).  Since it's part of the `$env` items in
the stash can be accessed in sub applications mounted under your main
[Catalyst](https://metacpan.org/pod/Catalyst) application.  For example if you delegate the response of an
action to another [Catalyst](https://metacpan.org/pod/Catalyst) application, that sub application will have
access to all the stash keys of the main one, and if can of course add
more keys of its own.  However those new keys will not 'bubble' back up
to the main application.

For more information the best thing to do is to review the test case:
t/middleware-stash.t in the distribution /t directory.

## $c->error

## $c->error($error, ...)

## $c->error($arrayref)

Returns an arrayref containing error messages.  If Catalyst encounters an
error while processing a request, it stores the error in $c->error.  This
method should only be used to store fatal error messages.

    my @error = @{ $c->error };

Add a new error.

    $c->error('Something bad happened');

Calling this will always return an arrayref (if there are no errors it
will be an empty arrayref.

## $c->state

Contains the return value of the last executed action.
Note that << $c->state >> operates in a scalar context which means that all
values it returns are scalar.

## $c->clear\_errors

Clear errors.  You probably don't want to clear the errors unless you are
implementing a custom error screen.

This is equivalent to running

    $c->error(0);

## $c->has\_errors

Returns true if you have errors

## $c->last\_error

Returns the most recent error in the stack (the one most recently added...)
or nothing if there are no errors.

## shift\_errors

shifts the most recently added error off the error stack and returns if.  Returns
nothing if there are no more errors.

## COMPONENT ACCESSORS

## $c->controller($name)

Gets a [Catalyst::Controller](https://metacpan.org/pod/Catalyst::Controller) instance by name.

    $c->controller('Foo')->do_stuff;

If the name is omitted, will return the controller for the dispatched
action.

If you want to search for controllers, pass in a regexp as the argument.

    # find all controllers that start with Foo
    my @foo_controllers = $c->controller(qr{^Foo});

## $c->model($name)

Gets a [Catalyst::Model](https://metacpan.org/pod/Catalyst::Model) instance by name.

    $c->model('Foo')->do_stuff;

Any extra arguments are directly passed to ACCEPT\_CONTEXT, if the model
defines ACCEPT\_CONTEXT.  If it does not, the args are discarded.

If the name is omitted, it will look for
 - a model object in $c->stash->{current\_model\_instance}, then
 - a model name in $c->stash->{current\_model}, then
 - a config setting 'default\_model', or
 - check if there is only one model, and return it if that's the case.

If you want to search for models, pass in a regexp as the argument.

    # find all models that start with Foo
    my @foo_models = $c->model(qr{^Foo});

## $c->view($name)

Gets a [Catalyst::View](https://metacpan.org/pod/Catalyst::View) instance by name.

    $c->view('Foo')->do_stuff;

Any extra arguments are directly passed to ACCEPT\_CONTEXT.

If the name is omitted, it will look for
 - a view object in $c->stash->{current\_view\_instance}, then
 - a view name in $c->stash->{current\_view}, then
 - a config setting 'default\_view', or
 - check if there is only one view, and return it if that's the case.

If you want to search for views, pass in a regexp as the argument.

    # find all views that start with Foo
    my @foo_views = $c->view(qr{^Foo});

## $c->controllers

Returns the available names which can be passed to $c->controller

## $c->models

Returns the available names which can be passed to $c->model

## $c->views

Returns the available names which can be passed to $c->view

## $c->comp($name)

## $c->component($name)

Gets a component object by name. This method is not recommended,
unless you want to get a specific component by full
class. `$c->controller`, `$c->model`, and `$c->view`
should be used instead.

If `$name` is a regexp, a list of components matched against the full
component name will be returned.

If Catalyst can't find a component by name, it will fallback to regex
matching by default. To disable this behaviour set
disable\_component\_resolution\_regex\_fallback to a true value.

    __PACKAGE__->config( disable_component_resolution_regex_fallback => 1 );

## CLASS DATA AND HELPER CLASSES

## $c->config

Returns or takes a hashref containing the application's configuration.

    __PACKAGE__->config( { db => 'dsn:SQLite:foo.db' } );

You can also use a `YAML`, `XML` or [Config::General](https://metacpan.org/pod/Config::General) config file
like `myapp.conf` in your applications home directory. See
[Catalyst::Plugin::ConfigLoader](https://metacpan.org/pod/Catalyst::Plugin::ConfigLoader).

### Cascading configuration

The config method is present on all Catalyst components, and configuration
will be merged when an application is started. Configuration loaded with
[Catalyst::Plugin::ConfigLoader](https://metacpan.org/pod/Catalyst::Plugin::ConfigLoader) takes precedence over other configuration,
followed by configuration in your top level `MyApp` class. These two
configurations are merged, and then configuration data whose hash key matches a
component name is merged with configuration for that component.

The configuration for a component is then passed to the `new` method when a
component is constructed.

For example:

    MyApp->config({ 'Model::Foo' => { bar => 'baz', overrides => 'me' } });
    MyApp::Model::Foo->config({ quux => 'frob', overrides => 'this' });

will mean that `MyApp::Model::Foo` receives the following data when
constructed:

    MyApp::Model::Foo->new({
        bar => 'baz',
        quux => 'frob',
        overrides => 'me',
    });

It's common practice to use a Moose attribute
on the receiving component to access the config value.

    package MyApp::Model::Foo;

    use Moose;

    # this attr will receive 'baz' at construction time
    has 'bar' => (
        is  => 'rw',
        isa => 'Str',
    );

You can then get the value 'baz' by calling $c->model('Foo')->bar
(or $self->bar inside code in the model).

**NOTE:** you MUST NOT call `$self->config` or `__PACKAGE__->config`
as a way of reading config within your code, as this **will not** give you the
correctly merged config back. You **MUST** take the config values supplied to
the constructor and use those instead.

## $c->log

Returns the logging object instance. Unless it is already set, Catalyst
sets this up with a [Catalyst::Log](https://metacpan.org/pod/Catalyst::Log) object. To use your own log class,
set the logger with the `__PACKAGE__->log` method prior to calling
`__PACKAGE__->setup`.

    __PACKAGE__->log( MyLogger->new );
    __PACKAGE__->setup;

And later:

    $c->log->info( 'Now logging with my own logger!' );

Your log class should implement the methods described in
[Catalyst::Log](https://metacpan.org/pod/Catalyst::Log).

## has\_encoding

Returned True if there's a valid encoding

## clear\_encoding

Clears the encoding for the current context

## encoding

Sets or gets the application encoding.  Setting encoding takes either an
Encoding object or a string that we try to resolve via [Encode::find\_encoding](https://metacpan.org/pod/Encode::find_encoding).

You would expect to get the encoding object back if you attempt to set it.  If
there is a failure you will get undef returned and an error message in the log.

## $c->debug

Returns 1 if debug mode is enabled, 0 otherwise.

You can enable debug mode in several ways:

- By calling myapp\_server.pl with the -d flag
- With the environment variables MYAPP\_DEBUG, or CATALYST\_DEBUG
- The -Debug option in your MyApp.pm
- By declaring `sub debug { 1 }` in your MyApp.pm.

The first three also set the log level to 'debug'.

Calling `$c->debug(1)` has no effect.

## $c->dispatcher

Returns the dispatcher instance. See [Catalyst::Dispatcher](https://metacpan.org/pod/Catalyst::Dispatcher).

## $c->engine

Returns the engine instance. See [Catalyst::Engine](https://metacpan.org/pod/Catalyst::Engine).

## UTILITY METHODS

## $c->path\_to(@path)

Merges `@path` with `$c->config->{home}` and returns a
[Path::Class::Dir](https://metacpan.org/pod/Path::Class::Dir) object. Note you can usually use this object as
a filename, but sometimes you will have to explicitly stringify it
yourself by calling the `->stringify` method.

For example:

    $c->path_to( 'db', 'sqlite.db' );

## MyApp->setup

Initializes the dispatcher and engine, loads any plugins, and loads the
model, view, and controller components. You may also specify an array
of plugins to load here, if you choose to not load them in the `use
Catalyst` line.

    MyApp->setup;
    MyApp->setup( qw/-Debug/ );

**Note:** You **should not** wrap this method with method modifiers
or bad things will happen - wrap the `setup_finalize` method instead.

**Note:** You can create a custom setup stage that will execute when the
application is starting.  Use this to customize setup.

    MyApp->setup(-Custom=value);

    sub setup_custom {
      my ($class, $value) = @_;
    }

Can be handy if you want to hook into the setup phase.

## $app->setup\_finalize

A hook to attach modifiers to. This method does not do anything except set the
`setup_finished` accessor.

Applying method modifiers to the `setup` method doesn't work, because of quirky things done for plugin setup.

Example:

    after setup_finalize => sub {
        my $app = shift;

        ## do stuff here..
    };

## $c->uri\_for( $path?, @args?, \\%query\_values? )

## $c->uri\_for( $action, \\@captures?, @args?, \\%query\_values? )

## $c->uri\_for( $action, \[@captures, @args\], \\%query\_values? )

Constructs an absolute [URI](https://metacpan.org/pod/URI) object based on the application root, the
provided path, and the additional arguments and query parameters provided.
When used as a string, provides a textual URI.  If you need more flexibility
than this (i.e. the option to provide relative URIs etc.) see
[Catalyst::Plugin::SmartURI](https://metacpan.org/pod/Catalyst::Plugin::SmartURI).

If no arguments are provided, the URI for the current action is returned.
To return the current action and also provide @args, use
`$c->uri_for( $c->action, @args )`.

If the first argument is a string, it is taken as a public URI path relative
to `$c->namespace` (if it doesn't begin with a forward slash) or
relative to the application root (if it does). It is then merged with
`$c->request->base`; any `@args` are appended as additional path
components; and any `%query_values` are appended as `?foo=bar` parameters.

If the first argument is a [Catalyst::Action](https://metacpan.org/pod/Catalyst::Action) it represents an action which
will have its path resolved using `$c->dispatcher->uri_for_action`. The
optional `\@captures` argument (an arrayref) allows passing the captured
variables that are needed to fill in the paths of Chained and Regex actions;
once the path is resolved, `uri_for` continues as though a path was
provided, appending any arguments or parameters and creating an absolute
URI.

The captures for the current request can be found in
`$c->request->captures`, and actions can be resolved using
`Catalyst::Controller->action_for($name)`. If you have a private action
path, use `$c->uri_for_action` instead.

    # Equivalent to $c->req->uri
    $c->uri_for($c->action, $c->req->captures,
        @{ $c->req->args }, $c->req->params);

    # For the Foo action in the Bar controller
    $c->uri_for($c->controller('Bar')->action_for('Foo'));

    # Path to a static resource
    $c->uri_for('/static/images/logo.png');

In general the scheme of the generated URI object will follow the incoming request
however if your targeted action or action chain has the Scheme attribute it will
use that instead.

Also, if the targeted Action or Action chain declares Args/CaptureArgs that have
type constraints, we will require that your proposed URL verify on those declared
constraints.

## $c->uri\_for\_action( $path, \\@captures\_and\_args?, @args?, \\%query\_values? )

## $c->uri\_for\_action( $action, \\@captures\_and\_args?, @args?, \\%query\_values? )

- $path

    A private path to the Catalyst action you want to create a URI for.

    This is a shortcut for calling `$c->dispatcher->get_action_by_path($path)` and passing the resulting `$action` and the remaining arguments to `$c->uri_for`.

    You can also pass in a Catalyst::Action object, in which case it is passed to
    `$c->uri_for`.

    Note that although the path looks like a URI that dispatches to the wanted action, it is not a URI, but an internal path to that action.

    For example, if the action looks like:

        package MyApp::Controller::Users;

        sub lst : Path('the-list') {}

    You can use:

        $c->uri_for_action('/users/lst')

    and it will create the URI /users/the-list.

- \\@captures\_and\_args?

    Optional array reference of Captures (i.e. `<CaptureArgs or $c-`req->captures>)
    and arguments to the request. Usually used with [Catalyst::DispatchType::Chained](https://metacpan.org/pod/Catalyst::DispatchType::Chained)
    to interpolate all the parameters in the URI.

- @args?

    Optional list of extra arguments - can be supplied in the
    `\@captures_and_args?` array ref, or here - whichever is easier for your
    code.

    Your action can have zero, a fixed or a variable number of args (e.g.
    `Args(1)` for a fixed number or `Args()` for a variable number)..

- \\%query\_values?

    Optional array reference of query parameters to append. E.g.

        { foo => 'bar' }

    will generate

        /rest/of/your/uri?foo=bar

## $c->welcome\_message

Returns the Catalyst welcome HTML page.

## run\_options

Contains a hash of options passed from the application script, including
the original ARGV the script received, the processed values from that
ARGV and any extra arguments to the script which were not processed.

This can be used to add custom options to your application's scripts
and setup your application differently depending on the values of these
options.

# INTERNAL METHODS

These methods are not meant to be used by end users.

## $c->components

Returns a hash of components.

## $c->context\_class

Returns or sets the context class.

## $c->counter

Returns a hashref containing coderefs and execution counts (needed for
deep recursion detection).

## $c->depth

Returns the number of actions on the current internal execution stack.

## $c->dispatch

Dispatches a request to actions.

## $c->dispatcher\_class

Returns or sets the dispatcher class.

## $c->dump\_these

Returns a list of 2-element array references (name, structure) pairs
that will be dumped on the error page in debug mode.

## $c->engine\_class

Returns or sets the engine class.

## $c->execute( $class, $coderef )

Execute a coderef in given class and catch exceptions. Errors are available
via $c->error.

## $c->finalize

Finalizes the request.

## $c->finalize\_body

Finalizes body.

## $c->finalize\_cookies

Finalizes cookies.

## $c->finalize\_error

Finalizes error.  If there is only one error in ["error"](#error) and it is an object that
does `as_psgi` or `code` we rethrow the error and presume it caught by middleware
up the ladder.  Otherwise we return the debugging error page (in debug mode) or we
return the default error page (production mode).

## $c->finalize\_headers

Finalizes headers.

## $c->finalize\_encoding

Make sure your body is encoded properly IF you set an encoding.  By
default the encoding is UTF-8 but you can disable it by explicitly setting the
encoding configuration value to undef.

We can only encode when the body is a scalar.  Methods for encoding via the
streaming interfaces (such as `write` and `write_fh` on [Catalyst::Response](https://metacpan.org/pod/Catalyst::Response)
are available).

See ["ENCODING"](#encoding).

## $c->finalize\_output

An alias for finalize\_body.

## $c->finalize\_read

Finalizes the input after reading is complete.

## $c->finalize\_uploads

Finalizes uploads. Cleans up any temporary files.

## $c->get\_action( $action, $namespace )

Gets an action in a given namespace.

## $c->get\_actions( $action, $namespace )

Gets all actions of a given name in a namespace and all parent
namespaces.

## $app->handle\_request( @arguments )

Called to handle each HTTP request.

## $class->prepare( @arguments )

Creates a Catalyst context from an engine-specific request (Apache, CGI,
etc.).

## $c->prepare\_action

Prepares action. See [Catalyst::Dispatcher](https://metacpan.org/pod/Catalyst::Dispatcher).

## $c->prepare\_body

Prepares message body.

## $c->prepare\_body\_chunk( $chunk )

Prepares a chunk of data before sending it to [HTTP::Body](https://metacpan.org/pod/HTTP::Body).

See [Catalyst::Engine](https://metacpan.org/pod/Catalyst::Engine).

## $c->prepare\_body\_parameters

Prepares body parameters.

## $c->prepare\_connection

Prepares connection.

## $c->prepare\_cookies

Prepares cookies by ensuring that the attribute on the request
object has been built.

## $c->prepare\_headers

Prepares request headers by ensuring that the attribute on the request
object has been built.

## $c->prepare\_parameters

Prepares parameters.

## $c->prepare\_path

Prepares path and base.

## $c->prepare\_query\_parameters

Prepares query parameters.

## $c->log\_request

Writes information about the request to the debug logs.  This includes:

- Request method, path, and remote IP address
- Query keywords (see ["query\_keywords" in Catalyst::Request](https://metacpan.org/pod/Catalyst::Request#query_keywords))
- Request parameters
- File uploads

## $c->log\_response

Writes information about the response to the debug logs by calling
`$c->log_response_status_line` and `$c->log_response_headers`.

## $c->log\_response\_status\_line($response)

Writes one line of information about the response to the debug logs.  This includes:

- Response status code
- Content-Type header (if present)
- Content-Length header (if present)

## $c->log\_response\_headers($headers);

Hook method which can be wrapped by plugins to log the response headers.
No-op in the default implementation.

## $c->log\_request\_parameters( query => {}, body => {} )

Logs request parameters to debug logs

## $c->log\_request\_uploads

Logs file uploads included in the request to the debug logs.
The parameter name, filename, file type, and file size are all included in
the debug logs.

## $c->log\_request\_headers($headers);

Hook method which can be wrapped by plugins to log the request headers.
No-op in the default implementation.

## $c->log\_headers($type => $headers)

Logs [HTTP::Headers](https://metacpan.org/pod/HTTP::Headers) (either request or response) to the debug logs.

## $c->prepare\_read

Prepares the input for reading.

## $c->prepare\_request

Prepares the engine request.

## $c->prepare\_uploads

Prepares uploads.

## $c->prepare\_write

Prepares the output for writing.

## $c->request\_class

Returns or sets the request class. Defaults to [Catalyst::Request](https://metacpan.org/pod/Catalyst::Request).

## $app->request\_class\_traits

An arrayref of [Moose::Role](https://metacpan.org/pod/Moose::Role)s which are applied to the request class.  

## $app->composed\_request\_class

This is the request class which has been composed with any request\_class\_traits.

## $c->response\_class

Returns or sets the response class. Defaults to [Catalyst::Response](https://metacpan.org/pod/Catalyst::Response).

## $app->response\_class\_traits

An arrayref of [Moose::Role](https://metacpan.org/pod/Moose::Role)s which are applied to the response class.

## $app->composed\_response\_class

This is the request class which has been composed with any response\_class\_traits.

## $c->read( \[$maxlength\] )

Reads a chunk of data from the request body. This method is designed to
be used in a while loop, reading `$maxlength` bytes on every call.
`$maxlength` defaults to the size of the request if not specified.

You have to set `MyApp->config(parse_on_demand => 1)` to use this
directly.

Warning: If you use read(), Catalyst will not process the body,
so you will not be able to access POST parameters or file uploads via
$c->request.  You must handle all body parsing yourself.

## $c->run

Starts the engine.

## $c->set\_action( $action, $code, $namespace, $attrs )

Sets an action in a given namespace.

## $c->setup\_actions($component)

Sets up actions for a component.

## $c->setup\_components

This method is called internally to set up the application's components.

It finds modules by calling the [locate\_components](https://metacpan.org/pod/locate_components) method, expands them to
package names with the [expand\_component\_module](https://metacpan.org/pod/expand_component_module) method, and then installs
each component into the application.

The `setup_components` config option is passed to both of the above methods.

Installation of each component is performed by the [setup\_component](https://metacpan.org/pod/setup_component) method,
below.

## $app->setup\_injected\_components

Called by setup\_compoents to setup components that are injected.

## $app->setup\_injected\_component( $injected\_component\_name, $config )

Setup a given injected component.

## $app->inject\_component($MyApp\_Component\_name => \\%args);

Add a component that is injected at setup:

    MyApp->inject_component( 'Model::Foo' => { from_component => 'Common::Foo' } );

Must be called before ->setup.  Expects a component name for your
current application and \\%args where

- from\_component

    The target component being injected into your application

- roles

    An arrayref of [Moose::Role](https://metacpan.org/pod/Moose::Role)s that are applied to your component.

Example

    MyApp->inject_component(
      'Model::Foo' => {
        from_component => 'Common::Model::Foo',
        roles => ['Role1', 'Role2'],
      });

## $app->inject\_components

Inject a list of components:

    MyApp->inject_components(
      'Model::FooOne' => {
        from_component => 'Common::Model::Foo',
        roles => ['Role1', 'Role2'],
      },
      'Model::FooTwo' => {
        from_component => 'Common::Model::Foo',
        roles => ['Role1', 'Role2'],
      });

## $c->locate\_components( $setup\_component\_config )

This method is meant to provide a list of component modules that should be
setup for the application.  By default, it will use [Module::Pluggable](https://metacpan.org/pod/Module::Pluggable).

Specify a `setup_components` config option to pass additional options directly
to [Module::Pluggable](https://metacpan.org/pod/Module::Pluggable). To add additional search paths, specify a key named
`search_extra` as an array reference. Items in the array beginning with `::`
will have the application class name prepended to them.

## $c->expand\_component\_module( $component, $setup\_component\_config )

Components found by `locate_components` will be passed to this method, which
is expected to return a list of component (package) names to be set up.

## $app->delayed\_setup\_component

Returns a coderef that points to a setup\_component instance.  Used
internally for when you want to delay setup until the first time
the component is called.

## $c->setup\_component

## $app->config\_for( $component\_name )

Return the application level configuration (which is not yet merged with any
local component configuration, via $component\_class->config) for the named
component or component object. Example:

    MyApp->config(
      'Model::Foo' => { a => 1, b => 2},
    );

    my $config = MyApp->config_for('MyApp::Model::Foo');

In this case $config is the hashref ` {a=`1, b=>2} >.

This is also handy for looking up configuration for a plugin, to make sure you follow
existing [Catalyst](https://metacpan.org/pod/Catalyst) standards for where a plugin should put its configuration.

## $c->setup\_dispatcher

Sets up dispatcher.

## $c->setup\_engine

Sets up engine.

## $c->apply\_default\_middlewares

Adds the following [Plack](https://metacpan.org/pod/Plack) middlewares to your application, since they are
useful and commonly needed:

[Plack::Middleware::LighttpdScriptNameFix](https://metacpan.org/pod/Plack::Middleware::LighttpdScriptNameFix) (if you are using Lighttpd),
[Plack::Middleware::IIS6ScriptNameFix](https://metacpan.org/pod/Plack::Middleware::IIS6ScriptNameFix) (always applied since this middleware
is smart enough to conditionally apply itself).

We will also automatically add [Plack::Middleware::ReverseProxy](https://metacpan.org/pod/Plack::Middleware::ReverseProxy) if we notice
that your HTTP $env variable `REMOTE_ADDR` is '127.0.0.1'.  This is usually
an indication that your server is running behind a proxy frontend.  However in
2014 this is often not the case.  We preserve this code for backwards compatibility
however I **highly** recommend that if you are running the server behind a front
end proxy that you clearly indicate so with the `using_frontend_proxy` configuration
setting to true for your environment configurations that run behind a proxy.  This
way if you change your front end proxy address someday your code would inexplicably
stop working as expected.

Additionally if we detect we are using Nginx, we add a bit of custom middleware
to solve some problems with the way that server handles $ENV{PATH\_INFO} and
$ENV{SCRIPT\_NAME}.

Please **NOTE** that if you do use `using_frontend_proxy` the middleware is now
adding via `registered_middleware` rather than this method.

If you are using Lighttpd or IIS6 you may wish to apply these middlewares.  In
general this is no longer a common case but we have this here for backward
compatibility.

## App->psgi\_app

## App->to\_app

Returns a PSGI application code reference for the catalyst application
`$c`. This is the bare application created without the `apply_default_middlewares`
method called.  We do however apply `registered_middleware` since those are
integral to how [Catalyst](https://metacpan.org/pod/Catalyst) functions.  Also, unlike starting your application
with a generated server script (via [Catalyst::Devel](https://metacpan.org/pod/Catalyst::Devel) and `catalyst.pl`) we do
not attempt to return a valid [PSGI](https://metacpan.org/pod/PSGI) application using any existing `${myapp}.psgi`
scripts in your $HOME directory.

**NOTE** `apply_default_middlewares` was originally created when the first PSGI
port was done for v5.90000.  These are middlewares that are added to achieve
backward compatibility with older applications.  If you start your application
using one of the supplied server scripts (generated with [Catalyst::Devel](https://metacpan.org/pod/Catalyst::Devel) and
the project skeleton script `catalyst.pl`) we apply `apply_default_middlewares`
automatically.  This was done so that pre and post PSGI port applications would
work the same way.

This is what you want to be using to retrieve the PSGI application code
reference of your Catalyst application for use in a custom `.psgi` or in your
own created server modules.

## $c->setup\_home

Sets up the home directory.

## $c->setup\_encoding

Sets up the input/output encoding. See [ENCODING](https://metacpan.org/pod/ENCODING)

## handle\_unicode\_encoding\_exception

Hook to let you customize how encoding errors are handled.  By default
we just throw an exception.  Receives a hashref of debug information.
Example:

    $c->handle_unicode_encoding_exception({
        param_value => $value,
        error_msg => $_,
            encoding_step => 'params',
        });

## $c->setup\_log

Sets up log by instantiating a [Catalyst::Log](https://metacpan.org/pod/Catalyst::Log) object and
passing it to `log()`. Pass in a comma-delimited list of levels to set the
log to.

This method also installs a `debug` method that returns a true value into the
catalyst subclass if the "debug" level is passed in the comma-delimited list,
or if the `$CATALYST_DEBUG` environment variable is set to a true value.

Note that if the log has already been setup, by either a previous call to
`setup_log` or by a call such as `__PACKAGE__->log( MyLogger->new )`,
that this method won't actually set up the log object.

## $c->setup\_plugins

Sets up plugins.

## $c->setup\_stats

Sets up timing statistics class.

## $c->registered\_plugins

Returns a sorted list of the plugins which have either been stated in the
import list.

If passed a given plugin name, it will report a boolean value indicating
whether or not that plugin is loaded.  A fully qualified name is required if
the plugin name does not begin with `Catalyst::Plugin::`.

    if ($c->registered_plugins('Some::Plugin')) {
        ...
    }

## default\_middleware

Returns a list of instantiated PSGI middleware objects which is the default
middleware that is active for this application (taking any configuration
options into account, excluding your custom added middleware via the `psgi_middleware`
configuration option).  You can override this method if you wish to change
the default middleware (although do so at risk since some middleware is vital
to application function.)

The current default middleware list is:

      Catalyst::Middleware::Stash
      Plack::Middleware::HTTPExceptions
      Plack::Middleware::RemoveRedundantBody
      Plack::Middleware::FixMissingBodyInRedirect
      Plack::Middleware::ContentLength
      Plack::Middleware::MethodOverride
      Plack::Middleware::Head

If the configuration setting `using_frontend_proxy` is true we add:

      Plack::Middleware::ReverseProxy

If the configuration setting `using_frontend_proxy_path` is true we add:

      Plack::Middleware::ReverseProxyPath

But **NOTE** that [Plack::Middleware::ReverseProxyPath](https://metacpan.org/pod/Plack::Middleware::ReverseProxyPath) is not a dependency of the
[Catalyst](https://metacpan.org/pod/Catalyst) distribution so if you want to use this option you should add it to
your project distribution file.

These middlewares will be added at ["setup\_middleware"](#setup_middleware) during the
["setup"](#setup) phase of application startup.

## registered\_middlewares

Read only accessor that returns an array of all the middleware in the order
that they were added (which is the REVERSE of the order they will be applied).

The values returned will be either instances of [Plack::Middleware](https://metacpan.org/pod/Plack::Middleware) or of a
compatible interface, or a coderef, which is assumed to be inlined middleware

## setup\_middleware (?@middleware)

Read configuration information stored in configuration key `psgi_middleware` or
from passed @args.

See under ["CONFIGURATION"](#configuration) information regarding `psgi_middleware` and how
to use it to enable [Plack::Middleware](https://metacpan.org/pod/Plack::Middleware)

This method is automatically called during 'setup' of your application, so
you really don't need to invoke it.  However you may do so if you find the idea
of loading middleware via configuration weird :).  For example:

    package MyApp;

    use Catalyst;

    __PACKAGE__->setup_middleware('Head');
    __PACKAGE__->setup;

When we read middleware definitions from configuration, we reverse the list
which sounds odd but is likely how you expect it to work if you have prior
experience with [Plack::Builder](https://metacpan.org/pod/Plack::Builder) or if you previously used the plugin
[Catalyst::Plugin::EnableMiddleware](https://metacpan.org/pod/Catalyst::Plugin::EnableMiddleware) (which is now considered deprecated)

So basically your middleware handles an incoming request from the first
registered middleware, down and handles the response from the last middleware
up.

## registered\_data\_handlers

A read only copy of registered Data Handlers returned as a Hash, where each key
is a content type and each value is a subref that attempts to decode that content
type.

## setup\_data\_handlers (?@data\_handler)

Read configuration information stored in configuration key `data_handlers` or
from passed @args.

See under ["CONFIGURATION"](#configuration) information regarding `data_handlers`.

This method is automatically called during 'setup' of your application, so
you really don't need to invoke it.

## default\_data\_handlers

Default Data Handlers that come bundled with [Catalyst](https://metacpan.org/pod/Catalyst).  Currently there are
only two default data handlers, for 'application/json' and an alternative to
'application/x-www-form-urlencoded' which supposed nested form parameters via
[CGI::Struct](https://metacpan.org/pod/CGI::Struct) or via [CGI::Struct::XS](https://metacpan.org/pod/CGI::Struct::XS) IF you've installed it.

The 'application/json' data handler is used to parse incoming JSON into a Perl
data structure.  It used either [JSON::MaybeXS](https://metacpan.org/pod/JSON::MaybeXS) or [JSON](https://metacpan.org/pod/JSON), depending on which
is installed.  This allows you to fail back to [JSON:PP](JSON:PP), which is a Pure Perl
JSON decoder, and has the smallest dependency impact.

Because we don't wish to add more dependencies to [Catalyst](https://metacpan.org/pod/Catalyst), if you wish to
use this new feature we recommend installing [JSON](https://metacpan.org/pod/JSON) or [JSON::MaybeXS](https://metacpan.org/pod/JSON::MaybeXS) in
order to get the best performance.  You should add either to your dependency
list (Makefile.PL, dist.ini, cpanfile, etc.)

## $c->stack

Returns an arrayref of the internal execution stack (actions that are
currently executing).

## $c->stats

Returns the current timing statistics object. By default Catalyst uses
[Catalyst::Stats](https://metacpan.org/pod/Catalyst::Stats), but can be set otherwise with
[stats\_class](#c-stats_class).

Even if [-Stats](#stats) is not enabled, the stats object is still
available. By enabling it with ` $c-`stats->enabled(1) >, it can be used to
profile explicitly, although MyApp.pm still won't profile nor output anything
by itself.

## $c->stats\_class

Returns or sets the stats (timing statistics) class. [Catalyst::Stats](https://metacpan.org/pod/Catalyst::Stats) is used by default.

## $app->stats\_class\_traits

A arrayref of [Moose::Role](https://metacpan.org/pod/Moose::Role)s that are applied to the stats\_class before creating it.

## $app->composed\_stats\_class

this is the stats\_class composed with any 'stats\_class\_traits'.

## $c->use\_stats

Returns 1 when [stats collection](#stats) is enabled.

Note that this is a static method, not an accessor and should be overridden
by declaring `sub use_stats { 1 }` in your MyApp.pm, not by calling `$c->use_stats(1)`.

## $c->write( $data )

Writes $data to the output stream. When using this method directly, you
will need to manually set the `Content-Length` header to the length of
your output data, if known.

## version

Returns the Catalyst version number. Mostly useful for "powered by"
messages in template systems.

# CONFIGURATION

There are a number of 'base' config variables which can be set:

- `always_catch_http_exceptions` - As of version 5.90060 Catalyst
rethrows errors conforming to the interface described by
[Plack::Middleware::HTTPExceptions](https://metacpan.org/pod/Plack::Middleware::HTTPExceptions) and lets the middleware deal with it.
Set true to get the deprecated behaviour and have Catalyst catch HTTP exceptions.
- `default_model` - The default model picked if you say `$c->model`. See ["$c->model($name)"](#c-model-name).
- `default_view` - The default view to be rendered or returned when `$c->view` is called. See ["$c->view($name)"](#c-view-name).
- `disable_component_resolution_regex_fallback` - Turns
off the deprecated component resolution functionality so
that if any of the component methods (e.g. `$c->controller('Foo')`)
are called then regex search will not be attempted on string values and
instead `undef` will be returned.
- `home` - The application home directory. In an uninstalled application,
this is the top level application directory. In an installed application,
this will be the directory containing `MyApp.pm`.
- `ignore_frontend_proxy` - See ["PROXY SUPPORT"](#proxy-support)
- `name` - The name of the application in debug messages and the debug and
welcome screens
- `parse_on_demand` - The request body (for example file uploads) will not be parsed
until it is accessed. This allows you to (for example) check authentication (and reject
the upload) before actually receiving all the data. See ["ON-DEMAND PARSER"](#on-demand-parser)
- `root` - The root directory for templates. Usually this is just a
subdirectory of the home directory, but you can set it to change the
templates to a different directory.
- `search_extra` - Array reference passed to Module::Pluggable to for additional
namespaces from which components will be loaded (and constructed and stored in
`$c->components`).
- `show_internal_actions` - If true, causes internal actions such as `_DISPATCH`
to be shown in hit debug tables in the test server.
- `use_request_uri_for_path` - Controls if the `REQUEST_URI` or `PATH_INFO` environment
variable should be used for determining the request path.

    Most web server environments pass the requested path to the application using environment variables,
    from which Catalyst has to reconstruct the request base (i.e. the top level path to / in the application,
    exposed as `$c->request->base`) and the request path below that base.

    There are two methods of doing this, both of which have advantages and disadvantages. Which method is used
    is determined by the `$c->config(use_request_uri_for_path)` setting (which can either be true or false).

    - use\_request\_uri\_for\_path => 0

        This is the default (and the) traditional method that Catalyst has used for determining the path information.
        The path is generated from a combination of the `PATH_INFO` and `SCRIPT_NAME` environment variables.
        The allows the application to behave correctly when `mod_rewrite` is being used to redirect requests
        into the application, as these variables are adjusted by mod\_rewrite to take account for the redirect.

        However this method has the major disadvantage that it is impossible to correctly decode some elements
        of the path, as RFC 3875 says: "`Unlike a URI path, the PATH_INFO is not URL-encoded, and cannot
        contain path-segment parameters.`" This means PATH\_INFO is **always** decoded, and therefore Catalyst
        can't distinguish / vs %2F in paths (in addition to other encoded values).

    - use\_request\_uri\_for\_path => 1

        This method uses the `REQUEST_URI` and `SCRIPT_NAME` environment variables. As `REQUEST_URI` is never
        decoded, this means that applications using this mode can correctly handle URIs including the %2F character
        (i.e. with `AllowEncodedSlashes` set to `On` in Apache).

        Given that this method of path resolution is provably more correct, it is recommended that you use
        this unless you have a specific need to deploy your application in a non-standard environment, and you are
        aware of the implications of not being able to handle encoded URI paths correctly.

        However it also means that in a number of cases when the app isn't installed directly at a path, but instead
        is having paths rewritten into it (e.g. as a .cgi/fcgi in a public\_html directory, with mod\_rewrite in a
        .htaccess file, or when SSI is used to rewrite pages into the app, or when sub-paths of the app are exposed
        at other URIs than that which the app is 'normally' based at with `mod_rewrite`), the resolution of
        `$c->request->base` will be incorrect.

- `using_frontend_proxy` - See ["PROXY SUPPORT"](#proxy-support).
- `using_frontend_proxy_path` - Enabled [Plack::Middleware::ReverseProxyPath](https://metacpan.org/pod/Plack::Middleware::ReverseProxyPath) on your application (if
installed, otherwise log an error).  This is useful if your application is not running on the
'root' (or /) of your host server.  **NOTE** if you use this feature you should add the required
middleware to your project dependency list since its not automatically a dependency of [Catalyst](https://metacpan.org/pod/Catalyst).
This has been done since not all people need this feature and we wish to restrict the growth of
[Catalyst](https://metacpan.org/pod/Catalyst) dependencies.
- `encoding` - See ["ENCODING"](#encoding)

    This now defaults to 'UTF-8'.  You my turn it off by setting this configuration
    value to undef.

- `abort_chain_on_error_fix`

    When there is an error in an action chain, the default behavior is to continue
    processing the remaining actions and then catch the error upon chain end.  This
    can lead to running actions when the application is in an unexpected state.  If
    you have this issue, setting this config value to true will promptly exit a
    chain when there is an error raised in any action (thus terminating the chain
    early.)

    use like:

        __PACKAGE__->config(abort_chain_on_error_fix => 1);

    In the future this might become the default behavior.

- `use_hash_multivalue_in_request`

    In [Catalyst::Request](https://metacpan.org/pod/Catalyst::Request) the methods `query_parameters`, `body_parametes`
    and `parameters` return a hashref where values might be scalar or an arrayref
    depending on the incoming data.  In many cases this can be undesirable as it
    leads one to writing defensive code like the following:

        my ($val) = ref($c->req->parameters->{a}) ?
          @{$c->req->parameters->{a}} :
            $c->req->parameters->{a};

    Setting this configuration item to true will make [Catalyst](https://metacpan.org/pod/Catalyst) populate the
    attributes underlying these methods with an instance of [Hash::MultiValue](https://metacpan.org/pod/Hash::MultiValue)
    which is used by [Plack::Request](https://metacpan.org/pod/Plack::Request) and others to solve this very issue.  You
    may prefer this behavior to the default, if so enable this option (be warned
    if you enable it in a legacy application we are not sure if it is completely
    backwardly compatible).

- `skip_complex_post_part_handling`

    When creating body parameters from a POST, if we run into a multpart POST
    that does not contain uploads, but instead contains inlined complex data
    (very uncommon) we cannot reliably convert that into field => value pairs.  So
    instead we create an instance of [Catalyst::Request::PartData](https://metacpan.org/pod/Catalyst::Request::PartData).  If this causes
    issue for you, you can disable this by setting `skip_complex_post_part_handling`
    to true (default is false).  

- `skip_body_param_unicode_decoding`

    Generally we decode incoming POST params based on your declared encoding (the
    default for this is to decode UTF-8).  If this is causing you trouble and you
    do not wish to turn all encoding support off (with the `encoding` configuration
    parameter) you may disable this step atomically by setting this configuration
    parameter to true.

- `do_not_decode_query`

    If true, then do not try to character decode any wide characters in your
    request URL query or keywords.  Most readings of the relevent specifications
    suggest these should be UTF-\* encoded, which is the default that [Catalyst](https://metacpan.org/pod/Catalyst)
    will use, hwoever if you are creating a lot of URLs manually or have external
    evil clients, this might cause you trouble.  If you find the changes introduced
    in Catalyst version 5.90080+ break some of your query code, you may disable 
    the UTF-8 decoding globally using this configuration.

    This setting takes precedence over `default_query_encoding` and
    `decode_query_using_global_encoding`

- `default_query_encoding`

    By default we decode query and keywords in your request URL using UTF-8, which
    is our reading of the relevent specifications.  This setting allows one to
    specify a fixed value for how to decode your query.  You might need this if
    you are doing a lot of custom encoding of your URLs and not using UTF-8.

    This setting take precedence over `decode_query_using_global_encoding`.

- `decode_query_using_global_encoding`

    Setting this to true will default your query decoding to whatever your
    general global encoding is (the default is UTF-8).

- `use_chained_args_0_special_case`

    In older versions of Catalyst, when more than one action matched the same path
    AND all those matching actions declared Args(0), we'd break the tie by choosing
    the first action defined.  We now normalized how Args(0) works so that it
    follows the same rule as Args(N), which is to say when we need to break a tie
    we choose the LAST action defined.  If this breaks your code and you don't
    have time to update to follow the new normalized approach, you may set this
    value to true and it will globally revert to the original chaining behavior.

- `psgi_middleware` - See ["PSGI MIDDLEWARE"](#psgi-middleware).
- `data_handlers` - See ["DATA HANDLERS"](#data-handlers).
- `stats_class_traits`

    An arrayref of [Moose::Role](https://metacpan.org/pod/Moose::Role)s that get componsed into your stats class.

- `request_class_traits`

    An arrayref of [Moose::Role](https://metacpan.org/pod/Moose::Role)s that get componsed into your request class.

- `response_class_traits`

    An arrayref of [Moose::Role](https://metacpan.org/pod/Moose::Role)s that get componsed into your response class.

- `inject_components`

    A Hashref of [Catalyst::Component](https://metacpan.org/pod/Catalyst::Component) subclasses that are 'injected' into configuration.
    For example:

        MyApp->config({
          inject_components => {
            'Controller::Err' => { from_component => 'Local::Controller::Errors' },
            'Model::Zoo' => { from_component => 'Local::Model::Foo' },
            'Model::Foo' => { from_component => 'Local::Model::Foo', roles => ['TestRole'] },
          },
          'Controller::Err' => { a => 100, b=>200, namespace=>'error' },
          'Model::Zoo' => { a => 2 },
          'Model::Foo' => { a => 100 },
        });

    Generally [Catalyst](https://metacpan.org/pod/Catalyst) looks for components in your Model/View or Controller directories.
    However for cases when you which to use an existing component and you don't need any
    customization (where for when you can apply a role to customize it) you may inject those
    components into your application.  Please note any configuration should be done 'in the
    normal way', with a key under configuration named after the component affix, as in the
    above example.

    Using this type of injection allows you to construct significant amounts of your application
    with only configuration!.  This may or may not lead to increased code understanding.

    Please not you may also call the ->inject\_components application method as well, although
    you must do so BEFORE setup.

# EXCEPTIONS

Generally when you throw an exception inside an Action (or somewhere in
your stack, such as in a model that an Action is calling) that exception
is caught by Catalyst and unless you either catch it yourself (via eval
or something like [Try::Tiny](https://metacpan.org/pod/Try::Tiny) or by reviewing the ["error"](#error) stack, it
will eventually reach ["finalize\_errors"](#finalize_errors) and return either the debugging
error stack page, or the default error page.  However, if your exception
can be caught by [Plack::Middleware::HTTPExceptions](https://metacpan.org/pod/Plack::Middleware::HTTPExceptions), [Catalyst](https://metacpan.org/pod/Catalyst) will
instead rethrow it so that it can be handled by that middleware (which
is part of the default middleware).  For example this would allow

    use HTTP::Throwable::Factory 'http_throw';

    sub throws_exception :Local {
      my ($self, $c) = @_;

      http_throw(SeeOther => { location =>
        $c->uri_for($self->action_for('redirect')) });

    }

# INTERNAL ACTIONS

Catalyst uses internal actions like `_DISPATCH`, `_BEGIN`, `_AUTO`,
`_ACTION`, and `_END`. These are by default not shown in the private
action table, but you can make them visible with a config parameter.

    MyApp->config(show_internal_actions => 1);

# ON-DEMAND PARSER

The request body is usually parsed at the beginning of a request,
but if you want to handle input yourself, you can enable on-demand
parsing with a config parameter.

    MyApp->config(parse_on_demand => 1);

# PROXY SUPPORT

Many production servers operate using the common double-server approach,
with a lightweight frontend web server passing requests to a larger
backend server. An application running on the backend server must deal
with two problems: the remote user always appears to be `127.0.0.1` and
the server's hostname will appear to be `localhost` regardless of the
virtual host that the user connected through.

Catalyst will automatically detect this situation when you are running
the frontend and backend servers on the same machine. The following
changes are made to the request.

    $c->req->address is set to the user's real IP address, as read from
    the HTTP X-Forwarded-For header.

    The host value for $c->req->base and $c->req->uri is set to the real
    host, as read from the HTTP X-Forwarded-Host header.

Additionally, you may be running your backend application on an insecure
connection (port 80) while your frontend proxy is running under SSL.  If there
is a discrepancy in the ports, use the HTTP header `X-Forwarded-Port` to
tell Catalyst what port the frontend listens on.  This will allow all URIs to
be created properly.

In the case of passing in:

    X-Forwarded-Port: 443

All calls to `uri_for` will result in an https link, as is expected.

Obviously, your web server must support these headers for this to work.

In a more complex server farm environment where you may have your
frontend proxy server(s) on different machines, you will need to set a
configuration option to tell Catalyst to read the proxied data from the
headers.

    MyApp->config(using_frontend_proxy => 1);

If you do not wish to use the proxy support at all, you may set:

    MyApp->config(ignore_frontend_proxy => 0);

## Note about psgi files

Note that if you supply your own .psgi file, calling
`MyApp->psgi_app(@_);`, then **this will not happen automatically**.

You either need to apply [Plack::Middleware::ReverseProxy](https://metacpan.org/pod/Plack::Middleware::ReverseProxy) yourself
in your psgi, for example:

    builder {
        enable "Plack::Middleware::ReverseProxy";
        MyApp->psgi_app
    };

This will unconditionally add the ReverseProxy support, or you need to call
`$app = MyApp->apply_default_middlewares($app)` (to conditionally
apply the support depending upon your config).

See [Catalyst::PSGI](https://metacpan.org/pod/Catalyst::PSGI) for more information.

# THREAD SAFETY

Catalyst has been tested under Apache 2's threading `mpm_worker`,
`mpm_winnt`, and the standalone forking HTTP server on Windows. We
believe the Catalyst core to be thread-safe.

If you plan to operate in a threaded environment, remember that all other
modules you are using must also be thread-safe. Some modules, most notably
[DBD::SQLite](https://metacpan.org/pod/DBD::SQLite), are not thread-safe.

# DATA HANDLERS

The [Catalyst::Request](https://metacpan.org/pod/Catalyst::Request) object uses [HTTP::Body](https://metacpan.org/pod/HTTP::Body) to populate 'classic' HTML
form parameters and URL search query fields.  However it has become common
for various alternative content types to be PUT or POSTed to your controllers
and actions.  People working on RESTful APIs, or using AJAX often use JSON,
XML and other content types when communicating with an application server.  In
order to better support this use case, [Catalyst](https://metacpan.org/pod/Catalyst) defines a global configuration
option, `data_handlers`, which lets you associate a content type with a coderef
that parses that content type into something Perl can readily access.

       package MyApp::Web;
    
       use Catalyst;
       use JSON::Maybe;
    
       __PACKAGE__->config(
         data_handlers => {
           'application/json' => sub { local $/; decode_json $_->getline },
         },
         ## Any other configuration.
       );
    
       __PACKAGE__->setup;

By default [Catalyst](https://metacpan.org/pod/Catalyst) comes with a generic JSON data handler similar to the
example given above, which uses [JSON::Maybe](https://metacpan.org/pod/JSON::Maybe) to provide either [JSON::PP](https://metacpan.org/pod/JSON::PP)
(a pure Perl, dependency free JSON parser) or [Cpanel::JSON::XS](https://metacpan.org/pod/Cpanel::JSON::XS) if you have
it installed (if you want the faster XS parser, add it to you project Makefile.PL
or dist.ini, cpanfile, etc.)

The `data_handlers` configuration is a hashref whose keys are HTTP Content-Types
(matched against the incoming request type using a regexp such as to be case
insensitive) and whose values are coderefs that receive a localized version of
`$_` which is a filehandle object pointing to received body.

This feature is considered an early access release and we reserve the right
to alter the interface in order to provide a performant and secure solution to
alternative request body content.  Your reports welcomed!

# PSGI MIDDLEWARE

You can define middleware, defined as [Plack::Middleware](https://metacpan.org/pod/Plack::Middleware) or a compatible
interface in configuration.  Your middleware definitions are in the form of an
arrayref under the configuration key `psgi_middleware`.  Here's an example
with details to follow:

       package MyApp::Web;
    
       use Catalyst;
       use Plack::Middleware::StackTrace;
    
       my $stacktrace_middleware = Plack::Middleware::StackTrace->new;
    
       __PACKAGE__->config(
         'psgi_middleware', [
           'Debug',
           '+MyApp::Custom',
           $stacktrace_middleware,
           'Session' => {store => 'File'},
           sub {
             my $app = shift;
             return sub {
               my $env = shift;
               $env->{myapp.customkey} = 'helloworld';
               $app->($env);
             },
           },
         ],
       );
    
       __PACKAGE__->setup;

So the general form is:

    __PACKAGE__->config(psgi_middleware => \@middleware_definitions);

Where `@middleware` is one or more of the following, applied in the REVERSE of
the order listed (to make it function similarly to [Plack::Builder](https://metacpan.org/pod/Plack::Builder):

Alternatively, you may also define middleware by calling the ["setup\_middleware"](#setup_middleware)
package method:

    package MyApp::Web;

    use Catalyst;

    __PACKAGE__->setup_middleware( \@middleware_definitions);
    __PACKAGE__->setup;

In the case where you do both (use 'setup\_middleware' and configuration) the
package call to setup\_middleware will be applied earlier (in other words its
middleware will wrap closer to the application).  Keep this in mind since in
some cases the order of middleware is important.

The two approaches are not exclusive.

- Middleware Object

    An already initialized object that conforms to the [Plack::Middleware](https://metacpan.org/pod/Plack::Middleware)
    specification:

           my $stacktrace_middleware = Plack::Middleware::StackTrace->new;
        
           __PACKAGE__->config(
             'psgi_middleware', [
               $stacktrace_middleware,
             ]);
        
        

- coderef

    A coderef that is an inlined middleware:

           __PACKAGE__->config(
             'psgi_middleware', [
               sub {
                 my $app = shift;
                 return sub {
                   my $env = shift;
                   if($env->{PATH_INFO} =~m/forced/) {
                     Plack::App::File
                       ->new(file=>TestApp->path_to(qw/share static forced.txt/))
                       ->call($env);
                   } else {
                     return $app->($env);
                   }
                },
             },
           ]);
        
        
        

- a scalar

    We assume the scalar refers to a namespace after normalizing it using the
    following rules:

    (1) If the scalar is prefixed with a "+" (as in `+MyApp::Foo`) then the full string
    is assumed to be 'as is', and we just install and use the middleware.

    (2) If the scalar begins with "Plack::Middleware" or your application namespace
    (the package name of your Catalyst application subclass), we also assume then
    that it is a full namespace, and use it.

    (3) Lastly, we then assume that the scalar is a partial namespace, and attempt to
    resolve it first by looking for it under your application namespace (for example
    if you application is "MyApp::Web" and the scalar is "MyMiddleware", we'd look
    under "MyApp::Web::Middleware::MyMiddleware") and if we don't find it there, we
    will then look under the regular [Plack::Middleware](https://metacpan.org/pod/Plack::Middleware) namespace (i.e. for the
    previous we'd try "Plack::Middleware::MyMiddleware").  We look under your application
    namespace first to let you 'override' common [Plack::Middleware](https://metacpan.org/pod/Plack::Middleware) locally, should
    you find that a good idea.

    Examples:

           package MyApp::Web;

           __PACKAGE__->config(
             'psgi_middleware', [
               'Debug',  ## MyAppWeb::Middleware::Debug->wrap or Plack::Middleware::Debug->wrap
               'Plack::Middleware::Stacktrace', ## Plack::Middleware::Stacktrace->wrap
               '+MyApp::Custom',  ## MyApp::Custom->wrap
             ],
           );
        

- a scalar followed by a hashref

    Just like the previous, except the following `HashRef` is used as arguments
    to initialize the middleware object.

        __PACKAGE__->config(
          'psgi_middleware', [
             'Session' => {store => 'File'},
        ]);

Please see [PSGI](https://metacpan.org/pod/PSGI) for more on middleware.

# ENCODING

Starting in [Catalyst](https://metacpan.org/pod/Catalyst) version 5.90080 encoding is automatically enabled
and set to encode all body responses to UTF8 when possible and applicable.
Following is documentation on this process.  If you are using an older
version of [Catalyst](https://metacpan.org/pod/Catalyst) you should review documentation for that version since
a lot has changed.

By default encoding is now 'UTF-8'.  You may turn it off by setting
the encoding configuration to undef.

    MyApp->config(encoding => undef);

This is recommended for temporary backwards compatibility only.

Encoding is automatically applied when the content-type is set to
a type that can be encoded.  Currently we encode when the content type
matches the following regular expression:

    $content_type =~ /^text|xml$|javascript$/

Encoding is set on the application, but it is copied to the context object
so that you can override it on a request basis.

Be default we don't automatically encode 'application/json' since the most
common approaches to generating this type of response (Either via [Catalyst::View::JSON](https://metacpan.org/pod/Catalyst::View::JSON)
or [Catalyst::Action::REST](https://metacpan.org/pod/Catalyst::Action::REST)) will do so already and we want to avoid double
encoding issues.

If you are producing JSON response in an unconventional manner (such
as via a template or manual strings) you should perform the UTF8 encoding
manually as well such as to conform to the JSON specification.

NOTE: We also examine the value of $c->response->content\_encoding.  If
you set this (like for example 'gzip', and manually gzipping the body)
we assume that you have done all the necessary encoding yourself, since
we cannot encode the gzipped contents.  If you use a plugin like
[Catalyst::Plugin::Compress](https://metacpan.org/pod/Catalyst::Plugin::Compress) you need to update to a modern version in order
to have this function correctly  with the new UTF8 encoding code, or you
can use [Plack::Middleware::Deflater](https://metacpan.org/pod/Plack::Middleware::Deflater) or (probably best) do your compression on
a front end proxy.

## Methods

- encoding

    Returns an instance of an `Encode` encoding

        print $c->encoding->name

- handle\_unicode\_encoding\_exception ($exception\_context)

    Method called when decoding process for a request fails.

    An `$exception_context` hashref is provided to allow you to override the
    behaviour of your application when given data with incorrect encodings.

    The default method throws exceptions in the case of invalid request parameters
    (resulting in a 500 error), but ignores errors in upload filenames.

    The keys passed in the `$exception_context` hash are:

    - param\_value

        The value which was not able to be decoded.

    - error\_msg

        The exception received from [Encode](https://metacpan.org/pod/Encode).

    - encoding\_step

        What type of data was being decoded. Valid values are (currently)
        `params` - for request parameters / arguments / captures
        and `uploads` - for request upload filenames.

# SUPPORT

IRC:

    Join #catalyst on irc.perl.org.

Mailing Lists:

    http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/catalyst
    http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/catalyst-dev

Web:

    http://catalyst.perl.org

Wiki:

    http://dev.catalyst.perl.org

# SEE ALSO

## [Task::Catalyst](https://metacpan.org/pod/Task::Catalyst) - All you need to start with Catalyst

## [Catalyst::Manual](https://metacpan.org/pod/Catalyst::Manual) - The Catalyst Manual

## [Catalyst::Component](https://metacpan.org/pod/Catalyst::Component), [Catalyst::Controller](https://metacpan.org/pod/Catalyst::Controller) - Base classes for components

## [Catalyst::Engine](https://metacpan.org/pod/Catalyst::Engine) - Core engine

## [Catalyst::Log](https://metacpan.org/pod/Catalyst::Log) - Log class.

## [Catalyst::Request](https://metacpan.org/pod/Catalyst::Request) - Request object

## [Catalyst::Response](https://metacpan.org/pod/Catalyst::Response) - Response object

## [Catalyst::Test](https://metacpan.org/pod/Catalyst::Test) - The test suite.

# PROJECT FOUNDER

sri: Sebastian Riedel <sri@cpan.org>

# CONTRIBUTORS

abw: Andy Wardley

acme: Leon Brocard <leon@astray.com>

abraxxa: Alexander Hartmaier <abraxxa@cpan.org>

andrewalker: André Walker <andre@cpan.org>

Andrew Bramble

Andrew Ford <A.Ford@ford-mason.co.uk>

Andrew Ruthven

andyg: Andy Grundman <andy@hybridized.org>

audreyt: Audrey Tang

bricas: Brian Cassidy <bricas@cpan.org>

Caelum: Rafael Kitover <rkitover@io.com>

chansen: Christian Hansen

chicks: Christopher Hicks

Chisel Wright `pause@herlpacker.co.uk`

Danijel Milicevic `me@danijel.de`

davewood: David Schmidt <davewood@cpan.org>

David Kamholz <dkamholz@cpan.org>

David Naughton, `naughton@umn.edu`

David E. Wheeler

dhoss: Devin Austin <dhoss@cpan.org>

dkubb: Dan Kubb <dan.kubb-cpan@onautopilot.com>

Drew Taylor

dwc: Daniel Westermann-Clark <danieltwc@cpan.org>

esskar: Sascha Kiefer

fireartist: Carl Franks <cfranks@cpan.org>

frew: Arthur Axel "fREW" Schmidt <frioux@gmail.com>

gabb: Danijel Milicevic

Gary Ashton Jones

Gavin Henry `ghenry@perl.me.uk`

Geoff Richards

groditi: Guillermo Roditi <groditi@gmail.com>

hobbs: Andrew Rodland <andrew@cleverdomain.org>

ilmari: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>

jcamacho: Juan Camacho

jester: Jesse Sheidlower `jester@panix.com`

jhannah: Jay Hannah <jay@jays.net>

Jody Belka

Johan Lindstrom

jon: Jon Schutz <jjschutz@cpan.org>

Jonathan Rockway `<jrockway@cpan.org>`

Kieren Diment `kd@totaldatasolution.com`

konobi: Scott McWhirter <konobi@cpan.org>

marcus: Marcus Ramberg <mramberg@cpan.org>

miyagawa: Tatsuhiko Miyagawa <miyagawa@bulknews.net>

mgrimes: Mark Grimes <mgrimes@cpan.org>

mst: Matt S. Trout <mst@shadowcatsystems.co.uk>

mugwump: Sam Vilain

naughton: David Naughton

ningu: David Kamholz <dkamholz@cpan.org>

nothingmuch: Yuval Kogman <nothingmuch@woobling.org>

numa: Dan Sully <daniel@cpan.org>

obra: Jesse Vincent

Octavian Rasnita

omega: Andreas Marienborg

Oleg Kostyuk <cub.uanic@gmail.com>

phaylon: Robert Sedlacek <phaylon@dunkelheit.at>

rafl: Florian Ragwitz <rafl@debian.org>

random: Roland Lammel <lammel@cpan.org>

Robert Sedlacek `<rs@474.at>`

SpiceMan: Marcel Montes

sky: Arthur Bergman

szbalint: Balint Szilakszi <szbalint@cpan.org>

t0m: Tomas Doran <bobtfish@bobtfish.net>

Ulf Edvinsson

vanstyn: Henry Van Styn <vanstyn@cpan.org>

Viljo Marrandi `vilts@yahoo.com`

Will Hawes `info@whawes.co.uk`

willert: Sebastian Willert <willert@cpan.org>

wreis: Wallace Reis <wreis@cpan.org>

Yuval Kogman, `nothingmuch@woobling.org`

rainboxx: Matthias Dietrich, `perl@rainboxx.de`

dd070: Dhaval Dhanani <dhaval070@gmail.com>

Upasana <me@upasana.me>

John Napiorkowski (jnap) <jjnapiork@cpan.org>

# COPYRIGHT

Copyright (c) 2005-2015, the above named PROJECT FOUNDER and CONTRIBUTORS.

# LICENSE

This library is free software. You can redistribute it and/or modify it under
the same terms as Perl itself.