[catagits/Catalyst-Runtime.git] / lib / Catalyst / Manual / Cookbook.pod

=head1 NAME

Catalyst::Manual::Cookbook - Cooking with Catalyst

=head1 DESCRIPTION

Yummy code like your mum used to bake!

=head1 RECIPES

=head2 Force debug screen

You can force Catalyst to display the debug screen at the end of the request by
placing a C<die()> call in the C<end> action.

     sub end : Private {
         my ( $self, $c ) = @_;
         die "forced debug";
     }

If you're tired of removing and adding this all the time, you can add a
condition in the C<end> action. For example:

    sub end : Private {  
        my ( $self, $c ) = @_;  
        die "forced debug" if $c->req->params->{dump_info};  
    }  

Then just add to your query string C<"&dump_info=1">, or the like, to
force debug output.


=head2 Disable statistics

Just add this line to your application class if you don't want those nifty
statistics in your debug messages.

    sub Catalyst::Log::info { }

=head2 Scaffolding

Scaffolding is very simple with Catalyst.

The recommended way is to use Catalyst::Helper::Controller::Scaffold.

Just install this module, and to scaffold a Class::DBI Model class, do the following:

./script/myapp_create.pl controller <name> Scaffold <CDBI::Class>Scaffolding




=head2 File uploads

=head3 Single file upload with Catalyst

To implement uploads in Catalyst, you need to have a HTML form similar to
this:

    <form action="/upload" method="post" enctype="multipart/form-data">
      <input type="hidden" name="form_submit" value="yes">
      <input type="file" name="my_file">
      <input type="submit" value="Send">
    </form>

It's very important not to forget C<enctype="multipart/form-data"> in
the form.

Catalyst Controller module 'upload' action:

    sub upload : Global {
        my ($self, $c) = @_;

        if ( $c->request->parameters->{form_submit} eq 'yes' ) {

            if ( my $upload = $c->request->upload('my_file') ) {

                my $filename = $upload->filename;
                my $target   = "/tmp/upload/$filename";

                unless ( $upload->link_to($target) || $upload->copy_to($target) ) {
                    die( "Failed to copy '$filename' to '$target': $!" );
                }
            }
        }

        $c->stash->{template} = 'file_upload.html';
    }

=head3 Multiple file upload with Catalyst

Code for uploading multiple files from one form needs a few changes:

The form should have this basic structure:

    <form action="/upload" method="post" enctype="multipart/form-data">
      <input type="hidden" name="form_submit" value="yes">
      <input type="file" name="file1" size="50"><br>
      <input type="file" name="file2" size="50"><br>
      <input type="file" name="file3" size="50"><br>
      <input type="submit" value="Send">
    </form>

And in the controller:

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

        if ( $c->request->parameters->{form_submit} eq 'yes' ) {

            for my $field ( $c->req->upload ) {

                my $upload   = $c->req->upload($field);
                my $filename = $upload->filename;
                my $target   = "/tmp/upload/$filename";

                unless ( $upload->link_to($target) || $upload->copy_to($target) ) {
                    die( "Failed to copy '$filename' to '$target': $!" );
                }
            }
        }

        $c->stash->{template} = 'file_upload.html';
    }

C<for my $field ($c-E<gt>req->upload)> loops automatically over all file
input fields and gets input names. After that is basic file saving code,
just like in single file upload.

Notice: C<die>ing might not be what you want to do, when an error
occurs, but it works as an example. A better idea would be to store
error C<$!> in $c->stash->{error} and show a custom error template
displaying this message.

For more information about uploads and usable methods look at
L<Catalyst::Request::Upload> and L<Catalyst::Request>.

=head2 Authentication with Catalyst::Plugin::Authentication

In this example, we'll use the
L<Catalyst::Plugin::Authentication::Store::DBIC> store and the
L<Catalyst::Plugin::Authentication::Credential::Password> credentials.

In the lib/MyApp.pm package, we'll need to change the C<use Catalyst;>
line to include the following modules:

    use Catalyst qw/
        ConfigLoader 
        Authentication
        Authentication::Store::DBIC
        Authentication::Credential::Password
        Session
        Session::Store::FastMmap
        Session::State::Cookie
        HTML::Widget
        Static::Simple
        /;

The Session, Session::Store::* and Session::State::* modules listed above
ensure that we stay logged-in across multiple page-views.

In our MyApp.yml configuration file, we'll need to add:

    authentication:
      dbic:
        user_class: MyApp::Model::DBIC::User
        user_field: username
        password_field: password
        password_type: hashed
        password_hash_type: SHA-1

'user_class' is a DBIx::Class package for your users table.
'user_field' tells which field (column) is used for username lookup.
'password_field' is the password field in your table.
The above settings for 'password_type' and 'password_hash_type' ensure that
the password won't be stored in the database in clear text.

In SQLite, the users table might be something like:

    CREATE TABLE user (
        id       INTEGER PRIMARY KEY,
        username VARCHAR(100),
        password VARCHAR(100)
    );

Now we need to create a DBIC::SchemaLoader component for this database
(changing "myapp.db" to wherever your SQLite database is).

    script/myapp_create.pl model DBIC DBIC::SchemaLoader 'dbi:SQLite:myapp.db'

Now we can start creating our page controllers and templates.
For our homepage, we create the file "root/index.tt" containing:

    <html>
    <body>
    [% IF c.user %]
        <p>hello [% c.user.username %]</p>
        <p><a href="[% c.uri_for( '/logout' ) %]">logout</a></p>
    [% ELSE %]
        <p><a href="[% c.uri_for( '/login' ) %]">login</a></p>
    [% END %]
    </body>
    </html>

If the user is logged in, they will be shown their name, and a logout link.
Otherwise, they will be shown a login link.

To display the homepage, we can uncomment the C<default> and C<end>
subroutines in lib/MyApp/Controller/Root.pm and populate them as so:

    sub default : Private {
        my ( $self, $c ) = @_;
    
        $c->stash->{template} = 'index.tt';
    }

    sub end : Private {
        my ( $self, $c ) = @_;
    
        $c->forward( $c->view('TT') )
            unless $c->response->body || $c->response->redirect;
    }

The login template is very simple, as L<HTML::Widget> will handle the
HTML form creation for use. This is saved as "root/login.tt".

    <html>
    <head>
    <link href="[% c.uri_for('/static/simple.css') %]" rel="stylesheet" type="text/css">
    </head>
    <body>
    [% result %]
    </body>
    </html>

For the HTML form to look correct, we also copy the C<simple.css> file
from the L<HTML::Widget> distribution into our "root/static" folder.
This file is automatically server by the L<Catalyst::Plugin::Static::Simple>
module which we loaded in our lib/MyApp.pm package.

To handle login requests, we first create a controller, like so:

    script/myapp_create.pl controller Login

In the lib/MyApp/Controller/Login.pm package, we can then uncomment the
C<default> subroutine, and populate it, as below.

First the widget is created, it needs the 'action' set, and 'username' and
'password' fields and a submit button added.

Then, if we've received a username and password in the request, we attempt
to login. If successful, we redirect to the homepage; if not the login form
will be displayed again.

    sub default : Private {
        my ( $self, $c ) = @_;
    
        $c->widget->method('POST')->action( $c->uri_for('/login') );
        $c->widget->element( 'Textfield', 'username' )->label( 'Username' );
        $c->widget->element( 'Password', 'password' )->label( 'Password' );
        $c->widget->element( 'Submit' )->value( 'Login' );
        
        my $result = $c->widget->process( $c->req );
        
        if ( my $user = $result->param('username')
            and my $pass = $result->param('password') )
        {    
            if ( $c->login( $user, $pass ) ) {
                $c->response->redirect( $c->uri_for( "/" ) );
                return;
            }
        }
        
        $c->stash->{template} = 'login.tt';
        $c->stash->{result}   = $result;
    }

To handle logout's, we create a new controller:

    script/myapp_create.pl controller Logout

Then in the lib/MyApp/Controller/Logout.pm package, we change the
C<default> subroutine, to logout and then redirect back to the
homepage.

    sub default : Private {
        my ( $self, $c ) = @_;
    
        $c->logout;
        
        $c->response->redirect( $c->uri_for( "/" ) );
    }

Remember that to test this, we would first need to add a user to the
database, ensuring that the password field is saved as the SHA1 hash
of our desired password.


=head2 Pass-through login (and other actions)

An easy way of having assorted actions that occur during the processing
of a request that are orthogonal to its actual purpose - logins, silent
commands etc. Provide actions for these, but when they're required for
something else fill e.g. a form variable __login and have a sub begin
like so:

    sub begin : Private {
      my ($self, $c) = @_;
      foreach my $action (qw/login docommand foo bar whatever/) {
        if ($c->req->params->{"__${action}"}) {
          $c->forward($action);
        }
      }
    }

=head2 How to use Catalyst without mod_perl

Catalyst applications give optimum performance when run under mod_perl.
However sometimes mod_perl is not an option, and running under CGI is 
just too slow.  There's also an alternative to mod_perl that gives
reasonable performance named FastCGI.

=head3 Using FastCGI

To quote from L<http://www.fastcgi.com/>: "FastCGI is a language 
independent, scalable, extension to CGI that provides high performance 
without the limitations of specific server APIs."  Web server support 
is provided for Apache in the form of C<mod_fastcgi> and there is Perl
support in the C<FCGI> module.  To convert a CGI Catalyst application 
to FastCGI one needs to initialize an C<FCGI::Request> object and loop 
while the C<Accept> method returns zero.  The following code shows how 
it is done - and it also works as a normal, single-shot CGI script.

    #!/usr/bin/perl
    use strict;
    use FCGI;
    use MyApp;

    my $request = FCGI::Request();
    while ($request->Accept() >= 0) {
        MyApp->run;
    }

Any initialization code should be included outside the request-accept 
loop.

There is one little complication, which is that C<MyApp-E<gt>run> outputs a
complete HTTP response including the status line (e.g.: 
"C<HTTP/1.1 200>").
FastCGI just wants a set of headers, so the sample code captures the 
output and  drops the first line if it is an HTTP status line (note: 
this may change).

The Apache C<mod_fastcgi> module is provided by a number of Linux 
distro's and is straightforward to compile for most Unix-like systems.  
The module provides a FastCGI Process Manager, which manages FastCGI 
scripts.  You configure your script as a FastCGI script with the 
following Apache configuration directives:

    <Location /fcgi-bin>
       AddHandler fastcgi-script fcgi
    </Location>

or:

    <Location /fcgi-bin>
       SetHandler fastcgi-script
       Action fastcgi-script /path/to/fcgi-bin/fcgi-script
    </Location>

C<mod_fastcgi> provides a number of options for controlling the FastCGI
scripts spawned; it also allows scripts to be run to handle the
authentication, authorization, and access check phases.

For more information see the FastCGI documentation, the C<FCGI> module 
and L<http://www.fastcgi.com/>.

=head2 Serving static content

Serving static content in Catalyst can be somewhat tricky; this recipe
shows one possible solution. Using this recipe will serve all static
content through Catalyst when developing with the built-in HTTP::Daemon
server, and will make it easy to use Apache to serve the content when
your app goes into production.

Static content is best served from a single directory within your root
directory. Having many different directories such as C<root/css> and
C<root/images> requires more code to manage, because you must separately
identify each static directory--if you decide to add a C<root/js>
directory, you'll need to change your code to account for it. In
contrast, keeping all static directories as subdirectories of a main
C<root/static> directory makes things much easier to manager. Here's an
example of a typical root directory structure:

    root/
    root/content.tt
    root/controller/stuff.tt
    root/header.tt
    root/static/
    root/static/css/main.css
    root/static/images/logo.jpg
    root/static/js/code.js


All static content lives under C<root/static> with everything else being
Template Toolkit files. Now you can identify the static content by
matching C<static> from within Catalyst.

=head3 Serving with HTTP::Daemon (myapp_server.pl)

To serve these files under the standalone server, we first must load the
Static plugin. Install L<Catalyst::Plugin::Static> if it's not already
installed.

In your main application class (MyApp.pm), load the plugin:

    use Catalyst qw/-Debug FormValidator Static OtherPlugin/;

You will also need to make sure your end method does I<not> forward
static content to the view, perhaps like this:

    sub end : Private {
        my ( $self, $c ) = @_;

        $c->forward( 'MyApp::View::TT' ) 
          unless ( $c->res->body || !$c->stash->{template} );
    }

This code will only forward to the view if a template has been
previously defined by a controller and if there is not already data in
C<$c-E<gt>res-E<gt>body>.

Next, create a controller to handle requests for the /static path. Use
the Helper to save time. This command will create a stub controller as
C<lib/MyApp/Controller/Static.pm>.

    $ script/myapp_create.pl controller Static

Edit the file and add the following methods:

    # serve all files under /static as static files
    sub default : Path('/static') {
        my ( $self, $c ) = @_;

        # Optional, allow the browser to cache the content
        $c->res->headers->header( 'Cache-Control' => 'max-age=86400' );

        $c->serve_static; # from Catalyst::Plugin::Static
    }

    # also handle requests for /favicon.ico
    sub favicon : Path('/favicon.ico') {
        my ( $self, $c ) = @_;

        $c->serve_static;
    }

You can also define a different icon for the browser to use instead of
favicon.ico by using this in your HTML header:

    <link rel="icon" href="/static/myapp.ico" type="image/x-icon" />

=head3 Common problems

The Static plugin makes use of the C<shared-mime-info> package to
automatically determine MIME types. This package is notoriously
difficult to install, especially on win32 and OS X. For OS X the easiest
path might be to install Fink, then use C<apt-get install
shared-mime-info>. Restart the server, and everything should be fine.

Make sure you are using the latest version (>= 0.16) for best
results. If you are having errors serving CSS files, or if they get
served as text/plain instead of text/css, you may have an outdated
shared-mime-info version. You may also wish to simply use the following
code in your Static controller:

    if ($c->req->path =~ /css$/i) {
        $c->serve_static( "text/css" );
    } else {
        $c->serve_static;
    }

=head3 Serving with Apache

When using Apache, you can completely bypass Catalyst and the Static
controller by intercepting requests for the C<root/static> path at the
server level. All that is required is to define a DocumentRoot and add a
separate Location block for your static content. Here is a complete
config for this application under mod_perl 1.x:

    <Perl>
        use lib qw(/var/www/MyApp/lib);
    </Perl>
    PerlModule MyApp

    <VirtualHost *>
        ServerName myapp.example.com
        DocumentRoot /var/www/MyApp/root
        <Location />
            SetHandler perl-script
            PerlHandler MyApp
        </Location>
        <LocationMatch "/(static|favicon.ico)">
            SetHandler default-handler
        </LocationMatch>
    </VirtualHost>

And here's a simpler example that'll get you started:

    Alias /static/ "/my/static/files/"
    <Location "/static">
        SetHandler none
    </Location>

=head2 Forwarding with arguments

Sometimes you want to pass along arguments when forwarding to another
action. As of version 5.30, arguments can be passed in the call to
C<forward>; in earlier versions, you can manually set the arguments in
the Catalyst Request object:

  # version 5.30 and later:
  $c->forward('/wherever', [qw/arg1 arg2 arg3/]);

  # pre-5.30
  $c->req->args([qw/arg1 arg2 arg3/]);
  $c->forward('/wherever');

(See the L<Catalyst::Manual::Intro> Flow_Control section for more 
information on passing arguments via C<forward>.)

=head2 Configure your application

You configure your application with the C<config> method in your
application class. This can be hard-coded, or brought in from a
separate configuration file.

=head3 Using YAML

YAML is a method for creating flexible and readable configuration
files. It's a great way to keep your Catalyst application configuration
in one easy-to-understand location.

In your application class (e.g. C<lib/MyApp.pm>):

  use YAML;
  # application setup
  __PACKAGE__->config( YAML::LoadFile(__PACKAGE__->config->{'home'} . '/myapp.yml') );
  __PACKAGE__->setup;

Now create C<myapp.yml> in your application home:

  --- #YAML:1.0
  # DO NOT USE TABS FOR INDENTATION OR label/value SEPARATION!!!
  name:     MyApp

  # session; perldoc Catalyst::Plugin::Session::FastMmap
  session:
    expires:        '3600'
    rewrite:        '0'
    storage:        '/tmp/myapp.session'

  # emails; perldoc Catalyst::Plugin::Email
  # this passes options as an array :(
  email:
    - SMTP
    - localhost

This is equivalent to:

  # configure base package
  __PACKAGE__->config( name => MyApp );
  # configure authentication
  __PACKAGE__->config->{authentication} = {
    user_class => 'MyApp::Model::MyDB::Customer',
    ...
  };
  # configure sessions
  __PACKAGE__->config->{session} = {
    expires => 3600,
    ...
  };
  # configure email sending
  __PACKAGE__->config->{email} = [qw/SMTP localhost/];

See also L<YAML>.

=head2 Using existing DBIC (etc.) classes with Catalyst

Many people have existing Model classes that they would like to use with
Catalyst (or, conversely, they want to write Catalyst models that can be
used outside of Catalyst, e.g.  in a cron job). It's trivial to write a
simple component in Catalyst that slurps in an outside Model:

    package MyApp::Model::DB;
    use base qw/Catalyst::Model::DBIC::Schema/;
    __PACKAGE__->config(
        schema_class => 'Some::DBIC::Schema',
        connect_info => ['dbi:SQLite:foo.db', '', '', {AutoCommit=>1}];
    );
    1;

and that's it! Now C<Some::DBIC::Schema> is part of your
Cat app as C<MyApp::Model::DB>.

=head2 Delivering a Custom Error Page

By default, Catalyst will display its own error page whenever it
encounters an error in your application. When running under C<-Debug>
mode, the error page is a useful screen including the error message and
L<Data::Dump> output of the relevant parts of the C<$c> context object. 
When not in C<-Debug>, users see a simple "Please come back later" screen.

To use a custom error page, use a special C<end> method to short-circuit
the error processing. The following is an example; you might want to
adjust it further depending on the needs of your application (for
example, any calls to C<fillform> will probably need to go into this
C<end> method; see L<Catalyst::Plugin::FillInForm>).

    sub end : Private {
        my ( $self, $c ) = @_;

        if ( scalar @{ $c->error } ) {
            $c->stash->{errors}   = $c->error;
            $c->stash->{template} = 'errors.tt';
            $c->forward('MyApp::View::TT');
            $c->error(0);
        }

        return 1 if $c->response->status =~ /^3\d\d$/;
        return 1 if $c->response->body;

        unless ( $c->response->content_type ) {
            $c->response->content_type('text/html; charset=utf-8');
        }

        $c->forward('MyApp::View::TT');
    }

You can manually set errors in your code to trigger this page by calling

    $c->error( 'You broke me!' );

=head2 Require user logins

It's often useful to restrict access to your application to a set of
registered users, forcing everyone else to the login page until they're
signed in.

To implement this in your application make sure you have a customer
table with username and password fields and a corresponding Model class
in your Catalyst application, then make the following changes:

=head3 lib/MyApp.pm

  use Catalyst qw/
      Authentication
      Authentication::Store::DBIC
      Authentication::Credential::Password
  /;

  __PACKAGE__->config->{authentication}->{dbic} = {
    'user_class'        => 'My::Model::DBIC::User',
    'user_field'        => 'username',
    'password_field'    => 'password'
    'password_type'     => 'hashed',
    'password_hash_type'=> 'SHA-1'
  };

  sub auto : Private {
    my ($self, $c) = @_;
    my $login_path = 'user/login';

    # allow people to actually reach the login page!
    if ($c->request->path eq $login_path) {
      return 1;
    }

    # if a user doesn't exist, force login
    if ( !$c->user_exists ) {
      # force the login screen to be shown
      $c->response->redirect($c->request->base . $login_path);
    }

    # otherwise, we have a user - continue with the processing chain
    return 1;
  }

=head3 lib/MyApp/Controller/User.pm

  sub login : Path('/user/login') {
    my ($self, $c) = @_;

    # default template
    $c->stash->{'template'} = "user/login.tt";
    # default form message
    $c->stash->{'message'} = 'Please enter your username and password';

    if ( $c->request->param('username') ) {
      # try to log the user in
      # login() is provided by ::Authentication::Credential::Password
      if( $c->login(
        $c->request->param('username'),
        $c->request->param('password'),
        ) {

        # if login() returns 1, user is now logged in
        $c->response->redirect('/some/page');
      }

      # otherwise we failed to login, try again!
      $c->stash->{'message'} = 
         'Unable to authenticate the login details supplied';
    }
  }

  sub logout : Path('/user/logout') {
    my ($self, $c) = @_;
    # log the user out
    $c->logout;

    # do the 'default' action
    $c->response->redirect($c->request->base);
  }


=head3 root/base/user/login.tt

 [% INCLUDE header.tt %]
 <form action="/user/login" method="POST" name="login_form">
    [% message %]<br />
    <label for="username">username:</label><br />
    <input type="text" id="username" name="username" /><br />

    <label for="password">password:</label><br />
    <input type="password" id="password" name="password" /><br />

    <input type="submit" value="log in" name="form_submit" />
  </form>
  [% INCLUDE footer.tt %]

=head2 Role-based Authorization

For more advanced access control, you may want to consider using role-based
authorization. This means you can assign different roles to each user, e.g.
"user", "admin", etc.

The C<login> and C<logout> methods and view template are exactly the same as
in the previous example.

The L<Catalyst::Plugin::Authorization::Roles> plugin is required when
implementing roles:

 use Catalyst qw/
    Authentication
    Authentication::Credential::Password
    Authentication::Store::Htpasswd
    Authorization::Roles
  /;

Roles are implemented automatically when using
L<Catalyst::Authentication::Store::Htpasswd>:

  # no additional role configuration required
  __PACKAGE__->config->{authentication}{htpasswd} = "passwdfile";

Or can be set up manually when using L<Catalyst::Authentication::Store::DBIC>:

  # Authorization using a many-to-many role relationship
  __PACKAGE__->config->{authorization}{dbic} = {
    'role_class'           => 'My::Model::DBIC::Role',
    'role_field'           => 'name',
    'user_role_user_field' => 'user',

    # DBIx::Class only (omit if using Class::DBI)
    'role_rel'             => 'user_role',

    # Class::DBI only, (omit if using DBIx::Class)
    'user_role_class'      => 'My::Model::CDBI::UserRole'
    'user_role_role_field' => 'role',
  };

To restrict access to any action, you can use the C<check_user_roles> method:

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

     $c->detach("unauthorized")
       unless $c->check_user_roles( "admin" );

     # do something restricted here
  }

You can also use the C<assert_user_roles> method. This just gives an error if
the current user does not have one of the required roles:

  sub also_restricted : Global {
    my ( $self, $c ) = @_;
    $c->assert_user_roles( qw/ user admin / );
  }
  
=head2 Building PAR Packages

You know the problem, you got a application perfectly running on your
development box, but then *shudder* you have to quickly move it to
another one for demonstration/deployment/testing...

PAR packages can save you from a lot of trouble here.
They are usual Zip files that contain a blib tree, you can even
include all prereqs and a perl interpreter by setting a few flags!

=head3 Follow these few points to try it out!

1. Install Catalyst 5.61 (or later) and PAR 0.89

    % perl -MCPAN -e 'install Catalyst'
    ...
    % perl -MCPAN -e 'install PAR'
    ...

2. Create a application

    % catalyst.pl MyApp
    ...
    % cd MyApp

3. Add these lines to Makefile.PL (below "catalyst_files();")

    catalyst_par_core();   # Include modules that are also included
                           # in the standard Perl distribution,
                           # this is optional but highly suggested

    catalyst_par();        # Generate a PAR as soon as the blib
                           # directory is ready

4. Prepare the Makefile, test your app, create a PAR (the two Makefile.PL calls are no typo)

    % perl Makefile.PL
    ...
    % make test
    ...
    % perl Makefile.PL
    ...

Future versions of Catalyst (5.62 and newer) will use a similar but more elegant calling convention.

    % perl Makefile.PL
    ...
    % make catalyst_par
    ...

Congratulations! Your package "myapp.par" is ready, the following
steps are just optional.

5. Test your PAR package with "parl" (no typo) :)

    % parl myapp.par
    Usage:
        [parl] myapp[.par] [script] [arguments]

      Examples:
        parl myapp.par myapp_server.pl -r
        myapp myapp_cgi.pl

      Available scripts:
        myapp_cgi.pl
        myapp_create.pl
        myapp_fastcgi.pl
        myapp_server.pl
        myapp_test.pl

    % parl myapp.par myapp_server.pl
    You can connect to your server at http://localhost:3000

Yes, this nifty little starter application gets automatically included.
You can also use "catalyst_par_script('myapp_server.pl')" to set a
default script to execute.

6. Want to create a binary that includes the Perl interpreter? No
problem!

    % pp -o myapp myapp.par
    % ./myapp myapp_server.pl
    You can connect to your server at http://localhost:3000

=head2 mod_perl Deployment

In today's entry, I'll be talking about deploying an application in
production using Apache and mod_perl.

=head3 Pros & Cons

mod_perl is the best solution for many applications, but I'll list some pros
and cons so you can decide for yourself.  The other production deployment
option is FastCGI, which I'll talk about in a future calendar article.

=head4 Pros

=head4 Speed

mod_perl is very fast and your app will benefit from being loaded in memory
within each Apache process.

=head4 Shared memory for multiple apps

If you need to run several Catalyst apps on the same server, mod_perl will
share the memory for common modules.

=head4 Cons

=head4 Memory usage

Since your application is fully loaded in memory, every Apache process will
be rather large.  This means a large Apache process will be tied up while
serving static files, large files, or dealing with slow clients.  For this
reason, it is best to run a two-tiered web architecture with a lightweight
frontend server passing dynamic requests to a large backend mod_perl
server.

=head4 Reloading

Any changes made to the core code of your app require a full Apache restart.
Catalyst does not support Apache::Reload or StatINC.  This is another good
reason to run a frontend web server where you can set up an
C<ErrorDocument 502> page to report that your app is down for maintenance.

=head4 Cannot run multiple versions of the same app

It is not possible to run two different versions of the same application in
the same Apache instance because the namespaces will collide.

=head4 Setup

Now that we have that out of the way, let's talk about setting up mod_perl
to run a Catalyst app.

=head4 1. Install Catalyst::Engine::Apache

You should install the latest versions of both Catalyst and 
Catalyst::Engine::Apache.  The Apache engines were separated from the
Catalyst core in version 5.50 to allow for updates to the engine without
requiring a new Catalyst release.

=head4 2. Install Apache with mod_perl

Both Apache 1.3 and Apache 2 are supported, although Apache 2 is highly
recommended.  With Apache 2, make sure you are using the prefork MPM and not
the worker MPM.  The reason for this is that many Perl modules are not
thread-safe and may have problems running within the threaded worker
environment.  Catalyst is thread-safe however, so if you know what you're
doing, you may be able to run using worker.

In Debian, the following commands should get you going.

    apt-get install apache2-mpm-prefork
    apt-get install libapache2-mod-perl2

=head4 3. Configure your application

Every Catalyst application will automagically become a mod_perl handler
when run within mod_perl.  This makes the configuration extremely easy.
Here is a basic Apache 2 configuration.

    PerlSwitches -I/var/www/MyApp/lib
    PerlModule MyApp
    
    <Location />
        SetHandler          modperl
        PerlResponseHandler MyApp
    </Location>

The most important line here is C<PerlModule MyApp>.  This causes mod_perl
to preload your entire application into shared memory, including all of your
controller, model, and view classes and configuration.  If you have -Debug
mode enabled, you will see the startup output scroll by when you first
start Apache.

For an example Apache 1.3 configuration, please see the documentation for
L<Catalyst::Engine::Apache::MP13>.

=head3 Test It

That's it, your app is now a full-fledged mod_perl application!  Try it out
by going to http://your.server.com/.

=head3 Other Options

=head4 Non-root location

You may not always want to run your app at the root of your server or virtual
host.  In this case, it's a simple change to run at any non-root location
of your choice.

    <Location /myapp>
        SetHandler          modperl
        PerlResponseHandler MyApp
    </Location>
    
When running this way, it is best to make use of the C<uri_for> method in
Catalyst for constructing correct links.

=head4 Static file handling

Static files can be served directly by Apache for a performance boost.

    DocumentRoot /var/www/MyApp/root
    <Location /static>
        SetHandler default-handler
    </Location>
    
This will let all files within root/static be handled directly by Apache.  In
a two-tiered setup, the frontend server should handle static files.
The configuration to do this on the frontend will vary.

=head2 Don't Repeat Yourself

DRY is a central principle in Catalyst, yet there is one piece of code
that is identical in 90% of all Catalyst applications.

  sub end : Private {
      my ($self,$c) = @_;
      return 1 if $c->res->body;
      return 1 if $c->response->status =~ /^3\d\d$/;
      $c->forward( 'MyApp::View::TT' );
  }

Basically, we want to render a template unless we already have a response,
or are redirecting. 

=head3 Catalyst::Plugin::DefaultEnd to the rescue!

So, rather than doing this again and again, I've made a plugin for you to use.
sure, it's not much code, but at least it's one function less to worry about.

Here's how to use it:

1. Open up MyApp.pm.

2. Add the DefaultEnd plugin like this:

  use Catalyst qw/-Debug DefaultEnd Static::Simple/;
  
3.  There is no step 3 :)

As an added bonus, you can now set dump_info=1 as a url parameter to force 
the end action to die, and display the debug info. Note that this is only
provided in Debug mode.

By default, DefaultEnd will forward to the first view it can find. If you have
more than one view, you might want to specifiy the active one, by setting 
$c->config->{view}.

If you need to add more things to your end action, you can extend it like this.

  sub end : Private {
      my ( $self, $c ) = @_;

      ... #code before view

      $c->NEXT::end( $c );
  
      ... #code after view
  }
  
=head2 YAML, YAML, YAML!

When you start a new Catalyst app you configure it directly
with __PACKAGE__->config, thats ok for development but admins
will hate you when they have to deploy this.

    __PACKAGE__->config( name => 'MyApp', 'View::TT' => { EVAL_PERL => 1 } );

You didn't know you could configure your view from the application class, eh? :)
Thats possible for every component that inherits from Catalyst::Component
or it's subclasses (Catalyst::Base, Catalyst::Controller, Catalyst::View,
Catalyst::Model).

    __PACKAGE__->config(
        name => 'MyApp',
        'View::TT' => {
            EVAL_PERL => 1
        },
        'Controller::Foo' => {
            fool => 'sri'
        }
    );
    
    
    package MyApp::Controller::Foo;
    use base 'Catalyst::Controller';
    
    __PACKAGE__->config( lalala => " can't sing!" );
    
    sub default : Private {
        my ( $self, $c ) = @_;
        $c->res->body( $self->{fool} . $self->{lalala} );
    }

But back to the topic, lets make our admins happy with this little idiom.

    use YAML ();
    
    __PACKAGE__->config( YAML::LoadFile( __PACKAGE__->path_to('myapp.yml') ) );

The C<path_to()> method is a nice little helper that returns paths relative to the
current application home.

Thats it, now just create a file C<myapp.yml>.

    ---
    name: MyApp
    View::TT:
      EVAL_PERL: 1
    Controller::Foo:
      fool: sri

=head2 Catalyst on shared hosting

So, you want to put your Catalyst app out there for the whole world to
see, but you don't want to break the bank. There is an answer - if you can
get shared hosting with FastCGI and a shell, you can install your Catalyst
app. First, run

  perl -MCPAN -e shell

and go through the standard CPAN configuration process. Then exit out
without installing anything. Next, open your .bashrc and add

  export PATH=$HOME/local/bin:$HOME/local/script:$PATH
  perlversion=`perl -v | grep 'built for' | awk '{print $4}' | sed -e 's/v//;'`
  export PERL5LIB=$HOME/local/share/perl/$perlversion:$HOME/local/lib/perl/$perlversion:$HOME/local/lib:$PERL5LIB

and log out, then back in again (or run ". .bashrc" if you prefer). Finally,
edit .cpan/CPAN/MyConfig.pm and add

  'make_install_arg' => qq[SITEPREFIX=$ENV{HOME}/local],
  'makepl_arg' => qq[INSTALLDIRS=site install_base=$ENV{HOME}/local],

Now you can install the modules you need with CPAN as normal, and perl will
pick them up. Finally, change directory into the root of your virtual host
and symlink your application's script directory in -

  cd path/to/mydomain.com
  ln -s ~/lib/MyApp/script script

And add the following lines to your .htaccess file (assuming the server is
setup to handle .pl as fcgi - you may need to rename the script to
myapp_fastcgi.fcgi and/or use a SetHandler directive) -

  RewriteEngine On
  RewriteCond %{REQUEST_URI} !^/?script/myapp_fastcgi.pl
  RewriteRule ^(.*)$ script/myapp_fastcgi.pl/$1 [PT,L]

http://mydomain.com/ should now Just Work. Congratulations, now you can
tell your friends about your new website (or in our case, tell the client
it's time to pay the invoice :)

=head2 Caching

Catalyst makes it easy to employ several different types of caching to speed
up your applications.

=head3 Cache Plugins

There are three wrapper plugins around common CPAN cache modules:
Cache::FastMmap, Cache::FileCache, and Cache::Memcached.  These can be used
to cache the result of slow operations. 

This very page you're viewing makes use of the FileCache plugin to cache the
rendered XHTML version of the source POD document.  This is an ideal
application for a cache because the source document changes infrequently but
may be viewed many times.

    use Catalyst qw/Cache::FileCache/;
    
    ...
    
    use File::stat;
    sub render_pod : Local {
        my ( self, $c ) = @_;
        
        # the cache is keyed on the filename and the modification time
        # to check for updates to the file.
        my $file  = $c->path_to( 'root', '2005', '11.pod' );
        my $mtime = ( stat $file )->mtime;
        
        my $cached_pod = $c->cache->get("$file $mtime");
        if ( !$cached_pod ) {
            $cached_pod = do_slow_pod_rendering();
            # cache the result for 12 hours
            $c->cache->set( "$file $mtime", $cached_pod, '12h' );
        }
        $c->stash->{pod} = $cached_pod;
    }
    
We could actually cache the result forever, but using a value such as 12 hours
allows old entries to be automatically expired when they are no longer needed.

=head3 Page Caching

Another method of caching is to cache the entire HTML page.  While this is
traditionally handled by a front-end proxy server like Squid, the Catalyst
PageCache plugin makes it trivial to cache the entire output from
frequently-used or slow actions.

Many sites have a busy content-filled front page that might look something
like this.  It probably takes a while to process, and will do the exact same
thing for every single user who views the page.

    sub front_page : Path('/') {
        my ( $self, $c ) = @_;
        
        $c->forward( 'get_news_articles' );
        $c->forward( 'build_lots_of_boxes' );
        $c->forward( 'more_slow_stuff' );
        
        $c->stash->{template} = 'index.tt';
    }

We can add the PageCache plugin to speed things up.

    use Catalyst qw/Cache::FileCache PageCache/;
    
    sub front_page : Path ('/') {
        my ( $self, $c ) = @_;
        
        $c->cache_page( 300 );
        
        # same processing as above
    }
    
Now the entire output of the front page, from <html> to </html>, will be
cached for 5 minutes.  After 5 minutes, the next request will rebuild the
page and it will be re-cached.

Note that the page cache is keyed on the page URI plus all parameters, so
requests for / and /?foo=bar will result in different cache items.  Also,
only GET requests will be cached by the plugin.

You can even get that front-end Squid proxy to help out by enabling HTTP
headers for the cached page.

    MyApp->config->{page_cache}->{set_http_headers} = 1;
    
This would now set the following headers so proxies and browsers may cache
the content themselves.

    Cache-Control: max-age=($expire_time - time)
    Expires: $expire_time
    Last-Modified: $cache_created_time
    
=head3 Template Caching

Template Toolkit provides support for caching compiled versions of your
templates.  To enable this in Catalyst, use the following configuration.
TT will cache compiled templates keyed on the file mtime, so changes will
still be automatically detected.

    package MyApp::View::TT;
    
    use strict;
    use warnings;
    use base 'Catalyst::View::TT';
    
    __PACKAGE__->config(
        COMPILE_DIR => '/tmp/template_cache',
    );
    
    1;
    
=head3 More Info

See the documentation for each cache plugin for more details and other
available configuration options.

L<http://search.cpan.org/dist/Catalyst-Plugin-Cache-FastMmap/lib/Catalyst/Plugin/Cache/FastMmap.pm>
L<http://search.cpan.org/dist/Catalyst-Plugin-Cache-FileCache/lib/Catalyst/Plugin/Cache/FileCache.pm>
L<http://search.cpan.org/dist/Catalyst-Plugin-Cache-Memcached/lib/Catalyst/Plugin/Cache/Memcached.pm>
L<http://search.cpan.org/dist/Catalyst-Plugin-PageCache/lib/Catalyst/Plugin/PageCache.pm>
L<http://search.cpan.org/dist/Template-Toolkit/lib/Template/Manual/Config.pod#Caching_and_Compiling_Options>

=head2 L<Catalyst::Plugin::Subrequest>

=head3 Component based sub-requests.

This is actually one of the features we brought over from L<Maypole>. There it 
was called L<Maypole::Plugin::Component>. Basically, the idea is to set up 
new request/response objects, and do an internal request, then return the 
output. It's quite handy for various situations, Simon's example was a 
shopping portal. I'm frequently using it to render parts of my site that I'm 
also rendering with ajax, to avoid duplication of code.

It's quite simple in use. You just call $c->subreq('</public/url>'); (or 
with TT, [% c.subreq('/public/url') %] .) This will localize enough 
of your request/response object so that it shouldn't affect your current
request, set up a new path/uri, and call the Dispatcher to force a full
request chain, including begin/end/auto/default and whatever else applies.
if you don't like 'subreq', theres an alias as well: 'sub_request'.

You can also set up the stash before the request, as well as pass parameters
to the request like a normal form POST by passing optional hashrefs to the 
subreq method. for example:

        my $text=$c->subreq('/foo',{ bar=>$c->stash->{bar} }, {id=>23});

This will dispatch to whatever handles '/foo', with bar in the stash, and
$c->req->param('id') returning 23.  After the request, $text will contain
whatever's in $c->res->output.

Note, by the way, that the uri path is relative to the application root, 
and not necessesarily the webserver root.

=head2 DBIx::Class as Catalyst Model

=head3 Our Database

This text will show you how to start using DBIx::Class as your model within
Catalyst. Let's assume, we have a relational set of tables:

  shell> sqlite3 myapp.db
  SQLite version 3.2.1
  Enter ".help" for instructions
  sqlite> CREATE TABLE person (
     ...>     id       INTEGER PRIMARY KEY AUTOINCREMENT,
     ...>     name     VARCHAR(100)
     ...> );
  sqlite> CREATE TABLE address (
     ...>     id       INTEGER PRIMARY KEY AUTOINCREMENT,
     ...>     person   INTEGER REFERENCES person
     ...>     address  TEXT,
     ...> );
  sqlite> .q

which we want to access from our C<MyApp> Catalyst application.

=head3 Setting up the models

We will cover the more convenient way to start with, and let our models be
set up automatically. If you want to define your models and their relations
manually, have a look at C<Catalyst::Model::DBIC::Plain>. We'll concentrate
on C<Catalyst::Model::DBIC>.

We let a helper do most of the work for us:

  shell> script/myapp_create.pl model DBIC DBIC \
         dbi:SQLite:/path/to/myapp.db
   exists "/path/MyApp/script/../lib/MyApp/Model"
   exists "/path/MyApp/script/../t"
  created "/path/MyApp/Model/DBIC.pm"
  created "/path/MyApp/Model/DBIC"
  created "/path/MyApp/Model/DBIC/Address.pm"
  created "/path/MyApp/Model/DBIC/Person.pm"
  created "/path/MyApp/Model/DBIC/SqliteSequence.pm"
   exists "/path/MyApp/script/../t"
  created "/path/MyApp/script/../t/model_DBIC-Address.t"
   exists "/path/MyApp/script/../t"
  created "/path/MyApp/script/../t/model_DBIC-Person.t"
   exists "/path/MyApp/script/../t"
  created "/path/MyApp/script/../t/model_DBIC-SqliteSequence.t"

The base class C<DBIC.pm> that does the setting-up part of the job is set up
as well as stub files of our modules to extend and the testing environment.

=head3 Table and Relationship Autodetection

If you start your Cat Application up, you can see the loaded tables and
model components in your debug output:

  shell> script/myapp_server.pl
  ...
  [Tue Dec 13 01:20:59 2005] [catalyst] [debug] Loaded 
  tables "address person sqlite_sequence"
  ...
  .------------------------------------+----------.
  | Class                              | Type     |
  +------------------------------------+----------+
  | MyApp::Model::DBIC                 | instance |
  | MyApp::Model::DBIC::Address        | class    |
  | MyApp::Model::DBIC::Person         | class    |
  | MyApp::Model::DBIC::SqliteSequence | class    |
  | MyApp::Model::DBIC::_db            | class    |
  '------------------------------------+----------'
  ...

And your models are ready to use! If you change the database schema,
your models will also change at startup. However, Catalyst will not touch 
your stub model files. 

=head3 Using the Models

You can create new objects:

  my $person = $c->model( 'DBIC::Person' )->create({
      name => 'Jon Doe',
  });

Or add related objects:

  my $adress = $person->add_to_addresses({
      address => 'We wish we knew.',
  });

Search and retrieve from the database:

  my $person = $c->model( 'DBIC::Person' )->find(1);
  my $address_iterator = $c->model( 'DBIC::Address' )
    ->search( { address => { like => '%Tokyo%' } } );

=head3 More Information

You can find the documentation of C<Catalyst::Model::DBIC> and its helper
at

L<http://search.cpan.org/dist/Catalyst-Model-DBIC/>

For information concerning DBIx::Class please visit the documentation and
Intro on CPAN:

L<http://search.cpan.org/dist/DBIx-Class/>
L<http://search.cpan.org/dist/DBIx-Class/lib/DBIx/Class/Manual/Intro.pod>

or its own Wiki

L<http://dbix-class.shadowcatsystems.co.uk/>

and of course, you can find support on irc.perl.org#catalyst and 
irc.perl.org#dbix-class.

=head2 Authentication/Authorization

This is done in several steps:

=over 4

=item Verification

Getting the user to identify themselves, by giving you some piece of
information known only to you and the user. Then you can assume that the user
is who they say they are. This is called B<credential verification>.

=item Authorization

Making sure the user only accesses functions you want them to access. This is
done by checking the verified users data against your internal list of groups,
or allowed persons for the current page.

=back

=head3 Modules

The Catalyst Authentication system is made up of many interacting modules, to
give you the most flexibility possible.

=head4 Credential verifiers

A Credential module tables the user input, and passes it to a Store, or some
other system, for verification. Typically, a user object is created by either
this module or the Store and made accessible by a C<< $c->user >> call.

Examples:

 Password - Simple username/password checking.
 HTTPD    - Checks using basic HTTP auth.
 TypeKey  - Check using the typekey system.

=head3 Storage backends

A Storage backend contains the actual data representing the users. It is
queried by the credential verifiers. Updating the store is not done within
this system, you will need to do it yourself.

Examples:

 DBIC     - Storage using a database.
 Minimal  - Storage using a simple hash (for testing).

=head3 User objects

A User object is created by either the storage backend or the credential
verifier, and filled with the retrieved user information.

Examples:

 Hash     - A simple hash of keys and values.

=head3 ACL authorization

ACL stands for Access Control List. The ACL plugin allows you to regulate
access on a path by path basis, by listing which users, or roles, have access
to which paths.

=head3 Roles authorization

Authorization by roles is for assigning users to groups, which can then be
assigned to ACLs, or just checked when needed.

=head3 Logging in

When you have chosen your modules, all you need to do is call the C<<
$c->login >> method. If called with no parameters, it will try to find
suitable parameters, such as B<username> and B<password>, or you can pass it
these values.

=head3 Checking roles

Role checking is done by using the C<< $c->check_user_roles >> method, this will
check using the currently logged in user (via C<< $c->user >>). You pass it
the name of a role to check, and it returns true if the user is a member.

=head3 EXAMPLE

 use Catalyst qw/Authentication
                 Authentication::Credential::Password
                 Authentication::Store::Htpasswd
                 Authorization::Roles/;

 __PACKAGE__->config->{authentication}{htpasswd} = "passwdfile";

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

     if (    my $user = $c->req->param("user")
         and my $password = $c->req->param("password") )
     {
         if ( $c->login( $user, $password ) ) {
              $c->res->body( "hello " . $c->user->name );
         } else {
            # login incorrect
         }
     }
     else {
         # invalid form input
     }
  }

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

     $c->detach("unauthorized")
       unless $c->check_user_roles( "admin" );

     # do something restricted here
  }

=head3 Using authentication in a testing environment

Ideally, to write tests for authentication/authorization code one would first
set up a test database with known data, then use
L<Test::WWW::Mechanize::Catalyst> to simulate a user logging in. Unfortunately
the former can be rather awkward, which is why it's a good thing that the
authentication framework is so flexible.

Instead of using a test database, one can simply change the authentication
store to something a bit easier to deal with in a testing
environment. Additionally, this has the advantage of not modifying one's
database, which can be problematic if one forgets to use the testing instead of
production database.

e.g.,

  use Catalyst::Plugin::Authentication::Store::Minimal::Backend;

  # Sets up the user `test_user' with password `test_pass'
  MyApp->default_auth_store(
    Catalyst::Plugin::Authentication::Store::Minimal::Backend->new({
      test_user => { password => 'test_pass' },
    })
  );

Now, your test code can call C<$c->login('test_user', 'test_pass')> and
successfully login, without messing with the database at all.

=head3 More information

L<http://search.cpan.org/perldoc?Catalyst::Plugin::Authentication> has a longer explanation.

=head2 Sessions

When you have your users identified, you will want to somehow remember that
fact, to save them from having to identify themselves for every single
page. One way to do this is to send the username and password parameters in
every single page, but that's ugly, and won't work for static pages. 

Sessions are a method of saving data related to some transaction, and giving
the whole collection a single ID. This ID is then given to the user to return
to us on every page they visit while logged in. The usual way to do this is
using a browser cookie.

Catalyst uses two types of plugins to represent sessions:

=head3 State

A State module is used to keep track of the state of the session between the
users browser, and your application.  

A common example is the Cookie state module, which sends the browser a cookie
containing the session ID. It will use default value for the cookie name and
domain, so will "just work" when used. 

=head3 Store

A Store module is used to hold all the data relating to your session, for
example the users ID, or the items for their shopping cart. You can store data
in memory (FastMmap), in a file (File) or in a database (DBI).

=head3 Authentication magic

If you have included the session modules in your application, the
Authentication modules will automagically use your session to save and
retrieve the user data for you.

=head3 Using a session

Once the session modules are loaded, the session is available as C<<
$c->session >>, and can be writen to and read from as a simple hash reference.

=head3 EXAMPLE

  use Catalyst qw/
                 Session
                 Session::Store::FastMmap
                 Session::State::Cookie
                 /;


  ## Write data into the session

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

     my $item_id = $c->req->param("item");

     push @{ $c->session->{items} }, $item_id;

  }

  ## A page later we retrieve the data from the session:

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

     $c->stash->{items_to_display} = $c->session->{items};

  }


=head3 More information

L<http://search.cpan.org/dist/Catalyst-Plugin-Session>

L<http://search.cpan.org/dist/Catalyst-Plugin-Session-State-Cookie>

L<http://search.cpan.org/dist/Catalyst-Plugin-Session-State-URI>

L<http://search.cpan.org/dist/Catalyst-Plugin-Session-Store-FastMmap>

L<http://search.cpan.org/dist/Catalyst-Plugin-Session-Store-File>

L<http://search.cpan.org/dist/Catalyst-Plugin-Session-Store-DBI>

=head2 Adding RSS feeds 

Adding RSS feeds to your stuff in Catalyst is really simple. I'll show two
different aproaches here, but the basic premise is that you forward to the
normal view action first to get the objects, then handle the output differently

=head3 Using TT templates

This is the aproach we chose in Agave (L<http://dev.rawmode.org/>).

    sub rss : Local {
        my ($self,$c) = @_;
        $c->forward('view');
        $c->stash->{template}='rss.tt';
    }

Then you need a template. Here's the one from Agave: 
L<http://svn.rawmode.org/repos/Agave/trunk/root/base/blog/rss.tt>

As you can see, it's pretty simple. 

=head3 Using XML::Feed

However, a more robust solution is to use XML::Feed, as we've done in this 
Advent Calendar. Assuming we have a 'view' action that populates 'entries' 
with some DBIx::Class/Class::DBI iterator, the code would look something like 
this:

    sub rss : Local {
        my ($self,$c) = @_;
        $c->forward('view'); # get the entries

        my $feed = XML::Feed->new('RSS');
        $feed->title( $c->config->{name} . ' RSS Feed' );
        $feed->link( $c->req->base ); # link to the site.
        $feed->description('Catalyst advent calendar'); Some description

        # Process the entries
        while( my $entry=$c->stash->{entries}->next ) {
            my $feed_entry = XML::Feed::Entry->new('RSS');
            $feed_entry->title($entry->title);
            $feed_entry->link( $c->uri_for($entry->link) );
            $feed_entry->issued( DateTime->from_epoch(epoch   => $entry->created) );
            $feed->add_entry($feed_entry);
        }
        $c->res->body( $feed->as_xml );
   }


A little more code in the controller, but with this approach you're pretty sure
to get something that validates. One little note regarding that tho, for both
of the above aproaches, you'll need to set the content type like this:

    $c->res->content_type('application/rss+xml');

=head2 Final words

Note that you could generalize the second variant easily by replacing 'RSS' 
with a variable, so you can generate Atom feeds with the same code.

Now, go ahead and make RSS feeds for all your stuff. The world *needs* updates
on your goldfish!

=head2 FastCGI Deployment

As a companion to Day 7's mod_perl article, today's article is about
production FastCGI deployment.

=head3 Pros

=head4 Speed

FastCGI performs equally as well as mod_perl.  Don't let the 'CGI' fool you;
your app runs as multiple persistent processes ready to receive connections
from the web server.

=head4 App Server

When using external FastCGI servers, your application runs as a standalone
application server.  It may be restarted independently from the web server.
This allows for a more robust environment and faster reload times when
pushing new app changes.  The frontend server can even be configured to
display a friendly "down for maintenance" page while the application is
restarting.

=head4 Load-balancing

You can launch your application on multiple backend servers and allow the
frontend web server to load-balance between all of them.  And of course, if
one goes down, your app continues to run fine.

=head4 Multiple versions of the same app

Each FastCGI application is a separate process, so you can run different
versions of the same app on a single server.

=head4 Can run with threaded Apache

Since your app is not running inside of Apache, the faster mpm_worker module
can be used without worrying about the thread safety of your application.

=head3 Cons

=head4 More complex environment

With FastCGI, there are more things to monitor and more processes running
than when using mod_perl.

=head3 Setup

=head4 1. Install Apache with mod_fastcgi

mod_fastcgi for Apache is a third party module, and can be found at
L<http://www.fastcgi.com/>.  It is also packaged in many distributions, for
example, libapache2-mod-fastcgi in Debian.

=head4 2. Configure your application

    # Serve static content directly
    DocumentRoot  /var/www/MyApp/root
    Alias /static /var/www/MyApp/root/static

    FastCgiServer /var/www/MyApp/script/myapp_fastcgi.pl -processes 3
    Alias /myapp/ /var/www/MyApp/script/myapp_fastcgi.pl/
    
    # Or, run at the root
    Alias / /var/www/MyApp/script/myapp_fastcgi.pl/
    
The above commands will launch 3 app processes and make the app available at
/myapp/

=head3 Standalone server mode

While not as easy as the previous method, running your app as an external
server gives you much more flexibility.

First, launch your app as a standalone server listening on a socket.

    script/myapp_fastcgi.pl -l /tmp/myapp.socket -n 5 -p /tmp/myapp.pid -d
    
You can also listen on a TCP port if your web server is not on the same
machine.

    script/myapp_fastcgi.pl -l :8080 -n 5 -p /tmp/myapp.pid -d
    
You will probably want to write an init script to handle starting/stopping
of the app using the pid file.

Now, we simply configure Apache to connect to the running server.

    # 502 is a Bad Gateway error, and will occur if the backend server is down
    # This allows us to display a friendly static page that says "down for
    # maintenance"
    Alias /_errors /var/www/MyApp/root/error-pages
    ErrorDocument 502 /_errors/502.html

    FastCgiExternalServer /tmp/myapp -socket /tmp/myapp.socket
    Alias /myapp/ /tmp/myapp/
    
    # Or, run at the root
    Alias / /tmp/myapp/
    
=head3 More Info

Lots more information is available in the new and expanded FastCGI docs that
will be part of Catalyst 5.62.  For now you may read them here:
L<http://dev.catalyst.perl.org/file/trunk/Catalyst/lib/Catalyst/Engine/FastCGI.pm>

=head2 Catalyst::View::TT

One of the first things you probably want to do when starting a new Catalyst application is set up your View. Catalyst doesn't care how you display your data; you can choose to generate HTML, PDF files, or plain text if you wanted.

Most Catalyst applications use a template system to generate their HTML, and though there are several template systems available, Template Toolkit is probably the most popular.

Once again, the Catalyst developers have done all the hard work, and made things easy for the rest of us. Catalyst::View::TT provides the interface to Template Toolkit, and provides Helpers which let us set it up that much more easily.

=head3 Creating your View

Catalyst::View::TT provides two different helpers for use to use: TT and TTSite.

=head4 TT

Create a basic Template Toolkit View using the provided helper script:

    script/myapp_create.pl view TT TT

This will create lib/MyApp/View/MyView.pm, which is going to be pretty empty to start. However, it sets everything up that you need to get started. You can now define which template you want and forward to your view. For instance:

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

        $c->stash->{template} = 'hello.tt';

        $c->forward( $c->view('TT') );
    }

In most cases, you will put the $c->forward into end(), and then you would only have to define which template you want to use. The S<DefaultEnd> plugin discussed on Day 8 is also commonly used.

=head4 TTSite

Although the TT helper does create a functional, working view, you may find yourself having to create the same template files and changing the same options every time you create a new application. The TTSite helper saves us even more time by creating the basic templates and setting some common options for us.

Once again, you can use the helper script:

    script/myapp_create.pl view TT TTSite

This time, the helper sets several options for us in the generated View.

    __PACKAGE__->config({
        CATALYST_VAR => 'Catalyst',
        INCLUDE_PATH => [
            MyApp->path_to( 'root', 'src' ),
            MyApp->path_to( 'root', 'lib' )
        ],
        PRE_PROCESS  => 'config/main',
        WRAPPER      => 'site/wrapper',
        ERROR        => 'error.tt2',
        TIMER        => 0
    });

=over

=item
INCLUDE_PATH defines the directories that Template Toolkit should search for the template files.

=item
PRE_PROCESS is used to process configuration options which are common to every template file.

=item
WRAPPER is a file which is processed with each template, usually used to easily provide a common header and footer for every page.

=back

In addition to setting these options, the TTSite helper also created the template and config files for us! In the 'root' directory, you'll notice two new directories: src and lib. 

Several configuration files in root/lib/config are called by PRE_PROCESS.

The files in root/lib/site are the site-wide templates, called by WRAPPER, and display the html framework, control the layout, and provide the templates for the header and footer of your page. Using the template organization provided makes it much easier to standardize pages and make changes when they are (inevitably) needed.

The template files that you will create for your application will go into root/src, and you don't need to worry about putting the the <html> or <head> sections; just put in the content. The WRAPPER will the rest of the page around your template for you.

=head2 $c->stash

Of course, having the template system include the header and footer for you isn't all that we want our templates to do. We need to be able to put data into our templates, and have it appear where and how we want it, right? That's where the stash comes in.

In our controllers, we can add data to the stash, and then access it from the template. For instance:

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

        $c->stash->{name} = 'Adam';

        $c->stash->{template} = 'hello.tt';

        $c->forward( $c->view('TT') );
    }

Then, in hello.tt:

    <strong>Hello, [% name %]!</strong>

When you view this page, it will display "Hello, Adam!"

All of the information in your stash is available, by its name/key, in your templates. And your data doesn't have to be plain, old, boring scalars. You can pass array references and hash references, too.

In your controller:

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

        $c->stash->{names} = [ 'Adam', 'Dave', 'John' ];

        $c->stash->{template} = 'hello.tt';

        $c->forward( $c->view('TT') );
    }

In hello.tt:

    [% FOREACH name IN names %]
        <strong>Hello, [% name %]!</strong><br />
    [% END %]

This allowed us to loop through each item in the arrayref, and display a line for each name that we have.

This is the most basic usage, but Template Toolkit is quite powerful, and allows you to truly keep your presentation logic separate from the rest of your application.

=head3 $c->uri_for()

One of my favorite things about Catalyst is the ability to move an application around without having to worry that everything is going to break. One of the areas that used to be a problem was with the http links in your template files. For example, suppose you have an application installed at http://www.domain.com/Calendar. The links point to "/Calendar", "/Calendar/2005", "/Calendar/2005/10", etc.  If you move the application to be at http://www.mydomain.com/Tools/Calendar, then all of those links will suddenly break.

That's where $c->uri_for() comes in. This function will merge its parameters with either the base location for the app, or its current namespace. Let's take a look at a couple of examples.

In your template, you can use the following:

    <a href="[% c.uri_for('/login') %]">Login Here</a>

Although the parameter starts with a forward slash, this is relative to the application root, not the webserver root. This is important to remember. So, if your application is installed at http://www.domain.com/Calendar, then the link would be http://www.mydomain.com/Calendar/Login. If you move your application to a different domain or path, then that link will still be correct.

Likewise,

    <a href="[% c.uri_for('2005','10', '24') %]">October, 24 2005</a>

The first parameter does NOT have a forward slash, and so it will be relative to the current namespace. If the application is installed at http://www.domain.com/Calendar. and if the template is called from MyApp::Controller::Display, then the link would become http://www.domain.com/Calendar/Display/2005/10/24.

Once again, this allows you to move your application around without having to worry about broken links. But there's something else, as well. Since the links are generated by uri_for, you can use the same template file by several different controllers, and each controller will get the links that its supposed to. Since we believe in Don't Repeat Yourself, this is particularly helpful if you have common elements in your site that you want to keep in one file.

Further Reading:

L<http://search.cpan.org/perldoc?Catalyst>

L<http://search.cpan.org/perldoc?Catalyst%3A%3AView%3A%3ATT>

L<http://search.cpan.org/perldoc?Template>

=head2 Testing

Catalyst provides a convenient way of testing your application during 
development and before deployment in a real environment.

C<Catalyst::Test> makes it possible to run the same tests both locally 
(without an external daemon) and against a remote server via HTTP.

=head3 Tests

Let's examine a skeleton application's C<t/> directory:

    mundus:~/MyApp chansen$ ls -l t/
    total 24
    -rw-r--r--  1 chansen  chansen   95 18 Dec 20:50 01app.t
    -rw-r--r--  1 chansen  chansen  190 18 Dec 20:50 02pod.t
    -rw-r--r--  1 chansen  chansen  213 18 Dec 20:50 03podcoverage.t

=over 4

=item C<01app.t>

Verifies that the application loads, compiles, and returns a successful
response.

=item C<02pod.t>

Verifies that all POD is free from errors. Only executed if the C<TEST_POD> 
environment variable is true.

=item C<03podcoverage.t>

Verifies that all methods/functions have POD coverage. Only executed if the
C<TEST_POD> environment variable is true.

=back

=head3 Creating tests

    mundus:~/MyApp chansen$ cat t/01app.t | perl -ne 'printf( "%2d  %s", $., $_ )'
    1  use Test::More tests => 2;
    2  use_ok( Catalyst::Test, 'MyApp' );
    3
    4  ok( request('/')->is_success );

The first line declares how many tests we are going to run, in this case
two. The second line tests and loads our application in test mode. The
fourth line verifies that our application returns a successful response.

C<Catalyst::Test> exports two functions, C<request> and C<get>. Each can
take three different arguments:

=over 4

=item A string which is a relative or absolute URI.

    request('/my/path');
    request('http://www.host.com/my/path');

=item An instance of C<URI>.

    request( URI->new('http://www.host.com/my/path') );

=item An instance of C<HTTP::Request>.

    request( HTTP::Request->new( GET => 'http://www.host.com/my/path') );

=back

C<request> returns an instance of C<HTTP::Response> and C<get> returns the 
content (body) of the response.

=head3 Running tests locally

    mundus:~/MyApp chansen$ CATALYST_DEBUG=0 TEST_POD=1 prove --lib lib/ t/
    t/01app............ok                                                        
    t/02pod............ok                                                        
    t/03podcoverage....ok                                                        
    All tests successful.
    Files=3, Tests=4,  2 wallclock secs ( 1.60 cusr +  0.36 csys =  1.96 CPU)
 
C<CATALYST_DEBUG=0> ensures that debugging is off; if it's enabled you
will see debug logs between tests.

C<TEST_POD=1> enables POD checking and coverage.

C<prove> A command-line tool that makes it easy to run tests. You can
find out more about it from the links below.

=head3 Running tests remotely

    mundus:~/MyApp chansen$ CATALYST_SERVER=http://localhost:3000/ prove --lib lib/ t/01app.t
    t/01app....ok                                                                
    All tests successful.
    Files=1, Tests=2,  0 wallclock secs ( 0.40 cusr +  0.01 csys =  0.41 CPU)

C<CATALYST_SERVER=http://localhost:3000/> is the absolute deployment URI of 
your application. In C<CGI> or C<FastCGI> it should be the host and path 
to the script.

=head3 C<Test::WWW::Mechanize> and Catalyst

Be sure to check out C<Test::WWW::Mechanize::Catalyst>. It makes it easy to
test HTML, forms and links. A short example of usage:

    use Test::More tests => 6;
    use_ok( Test::WWW::Mechanize::Catalyst, 'MyApp' );

    my $mech = Test::WWW::Mechanize::Catalyst->new;
    $mech->get_ok("http://localhost/", 'Got index page');
    $mech->title_like( qr/^MyApp on Catalyst/, 'Got right index title' );
    ok( $mech->find_link( text_regex => qr/^Wiki/i ), 'Found link to Wiki' );
    ok( $mech->find_link( text_regex => qr/^Mailing-List/i ), 'Found link to Mailing-List' );
    ok( $mech->find_link( text_regex => qr/^IRC channel/i ), 'Found link to IRC channel' );

=head3 Further Reading

=over 4

=item Catalyst::Test

L<http://search.cpan.org/dist/Catalyst/lib/Catalyst/Test.pm>

=item Test::WWW::Mechanize::Catalyst

L<http://search.cpan.org/dist/Test-WWW-Mechanize-Catalyst/lib/Test/WWW/Mechanize/Catalyst.pm>

=item Test::WWW::Mechanize

L<http://search.cpan.org/dist/Test-WWW-Mechanize/Mechanize.pm>

=item WWW::Mechanize

L<http://search.cpan.org/dist/WWW-Mechanize/lib/WWW/Mechanize.pm>

=item LWP::UserAgent

L<http://search.cpan.org/dist/libwww-perl/lib/LWP/UserAgent.pm>

=item HTML::Form

L<http://search.cpan.org/dist/libwww-perl/lib/HTML/Form.pm>

=item HTTP::Message

L<http://search.cpan.org/dist/libwww-perl/lib/HTTP/Message.pm>

=item HTTP::Request

L<http://search.cpan.org/dist/libwww-perl/lib/HTTP/Request.pm>

=item HTTP::Request::Common

L<http://search.cpan.org/dist/libwww-perl/lib/HTTP/Request/Common.pm>

=item HTTP::Response

L<http://search.cpan.org/dist/libwww-perl/lib/HTTP/Response.pm>

=item HTTP::Status

L<http://search.cpan.org/dist/libwww-perl/lib/HTTP/Status.pm>

=item URI

L<http://search.cpan.org/dist/URI/URI.pm>

=item Test::More

L<http://search.cpan.org/dist/Test-Simple/lib/Test/More.pm>

=item Test::Pod

L<http://search.cpan.org/dist/Test-Pod/Pod.pm>

=item Test::Pod::Coverage

L<http://search.cpan.org/dist/Test-Pod-Coverage/Coverage.pm>

=item prove (Test::Harness)

L<http://search.cpan.org/dist/Test-Harness/bin/prove>

=back

=head2 XMLRPC

Today we'll discover the wonderful world of web services.
XMLRPC is unlike SOAP a very simple (and imo elegant) protocol,
exchanging small XML messages like these.

Request:

    POST /api HTTP/1.1
    TE: deflate,gzip;q=0.3
    Connection: TE, close
    Accept: text/xml
    Accept: multipart/*
    Host: 127.0.0.1:3000
    User-Agent: SOAP::Lite/Perl/0.60
    Content-Length: 192
    Content-Type: text/xml

    <?xml version="1.0" encoding="UTF-8"?>
    <methodCall>
        <methodName>add</methodName>
        <params>
            <param><value><int>1</int></value></param>
            <param><value><int>2</int></value></param>
        </params>
    </methodCall>

Response:

    Connection: close
    Date: Tue, 20 Dec 2005 07:45:55 GMT
    Content-Length: 133
    Content-Type: text/xml
    Status: 200
    X-Catalyst: 5.62

    <?xml version="1.0" encoding="us-ascii"?>
    <methodResponse>
        <params>
            <param><value><int>3</int></value></param>
        </params>
    </methodResponse>

Sweet little protocol, isn't it? :)

Now follow these few steps to implement the application.

1. Install Catalyst (5.61 or later), Catalyst::Plugin::XMLRPC (0.06 or later) and SOAP::Lite (for XMLRPCsh.pl)

    % perl -MCPAN -e'install Catalyst'
    ...
    % perl -MCPAN -e'install Catalyst::Plugin::XMLRPC'
    ...

2. Create a myapp

    % catalyst.pl MyApp
    ...
    % cd MyApp

3. Add the XMLRPC plugin to MyApp.pm

    use Catalyst qw/-Debug Static::Simple XMLRPC/;

4. Add a api controller

    % ./script/myapp_create.pl controller API

5. Add a XMLRPC redispatch method and a add method with Remote attribute
to lib/MyApp/Controller/API.pm

    sub default : Private {
        my ( $self, $c ) = @_;
        $c->xmlrpc;
    }

    sub add : Remote {
        my ( $self, $c, $a, $b ) = @_;
        return $a + $b;
    }

The default action is the entry point for each XMLRPC request, it will
redispatch every request to methods with Remote attribute in the same class.

The add method is no traditional action, it has no private or public path.
Only the XMLRPC dispatcher knows it exists.

6. Thats it! You have built your first web service, lets test it with
XMLRPCsh.pl (part of SOAP::Lite)

    % ./script/myapp_server.pl
    ...
    % XMLRPCsh.pl http://127.0.0.1:3000/api
    Usage: method[(parameters)]
    > add( 1, 2 )
    --- XMLRPC RESULT ---
    '3'

=head3 Tip Of The Day

Your return data type is usually auto-detected, but you can easily
enforce a specific one.

    sub add : Remote {
        my ( $self, $c, $a, $b ) = @_;
        return RPC::XML::int->new( $a + $b );
    }
    
=head2 Action Types

=head3 Introduction

A Catalyst application is driven by one or more Controller modules. There are
a number of ways that Catalyst can decide which of the methods in your
controller modules it should call. Controller methods are also called actions,
because they determine how your catalyst application should (re-)act to any
given URL. When the application is started up, catalyst looks at all your
actions, and decides which URLs they map to.

=head3 Type attributes

Each action is a normal method in your controller, except that it has an
L<attribute|http://search.cpan.org/~nwclark/perl-5.8.7/lib/attributes.pm>
attached. These can be one of several types.

Assume our Controller module starts with the following package declaration:

 package MyApp::Controller::Buckets;

and we are running our application on localhost, port 3000 (the test server default).

=over 4

=item Path

A Path attribute also takes an argument, this can be either a relative or an
absolute path. A relative path will be relative to the controller namespace,
an absolute path will represent an exact matching URL.

 sub my_handles : Path('handles') { .. }

becomes

 http://localhost:3000/buckets/handles

and

 sub my_handles : Path('/handles') { .. }

becomes 

 http://localhost:3000/handles

=item Local

When using a Local attribute, no parameters are needed, instead, the name of
the action is matched in the URL. The namespaces created by the name of the
controller package is always part of the URL.

 sub my_handles : Local { .. }

becomes

 http://localhost:3000/buckets/my_handles

=item Global

A Global attribute is similar to a Local attribute, except that the namespace
of the controller is ignored, and matching starts at root.

 sub my_handles : Global { .. }

becomes

 http://localhost:3000/my_handles

=item Regex

By now you should have figured that a Regex attribute is just what it sounds
like. This one takes a regular expression, and matches starting from
root. These differ from the rest as they can match multiple URLs.

 sub my_handles : Regex('^handles') { .. }

matches

 http://localhost:3000/handles

and 

 http://localhost:3000/handles_and_other_parts

etc.

=item LocalRegex

A LocalRegex is similar to a Regex, except it only matches below the current
controller namespace.

 sub my_handles : LocalRegex(^handles') { .. }

matches

 http://localhost:3000/buckets/handles

and

 http://localhost:3000/buckets/handles_and_other_parts

etc.

=item Private

Last but not least, there is the Private attribute, which allows you to create
your own internal actions, which can be forwarded to, but won't be matched as
URLs.

 sub my_handles : Private { .. }

becomes nothing at all..

Catalyst also predefines some special Private actions, which you can override,
these are:

=over 4

=item default

The default action will be called, if no other matching action is found. If
you don't have one of these in your namespace, or any sub part of your
namespace, you'll get an error page instead. If you want to find out where it
was the user was trying to go, you can look in the request object using 
C<< $c->req->path >>.

 sub default : Private { .. }

works for all unknown URLs, in this controller namespace, or every one if put
directly into MyApp.pm.

=item index 

The index action is called when someone tries to visit the exact namespace of
your controller. If index, default and matching Path actions are defined, then
index will be used instead of default and Path.

 sub index : Private { .. }

becomes

 http://localhost:3000/buckets

=item begin

The begin action is called at the beginning of every request involving this
namespace directly, before other matching actions are called. It can be used
to set up variables/data for this particular part of your app. A single begin
action is called, its always the one most relevant to the current namespace.

 sub begin : Private { .. }

is called once when 

 http://localhost:3000/bucket/(anything)?

is visited.

=item end

Like begin, this action is always called for the namespace it is in, after
every other action has finished. It is commonly used to forward processing to
the View component. A single end action is called, its always the one most
relevant to the current namespace. 


 sub end : Private { .. }

is called once after any actions when

 http://localhost:3000/bucket/(anything)?

is visited.

=item auto

Lastly, the auto action is magic in that B<every> auto action in
the chain of paths up to and including the ending namespace, will be
called. (In contrast, only one of the begin/end/default actions will be
called, the relevant one).

 package MyApp.pm;
 sub auto : Private { .. }

and 

 sub auto : Private { .. }

will both be called when visiting 

 http://localhost:3000/bucket/(anything)?

=back

=back

=head3 A word of warning

Due to possible namespace conflicts with Plugins, it is advised to only put the
pre-defined Private actions in your main MyApp.pm file, all others should go
in a Controller module.

=head3 More Information

L<http://search.cpan.org/author/SRI/Catalyst-5.61/lib/Catalyst/Manual/Intro.pod>

L<http://dev.catalyst.perl.org/wiki/FlowChart>

=head2 Static::Simple

=head3 Introduction

Static::Simple is a plugin that will help to serve static content for your
application. By default, it will serve most types of files, excluding some
standard Template Toolkit extensions, out of your B<root> file directory. All
files are served by path, so if B<images/me.jpg> is requested, then
B<root/images/me.jpg> is found and served.

=head3 Usage

Using the plugin is as simple as setting your use line in MyApp.pm to:

 use Catalyst qw/Static::Simple/;

and already files will be served.

=head3 Configuring

=over 4

=item Include Path

You may of course want to change the default locations, and make
Static::Simple look somewhere else, this is as easy as:

 MyApp->config->{static}->{include_path} = [
  MyApp->config->{root},
  '/path/to/my/files' 
 ];

When you override include_path, it will not automatically append the normal
root path, so you need to add it yourself if you still want it. These will be
searched in order given, and the first matching file served.

=item Static directories

If you want to force some directories to be only static, you can set them
using paths relative to the root dir, or regular expressions:

 MyApp->config->{static}->{dirs} = [
   'static',
   qr/^(images|css)/,
 ];

=item File extensions

By default, the following extensions are not served: B<tmpl, tt, tt2, html,
xhtml>. This list can be replaced easily:

 MyApp->config->{static}->{ignore_extensions} = [
    qw/tmpl tt tt2 html xhtml/ 
 ];

=item Ignoring directories

Entire directories can be ignored. If used with include_path, directories
relative to the include_path dirs will also be ignored:

 MyApp->config->{static}->{ignore_dirs} = [ qw/tmpl css/ ];

=back

=head3 More information

L<http://search.cpan.org/dist/Catalyst-Plugin-Static-Simple/>

=head2 Authorization

=head3 Introduction

Authorization is the step that comes after authentication. Authentication
establishes that the user agent is really representing the user we think it's
representing, and then authorization determines what this user is allowed to
do.

=head3 Role Based Access Control

Under role based access control each user is allowed to perform any number of
roles. For example, at a zoo no one but specially trained personnel can enter
the moose cage (Mynd you, møøse bites kan be pretty nasti!). For example: 

    package Zoo::Controller::MooseCage;

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

        $c->model( "Moose" )->eat( $c->req->param("food") );
    }

With this action, anyone can just come into the moose cage and feed the moose,
which is a very dangerous thing. We need to restrict this action, so that only
a qualified moose feeder can perform that action.

The Authorization::Roles plugin let's us perform role based access control
checks. Let's load it:

    use Catalyst qw/
        Authentication # yadda yadda
        Authorization::Roles
    /;

And now our action should look like this:

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

        if ( $c->check_roles( "moose_feeder" ) ) {
            $c->model( "Moose" )->eat( $c->req->param("food") );
        } else {
            $c->stash->{error} = "unauthorized";
        }
    }

This checks C<< $c->user >>, and only if the user has B<all> the roles in the
list, a true value is returned.

C<check_roles> has a sister method, C<assert_roles>, which throws an exception
if any roles are missing.

Some roles that might actually make sense in, say, a forum application:

=over 4

=item *

administrator

=item *

moderator

=back

each with a distinct task (system administration versus content administration).

=head3 Access Control Lists

Checking for roles all the time can be tedious and error prone.

The Authorization::ACL plugin let's us declare where we'd like checks to be
done automatically for us.

For example, we may want to completely block out anyone who isn't a
C<moose_feeder> from the entire C<MooseCage> controller:

    Zoo->deny_access_unless( "/moose_cage", [qw/moose_feeder/] );

The role list behaves in the same way as C<check_roles>. However, the ACL
plugin isn't limited to just interacting with the Roles plugin. We can use a
code reference instead. For example, to allow either moose trainers or moose
feeders into the moose cage, we can create a more complex check:

    Zoo->deny_access_unless( "/moose_cage", sub {
        my $c = shift;
        $c->check_roles( "moose_trainer" ) || $c->check_roles( "moose_feeder" );
    });

The more specific a role, the earlier it will be checked. Let's say moose
feeders are now restricted to only the C<feed_moose> action, while moose
trainers get access everywhere:

    Zoo->deny_access_unless( "/moose_cage", [qw/moose_trainer/] );
    Zoo->allow_access_if( "/moose_cage/feed_moose", [qw/moose_feeder/]);

When the C<feed_moose> action is accessed the second check will be made. If the
user is a C<moose_feeder>, then access will be immediately granted. Otherwise,
the next rule in line will be tested - the one checking for a C<moose_trainer>.
If this rule is not satisfied, access will be immediately denied.

Rules applied to the same path will be checked in the order they were added.

Lastly, handling access denial events is done by creating an C<access_denied>
private action:

    sub access_denied : Private {
        my ( $self, $c, $action ) = @_;

        
    }

This action works much like auto, in that it is inherited across namespaces
(not like object oriented code). This means that the C<access_denied> action
which is B<nearest> to the action which was blocked will be triggered.

If this action does not exist, an error will be thrown, which you can clean up
in your C<end> private action instead.

Also, it's important to note that if you restrict access to "/" then C<end>,
C<default>, etc will also be restricted.

   MyApp->acl_allow_root_internals;

will create rules that permit access to C<end>, C<begin>, and C<auto> in the
root of your app (but not in any other controller).

=head3 More Information

L<http://search.cpan.org/perldoc?Catalyst::Plugin::Authorization::Roles>
L<http://search.cpan.org/perldoc?Catalyst::Plugin::Authorization::ACL>

=head1 AUTHORS

Sebastian Riedel, C<sri@oook.de>
Danijel Milicevic, C<me@danijel.de>
Viljo Marrandi, C<vilts@yahoo.com>  
Marcus Ramberg, C<mramberg@cpan.org>
Jesse Sheidlower, C<jester@panix.com>
Andy Grundman, C<andy@hybridized.org> 
Chisel Wright, C<pause@herlpacker.co.uk>
Will Hawes, C<info@whawes.co.uk>
Gavin Henry, C<ghenry@perl.me.uk>


=head1 COPYRIGHT

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