Provided by: libcgi-application-perl_4.61-1_all bug


       CGI::Application - Framework for building reusable web-applications


         # In ""...
         package WebApp;
         use base 'CGI::Application';

         # ( setup() can even be skipped for common cases. See docs below. )
         sub setup {
               my $self = shift;
                       'mode1' => 'do_stuff',
                       'mode2' => 'do_more_stuff',
                       'mode3' => 'do_something_else'
         sub do_stuff { ... }
         sub do_more_stuff { ... }
         sub do_something_else { ... }

         ### In "webapp.cgi"...
         use WebApp;
         my $webapp = WebApp->new();

         ### Or, in a PSGI file, webapp.psgi
         use WebApp;


       CGI::Application makes it easier to create sophisticated, high-performance, reusable web-
       based applications.  CGI::Application helps makes your web applications easier to design,
       write, and evolve.

       CGI::Application judiciously avoids employing technologies and techniques which would bind
       a developer to any one set of tools, operating system or web server.

       It is lightweight in terms of memory usage, making it suitable for common CGI
       environments, and a high performance choice in persistent environments like FastCGI or

       By adding PLUG-INS as your needs grow, you can add advanced and complex features when you
       need them.

       First released in 2000 and used and expanded by a number of professional website
       developers, CGI::Application is a stable, reliable choice.


       Imagine you have to write an application to search through a database of widgets.  Your
       application has three screens:

          1. Search form
          2. List of results
          3. Detail of a single record

       To write this application using CGI::Application you will create two files:

          1. -- Your "Application Module"
          2. widgetview.cgi -- Your "Instance Script"

       The Application Module contains all the code specific to your application functionality,
       and it exists outside of your web server's document root, somewhere in the Perl library
       search path.

       The Instance Script is what is actually called by your web server.  It is a very small,
       simple file which simply creates an instance of your application and calls an inherited
       method, run().  Following is the entirety of "widgetview.cgi":

          #!/usr/bin/perl -w
          use WidgetView;
          my $webapp = WidgetView->new();

       As you can see, widgetview.cgi simply "uses" your Application module (which implements a
       Perl package called "WidgetView").  Your Application Module, "", is somewhat
       more lengthy:

          package WidgetView;
          use base 'CGI::Application';
          use strict;

          # Needed for our database connection
          use CGI::Application::Plugin::DBH;

          sub setup {
               my $self = shift;
                       'mode1' => 'showform',
                       'mode2' => 'showlist',
                       'mode3' => 'showdetail'

               # Connect to DBI database, with the same args as DBI->connect();

          sub teardown {
               my $self = shift;

               # Disconnect when we're done, (Although DBI usually does this automatically)

          sub showform {
               my $self = shift;

               # Get CGI query object
               my $q = $self->query();

               my $output = '';
               $output .= $q->start_html(-title => 'Widget Search Form');
               $output .= $q->start_form();
               $output .= $q->textfield(-name => 'widgetcode');
               $output .= $q->hidden(-name => 'rm', -value => 'mode2');
               $output .= $q->submit();
               $output .= $q->end_form();
               $output .= $q->end_html();

               return $output;

          sub showlist {
               my $self = shift;

               # Get our database connection
               my $dbh = $self->dbh();

               # Get CGI query object
               my $q = $self->query();
               my $widgetcode = $q->param("widgetcode");

               my $output = '';
               $output .= $q->start_html(-title => 'List of Matching Widgets');

               ## Do a bunch of stuff to select "widgets" from a DBI-connected
               ## database which match the user-supplied value of "widgetcode"
               ## which has been supplied from the previous HTML form via a
               ## query object.
               ## Each row will contain a link to a "Widget Detail" which
               ## provides an anchor tag, as follows:
               ##   "widgetview.cgi?rm=mode3&widgetid=XXX"
               ##  ...Where "XXX" is a unique value referencing the ID of
               ## the particular "widget" upon which the user has clicked.

               $output .= $q->end_html();

               return $output;

          sub showdetail {
               my $self = shift;

               # Get our database connection
               my $dbh = $self->dbh();

               # Get CGI query object
               my $q = $self->query();
               my $widgetid = $q->param("widgetid");

               my $output = '';
               $output .= $q->start_html(-title => 'Widget Detail');

               ## Do a bunch of things to select all the properties of
               ## the particular "widget" upon which the user has
               ## clicked.  The key id value of this widget is provided
               ## via the "widgetid" property, accessed via the
               ## query object.

               $output .= $q->end_html();

               return $output;

          1;  # Perl requires this at the end of all modules

       CGI::Application takes care of implementing the new() and the run() methods.  Notice that
       at no point do you call print() to send any output to STDOUT.  Instead, all output is
       returned as a scalar.

       CGI::Application's most significant contribution is in managing the application state.
       Notice that all which is needed to push the application forward is to set the value of a
       HTML form parameter 'rm' to the value of the "run mode" you wish to handle the form
       submission.  This is the key to CGI::Application.


       The guiding philosophy behind CGI::Application is that a web-based application can be
       organized into a specific set of "Run Modes."  Each Run Mode is roughly analogous to a
       single screen (a form, some output, etc.).  All the Run Modes are managed by a single
       "Application Module" which is a Perl module.  In your web server's document space there is
       an "Instance Script" which is called by the web server as a CGI (or an Apache::Registry
       script if you're using Apache + mod_perl).

       This methodology is an inversion of the "Embedded" philosophy (ASP, JSP, EmbPerl, Mason,
       etc.) in which there are "pages" for each state of the application, and the page drives
       functionality.  In CGI::Application, form follows function -- the Application Module
       drives pages, and the code for a single application is in one place; not spread out over
       multiple "pages".  If you feel that Embedded architectures are confusing, unorganized,
       difficult to design and difficult to manage, CGI::Application is the methodology for you!

       Apache is NOT a requirement for CGI::Application.  Web applications based on
       CGI::Application will run equally well on NT/IIS or any other CGI-compatible environment.
       CGI::Application-based projects are, however, ripe for use on Apache/mod_perl servers, as
       they naturally encourage Good Programming Practices and will often work in persistent
       environments without modification.

       For more information on using CGI::Application with mod_perl, please see our website at, as well as CGI::Application::Plugin::Apache, which integrates
       with Apache::Request.


       It is intended that your Application Module will be implemented as a sub-class of
       CGI::Application. This is done simply as follows:

           package My::App;
           use base 'CGI::Application';

       Notation and Conventions

       For the purpose of this document, we will refer to the following conventions:
   The Perl module which implements your Application Module class.
         WebApp      Your Application Module class; a sub-class of CGI::Application.
         webapp.cgi  The Instance Script which implements your Application Module.
         $webapp     An instance (object) of your Application Module class.
         $c          Same as $webapp, used in instance methods to pass around the
                     current object. (Sometimes referred as "$self" in other code)

   Instance Script Methods
       By inheriting from CGI::Application you have access to a number of built-in methods.  The
       following are those which are expected to be called from your Instance Script.


       The new() method is the constructor for a CGI::Application.  It returns a blessed
       reference to your Application Module package (class).  Optionally, new() may take a set of
       parameters as key => value pairs:

           my $webapp = WebApp->new(
                       TMPL_PATH => 'App/',
                       PARAMS => {
                               'custom_thing_1' => 'some val',
                               'another_custom_thing' => [qw/123 456/]

       This method may take some specific parameters:

       TMPL_PATH - This optional parameter defines a path to a directory of templates.  This is
       used by the load_tmpl() method (specified below), and may also be used for the same
       purpose by other template plugins.  This run-time parameter allows you to further
       encapsulate instantiating templates, providing potential for more re-usability.  It can be
       either a scalar or an array reference of multiple paths.

       QUERY - This optional parameter allows you to specify an already-created query
       object.  Under normal use, CGI::Application will instantiate its own query object.
       Under certain conditions, it might be useful to be able to use one which has already been

       PARAMS - This parameter, if used, allows you to set a number of custom parameters at run-
       time.  By passing in different values in different instance scripts which use the same
       application module you can achieve a higher level of re-usability.  For instance, imagine
       an application module, "".  The application takes the contents of a HTML form
       and emails it to a specified recipient.  You could have multiple instance scripts
       throughout your site which all use this "" module, but which set different
       recipients or different forms.

       One common use of instance scripts is to provide a path to a config file.  This design
       allows you to define project wide configuration objects used by many several instance
       scripts. There are several plugins which simplify the syntax for this and provide lazy
       loading. Here's an example using CGI::Application::Plugin::ConfigAuto, which uses
       Config::Auto to support many configuration file formats.

        my $app = WebApp->new(PARAMS => { cfg_file => '' });

        # Later in your app:
        my %cfg = $self->cfg()
        # or ... $self->cfg('HTML_ROOT_DIR');

       See the list of plugins below for more config file integration solutions.


       The run() method is called upon your Application Module object, from your Instance Script.
       When called, it executes the functionality in your Application Module.

           my $webapp = WebApp->new();

       This method first determines the application state by looking at the value of the CGI
       parameter specified by mode_param() (defaults to 'rm' for "Run Mode"), which is expected
       to contain the name of the mode of operation.  If not specified, the state defaults to the
       value of start_mode().

       Once the mode has been determined, run() looks at the dispatch table stored in run_modes()
       and finds the function pointer which is keyed from the mode name.  If found, the function
       is called and the data returned is print()'ed to STDOUT and to the browser.  If the
       specified mode is not found in the run_modes() table, run() will croak().

   PSGI support
       CGI::Application offers native PSGI support. The default query object for this is
       CGI::PSGI, which simply wrappers to provide PSGI support to it.


        $psgi_coderef = WebApp->psgi_app({ ... args to new() ... });

       The simplest way to create and return a PSGI-compatible coderef. Pass in arguments to a
       hashref just as would to new. This returns a PSGI-compatible coderef, using CGI:::PSGI as
       the query object. To use a different query object, construct your own object using
       "run_as_psgi()", as shown below.

       It's possible that we'll change from CGI::PSGI to a different-but-compatible query object
       for PSGI support in the future, perhaps if adds native PSGI support.


        my $psgi_aref = $webapp->run_as_psgi;

       Just like "run", but prints no output and returns the data structure required by the PSGI
       specification. Use this if you want to run the application on top of a PSGI-compatible
       handler, such as Plack provides.

       If you are just getting started, just use "run()". It's easy to switch to using
       "run_as_psgi" later.

       Why use "run_as_psgi()"? There are already solutions to run CGI::Application-based
       projects on several web servers with dozens of plugins.  Running as a PSGI-compatible
       application provides the ability to run on additional PSGI-compatible servers, as well as
       providing access to all of the "Middleware" solutions available through the Plack project.

       The structure returned is an arrayref, containing the status code, an arrayref of header
       key/values and an arrayref containing the body.

        [ 200, [ 'Content-Type' => 'text/html' ], [ $body ] ]

       By default the body is a single scalar, but plugins may modify this to return other value
       PSGI values.  See "The Response" in PSGI for details about the response format.

       Note that calling "run_as_psgi" only handles the output portion of the PSGI spec. to
       handle the input, you need to use a query object that is PSGI-compliant, such
       as CGI::PSGI. This query object must provide psgi_header and psgi_redirect methods.

       The final result might look like this:

           use WebApp;
           use CGI::PSGI;

           my $handler = sub {
               my $env = shift;
               my $webapp = WebApp->new({ QUERY => CGI::PSGI->new($env) });

   Additional PSGI Return Values
       The PSGI Specification allows for returning a file handle or a subroutine reference
       instead of byte strings.  In PSGI mode this is supported directly by CGI::Application.
       Have your run mode return a file handle or compatible subref as follows:

               sub returning_a_file_handle {
                   my $self = shift;

                   $self->header_props(-type => 'text/plain');

               open my $fh, "<", 'test_file.txt' or die "OOPS! $!";

                   return $fh;

           sub returning_a_subref {
               my $self = shift;

               $self->header_props(-type => 'text/plain');
               return sub {
                  my $writer = shift;
                  foreach my $i (1..10) {
                      #sleep 1;
                      $writer->write("check $i: " . time . "\n");

   Methods to possibly override
       CGI::Application implements some methods which are expected to be overridden by
       implementing them in your sub-class module.  These methods are as follows:


       This method is called by the inherited new() constructor method.  The setup() method
       should be used to define the following property/methods:

           mode_param() - set the name of the run mode CGI param.
           start_mode() - text scalar containing the default run mode.
           error_mode() - text scalar containing the error mode.
           run_modes() - hash table containing mode => function mappings.
           tmpl_path() - text scalar or array reference containing path(s) to template files.

       Your setup() method may call any of the instance methods of your application.  This
       function is a good place to define properties specific to your application via the
       $webapp->param() method.

       Your setup() method might be implemented something like this:

               sub setup {
                       my $self = shift;
                               'putform'  => 'my_putform_func',
                               'postdata' => 'my_data_func'
                       $self->param('myprop2', 'prop2value');
                       $self->param('myprop3', ['p3v1', 'p3v2', 'p3v3']);

       However, often times all that needs to be in setup() is defining your run modes and your
       start mode. CGI::Application::Plugin::AutoRunmode allows you to do this with a simple
       syntax, using run mode attributes:

        use CGI::Application::Plugin::AutoRunmode;

        sub show_first : StartRunmode { ... };
        sub do_next : Runmode { ... }


       If implemented, this method is called automatically after your application runs.  It can
       be used to clean up after your operations.  A typical use of the teardown() function is to
       disconnect a database connection which was established in the setup() function.  You could
       also use the teardown() method to store state information about the application to the


       If implemented, this method is called automatically right before the setup() method is
       called.  This method provides an optional initialization hook, which improves the object-
       oriented characteristics of CGI::Application.  The cgiapp_init() method receives, as its
       parameters, all the arguments which were sent to the new() method.

       An example of the benefits provided by utilizing this hook is creating a custom
       "application super-class" from which all your web applications would inherit, instead of

       Consider the following:

         # In
         package MySuperclass;
         use base 'CGI::Application';
         sub cgiapp_init {
               my $self = shift;
               # Perform some project-specific init behavior
               # such as to load settings from a database or file.

         # In
         package MyApplication;
         use base 'MySuperclass';
         sub setup { ... }
         sub teardown { ... }
         # The rest of your CGI::Application-based follows...

       By using CGI::Application and the cgiapp_init() method as illustrated, a suite of
       applications could be designed to share certain characteristics.  This has the potential
       for much cleaner code built on object-oriented inheritance.


       If implemented, this method is called automatically right before the selected run mode
       method is called.  This method provides an optional pre-runmode hook, which permits
       functionality to be added at the point right before the run mode method is called.  To
       further leverage this hook, the value of the run mode is passed into cgiapp_prerun().

       Another benefit provided by utilizing this hook is creating a custom "application super-
       class" from which all your web applications would inherit, instead of CGI::Application.

       Consider the following:

         # In
         package MySuperclass;
         use base 'CGI::Application';
         sub cgiapp_prerun {
               my $self = shift;
               # Perform some project-specific init behavior
               # such as to implement run mode specific
               # authorization functions.

         # In
         package MyApplication;
         use base 'MySuperclass';
         sub setup { ... }
         sub teardown { ... }
         # The rest of your CGI::Application-based follows...

       By using CGI::Application and the cgiapp_prerun() method as illustrated, a suite of
       applications could be designed to share certain characteristics.  This has the potential
       for much cleaner code built on object-oriented inheritance.

       It is also possible, within your cgiapp_prerun() method, to change the run mode of your
       application.  This can be done via the prerun_mode() method, which is discussed elsewhere
       in this POD.


       If implemented, this hook will be called after the run mode method has returned its
       output, but before HTTP headers are generated.  This will give you an opportunity to
       modify the body and headers before they are returned to the web browser.

       A typical use for this hook is pipelining the output of a CGI-Application through a series
       of "filter" processors.  For example:

         * You want to enclose the output of all your CGI-Applications in
           an HTML table in a larger page.

         * Your run modes return structured data (such as XML), which you
           want to transform using a standard mechanism (such as XSLT).

         * You want to post-process CGI-App output through another system,
           such as HTML::Mason.

         * You want to modify HTTP headers in a particular way across all
           run modes, based on particular criteria.

       The cgiapp_postrun() hook receives a reference to the output from your run mode method, in
       addition to the CGI-App object.  A typical cgiapp_postrun() method might be implemented as

         sub cgiapp_postrun {
           my $self = shift;
           my $output_ref = shift;

           # Enclose output HTML table
           my $new_output = "<table border=1>";
           $new_output .= "<tr><td> Hello, World! </td></tr>";
           $new_output .= "<tr><td>". $$output_ref ."</td></tr>";
           $new_output .= "</table>";

           # Replace old output with new output
           $$output_ref = $new_output;

       Obviously, with access to the CGI-App object you have full access to use all the methods
       normally available in a run mode.  You could, for example, use "load_tmpl()" to replace
       the static HTML in this example with HTML::Template.  You could change the HTTP headers
       (via "header_type()" and "header_props()" methods) to set up a redirect.  You could also
       use the objects properties to apply changes only under certain circumstance, such as a in
       only certain run modes, and when a "param()" is a particular value.


        my $q = $webapp->cgiapp_get_query;

       Override this method to retrieve the query object if you wish to use a different query
       interface instead of is only loaded if it is used on a given request.

       If you can use an alternative to, it needs to have some compatibility with the API. For normal use, just having a compatible "param" method should be sufficient.

       If you use the "path_info" option to the mode_param() method, then we will call the
       "path_info()" method on the query object.

       If you use the "Dump" method in CGI::Application, we will call the "Dump" and "escapeHTML"
       methods on the query object.

   Essential Application Methods
       The following methods are inherited from CGI::Application, and are available to be called
       by your application within your Application Module. They are called essential because you
       will use all are most of them to get any application up and running.  These functions are
       listed in alphabetical order.


           my $tmpl_obj = $webapp->load_tmpl;
           my $tmpl_obj = $webapp->load_tmpl('some.html');
           my $tmpl_obj = $webapp->load_tmpl( \$template_content );
           my $tmpl_obj = $webapp->load_tmpl( FILEHANDLE );

       This method takes the name of a template file, a reference to template data or a
       FILEHANDLE and returns an HTML::Template object. If the filename is undefined or missing,
       CGI::Application will default to trying to use the current run mode name, plus the
       extension ".html".

       If you use the default template naming system, you should also use
       CGI::Application::Plugin::Forward, which simply helps to keep the current name accurate
       when you pass control from one run mode to another.

       ( For integration with other template systems and automated template names, see
       "Alternatives to load_tmpl() below. )

       When you pass in a filename, the HTML::Template->new_file() constructor is used for create
       the object.  When you pass in a reference to the template content, the
       HTML::Template->new_scalar_ref() constructor is used and when you pass in a filehandle,
       the HTML::Template->new_filehandle() constructor is used.

       Refer to HTML::Template for specific usage of HTML::Template.

       If tmpl_path() has been specified, load_tmpl() will set the HTML::Template "path" option
       to the path(s) provided.  This further assists in encapsulating template usage.

       The load_tmpl() method will pass any extra parameters sent to it directly to
       HTML::Template->new_file() (or new_scalar_ref() or new_filehandle()).  This will allow the
       HTML::Template object to be further customized:

           my $tmpl_obj = $webapp->load_tmpl('some_other.html',
                die_on_bad_params => 0,
                cache => 1

       Note that if you want to pass extra arguments but use the default template name, you still
       need to provide a name of "undef":

           my $tmpl_obj = $webapp->load_tmpl(undef,
                die_on_bad_params => 0,
                cache => 1

       Alternatives to load_tmpl()

       If your application requires more specialized behavior than this, you can always replace
       it by overriding load_tmpl() by implementing your own load_tmpl() in your CGI::Application
       sub-class application module.

       First, you may want to check out the template related plugins.

       CGI::Application::Plugin::TT focuses just on Template Toolkit integration, and features
       pre-and-post features, singleton support and more.

       CGI::Application::Plugin::Stream can help if you want to return a stream and not a file.
       It features a simple syntax and MIME-type detection.

       specifying the template class with html_tmpl_class()

       You may specify an API-compatible alternative to HTML::Template by setting a new


       The default is "HTML::Template". The alternate class should provide at least the following
       parts of the HTML::Template API:

        $t = $class->new( scalarref => ... );  # If you use scalarref templates
        $t = $class->new( filehandle => ... ); # If you use filehandle templates
        $t = $class->new( filename => ... );

       Here's an example case allowing you to precisely test what's sent to your templates:

           $ENV{CGI_APP_RETURN_ONLY} = 1;
           my $webapp = WebApp->new;
           my $out_str = $webapp->run;
           my $tmpl_href = eval "$out_str";

           # Now Precisely test what would be set to the template
           is ($tmpl_href->{pet_name}, 'Daisy', "Daisy is sent template");

       This is a powerful technique because HTML::Template::Dumper loads and considers the
       template file that would actually be used. If the 'pet_name' token was missing in the
       template, the above test would fail. So, you are testing both your code and your templates
       in a much more precise way than using simple regular expressions to see if the string
       "Daisy" appeared somewhere on the page.

       The load_tmpl() callback

       Plugin authors will be interested to know that you can register a callback that will be
       executed just before load_tmpl() returns:


       When "your_method()" is executed, it will be passed three arguments:

        1. A hash reference of the extra params passed into C<load_tmpl>
        2. Followed by a hash reference to template parameters.
           With both of these, you can modify them by reference to affect
           values that are actually passed to the new() and param() methods of the
           template object.
        3. The name of the template file.

       Here's an example stub for a load_tmpl() callback:

           sub my_load_tmpl_callback {
               my ($c, $ht_params, $tmpl_params, $tmpl_file) = @_
               # modify $ht_params or $tmpl_params by reference...


           $webapp->param('pname', $somevalue);

       The param() method provides a facility through which you may set application instance
       properties which are accessible throughout your application.

       The param() method may be used in two basic ways.  First, you may use it to get or set the
       value of a parameter:

           $webapp->param('scalar_param', '123');
           my $scalar_param_values = $webapp->param('some_param');

       Second, when called in the context of an array, with no parameter name specified, param()
       returns an array containing all the parameters which currently exist:

           my @all_params = $webapp->param();

       The param() method also allows you to set a bunch of parameters at once by passing in a
       hash (or hashref):

               'key1' => 'val1',
               'key2' => 'val2',
               'key3' => 'val3',

       The param() method enables a very valuable system for customizing your applications on a
       per-instance basis.  One Application Module might be instantiated by different Instance
       Scripts.  Each Instance Script might set different values for a set of parameters.  This
       allows similar applications to share a common code-base, but behave differently.  For
       example, imagine a mail form application with a single Application Module, but multiple
       Instance Scripts.  Each Instance Script might specify a different recipient.  Another
       example would be a web bulletin boards system.  There could be multiple boards, each with
       a different topic and set of administrators.

       The new() method provides a shortcut for specifying a number of run-time parameters at
       once.  Internally, CGI::Application calls the param() method to set these properties.  The
       param() method is a powerful tool for greatly increasing your application's re-usability.


           my $q = $webapp->query();
           my $remote_user = $q->remote_user();

       This method retrieves the query object which has been created by instantiating your
       Application Module.  For details on usage of this query object, refer to CGI.
       CGI::Application is built on the CGI module.  Generally speaking, you will want to become
       very familiar with, as you will use the query object whenever you want to interact
       with form data.

       When the new() method is called, a CGI query object is automatically created.  If, for
       some reason, you want to use your own CGI query object, the new() method supports passing
       in your existing query object on construction using the QUERY attribute.

       There are a few rare situations where you want your own query object to be used after your
       Application Module has already been constructed. In that case you can pass it to
       c<query()> like this:

           my $q = $webapp->query(); # now uses $new_query_object


           # The common usage: an arrayref of run mode names that exactly match subroutine names

          # With a hashref, use a different name or a code ref
                  'mode1' => 'some_sub_by_name',
                  'mode2' => \&some_other_sub_by_ref

       This accessor/mutator specifies the dispatch table for the application states, using the
       syntax examples above. It returns the dispatch table as a hash.

       The run_modes() method may be called more than once.  Additional values passed into
       run_modes() will be added to the run modes table.  In the case that an existing run mode
       is re-defined, the new value will override the existing value.  This behavior might be
       useful for applications which are created via inheritance from another application, or
       some advanced application which modifies its own capabilities based on user input.

       The run() method uses the data in this table to send the application to the correct
       function as determined by reading the CGI parameter specified by mode_param() (defaults to
       'rm' for "Run Mode").  These functions are referred to as "run mode methods".

       The hash table set by this method is expected to contain the mode name as a key.  The
       value should be either a hard reference (a subref) to the run mode method which you want
       to be called when the application enters the specified run mode, or the name of the run
       mode method to be called:

           'mode_name_by_ref'  => \&mode_function
           'mode_name_by_name' => 'mode_function'

       The run mode method specified is expected to return a block of text (e.g.: HTML) which
       will eventually be sent back to the web browser.  The run mode method may return its block
       of text as a scalar or a scalar-ref.

       An advantage of specifying your run mode methods by name instead of by reference is that
       you can more easily create derivative applications using inheritance.  For instance, if
       you have a new application which is exactly the same as an existing application with the
       exception of one run mode, you could simply inherit from that other application and
       override the run mode method which is different.  If you specified your run mode method by
       reference, your child class would still use the function from the parent class.

       An advantage of specifying your run mode methods by reference instead of by name is
       performance.  Dereferencing a subref is faster than eval()-ing a code block.  If run-time
       performance is a critical issue, specify your run mode methods by reference and not by
       name.  The speed differences are generally small, however, so specifying by name is

       Specifying the run modes by array reference:

           $webapp->run_modes([ 'mode1', 'mode2', 'mode3' ]);

       This is the same as using a hash, with keys equal to values

               'mode1' => 'mode1',
               'mode2' => 'mode2',
               'mode3' => 'mode3'

       Often, it makes good organizational sense to have your run modes map to methods of the
       same name.  The array-ref interface provides a shortcut to that behavior while reducing
       verbosity of your code.

       Note that another importance of specifying your run modes in either a hash or array-ref is
       to assure that only those Perl methods which are specifically designated may be called via
       your application.  Application environments which don't specify allowed methods and
       disallow all others are insecure, potentially opening the door to allowing execution of
       arbitrary code.  CGI::Application maintains a strict "default-deny" stance on all method
       invocation, thereby allowing secure applications to be built upon it.


       Your application should *NEVER* print() to STDOUT.  Using print() to send output to STDOUT
       (including HTTP headers) is exclusively the domain of the inherited run() method.
       Breaking this rule is a common source of errors.  If your program is erroneously sending
       content before your HTTP header, you are probably breaking this rule.


       If CGI::Application is asked to go to a run mode which doesn't exist it will usually
       croak() with errors.  If this is not your desired behavior, it is possible to catch this
       exception by implementing a run mode with the reserved name "AUTOLOAD":

               "AUTOLOAD" => \&catch_my_exception

       Before CGI::Application calls croak() it will check for the existence of a run mode called
       "AUTOLOAD".  If specified, this run mode will in invoked just like a regular run mode,
       with one exception:  It will receive, as an argument, the name of the run mode which
       invoked it:

         sub catch_my_exception {
               my $self = shift;
               my $intended_runmode = shift;

               my $output = "Looking for '$intended_runmode', but found 'AUTOLOAD' instead";
               return $output;

       This functionality could be used for a simple human-readable error screen, or for more
       sophisticated application behaviors.



       The start_mode contains the name of the mode as specified in the run_modes() table.
       Default mode is "start".  The mode key specified here will be used whenever the value of
       the CGI form parameter specified by mode_param() is not defined.  Generally, this is the
       first time your application is executed.



       This access/mutator method sets the file path to the directory (or directories) where the
       templates are stored.  It is used by load_tmpl() to find the template files, using
       HTML::Template's "path" option. To set the path you can either pass in a text scalar or an
       array reference of multiple paths.

   More Application Methods
       You can skip this section if you are just getting started.

       The following additional methods are inherited from CGI::Application, and are available to
       be called by your application within your Application Module.  These functions are listed
       in alphabetical order.



       The delete() method is used to delete a parameter that was previously stored inside of
       your application either by using the PARAMS hash that was passed in your call to new() or
       by a call to the param() method.  This is similar to the delete() method of It is
       useful if your application makes decisions based on the existence of certain params that
       may have been removed in previous sections of your app or simply to clean-up your


           print STDERR $webapp->dump();

       The dump() method is a debugging function which will return a chunk of text which contains
       all the environment and web form data of the request, formatted nicely for human
       readability.  Useful for outputting to STDERR.


           my $output = $webapp->dump_html();

       The dump_html() method is a debugging function which will return a chunk of text which
       contains all the environment and web form data of the request, formatted nicely for human
       readability via a web browser.  Useful for outputting to a browser. Please consider the
       security implications of using this in production code.



       If the runmode dies for whatever reason, "run() will" see if you have set a value for
       "error_mode()". If you have, "run()" will call that method as a run mode, passing $@ as
       the only parameter.

       Plugins authors will be interested to know that just before "error_mode()" is called, the
       "error" hook will be executed, with the error message passed in as the only parameter.

       No "error_mode" is defined by default.  The death of your "error_mode()" run mode is not
       trapped, so you can also use it to die in your own special way.

       For a complete integrated logging solution, check out



       The "get_current_runmode()" method will return a text scalar containing the name of the
       run mode which is currently being executed.  If the run mode has not yet been determined,
       such as during setup(), this method will return undef.


           # add or replace the 'type' header
           $webapp->header_add( -type => 'image/png' );

           - or -

           # add an additional cookie

       The "header_add()" method is used to add one or more headers to the outgoing response
       headers.  The parameters will eventually be passed on to the header() method, so
       refer to the CGI docs for exact usage details.

       Unlike calling "header_props()", "header_add()" will preserve any existing headers. If a
       scalar value is passed to "header_add()" it will replace the existing value for that key.

       If an array reference is passed as a value to "header_add()", values in that array ref
       will be appended to any existing values for that key.  This is primarily useful for
       setting an additional cookie after one has already been set.


           # Set a complete set of headers
           %set_headers = $webapp->header_props(-type=>'image/gif',-expires=>'+3d');

           # clobber / reset all headers
           %set_headers = $webapp->header_props({});

           # Just retrieve the headers
           %set_headers = $webapp->header_props();

       The "header_props()" method expects a hash of HTTP header properties.
       These properties will be passed directly to the "header()" or "redirect()" methods of the
       query() object. Refer to the docs of your query object for details. (Be default, it's

       Calling header_props with an empty hashref clobber any existing headers that have
       previously set.

       "header_props()" returns a hash of all the headers that have currently been set. It can be
       called with no arguments just to get the hash current headers back.

       To add additional headers later without clobbering the old ones, see "header_add()".


       It is through the "header_props()" and "header_add()" method that you may modify the
       outgoing HTTP headers.  This is necessary when you want to set a cookie, set the mime type
       to something other than "text/html", or perform a redirect.  The header_props() method
       works in conjunction with the header_type() method.  The value contained in header_type()
       determines if we use CGI::header() or CGI::redirect().  The content of header_props() is
       passed as an argument to whichever function is called.

       Understanding this relationship is important if you wish to manipulate the HTTP header



       This method used to declare that you are setting a redirection header, or that you want no
       header to be returned by the framework.

       The value of 'header' is almost never used, as it is the default.

       Example of redirecting:

         sub some_redirect_mode {
           my $self = shift;
           # do stuff here....
           $self->header_props(-url=>  "http://site/path/doc.html" );

       To simplify that further, use CGI::Application::Plugin::Redirect:

           return $self->redirect('');

       Setting the header to 'none' may be useful if you are streaming content.  In other
       contexts, it may be more useful to set "$ENV{CGI_APP_RETURN_ONLY} = 1;", which suppresses
       all printing, including headers, and returns the output instead.

       That's commonly used for testing, or when using CGI::Application as a controller for a
       cron script!


        # Name the CGI form parameter that contains the run mode name.
        # This is the default behavior, and is often sufficient.

        # Set the run mode name directly from a code ref

        # Alternate interface, which allows you to set the run
        # mode name directly from $ENV{PATH_INFO}.
               path_info=> 1,
               param =>'rm'

       This accessor/mutator method is generally called in the setup() method.  It is used to
       help determine the run mode to call. There are three options for calling it.


       Here, a CGI form parameter is named that will contain the name of the run mode to use.
       This is the default behavior, with 'rm' being the parameter named used.


       Here a code reference is provided. It will return the name of the run mode to use
       directly. Example:

        sub some_method {
          my $self = shift;
          return 'run_mode_x';

       This would allow you to programmatically set the run mode based on arbitrary logic.

               path_info=> 1,
               param =>'rm'

       This syntax allows you to easily set the run mode from $ENV{PATH_INFO}.  It will try to
       set the run mode from the first part of $ENV{PATH_INFO} (before the first "/"). To specify
       that you would rather get the run mode name from the 2nd part of $ENV{PATH_INFO}:

        $webapp->mode_param( path_info=> 2 );

       This also demonstrates that you don't need to pass in the "param" hash key. It will still
       default to "rm".

       You can also set "path_info" to a negative value. This works just like a negative list
       index: if it is -1 the run mode name will be taken from the last part of $ENV{PATH_INFO},
       if it is -2, the one before that, and so on.

       If no run mode is found in $ENV{PATH_INFO}, it will fall back to looking in the value of a
       the CGI form field defined with 'param', as described above.  This allows you to use the
       convenient $ENV{PATH_INFO} trick most of the time, but also supports the edge cases, such
       as when you don't know what the run mode will be ahead of time and want to define it with

       More about $ENV{PATH_INFO}.

       Using $ENV{PATH_INFO} to name your run mode creates a clean separation between the form
       variables you submit and how you determine the processing run mode. It also creates URLs
       that are more search engine friendly. Let's look at an example form submission using this

               <form action="/cgi-bin/instance.cgi/edit_form" method=post>
                       <input type="hidden" name="breed_id" value="4">

       Here the run mode would be set to "edit_form". Here's another example with a query string:


       This demonstrates that you can use $ENV{PATH_INFO} and a query string together without
       problems. $ENV{PATH_INFO} is defined as part of the CGI specification should be supported
       by any web server that supports CGI scripts.



       The prerun_mode() method is an accessor/mutator which can be used within your
       cgiapp_prerun() method to change the run mode which is about to be executed.  For example,

         # In
         package WebApp;
         use base 'CGI::Application';
         sub cgiapp_prerun {
               my $self = shift;

               # Get the web user name, if any
               my $q = $self->query();
               my $user = $q->remote_user();

               # Redirect to login, if necessary
               unless ($user) {

       In this example, the web user will be forced into the "login" run mode unless they have
       already logged in.  The prerun_mode() method permits a scalar text string to be set which
       overrides whatever the run mode would otherwise be.

       The use of prerun_mode() within cgiapp_prerun() differs from setting mode_param() to use a
       call-back via subroutine reference.  It differs because cgiapp_prerun() allows you to
       selectively set the run mode based on some logic in your cgiapp_prerun() method.  The
       call-back facility of mode_param() forces you to entirely replace CGI::Application's
       mechanism for determining the run mode with your own method.  The prerun_mode() method
       should be used in cases where you want to use CGI::Application's normal run mode switching
       facility, but you want to make selective changes to the mode under specific conditions.

       Note:  The prerun_mode() method may ONLY be called in the context of a cgiapp_prerun()
       method.  Your application will die() if you call prerun_mode() elsewhere, such as in
       setup() or a run mode method.

   Dispatching Clean URIs to run modes
       Modern web frameworks dispense with cruft in URIs, providing in clean URIs instead.
       Instead of:


       A clean URI to describe the same resource might be:


       The process of mapping these URIs to run modes is called dispatching and is handled by
       CGI::Application::Dispatch. Dispatching is not required and is a layer you can fairly
       easily add to an application later.

   Offline website development
       You can work on your CGI::Application project on your desktop or laptop without installing
       a full-featured web-server like Apache. Instead, install CGI::Application::Server from
       CPAN. After a few minutes of setup, you'll have your own private application server up and

   Automated Testing
       Test::WWW::Mechanize::CGIApp allows functional testing of a CGI::App-based project without
       starting a web server. Test::WWW::Mechanize could be used to test the app through a real
       web server.

       Direct testing is also easy. CGI::Application will normally print the output of it's run
       modes directly to STDOUT. This can be suppressed with an environment variable,
       CGI_APP_RETURN_ONLY. For example:

         $ENV{CGI_APP_RETURN_ONLY} = 1;
         $output = $webapp->run();
         like($output, qr/good/, "output is good");

       Examples of this style can be seen in our own test suite.


       CGI::Application has a plug-in architecture that is easy to use and easy to develop new
       plug-ins for.

   Recommended Plug-ins
       The following plugins are recommended for general purpose web/db development:

       ·   CGI::Application::Plugin::Redirect - is a simple plugin to provide a shorter syntax
           for executing a redirect.

       ·   CGI::Application::Plugin::ConfigAuto - Keeping your config details in a separate file
           is recommended for every project. This one integrates with Config::Auto. Several more
           config plugin options are listed below.

       ·   CGI::Application::Plugin::DBH - Provides easy management of one or more database
           handles and can delay making the database connection until the moment it is actually

       ·   CGI::Application::Plugin::FillInForm - makes it a breeze to fill in an HTML form from
           data originating from a CGI query or a database record.

       ·   CGI::Application::Plugin::Session - For a project that requires session management,
           this plugin provides a useful wrapper around CGI::Session

       ·   CGI::Application::Plugin::ValidateRM - Integration with Data::FormValidator and

   More plug-ins
       Many more plugins are available as alternatives and for specific uses. For a current
       complete list, please consult CPAN:

       ·   CGI::Application::Plugin::AnyTemplate - Use any templating system from within
           CGI::Application using a unified interface

       ·   CGI::Application::Plugin::Apache - Use Apache::* modules without interference

       ·   CGI::Application::Plugin::AutoRunmode - Automatically register runmodes

       ·   CGI::Application::Plugin::Config::Context - Integration with Config::Context.

       ·   CGI::Application::Plugin::Config::General - Integration with Config::General.

       ·   CGI::Application::Plugin::Config::Simple - Integration with Config::Simple.

       ·   CGI::Application::Plugin::CompressGzip - Add Gzip compression

       ·   CGI::Application::Plugin::LogDispatch - Integration with Log::Dispatch

       ·   CGI::Application::Plugin::Stream - Help stream files to the browser

       ·   CGI::Application::Plugin::TemplateRunner - Allows for more of an ASP-style code
           structure, with the difference that code and HTML for each screen are in separate

       ·   CGI::Application::Plugin::TT - Use Template::Toolkit as an alternative to

       Consult each plug-in for the exact usage syntax.

   Writing Plug-ins
       Writing plug-ins is simple. Simply create a new package, and export the methods that you
       want to become part of a CGI::Application project. See
       CGI::Application::Plugin::ValidateRM for an example.

       In order to avoid namespace conflicts within a CGI::Application object, plugin developers
       are recommended to use a unique prefix, such as the name of plugin package, when storing
       information. For instance:

        $app->{__PARAM} = 'foo'; # BAD! Could conflict.
        $app->{'MyPlugin::Module::__PARAM'} = 'foo'; # Good.
        $app->{'MyPlugin::Module'}{__PARAM} = 'foo'; # Good.

   Writing Advanced Plug-ins - Using callbacks
       When writing a plug-in, you may want some action to happen automatically at a particular
       stage, such as setting up a database connection or initializing a session. By using these
       'callback' methods, you can register a subroutine to run at a particular phase,
       accomplishing this goal.

       Callback Examples

         # register a callback to the standard CGI::Application hooks
         #   one of 'init', 'prerun', 'postrun', 'teardown' or 'load_tmpl'
         # As a plug-in author, this is probably the only method you need.

         # Class-based: callback will persist for all runs of the application
         $class->add_callback('init', \&some_other_method);

         # Object-based: callback will only last for lifetime of this object
         $self->add_callback('prerun', \&some_method);

         # If you want to create a new hook location in your application,
         # You'll need to know about the following two methods to create
         # the hook and call it.

         # Create a new hook

         # Then later execute all the callbacks registered at this hook

       Callback Methods


               $self->add_callback ('teardown', \&callback);
               $class->add_callback('teardown', 'method');

       The add_callback method allows you to register a callback function that is to be called at
       the given stage of execution.  Valid hooks include 'init', 'prerun', 'postrun' and
       'teardown', 'load_tmpl', and any other hooks defined using the "new_hook" method.

       The callback should be a reference to a subroutine or the name of a method.

       If multiple callbacks are added to the same hook, they will all be executed one after the
       other.  The exact order depends on which class installed each callback, as described below
       under Callback Ordering.

       Callbacks can either be object-based or class-based, depending upon whether you call
       "add_callback" as an object method or a class method:

               # add object-based callback
               $self->add_callback('teardown', \&callback);

               # add class-based callbacks
               $class->add_callback('teardown', \&callback);
               My::Project->add_callback('teardown', \&callback);

       Object-based callbacks are stored in your web application's $c object; at the end of the
       request when the $c object goes out of scope, the callbacks are gone too.

       Object-based callbacks are useful for one-time tasks that apply only to the current
       running application.  For instance you could install a "teardown" callback to trigger a
       long-running process to execute at the end of the current request, after all the HTML has
       been sent to the browser.

       Class-based callbacks survive for the duration of the running Perl process.  (In a
       persistent environment such as "mod_perl" or "PersistentPerl", a single Perl process can
       serve many web requests.)

       Class-based callbacks are useful for plugins to add features to all web applications.

       Another feature of class-based callbacks is that your plugin can create hooks and add
       callbacks at any time - even before the web application's $c object has been initialized.
       A good place to do this is in your plugin's "import" subroutine:

               package CGI::Application::Plugin::MyPlugin;
               use base 'Exporter';
               sub import {
                       my $caller = scalar(caller);
                       $caller->add_callback('init', 'my_setup');
                       goto &Exporter::import;

       Notice that "$caller->add_callback" installs the callback on behalf of the module that
       contained the line:

               use CGI::Application::Plugin::MyPlugin;



       The "new_hook()" method can be used to create a new location for developers to register
       callbacks.  It takes one argument, a hook name. The hook location is created if it does
       not already exist. A true value is always returned.

       For an example, CGI::Application::Plugin::TT adds hooks before and after every template is

       See "call_hook(HOOK)" for more details about how hooks are called.


           $self->call_hook('pretemplate', @args);

       The "call_hook" method is used to executed the callbacks that have been registered at the
       given hook.  It is used in conjunction with the "new_hook" method which allows you to
       create a new hook location.

       The first argument to "call_hook" is the hook name. Any remaining arguments are passed to
       every callback executed at the hook location. So, a stub for a callback at the
       'pretemplate' hook would look like this:

        sub my_hook {
           my ($c,@args) = @_;
           # ....

       Note that hooks are semi-public locations. Calling a hook means executing callbacks that
       were registered to that hook by the current object and also those registered by any of the
       current object's parent classes.  See below for the exact ordering.

       Callback Ordering

       Object-based callbacks are run before class-based callbacks.

       The order of class-based callbacks is determined by the inheritance tree of the running
       application. The built-in methods of "cgiapp_init", "cgiapp_prerun", "cgiapp_postrun", and
       "teardown" are also executed this way, according to the ordering below.

       In a persistent environment, there might be a lot of applications in memory at the same
       time.  For instance:

                 Other::Project   # uses CGI::Application::Plugin::Baz
                        Other::App    # uses CGI::Application::Plugin::Bam

                 My::Project      # uses CGI::Application::Plugin::Foo
                        My::App       # uses CGI::Application::Plugin::Bar

       Suppose that each of the above plugins each added a callback to be run at the 'init'

               Plugin                           init callback
               ------                           -------------
               CGI::Application::Plugin::Baz    baz_startup
               CGI::Application::Plugin::Bam    bam_startup

               CGI::Application::Plugin::Foo    foo_startup
               CGI::Application::Plugin::Bar    bar_startup

       When "My::App" runs, only "foo_callback" and "bar_callback" will run.  The other callbacks
       are skipped.

       The @ISA list of "My::App" is:


       This order determines the order of callbacks run.

       When "call_hook('init')" is run on a "My::App" application, callbacks installed by these
       modules are run in order, resulting in: "bar_startup", "foo_startup", and then finally

       If a single class installs more than one callback at the same hook, then these callbacks
       are run in the order they were registered (FIFO).


       Therese are primary resources available for those who wish to learn more about
       CGI::Application and discuss it with others.


       This is a community built and maintained resource that anyone is welcome to contribute to.
       It contains a number of articles of its own and links to many other CGI::Application
       related pages:


       Support Mailing List

       If you have any questions, comments, bug reports or feature suggestions, post them to the
       support mailing list!  To join the mailing list, visit

       Source Code

       This project is managed using git and is available on Github:



       o   CGI

       o   HTML::Template

       o   CGI::Application::Framework - A full-featured web application based on


       If you're interested in finding out more about CGI::Application, the following articles
       are available on

           Using CGI::Application

           Rapid Website Development with CGI::Application

       Thanks to O'Reilly for publishing these articles, and for the incredible value they
       provide to the Perl community!


       Jesse Erlbaum <>

       Mark Stosberg has served as a co-maintainer since version 3.2, Martin McGrath became a co-
       maintainer as of version 4.51, with the help of the numerous contributors documented in
       the Changes file.


       CGI::Application was originally developed by The Erlbaum Group, a software engineering and
       consulting firm in New York City.

       Thanks to Vanguard Media ( for funding the initial development of this
       library and for encouraging Jesse Erlbaum to release it to the world.

       Many thanks to Sam Tregar (author of the most excellent HTML::Template module!) for his
       innumerable contributions to this module over the years, and most of all for getting me
       off my ass to finally get this thing up on CPAN!

       Many other people have contributed specific suggestions or patches, which are documented
       in the "Changes" file.

       Thanks also to all the members of the CGI-App mailing list!  Your ideas, suggestions,
       insights (and criticism!) have helped shape this module immeasurably.  (To join the
       mailing list, visit )


       CGI::Application : Framework for building reusable web-applications Copyright (C)
       2000-2003 Jesse Erlbaum <>

       This module is free software; you can redistribute it and/or modify it under the terms of

       a) the GNU General Public License as published by the Free Software Foundation; either
       version 1, or (at your option) any later version,


       b) the "Artistic License" which comes with this module.

       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
       without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
       See either the GNU General Public License or the Artistic License for more details.

       You should have received a copy of the Artistic License with this module, in the file
       ARTISTIC.  If not, I'll be glad to provide one.

       You should have received a copy of the GNU General Public License along with this program;
       if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
       MA 02111-1307 USA