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CGI::Application::Plugin::MessageStack - A message stack for your CGI::Application


Version 0.34


This plugin gives you a few support methods that you can call within your cgiapp to pass along messages between requests for a given user.

 use CGI::Application::Plugin::Session;
 use CGI::Application::Plugin::MessageStack;

 sub mainpage {
   my $self = shift;
   my $template = $self->load_tmpl( 'mainpage.TMPL', 'die_on_bad_params' => 0 );
   # ...

 sub process {
   my $self = shift;
       -scope          => 'mainpage',
       -message        => 'Your listing has been updated',
       -classification => 'INFO',
   $self->forward( 'mainpage' );

 sub cgiapp_init {
   # setup your session object as usual...

Meanwhile, in your (HTML::Template) template code:

 <style type="text/css">
   .INFO {
     font-weight: bold;
   .ERROR {
     color: red;
 <!-- TMPL_LOOP NAME="CAP_Messages" -->
   <div class="<!-- TMPL_VAR NAME="classification" -->">
     <!-- TMPL_VAR NAME="message" -->
 <!-- /TMPL_LOOP -->

It's a good idea to turn off 'die_on_bad_params' in HTML::Template - in case this plugin tries to put in the parameters and they're not available in your template.

Here's a quick TT example:

 <style type="text/css">
   .INFO {
     font-weight: bold;
   .ERROR {
     color: red;
 [% FOREACH CAP_Messages %]
    <div class="[% classification %]">[% message %]</div>
 [% END %]

If you use TT, I recommend using CAP-TT and a more recent version (0.09), which supports cgiapp's load_tmpl hook and then this plugin will automatically supply TT with the relevant messages. Your runmode could be this simple:

 sub start {
     my $self = shift;
     my $session = $self->session;
     return $self->tt_process( '' );

I don't have the experience to weigh in on how you'd do this with other templates (HTDot, Petal), but basically, this plugin will put in a loop parameter called 'CAP_Messages'. Within each element of that loop, you'll have two tags, 'classification' and 'message'.

NOTE: I have broken backwards compatibility with this release (0.30) and the loop parameter's default name is now 'CAP_Messages'. If you used the old __CAP_Messages or want to use another name, feel free to use the capms_config to override the -loop_param_name.


This plugin by default needs a session object to tuck away the message(s). It's recommended that you use this in conjunction with CGI::Application::Plugin::Session. You can opt to not have the messages persist and thereby, not use CAP-Session by using the -dont_use_session option in the capms_config method.

This plugin hooks into cgiapp's load_tmpl method and if you've pushed any messages in the stack, will automatically add the message parameters.

In the functions, there are scope & classification keys and when they're used for either display or your API purposes (clearing, pop'ing, etc), the classification is an exclusive specification. Meaning, if you ask for messages with the 'ERROR' classification, it will only deal with messages that you've pushed in with the 'ERROR' classification. Any messages that have no classification aren't included.

The scope key is not exclusive, meaning that if you ask for messages with a 'mainpage' scope, it will deal with messages that you've pushed with that scope as well as any messages that you've pushed in without a scope.

If you use both scope & classification, it blends both of those rules, first getting all matching messages with the same classification and then filtering out messages that are scoped and don't match the scope you're looking for.

This logic may change as I get feedback from more saavy developers. What we may end up doing is have a plugin configuration where you can dictate the logic that's used.



     -scope          => 'mainpage',
     -message        => 'Your listing has been updated',
     -classification => 'INFO',

You provide a hash to the push_message() method with three possible keys:

The scope & classification keys are optional. If you don't provide a scope, it will assume a global presence.


 my @messages = $self->messages();
 my @messages = $self->messages( -scope => 'mainpage' );
 my @messages = $self->messages( -scope => 'mainpage', -classification => 'ERROR' );
 my @messages = $self->messages( -classification => 'ERROR' );

If you want to take a gander at the message stack data structure, you can use this method.

Optionally, you can use a hash parameters to get a slice of the messages, using the same keys as specified in the push_message() method.

It will return an array reference of the matching messages or 'undef', if there's either no messages in the stack or no messages that match your specification(s).


 my $message = $self->pop_message();
 my $message = $self->pop_message( -scope => 'mainpage' );
 my $message = $self->pop_message( -scope => 'mainpage', -classification => 'WARNING' );
 my $message = $self->pop_message( -classification => 'ERROR' );

Pops off the last message from the stack and returns it. Note that this just returns the -message part.

You can pop off an exact message, given a hash parameters, using the same keys as specified in the push_message() method.

Otherwise, it will pop off the message, given the current runmode and the last message added.


 $self->clear_messages( -scope => 'mainpage' );
 $self->clear_messages( -scope => 'mainpage', -classification => 'ERROR' );
 $self->clear_messages( -classification => 'ERROR' );

Clears the message stack.

Optionally, you can clear particular slices of the message stack, given a hash parameters, using the same keys as specified in the push_message() method.

If you specify a scope, it will clear any messages that are either global or match that scope

If you specify a classification, it will clear any messages that have that classification (but not any messages that don't have any classification).

If you specify both, it will combine both that logic in an AND fashion.


     -automatic_clearing            => 1,
     -dont_use_session              => 1,
     -loop_param_name               => 'MyOwnLoopName',
     -message_param_name            => 'MyOwnMessageName',
     -classification_param_name     => 'MyOwnClassificationName',

There is a configuration option that you, as the developer can specify:


Jason Purdy, <Jason@Purdy.INFO>


CGI::Application and CGI::Application::Plugin::Session


Please report any bugs or feature requests to, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

I suspect that this code could use some expert guidance. I hacked it together and I'd hate to think that it would be responsible for slowing templates down. Please feel free to submit patches, guiding comments, etc.


Thanks to the guys on the #cgiapp channel


Copyright 2005 Jason Purdy, all rights reserved.

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

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