Author image Randal L. Schwartz


CGI::Prototype::Hidden - Create a CGI application by subclassing - hidden field


  # in My/ ---
  package My::App;
  use base qw(CGI::Prototype::Hidden);

  # in /some/cgi-bin/program

  use lib qw(/location);
  use My::App;


CGI::Prototype::Hidden extends CGI::Prototype by providing a hidden field mechanism for state, and a dispatching algorithm based on that hidden field. In particular,

  1. Dispatching to a particular paged based on the "state" of the application is performed according to param field.

  2. The name of the state is appended to an application-wide package prefix to determine an appropriate class to handle the request.

  3. The package for the class is autoloaded if needed.

  4. The template for the class replaces .pm with .tt (configurable), found in the same @INC path, and is therefore likely to be in the same directory.

  5. A "wrapper" template is automatically provided.

Thus, a simple 10-page CGI application will require 23 files: 10 classes, 10 corresponding templates, a wrapper template, a master application class, and a CGI script that loads the master application class and activates it.

The default class is My::App, but this can be overridden. The default state is welcome, but this too can be overridden. The default hidden param name for the state is _state, and if you think this can be overridden, you are correct. See the trend here?

A sample app is the best way to show all of this, of course. We don't have one yet... that's on the TODO list. However, the functions have all been exercised in the tests for this module, including an artificial application, so check that out for at least an example of the interfaces.


These methods or values are the ones you'll most likely change in your application, although you can leave them all alone and it'll still be a valid framework to create your entire application.


The name of the hidden field which will contain the state, defaulting to _state.

In any form you create, or any constructed URL, you must be sure to include this param as part of the form so that the right response can be matched up for the submitted data. For example:

<form> [% self.CGI.hidden(self.config_state_param) %] First name:[% self.CGI.textfield("first_name") %]<br> Last name: [% self.CGI.textfield("last_name") %] <input type=submit> </form>


The class prefix placed ahead of the state name, default My::App. For example, the controller class for the welcome state will be <My::App::welcome>.

You should change this if you are using mod_perl to something that won't conflict with other usages of the same server space. For CGI scripts, the default is an easy classname to remember.

Note that the template also use this name as their prefix, so that your controller and template files end up in the same directory.


The initial page if the state is missing, default welcome.


The name of the WRAPPER template, default My/App/

If you change config_class_prefix, you'll want to change this as well so that ends up in the right directory. (I debated doing that for you so you could just say "WRAPPER.TT", but that'd make more complicated versions of this callback be even more and more complicated.)

The wrapper template is called with template set to the wrapped template, which should be processed in the wrapper. The smallest wrapper is therefore:

  [% PROCESS $template %]

However, typically, you'll want to define app-wide blocks and variables, and maybe wrap the statement above in an exception catcher. For example:

    content = PROCESS $template;
  ### exceptions
  ## for errors:
  An error has occurred.  Remain calm.
  Authorities have been notified.  Do not leave the general area.
    FILTER stderr -%]
  ** [% template.filename %] error: [% %] **
  END; # TRY

This sends back a plain message to the browser, as well as logging the precise error text to STDERR, and hopefully the web error log.


The location of the compiled Perl templates, default "/tmp/compile-dir.$<" (where $< is the current user's numeric user ID). You'll want this to be some place that the process can write, but nobody else can. The default is functional, but not immune to other hostile users on the same box, so you'll want to override that for those cases.


The suffix replacing .pm when the module name is mapped to the template name. By default, it's .tt.


You will most likely not need to change these, but you'll want to stay away from their names.


Called with a page name, returns a page object. Will also autoload the package.


This is still an experimental feature that will be reworked in future releases.

Called with a page name, returns a new page object that can be used as self in a template, mixing in the code from the page's class for additional heavy lifting.

For example, to have a "subpage" plugin, create a and file, then include the tt with:

  [% INCLUDE My/App/
       self = self.plugin("subpage")
       other = parms
       go = here

Now, within, calls to self.SomeMethod will first search the original page's lineage, and then the plugin class lineage for a definition for SomeMethod.


Overridden from CGI::Prototype. Selects either the hidden field state, or the default state, and returns the page object.


Returns the simple name for the current page object by stripping off the config_class_prefix. Note that this will fail in the event of prototype page constructed on the fly, rather than a named class. Hmm, I'll have to think about what that implies.


Overridden from CGI::Prototype. Forces the hidden state param to the shortname of the current object, then calls render_enter_per_page.


If you need page-specific render_enter items, put them here. The default definition does nothing. This is to keep from having to call superclass methods for render_enter.


Overridden from CGI::Prototype. Calls respond_per_app and then respond_per_page, looking for a true value, which is then returned.

If you have site-wide buttons (like a button-bar on the side or top of your form), look for them in respond_per_app, and return the new page from there. Otherwise, return undef, and it'll fall through to the per-page response.


A hook for application-wide responses, defaulting to undef. Should return either a page object (to be rendered) or a false value (selecting the per-page respond).


If respond_per_app returns false, this hook is then evaluated. It should return a page object to be rendered. The default returns the current page object, so you "stay here" for rendering.


Overridden from CGI::Prototype. Returns the name of a template, defined by replacing the double-colons in the classname of the current page with forward slashes, and then appending .tt (by default, see config_tt_extension). Because @INC is added to the INCLUDE_PATH for the engine, this should find the .tt file in the same directory as the .pm file.


Overridden from CGI::Prototype, so that the cached Template object that is essentially:

     POST_CHOMP => 1,
     INCLUDE_PATH => [@INC],
     COMPILE_DIR => $self->config_compile_dir,
     PROCESS => [$self->config_wrapper],


CGI::Prototype, Template::Manual


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.


Randal L. Schwartz, <>

Special thanks to and an unnamed large university for providing funding for the development of this module.


Copyright (C) 2003, 2004, 2005 by Randal L. Schwartz

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.5 or, at your option, any later version of Perl 5 you may have available.