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NAME

CGI::Application::Plugin::FormState - Store Form State without Hidden Fields

VERSION

Version 0.01

SYNOPSIS

FormState is just a temporary stash that you can use for storing and retrieving private parameters in your multi-page form.

    use CGI::Application::Plugin::FormState;

    my $form = <<EOF;
       <form action="app.cgi">
       <input type="hidden" name="run_mode" value="form_process_runmode">
       <input type="hidden" name="some_storage_name" value="<tmpl_var some_storage_name>">
       ...
       </form>
    EOF

    sub form_display_runmode {
        my $self = shift;

        $self->form_state->init('some_storage_name');

        # Store some parameters
        $self->form_state->param('name'       => 'Road Runner');
        $self->form_state->param('occupation' => 'Having Fun');

        my $t = $self->load_tmpl(scalarref => \$form);
        return $t->output;

    }

    sub form_process_runmode {
        my $self = shift;

        $self->form_state->init('some_storage_name');

        # Retrieve some parameters
        print $self->form_state->param('name');       # 'Road Runner'
        print $self->form_state->param('occupation'); # 'Having Fun'
    }

EXAMPLE

This is a more complete example, using CGI::Application::Plugin::ValidateRM.

    use CGI::Application::Plugin::Session;
    use CGI::Application::Plugin::FormState;
    use CGI::Application::Plugin::ValidateRM;

    my $form = <<EOF;
       <form action="app.cgi">
       <input type="hidden" name="run_mode" value="my_form_process">
       <input type="hidden" name="myform_data" value="<tmpl_var myform_data>">
       ...
       </form>
    EOF

    sub my_form_display {
        my $self     = shift;
        my $errs     = shift;
        my $t        = $self->load_tmpl(scalarref => \$form);

        # Initialize the form state
        $self->form_state->init('myform_data');

        # Stash some data into it
        $self->form_state->param('name'       => 'Wile E. Coyote');
        $self->form_state->param('occupation' => 'Mining Engineer');

        # Normal ValidateRM error handling
        $t->param($errs) if $errs;
        return $t->output;
    }

    sub my_form_process {
        my $self;

        # Normal ValidateRM validation
        my ($results, $err_page) = $self->check_rm('my_form_display','_my_form_profile');
        return $err_page if $err_page;

        # The data from the submitted form
        my $params = $self->dfv_results;

        # Now merge the additional data that we stored in the Form State
        $self->form_state->init('myform_data');

        $params->{'name'}       = $self->form_state->param('name');       # 'Wile E. Coyote'
        $params->{'occupation'} = $self->form_state->param('occupation'); # 'Mining Engineer'


        # Now do something interesting with $params
        # ...


        my $t = $self->load_tmpl('success.html');
        return $t->output;
    }

    # Standard ValiateRM profile
    sub _my_form_profile {
        return {
            required => 'email',
            msgs => {
                    any_errors => 'some_errors',
                    prefix => 'err_',
            },
        };
    }

DESCRIPTION

CGI::Application::Plugin::FormState provides a temporary storage area within the user's session for storing form-related data.

The main use of this is for multi-page forms. Instead of using hidden fields to store data related to the form, you store and retrieve values from the form state.

In the first instance of your app:

    $self->form_state->init('my_storage_name');
    $self->form_state->param('some_name' => 'some_value');
    $self->form_state->param('some_other_name' => 'some_other_value');

And later, in a different instance of your app:

    $self->form_state->init('my_storage_name');
    $val1 = $self->form_state->param('some_name');
    $val2 = $self->form_state->param('some_other_name');

To connect the first instance and the second, you put a single hidden field in your template:

    <input type="hidden" name="my_storage_name" value="<tmpl_var my_storage_name>">

You don't have to worry about creating the template param my_storage_name; it is added automatically to your template parameters via the load_tmpl hook. Just make sure that the hidden field name and template parameter name both match the form state storage name, as passed to init.

If you're skeptical about whether all this abstraction is a good idea, see "MOTIVATION", below.

IMPLEMENTATION

When you call $self->form_state->init for the first time, a top-level key is created in the user's session. This key contains a random, hard-to-guess element. If your storage name is called 'my_data', it might look something like:

   form_state_my_data_84eb13cfed01764d9c401219faa56d53

All data you place in the form state with param is stored in the user's session under this key.

You pass the name of this key on to the next instance of your application by means of a hidden field in your form:

    <input type="hidden" name="my_data" value="<tmpl_var my_data>">

You manually put this hidden field in your template. The template parameter my_data is automatically added to your template parameters via the load_tmpl hook. It contains the random, hard-to-guess portion (e.g. 84eb13cfed01764d9c401219faa56d53). When the template is filled, the hidden field will look something like this:

    <input type="hidden" name="my_data" value="84eb13cfed01764d9c401219faa56d53">

In the application that receives this form submission, when you call $self->form_state->init('my_data'), the form state is initialized from the pre-existing key in the user's session.

Since all values are stored on the server in the user's session, the user can't tamper with any of them.

To keep old form_data from cluttering up the user's session, the system uses CGI::Session's expire feature to expire old form state keys after a reasonable amount of time has passed (1 day by default).

METHODS

init('storage_name', %options)

Initializes the form state storage, using the name storage_name.

If a query parameter named storage_name already exists, then the form state of that name is restored from the user's session.

If a query parameter named storage_name does not exist, then a storage for the form state of that name is created in the user's session.

To connect the app writing the form state with the app reading it, you need to add a hidden field to your form:

    <input type="hidden" name="storage_name" value="<tmpl_var storage_name>">

(Although you do not have to add the template parameter storage_name; it is added automatically)

Named options follow the storage_name:

    $self->form_state->init('storage_name', expires => '2d');

The following option is currently available:

expires

Indicates when this form state storage should expire and disappear from the user's session. Uses the same format as CGI::Session's expire. Defaults to 1 day ('1d'). To cancel expiration and make the form state last as long as the user's session does, use:

    $self->form_state->init('storage_name', expires => 0);
param

Read and set values in the form state storage. It acts like the param method typically does in modules such as CGI, CGI::Application, CGI::Session, HTML::Template etc.

    # set a value
    $self->form_state->param('some_name' => 'some_value');

    # retrieve a value
    my $val = $self->form_state->param('some_name');

    # set multiple values
    $self->form_state->param(
        'some_name'       => 'some_value',
        'some_other_name' => 'some_other_value',
    );

    # retrive the names of all the keys
    my @keys = $self->form_state->param;
clear_params

Clear all of the values in the form state storage:

   $self->form_state->param('name' => 'Road Runner');
   $self->form_state->clear_params;
   print $self->form_state->param('name'); # undef

MOTIVATION

Why not just use hidden fields?

Hidden fields are not secure. The end user could save a local copy of your form, change the hidden fields and tamper with your app's form state.

Why not just use the user's session?

With CGI::Application::Plugin::FormState the data is associated with a particular instance of a form, not with the user. If the user gives up halfway through your multi-page form, you don't want their session to be cluttered up with the incomplete form state data.

If a user opens up your application in two browser windows (both sharing the same user session), each window should have it's own independent form state.

For instance, in an email application the user might have one window open for the inbox and another open for the outbox. If you store the value of "current_mailbox" in the user's session, then one of these windows will go to the wrong mailbox.

Finally, the user's session probably sticks around longer than the form state should.

AUTHOR

Michael Graham, <mag-perl@occamstoothbrush.com>

BUGS

Please report any bugs or feature requests to bug-cgi-application-plugin-formstate@rt.cpan.org, or through the web interface at http://rt.cpan.org. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

ACKNOWLEDGEMENTS

Thanks to Richard Dice and Cees Hek for helping me sort out the issues with this approach.

COPYRIGHT & LICENSE

Copyright 2005 Michael Graham, All Rights Reserved.

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