CGI::Application - Framework for building reusable web-applications
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NAME
CGI::Application - Framework for building reusable web-applications
SYNOPSIS
# In "WebApp.pm"...
package WebApp;
use base 'CGI::Application';
# ( setup() can even be skipped for common cases. See docs below. )
sub setup {
my $self = shift;
$self->start_mode('mode1');
$self->mode_param('rm');
$self->run_modes(
'mode1' => 'do_stuff',
'mode2' => 'do_more_stuff',
'mode3' => 'do_something_else'
);
}
sub do_stuff { ... }
sub do_more_stuff { ... }
sub do_something_else { ... }
1;
### In "webapp.cgi"...
use WebApp;
my $webapp = WebApp->new();
$webapp->run();
INTRODUCTION
CGI::Application is intended to make it easier to create sophisticated,
high-performance, reusable web-based applications. This module
implements a methodology which, if followed, will make your web software
easier to design, easier to document, easier to write, and easier to
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.
USAGE EXAMPLE
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. WidgetView.pm -- 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();
$webapp->run();
As you can see, widgetview.cgi simply "uses" your Application module
(which implements a Perl package called "WidgetView"). Your Application
Module, "WidgetView.pm", 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;
$self->start_mode('mode1');
$self->run_modes(
'mode1' => 'showform',
'mode2' => 'showlist',
'mode3' => 'showdetail'
);
# Connect to DBI database, with the same args as DBI->connect();
$self->dbh_config();
}
sub teardown {
my $self = shift;
# Disconnect when we're done, (Although DBI usually does this automatically)
$self->dbh->disconnect();
}
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
## CGI.pm 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 CGI.pm
## 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.
ABSTRACT
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 http://www.cgi-app.org/, as well as
CGI::Application::Plugin::Apache, which integates with Apache::Request.
DESCRIPTION
CGI::Application is an Object-Oriented Perl module which implements an
Abstract Class. It is not intended that this package be instantiated
directly. Instead, it is intended that your Application Module will be
implemented as a Sub-Class of CGI::Application.
To inherit from CGI::Application, the following code should go at the
beginning of your Application Module, after your package declaration:
use base 'CGI::Application';
Notation and Conventions
For the purpose of this document, we will refer to the following
conventions:
WebApp.pm 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.
$self Same as $webapp, used in instance methods to pass around the
current object. (Standard Perl Object-Oriented technique)
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.
new()
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 = App->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 CGI.pm query object. Under normal use,
CGI::Application will instantiate its own CGI.pm query object. Under
certain conditions, it might be useful to be able to use one which
has already been created.
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, "Mailform.pm". 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 "Mailform.pm" 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 => 'config.pl' });
# Later in your app:
my %cfg = $self->cfg()
# or ... $self->cfg('HTML_ROOT_DIR');
See the list of of plugins below for more config file integration
solutions.
run()
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();
$webapp->run();
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().
Handling unexpected death
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. This hook is
still considered experimental, although it is unlikely to change.
For a complete integrated logging solution, check out
CGI::Application::Plugin::LogDispatch.
Sub-classing and Override Methods
CGI::Application implements some methods which are expected to be
overridden by implementing them in your sub-class module. These methods
are as follows:
setup()
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 refefence 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;
$self->tmpl_path('/path/to/my/templates/');
$self->start_mode('putform');
$self->error_mode('my_error_rm');
$self->run_modes({
'putform' => 'my_putform_func',
'postdata' => 'my_data_func'
});
$self->param('myprop1');
$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 { ... }
teardown()
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 server.
cgiapp_init()
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 which all
your web applications would inherit, instead of CGI::Application.
Consider the following:
# In MySuperclass.pm:
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 MyApplication.pm:
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.
cgiapp_prerun()
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 MySuperclass.pm:
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 MyApplication.pm:
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.
cgiapp_postrun()
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 follows:
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.
cgiapp_get_query()
This method is called when CGI::Application retrieves the query
object. The cgiapp_get_query() method loads CGI.pm via "require" and
returns a CGI.pm query object. The implementation is as follows:
sub cgiapp_get_query {
my $self = shift;
require CGI;
return CGI->new();
}
You may override this method if you wish to use a different query
interface instead of CGI.pm. Note, however, that your query
interface must be compatible with CGI.pm, or you must wrap your
chosen query interface in a "wrapper" class to achieve
compatibility.
Application Module Methods
The following 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.
delete()
$webapp->delete('my_param');
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
CGI.pm. 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 param()s.
dump()
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.
dump_html()
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.
error_mode()
$webapp->error_mode('my_error_rm');
The error_mode contains the name of a run mode to call in the event
that the planned run mode call fails "eval". 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.
get_current_runmode()
$webapp->get_current_runmode();
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.
header_add()
# add or replace the 'type' header
$webapp->header_add( -type => 'image/png' );
- or -
# add an additional cookie
$webapp->header_add(-cookie=>[$extra_cookie]);
The header_add() method is used to add one or more headers to the
outgoing response headers. The parameters will eventuallly be passed
on to the CGI.pm 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 values for
that key. This is primarily useful for setting an additional cookie
after one has already been set.
header_props()
$webapp->header_props(-type=>'image/gif',-expires=>'+3d');
The header_props() method expects a hash of CGI.pm-compatible HTTP
header properties. These properties will be passed directly to
CGI.pm's header() or redirect() methods. Refer to CGI for exact
usage details.
Calling header_props will clobber any existing headers that have
previously set.
To add additional headers later without clobbering the old ones, see
header_add().
header_props() return a hash of all the headers that have currently
been set.
IMPORTANT NOTE REGARDING HTTP HEADERS
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
CGI.pm function is called.
Understanding this relationship is important if you wish to
manipulate the HTTP header properly.
header_type([<'header' || 'redirect' || 'none'>])
$webapp->header_type('redirect');
The header_type() method expects to be passed either 'header',
'redirect', or 'none'. This method specifies the type of HTTP
headers which should be sent back to the browser. If not specified,
defaults is 'header'. See the header section of CGI for details.
To perform a redirect using CGI::Application (and CGI.pm), you would
do the following:
sub some_redirect_mode {
my $self = shift;
my $new_url = "http://site/path/doc.html";
$self->header_type('redirect');
$self->header_props(-url=>$new_url);
return "Redirecting to $new_url";
}
If you wish to suppress HTTP headers entirely (as might be the case
if you're working in a slightly more exotic environment), you can
set header_type() to "none". This will completely hide headers.
load_tmpl()
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::AnyTemplate provides a consistent
interface to HTML::Template, Template Toolkit, and Petal, automatic
default file names, and other features. Check this one out first.
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.
The load_tmpl() callback
Plugin authors will be intersted to know that you can register a
callback that will be executed just before load_tmpl() returns:
$self->add_callback('load_tmpl',\&your_method);
When "your_method()" is executed, it will be passed three arguments:
1. A hash reference of the extra params passed into C<load_tmpl>
2. Followed by a hash reference to template parameters.
With both of these, you can modify them by reference to affect
values that are actually passed to the new() and param() methods of the
template object.
3. The name of the template file.
Here's an example stub for a load_tmpl() callback:
sub my_load_tmpl_callback {
my ($self, $ht_params, $tmpl_params, $tmpl_file) = @_
# modify $ht_params or $tmpl_params by reference...
}
mode_param()
# Name the CGI form parameter that contains the run mode name.
# This is the the default behavior, and is often sufficient.
$webapp->mode_param('rm');
# Set the run mode name directly from a code ref
$webapp->mode_param(\&some_method);
# Alternate interface, which allows you to set the run
# mode name directly from $ENV{PATH_INFO}.
$webapp->mode_param(
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.
$webapp->mode_param('rm');
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.
$webapp->mode_param(\&some_method);
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.
$webapp->mode_param(
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 JavaScript.
More about $ENV{PATH_INFO}.
Using $ENV{PATH_INFO} to name your run mode creates a clean
seperation 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 syntax:
<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:
/cgi-bin/instance.cgi/edit_form?breed_id=2
This demostrates 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.
param()
$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):
$webapp->param(
'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.
prerun_mode()
$webapp->prerun_mode('new_run_mode');
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, consider:
# In WebApp.pm:
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) {
$self->prerun_mode('login');
}
}
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.
query()
my $q = $webapp->query();
my $remote_user = $q->remote_user();
This method retrieves the CGI.pm 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 CGI.pm, 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.
run_modes()
# The common usage: an arrayref of run mode names that exactly match subroutine names
$webapp->run_modes([qw/
form_display
form_process
/]);
# With a hashref, use a different name or a code ref
$webapp->run_modes(
'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 preferred.
Specifying the run modes by array reference:
$webapp->run_modes([ 'mode1', 'mode2', 'mode3' ]);
Is is the same as using a hash, with keys equal to values
$webapp->run_modes(
'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.
IMPORTANT NOTE ABOUT RUN MODE METHODS
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.
THE RUN MODE OF LAST RESORT: "AUTOLOAD"
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":
$self->run_modes(
"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.
start_mode()
$webapp->start_mode('mode1');
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.
tmpl_path()
$webapp->tmpl_path('/path/to/some/templates/');
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.
Testing
CGI::Application currently has no built-in testing methodology but we
leave that up to you. There are many testing structures and frameworks
that are available for testing Perl modules (ie, Test::Harness,
Test::More). There are large numbers of tools and frameworks for testing
live web applications (WWW::Mechanize, HTTP::Test, Apache::Test). We
encourage you to look around CPAN and find the one that best meets your
needs.
Since most of the module level testing frameworks require the output
that is sent to STDOUT be of a certain format, and since
CGI::Application will print the output of it's run modes directly to
STDOUT this could cause problems. To avoid this simple set the
environment variable 'CGI_APP_RETURN_ONLY' to true and you can catch
your output and test it and then print your own message to STDOUT. For
example
$ENV{CGI_APP_RETURN_ONLY} = 1;
$output = $webapp->run();
#perform whatever test on the output that you want and then print to STDOUT
if($output =~ /GOOD/){
print "ok 11\n";
} else {
print "not ok 11\n";
}
PLUG-INS
CGI::Application has a plug-in architecture that is easy to use and easy
to develop new plug-ins for.
Existing plug-ins
Here are some plug-ins that have already been developed for
CGI::Application. For a current complete list, please consult CPAN:
http://search.cpan.org/search?m=dist&q=CGI%2DApplication%2DPlugin
* 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::ConfigAuto - Integration with
Config::Auto.
* 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::DBH - Integration with DBI.
* CGI::Application::Plugin::FillInForm - Integration with
HTML::FillInForm.
* CGI::Application::Plugin::LogDispatch - Integration with
Log::Dispatch
* CGI::Application::Plugin::Session - Integration with CGI::Session
* 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 seperate files.
* CGI::Application::Plugin::TT - Use Template::Toolkit as an
alternative to HTML::Template.
* CGI::Application::Plugin::ValidateRM - Integration with
Data::FormValidator and HTML::FillInForm
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
$self->new_hook('pretemplate');
# Then later execute all the callbacks registered at this hook
$self->call_hook('pretemplate');
Callback Methods
add_callback(HOOK, CALLBACK)
$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 $self
object; at the end of the request when the $self 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 $self 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;
new_hook(HOOK)
$self->new_hook('pretemplate');
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 processed.
See call_hook(HOOK) for more details about how hooks are called.
call_hook(HOOK)
$self->call_hook('pretemplate', @args);
The "call_hook" method is used to executed the callbacks that have
been registered at the given hook. It is used in conjunction with
the "new_hook" method which allows you to create a new hook
location.
The first argument to "call_hook" is the hook name. Any remaining
arguments are passed to every callback executed at the hook
location. So, a stub for a callback at the 'pretemplate' hook would
look like this:
sub my_hook {
my ($self,@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:
CGI::Application
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' stage:
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:
My::App
My::Project
CGI::Application
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 "cgiapp_init".
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).
COMMUNITY
Therese are primary resources available for those who wish to learn more
about CGI::Application and discuss it with others.
Wiki
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:
<http://www.cgi-app.org>
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, simply
send a blank message to "cgiapp-subscribe@lists.erlbaum.net".
IRC
You can also drop by "#cgiapp" on "irc.perl.org" with a good chance of
finding some people involved with the project there.
SEE ALSO
o CGI
o HTML::Template
o CGI::Application::Framework - A full-featured web application based
on CGI::Application. http://www.cafweb.org/
AUTHOR
Jesse Erlbaum <jesse@erlbaum.net>
Mark Stosberg has served as a co-maintainer since version 3.2, with the
help of the numerous contributors documented in the Changes file.
More Reading
If you're interested in finding out more about CGI::Application, the
following article is available on Perl.com:
Using CGI::Application
http://www.perl.com/pub/a/2001/06/05/cgi.html
Thanks to Simon Cozens and the O'Reilly network for publishing this
article, and for the incredible value they provide to the Perl
community!
CREDITS
CGI::Application is developed by The Erlbaum Group, a software
engineering and consulting firm in New York City. If you are looking for
a company to develop your web site or individual developers to augment
your team please contact us:
The Erlbaum Group, LLC
826 Broadway, Suite 933
New York, NY 10003
Phone: 212-684-6161
Fax: 212-684-6226
Email: info@erlbaum.net
Web: http://www.erlbaum.net
Thanks to Vanguard Media (http://www.vm.com) for funding the initial
development of this library and for encouraging me 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, simply send a blank message to
"cgiapp-subscribe@lists.erlbaum.net".)
LICENSE
CGI::Application : Framework for building reusable web-applications
Copyright (C) 2000-2003 Jesse Erlbaum <jesse@erlbaum.net>
This module is free software; you can redistribute it and/or modify it
under the terms of either:
a) the GNU General Public License as published by the Free Software
Foundation; either version 1, or (at your option) any later version,
or
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
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