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CGI::Application(3pm) User Contributed Perl Documentation CGI::Application(3pm)
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();
### Or, in a PSGI file, webapp.psgi
use WebApp;
WebApp->psgi_app();
INTRODUCTION
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
mod_perl.
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.
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 integrates
with Apache::Request.
DESCRIPTION
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:
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.
$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.
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 = 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 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 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().
PSGI support
CGI::Application offers native PSGI support. The default query object for this is
CGI::PSGI, which simply wrappers CGI.pm to provide PSGI support to it.
psgi_app()
$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 CGI.pm adds native PSGI support.
run_as_psgi()
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 CGI.pm-like 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) });
$webapp->run_as_psgi;
};
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:
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 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;
$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 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()
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 CGI.pm.
CGI.pm is only loaded if it is used on a given request.
If you can use an alternative to CGI.pm, it needs to have some compatibility with the
CGI.pm 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.
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::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
"html_tmpl_class()":
$self->html_tmpl_class('HTML::Template::Dumper');
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 => ... );
$t->param(...);
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;
$webapp->html_tmpl_class('HTML::Template::Dumper');
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:
$self->add_callback('load_tmpl',\&your_method);
When "your_method()" is executed, it will be passed three arguments:
1. A hash reference of the extra params passed into C<load_tmpl>
2. Followed by a hash reference to template parameters.
With both of these, you can modify them by reference to affect
values that are actually passed to the new() and param() methods of the
template object.
3. The name of the template file.
Here's an example stub for a load_tmpl() callback:
sub my_load_tmpl_callback {
my ($c, $ht_params, $tmpl_params, $tmpl_file) = @_
# modify $ht_params or $tmpl_params by reference...
}
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.
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.
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:
$webapp->query($new_query_object);
my $q = $webapp->query(); # now uses $new_query_object
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' ]);
This 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.
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.
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. Please consider the
security implications of using this in production code.
error_mode()
$webapp->error_mode('my_error_rm');
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
CGI::Application::Plugin::LogDispatch.
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 eventually 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 for that key. This is primarily useful for
setting an additional cookie after one has already been set.
header_props()
# 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 CGI.pm-compatible 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
CGI.pm).
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()".
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()
$webapp->header_type('redirect');
$webapp->header_type('none');
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_type('redirect');
$self->header_props(-url=> "http://site/path/doc.html" );
}
To simplify that further, use CGI::Application::Plugin::Redirect:
return $self->redirect('http://www.example.com/');
Setting the header to 'none' may be useful if you are streaming content. In other
contexts, it may be more useful to set "$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!
mode_param()
# Name the CGI form parameter that contains the run mode name.
# This is 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 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
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 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.
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.
Dispatching Clean URIs to run modes
Modern web frameworks dispense with cruft in URIs, providing in clean URIs instead.
Instead of:
/cgi-bin/item.cgi?rm=view&id=15
A clean URI to describe the same resource might be:
/item/15/view
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
running.
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.
PLUG-INS
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:
o CGI::Application::Plugin::Redirect - is a simple plugin to provide a shorter syntax
for executing a redirect.
o 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.
o 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
used.
o 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.
o CGI::Application::Plugin::Session - For a project that requires session management,
this plugin provides a useful wrapper around CGI::Session
o CGI::Application::Plugin::ValidateRM - Integration with Data::FormValidator and
HTML::FillInForm
More plug-ins
Many more plugins are available as alternatives and for specific uses. For a current
complete list, please consult CPAN:
http://search.cpan.org/search?m=dist&q=CGI%2DApplication%2DPlugin
o CGI::Application::Plugin::AnyTemplate - Use any templating system from within
CGI::Application using a unified interface
o CGI::Application::Plugin::Apache - Use Apache::* modules without interference
o CGI::Application::Plugin::AutoRunmode - Automatically register runmodes
o CGI::Application::Plugin::Config::Context - Integration with Config::Context.
o CGI::Application::Plugin::Config::General - Integration with Config::General.
o CGI::Application::Plugin::Config::Simple - Integration with Config::Simple.
o CGI::Application::Plugin::CompressGzip - Add Gzip compression
o CGI::Application::Plugin::LogDispatch - Integration with Log::Dispatch
o CGI::Application::Plugin::Stream - Help stream files to the browser
o 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
files.
o CGI::Application::Plugin::TT - Use Template::Toolkit as an alternative to
HTML::Template.
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()
$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;
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)
$self->call_hook('pretemplate', @args);
The "call_hook" method is used to executed the callbacks that have been registered at the
given hook. It is used in conjunction with the "new_hook" method which allows you to
create a new hook location.
The first argument to "call_hook" is the hook name. Any remaining arguments are passed to
every callback executed at the hook location. So, a stub for a callback at the
'pretemplate' hook would look like this:
sub my_hook {
my ($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:
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, visit
http://lists.openlib.org/mailman/listinfo/cgiapp
Source Code
This project is managed using git and is available on Github:
<https://github.com/MartinMcGrath/CGI--Application>
SEE ALSO
o CGI
o HTML::Template
o CGI::Application::Framework - A full-featured web application based on
CGI::Application. http://www.cafweb.org/
MORE READING
If you're interested in finding out more about CGI::Application, the following articles
are available on Perl.com:
Using CGI::Application
http://www.perl.com/pub/a/2001/06/05/cgi.html
Rapid Website Development with CGI::Application
http://www.perl.com/pub/a/2006/10/19/cgi_application.html
Thanks to O'Reilly for publishing these articles, and for the incredible value they
provide to the Perl community!
AUTHOR
Jesse Erlbaum <jesse AT erlbaum.net>
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.
CREDITS
CGI::Application was originally developed by The Erlbaum Group, a software engineering and
consulting firm in New York City.
Thanks to Vanguard Media (http://www.vm.com) 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 http://lists.openlib.org/mailman/listinfo/cgiapp )
LICENSE
CGI::Application : Framework for building reusable web-applications Copyright (C)
2000-2003 Jesse Erlbaum <jesse AT 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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