Provided by: libmasonx-interp-withcallbacks-perl_1.19-4_all 
NAME
MasonX::Interp::WithCallbacks - Mason callback support via Params::CallbackRequest.
SYNOPSIS
In your Mason component:
% if (exists $ARGS{answer}) {
<p><b>Answer: <% $ARGS{answer} %></b></p>
% } else {
<form>
<p>Enter an epoch time: <input type="text" name="epoch_time" /><br />
<input type="submit" name="myCallbacker|calc_time_cb" value="Calculate" />
</p>
</form>
% }
In handler.pl:
use strict;
use MasonX::Interp::WithCallbacks;
sub calc_time {
my $cb = shift;
my $params = $cb->params;
my $val = $cb->value;
$params->{answer} = localtime($val || time);
}
my $ah = HTML::Mason::ApacheHandler->new
( interp_class => 'MasonX::Interp::WithCallbacks',
callbacks => [ { cb_key => 'calc_time',
pkg_key => 'myCallbacker',
cb => \&calc_time } ]
);
sub handler {
my $r = shift;
$ah->handle_request($r);
}
Or, in a subclass of Params::Callback:
package MyApp::CallbackHandler;
use base qw(Params::Callback);
__PACKAGE__->register_subclass( class_key => 'myCallbacker' );
sub calc_time : Callback {
my $self = shift;
my $params = $self->params;
my $val = $cb->value;
$params->{answer} = localtime($val || time);
}
And then, in handler.pl:
# Load order is important here!
use MyApp::CallbackHandler;
use MasonX::Interp::WithCallbacks;
my $ah = HTML::Mason::ApacheHandler->new
( interp_class => 'MasonX::Interp::WithCallbacks',
cb_classes => [qw(myCallbacker)] );
sub handler {
my $r = shift;
$ah->handle_request($r);
}
Or, just use MasonX::Interp::WithCallbacks directly:
use MyApp::CallbackHandler;
use MasonX::Interp::WithCallbacks;
my $interp = MasonX::Interp::WithCallbacks->new
( cb_classes => [qw(myCallbacker)] );
$interp->exec($comp, %args);
DESCRIPTION
MasonX::Interp::WithCallbacks subclasses HTML::Mason::Interp in order to provide a Mason
callback system built on Params::CallbackRequest. Callbacks may be either code references
provided to the "new()" constructor, or methods defined in subclasses of Params::Callback.
Callbacks are triggered either for every request or by specially named keys in the Mason
request arguments, and all callbacks are executed at the beginning of a request, just
before Mason creates and executes the request component stack.
This module brings support for a sort of plugin architecture based on
Params::CallbackRequest to Mason. Mason then executes code before executing any
components. This approach allows you to carry out logical processing of data submitted
from a form, to affect the contents of the Mason request arguments (and thus the %ARGS
hash in components), and even to redirect or abort the request before Mason handles it.
Much of the documentation here is based on that in Params::CallbackRequest, although it
prefers using HTML form fields for its examples rather than Perl hashes. But see the
Params::CallbackRequest documentation for the latest on its interface.
JUSTIFICATION
Why would you want to do this? Well, there are a number of reasons. Some I can think of
offhand include:
Stricter separation of logic from presentation
Most application logic handled in Mason components takes place in "<%init>" blocks,
often in the same component as presentation logic. By moving the application logic
into Perl modules and then directing Mason to execute that code as callbacks, you
obviously benefit from a cleaner separation of application logic and presentation.
Widgitization
Thanks to their ability to preprocess arguments, callbacks enable developers to
develop easier-to-use, more dynamic widgets that can then be used in any and all Mason
component, or even with other templating systems. For example, a widget that puts many
related fields into a form (such as a date selection widget) can have its fields
preprocessed by a callback (for example, to properly combine the fields into a unified
date field) before the Mason component that responds to the form submission gets the
data. See Params::Callback for an example solution for this very problem.
Shared Memory
Callbacks are just Perl subroutines in modules, and are therefore loaded at server
startup time in a mod_perl environment. Thus the memory they consume is all in the
Apache parent process, and shared by the child processes. For code that executes
frequently, this can be much less resource-intensive than code in Mason components,
since components are loaded separately in each Apache child process (unless they're
preloaded via the "preloads" parameter to the HTML::Mason::Interp constructor).
Performance
Since they're executed before Mason creates a component stack and executes the
components, callbacks have the opportunity to short-circuit the Mason processing by
doing something else. A good example is redirection. Often the application logic in
callbacks does its thing and then redirects the user to a different page. Executing
the redirection in a callback eliminates a lot of extraneous processing that would
otherwise be executed before the redirection, creating a snappier response for the
user.
Testing
Mason components are not easy to test via a testing framework such as Test::Harness.
Subroutines in modules, on the other hand, are fully testable. This means that you can
write tests in your application test suite to test your callback subroutines.
And if those aren't enough reasons, then just consider this: Callbacks are just way cool.
USAGE
MasonX::Interp::WithCallbacks uses Params::CallbackRequest for its callback architecture,
and therefore supports its two different types of callbacks: those triggered by a
specially named key in the Mason request arguments hash, and those executed for every
request.
Argument-Triggered Callbacks
Argument-triggered callbacks are triggered by specially named request argument keys. These
keys are constructed as follows: The package name followed by a pipe character ("|"), the
callback key with the string "_cb" appended to it, and finally an optional priority number
at the end. For example, if you specified a callback with the callback key "save" and the
package key "world", a callback field might be added to an HTML form like this:
<input type="button" value="Save World" name="world|save_cb" />
This field, when submitted to the Mason server, would trigger the callback associated with
the "save" callback key in the "world" package. If such a callback hasn't been configured,
then Params::CallbackRequest will throw a Params::CallbackReuest::Exception::InvalidKey
exception. Here's how to configure a functional callback when constructing your
MasonX::Interp::WithCallbacks object so that that doesn't happen:
my $interp = MasonX::Interp::WithCallbacks->new
( callbacks => [ { pkg_key => 'world',
cb_key => 'save',
cb => \&My::World::save } ] );
With this configuration, the request argument created by the above HTML form field will
trigger the execution of the &My::World::save subroutine.
Functional Callback Subroutines
Functional callbacks use a code reference for argument-triggered callbacks, and
Params::CallbackRequest executes them with a single argument, a Params::Callback object.
Thus, a callback subroutine will generally look something like this:
sub foo {
my $cb = shift;
# Do stuff.
}
The Params::Callback object provides accessors to data relevant to the callback, including
the callback key, the package key, and the request arguments (or parameters). It also
includes "redirect()" and "abort()" methods. See the Params::Callback documentation for
all the goodies.
Note that all callbacks are executed in a "eval {}" block, so if any of your callback
subroutines "die", Params::CallbackRequest will throw an
Params::CallbackRequest::Exception::Execution exception If you don't like this, use the
"cb_exception_handler" parameter to "new()" to install your own exception handler.
Object-Oriented Callback Methods
Object-oriented callback methods are defined in subclasses of Params::Callback. Unlike
functional callbacks, they are not called with a Params::Callback object, but with an
instance of the callback subclass. These classes inherit all the goodies provided by
Params::Callback, so you can essentially use their instances exactly as you would use the
Params::Callback object in functional callback subroutines. But because they're
subclasses, you can add your own methods and attributes. See Params::Callback for all the
gory details on subclassing, along with a few examples. Generally, callback methods will
look like this:
sub foo : Callback {
my $self = shift;
# Do stuff.
}
As with functional callback subroutines, method callbacks are executed in a "eval {}"
block. Again, see the "cb_exception_handler" parameter to install your own exception
handler.
Note: It's important that you "use" any and all MasonX::Callback subclasses before you
"use MasonX::Interp::WithCallbacks" or "use Params::CallbackRequest". This is to get
around an issue with identifying the names of the callback methods in mod_perl. Read the
comments in the MasonX::Callback source code if you're interested in learning more.
The Package Key
The use of the package key is a convenience so that a system with many functional
callbacks can use callbacks with the same keys but in different packages. The idea is that
the package key will uniquely identify the module in which each callback subroutine is
found, but it doesn't necessarily have to be so. Use the package key any way you wish, or
not at all:
my $interp = MasonX::Interp::WithCallbacks->new
( callbacks => [ { cb_key => 'save',
cb => \&My::World::save } ] );
But note that if you don't use the package key at all, you'll still need to provide one in
the parameters to be submitted to "exec()" By default, that key is "DEFAULT". Such a
callback field in an HTML form would then look like this:
<input type="button" value="Save World" name="DEFAULT|save_cb" />
If you don't like the "DEFAULT" package name, you can set an alternative default using the
"default_pkg_name" parameter to "new()":
my $interp = MasonX::Interp::WithCallbacks->new
( callbacks => [ { cb_key => 'save',
cb => \&My::World::save } ],
default_pkg_name => 'MyPkg' );
Then, of course, any callbacks without a specified package key of their own will then use
the custom default:
<input type="button" value="Save World" name="MyPkg|save_cb" />
The Class Key
The class key is essentially a synonym for the package key, but applies more directly to
object-oriented callbacks. The difference is mainly that it corresponds to an actual
class, and that all Params::Callback subclasses are required to have a class key; it's not
optional as it is with functional callbacks. The class key may be declared in your
Params::Callback subclass like so:
package MyApp::CallbackHandler;
use base qw(Params::Callback);
__PACKAGE__->register_subclass( class_key => 'MyCBHandler' );
The class key can also be declared by implementing a "CLASS_KEY()" method, like so:
package MyApp::CallbackHandler;
use base qw(Params::Callback);
__PACKAGE__->register_subclass;
use constant CLASS_KEY => 'MyCBHandler';
If no class key is explicitly defined, Params::Callback will use the subclass name,
instead. In any event, the "register_callback()" method must be called to register the
subclass with Params::Callback. See the Params::Callback documentation for complete
details.
Priority
Sometimes one callback is more important than another. For example, you might rely on the
execution of one callback to set up variables needed by another. Since you can't rely on
the order in which callbacks are executed (the Mason request arguments are stored in a
hash, and the processing of a hash is, of course, unordered), you need a method of
ensuring that the setup callback executes first.
In such a case, you can set a higher priority level for the setup callback than for
callbacks that depend on it. For functional callbacks, you can do it like this:
my $interp = MasonX::Interp::WithCallbacks->new
( callbacks => [ { cb_key => 'setup',
priority => 3,
cb => \&setup },
{ cb_key => 'save',
cb => \&save }
] );
For object-oriented callbacks, you can define the priority right in the callback method
declaration:
sub setup : Callback( priority => 3 ) {
my $self = shift;
# ...
}
sub save : Callback {
my $self = shift;
# ...
}
In these examples, the "setup" callback has been configured with a priority level of "3".
This ensures that it will always execute before the "save" callback, which has the default
priority of "5". This is true regardless of the order of the fields in the corresponding
HTML::Form:
<input type="button" value="Save World" name="DEFAULT|save_cb" />
<input type="hidden" name="DEFAULT|setup_cb" value="1" />
Despite the fact that the "setup" callback field appears after the "save" field (and will
generally be submitted by the browser in that order), the "setup" callback will always
execute first because of its higher priority.
Although the "save" callback got the default priority of "5", this too can be customized
to a different priority level via the "default_priority" parameter to "new()" for
functional callbacks and the "default_priority" to the class declaration for object-
oriented callbacks For example, this functional callback configuration:
my $interp = MasonX::Interp::WithCallbacks->new
( callbacks => [ { cb_key => 'setup',
priority => 3,
cb => \&setup },
{ cb_key => 'save',
cb => \&save }
],
default_priority => 2 );
And this Params::Callback subclass declaration:
package MyApp::CallbackHandler;
use base qw(Params::Callback);
__PACKAGE__->register_subclass( class_key => 'MyCBHandler',
default_priority => 2 );
Will cause the "save" callback to always execute before the "setup" callback, since its
priority level will default to "2".
In addition, the priority level can be overridden via the form submission field itself by
appending a priority level to the end of the callback field name. Hence, this example:
<input type="button" value="Save World" name="DEFAULT|save_cb2" />
<input type="hidden" name="DEFAULT|setup_cb" value="1" />
Causes the "save" callback to execute before the "setup" callback by overriding the "save"
callback's priority to level "2". Of course, any other form field that triggers the "save"
callback without a priority override will still execute "save" at its configured level.
Request Callbacks
Request callbacks come in two separate flavors: those that execute before the argument-
triggered callbacks, and those that execute after the argument-triggered callbacks. All of
them execute before the Mason component stack executes. Functional request callbacks may
be specified via the "pre_callbacks" and "post_callbacks" parameters to "new()",
respectively:
my $interp = MasonX::Interp::WithCallbacks->new
( pre_callbacks => [ \&translate, \&foobarate ],
post_callbacks => [ \&escape, \&negate ] );
Object-oriented request callbacks may be declared via the "PreCallback" and "PostCallback"
method attributes, like so:
sub translate : PreCallback { ... }
sub foobarate : PreCallback { ... }
sub escape : PostCallback { ... }
sub negate : PostCallback { ... }
In these examples, the "translate()" and "foobarate()" subroutines or methods will execute
(in that order) before any argument-triggered callbacks are executed (none will be in
these examples, since none are specified).
Conversely, the "escape()" and "negate()" subroutines or methods will be executed (in that
order) after all argument-triggered callbacks have been executed. And regardless of what
argument-triggered callbacks may be triggered, the request callbacks will always be
executed for every request.
Although they may be used for different purposes, the "pre_callbacks" and "post_callbacks"
functional callback code references expect the same argument as argument-triggered
functional callbacks: a Params::Callback object:
sub foo {
my $cb = shift;
# Do your business here.
}
Similarly, object-oriented request callback methods will be passed an object of the class
defined in the class key portion of the callback trigger -- either an object of the class
in which the callback is defined, or an object of a subclass:
sub foo : PostCallback {
my $self = shift;
# ...
}
Of course, the attributes of the Params::Callback or subclass object will be different
than in argument-triggered callbacks. For example, the "priority", "pkg_key", and "cb_key"
attributes will naturally be undefined. It will, however, be the same instance of the
object passed to all other functional callbacks -- or to all other class callbacks with
the same class key -- in a single request.
Like the argument-triggered callbacks, request callbacks are executed in a "eval {}"
block, so if any of them "die"s, an Params::CallbackRequest::Exception::Execution
exception will be thrown. Use the "cb_exception_handler" parameter to "new()" if you don't
like this.
INTERFACE
Parameters To The "new()" Constructor
In addition to those offered by the HTML::Mason::Interp base class, this module supports a
number of its own parameters to the "new()" constructor based on those required by
Params::CallbackRequest. Each also has a corresponding httpd.conf variable as well, so, if
you really want to, you can use MasonX::Interp::WithCallbacks right in your httpd.conf
file:
PerlModule MasonX::Interp::WithCallbacks
PerlSetVar MasonInterpClass MasonX::Interp::WithCallbacks
SetHandler perl-script
PerlHandler HTML::Mason::ApacheHandler
The parameters to "new()" and their corresponding httpd.conf variables are as follows:
"callbacks"
Argument-triggered functional callbacks are configured via the "callbacks" parameter.
This parameter is an array reference of hash references, and each hash reference
specifies a single callback. The supported keys in the callback specification hashes
are:
"cb_key"
Required. A string that, when found in a properly-formatted Mason request argument
key, will trigger the execution of the callback.
"cb"
Required. A reference to the Perl subroutine that will be executed when the
"cb_key" has been found in a Mason request argument key. Each code reference
should expect a single argument: a Params::Callback object. The same instance of a
Params::Callback object will be used for all functional callbacks in a single
request.
"pkg_key"
Optional. A key to uniquely identify the package in which the callback subroutine
is found. This parameter is useful in systems with many callbacks, where
developers may wish to use the same "cb_key" for different subroutines in
different packages. The default package key may be set via the "default_pkg_key"
parameter.
"priority"
Optional. Indicates the level of priority of a callback. Some callbacks are more
important than others, and should be executed before the others.
Params::CallbackRequest supports priority levels ranging from "0" (highest
priority) to "9" (lowest priority). The default priority for functional callbacks
may be set via the "default_priority" parameter.
The <callbacks> parameter can also be specified via the httpd.conf configuration
variable "MasonCallbacks". Use "PerlSetVar" to specify several callbacks; each one
should be an "eval"able string that converts into a hash reference as specified here.
For example, to specify two callbacks, use this syntax:
PerlAddVar MasonCallbacks "{ cb_key => 'foo', cb => sub { ... }"
PerlAddVar MasonCallbacks "{ cb_key => 'bar', cb => sub { ... }"
Note that the "eval"able string must be entirely on its own line in the httpd.conf
file.
"pre_callbacks"
This parameter accepts an array reference of code references that should be executed
for every request before any other callbacks. They will be executed in the order in
which they're listed in the array reference. Each code reference should expect a
single Params::Callback argument. The same instance of a Params::Callback object will
be used for all functional callbacks in a single request. Use pre-argument-triggered
request callbacks when you want to do something with the arguments submitted for every
request, such as convert character sets.
The <pre_callbacks> parameter can also be specified via the httpd.conf configuration
variable "MasonPreCallbacks". Use multiple "PerlAddVar" to add multiple pre-request
callbacks; each one should be an "eval"able string that converts into a code
reference:
PerlAddVar MasonPreCallbacks "sub { ... }"
PerlAddVar MasonPreCallbacks "sub { ... }"
"post_callbacks"
This parameter accepts an array reference of code references that should be executed
for every request after all other callbacks have been called. They will be executed in
the order in which they're listed in the array reference. Each code reference should
expect a single Params::Callback argument. The same instance of a Params::Callback
object will be used for all functional callbacks in a single request. Use post-
argument-triggered request callbacks when you want to do something with the arguments
submitted for every request, such as HTML-escape their values.
The <post_callbacks> parameter can also be specified via the httpd.conf configuration
variable "MasonPostCallbacks". Use multiple "PerlAddVar" to add multiple post-request
callbacks; each one should be an "eval"able string that converts into a code
reference:
PerlAddVar MasonPostCallbacks "sub { ... }"
PerlAddVar MasonPostCallbacks "sub { ... }"
"cb_classes"
An array reference listing the class keys of all of the Params::Callback subclasses
containing callback methods that you want included in your
MasonX::Interp::WithCallbacks object. Alternatively, the "cb_classes" parameter may
simply be the word "ALL", in which case all Params::Callback subclasses will have
their callback methods registered with your MasonX::Interp::WithCallbacks object. See
the Params::Callback documentation for details on creating callback classes and
methods.
Note: Be sure to "use MasonX::Interp::WithCallbacks" or "use Params::CallbackRequest"
only after you've "use"d all of the Params::Callback subclasses you need or else you
won't be able to use their callback methods.
The <cb_classes> parameter can also be specified via the httpd.conf configuration
variable "MasonCbClasses". Use multiple "PerlAddVar" to add multiple callback class
keys. But, again, be sure to load MasonX::Interp::WithCallbacks or
Params::CallbackRequest only after you've loaded all of your MasonX::Callback handler
subclasses:
PerlModule My::CBClass
PerlModule Your::CBClass
PerlSetVar MasonCbClasses myCBClass
PerlAddVar MasonCbClasses yourCBClass
# Load MasonX::Interp::WithCallbacks last!
PerlModule MasonX::Interp::WithCallbacks
"default_priority"
The priority level at which functional callbacks will be executed. Does not apply to
object-oriented callbacks. This value will be used in each hash reference passed via
the "callbacks" parameter to "new()" that lacks a "priority" key. You may specify a
default priority level within the range of "0" (highest priority) to "9" (lowest
priority). If not specified, it defaults to "5".
Use the "MasonDefaultPriority" variable to set the the "default_priority" parameter in
your httpd.conf file:
PerlSetVar MasonDefaultPriority 3
"default_pkg_key"
The default package key for functional callbacks. Does not apply to object-oriented
callbacks. This value that will be used in each hash reference passed via the
"callbacks" parameter to "new()" that lacks a "pkg_key" key. It can be any string that
evaluates to a true value, and defaults to "DEFAULT" if not specified.
Use the "MasonDefaultPkgKey" variable to set the the "default_pkg_key" parameter in
your httpd.conf file:
PerlSetVar MasonDefaultPkgKey CBFoo
"ignore_nulls"
By default, Params::CallbackRequest will execute all request callbacks. However, in
many situations it may be desirable to skip any callbacks that have no value for the
callback field. One can do this by simply checking "$cb->value" in the callback, but
if you need to disable the execution of all callbacks, pass the "ignore_nulls"
parameter with a true value. It is set to a false value by default.
Use the "MasonIgnoreNulls" variable to set the the "ignore_nulls" parameter in your
httpd.conf file:
PerlSetVar MasonIgnoreNulls 1
"cb_exception_handler"
When Params::CallbackRequest encounters an exception during the execution of
callbacks, it normally calls "Params::CallbackRequest::Exceptions::rethrow_exception"
to handle the exception. But if you throw your own exceptions in your callbacks, and
want to handle them differently (say, to handle them and then let the request
continue), pass the "cb_exception_handler" parameter a code reference to do what you
need.
Use the "MasonCbExceptionHandler" variable to set the "cb_exception_handler" parameter
in your httpd.conf file:
MasonCbExceptionHandler "sub {...}"
Note: This is the only parameter that differs in name from the same parameter to
"Params::CallbackRequest->new". This is so that it can be easily distinguished from
the possible addition of a "exception_handler" parameter to a future version of Mason.
Accessor Methods
All of the above parameters to "new()" are passed to the Params::CallbackRequest
constructor and deleted from the MasonX::Interp::WithCallbacks object.
MasonX::Interp::WithCallbacks then contains a Params::CallbackRequest object that it uses
to handle the execution of all callbacks for each request.
cb_request
my $interp = MasonX::Interp::WithCallbacks->new;
my $cb_request = $interp->cb_request;
Returns the Params::CallbackRequest object in use during the execution of
"make_request()".
comp_path
my $comp_path = $interp->comp_path;
$interp->comp_path($comp_path);
Returns the component path resolved by Mason during the execution of "handle_request()".
The cool thing is that it can be changed during the execution of callback methods:
sub change_path :Callback {
my $cb = shift;
my $interp = $cb->requester;
$inpter->comp_path($some_other_path);
}
In this example, we have overridden the component path determined by the Mason resolver in
favor of an alternate component, which will be executed, instead.
Requester
The MasonX::Interp::WithCallbacks object is available in all callback methods via the
"requester()" accessor:
sub access_interp :Callback {
my $cb = shift;
my $interp = $cb->requester;
# ...
}
Notes
$interp->cb_request->notes($key => $value);
my $note = $interp->cb_request->notes($key);
my $notes = $interp->cb_request->notes;
The Params::CallbackRequest notes interface remains available via the "notes()" method of
both Params::CallbackRequest and Params::Callback. Notes stored via this interface will be
copied to the HTML::Mason::Request "notes()" interface before the execution of the
request, and continue to be available for the lifetime of the Mason request via
"$interp->cb_request->notes". Notes will be cleared out at the end of the request, just as
with "$r->pnotes".
SUPPORT
This module is stored in an open GitHub repository <http://github.com/theory/masonx-
interp-withcallbacks/>. Feel free to fork and contribute!
Please file bug reports via GitHub Issues <http://github.com/theory/masonx-interp-
withcallbacks/issues/> or by sending mail to bug-MasonX-Interp-WithCallbacks.cpan.org
<mailto:bug-MasonX-Interp-WithCallbacks.cpan.org>.
SEE ALSO
Params::CallbackRequest handles the processing of the Mason request arguments and the
execution of callbacks. See its documentation for the most up-to-date documentation of the
underlying callback architecture.
Params::Callback objects get passed as the sole argument to all functional callbacks, and
offer access to data relevant to the callback. Params::Callback also defines the object-
oriented callback interface, making its documentation a must-read for anyone who wishes to
create callback classes and methods.
This module works with HTML::Mason by subclassing HTML::Mason::Interp. Inspired by the
implementation of callbacks in Bricolage (<http://bricolage.cc/>), it is however a
completely new code base with a rather different approach.
AUTHOR
David E. Wheeler <david@justatheory.com>
COPYRIGHT AND LICENSE
Copyright 2003-2011 by David E. Wheeler. Some Rights Reserved.
This library is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.