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Man Pages


Manual Reference Pages  -  MASONX::WEBAPP (3)

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NAME

MasonX::WebApp - Works with Mason to do processing before Mason is invoked

CONTENTS

SYNOPSIS



  # Create a subclass of MasonX::WebApp
  package My::WebApp;

  use base MasonX::WebApp;

  sub _init
  {
      # do something interesting, like making sure all incoming
      # arguments are UTF-8
  }

  # Create a handler() for it

  package My::MasonHandler;

  my $ah = MasonX::WebApp::ApacheHandler->new( ... );

  sub handler
  {
      # see docs for details
  }

  # In your Apache config file

  <Location />
    SetHandler   perl-script
    PerlHandler  My::MasonHandler
  </Location>



DESCRIPTION

MasonX::WebApp works with Mason to let you do processing before Mason is ever invoked. There are a number of things that one might want to do:
o Argument munging

You might want to make sure all incoming arguments are UTF-8 encoded. Or you might want to create some objects which Mason will see as incoming arguments. For example, a user_id parameter could be turned into a user object.

o Handle requests without Mason

If you’re not generating output for the browser other than a redirect, then there’s no reason to use Mason. You can use a MasonX::WebApp subclass to handle all form submissions, for example.

This has the added benefit of making it easier to preload this code once during server startup.

o Authorization checks

Why do authorization checks in Mason if a failed check just leads to a redirect or NOT FOUND return code?

USAGE

To use MasonX::WebApp, you should create a MasonX::WebApp subclass. By itself, MasonX::WebApp won’t do a whole lot for you, but it provides a nice framework for building on.

    What MasonX::WebApp Provides

MasonX::WebApp, out of the box, provides the following:
o Session creation

You can declare your session parameters, and MasonX::WebApp will create an Apache::Session::Wrapper object for you, available via the session() method. Alternately, you can implement your own session creation method in your subclass.

o Argument munging

The arguments which will eventually be passed to Mason are available via the args() method. This method returns a hashref, and any changes made to this reference will affect the arguments eventually passed to Mason.

o Actions

MasonX::WebApp will call appropriate methods based on the URI. These methods are determined by removing a prefix from the URI (settable via a class method), and then using the remainder as a method name to be called on the webapp object.

o Generate output without using Mason

If you want to generate output that doesn’t really need, like sending a PDF file for download, you can do that with your webapp object before Mason is invoked.

o Messages, errors, and saved arguments

If you are using sessions, the webapp object provides methods to store regular messages, error messages, and save arguments (to re-populate a form, for example) in the session. It also provides methods to retrieve these.

o Convenient uri creation

The uri() method provides a nice flexible API for creating URIs.

You can set some parameters for your subclass declaratively, by calling class methods. These methods store data using Class::Data::Inheritable, so you can inherit from your subclasses and inherit these parameters.

    Declarative Parameters

The following class methods are offered for declaring parameters:
o ActionURIPrefix

This is the prefix used to determine which, if any, action method should be called on the webapp object. By default, this is /submit/. So if a request comes in for /submit/login, then the login() method will be called.

If you change this, your prefix must also start and with a slash (/).

Setting this will override a previous setting of ActionURIPrefixRegex, so do not set both of these parameters in your subclass.

o ActionURIPrefixRegex

If you want to do something more complex than specifying one prefix, you can use this method to specify a regex which determines if a URI is calling an action. For example, you might want to allow both /submit/ and /download/ as prefixes:



  $self->ActionURIPrefixRegex( qr{^/(?:submit|download)/} );



o ApacheHandlerParams

This should be a hash reference of options that will be passed to the MasonX::WebApp::ApacheHandler class’s new() method when creating a new ApacheHandler object. You don’t need to set this if you are creating the ApacheHandler from scratch in your subclass, and/or if you are providing your own mod_perl handler() subroutine/method.

The default handler() will create a new MasonX::WebApp::ApacheHandler object on every request, using these parameters.

o MasonGlobalName

The variable name to use for the webapp object in Mason components. The default handler() sets this global.

The default value for this is $WebApp.

o RequireAbortAfterAction

If this is true, then an exception will be thrown if an action is handled but no abort is generated inside the action method. A redirect is a form of abort.

This defaults to true.

o SessionWrapperParams

A hash reference of parameters to be passed to the Apache::Session::Wrapper class’s new() method.

You don’t need to set this if you are creating your own session wrapper object.

Setting this also causes UseSession to be set to a true value.

o UseSession

Set this to true if you are creating your own session wrapper object, so that MasonX::WebApp knows it can call session() internally.

    Exceptions

Some methods throw exceptions. Exceptions classes are created using Exception::Class.

    Public Methods

The folowing methods are public, and can be called from subclasses or from elsewhere, like in Mason components.
o new()

This is the constructor method. It expects to receive at least two arguments:
o apache_req

An Apache request object, which must be an Apache object or a subclass’s object.

o args

A hash reference of arguments. If you are using the MasonX::WebApp::ApacheHandler class, you can use the return value of its request_args() method.

The new method will do the following:

Call _set_session() if UseSession() is true.

Call _init(). If additional arguments are given then they will be passed along to your _init() method, if you have one. The call to _init() is wrapped in an eval block. If an exception is thrown, and that exception is not a MasonX::WebApp::Exception::Redirect exception, then it will be rethrown. Redirect exceptions are not rethrown.

Call _handle_action().

Return the newly created webapp object.

o apache_req()

Returns the Apache request given to the new() method.

o args()

Returns a hash reference containing the arguments passed to the new() method. Since this is the same reference as is stored in the MasonX::WebApp::ApacheHandler object, any changes to this reference will be visible to Mason components.

o session_wrapper()

Returns the Apache::Session::Wrapper object for the webapp object.

If UseSession() is not true, calling this method throws an exception.

o session()

A shortcut for calling $webapp->session_wrapper->session.

If UseSession() is not true, calling this method throws an exception.

o redirect()

This method can take a number of named parameters. If it is given a uri parameter, then it uses this URI for the redirection. Otherwise, it takes any parameters it is given and calls the uri() method with them. When it calls uri(), it sets the xhtml parameter to false, so you do not need to do this.

If called inside the context of a Mason request, it calls redirect() on the Mason request object.

Otherwise it sets the value of aborted() to true, sends a redirect using the apache request object, and then throws a MasonX::WebApp::Exception::Aborted exception.

o abort( $status )

Stops processing by throwing a MasonX::WebApp::Exception::Aborted exception. You can pass a status code (from Apache::Constants) as an optional argument. If nothing is given then this will default to OK. This status code will be available via the status_code() method.

You will need to use this method if you generate your own output in an action handling method and don’t want to pass control to Mason afterwards.

o aborted()

Returns a boolean value indicating whether or not abort() has been called on the webapp object. This will be true if the redirect() method was called, since it uses abort().

o abort_status()

The value passed to the abort() method. If no value was passed, this will the OK constant from Apache::Constants.

o uri()

This creates a URI string based on the parameters it receives. It accepts the following parameters:
o path

The path portion of the URI. This is the only required parameter.

o query

A hash reference which will be turned into a query string. The keys of the hash reference may point to scalars, array references, or hash references. Hash reference values are treated the same way as array references.

o fragment

Optional

o host

Optional. By default, URIs are relative, and this is not used.

o port

Optional. This is ignored unless host is also passed.

o scheme

Defaults to http, but since URIs are relative by default, this is ignored unless host is also passed.

o username
o password

Optional. These are both ignored unless host is also passed. If password is passed without a username, it is ignored.

o xhtml

Defaults to true. If this is true, then the returned URI will have any ampersands (&) in the query string HTML-escaped (&).

o messages()

Returns an array of non-error messages stored in the session. This method is destructive, as calling it removes the messages from the session.

If you are not using sessions, calling this method throws an exception.

o errors()

Returns an array of error messages stored in the session. This method is destructive, as calling it removes the error messages from the session.

If you are not using sessions, calling this method throws an exception.

o saved_args()

Returns a hash reference of arguments saved in the session. This method is not destructive. If you are saving arguments in the session, you should probably make sure that clean_session() is called at the end of every request. The default handler() sub does this.

If you are not using sessions, calling this method throws an exception.

o clean_session()

Removes any messages, error messages, and saved args stored in the session. This should be called a the end of each request in order to prevent these value leaking over into the next request.

If you are not using sessions, calling this method throws an exception.

    Protected Methods

These methods are intended to be called directly or overridden by your subclass.
o _LoadActions()

If you want to define actions in other files, like My::WebApp::User, this method provides a handy way to load all of them at once. It looks for modules under your subclass’s package name and loads them. So if your subclass is in the package My::WebApp, then it looks for modules matching My::WebApp::*.

Note that because MasonX::WebApp will call action methods on $self, all of these modules must set the package to the same thing. In the example, above, all of the action modules would need to set their package to My::WebApp.

You can always override _handle_action() to implement your own action dispaching if you dislike this restriction.

o _init()

Called from the new() method. By default this does nothing, but you can override it to do something interesting with the newly created object.

o _is_valid_action()

This method takes an action name and returns a boolean value indicating whether or not the action is valid. By default, this simply checks if $self->can($action), but you should consider overriding this to restrict what methods can be called via a URI.

o _make_session_wrapper()

This method is called during object construction if UseSession is true. By default, it creates a new Apache::Session::Wrapper object with the parameters from SessionWrapperParams. You can override this method to provide your own session wrapper creation.

o _handle_action()

This method is called during object construction. If a redirect was done earlier in the object creation process, then it does nothing. Otherwise, it looks at the requested URI to see if it matches the ActionURIPrefix. If it does, it turns the URI into a method name by stripping off the prefix, and it calls that method on the webapp object.

You can override this to provide your own dispatching system for requests.

Note that this method should not call out to Mason. It should only be used for actions that don’t need Mason.

o _save_arg()

Given a key and value, this method saves them in the session so that they will be available via the saved_args() method.

If UseSession() is not true, calling this method throws an exception.

o _add_message()

Given a string, this method stores that string in the session so that it is available via the messages() method.

If UseSession() is not true, calling this method throws an exception.

o _add_error_message()

Given a string, this method stores that string in the session so that it is available via the errors() method.

If UseSession() is not true, calling this method throws an exception.

o _handle_error()

This method can be used to handle exceptions that occur during actions.

It provides a quick way to store error messages and arguments in the session, and then issue a redirect.

It takes several parameters:
o error

This should be either a scalar, an array reference or an object. If it is a scalar, this is assumed to be an error message. If it an array reference, it is assumed to be an array reference of scalars, each of which contains a single message.

If an object is given, then it first looks for a messages() method in that object. This method should return an array of scalars, each of which represents an error message.

Otherwise it looks for a method called message(), which should return a single scalar.

It adds each error message to the session via the _add_error_message() method.

o save_args

This is a hash reference of arguments that should be saved in the session. Each key/value pair will be saved by calling the the _save_arg() method.

All other arguments are passed along to the redirect() method.

If UseSession() is not true, calling this method throws an exception.

o _apache_handler_object()

This method is called in the default handler() method in order to create a new MasonX::WebApp::ApacheHandler object. It simply calls that class’s new() method with the parameters set via ApacheHandlerParams.

    Hash Keys in the WebApp and Session Objects

In order to avoid stepping on your toes, all hash keys in the webapp object, and all keys that it creates in the session object, are of the form __blahblah__. In other words, they always start and end with two underscores (__). This should make it easy to avoid name conflicts when subclassing this module or when using the session it provides.

The Default handler() Method

The MasonX::WebApp class provides a default handler method.

I would recommend that instead of using this method, you create your own mod_perl handler that does something similar, because the default is not very efficient, given that it creates a new MasonX::WebApp::ApacheHandler object for each request. It is provided primarily as a reference implementation, and so that others can experiment with this webapp code quickly.

When creating your own handler, it might be useful to copy the one in this module as a reference.

In your own handler, there are several important guidelines you should follow.
o First of all, your handler() should use the MasonX::WebApp::ApacheHandler class for the ApacheHandler object, not HTML::Mason::ApacheHandler. The MasonX subclass caches the value of request_args(). This is done so that these arguments can be passed to the MasonX::WebApp constructor and still be made available to Mason. It also makes sure that Mason’s arguments are the same hash reference as is available from the args() method. This is very important if you want to do any argument munging in your subclass. Also, since mod_perl will only read POSTed data once, without this caching Mason would not see any arguments at all!
o Get the request arguments by calling request_args() on the ApacheHandler object, passing an Apache object as the method’s argument. Unless you set the ApacheHandler’s args_method parameter to CGI, you must pass in an ApacheRequest object.

You will need to pass the hash reference returned by this method to the constructor for your WebApp object.

o After creating a new webapp object, make sure to check the value of the aborted() method for that object. If it is true, you should return the status code given by the abort_status() method from your handler(). Remember, this will default to OK if no status was given to the abort() method.
o If you are using the message, error message, or saved arg features, you should make sure that clean_session() is called at the end of every request. This means that you need to wrap the call to the ApacheHandler’s handle_request() method in an eval block, as in the default handler()
o If you use the set_global() method to make the webapp object available to your components, <B>andB> your ApacheHandler objects persist across requests, then you need to call set_global() again after the request is handled, and this time set that global to undef. This ensures that the webapp object will be destroyed.

A safer alternative, if you know what class your components will be compiled in, is to do this:



 local $HTML::Mason::Commands::App = $app;



The use of local ensures that $app will go out of scope at the end of handler() subroutine.

You can, of course, do anything you want in your own handler() method. I often create an Apache::Request object with a POST_MAX parameter, in order to prevent a DoS from a ridiculously large POST.

I also often handle errors without dying, and instead will log them and present a more friendly page to the user. If you want to do this, keep in mind that constructing a webapp object can throw exceptions, so you may want to trap these in an eval block.

If you do something cool with this code, write about it on the Mason HQ site, masonhq.com (which is a big wiki), or send a post to the Mason users list.

Example handler()

Here is an example of an alternate handler(). This one is written as a function, not a method.



  package My::MasonHandler;

  sub handler
  {
      my $apr = Apache::Request->new(shift);

      my $args = $ah->request_args($apr);

      my $app = $class->new( apache_req => $apr, args => $args );

      return $app->abort_status if $app->aborted;

      local $My::ComponentPackage::WebApp = $app;

      my $return = eval { $ah->handle_request($r) };

      my $err = $@;

      $app->clean_session if $class->UseSession;

      die $err if $err;

      return $return;
   }



Then in your Apache configuration, you would use this handler:



  <Location />
    SetHandler   perl-script
    PerlHandler  My::MasonHandler
  </Location>



SEE ALSO

If you like the basic idea of this code (run things before a Mason component is invoked), but you don’t want to create a subclass, I encourage you to take a look at David Wheeler’s MasonX::Interp::WithCallbacks module. In fact, I encourage you to take a look at it anyway, since it may be more appropriate than this one, depending on your needs.

SUPPORT

Bug reports and requests for help should be sent to the mason-users list. See http://www.masonhq.com/resources/mailing_lists.html for more details.

AUTHOR

Dave Rolsky, <autarch@urth.org>

COPYRIGHT

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

The full text of the license can be found in the LICENSE file included with this module.

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