Apache2::Controller::Dispatch - dispatch base class for Apache::Controller

Version 1.000.111

Synopsis examples use Apache2::Controller::Dispatch::Simple, but you may want to check out Apache2::Controller::Dispatch::HashTree or write your own. All use the A2C_Dispatch_Map directive, but the hash structure differs between subclasses.

This only works if you have one website on the whole server (under forked mpm) because the intepreter only loads the module once and then it won't load another dispatch map for other uri's.

 # vhost.conf:
 <Location />
     SetHandler modperl
     A2C_Dispatch_Map   /path/to/yaml/syck/dispatch/hash/file.yaml
     PerlInitHandler    Apache2::Controller::Dispatch::Simple
 </Location>

The normal way supports many separate dispatch maps on a server, but each application must subclass a dispatch class, even if it has no methods.

 # vhost.conf:
 PerlLoadModule MyApp::Dispatch;
 <Location />
     SetHandler modperl
     A2C_Dispatch_Map   /etc/myapp/dispatch.yaml
     PerlInitHandler    MyApp::Dispatch
 </Location>

 # /etc/myapp/dispatch.yaml:
 foo:       MyApp::Controller::Foo
 bar:       MyApp::Controller::Bar
 biz:       MyApp::C::Biz
 'biz/baz': MyApp::Controller::Biz::Baz

 # lib/MyApp/Dispatch.pm:
 package MyApp::Dispatch;
 use base qw( Apache2::Controller::Dispatch::Simple );
 1;

 # vhost.conf:
 PerlModule MyApp::Dispatch

 <Location />
     SetHandler modperl
     PerlInitHandler MyApp::Dispatch
 </Location>

 # lib/MyApp/Dispatch.pm:

 package MyApp::Dispatch;

 use strict;
 use warnings FATAL => 'all';

 use base qw( Apache2::Controller::Dispatch::Simple );

 # return a hash reference from dispatch_map()
 sub dispatch_map { return {
     foo        => 'MyApp::C::Foo',
     bar        => 'MyApp::C::Bar',
     biz        => 'MyApp::C::Biz',
     'biz/baz'  => 'MyApp::C::Biz::Baz',
 } }

 # or use directive A2C_Dispatch_Map to refer to a YAML file.

 1;

Apache2::Controller::Dispatch forms the base for the PerlInitHandler module to dispatch incoming requests to libraries based on their URL.

You don't use this module. You use one of its subclasses as a base for your dispatch module.

Natively, this does not try to figure out the appropriate module using any complex magic. Instead, you spell out the uris under the handler location and what controller modules you want to handle paths under that URL, using a directive. (A2C_Dispatch_Map in Apache2::Controller::Directives)

The trouble with automatic controller module detectors is that parsing the URI and doing eval "use lib $blah" up through the URI path is that is computationally expensive.

Maintaining a URI map file is not that difficult and also is convenient because you can move libraries around, point different URI's to the same controller library, etc. For example to bring part of your site off-line and see 'under construction', create a controller to print the right message, change all the uri's in the map and bump the server.

(Can I trap a signal so it clears and reloads map files if Apache2 is HUP'd? That would be cool. Or a timeout that would cause children to reload the file.)

Different dispatch types use different structure in the map, but it is conceptually the same. The structure is loaded into memory and then the uri can be parsed very quickly to locate the correct controller.

Subclasses of this module implement find_controller() in different ways, usually interpreting the URI from a hash reference returned by dispatch_map() in your subclass. Or, if you provide the directive A2C_Dispatch_Map to specify a map file, this module will load it with LoadFile in YAML::Syck.

See Apache2::Controller::Dispatch::Simple and Apache2::Controller::Dispatch::HashTree for other dispatch possibilities.

Any implementation of find_controller() should throw an Apache2::Controller::X with status Apache2::Const::NOT_FOUND in the event that the detected method selected does not appear in the list of allowed_methods() in the controller module. ex:

 a2cx status => Apache2::Const::NOT_FOUND;

See check_allowed_method in Apache2::Controller::Funk. This is internal stuff mostly, you don't have to implement your own type of dispatch mechanism unless you are a nut like me.

Successful run of find_controller() should result in four items of data being set in request->pnotes->{a2c}:

pnotes->{a2c}{relative_uri} = matching part of uri relative to location

This is the uri relative to the location. For example, if the dispatch module is the init handler in a <Location /subdir> config block, then for /subdir/foo/bar/biz/zip in this example code, relative_uri should be 'foo/bar' because this is the key of %dispatch_map that was matched. /subdir/foo/bar is the 'virtual directory.'

If there is no relative uri, for example if the uri requested was /subdir and this is the same as the location, then pnotes-{a2c}{relative_uri} > would be set to the empty string.

pnotes->{a2c}{controller} = selected package name

This should be the name (string) of an Apache2::Controller subclass selected for dispatch.

pnotes->{a2c}{method} = method name in controller to process the uri

This is the name of the method of the controller to use for this request.

pnotes->{a2c}{path_args} = [ remaining path_info ]

The remaining 'virtual directory' arguments of the uri. In the example above for pnotes->{a2c}{relative_uri}, this is [ 'biz', 'zip' ].

@path_args is the array of remaining elements. For example if your dispatch map contains the URI 'foo', and the incoming URI was '/foo/bar/baz', then $r->pnotes->{a2c}{path_args} should be ['bar', 'baz'] before returning.

process() is the main guts of Apache2::Controller::Dispatch logic. It calls $self->find_controller(), which is implemented in another base class. (See Apache2::Controller::Dispatch::Simple.) If that works, then it creates an Apache2::Request object from $r, which will supposedly parse the query string once for all further handlers that create Apache2::Request objects.

The base class method relies on having directive A2C_Dispatch_Map. This loads a YAML::Syck file at server startup for every instance of the directive. This is your best bet if you want to use a file, because the file will be loaded only once, instead of every time a mod_perl child process spawns.

If you want to return a hash yourself, overload this in a dispatch subclass.

Get the cached \%dispatch_map of the dispatch handler object's class. Caches references here in parent package space and checks with exists.

In your dispatch subclass, you define dispatch_map() which returns a hash reference of the dispatch map.

 # configuration for <Location>:
 # PerlInitHandler MyApp::Dispatch

 package MyApp::Dispatch;
 use base qw( 
     Apache2::Controller::Dispatch
     Apache2::Controller::Dispatch::Simple
 );

 my @LIMIT_HTTP_METHODS = qw( GET );

 sub dispatch_map { {                   # return a hash reference
     foo        => 'MyApp::C::Foo',
     bar        => 'MyApp::C::Bar',
     biz        => 'MyApp::C::Biz',
 } }

 1;

Apache2::Controller::Dispatch::HashTree

Apache2::Controller::Dispatch::Simple

Apache2::Controller

Mark Hedges, <hedges at formdata.biz>

Copyright 2008-2010 Mark Hedges, all rights reserved.

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

This software is provided as-is, with no warranty and no guarantee of fitness for any particular purpose.