Provided by: libcatalyst-perl_5.90124-1_all bug

Name

       Catalyst::RouteMatching - How Catalyst maps an incoming URL to actions in controllers.

Description

       This is a WIP document intended to help people understand the logic that Catalyst uses to
       determine how to match in incoming request to an action (or action chain) in a controller.

   Request to Controller/Action Matching
       Catalyst maps requests to action using a 'longest path wins' approach.  That means that if
       the request is '/foo/bar/baz' That means the action 'baz' matches:

           package MyApp::Controller::Foo;

           use Moose;
           use MooseX::MethodAttributes

           extends 'Catalyst::Controller';

           sub bar :Path('bar') Args(1) { ...}
           sub baz :Path('bar/baz') Args(0) { ... }

       Path length matches take precedence over all other types of matches (included HTTP Method,
       Scheme, etc.).  The same holds true for Chained actions.  Generally the chain that matches
       the most PathParts wins.

   Args(N) versus Args
       'Args' matches any number of args.  Because this functions as a sort of catchall, we treat
       'Args' as the lowest precedence of any Args(N) when N is 0 to infinity.  An action with
       'Args' always get the last chance to match.

   When two or more actions match a given Path
       Sometimes two or more actions match the same path and all have the same PathPart length.
       For example:

           package MyApp::Controller::Root;

           use Moose;
           use MooseX::MethodAttributes

           extends 'Catalyst::Controller';

           sub root :Chained(/) CaptureArgs(0) { }

             sub one :Chained(root) PathPart('') Args(0) { }
             sub two :Chained(root) PathPart('') Args(0) { }
             sub three :Chained(root) PathPart('') Args(0) { }

           __PACKAGE__->meta->make_immutable;

       In this case the last defined action wins (for the example that is action 'three').

       This is most common to happen when you are using action matching beyond paths, such as
       when using method matching:

           package MyApp::Controller::Root;

           use Moose;
           use MooseX::MethodAttributes

           extends 'Catalyst::Controller';

           sub root :Chained(/) CaptureArgs(0) { }

             sub any :Chained(root) PathPart('') Args(0) { }
             sub get :GET Chained(root) PathPart('') Args(0) { }

           __PACKAGE__->meta->make_immutable;

       In the above example GET /root could match both actions.  In this case you should define
       your 'catchall' actions higher in the controller.

   Type Constraints in Args and Capture Args
       Beginning in Version 5.90090+ you may use Moose, MooseX::Types or Type::Tiny type
       constraints to further declare allowed matching for Args or CaptureArgs.  Here is a simple
       example:

           package MyApp::Controller::User;

           use Moose;
           use MooseX::MethodAttributes;
           use MooseX::Types::Moose qw(Int);

           extends 'Catalyst::Controller';

           sub find :Path('') Args(Int) {
             my ($self, $c, $int) = @_;
           }

           __PACKAGE__->meta->make_immutable;

       In this case the incoming request "http://localhost:/user/100" would match the action
       "find" but "http://localhost:/user/not_a_number" would not. You may find declaring
       constraints in this manner aids with debugging, automatic generation of documentation and
       reducing the amount of manual checking you might need to do in your actions.  For example
       if the argument in the given action was going to be used to lookup a row in a database, if
       the matching field expected an integer, a string might cause a database exception,
       prompting you to add additional checking of the argument prior to using it.  In general it
       is hoped this feature can lead to reduced validation boilerplate and more easily
       understood and declarative actions.

       More than one argument may be added by comma separating your type constraint names, for
       example:

           use Types::Standard qw/Int Str/;

           sub find :Path('') Args(Int,Int,Str) {
             my ($self, $c, $int1, $int2, $str) = @_;
           }

       Would require three arguments, an integer, integer and a string.  Note in this example we
       constrained the args using imported types via Types::Standard.  Although you may use
       stringy Moose types, we recommend imported types since this is less ambiguous to your
       readers.  If you want to use Moose stringy types. you must quote them (either "Int" or
       'Int' is fine).

       Conversely, you should not quote types that are imported!

       Using type constraints in a controller

       By default Catalyst allows all the standard, built-in, named type constraints that come
       bundled with Moose.  However it is trivial to create your own Type constraint libraries
       and export them to a controller that wishes to use them.  We recommend using Type::Tiny or
       MooseX::Types for this.  Here is an example using some extended type constraints via the
       Types::Standard library that is packaged with Type::Tiny:

           package MyApp::Controller::User;

           use Moose;
           use MooseX::MethodAttributes;
           use Types::Standard qw/StrMatch Int/;

           extends 'Catalyst::Controller';

           sub looks_like_a_date :Path('') Args(StrMatch[qr{\d\d-\d\d-\d\d}]) {
             my ($self, $c, $int) = @_;
           }

           __PACKAGE__->meta->make_immutable;

       This would match URLs like "http://localhost/user/11-11-2015" for example.  If you've been
       missing the old RegExp matching, this can emulate a good chunk of that ability, and more.

       A tutorial on how to make custom type libraries is outside the scope of this document.
       I'd recommend looking at the copious documentation in Type::Tiny or in MooseX::Types if
       you prefer that system.  The author recommends Type::Tiny if you are unsure which to use.

       Type constraint namespace.

       By default we assume the namespace which defines the type constraint is in the package
       which contains the action declaring the arg or capture arg.  However if you do not wish to
       import type constraints into you package, you may use a fully qualified namespace for your
       type constraint.  If you do this you must install Type::Tiny which defines the code used
       to lookup and normalize the various types of Type constraint libraries.

       Example:

           package MyApp::Example;

           use Moose;
           use MooseX::MethodAttributes;

           extends 'Catalyst::Controller';

           sub an_int_ns :Local Args(MyApp::Types::Int) {
             my ($self, $c, $int) = @_;
             $c->res->body('an_int (withrole)');
           }

       Would basically work the same as:

           package MyApp::Example;

           use Moose;
           use MooseX::MethodAttributes;
           use MyApp::Types 'Int';

           extends 'Catalyst::Controller';

           sub an_int_ns :Local Args(Int) {
             my ($self, $c, $int) = @_;
             $c->res->body('an_int (withrole)');
           }

       namespace::autoclean

       If you want to use namespace::autoclean in your controllers you must 'except' imported
       type constraints since the code that resolves type constraints in args / capture args run
       after the cleaning.  For example:

           package MyApp::Controller::Autoclean;

           use Moose;
           use MooseX::MethodAttributes;
           use namespace::autoclean -except => 'Int';
           use MyApp::Types qw/Int/;

           extends 'Catalyst::Controller';

           sub an_int :Local Args(Int) {
             my ($self, $c, $int) = @_;
             $c->res->body('an_int (autoclean)');
           }

       Using roles and base controller with type constraints

       If your controller is using a base class or a role that has an action with a type
       constraint you should declare your use of the type constraint in that role or base
       controller in the same way as you do in main controllers.  Catalyst will try to find the
       package with declares the type constraint first by looking in any roles and then in
       superclasses.  It will use the first package that defines the type constraint.  For
       example:

           package MyApp::Role;

           use Moose::Role;
           use MooseX::MethodAttributes::Role;
           use MyApp::Types qw/Int/;

           sub an_int :Local Args(Int) {
             my ($self, $c, $int) = @_;
             $c->res->body('an_int (withrole)');
           }

           sub an_int_ns :Local Args(MyApp::Types::Int) {
             my ($self, $c, $int) = @_;
             $c->res->body('an_int (withrole)');
           }

           package MyApp::BaseController;

           use Moose;
           use MooseX::MethodAttributes;
           use MyApp::Types qw/Int/;

           extends 'Catalyst::Controller';

           sub from_parent :Local Args(Int) {
             my ($self, $c, $id) = @_;
             $c->res->body('from_parent $id');
           }

           package MyApp::Controller::WithRole;

           use Moose;
           use MooseX::MethodAttributes;

           extends 'MyApp::BaseController';

           with 'MyApp::Role';

       If you have complex controller hierarchy, we do not at this time attempt to look for all
       packages with a match type constraint, but instead take the first one found.  In the
       future we may add code that attempts to insure a sane use of subclasses with type
       constraints but right now there are no clear use cases so report issues and interests.

       Match order when more than one Action matches a path.

       As previously described, Catalyst will match 'the longest path', which generally means
       that named path / path_parts will take precedence over Args or CaptureArgs.  However, what
       will happen if two actions match the same path with equal args?  For example:

           sub an_int :Path(user) Args(Int) {
           }

           sub an_any :Path(user) Args(1) {
           }

       In this case Catalyst will check actions starting from the LAST one defined.  Generally
       this means you should put your most specific action rules LAST and your 'catch-alls'
       first.  In the above example, since Args(1) will match any argument, you will find that
       that 'an_int' action NEVER gets hit.  You would need to reverse the order:

           sub an_any :Path(user) Args(1) {
           }

           sub an_int :Path(user) Args(Int) {
           }

       Now requests that match this path would first hit the 'an_int' action and will check to
       see if the argument is an integer.  If it is, then the action will execute, otherwise it
       will pass and the dispatcher will check the next matching action (in this case we fall
       through to the 'an_any' action).

       Type Constraints and Chained Actions

       Using type constraints in Chained actions works the same as it does for Path and Local or
       Global actions.  The only difference is that you may declare type constraints on
       CaptureArgs as well as Args.  For Example:

         use Types::Standard qw/Int Tuple/;

         sub chain_base :Chained(/) CaptureArgs(1) { }

           sub any_priority_chain :GET Chained(chain_base) PathPart('') Args(1) {  }

           sub int_priority_chain :Chained(chain_base) PathPart('') Args(Int) {  }

           sub link_any :Chained(chain_base) PathPart('') CaptureArgs(1) { }

             sub any_priority_link_any :Chained(link_any) PathPart('') Args(1) {  }

             sub int_priority_link_any :Chained(link_any) PathPart('') Args(Int) {  }

           sub link_int :Chained(chain_base) PathPart('') CaptureArgs(Int) { }

             sub any_priority_link :Chained(link_int) PathPart('') Args(1) {  }

             sub int_priority_link :Chained(link_int) PathPart('') Args(Int) {  }

           sub link_int_int :Chained(chain_base) PathPart('') CaptureArgs(Int,Int) { }

             sub any_priority_link2 :Chained(link_int_int) PathPart('') Args(1) {  }

             sub int_priority_link2 :Chained(link_int_int) PathPart('') Args(Int) {  }

           sub link_tuple :Chained(chain_base) PathPart('') CaptureArgs(Tuple[Int,Int,Int]) { }

             sub any_priority_link3 :Chained(link_tuple) PathPart('') Args(1) {  }

             sub int_priority_link3 :Chained(link_tuple) PathPart('') Args(Int) {  }

       These chained actions might create match tables like the following:

           [debug] Loaded Chained actions:
           .-------------------------------------+--------------------------------------.
           | Path Spec                           | Private                              |
           +-------------------------------------+--------------------------------------+
           | /chain_base/*/*                     | /chain_base (1)                      |
           |                                     | => GET /any_priority_chain (1)       |
           | /chain_base/*/*/*                   | /chain_base (1)                      |
           |                                     | -> /link_int (Int)                   |
           |                                     | => /any_priority_link (1)            |
           | /chain_base/*/*/*/*                 | /chain_base (1)                      |
           |                                     | -> /link_int_int (Int,Int)           |
           |                                     | => /any_priority_link2 (1)           |
           | /chain_base/*/*/*/*/*               | /chain_base (1)                      |
           |                                     | -> /link_tuple (Tuple[Int,Int,Int])  |
           |                                     | => /any_priority_link3 (1)           |
           | /chain_base/*/*/*                   | /chain_base (1)                      |
           |                                     | -> /link_any (1)                     |
           |                                     | => /any_priority_link_any (1)        |
           | /chain_base/*/*/*/*/*/*             | /chain_base (1)                      |
           |                                     | -> /link_tuple (Tuple[Int,Int,Int])  |
           |                                     | -> /link2_int (UserId)               |
           |                                     | => GET /finally (Int)                |
           | /chain_base/*/*/*/*/*/...           | /chain_base (1)                      |
           |                                     | -> /link_tuple (Tuple[Int,Int,Int])  |
           |                                     | -> /link2_int (UserId)               |
           |                                     | => GET /finally2 (...)               |
           | /chain_base/*/*                     | /chain_base (1)                      |
           |                                     | => /int_priority_chain (Int)         |
           | /chain_base/*/*/*                   | /chain_base (1)                      |
           |                                     | -> /link_int (Int)                   |
           |                                     | => /int_priority_link (Int)          |
           | /chain_base/*/*/*/*                 | /chain_base (1)                      |
           |                                     | -> /link_int_int (Int,Int)           |
           |                                     | => /int_priority_link2 (Int)         |
           | /chain_base/*/*/*/*/*               | /chain_base (1)                      |
           |                                     | -> /link_tuple (Tuple[Int,Int,Int])  |
           |                                     | => /int_priority_link3 (Int)         |
           | /chain_base/*/*/*                   | /chain_base (1)                      |
           |                                     | -> /link_any (1)                     |
           |                                     | => /int_priority_link_any (Int)      |
           '-------------------------------------+--------------------------------------'

       As you can see the same general path could be matched by various action chains.  In this
       case the rule described in the previous section should be followed, which is that Catalyst
       will start with the last defined action and work upward.  For example the action
       "int_priority_chain" would be checked before "any_priority_chain".  The same applies for
       actions that are midway links in a longer chain.  In this case "link_int" would be checked
       before "link_any".  So as always we recommend that you place you priority or most
       constrained actions last and you least or catch-all actions first.

       Although this reverse order checking may seen counter intuitive it does have the added
       benefit that when inheriting controllers any new actions added would take check precedence
       over those in your parent controller or consumed role.

       Please note that your declared type constraint names will now appear in the debug console.

Author

       John Napiorkowski jjnapiork@cpan.org <email:jjnapiork@cpan.org>