NAME

Apache::Dispatch - call PerlHandlers with the ease of Registry scripts

SYNOPSIS

Makefile.PL:

# require util since it can be used outside an apache process
PREREQ_PM    => {
    'Apache::Dispatch::Util'    => 0.11,
}

httpd.conf:

PerlModule Apache::Dispatch
PerlModule Bar

DispatchExtras Pre Post Error
DispatchStat On
DispatchISA "My::Utils"
DispatchAUTOLOAD Off

<Location /Foo>
  SetHandler perl-script
  PerlHandler Apache::Dispatch

  DispatchPrefix Bar
  DispatchFilter Off
</Location>

DESCRIPTION

Apache::Dispatch translates $r->uri into a class and method and runs it as a PerlHandler. Basically, this allows you to call PerlHandlers as you would Regsitry scripts without having to load your httpd.conf with a slurry of <Location> tags.

EXAMPLE

in httpd.conf

  PerlModule Apache::Dispatch
  PerlModule Bar

  <Location /Foo>
    SetHandler perl-script
    PerlHandler Apache::Dispatch

    DispatchPrefix Bar
  </Location>

in browser:
  http://localhost/Foo/baz

the results are the same as if your httpd.conf looked like:
  <Location /Foo>
    SetHandler perl-script
    PerlHandler Bar->dispatch_baz
  </Location>

but with the additional security of protecting the class name from the browser and keeping the method name from being called directly. Because any class under the Bar:: hierarchy can be called, one <Location> directive is able to handle all the methods of Bar, Bar::Baz, etc...

CONFIGURATION DIRECTIVES

DispatchPrefix
  The base class to be substituted for the $r->location part of the
  uri.

DispatchLocation
  Using Apache::Dispatch from a <Directory> directive, either 
  directly or from a .htaccess file, will _require_ the use of
  DispatchLocation, which defines the location from which
  Apache::Dispatch will start class->method() translation.
  For example:

    httpd.conf
      DocumentRoot /usr/local/apache/htdocs
      <Directory /usr/local/apache/htdocs/>
        ...
      <Directory>

   .htaccess (in /usr/local/apache/htdocs/Foo)
      SetHandler perl-script
      PerlHandler Apache::Dispatch
      DispatchPrefix Baz
      DispatchLocation /Foo

  This allows a request to /Foo/Bar/biff to properly map to
  Baz::Bar->biff().  

  While intended specifically for <Directory> configurations, one
  could use DispatchLocation to further obscure uri translations
  within <Location> sections as well by changing the part of
  the uri that is substitued with your module.

DispatchExtras
  An optional list of extra processing to enable per-request.  If
  the main handler is not a valid method call, the request is 
  declined prior to the execution of any of the extra methods.

    Pre   - eval()s Foo->pre_dispatch($r) prior to dispatching the
            uri.  The $@ of the eval is not checked in any way.

    Post  - eval()s Foo->post_dispatch($r) after dispatching the
            uri.  The $@ of the eval is not checked in any way.

    Error - If the main handler returns other than OK then 
            Foo->error_dispatch($r, $@) is called and return status
            of it is returned instead.  Unlike the pre and post
            processing routines above, error_dispatch is not wrapped
            in an eval, so if it dies, the Apache::Dispatch dies,
            and Apache will process the error using ErrorDocument,
            custom_response(), etc.
            With error_dispatch() disabled, the return status of the
            the main handler is returned to the client.

DispatchRequire
  An optional directive that enables require()ing of the module that
  is the result of the uri to class->method translation.  This allows
  your configuration to be a bit more dynamic, but also decreases
  security somewhat.  And don't forget that you really should be
  pre-loading frequently used modules in the parent process to reduce
  overhead - DispatchRequire is a directive of conveinence.

    On    - require() the module

    Off   - Do not require() the module (Default)

DispatchStat
  An optional directive that enables reloading of the module that is
  the result of the uri to class->method translation, similar to
  Apache::Registry, Apache::Reload, or Apache::StatINC.

    On    - Test the called package for modification and reload on
            change

    Off   - Do not test or reload the package (Default)

    ISA   - Test the called package, and all other packages in the
            called package's @ISA, and reload on change

DispatchAUTOLOAD
  An optional directive that enables unknown methods to use 
  AutoLoader.  It may be applied on a per-server or per-location
  basis and defaults to Off.  Please see the special section on 
  AUTOLOAD below.

    On    - Allow for methods to be defined in AUTOLOAD method

    Off   - Turn off search for AUTOLOAD method (Default)
  
DispatchISA
  An optional list of parent classes you want your dispatched class
  to inherit from.

DispatchFilter 
  If you have Apache::Filter 1.013 or above installed, you can take
  advantage of other Apache::Filter aware modules.  Please see the
  section on FILTERING below.  In keeping with Apache::Filter
  standards, PerlSetVar Filter has the same effect as DispatchFilter
  but with lower precedence.

    On    - make the output of your module Apache::Filter aware

    Off   - do not use Apache::Filter (Default)

DispatchDebug
  Set DispatchDebug to 1 or 2 to control the verbosity of
  debug statements.

SPECIAL CODING GUIDELINES

Migrating to Apache::Dispatch is relatively painless - it requires only a few minor code changes. The good news is that once you adapt code to work with Dispatch, it can be used as a conventional mod_perl method handler, requiring only a few considerations. Below are a few things that require attention.

In the interests of security, all handler methods must be prefixed with 'dispatch_', which is added to the uri behind the scenes. Unlike ordinary mod_perl handlers, for Apache::Dispatch there is no default method (with a tiny exception - see NOTES below).

Apache::Dispatch uses object oriented calls behind the scenes. This means that you either need to account for your handler to be called as a method handler, such as

sub dispatch_bar {
  my $self  = shift;  # your class
  my $r     = shift;
}

or get the Apache request object directly via

sub dispatch_bar {
  my $r     = Apache->request;
}

If you want to use the handler unmodified outside of Apache::Dispatch, you must do three things:

prototype your handler:

  sub dispatch_baz ($$) {
    my $self  = shift;
    my $r     = shift;
  }

change your httpd.conf entry:

  <Location /Foo>
    SetHandler perl-script
    PerlHandler Bar->dispatch_baz
  </Location>

pre-load your module:
  PerlModule Bar
    or
  PerlRequire startup.pl
  # where startup.pl contains
  # use Bar;

That's it - now the handler can be swapped in and out of Dispatch without further modification. See the Eagle book on method handlers for more details.

FILTERING

Apache::Dispatch provides for output filtering using Apache::Filter 1.013 and above.

<Location /Foo>
  SetHandler perl-script
  PerlHandler Apache::Dispatch Apache::Compress

  DispatchPrefix Bar
  DispatchFilter On
</Location>

Your handler need do nothing special to make its output the start of the chain - Apache::Dispatch registers itself with Apache::Filter and hides the task from your handler. Thus, any dispatched handler is automatically Apache::Filter ready without the need for additional code.

The only caveat is that you must use the request object that is passed to the handler and not get it directly using Apache->request.

AUTOLOAD

Support for AUTOLOAD has been made optional, but requires special care. Please take the time to read the camel book on using AUTOLOAD with can() and subroutine declarations (3rd ed pp326-329).

Basically, you declare the methods you want AUTOLOAD to capture by name at the top of your script. This is necessary because can() will return true if your class (or any parent class) contains an AUTOLOAD method, but $AUTOLOAD will only be populated for declared method calls. Hence, without a declaration you won't be able to get at the name of the method you want to AUTOLOAD.

DispatchISA introduced some convenience, but some headaches as well - if you inherit from a class that uses AutoLoader then ALL method calls are true. And as just explained, AUTOLOAD() will not know what the called method was. This may represent a problem if you aren't aware that, say, CGI.pm uses AutoLoader and spend a few hours trying to figure out why all of a sudden every URL under Dispatch is bombing. You may want to check out NEXT.pm (available from CPAN) for use in your AUTOLOAD routines to help circumvent this partucular feature.

If you decide to use DispatchISA it is HIGHLY SUGGESTED that you do so with DispatchAUTOLOAD Off (which is the default behavior).

NOTES

If you define a dispatch_index() method calls to /Foo will default to it. Unfortunately, this implicit translation only happens at the highest level - calls to /Foo/Bar will translate to Foo->Bar() (that is, unless Foo::Bar is your DispatchPrefix, in which case it will work but /Foo/Bar/Baz will not, etc). Explicit calls to /Foo/index follow the normal dispatch rules.

If the uri can be dispatched but contains anything other than [a-zA-Z0-9_/-] Apache::Dispatch declines to handle the request.

Like everything in perl, the package names are case sensitive.

Warnings have been left on, so if you set an invalid class with DispatchISA you will see a message like: Can't locate package Foo::Bar for @Bar::Baz::ISA at .../Apache/Dispatch.pm line 277.

This is alpha software, and as such has not been tested on multiple platforms or environments for security, stability or other concerns. It requires PERL_DIRECTIVE_HANDLERS=1, PERL_LOG_API=1, PERL_HANDLER=1, and maybe other hooks to function properly.

FEATURES/BUGS

If a module fails reload under DispatchStat, Apache::Dispatch declines the request. This might change to SERVER_ERROR in the future...

SEE ALSO

perl(1), mod_perl(1), Apache(3), Apache::Filter(3), Apache::Reload(3), Apache::StatINC(3)

MAINTAINER

Fred Moyer <phred@apache.org>

AUTHOR

Geoffrey Young <geoff@cpan.org>

COPYRIGHT

Copyright 2001-2006 Geoffrey Young - all rights reserved.

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