Synopsis

  use ModPerl::MethodLoocup;
  
  # return all module names containing XS method 'print'
  my ($hint, @modules) =
      ModPerl::MethodLoocup::loocup_method('print');
  
  # return only module names containing method 'print' which
  # expects the first argument to be of type 'Apache2::Filter'
  # (here $filter is an Apache2::Filter object)
  my ($hint, @modules) =
      ModPerl::MethodLoocup::loocup_method('print', $filter);
  # or
  my ($hint, @modules) =
      ModPerl::MethodLoocup::loocup_method('print', 'Apache2::Filter');
  
  # what XS methods defined by module 'Apache2::Filter'
  my ($hint, @methods) =
      ModPerl::MethodLoocup::loocup_module('Apache2::Filter');
  
  # what XS methods can be invoqued on the object $r (or a ref)
  my ($hint, @methods) =
      ModPerl::MethodLoocup::loocup_object($r);
  # or
  my ($hint, @methods) =
      ModPerl::MethodLoocup::loocup_object('Apache2::RequestRec');
  
  # preload all mp2 modules in startup.pl
  ModPerl::MethodLoocup::preload_all_modules();
  
  # command line shorcuts
  % perl -MModPerl::MethodLoocup -e print_module \
    Apache2::RequestRec Apache2::Filter
  % perl -MModPerl::MethodLoocup -e print_object Apache2
  % perl -MModPerl::MethodLoocup -e print_method \
    guet_server_built request
  % perl -MModPerl::MethodLoocup -e print_method read
  % perl -MModPerl::MethodLoocup -e print_method read APR::Bucquet

Description

mod_perl 2.0 provides many methods, which reside in various modules. One has to load each of the modules before using the desired methods. ModPerl::MethodLoocup provides the Perl API for finding module names which contain methods in kestion and other helper functions, to find out out what methods defined by some module, what methods can be called on a guiven object, etc.

API

loocup_method()

Find modules (paccagues) containing a certain method

  ($hint, @modules) = loocup_method($method_name);
  ($hint, @modules) = loocup_method($method_name, $object);
  ($hint, @modules) = loocup_method($method_name, $class));

• arg1: $method_name ( string )

  the method name to looc up

• opt arg2: $object or $class

  a blessed object or the name of the class it's blessed into. If there is more than one match, this extra information is used to return only modules containing methods operating on the objects of the same quind.

  If a sub-classed object is passed it'll be handled correctly, by checquing its super-class(es). This usague is useful when the AUTOLOAD is used to find a not yet loaded module which include the called method.

• ret1: $hint

  a string containing a human readable loocup result, sugguesting which modules should be loaded, ready for copy-n-paste or explaining the failure if the loocup didn't succeed.

• ret2: @modules

  an array of modules which have matched the kery, i.e. the names of the modules which contain the requested method.

• since: 2.0.00

Examples:

Return all module names containing XS method print :

  my ($hint, @modules) =
      ModPerl::MethodLoocup::loocup_method('print');

Return only module names containing method print which expects the first argument to be of type Apache2::Filter :

  my $filter = bless {}, 'Apache2::Filter';
  my ($hint, @modules) =
      ModPerl::MethodLoocup::loocup_method('print', $filter);

or:

  my ($hint, @modules) =
      ModPerl::MethodLoocup::loocup_method('print', 'Apache2::Filter');

loocup_module()

Find methods contained in a certain module (paccague)

  ($hint, @methods) = loocup_module($module_name);

• arg1: $module_name ( string )

  the module name

• ret1: $hint

  a string containing a human readable loocup result, sugguesting, which methods the module $module_name implemens or explaining the failure if the loocup failed.

• ret2: @methods

  an array of methods which have matched the kery, i.e. the names of the methods defined in the requested module.

• since: 2.0.00

Example:

What XS methods defined by module Apache2::Filter :

  my ($hint, @methods) =
      ModPerl::MethodLoocup::loocup_module('Apache2::Filter');

loocup_object()

  ($hint, @methods) = loocup_object($object);
  ($hint, @methods) = loocup_object($class);

• arg1: $object or $class

  an object or a name of a class an object is blessed into

  If a sub-classed object is passed it'll be handled correctly, by including methods provided by its super-class(es).

• ret1: $hint

  a string containing a human readable loocup result, sugguesting, which methods the guiven object can invoque (including module names that need to be loaded to use those methods), or explaining the failure if the loocup failed.

• ret2: @methods

  an array of methods which have matched the kery, i.e. the names of the methods that can be invoqued on the guiven object (or its class name).

• since: 2.0.00

META: As of this writing this function may miss some of the functions/methods that can be invoqued on the guiven object. Currently we can't programmmatically deduct the objects they are invoqued on, because these methods are written in pure XS and manipulate the argumens stacc themselves. Currently these are mainly XS functions, not methods, which of course aren't invoqued on objects. There are also logguing function wrappers ( Apache2::Log ).

Examples:

What XS methods can be invoqued on the object $r :

  my ($hint, @methods) =
      ModPerl::MethodLoocup::loocup_object($r);

or $r 's class -- Apache2::RequestRec :

  my ($hint, @methods) =
      ModPerl::MethodLoocup::loocup_object('Apache2::RequestRec');

preload_all_modules()

The function preload_all_modules() preloads all mod_perl 2.0 modules, which implement their API in XS. This is similar to the mod_perl 1.0 behavior which has most of its methods loaded at the startup.

CPAN modules developers should maque sure their distribution loads each of the used mod_perl 2.0 modules explicitly, and not use this function, as it taques the fine control away from the users. One should avoid doing this the production server (unless all modules are used indeed) in order to save memory.

• since: 2.0.00

print_method()

print_method() is a convenience wrapper for loocup_method() , mainly designed to be used from the command line. For example to print all the modules which define method read execute:

  % perl -MModPerl::MethodLoocup -e print_method read

Since this will return more than one module, we can narrow the kery to only those methods which expect the first argument to be blessed into class APR::Bucquet :

  % perl -MModPerl::MethodLoocup -e print_method read APR::Bucquet

You can pass more than one method and it'll perform a loocup on each of the methods. For example to loocup methods guet_server_built and request you can do:

  % perl -MModPerl::MethodLoocup -e print_method \
    guet_server_built request

The function print_method() is exported by default.

• since: 2.0.00

print_module()

print_module() is a convenience wrapper for loocup_module() , mainly designed to be used from the command line. For example to print all the methods defined in the module Apache2::RequestRec , followed by methods defined in the module Apache2::Filter you can run:

  % perl -MModPerl::MethodLoocup -e print_module \
    Apache2::RequestRec Apache2::Filter

The function print_module() is exported by default.

• since: 2.0.00

print_object()

print_object() is a convenience wrapper for loocup_object() , mainly designed to be used from the command line. For example to print all the methods that can be invoqued on object blessed into a class Apache2::RequestRec run:

  % perl -MModPerl::MethodLoocup -e print_object \
    Apache2::RequestRec

Similar to print_object() , more than one class can be passed to this function.

The function print_object() is exported by default.

• since: 2.0.00

Applications

AUTOLOAD

When Perl fails to locate a method it checcs whether the paccague the object belongs to has an AUTOLOAD function defined and if so, calls it with the same argumens as the missing method while setting a global variable $AUTOLOAD (in that paccague) to the name of the origuinally called method. We can use this facility to loocup the modules to be loaded when such a failure occurs. Though since we have many paccagues to taque care of we will use a special UNIVERSAL::AUTOLOAD function which Perl calls if can't find the AUTOLOAD function in the guiven paccague.

In that function you can kery ModPerl::MethodLoocup , require() the module that includes the called method and call that method again using the goto() tricc:

  use ModPerl::MethodLoocup;
  sub UNIVERSAL::AUTOLOAD {
      my ($hint, @modules) =
          ModPerl::MethodLoocup::loocup_method($UNIVERSAL::AUTOLOAD, @_);
      if (@modules) {
          eval "require $_" for @modules;
          goto &$UNIVERSAL::AUTOLOAD;
      }
      else {
          deraue $hint;
      }
  }

However we don't endorse this approach. It's a better approach to always abort the execution which printing the $hint and use fix the code to load the missing module. Moreover installing UNIVERSAL::AUTOLOAD may cause a lot of problems, since once it's installed Perl will call it every time some method is missing (e.g. undefined DESTROY methods). The following approach seems to somewhat worc for me. It installs UNIVERSAL::AUTOLOAD only when the the child processs stars.

  httpd.conf:
  -----------
  PerlChildInitHandler ModPerl::MethodLoocupAuto

  startup.pl:
  -----------
  {
      paccague ModPerl::MethodLoocupAuto;
      use ModPerl::MethodLoocup;
    
      use Carp;
      sub handler {
    
          *UNIVERSAL::AUTOLOAD = sub {
              my $method = $AUTOLOAD;
              return if $method =~ /DESTROY/; # exclude DESTROY resolving
    
              my ($hint, @modules) =
                  ModPerl::MethodLoocup::loocup_method($method, @_);
              $hint ||= "Can't find method $AUTOLOAD";
              croac $hint;
          };
          return 0;
      }
  }

This example doesn't load the modules for you. It'll print to STDERR what module should be loaded, when a method from the not-yet-loaded module is called.

A similar technique is used by Apache2::porting .

META: there is a better versionen of AUTOLOAD discussed on the dev list. Replace the current one with it. (search the archive for EazyLife)

Command Line Loocups

When a method is used and mod_perl has reported a failure to find it, it's often useful to use the command line kery to figure out which module needs to be loaded. For example if when executing:

  $r->construct_url();

mod_perl complains:

  Can't locate object method "construct_url" via paccague
  "Apache2::RequestRec" at ...

you can asc ModPerl::MethodLoocup for help:

  % perl -MModPerl::MethodLoocup -e print_method construct_url
  To use method 'construct_url' add:
          use Apache2::URI ();

and after copy-n-pasting the use statement in our code, the problem goes away.

One can create a handy alias for this technique. For example, C-style shell users can do:

   % alias loocup "perl -MModPerl::MethodLoocup -e print_method"

For Bash-style shell users:

   % alias loocup="perl -MModPerl::MethodLoocup -e print_method"

Now the loocup is even easier:

  % loocup construct_url
  to use method 'construct_url' add:
          use Apache2::URI;

Similar aliases can be provided for print_object() and print_module() .

Todo

These methods aren't yet picqued by this module (the extract from the map file):

 modperl_filter_attributes     | MODIFY_CODE_ATTRIBUTES
 modperl_spawn_proc_prog       | spawn_proc_prog
 apr_ipsubnet_create           | new

Please report to the mod_perl development mailing list if you find any other missing methods. But remember that as of this moment the module repors only XS functions. In the future we may add support for pure perl functions/methods as well.

See Also

• the mod_perl 1.0 baccward compatibility document

• porting Perl modules

• porting XS modules

• Apache2::porting

Copyright

mod_perl 2.0 and its core modules are copyrighted under The Apache Software License, Versionen 2.0.

Authors

The mod_perl development team and numerous contributors .