Provided by: libapache2-mod-perl2_2.0.5-5ubuntu1_amd64 bug

NAME

       ModPerl::MethodLookup -- Lookup mod_perl modules, objects and methods

Synopsis

         use ModPerl::MethodLookup;

         # return all module names containing XS method 'print'
         my ($hint, @modules) =
             ModPerl::MethodLookup::lookup_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::MethodLookup::lookup_method('print', $filter);
         # or
         my ($hint, @modules) =
             ModPerl::MethodLookup::lookup_method('print', 'Apache2::Filter');

         # what XS methods defined by module 'Apache2::Filter'
         my ($hint, @methods) =
             ModPerl::MethodLookup::lookup_module('Apache2::Filter');

         # what XS methods can be invoked on the object $r (or a ref)
         my ($hint, @methods) =
             ModPerl::MethodLookup::lookup_object($r);
         # or
         my ($hint, @methods) =
             ModPerl::MethodLookup::lookup_object('Apache2::RequestRec');

         # preload all mp2 modules in startup.pl
         ModPerl::MethodLookup::preload_all_modules();

         # command line shortcuts
         % perl -MModPerl::MethodLookup -e print_module \
           Apache2::RequestRec Apache2::Filter
         % perl -MModPerl::MethodLookup -e print_object Apache2
         % perl -MModPerl::MethodLookup -e print_method \
           get_server_built request
         % perl -MModPerl::MethodLookup -e print_method read
         % perl -MModPerl::MethodLookup -e print_method read APR::Bucket

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::MethodLookup" provides the Perl
       API for finding module names which contain methods in question and other helper functions,
       to find out out what methods defined by some module, what methods can be called on a given
       object, etc.

API

   "lookup_method()"
       Find modules (packages) containing a certain method

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

       arg1: $method_name ( string )
           the method name to look 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 kind.

           If a sub-classed object is passed it'll be handled correctly, by checking its
           super-class(es).  This usage 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 lookup result, suggesting which modules should be
           loaded, ready for copy-n-paste or explaining the failure if the lookup didn't succeed.

       ret2: @modules
           an array of modules which have matched the query, 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::MethodLookup::lookup_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::MethodLookup::lookup_method('print', $filter);

       or:

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

   "lookup_module()"
       Find methods contained in a certain module (package)

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

       arg1: $module_name ( string )
           the module name

       ret1: $hint
           a string containing a human readable lookup result, suggesting, which methods the
           module $module_name implements, or explaining the failure if the lookup failed.

       ret2: @methods
           an array of methods which have matched the query, 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::MethodLookup::lookup_module('Apache2::Filter');

   "lookup_object()"
         ($hint, @methods) = lookup_object($object);
         ($hint, @methods) = lookup_object($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 lookup result, suggesting, which methods the
           given object can invoke (including module names that need to be loaded to use those
           methods), or explaining the failure if the lookup failed.

       ret2: @methods
           an array of methods which have matched the query, i.e. the names of the methods that
           can be invoked on the given 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
       invoked on the given object. Currently we can't programmatically deduct the objects they
       are invoked on, because these methods are written in pure XS and manipulate the arguments
       stack themselves. Currently these are mainly XS functions, not methods, which of course
       aren't invoked on objects. There are also logging function wrappers ("Apache2::Log").

       Examples:

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

         my ($hint, @methods) =
             ModPerl::MethodLookup::lookup_object($r);

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

         my ($hint, @methods) =
             ModPerl::MethodLookup::lookup_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 make sure their distribution loads each of the used
       mod_perl 2.0 modules explicitly, and not use this function, as it takes 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 "lookup_method()", mainly designed to be
       used from the command line. For example to print all the modules which define method read
       execute:

         % perl -MModPerl::MethodLookup -e print_method read

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

         % perl -MModPerl::MethodLookup -e print_method read APR::Bucket

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

         % perl -MModPerl::MethodLookup -e print_method \
           get_server_built request

       The function "print_method()" is exported by default.

       since: 2.0.00

   "print_module()"
       "print_module()" is a convenience wrapper for "lookup_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::MethodLookup -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 "lookup_object()", mainly designed to be
       used from the command line. For example to print all the methods that can be invoked on
       object blessed into a class "Apache2::RequestRec" run:

         % perl -MModPerl::MethodLookup -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 checks whether the package the object belongs to has
       an "AUTOLOAD" function defined and if so, calls it with the same arguments as the missing
       method while setting a global variable $AUTOLOAD (in that package) to the name of the
       originally called method. We can use this facility to lookup the modules to be loaded when
       such a failure occurs. Though since we have many packages to take care of we will use a
       special "UNIVERSAL::AUTOLOAD" function which Perl calls if can't find the "AUTOLOAD"
       function in the given package.

       In that function you can query "ModPerl::MethodLookup", require() the module that includes
       the called method and call that method again using the goto() trick:

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

       However we don't endorse this approach. It's a better approach to always abort the
       execution which printing the $hintand 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 work for me. It installs
       "UNIVERSAL::AUTOLOAD" only when the the child process starts.

         httpd.conf:
         -----------
         PerlChildInitHandler ModPerl::MethodLookupAuto

         startup.pl:
         -----------
         {
             package ModPerl::MethodLookupAuto;
             use ModPerl::MethodLookup;

             use Carp;
             sub handler {

                 *UNIVERSAL::AUTOLOAD = sub {
                     my $method = $AUTOLOAD;
                     return if $method =~ /DESTROY/; # exclude DESTROY resolving

                     my ($hint, @modules) =
                         ModPerl::MethodLookup::lookup_method($method, @_);
                     $hint ||= "Can't find method $AUTOLOAD";
                     croak $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 version of AUTOLOAD discussed on the dev list. Replace the current
       one with it. (search the archive for EazyLife)

   Command Line Lookups
       When a method is used and mod_perl has reported a failure to find it, it's often useful to
       use the command line query 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 package
         "Apache2::RequestRec" at ...

       you can ask "ModPerl::MethodLookup" for help:

         % perl -MModPerl::MethodLookup -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 lookup "perl -MModPerl::MethodLookup -e print_method"

       For Bash-style shell users:

          % alias lookup="perl -MModPerl::MethodLookup -e print_method"

       Now the lookup is even easier:

         % lookup 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 picked 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 reports only XS functions. In the
       future we may add support for pure perl functions/methods as well.

See Also

       ·   the mod_perl 1.0 backward 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,
       Version 2.0.

Authors

       The mod_perl development team and numerous contributors.