ModPerl::MethodLookup -- Lookup mod_perl modules, objects and methods
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
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.
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));
$method_name ( string )
$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.
$hint
@modules
Examples:
Return all module names containing XS method print:
my ($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);
$module_name ( string )
$hint
$module_name implements, or explaining the
failure if the lookup failed.
@methods
Example:
What XS methods defined by module Apache2::Filter:
my ($hint, @methods) =
ModPerl::MethodLookup::lookup_module('Apache2::Filter');
lookup_object()
($hint, @methods) = lookup_object($object); ($hint, @methods) = lookup_object($class);
$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).
$hint
@methods
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.
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.
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.
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.
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)
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().
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.
Apache2::porting
mod_perl 2.0 and its core modules are copyrighted under The Apache Software License, Version 2.0.