Apache2::compat (3)

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NAME

Apache2::compat -- 1.0 backward compatibility functions deprecated in 2.0

Synopsis

  # either add at the very beginning of startup.pl
  use Apache2::compat;
  # or httpd.conf
  PerlModule Apache2::compat

  # override and restore compat functions colliding with mp2 API
  Apache2::compat::override_mp2_api('Apache2::Connection::local_addr');
  my ($local_port, $local_addr) = sockaddr_in($c->local_addr);
  Apache2::compat::restore_mp2_api('Apache2::Connection::local_addr');

Description

"Apache2::compat" provides mod_perl 1.0 compatibility layer and can be used to smooth the transition process to mod_perl 2.0.

It includes functions that have changed their

or were removed in mod_perl 2.0. If your code uses any of those functions, you should load this module at the server startup, and everything should work as it did in 1.0. If it doesn't please report the bug, but before you do that please make sure that your code does work properly under mod_perl 1.0.

However, remember, that it's implemented in pure Perl and not C, therefore its functionality is not optimized and it's the best to try to port your code not to use deprecated functions and stop using the compatibility layer.

Compatibility Functions Colliding with mod_perl 2.0 API

Most of the functions provided by Apache2::compat don't interfere with mod_perl 2.0 However there are several functions which have the same name in the mod_perl 1.0 and mod_perl 2.0 accept the same number of arguments, but either the arguments themselves aren't the same or the return values are different. For example the mod_perl 1.0 code:

  require Socket;
  my $sockaddr_in = $c->local_addr;
  my ($local_port, $local_addr) = Socket::sockaddr_in($sockaddr_in);

should be adjusted to be:

  require Apache2::Connection;
  require APR::SockAddr;
  my $sockaddr = $c->local_addr;
  my ($local_port, $local_addr) = ($sockaddr->port, $sockaddr->ip_get);

to work under mod_perl 2.0.

As you can see in mod_perl 1.0

local_addr() was returning a object (see the Socket perl manpage), in mod_perl 2.0 it returns an "APR::SockAddr" object, which is a totally different beast. If Apache2::compat overrides the function "local_addr()" to be back-compatible with mod_perl 1.0 Any code that relies on this function to work as it should under mod_perl 2.0 will be broken. Therefore the solution is not to override "local_addr()" by default. Instead a special is provided which overrides colliding functions only when needed and which can be restored when no longer needed. So for example if you have code from mod_perl 1.0:

  my ($local_port, $local_addr) = Socket::sockaddr_in($c->local_addr);

and you aren't ready to port it to to use the mp2

  my ($local_port, $local_addr) = ($c->local_addr->port,
                                   $c->local_addr->ip_get);

you could do the following:

  Apache2::compat::override_mp2_api('Apache2::Connection::local_addr');
  my ($local_port, $local_addr) = Socket::sockaddr_in($c->local_addr);
  Apache2::compat::restore_mp2_api('Apache2::Connection::local_addr');

Notice that you need to restore the

as soon as possible.

Both "override_mp2_api()" and "restore_mp2_api()" accept a list of functions to operate on.

Available Overridable Functions

At the moment the following colliding functions are available for overriding:

Apache2::RequestRec::notes

Apache2::RequestRec::filename

Apache2::RequestRec::finfo

Apache2::Connection::local_addr

Apache2::Connection::remote_addr

Apache2::Util::ht_time

Apache2::Module::top_module

Apache2::Module::get_config

APR::URI::unparse

Use in CPAN Modules

The short answer: Do not use "Apache2::compat" in modules.

The long answer:

"Apache2::compat" is useful during the mod_perl 1.0 code porting. Though remember that it's implemented in pure Perl. In certain cases it overrides mod_perl 2.0 methods, because their

is very different and doesn't map 1:1 to mod_perl 1.0. So if anything, not under user's control, loads "Apache2::compat" user's code is forced to use the potentially slower method. Which is quite bad.

Some users may choose to keep using "Apache2::compat" in production and it may perform just fine. Other users will choose not to use that module, by porting their code to use mod_perl 2.0

However it should be users' choice whether to load this module or not and not to be enforced by modules.

If you port your

modules to work with mod_perl 2.0, you should follow the porting Perl and module guidelines.

Users that are stuck with

modules preloading "Apache2::compat", can prevent this from happening by adding

  $INC{'Apache2/compat.pm'} = __FILE__;

at the very beginning of their startup.pl. But this will most certainly break the module that needed this module.

API

You should be reading the mod_perl 1.0 docs for usage of the methods and functions in this package, since what this module is doing is providing a backwards compatibility and it makes no sense to duplicate documentation.

Another important document to read is: Migrating from mod_perl 1.0 to mod_perl 2.0 which covers all mod_perl 1.0 constants, functions and methods that have changed in mod_perl 2.0.

See Also

mod_perl 2.0 documentation.

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.