mod_perl-2.0.9::docs::api::Apache2::compat(3)

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 API 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 API. However there are several functions which have the same name in the mod_perl 1.0 and mod_perl 2.0 API, 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 API local_addr() was returning a SOCKADDR_IN object (see the Socket perl manpage), in mod_perl 2.0 API 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 API. 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 API 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 API:

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

If you port your CPAN modules to work with mod_perl 2.0, you should follow the porting Perl and XS module guidelines.

Users that are stuck with CPAN 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 API 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.