=head1 NAME

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





=head1 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');






=head1 Description

C<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 L<report the
bug|docs::2.0::user::help::help/Reporting_Problems>, 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 L<port your
code|docs::2.0::user::porting::porting> not to use deprecated
functions and stop using the compatibility layer.






=head1 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 C<L<APR::SockAddr|docs::2.0::api::APR::SockAddr>>
object, which is a totally different beast. If Apache2::compat
overrides the function C<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 C<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 C<override_mp2_api()> and C<restore_mp2_api()> accept a list of
functions to operate on.






=head2 Available Overridable Functions

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

=over

=item * C<Apache2::RequestRec::notes>

=item * C<Apache2::RequestRec::filename>

=item * C<Apache2::RequestRec::finfo>

=item * C<Apache2::Connection::local_addr>

=item * C<Apache2::Connection::remote_addr>

=item * C<Apache2::Util::ht_time>

=item * C<APR::URI::unparse>

=back










=head1 Use in CPAN Modules

The short answer: B<Do not use> C<Apache2::compat> in CPAN modules.

The long answer:

C<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 C<Apache2::compat> user's code is
forced to use the potentially slower method. Which is quite bad.

Some users may choose to keep using C<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 L<Perl|docs::2.0::user::porting::porting> and
L<XS|docs::2.0::devel::porting::porting> module guidelines.

Users that are stuck with CPAN modules preloading C<Apache2::compat>,
can prevent this from happening by adding

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

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






=head1 API

You should be reading the mod_perl 1.0 L<API
docs|docs::1.0::api::index> 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: L<Migrating from mod_perl 1.0
to mod_perl 2.0|docs::2.0::user::porting::compat> which covers all
mod_perl 1.0 constants, functions and methods that have changed in
mod_perl 2.0.






=head1 See Also

L<mod_perl 2.0 documentation|docs::2.0::index>.




=head1 Copyright

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




=head1 Authors

L<The mod_perl development team and numerous
contributors|about::contributors::people>.

=cut
