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Apache2::compat -- 1.0 backward compatibility functions deprecated in 2.0
# 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');
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.
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, $sockaddr->ip_get);
to work under mod_perl 2.0.
As you can see in mod_perl 1.0 API local_addr() was returning a
SOCKADDR_IN object (see the Socket perl manpage), in mod_perl 2.0 API
it returns an APR::SockAddr|docs::2.0::api::APR::SockAddr
object, which is a totally different beast. If Apache2::compat
overrides the function local_addr() to be back-compatible with
mod_perl 1.0 API. Any code that relies on this function to work as it
should under mod_perl 2.0 will be broken. Therefore the solution is
not to override local_addr() by default. Instead a special API is
provided which overrides colliding functions only when needed and
which can be restored when no longer needed. So for example if you
have code from mod_perl 1.0:
my ($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.
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
APR::URI::unparse
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.
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.
mod_perl 2.0 and its core modules are copyrighted under The Apache Software License, Version 2.0.