Package ==
extends CGI::Session::ErrorHandler
=head1 NAME
CGI::Session::Driver - CGI::Session driver specifications
=head1 WARNING
Version 4.0 of CGI::Session's driver specification is B
backward compatible with previous specification. If you already have a driver developed to work with the previous version you're highly encouraged to upgrade your driver code to make it compatible with the current version. Fortunately, current driver specs are a lot easier to adapt to.
If you need any help converting your driver to meet current specs, send me an e-mail. For support information see
L<CGI::Session|CGI::Session>
=head1 SYNOPSIS
require CGI::Session::Driver;
@ISA = qw( CGI::Session::Driver );
=head1 DESCRIPTION
CGI::Session::Driver is a base class for all CGI::Session's native drivers. It also documents driver specifications for those willing to write drivers for different databases not currently supported by CGI::Session.
=head1 WHAT IS A DRIVER
Driver is a piece of code that helps CGI::Session library to talk to specific database engines, or storage mechanisms. To be more precise, driver is a F<.pm> file that inherits from CGI::Session::Driver and defines L<retrieve()|/"retrieve($self, $sid)">, L<store()|/"store($self, $sid, $datastr)"> and L<remove()|/"remove($self, $sid)"> methods.
=head2 BLUEPRINT
The best way of learning the specs is to look at a blueprint of a driver:
package CGI::Session::Driver::your_driver_name;
use strict;
use base qw( CGI::Session::Driver CGI::Session::ErrorHandler );
sub init {
my ($self) = @_;
# optional
}
sub DESTROY {
my ($self) = @_;
# optional
}
sub store {
my ($self, $sid, $datastr) = @_;
# Store $datastr, which is an already serialized string of data.
}
sub retrieve {
my ($self, $sid) = @_;
# Return $datastr, which was previously stored using above store() method.
# Return $datastr if $sid was found. Return 0 or "" if $sid doesn't exist
}
sub remove {
my ($self, $sid) = @_;
# Remove storage associated with $sid. Return any true value indicating success,
# or undef on failure.
}
sub traverse {
my ($self, $coderef) = @_;
# execute $coderef for each session id passing session id as the first and the only
# argument
}
1;
All the attributes passed as the second argument to CGI::Session's new() or load() methods will automatically
be made driver's object attributes. For example, if session object was initialized as following:
$s = CGI::Session->new("driver:your_driver_name", undef, {Directory=>'/tmp/sessions'});
You can access value of 'Directory' from within your driver like so:
sub store {
my ($self, $sid, $datastr) = @_;
my $dir = $self->{Directory}; # <-- in this example will be '/tmp/sessions'
}
Optionally, you can define C<init()> method within your driver to do driver specific global initialization. C<init()> method will be invoked only once during the lifecycle of your driver, which is the same as the lifecycle of a session object.
For examples of C<init()> look into the source code of native CGI::Session drivers.
=head1 METHODS
This section lists and describes all driver methods. All the driver methods will receive driver object ($self) as the first argument. Methods that pertain to an individual session (such as C<retrieve()>, C<store()> and C<remove()>) will also receive session id ($sid) as the second argument.
Following list describes every driver method, including its argument list and what step of session's life they will be invoked. Understanding this may help driver authors.
=over 4
=item retrieve($self, $sid)
Called whenever a specific session is requested either via C<< CGI::Session->new() >> or C<< CGI::Session->load() >> syntax. Method should try to retrieve data associated with C< $sid > and return it. In case no data could be retrieved for C< $sid > 0 (zero) or "" should be returned. undef must be returned only to signal error. Error message should be set via set_error(), which can be inherited from L<CGI::Session::ErrorHandler|CGI::Session::ErrorHandler>.
Tip: set_error() always returns undef. Use it for your advantage.
=item store($self, $sid, $datastr)
Called whenever modified session data is to be stored back to disk. This happens whenever CGI::Session->flush() is called on modified session. Since CGI::Session->DESTROY() calls flush(), store() gets requested each time session object is to be terminated.
C< store() > is called both to store new sessions and to update already stored sessions. It's driver author's job to figure out which operation needs to be performed.
$datastr, which is passed as the third argument to represents B session data that needs to be saved.
store() can return any true value indicating success or undef on failure. Error message should be passed to set_error()
=item remove($self, $sid)
Called whenever session data is to be deleted, which is when CGI::Session->delete() is called. Should return any true value indicating success, undef on failure. Error message should be logged in set_error().
=item traverse($self, \&coderef)
Called only from within CGI::Session->find(). Job of traverse() is to call \&coderef for every single session stored in disk passing session's id as the first and only argument: C<< $coderef->( $sid ) >>
=item init($self)
Optional. Called whenever driver object is to be initialized, which happens only once during the lifecycle of CGI::Session object. Here you can do driver-wide initialization, such as to open connection to a database server.
=item DESTROY($self)
Optional. Perl automatically calls this method on objects just before they are to be terminated. This gives your driver chance to close any database connections or close any open file handles.
=back
=head2 NOTES
=over 4
=item *
All driver F<.pm> files must be lowercase!
=item *
DBI-related drivers are better off using L<CGI::Session::Driver::DBI|CGI::Session::Driver::DBI> as base, but don't have to.
=back
=head1 LICENSING
For support and licensing see L<CGI::Session|CGI::Session>. 
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