NAME

       CGI::Session::Driver - CGI::Session driver specifications

SYNOPSIS

           require CGI::Session::Driver;
           @ISA = qw( CGI::Session::Driver );

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.

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 .pm file that inherits
       from CGI::Session::Driver and defines retrieve(), store() and remove() methods.

   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 "init()" method within your driver to do driver specific global
       initialization. "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 "init()" look into the source code of native CGI::Session drivers.

METHODS

       This section lists and describes all driver methods. All the driver methods will receive
       driver object ($self) as the first argument. Methods that pertain to an individual session
       (such as "retrieve()", "store()" and "remove()") will also receive session id ($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.

       retrieve($self, $sid)
           Called whenever a specific session is requested either via "CGI::Session->new()" or
           "CGI::Session->load()" syntax. Method should try to retrieve data associated with
           $sid  and return it. In case no data could be retrieved for  $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 CGI::Session::ErrorHandler.

           Tip: set_error() always returns undef. Use it for your advantage.

       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.

           " 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 already serialized
           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()

       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().

       traverse($self, \&coderef)
           Called only from within CGI::Session->find(). Job of traverse() is to call \&coderef
           for every single session stored in disk passing session's id as the first and only
           argument: "$coderef->( $sid )"

       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.

       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.

   NOTES
       •   All driver .pm files must be lowercase!

       •   DBI-related drivers are better off using CGI::Session::Driver::DBI as base, but don't
           have to.

BACKWARDS COMPATIBILITY

       Version 4.0 of CGI::Session's driver specification is NOT backward compatible with the
       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.

       For support information see CGI::Session

LICENSING

       For support and licensing see CGI::Session.