data/TWiki/CGISessionDriverDotPm.txt
author Colas Nahaboo <colas@nahaboo.net>
Sat, 26 Jan 2008 15:50:53 +0100
changeset 0 414e01d06fd5
permissions -rw-r--r--
RELEASE 4.2.0 freetown
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---+ Package ==
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*extends* <tt>CGI::Session::ErrorHandler</tt>
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%TOC%
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=head1 NAME
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CGI::Session::Driver - CGI::Session driver specifications
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=head1 WARNING
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Version 4.0 of CGI::Session's driver specification is B<NOT> 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.
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If you need any help converting your driver to meet current specs, send me an e-mail. For support information see
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L<CGI::Session|CGI::Session>
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=head1 SYNOPSIS
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    require CGI::Session::Driver;
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    @ISA = qw( CGI::Session::Driver );
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=head1 DESCRIPTION
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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.
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=head1 WHAT IS A DRIVER
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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, $sid)"> methods.
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=head2 BLUEPRINT
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The best way of learning the specs is to look at a blueprint of a driver:
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    package CGI::Session::Driver::your_driver_name;
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    use strict;
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    use base qw( CGI::Session::Driver CGI::Session::ErrorHandler );
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    sub init {
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        my ($self) = @_;
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        # optional
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    }
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    sub DESTROY {
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        my ($self) = @_;
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        # optional
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    }
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    sub store {
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        my ($self, $sid, $datastr) = @_;
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        # Store $datastr, which is an already serialized string of data.
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    }
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    sub retrieve {
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        my ($self, $sid) = @_;
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        # Return $datastr, which was previously stored using above store() method.
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        # Return $datastr if $sid was found. Return 0 or "" if $sid doesn't exist
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        }
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    sub remove {
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        my ($self, $sid) = @_;
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        # Remove storage associated with $sid. Return any true value indicating success,
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        # or undef on failure.
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    }
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    sub traverse {
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        my ($self, $coderef) = @_;
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        # execute $coderef for each session id passing session id as the first and the only
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        # argument
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    }
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    1;
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All the attributes passed as the second argument to CGI::Session's new() or load() methods will automatically
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be made driver's object attributes. For example, if session object was initialized as following:
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    $s = CGI::Session->new("driver:your_driver_name", undef, {Directory=>'/tmp/sessions'});
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You can access value of 'Directory' from within your driver like so:
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    sub store {
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        my ($self, $sid, $datastr) = @_;
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        my $dir = $self->{Directory};   # <-- in this example will be '/tmp/sessions'
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    }
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Optionally, you can define C<init()> method within your driver to do driver specific global initialization. C<init()> method will be invoked only once during the lifecycle of your driver, which is the same as the lifecycle of a session object.
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For examples of C<init()> look into the source code of native CGI::Session drivers.
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=head1 METHODS
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This section lists and describes all driver methods. All the driver methods will receive driver object ($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 ($sid) as the second argument.
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Following list describes every driver method, including its argument list and what step of session's life they will be invoked. Understanding this may help driver authors.
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=over 4
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=item retrieve($self, $sid)
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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< $sid > 0 (zero) or "" should be returned. undef must be returned only to signal error. Error message should be set via set_error(), which can be inherited from L<CGI::Session::ErrorHandler|CGI::Session::ErrorHandler>. 
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Tip: set_error() always returns undef. Use it for your advantage.
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=item store($self, $sid, $datastr)
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Called whenever modified session data is to be stored back to disk. This happens whenever CGI::Session->flush() is called on modified session. Since CGI::Session->DESTROY() calls flush(), store() gets requested each time session object is to be terminated.
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C< store() > is called both to store new sessions and to update already stored sessions. It's driver author's job to figure out which operation needs to be performed.
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$datastr, which is passed as the third argument to represents B<already serialized> session data that needs to be saved.
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store() can return any true value indicating success or undef on failure. Error message should be passed to set_error()
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=item remove($self, $sid)
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Called whenever session data is to be deleted, which is when CGI::Session->delete() is called. Should return any true value indicating success, undef on failure. Error message should be logged in set_error().
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=item traverse($self, \&coderef)
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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->( $sid ) >>
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=item init($self)
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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.
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=item DESTROY($self)
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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.
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=back
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=head2 NOTES
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=over 4
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=item *
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All driver F<.pm> files must be lowercase!
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=item *
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DBI-related drivers are better off using L<CGI::Session::Driver::DBI|CGI::Session::Driver::DBI> as base, but don't have to.
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=back
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=head1 LICENSING
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For support and licensing see L<CGI::Session|CGI::Session>.
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