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
     1 ---+ Package ==
     2 *extends* <tt>CGI::Session::ErrorHandler</tt>
     3 
     4 
     5 %TOC%
     6 =head1 NAME
     7 
     8 CGI::Session::Driver - CGI::Session driver specifications
     9 
    10 =head1 WARNING
    11 
    12 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.
    13 
    14 If you need any help converting your driver to meet current specs, send me an e-mail. For support information see
    15 L<CGI::Session|CGI::Session>
    16 
    17 =head1 SYNOPSIS
    18 
    19     require CGI::Session::Driver;
    20     @ISA = qw( CGI::Session::Driver );
    21 
    22 =head1 DESCRIPTION
    23 
    24 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.
    25 
    26 =head1 WHAT IS A DRIVER
    27 
    28 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, $sid)"> methods.
    29 
    30 =head2 BLUEPRINT
    31 
    32 The best way of learning the specs is to look at a blueprint of a driver:
    33 
    34     package CGI::Session::Driver::your_driver_name;
    35     use strict;
    36     use base qw( CGI::Session::Driver CGI::Session::ErrorHandler );
    37 
    38     sub init {
    39         my ($self) = @_;
    40         # optional
    41     }
    42 
    43     sub DESTROY {
    44         my ($self) = @_;
    45         # optional
    46     }
    47 
    48     sub store {
    49         my ($self, $sid, $datastr) = @_;
    50         # Store $datastr, which is an already serialized string of data.
    51     }
    52 
    53     sub retrieve {
    54         my ($self, $sid) = @_;
    55         # Return $datastr, which was previously stored using above store() method.
    56         # Return $datastr if $sid was found. Return 0 or "" if $sid doesn't exist
    57         }
    58 
    59     sub remove {
    60         my ($self, $sid) = @_;
    61         # Remove storage associated with $sid. Return any true value indicating success,
    62         # or undef on failure.
    63     }
    64 
    65     sub traverse {
    66         my ($self, $coderef) = @_;
    67         # execute $coderef for each session id passing session id as the first and the only
    68         # argument
    69     }
    70 
    71     1;
    72 
    73 All the attributes passed as the second argument to CGI::Session's new() or load() methods will automatically
    74 be made driver's object attributes. For example, if session object was initialized as following:
    75 
    76     $s = CGI::Session->new("driver:your_driver_name", undef, {Directory=>'/tmp/sessions'});
    77 
    78 You can access value of 'Directory' from within your driver like so:
    79 
    80     sub store {
    81         my ($self, $sid, $datastr) = @_;
    82         my $dir = $self->{Directory};   # <-- in this example will be '/tmp/sessions'
    83     }
    84 
    85 Optionally, you can define C<init()> method within your driver to do driver specific global initialization. C<init()> method will be invoked only once during the lifecycle of your driver, which is the same as the lifecycle of a session object.
    86 
    87 For examples of C<init()> look into the source code of native CGI::Session drivers.
    88 
    89 =head1 METHODS
    90 
    91 This section lists and describes all driver methods. All the driver methods will receive driver object ($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 ($sid) as the second argument.
    92 
    93 Following list describes every driver method, including its argument list and what step of session's life they will be invoked. Understanding this may help driver authors.
    94 
    95 =over 4
    96 
    97 =item retrieve($self, $sid)
    98 
    99 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< $sid > 0 (zero) or "" should be returned. undef must be returned only to signal error. Error message should be set via set_error(), which can be inherited from L<CGI::Session::ErrorHandler|CGI::Session::ErrorHandler>. 
   100 
   101 Tip: set_error() always returns undef. Use it for your advantage.
   102 
   103 =item store($self, $sid, $datastr)
   104 
   105 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.
   106 
   107 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.
   108 
   109 $datastr, which is passed as the third argument to represents B<already serialized> session data that needs to be saved.
   110 
   111 store() can return any true value indicating success or undef on failure. Error message should be passed to set_error()
   112 
   113 =item remove($self, $sid)
   114 
   115 Called whenever session data is to be deleted, which is when CGI::Session->delete() is called. Should return any true value indicating success, undef on failure. Error message should be logged in set_error().
   116 
   117 =item traverse($self, \&coderef)
   118 
   119 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->( $sid ) >>
   120 
   121 =item init($self)
   122 
   123 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.
   124 
   125 =item DESTROY($self)
   126 
   127 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.
   128 
   129 =back
   130 
   131 =head2 NOTES
   132 
   133 =over 4
   134 
   135 =item *
   136 
   137 All driver F<.pm> files must be lowercase!
   138 
   139 =item *
   140 
   141 DBI-related drivers are better off using L<CGI::Session::Driver::DBI|CGI::Session::Driver::DBI> as base, but don't have to.
   142 
   143 =back
   144 
   145 =head1 LICENSING
   146 
   147 For support and licensing see L<CGI::Session|CGI::Session>.
   148