Session(3) User Contributed Perl Documentation Session(3)NAMEApache::Session - A persistence framework for session data
SYNOPSIS
use Apache::Session::MySQL;
my %session;
#make a fresh session for a first-time visitor
tie %session, 'Apache::Session::MySQL';
#stick some stuff in it
$session{visa_number} = "1234 5678 9876 5432";
#get the session id for later use
my $id = $session{_session_id};
#...time passes...
#get the session data back out again during some other request
my %session;
tie %session, 'Apache::Session::MySQL', $id;
&validate($session{visa_number});
#delete a session from the object store permanently
tied(%session)->delete;
DESCRIPTIONApache::Session is a persistence framework which is particularly useful
for tracking session data between httpd requests. Apache::Session is
designed to work with Apache and mod_perl, but it should work under CGI
and other web servers, and it also works outside of a web server alto-
gether.
Apache::Session consists of five components: the interface, the object
store, the lock manager, the ID generator, and the serializer. The
interface is defined in Session.pm, which is meant to be easily sub-
classed. The object store can be the filesystem, a Berkeley DB, a
MySQL DB, an Oracle DB, a Postgres DB, Sybase, or Informix. Locking is
done by lock files, semaphores, or the locking capabilities of the var-
ious databases. Serialization is done via Storable, and optionally
ASCII-fied via MIME or pack(). ID numbers are generated via MD5. The
reader is encouraged to extend these capabilities to meet his own
requirements.
A derived class of Apache::Session is used to tie together the three
components. The derived class inherits the interface from Apache::Ses-
sion, and specifies which store and locker classes to use.
Apache::Session::MySQL, for instance, uses the MySQL storage class and
also the MySQL locking class. You can easily plug in your own object
store or locker class.
INTERFACE
The interface to Apache::Session is very simple: tie a hash to the
desired class and use the hash as normal. The constructor takes two
optional arguments. The first argument is the desired session ID num-
ber, or undef for a new session. The second argument is a hash of
options that will be passed to the object store and locker classes.
tieing the session
Get a new session using DBI:
tie %session, 'Apache::Session::MySQL', undef,
{ DataSource => 'dbi:mysql:sessions' };
Restore an old session from the database:
tie %session, 'Apache::Session::MySQL', $session_id,
{ DataSource => 'dbi:mysql:sessions' };
Storing and retrieving data to and from the session
Hey, how much easier could it get?
$session{first_name} = "Chuck";
$session{an_array_ref} = [ $one, $two, $three ];
$session{an_object} = new Some::Class;
Reading the session ID
The session ID is the only magic entry in the session object, but any-
thing beginning with a "_" is considered reserved for future use.
my $id = $session{_session_id};
Permanently removing the session from storage
tied(%session)->delete;
BEHAVIORApache::Session tries to behave the way the author believes that you
would expect. When you create a new session, Session immediately saves
the session to the data store, or calls die() if it cannot. It also
obtains an exclusive lock on the session object. If you retrieve an
existing session, Session immediately restores the object from storage,
or calls die() in case of an error. Session also obtains an non-exclu-
sive lock on the session.
As you put data into the session hash, Session squirrels it away for
later use. When you untie() the session hash, or it passes out of
scope, Session checks to see if anything has changed. If so, Session
gains an exclusive lock and writes the session to the data store. It
then releases any locks it has acquired.
Note that Apache::Session does only a shallow check to see if anything
has changed. If nothing changes in the top level tied hash, the data
will not be updated in the backing store. You are encouraged to time-
stamp the session hash so that it is sure to be updated.
When you call the delete() method on the session object, the object is
immediately removed from the object store, if possible.
When Session encounters an error, it calls die(). You will probably
want to wrap your session logic in an eval block to trap these errors.
LOCKING AND TRANSACTIONS
By default, most Apache::Session implementations only do locking to
prevent data corruption. The locking scheme does not provide transac-
tional consistency, such as you might get from a relational database.
If you desire transactional consistency, you must provide the Transac-
tion argument with a true value when you tie the session hash. For
example:
tie %s, 'Apache::Session::File', $id {
Directory => '/tmp/sessions',
LockDirectory => '/var/lock/sessions',
Transaction => 1
};
Note that the Transaction argument has no practical effect on the MySQL
and Postgres implementations. The MySQL implementation only supports
exclusive locking, and the Postgres implementation uses the transaction
features of that database.
IMPLEMENTATION
The way you implement Apache::Session depends on what you are trying to
accomplish. Here are some hints on which classes to use in what situa-
tions
STRATEGIESApache::Session is mainly designed to track user session between http
requests. However, it can also be used for any situation where data
persistence is desirable. For example, it could be used to share
global data between your httpd processes. The following examples are
short mod_perl programs which demonstrate some session handling basics.
Sharing data between Apache processes
When you share data between Apache processes, you need to decide on a
session ID number ahead of time and make sure that an object with that
ID number is in your object store before starting you Apache. How you
accomplish that is your own business. I use the session ID "1". Here
is a short program in which we use Apache::Session to store out data-
base access information.
use Apache;
use Apache::Session::File;
use DBI;
use strict;
my %global_data;
eval {
tie %global_data, 'Apache::Session::File', 1,
{Directory => '/tmp/sessiondata'};
};
if ($@) {
die "Global data is not accessible: $@";
}
my $dbh = DBI->connect($global_data{datasource},
$global_data{username}, $global_data{password}) || die $DBI::errstr;
undef %global_data;
#program continues...
As shown in this example, you should undef or untie your session hash
as soon as you are done with it. This will free up any locks associ-
ated with your process.
Tracking users with cookies
The choice of whether to use cookies or path info to track user IDs is
a rather religious topic among Apache users. This example uses cook-
ies. The implementation of a path info system is left as an exercise
for the reader.
Note that Apache::Session::Generate::ModUsertrack uses Apache's
mod_usertrack cookies to generate and maintain session IDs.
use Apache::Session::MySQL;
use Apache;
use strict;
#read in the cookie if this is an old session
my $r = Apache->request;
my $cookie = $r->header_in('Cookie');
$cookie =~ s/SESSION_ID=(\w*)/$1/;
#create a session object based on the cookie we got from the browser,
#or a new session if we got no cookie
my %session;
tie %session, 'Apache::Session::MySQL', $cookie, {
DataSource => 'dbi:mysql:sessions', #these arguments are
UserName => 'mySQL_user', #required when using
Password => 'password', #MySQL.pm
LockDataSource => 'dbi:mysql:sessions',
LockUserName => 'mySQL_user',
LockPassword => 'password'
};
#Might be a new session, so lets give them their cookie back
my $session_cookie = "SESSION_ID=$session{_session_id};";
$r->header_out("Set-Cookie" => $session_cookie);
#program continues...
SEE ALSO
Apache::Session::MySQL, Apache::Session::Postgres, Apache::Ses-
sion::File, Apache::Session::DB_File, Apache::Session::Oracle,
Apache::Session::Sybase
The O Reilly book "Apache Modules in Perl and C", by Doug MacEachern
and Lincoln Stein, has a chapter on keeping state.
CGI::Session uses OO interface to do same thing. It is better main-
tained, but less possibilies.
AUTHORS
Jeffrey Baker <jwbaker@acm.org> is the author of Apache::Session.
Tatsuhiko Miyagawa <miyagawa@bulknews.net> is the author of Gener-
ate::ModUniqueID and Generate::ModUsertrack
Erik Rantapaa <rantapaa@fanbuzz.com> found errors in both Lock::File
and Store::File
Bart Schaefer <schaefer@zanshin.com> notified me of a bug in
Lock::File.
Chris Winters <cwinters@intes.net> contributed the Sybase code.
Michael Schout <mschout@gkg.net> fixed a commit policy bug in 1.51.
Andreas J. Koenig <andreas.koenig@anima.de> contributed valuable CPAN
advice and also Apache::Session::Tree and Apache::Session::Counted.
Gerald Richter <richter@ecos.de> had the idea for a tied hash interface
and provided the initial code for it. He also uses Apache::Session in
his Embperl module and is the author of Apache::Session::Embperl
Jochen Wiedmann <joe@ipsoft.de> contributed patches for bugs and
improved performance.
Steve Shreeve <shreeve@uci.edu> squashed a bug in 0.99.0 whereby a
cleared hash or deleted key failed to set the modified bit.
Peter Kaas <Peter.Kaas@lunatech.com> sent quite a bit of feedback with
ideas for interface improvements.
Randy Harmon <rjharmon@uptimecomputers.com> contributed the original
storage-independent object interface with input from:
Bavo De Ridder <bavo@ace.ulyssis.student.kuleuven.ac.be>
Jules Bean <jmlb2@hermes.cam.ac.uk>
Lincoln Stein <lstein@cshl.org>
Jamie LeTaul <jletual@kmtechnologies.com> fixed file locking on Win-
dows.
Scott McWhirter <scott@surreytech.co.uk> contributed verbose error mes-
sages for file locking.
Corris Randall <corris@line6.net> gave us the option to use any table
name in the MySQL store.
Oliver Maul <oliver.maul@ixos.de> updated the Sybase modules
Innumerable users sent a patch for the reversed file age test in the
file locking module.
Langen Mike <mike.langen@tamedia.ch> contributed Informix modules.
perl v5.8.8 2007-03-19 Session(3)
