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Session(3pm) User Contributed Perl Documentation Session(3pm)
NAME
Apache::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;
DESCRIPTION
Apache::Session is a persistence framework which is particularly useful for tracking ses-
sion 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 altogether.
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 subclassed. The object store can be the filesystem, a Berke-
ley 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 various databases. Serializa-
tion 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 following components.
The derived class inherits the interface from Apache::Session, 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 number, 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 anything beginning with
an "_" is considered reserved for future use.
my $id = $session{_session_id};
Permanently removing the session from storage
tied(%session)->delete;
BEHAVIOR
Apache::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 a non-exclusive lock on the ses-
sion.
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 timestamp 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 corrup-
tion. The locking scheme does not provide transactional consistency, such as you might
get from a relational database. If you desire transactional consistency, you must provide
the Transaction argument with a true value when you tie the session hash. For example:
tie %s, 'Apache::Session::File', $id {
Directory => '/tmp/sessions',
LockDirectory => '/var/lock/sessions',
Transaction => 1
};
Note that the Transaction argument has no practical effect on the MySQL and Postgres
implementations. The MySQL implementation only supports exclusive locking, and the Post-
gres implementation uses the transaction features of that database.
IMPLEMENTATION
The way you implement Apache::Session depends on what you are trying to accomplish. Here
are some hints on which classes to use in what situations
STRATEGIES
Apache::Session is mainly designed to track user session between http requests. However,
it can also be used for any situation where data persistence is desirable. For example,
it could be used to share global data between your httpd processes. The following exam-
ples are short mod_perl programs which demonstrate some session handling basics.
Sharing data between Apache processes
When you share data between Apache processes, you need to decide on a session ID number
ahead of time and make sure that an object with that ID number is in your object store
before starting your Apache. How you accomplish that is your own business. I use the
session ID "1". Here is a short program in which we use Apache::Session to store out
database access information.
use Apache;
use Apache::Session::File;
use DBI;
use strict;
my %global_data;
eval {
tie %global_data, 'Apache::Session::File', 1,
{Directory => '/tmp/sessiondata'};
};
if ($@) {
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 associated 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 cookies. 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::Session::File, Apache::Ses-
sion::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 maintained, but less possi-
bilies.
Catalyst::Plugin::Session - support of sessions in Catalyst
Session - OO interface to Apache::Session
AUTHORS
Jeffrey Baker <jwbaker AT acm.org> is the author of Apache::Session.
Tatsuhiko Miyagawa <miyagawa AT bulknews.net> is the author of Generate::ModUniqueID and Gen-
erate::ModUsertrack
Erik Rantapaa <rantapaa AT fanbuzz.com> found errors in both Lock::File and Store::File
Bart Schaefer <schaefer AT zanshin.com> notified me of a bug in Lock::File.
Chris Winters <cwinters AT intes.net> contributed the Sybase code.
Michael Schout <mschout AT gkg.net> fixed a commit policy bug in 1.51.
Andreas J. Koenig <andreas.koenig AT anima.de> contributed valuable CPAN advice and also
Apache::Session::Tree and Apache::Session::Counted.
Gerald Richter <richter AT 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 AT ipsoft.de> contributed patches for bugs and improved performance.
Steve Shreeve <shreeve AT 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 AT lunatech.com> sent quite a bit of feedback with ideas for interface
improvements.
Randy Harmon <rjharmon AT uptimecomputers.com> contributed the original storage-independent
object interface with input from:
Bavo De Ridder <bavo AT ace.be>
Jules Bean <jmlb2 AT hermes.uk>
Lincoln Stein <lstein AT cshl.org>
Jamie LeTaul <jletual AT kmtechnologies.com> fixed file locking on Windows.
Scott McWhirter <scott AT surreytech.uk> contributed verbose error messages for file lock-
ing.
Corris Randall <corris AT line6.net> gave us the option to use any table name in the MySQL
store.
Oliver Maul <oliver.maul AT 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 AT tamedia.ch> contributed Informix modules.
perl v5.8.8 2008-02-03 Session(3pm)
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On Apache
Under GNU General Public License
2012-05-19 16:24 @38.107.179.237 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)