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Plack::Middleware::Session - Middleware for session management


use Plack::Builder;

my $app = sub {
    my $env = shift;
    my $session = $env->{'psgix.session'};
    return [
        [ 'Content-Type' => 'text/plain' ],
        [ "Hello, you've been here for ", $session->{counter}++, "th time!" ],

builder {
    enable 'Session';

# Or, use the File store backend (great if you use multiprocess server)
# For more options, see perldoc Plack::Session::Store::File
builder {
    enable 'Session', store => 'File';


This is a Plack Middleware component for session management. By default it will use cookies to keep session state and store data in memory. This distribution also comes with other state and store solutions. See perldoc for these backends how to use them.

It should be noted that we store the current session as a hash reference in the psgix.session key inside the $env where you can access it as needed.

NOTE: As of version 0.04 the session is stored in psgix.session instead of plack.session.


  • Plack::Session::State

    This will maintain session state by passing the session through the request params. It does not do this automatically though, you are responsible for passing the session param.

  • Plack::Session::State::Cookie

    This will maintain session state using browser cookies.


  • Plack::Session::Store

    This is your basic in-memory session data store. It is volatile storage and not recommended for multiprocessing environments. However it is very useful for development and testing.

  • Plack::Session::Store::File

    This will persist session data in a file. By default it uses Storable but it can be configured to have a custom serializer and deserializer.

  • Plack::Session::Store::Cache

    This will persist session data using the Cache interface.

  • Plack::Session::Store::Null

    Sometimes you don't care about storing session data, in that case you can use this noop module.


The following are options that can be passed to this module.


In addition to providing a psgix.session key in $env for persistent session information, this module also provides a psgix.session.options key which can be used to control the behavior of the module per-request. The following sub-keys exist:

  • change_id

    If set to a true value, forces the session identifier to change (rotate). This should always be done after logging in, to prevent session fixation attacks from subdomains; see

  • expire

    If set to a true value, expunges the session from the store, and clears the state in the client.

  • no_store

    If set to a true value, no changes made to the session in this request will be saved to the store. Either "expire" and "change_id" take precedence over this, as both need to update the session store.

  • late_store

    If set to a true value, the session will be saved at the end of the request, after all data has been sent to the client -- this may be required if streaming responses attempt to alter the session after the header has already been sent to the client. Note, however, that it introduces a possible race condition, where the server attempts to store the updated session before the client makes the next request. For redirects, or other responses on which the client needs do minimal processing before making a second request, this race is quite possible to win -- causing the second request to obtain stale session data.

  • id

    This key contains the session identifier of the session. It should be considered read-only; to generate a new identifier, use "change_id".


All complex software has bugs lurking in it, and this module is no exception. If you find a bug please either email me, or add the bug to cpan-RT.


Tatsuhiko Miyagawa

Stevan Little


Copyright 2009, 2010 Infinity Interactive, Inc.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.


A very minimalist session library for Plack




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