Catalyst::Plugin::Session - Generic Session plugin - ties together
    server side storage and client side state required to maintain session

        # To get sessions to "just work", all you need to do is use these plugins:

        use Catalyst qw/

        # you can replace Store::FastMmap with Store::File - both have sensible
        # default configurations (see their docs for details)

        # more complicated backends are available for other scenarios (DBI storage,
        # etc)

        # after you've loaded the plugins you can save session data
        # For example, if you are writing a shopping cart, it could be implemented
        # like this:

        sub add_item : Local {
            my ( $self, $c ) = @_;

            my $item_id = $c->req->param("item");

            # $c->session is a hash ref, a bit like $c->stash
            # the difference is that it' preserved across requests

            push @{ $c->session->{items} }, $item_id;


        sub display_items : Local {
            my ( $self, $c ) = @_;

            # values in $c->session are restored
            $c->stash->{items_to_display} =
              [ map { MyModel->retrieve($_) } @{ $c->session->{items} } ];


    The Session plugin is the base of two related parts of functionality
    required for session management in web applications.

    The first part, the State, is getting the browser to repeat back a
    session key, so that the web application can identify the client and
    logically string several requests together into a session.

    The second part, the Store, deals with the actual storage of information
    about the client. This data is stored so that the it may be revived for
    every request made by the same client.

    This plugin links the two pieces together.

        The only really sane way to do state is using cookies.

        A portable backend, based on Cache::File.

        A fast and flexible backend, based on Cache::FastMmap.

        An accessor for the session ID value.

        Returns a hash reference that might contain unserialized values from
        previous requests in the same session, and whose modified value will
        be saved for future requests.

        This method will automatically create a new session and session ID
        if none exists.

        You can also set session keys by passing a list of key/value pairs
        or a hashref.

            $c->session->{foo} = "bar";      # This works.
            $c->session(one => 1, two => 2); # And this.
            $c->session({ answer => 42 });   # And this.

        This method returns the time when the current session will expire,
        or 0 if there is no current session. If there is a session and it
        already expired, it will delete the session and return 0 as well.

        This is like Ruby on Rails' flash data structure. Think of it as a
        stash that lasts for longer than one request, letting you redirect
        instead of forward.

        The flash data will be cleaned up only on requests on which actually
        use $c->flash (thus allowing multiple redirections), and the policy
        is to delete all the keys which haven't changed since the flash data
        was loaded at the end of every request.

        Note that use of the flash is an easy way to get data across
        requests, but it's also strongly disrecommended, due it it being
        inherently plagued with race conditions. This means that it's
        unlikely to work well if your users have multiple tabs open at once,
        or if your site does a lot of AJAX requests.

        Catalyst::Plugin::StatusMessage is the recommended alternative
        solution, as this doesn't suffer from these issues.

            sub moose : Local {
                my ( $self, $c ) = @_;

                $c->flash->{beans} = 10;
                $c->response->redirect( $c->uri_for("foo") );

            sub foo : Local {
                my ( $self, $c ) = @_;

                my $value = $c->flash->{beans};

                # ...

                $c->response->redirect( $c->uri_for("bar") );

            sub bar : Local {
                my ( $self, $c ) = @_;

                if ( exists $c->flash->{beans} ) { # false


        Zap all the keys in the flash regardless of their current state.

    keep_flash @keys
        If you want to keep a flash key for the next request too, even if it
        hasn't changed, call "keep_flash" and pass in the keys as arguments.

    delete_session REASON
        This method is used to invalidate a session. It takes an optional
        parameter which will be saved in "session_delete_reason" if

        NOTE: This method will also delete your flash data.

        This accessor contains a string with the reason a session was
        deleted. Possible values include:

        *   "address mismatch"

        *   "session expired"

    session_expire_key $key, $ttl
        Mark a key to expire at a certain time (only useful when shorter
        than the expiry time for the whole session).

        For example:

            __PACKAGE__->config('Plugin::Session' => { expires => 10000000000 }); # "forever"
            (NB If this number is too large, Y2K38 breakage could result.)

            # later

            $c->session_expire_key( __user => 3600 );

        Will make the session data survive, but the user will still be
        logged out after an hour.

        Note that these values are not auto extended.

        By calling this method you can force a session id change while
        keeping all session data. This method might come handy when you are
        paranoid about some advanced variations of session fixation attack.

        If you want to prevent this session fixation scenario:

            0) let us have WebApp with anonymous and authenticated parts
            1) a hacker goes to vulnerable WebApp and gets a real sessionid,
               just by browsing anonymous part of WebApp
            2) the hacker inserts (somehow) this values into a cookie in victim's browser
            3) after the victim logs into WebApp the hacker can enter his/her session

        you should call change_session_id in your login controller like

              if ($c->authenticate( { username => $user, password => $pass } )) {
                # login OK
              } else {
                # login FAILED

    change_session_expires $expires
        You can change the session expiration time for this session;

            $c->change_session_expires( 4000 );

        Note that this only works to set the session longer than the config

        This method is extended to also make calls to
        "check_session_plugin_requirements" and "setup_session".

        This method ensures that a State and a Store plugin are also in use
        by the application.

        This method populates "$c->config('Plugin::Session')" with the
        default values listed in "CONFIGURATION".

        This method is extended.

        Its only effect is if the (off by default) "flash_to_stash"
        configuration parameter is on - then it will copy the contents of
        the flash to the stash at prepare time.

        This method is extended and will extend the expiry time before
        sending the response.

        This method is extended and will call finalize_session before the
        other finalize_body methods run. Here we persist the session data if
        a session exists.

        This method will initialize the internal structure of the session,
        and is called by the "session" method if appropriate.

        Creates a new session ID using "generate_session_id" if there is no
        session ID yet.

    validate_session_id SID
        Make sure a session ID is of the right format.

        This currently ensures that the session ID string is any amount of
        case insensitive hexadecimal characters.

        This method will return a string that can be used as a session ID.
        It is supposed to be a reasonably random string with enough bits to
        prevent collision. It basically takes "session_hash_seed" and hashes
        it using SHA-1, MD5 or SHA-256, depending on the availability of
        these modules.

        This method is actually rather internal to generate_session_id, but
        should be overridable in case you want to provide more random data.

        Currently it returns a concatenated string which contains:

        *   A counter

        *   The current time

        *   One value from "rand".

        *   The stringified value of a newly allocated hash reference

        *   The stringified value of the Catalyst context object

        in the hopes that those combined values are entropic enough for most
        uses. If this is not the case you can replace "session_hash_seed"
        with e.g.

            sub session_hash_seed {
                open my $fh, "<", "/dev/random";
                read $fh, my $bytes, 20;
                close $fh;
                return $bytes;

        Or even more directly, replace "generate_session_id":

            sub generate_session_id {
                open my $fh, "<", "/dev/random";
                read $fh, my $bytes, 20;
                close $fh;
                return unpack("H*", $bytes);

        Also have a look at Crypt::Random and the various openssl bindings -
        these modules provide APIs for cryptographically secure random data.

        Clean up the session during "finalize".

        This clears the various accessors after saving to the store.

        See "dump_these" in Catalyst - ammends the session data structure to
        the list of dumped objects if session ID is defined.

        Note: this is *not* used to give an individual user a longer
        session. See 'change_session_expires'.


    The earliest point in time at which you may use the session data is
    after Catalyst::Plugin::Session's "prepare_action" has finished.

    State plugins must set $c->session ID before "prepare_action", and
    during "prepare_action" Catalyst::Plugin::Session will actually load the
    data from the store.

        sub prepare_action {
            my $c = shift;

            # don't touch $c->session yet!

            $c->NEXT::prepare_action( @_ );

            $c->session;  # this is OK
            $c->sessionid; # this is also OK

        $c->config('Plugin::Session' => {
            expires => 1234,

    All configuation parameters are provided in a hash reference under the
    "Plugin::Session" key in the configuration hash.

        The time-to-live of each session, expressed in seconds. Defaults to
        7200 (two hours).

        Only update the session expiry time if it would otherwise expire
        within this many seconds from now.

        The purpose of this is to keep the session store from being updated
        when nothing else in the session is updated.

        Defaults to 0 (in which case, the expiration will always be

        When true, "$c->request->address" will be checked at prepare time.
        If it is not the same as the address that initiated the session, the
        session is deleted.

        Defaults to false.

        When true, "$c->request->user_agent" will be checked at prepare
        time. If it is not the same as the user agent that initiated the
        session, the session is deleted.

        Defaults to false.

        This option makes it easier to have actions behave the same whether
        they were forwarded to or redirected to. On prepare time it copies
        the contents of "flash" (if any) to the stash.

    The hash reference returned by "$c->session" contains several keys which
    are automatically set:

        This key no longer exists. Use "session_expires" instead.

        The last time a session was saved to the store.

        The time when the session was first created.

        The value of "$c->request->address" at the time the session was
        created. This value is only populated if "verify_address" is true in
        the configuration.

        The value of "$c->request->user_agent" at the time the session was
        created. This value is only populated if "verify_user_agent" is true
        in the configuration.

  Round the Robin Proxies
    "verify_address" could make your site inaccessible to users who are
    behind load balanced proxies. Some ISPs may give a different IP to each
    request by the same client due to this type of proxying. If addresses
    are verified these users' sessions cannot persist.

    To let these users access your site you can either disable address
    verification as a whole, or provide a checkbox in the login dialog that
    tells the server that it's OK for the address of the client to change.
    When the server sees that this box is checked it should delete the
    "__address" special key from the session hash when the hash is first

  Race Conditions
    In this day and age where cleaning detergents and Dutch football (not
    the American kind) teams roam the plains in great numbers, requests may
    happen simultaneously. This means that there is some risk of session
    data being overwritten, like this:

    1.  request a starts, request b starts, with the same session ID

    2.  session data is loaded in request a

    3.  session data is loaded in request b

    4.  session data is changed in request a

    5.  request a finishes, session data is updated and written to store

    6.  request b finishes, session data is updated and written to store,
        overwriting changes by request a

    For applications where any given user's session is only making one
    request at a time this plugin should be safe enough.

    Andy Grundman

    Christian Hansen

    Yuval Kogman, ""

    Sebastian Riedel

    Tomas Doran (t0m) "" (current maintainer)

    Sergio Salvi

    kmx ""

    Florian Ragwitz (rafl) ""

    Kent Fredric (kentnl)

    And countless other contributers from #catalyst. Thanks guys!

    Devin Austin (dhoss) <>

    Robert Rothenberg <> (on behalf of Foxtons Ltd.)

        Copyright (c) 2005 the aforementioned authors. All rights
        reserved. This program is free software; you can redistribute
        it and/or modify it under the same terms as Perl itself.