# Web Session Usage

Status: | Work in progress

## Why Use Sessions?

Sessions are a common way to keep simple browsing data attached to a user’s browser. This is generally used to store simple data that does not need to be persisted in a database.

Sessions in TurboGears can be backed by the filesystem, memcache, the database, or by hashed cookie values. By default, cookies are used for storing the session data, which is only good for storing very little amounts of data in the session since all data will be sent back and forth within the cookie. If you are storing lots of data in the session, Memcache is recommended.

Warning

Using cookies for storing the whole session’s content exposes your application to possible exploits if the attacker gets to know the secret key which is used for the encryption of the cookies. Considering this, it is probably better to use the filesystem storage if you don’t want to set up memcache.

Note

When using the filesystem backed storage, you must be aware of the fact, that beaker does not clean up the session files at all. You have to make sure to clean up the data directory on a regular basis yourself. Refer to the Beaker documentation for more details.

## How To Use Sessions?

If you just quickstarted a TurboGears 2 application, the session system is pre-configured and ready to be used.

By default we are using the Beaker session system. This system is configured to use hashed cookies for session storage.

Each time a client connects, the session middleware (Beaker) will inspect the cookie using the cookie name we have defined in the configuration file.

If the cookie is not found it will be set in the browser. On all subsequent visits, the middleware will find the cookie and make use of it.

When using the cookie based backend, all data that you put into the session will be pickled, hashed and encrypted by the middleware when sending the response to the browser and vice-versa when reading the request.

In the other backends, the cookie only contains a large random key that was set at the first visit and has been associated behind the scenes to a file in the file system cache. This key is then used to lookup and retrieve the session data from the proper datastore.

OK, enough with theory! Let’s get to some real life (sort of) examples. Open up your root controller and add the following import at the top the file:

    from tg import session

What you get is a Session instance that is always request-local, in other words, it’s the session for this particular user. The session can be manipulated in much the same way as a standard python dictionary.

Here is how you search for a key in the session:

    if session.get('mysuperkey', None):
        # do something intelligent
        pass

and here is how to set a key in the session:

    session['mysuperkey'] = 'some python data I need to store'
    session.save()

You should note that you need to explicitly save the session in order for your keys to be stored in the session.

You can delete all user session with the delete() method of the session object:

    session.delete()

Even though it’s not customary to delete all user sessions on a production environment, you will typically do it for cleaning up after usability or functional tests.

## Avoid automatic session extension

TurboGears by default automatically extends session life time at every request if a session is already available. You can avoid this behavior by changing your application configuration

    beaker.session.tg_avoid_touch = true

This will also prevent TurboGears from causing an automatic session save at every request.