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Sessions are the most complicated topic covered in this series of examples, and because of that it is going to take a few examples to cover all of the different aspects. This first example demonstrates the very basics of the Twisted Web session API: how to get the session object for the current request and how to prematurely expire a session.
Before diving into the APIs, let's look at the big picture of
sessions in Twisted Web. Sessions are represented by instances
of :py:class:`Session <twisted.web.server.Session>` . The :py:class:`Site <twisted.web.server.Site>` creates a new instance
of Session
the first time an application asks for it for
a particular session. Session
instances are kept on
the Site
instance until they expire (due to inactivity or
because they are explicitly expired). Each time after the first that a
particular session's Session
object is requested, it is
retrieved from the Site
.
With the conceptual underpinnings of the upcoming API in place, here comes the example. This will be a very simple :doc:`rpy script <rpy-scripts>` which tells a user what its unique session identifier is and lets it prematurely expire the session.
First, we'll import :py:class:`Resource <twisted.web.resource.Resource>` so we can define a couple of subclasses of it:
from twisted.web.resource import Resource
Next we'll define the resource which tells the client what its session identifier is. This is done easily by first getting the session object using :py:meth:`Request.getSession <twisted.web.server.Request.getSession>` and then getting the session object's uid attribute:
class ShowSession(Resource):
def render_GET(self, request):
return b'Your session id is: ' + request.getSession().uid
To let the client expire its own session before it times out, we'll define another resource which expires whatever session it is requested with. This is done using the :py:meth:`Session.expire <twisted.web.server.Session.expire>` method:
class ExpireSession(Resource):
def render_GET(self, request):
request.getSession().expire()
return b'Your session has been expired.'
Finally, to make the example an rpy script, we'll make an instance
of ShowSession
and give it an instance
of ExpireSession
as a child using :py:meth:`Resource.putChild <twisted.web.resource.Resource.putChild>` :
resource = ShowSession()
resource.putChild(b"expire", ExpireSession())
And that is the complete example. You can fire this up and load the top
page. You'll see a (rather opaque) session identifier that remains the same
across reloads (at least until you flush the TWISTED_SESSION
cookie
from your browser or enough time passes). You can then visit
the expire
child and go back to the top page and see that you have
a new session.
Here's the complete source for the example:
from twisted.web.resource import Resource
class ShowSession(Resource):
def render_GET(self, request):
return b'Your session id is: ' + request.getSession().uid
class ExpireSession(Resource):
def render_GET(self, request):
request.getSession().expire()
return b'Your session has been expired.'
resource = ShowSession()
resource.putChild(b"expire", ExpireSession())