def items(request):
    """
        Called when a items retrieval request has been received.

        @param request: The publish-subscribe request.
        @type request: L{wokkel.pubsub.PubSubRequest}
        @return: A deferred that fires with a C{list} of L{pubsub.Item}.
        @rtype: L{Deferred<twisted.internet.defer.Deferred>}
        """
