Added a signal for processing event requests

doc/development/api/general.rst

@@ -72,3 +72,9 @@ Periodic tasks
 
 .. automodule:: pretix.base.signals
    :members: periodic_task
+
+Request flow
+------------
+
+.. automodule:: pretix.presale.signals
+   :members: process_request

src/pretix/presale/signals.py

@@ -45,3 +45,19 @@ This signal is sent out to display additional information on the order detail pa
 
 As with all plugin signals, the ``sender`` keyword argument will contain the event.
 """
+
+process_request = EventPluginSignal(
+    providing_args=["request"]
+)
+"""
+This signal is sent out whenever a request is made to a event presale page. Most of the
+time, this will be called from the middleware layer (except on plugin-provided pages
+this will be caled by the @event_view decorator). Similarly to Django's process_request
+middleware method, if you return a Response, that response will be used and the request
+won't be processed any further down the stack.
+
+WARNING: Be very careful about using this signal as listening to it makes it really
+easy to cause serious performance problems.
+
+As with all plugin signals, the ``sender`` keyword argument will contain the event.
+"""

src/pretix/presale/utils.py

@@ -9,6 +9,7 @@ from django.utils.translation import ugettext_lazy as _
 from pretix.base.middleware import LocaleMiddleware
 from pretix.base.models import Event, EventPermission, Organizer
 from pretix.multidomain.urlreverse import get_domain
+from pretix.presale.signals import process_request
 
 
 def _detect_event(request):
@@ -63,6 +64,10 @@ def _detect_event(request):
                         event=request.event, user=request.user).exists():
                     raise PermissionDenied(_('The selected ticket shop is currently not available.'))
 
+            for receiver, response in process_request.send(request.event, request=request):
+                if response:
+                    return response
+
     except Event.DoesNotExist:
         raise Http404(_('The selected event was not found.'))
     except Organizer.DoesNotExist: