Check-in API: Work around libpretixsync issue with space encoding

src/pretix/api/views/checkin.py

@@ -430,7 +430,13 @@ class CheckinListPositionViewSet(viewsets.ReadOnlyModelViewSet):
             if self.kwargs['pk'].isnumeric():
                 op = queryset.get(Q(pk=self.kwargs['pk']) | Q(secret=self.kwargs['pk']))
             else:
-                op = queryset.get(secret=self.kwargs['pk'])
+                # In application/x-www-form-urlencoded, you can encodes space ' ' with '+' instead of '%20'.
+                # `id`, however, is part of a path where this technically is not allowed. Old versions of our
+                # scan apps still do it, so we try work around it!
+                try:
+                    op = queryset.get(secret=self.kwargs['pk'])
+                except OrderPosition.DoesNotExist:
+                    op = queryset.get(secret=self.kwargs['pk'].replace('+', ' '))
         except OrderPosition.DoesNotExist:
             revoked_matches = list(self.request.event.revoked_secrets.filter(secret=self.kwargs['pk']))
             if len(revoked_matches) == 0:

src/tests/api/test_checkin.py

@@ -687,6 +687,19 @@ def test_by_secret_special_chars(token_client, organizer, clist, event, order):
     assert resp.data['status'] == 'ok'
 
 
+@pytest.mark.django_db
+def test_by_secret_special_chars_space_fallback(token_client, organizer, clist, event, order):
+    with scopes_disabled():
+        p = order.positions.first()
+    p.secret = "foo bar"
+    p.save()
+    resp = token_client.post('/api/v1/organizers/{}/events/{}/checkinlists/{}/positions/{}/redeem/'.format(
+        organizer.slug, event.slug, clist.pk, "foo+bar"
+    ), {}, format='json')
+    assert resp.status_code == 201
+    assert resp.data['status'] == 'ok'
+
+
 @pytest.mark.django_db
 def test_only_once(token_client, organizer, clist, event, order):
     with scopes_disabled():