Ignore duplicate notifications

Adyen duplicates many notifications. Luckily, our audit trail gives us
an easy way to check for duplicates. We ignore duplicated notifications,
but acknowledge them nonetheless.

adyen/facade.py

@@ -219,6 +219,17 @@ def assess_notification_relevance(self, request):
         if request.POST.get(Constants.EVENT_CODE) != Constants.EVENT_CODE_AUTHORISATION:
             return False, True
 
+        # Adyen duplicates many notifications. This bit makes sure we ignore them.
+        # "Duplicate notifications have the same corresponding values for their eventCode and
+        # pspReference fields."  https://docs.adyen.com/display/TD/Accept+notifications
+        reference = request.POST[Constants.PSP_REFERENCE]
+        # The event code gets checked above, so we only need to check for the reference now.
+        if AdyenTransaction.objects.filter(reference=reference).exists():
+            # We already stored a transaction with this reference, so we can ignore the
+            # notification. As above, we still acknowledge it to Adyen, in case it missed
+            # our previous acknowledgment.
+            return False, True
+
         # Seems legit, just do it :)
         return True, True
 

tests/test_adyen.py

@@ -421,3 +421,22 @@ def test_assess_notification_relevance(self):
         self.request.POST['eventCode'] = 'REPORT_AVAILABLE'
         must_process, must_ack = self.scaffold.assess_notification_relevance(self.request)
         self.assertTupleEqual((must_process, must_ack), (False, True))
+
+    def test_assert_duplicate_notifications(self):
+        """
+        This test tests that duplicate notifications are ignored.
+        """
+        self.request.method = 'POST'
+        self.request.POST = deepcopy(AUTHORISED_PAYMENT_PARAMS_POST)
+
+        # We have a valid request. So let's confirm that we think we should process
+        # and acknowledge it.
+        assert (True, True) == self.scaffold.assess_notification_relevance(self.request)
+
+        # Let's process it then.
+        __, __, __ = self.scaffold.handle_payment_feedback(self.request)
+
+        # As we have already processed that request, we now shouldn't process the request
+        # any more. But we still acknowledge it.
+        assert (False, True) == self.scaffold.assess_notification_relevance(self.request)
+