Rewrite prune_old_outbound_device_pokes for efficiency (#7159)

make sure we clear out all but one update for the user

tests/federation/test_federation_sender.py

@@ -370,6 +370,98 @@ class FederationSenderDevicesTestCases(HomeserverTestCase):
         devices = {edu["content"]["device_id"] for edu in self.edus}
         self.assertEqual({"D1", "D2", "D3"}, devices)
 
+    def test_prune_outbound_device_pokes1(self):
+        """If a destination is unreachable, and the updates are pruned, we should get
+        a single update.
+
+        This case tests the behaviour when the server has never been reachable.
+        """
+        mock_send_txn = self.hs.get_federation_transport_client().send_transaction
+        mock_send_txn.side_effect = lambda t, cb: defer.fail("fail")
+
+        # create devices
+        u1 = self.register_user("user", "pass")
+        self.login("user", "pass", device_id="D1")
+        self.login("user", "pass", device_id="D2")
+        self.login("user", "pass", device_id="D3")
+
+        # delete them again
+        self.get_success(
+            self.hs.get_device_handler().delete_devices(u1, ["D1", "D2", "D3"])
+        )
+
+        self.assertGreaterEqual(mock_send_txn.call_count, 4)
+
+        # run the prune job
+        self.reactor.advance(10)
+        self.get_success(
+            self.hs.get_datastore()._prune_old_outbound_device_pokes(prune_age=1)
+        )
+
+        # recover the server
+        mock_send_txn.side_effect = self.record_transaction
+        self.hs.get_federation_sender().send_device_messages("host2")
+        self.pump()
+
+        # there should be a single update for this user.
+        self.assertEqual(len(self.edus), 1)
+        edu = self.edus.pop(0)
+        self.assertEqual(edu["edu_type"], "m.device_list_update")
+        c = edu["content"]
+
+        # synapse uses an empty prev_id list to indicate "needs a full resync".
+        self.assertEqual(c["prev_id"], [])
+
+    def test_prune_outbound_device_pokes2(self):
+        """If a destination is unreachable, and the updates are pruned, we should get
+        a single update.
+
+        This case tests the behaviour when the server was reachable, but then goes
+        offline.
+        """
+
+        # create first device
+        u1 = self.register_user("user", "pass")
+        self.login("user", "pass", device_id="D1")
+
+        # expect the update EDU
+        self.assertEqual(len(self.edus), 1)
+        self.check_device_update_edu(self.edus.pop(0), u1, "D1", None)
+
+        # now the server goes offline
+        mock_send_txn = self.hs.get_federation_transport_client().send_transaction
+        mock_send_txn.side_effect = lambda t, cb: defer.fail("fail")
+
+        self.login("user", "pass", device_id="D2")
+        self.login("user", "pass", device_id="D3")
+
+        # delete them again
+        self.get_success(
+            self.hs.get_device_handler().delete_devices(u1, ["D1", "D2", "D3"])
+        )
+
+        self.assertGreaterEqual(mock_send_txn.call_count, 3)
+
+        # run the prune job
+        self.reactor.advance(10)
+        self.get_success(
+            self.hs.get_datastore()._prune_old_outbound_device_pokes(prune_age=1)
+        )
+
+        # recover the server
+        mock_send_txn.side_effect = self.record_transaction
+        self.hs.get_federation_sender().send_device_messages("host2")
+        self.pump()
+
+        # ... and we should get a single update for this user.
+        self.assertEqual(len(self.edus), 1)
+        edu = self.edus.pop(0)
+        self.assertEqual(edu["edu_type"], "m.device_list_update")
+        c = edu["content"]
+
+        # synapse uses an empty prev_id list to indicate "needs a full resync".
+        self.assertEqual(c["prev_id"], [])
+
     def check_device_update_edu(
         self,
         edu: JsonDict,