Refactor MSC3030 `/timestamp_to_event` to move away from our snowflake pull from `destination` pattern (#14096)

 1. `federation_client.timestamp_to_event(...)` now handles all `destination` looping and uses our generic `_try_destination_list(...)` helper.
 2. Consistently handling `NotRetryingDestination` and `FederationDeniedError` across `get_pdu` , backfill, and the generic `_try_destination_list` which is used for many places we use this pattern.
 3. `get_pdu(...)` now returns `PulledPduInfo` so we know which `destination` we ended up pulling the PDU from

1 files changed, 8 insertions, 4 deletions

diff --git a/tests/federation/test_federation_client.py b/tests/federation/test_federation_client.py
index 51d3bb8fff..e67f405826 100644
--- a/tests/federation/test_federation_client.py
+++ b/tests/federation/test_federation_client.py
@@ -142,14 +142,14 @@ class FederationClientTest(FederatingHomeserverTestCase):
 
     def test_get_pdu_returns_nothing_when_event_does_not_exist(self):
         """No event should be returned when the event does not exist"""
-        remote_pdu = self.get_success(
+        pulled_pdu_info = self.get_success(
             self.hs.get_federation_client().get_pdu(
                 ["yet.another.server"],
                 "event_should_not_exist",
                 RoomVersions.V9,
             )
         )
-        self.assertEqual(remote_pdu, None)
+        self.assertEqual(pulled_pdu_info, None)
 
     def test_get_pdu(self):
         """Test to make sure an event is returned by `get_pdu()`"""
@@ -169,13 +169,15 @@ class FederationClientTest(FederatingHomeserverTestCase):
         remote_pdu.internal_metadata.outlier = True
 
         # Get the event again. This time it should read it from cache.
-        remote_pdu2 = self.get_success(
+        pulled_pdu_info2 = self.get_success(
             self.hs.get_federation_client().get_pdu(
                 ["yet.another.server"],
                 remote_pdu.event_id,
                 RoomVersions.V9,
             )
         )
+        self.assertIsNotNone(pulled_pdu_info2)
+        remote_pdu2 = pulled_pdu_info2.pdu
 
         # Sanity check that we are working against the same event
         self.assertEqual(remote_pdu.event_id, remote_pdu2.event_id)
@@ -215,13 +217,15 @@ class FederationClientTest(FederatingHomeserverTestCase):
             )
         )
 
-        remote_pdu = self.get_success(
+        pulled_pdu_info = self.get_success(
             self.hs.get_federation_client().get_pdu(
                 ["yet.another.server"],
                 "event_id",
                 RoomVersions.V9,
             )
         )
+        self.assertIsNotNone(pulled_pdu_info)
+        remote_pdu = pulled_pdu_info.pdu
 
         # check the right call got made to the agent
         self._mock_agent.request.assert_called_once_with(