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, 9 insertions, 6 deletions

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py

index 4fbc79a6cb..5fc3b8bc8c 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -442,6 +442,15 @@ class FederationHandler:
                     # appropriate stuff.
                     # TODO: We can probably do something more intelligent here.
                     return True
+                except NotRetryingDestination as e:
+                    logger.info("_maybe_backfill_inner: %s", e)
+                    continue
+                except FederationDeniedError:
+                    logger.info(
+                        "_maybe_backfill_inner: Not attempting to backfill from %s because the homeserver is not on our federation whitelist",
+                        dom,
+                    )
+                    continue
                 except (SynapseError, InvalidResponseError) as e:
                     logger.info("Failed to backfill from %s because %s", dom, e)
                     continue
@@ -477,15 +486,9 @@ class FederationHandler:
 
                     logger.info("Failed to backfill from %s because %s", dom, e)
                     continue
-                except NotRetryingDestination as e:
-                    logger.info(str(e))
-                    continue
                 except RequestSendFailed as e:
                     logger.info("Failed to get backfill from %s because %s", dom, e)
                     continue
-                except FederationDeniedError as e:
-                    logger.info(e)
-                    continue
                 except Exception as e:
                     logger.exception("Failed to backfill from %s because %s", dom, e)
                     continue