Refactor the way we set `outlier` (#11634)

* `_auth_and_persist_outliers`: mark persisted events as outliers

Mark any events that get persisted via `_auth_and_persist_outliers` as, well,
outliers.

Currently this will be a no-op as everything will already be flagged as an
outlier, but I'm going to change that.

* `process_remote_join`: stop flagging as outlier

The events are now flagged as outliers later on, by `_auth_and_persist_outliers`.

* `send_join`: remove `outlier=True`

The events created here are returned in the result of `send_join` to
`FederationHandler.do_invite_join`. From there they are passed into
`FederationEventHandler.process_remote_join`, which passes them to
`_auth_and_persist_outliers`... which sets the `outlier` flag.

* `get_event_auth`: remove `outlier=True`

stop flagging the events returned by `get_event_auth` as outliers. This method
is only called by `_get_remote_auth_chain_for_event`, which passes the results
into `_auth_and_persist_outliers`, which will flag them as outliers.

* `_get_remote_auth_chain_for_event`: remove `outlier=True`

we pass all the events into `_auth_and_persist_outliers`, which will now flag
the events as outliers.

* `_check_sigs_and_hash_and_fetch`: remove unused `outlier` parameter

This param is now never set to True, so we can remove it.

* `_check_sigs_and_hash_and_fetch_one`: remove unused `outlier` param

This is no longer set anywhere, so we can remove it.

* `get_pdu`: remove unused `outlier` parameter

... and chase it down into `get_pdu_from_destination_raw`.

* `event_from_pdu_json`: remove redundant `outlier` param

This is never set to `True`, so can be removed.

* changelog

* update docstring

5 files changed, 16 insertions, 47 deletions

diff --git a/changelog.d/11634.misc b/changelog.d/11634.misc
new file mode 100644
index 0000000000..4069cbc2f4
--- /dev/null
+++ b/changelog.d/11634.misc
@@ -0,0 +1 @@
+Refactor the way that the `outlier` flag is set on events received over federation.
diff --git a/synapse/federation/federation_base.py b/synapse/federation/federation_base.py
index 4df90e02d7..addc0bf000 100644
--- a/synapse/federation/federation_base.py
+++ b/synapse/federation/federation_base.py
@@ -215,15 +215,12 @@ def _is_invite_via_3pid(event: EventBase) -> bool:
     )
 
 
-def event_from_pdu_json(
-    pdu_json: JsonDict, room_version: RoomVersion, outlier: bool = False
-) -> EventBase:
+def event_from_pdu_json(pdu_json: JsonDict, room_version: RoomVersion) -> EventBase:
     """Construct an EventBase from an event json received over federation
 
     Args:
         pdu_json: pdu as received over federation
         room_version: The version of the room this event belongs to
-        outlier: True to mark this event as an outlier
 
     Raises:
         SynapseError: if the pdu is missing required fields or is otherwise
@@ -247,6 +244,4 @@ def event_from_pdu_json(
         validate_canonicaljson(pdu_json)
 
     event = make_event_from_dict(pdu_json, room_version)
-    event.internal_metadata.outlier = outlier
-
     return event
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 7353c2b6b1..6ea4edfc71 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -265,10 +265,7 @@ class FederationClient(FederationBase):
 
         room_version = await self.store.get_room_version(room_id)
 
-        pdus = [
-            event_from_pdu_json(p, room_version, outlier=False)
-            for p in transaction_data_pdus
-        ]
+        pdus = [event_from_pdu_json(p, room_version) for p in transaction_data_pdus]
 
         # Check signatures and hash of pdus, removing any from the list that fail checks
         pdus[:] = await self._check_sigs_and_hash_and_fetch(
@@ -282,7 +279,6 @@ class FederationClient(FederationBase):
         destination: str,
         event_id: str,
         room_version: RoomVersion,
-        outlier: bool = False,
         timeout: Optional[int] = None,
     ) -> Optional[EventBase]:
         """Requests the PDU with given origin and ID from the remote home
@@ -292,9 +288,6 @@ class FederationClient(FederationBase):
             destination: Which homeserver to query
             event_id: event to fetch
             room_version: version of the room
-            outlier: Indicates whether the PDU is an `outlier`, i.e. if
-                it's from an arbitrary point in the context as opposed to part
-                of the current block of PDUs. Defaults to `False`
             timeout: How long to try (in ms) each destination for before
                 moving to the next destination. None indicates no timeout.
 
@@ -316,8 +309,7 @@ class FederationClient(FederationBase):
         )
 
         pdu_list: List[EventBase] = [
-            event_from_pdu_json(p, room_version, outlier=outlier)
-            for p in transaction_data["pdus"]
+            event_from_pdu_json(p, room_version) for p in transaction_data["pdus"]
         ]
 
         if pdu_list and pdu_list[0]:
@@ -334,7 +326,6 @@ class FederationClient(FederationBase):
         destinations: Iterable[str],
         event_id: str,
         room_version: RoomVersion,
-        outlier: bool = False,
         timeout: Optional[int] = None,
     ) -> Optional[EventBase]:
         """Requests the PDU with given origin and ID from the remote home
@@ -347,9 +338,6 @@ class FederationClient(FederationBase):
             destinations: Which homeservers to query
             event_id: event to fetch
             room_version: version of the room
-            outlier: Indicates whether the PDU is an `outlier`, i.e. if
-                it's from an arbitrary point in the context as opposed to part
-                of the current block of PDUs. Defaults to `False`
             timeout: How long to try (in ms) each destination for before
                 moving to the next destination. None indicates no timeout.
 
@@ -377,7 +365,6 @@ class FederationClient(FederationBase):
                     destination=destination,
                     event_id=event_id,
                     room_version=room_version,
-                    outlier=outlier,
                     timeout=timeout,
                 )
 
@@ -435,7 +422,6 @@ class FederationClient(FederationBase):
         origin: str,
         pdus: Collection[EventBase],
         room_version: RoomVersion,
-        outlier: bool = False,
     ) -> List[EventBase]:
         """Takes a list of PDUs and checks the signatures and hashes of each
         one. If a PDU fails its signature check then we check if we have it in
@@ -451,7 +437,6 @@ class FederationClient(FederationBase):
             origin
             pdu
             room_version
-            outlier: Whether the events are outliers or not
 
         Returns:
             A list of PDUs that have valid signatures and hashes.
@@ -466,7 +451,6 @@ class FederationClient(FederationBase):
             valid_pdu = await self._check_sigs_and_hash_and_fetch_one(
                 pdu=pdu,
                 origin=origin,
-                outlier=outlier,
                 room_version=room_version,
             )
 
@@ -482,7 +466,6 @@ class FederationClient(FederationBase):
         pdu: EventBase,
         origin: str,
         room_version: RoomVersion,
-        outlier: bool = False,
     ) -> Optional[EventBase]:
         """Takes a PDU and checks its signatures and hashes. If the PDU fails
         its signature check then we check if we have it in the database and if
@@ -494,9 +477,6 @@ class FederationClient(FederationBase):
             origin
             pdu
             room_version
-            outlier: Whether the events are outliers or not
-            include_none: Whether to include None in the returned list
-                for events that have failed their checks
 
         Returns:
             The PDU (possibly redacted) if it has valid signatures and hashes.
@@ -521,7 +501,6 @@ class FederationClient(FederationBase):
                     destinations=[pdu_origin],
                     event_id=pdu.event_id,
                     room_version=room_version,
-                    outlier=outlier,
                     timeout=10000,
                 )
             except SynapseError:
@@ -541,13 +520,10 @@ class FederationClient(FederationBase):
 
         room_version = await self.store.get_room_version(room_id)
 
-        auth_chain = [
-            event_from_pdu_json(p, room_version, outlier=True)
-            for p in res["auth_chain"]
-        ]
+        auth_chain = [event_from_pdu_json(p, room_version) for p in res["auth_chain"]]
 
         signed_auth = await self._check_sigs_and_hash_and_fetch(
-            destination, auth_chain, outlier=True, room_version=room_version
+            destination, auth_chain, room_version=room_version
         )
 
         return signed_auth
@@ -816,7 +792,6 @@ class FederationClient(FederationBase):
                 valid_pdu = await self._check_sigs_and_hash_and_fetch_one(
                     pdu=event,
                     origin=destination,
-                    outlier=True,
                     room_version=room_version,
                 )
 
@@ -864,7 +839,6 @@ class FederationClient(FederationBase):
                 valid_pdu = await self._check_sigs_and_hash_and_fetch_one(
                     pdu=pdu,
                     origin=destination,
-                    outlier=True,
                     room_version=room_version,
                 )
 
@@ -1235,7 +1209,7 @@ class FederationClient(FederationBase):
             ]
 
             signed_events = await self._check_sigs_and_hash_and_fetch(
-                destination, events, outlier=False, room_version=room_version
+                destination, events, room_version=room_version
             )
         except HttpResponseException as e:
             if not e.code == 400:
diff --git a/synapse/handlers/federation_event.py b/synapse/handlers/federation_event.py
index 7c81e3651f..11771f3c9c 100644
--- a/synapse/handlers/federation_event.py
+++ b/synapse/handlers/federation_event.py
@@ -421,9 +421,6 @@ class FederationEventHandler:
         Raises:
             SynapseError if the response is in some way invalid.
         """
-        for e in itertools.chain(auth_events, state):
-            e.internal_metadata.outlier = True
-
         event_map = {e.event_id: e for e in itertools.chain(auth_events, state)}
 
         create_event = None
@@ -1194,7 +1191,6 @@ class FederationEventHandler:
                         [destination],
                         event_id,
                         room_version,
-                        outlier=True,
                     )
                     if event is None:
                         logger.warning(
@@ -1223,9 +1219,10 @@ class FederationEventHandler:
         """Persist a batch of outlier events fetched from remote servers.
 
         We first sort the events to make sure that we process each event's auth_events
-        before the event itself, and then auth and persist them.
+        before the event itself.
 
-        Notifies about the events where appropriate.
+        We then mark the events as outliers, persist them to the database, and, where
+        appropriate (eg, an invite), awake the notifier.
 
         Params:
             room_id: the room that the events are meant to be in (though this has
@@ -1276,7 +1273,8 @@ class FederationEventHandler:
         Persists a batch of events where we have (theoretically) already persisted all
         of their auth events.
 
-        Notifies about the events where appropriate.
+        Marks the events as outliers, auths them, persists them to the database, and,
+        where appropriate (eg, an invite), awakes the notifier.
 
         Params:
             origin: where the events came from
@@ -1314,6 +1312,9 @@ class FederationEventHandler:
                         return None
                     auth.append(ae)
 
+                # we're not bothering about room state, so flag the event as an outlier.
+                event.internal_metadata.outlier = True
+
                 context = EventContext.for_outlier()
                 try:
                     validate_event_for_room_version(room_version_obj, event)
diff --git a/tests/handlers/test_federation.py b/tests/handlers/test_federation.py
index e1557566e4..496b581726 100644
--- a/tests/handlers/test_federation.py
+++ b/tests/handlers/test_federation.py
@@ -373,9 +373,7 @@ class FederationTestCase(unittest.HomeserverTestCase):
             destination: str, room_id: str, event_id: str
         ) -> List[EventBase]:
             return [
-                event_from_pdu_json(
-                    ae.get_pdu_json(), room_version=room_version, outlier=True
-                )
+                event_from_pdu_json(ae.get_pdu_json(), room_version=room_version)
                 for ae in auth_events
             ]