Make historical events discoverable from backfill for servers without any scrollback history (MSC2716) (federation)

changelog.d/10245.feature

@@ -0,0 +1 @@
+Make historical events discoverable from backfill for servers without any scrollback history (part of MSC2716).

synapse/api/constants.py

@@ -198,9 +198,6 @@ class EventContentFields:
     MSC2716_CHUNK_ID = "org.matrix.msc2716.chunk_id"
     # For "marker" events
     MSC2716_MARKER_INSERTION = "org.matrix.msc2716.marker.insertion"
-    MSC2716_MARKER_INSERTION_PREV_EVENTS = (
-        "org.matrix.msc2716.marker.insertion_prev_events"
-    )
 
 
 class RoomTypes:

synapse/api/room_versions.py

@@ -73,6 +73,9 @@ class RoomVersion:
     # MSC2403: Allows join_rules to be set to 'knock', changes auth rules to allow sending
     # m.room.membership event with membership 'knock'.
     msc2403_knocking = attr.ib(type=bool)
+    # MSC2716: Adds m.room.power_levels -> content.historical field to control
+    # whether "insertion", "chunk", "marker" events can be sent
+    msc2716_historical = attr.ib(type=bool)
 
 
 class RoomVersions:
@@ -88,6 +91,7 @@ class RoomVersions:
         msc2176_redaction_rules=False,
         msc3083_join_rules=False,
         msc2403_knocking=False,
+        msc2716_historical=False,
     )
     V2 = RoomVersion(
         "2",
@@ -101,6 +105,7 @@ class RoomVersions:
         msc2176_redaction_rules=False,
         msc3083_join_rules=False,
         msc2403_knocking=False,
+        msc2716_historical=False,
     )
     V3 = RoomVersion(
         "3",
@@ -114,6 +119,7 @@ class RoomVersions:
         msc2176_redaction_rules=False,
         msc3083_join_rules=False,
         msc2403_knocking=False,
+        msc2716_historical=False,
     )
     V4 = RoomVersion(
         "4",
@@ -127,6 +133,7 @@ class RoomVersions:
         msc2176_redaction_rules=False,
         msc3083_join_rules=False,
         msc2403_knocking=False,
+        msc2716_historical=False,
     )
     V5 = RoomVersion(
         "5",
@@ -140,6 +147,7 @@ class RoomVersions:
         msc2176_redaction_rules=False,
         msc3083_join_rules=False,
         msc2403_knocking=False,
+        msc2716_historical=False,
     )
     V6 = RoomVersion(
         "6",
@@ -153,6 +161,7 @@ class RoomVersions:
         msc2176_redaction_rules=False,
         msc3083_join_rules=False,
         msc2403_knocking=False,
+        msc2716_historical=False,
     )
     MSC2176 = RoomVersion(
         "org.matrix.msc2176",
@@ -166,6 +175,7 @@ class RoomVersions:
         msc2176_redaction_rules=True,
         msc3083_join_rules=False,
         msc2403_knocking=False,
+        msc2716_historical=False,
     )
     MSC3083 = RoomVersion(
         "org.matrix.msc3083",
@@ -179,6 +189,7 @@ class RoomVersions:
         msc2176_redaction_rules=False,
         msc3083_join_rules=True,
         msc2403_knocking=False,
+        msc2716_historical=False,
     )
     V7 = RoomVersion(
         "7",
@@ -192,6 +203,21 @@ class RoomVersions:
         msc2176_redaction_rules=False,
         msc3083_join_rules=False,
         msc2403_knocking=True,
+        msc2716_historical=False,
+    )
+    MSC2716 = RoomVersion(
+        "org.matrix.msc2716",
+        RoomDisposition.STABLE,
+        EventFormatVersions.V3,
+        StateResolutionVersions.V2,
+        enforce_key_validity=True,
+        special_case_aliases_auth=False,
+        strict_canonicaljson=True,
+        limit_notifications_power_levels=True,
+        msc2176_redaction_rules=False,
+        msc3083_join_rules=False,
+        msc2403_knocking=True,
+        msc2716_historical=True,
     )
 
 
@@ -207,6 +233,7 @@ class RoomVersions:
         RoomVersions.MSC2176,
         RoomVersions.MSC3083,
         RoomVersions.V7,
+        RoomVersions.MSC2716,
     )
 }
 

synapse/event_auth.py

@@ -193,6 +193,13 @@ def check(
     if event.type == EventTypes.Redaction:
         check_redaction(room_version_obj, event, auth_events)
 
+    if (
+        event.type == EventTypes.MSC2716_INSERTION
+        or event.type == EventTypes.MSC2716_CHUNK
+        or event.type == EventTypes.MSC2716_MARKER
+    ):
+        check_historical(room_version_obj, event, auth_events)
+
     logger.debug("Allowing! %s", event)
 
 
@@ -504,6 +511,37 @@ def check_redaction(
     raise AuthError(403, "You don't have permission to redact events")
 
 
+def check_historical(
+    room_version_obj: RoomVersion,
+    event: EventBase,
+    auth_events: StateMap[EventBase],
+) -> None:
+    """Check whether the event sender is allowed to send historical related
+    events like "insertion", "chunk", and "marker".
+
+    Returns:
+        None
+
+    Raises:
+        AuthError if the event sender is not allowed to send historical related events
+        ("insertion", "chunk", and "marker").
+    """
+    # Ignore the auth checks in room versions that do not support historical
+    # events
+    if not room_version_obj.msc2716_historical:
+        return
+
+    user_level = get_user_power_level(event.user_id, auth_events)
+
+    historical_level = _get_named_level(auth_events, "historical", 100)
+
+    if user_level < historical_level:
+        raise AuthError(
+            403,
+            'You don\'t have permission to send send historical related events ("insertion", "chunk", and "marker")',
+        )
+
+
 def _check_power_levels(
     room_version_obj: RoomVersion,
     event: EventBase,

synapse/events/utils.py

@@ -124,6 +124,9 @@ def add_fields(*fields):
         if room_version.msc2176_redaction_rules:
             add_fields("invite")
 
+        if room_version.msc2716_historical:
+            add_fields("historical")
+
     elif event_type == EventTypes.Aliases and room_version.special_case_aliases_auth:
         add_fields("aliases")
     elif event_type == EventTypes.RoomHistoryVisibility:

synapse/handlers/federation.py

@@ -2714,9 +2714,11 @@ async def _update_auth_events_and_context_for_auth(
                             event.event_id,
                             e.event_id,
                         )
-                        context = await self.state_handler.compute_event_context(e)
+                        missing_auth_event_context = (
+                            await self.state_handler.compute_event_context(e)
+                        )
                         await self._auth_and_persist_event(
-                            origin, e, context, auth_events=auth
+                            origin, e, missing_auth_event_context, auth_events=auth
                         )
 
                         if e.event_id in event_auth_events:

synapse/handlers/room.py

@@ -951,6 +951,7 @@ async def send(etype: str, content: JsonDict, **kwargs) -> int:
                 "kick": 50,
                 "redact": 50,
                 "invite": 50,
+                "historical": 100,
             }
 
             if config["original_invitees_have_ops"]:

synapse/rest/client/v1/room.py

@@ -504,7 +504,6 @@ async def on_POST(self, request, room_id):
 
         events_to_create = body["events"]
 
-        prev_event_ids = prev_events_from_query
         inherited_depth = await self._inherit_depth_from_prev_ids(
             prev_events_from_query
         )
@@ -516,6 +515,10 @@ async def on_POST(self, request, room_id):
         chunk_id_to_connect_to = chunk_id_from_query
         base_insertion_event = None
         if chunk_id_from_query:
+            #  All but the first base insertion event should point at a fake
+            #  event, which causes the HS to ask for the state at the start of
+            #  the chunk later.
+            prev_event_ids = [fake_prev_event_id]
             # TODO: Verify the chunk_id_from_query corresponds to an insertion event
             pass
         # Otherwise, create an insertion event to act as a starting point.
@@ -526,6 +529,8 @@ async def on_POST(self, request, room_id):
         # an insertion event), in which case we just create a new insertion event
         # that can then get pointed to by a "marker" event later.
         else:
+            prev_event_ids = prev_events_from_query
+
             base_insertion_event_dict = self._create_insertion_event_dict(
                 sender=requester.user.to_string(),
                 room_id=room_id,

synapse/storage/databases/main/event_federation.py

@@ -936,15 +936,46 @@ def _get_backfill_events(self, txn, room_id, event_list, limit):
         # We want to make sure that we do a breadth-first, "depth" ordered
         # search.
 
-        query = (
-            "SELECT depth, prev_event_id FROM event_edges"
-            " INNER JOIN events"
-            " ON prev_event_id = events.event_id"
-            " WHERE event_edges.event_id = ?"
-            " AND event_edges.is_state = ?"
-            " LIMIT ?"
-        )
+        # Look for the prev_event_id connected to the given event_id
+        query = """
+            SELECT depth, prev_event_id FROM event_edges
+            /* Get the depth of the prev_event_id from the events table */
+            INNER JOIN events
+            ON prev_event_id = events.event_id
+            /* Find an event which matches the given event_id */
+            WHERE event_edges.event_id = ?
+            AND event_edges.is_state = ?
+            LIMIT ?
+        """
+
+        # Look for the "insertion" events connected to the given event_id
+        connected_insertion_event_query = """
+            SELECT e.depth, i.event_id FROM insertion_event_edges AS i
+            /* Get the depth of the insertion event from the events table */
+            INNER JOIN events AS e USING (event_id)
+            /* Find an insertion event which points via prev_events to the given event_id */
+            WHERE i.insertion_prev_event_id = ?
+            LIMIT ?
+        """
+
+        # Find any chunk connections of a given insertion event
+        chunk_connection_query = """
+            SELECT e.depth, c.event_id FROM insertion_events AS i
+            /* Find the chunk that connects to the given insertion event */
+            INNER JOIN chunk_events AS c
+            ON i.next_chunk_id = c.chunk_id
+            /* Get the depth of the chunk start event from the events table */
+            INNER JOIN events AS e USING (event_id)
+            /* Find an insertion event which matches the given event_id */
+            WHERE i.event_id = ?
+            LIMIT ?
+        """
 
+        # In a PriorityQueue, the lowest valued entries are retrieved first.
+        # We're using depth as the priority in the queue.
+        # Depth is lowest at the oldest-in-time message and highest and
+        # newest-in-time message. We add events to the queue with a negative depth so that
+        # we process the newest-in-time messages first going backwards in time.
         queue = PriorityQueue()
 
         for event_id in event_list:
@@ -970,9 +1001,48 @@ def _get_backfill_events(self, txn, room_id, event_list, limit):
 
             event_results.add(event_id)
 
+            # Try and find any potential historical chunks of message history.
+            #
+            # First we look for an insertion event connected to the current
+            # event (by prev_event). If we find any, we need to go and try to
+            # find any chunk events connected to the insertion event (by
+            # chunk_id). If we find any, we'll add them to the queue and
+            # navigate up the DAG like normal in the next iteration of the loop.
+            txn.execute(
+                connected_insertion_event_query, (event_id, limit - len(event_results))
+            )
+            connected_insertion_event_id_results = txn.fetchall()
+            logger.debug(
+                "_get_backfill_events: connected_insertion_event_query %s",
+                connected_insertion_event_id_results,
+            )
+            for row in connected_insertion_event_id_results:
+                connected_insertion_event_depth = row[0]
+                connected_insertion_event = row[1]
+                queue.put((-connected_insertion_event_depth, connected_insertion_event))
+
+                # Find any chunk connections for the given insertion event
+                txn.execute(
+                    chunk_connection_query,
+                    (connected_insertion_event, limit - len(event_results)),
+                )
+                chunk_start_event_id_results = txn.fetchall()
+                logger.debug(
+                    "_get_backfill_events: chunk_start_event_id_results %s",
+                    chunk_start_event_id_results,
+                )
+                for row in chunk_start_event_id_results:
+                    if row[1] not in event_results:
+                        queue.put((-row[0], row[1]))
+
+            # Navigate up the DAG by prev_event
             txn.execute(query, (event_id, False, limit - len(event_results)))
+            prev_event_id_results = txn.fetchall()
+            logger.debug(
+                "_get_backfill_events: prev_event_ids %s", prev_event_id_results
+            )
 
-            for row in txn:
+            for row in prev_event_id_results:
                 if row[1] not in event_results:
                     queue.put((-row[0], row[1]))