Fix message duplication if something goes wrong after persisting the event

changelog.d/8476.bugfix

@@ -0,0 +1 @@
+Fix message duplication if something goes wrong after persisting the event.

synapse/handlers/federation.py

@@ -2966,17 +2966,20 @@ async def persist_events_and_notify(
             return result["max_stream_id"]
         else:
             assert self.storage.persistence
-            max_stream_token = await self.storage.persistence.persist_events(
+
+            # Note that this returns the events that were persisted, which may not be
+            # the same as were passed in if some were deduplicated due to transaction IDs.
+            events, max_stream_token = await self.storage.persistence.persist_events(
                 event_and_contexts, backfilled=backfilled
             )
 
             if self._ephemeral_messages_enabled:
-                for (event, context) in event_and_contexts:
+                for event in events:
                     # If there's an expiry timestamp on the event, schedule its expiry.
                     self._message_handler.maybe_schedule_expiry(event)
 
             if not backfilled:  # Never notify for backfilled events
-                for event, _ in event_and_contexts:
+                for event in events:
                     await self._notify_persisted_event(event, max_stream_token)
 
             return max_stream_token.stream

synapse/handlers/message.py

@@ -686,7 +686,7 @@ async def create_and_send_nonmember_event(
                 send this event.
 
         Returns:
-            The event, and its stream ordering (if state event deduplication happened,
+            The event, and its stream ordering (if deduplication happened,
             the previous, duplicate event).
 
         Raises:
@@ -709,6 +709,19 @@ async def create_and_send_nonmember_event(
         # extremities to pile up, which in turn leads to state resolution
         # taking longer.
         with (await self.limiter.queue(event_dict["room_id"])):
+            if txn_id and requester.access_token_id:
+                existing_event_id = await self.store.get_event_id_from_transaction_id(
+                    event_dict["room_id"],
+                    requester.user.to_string(),
+                    requester.access_token_id,
+                    txn_id,
+                )
+                if existing_event_id:
+                    event = await self.store.get_event(existing_event_id)
+                    # we know it was persisted, so must have a stream ordering
+                    assert event.internal_metadata.stream_ordering
+                    return event, event.internal_metadata.stream_ordering
+
             event, context = await self.create_event(
                 requester, event_dict, token_id=requester.access_token_id, txn_id=txn_id
             )
@@ -910,10 +923,20 @@ async def handle_new_client_event(
                     extra_users=extra_users,
                 )
                 stream_id = result["stream_id"]
-                event.internal_metadata.stream_ordering = stream_id
+                event_id = result["event_id"]
+                if event_id != event.event_id:
+                    # If we get a different event back then it means that its
+                    # been de-duplicated, so we replace the given event with the
+                    # one already persisted.
+                    event = await self.store.get_event(event_id)
+                else:
+                    # If we newly persisted the event then we need to update its
+                    # stream_ordering entry manually (as it was persisted on
+                    # another worker).
+                    event.internal_metadata.stream_ordering = stream_id
                 return event
 
-            stream_id = await self.persist_and_notify_client_event(
+            event = await self.persist_and_notify_client_event(
                 requester, event, context, ratelimit=ratelimit, extra_users=extra_users
             )
 
@@ -962,11 +985,16 @@ async def persist_and_notify_client_event(
         context: EventContext,
         ratelimit: bool = True,
         extra_users: List[UserID] = [],
-    ) -> int:
+    ) -> EventBase:
         """Called when we have fully built the event, have already
         calculated the push actions for the event, and checked auth.
 
         This should only be run on the instance in charge of persisting events.
+
+        Returns:
+            The persisted event. This may be different than the given event if
+            it was de-duplicated (e.g. because we had already persisted an
+            event with the same transaction ID.)
         """
         assert self.storage.persistence is not None
         assert self._events_shard_config.should_handle(
@@ -1134,9 +1162,13 @@ def is_inviter_member_event(e):
             if prev_state_ids:
                 raise AuthError(403, "Changing the room create event is forbidden")
 
-        event_pos, max_stream_token = await self.storage.persistence.persist_event(
-            event, context=context
-        )
+        # Note that this returns the event that was persisted, which may not be
+        # the same as we passed in if it was deduplicated due transaction IDs.
+        (
+            event,
+            event_pos,
+            max_stream_token,
+        ) = await self.storage.persistence.persist_event(event, context=context)
 
         if self._ephemeral_events_enabled:
             # If there's an expiry timestamp on the event, schedule its expiry.
@@ -1157,7 +1189,7 @@ def _notify():
             # matters as sometimes presence code can take a while.
             run_in_background(self._bump_active_time, requester.user)
 
-        return event_pos.stream
+        return event
 
     async def _bump_active_time(self, user: UserID) -> None:
         try:

synapse/handlers/room_member.py

@@ -171,6 +171,17 @@ async def _local_membership_update(
         if requester.is_guest:
             content["kind"] = "guest"
 
+        # Check if we already have an event with a matching transaction ID. (We
+        # do this check just before we persist an event as well, but may as well
+        # do it up front for efficiency.)
+        if txn_id and requester.access_token_id:
+            existing_event_id = await self.store.get_event_id_from_transaction_id(
+                room_id, requester.user.to_string(), requester.access_token_id, txn_id,
+            )
+            if existing_event_id:
+                event_pos = await self.store.get_position_for_event(existing_event_id)
+                return existing_event_id, event_pos.stream
+
         event, context = await self.event_creation_handler.create_event(
             requester,
             {
@@ -679,7 +690,7 @@ async def send_membership_event(
             if is_blocked:
                 raise SynapseError(403, "This room has been blocked on this server")
 
-        await self.event_creation_handler.handle_new_client_event(
+        event = await self.event_creation_handler.handle_new_client_event(
             requester, event, context, extra_users=[target_user], ratelimit=ratelimit
         )
 

synapse/replication/http/send_event.py

@@ -46,6 +46,12 @@ class ReplicationSendEventRestServlet(ReplicationEndpoint):
             "ratelimit": true,
             "extra_users": [],
         }
+
+        200 OK
+
+        { "stream_id": 12345, "event_id": "$abcdef..." }
+
+    The returned event ID may not match the sent event if it was deduplicated.
     """
 
     NAME = "send_event"
@@ -116,11 +122,17 @@ async def _handle_request(self, request, event_id):
             "Got event to send with ID: %s into room: %s", event.event_id, event.room_id
         )
 
-        stream_id = await self.event_creation_handler.persist_and_notify_client_event(
+        event = await self.event_creation_handler.persist_and_notify_client_event(
             requester, event, context, ratelimit=ratelimit, extra_users=extra_users
         )
 
-        return 200, {"stream_id": stream_id}
+        return (
+            200,
+            {
+                "stream_id": event.internal_metadata.stream_ordering,
+                "event_id": event.event_id,
+            },
+        )
 
 
 def register_servlets(hs, http_server):

synapse/storage/databases/main/events.py

@@ -361,6 +361,8 @@ def _persist_events_txn(
 
         self._store_event_txn(txn, events_and_contexts=events_and_contexts)
 
+        self._persist_transaction_ids_txn(txn, events_and_contexts)
+
         # Insert into event_to_state_groups.
         self._store_event_state_mappings_txn(txn, events_and_contexts)
 
@@ -405,6 +407,35 @@ def _persist_events_txn(
         # room_memberships, where applicable.
         self._update_current_state_txn(txn, state_delta_for_room, min_stream_order)
 
+    def _persist_transaction_ids_txn(
+        self,
+        txn: LoggingTransaction,
+        events_and_contexts: List[Tuple[EventBase, EventContext]],
+    ):
+        """Persist the mapping from transaction IDs to event IDs (if defined).
+        """
+
+        to_insert = []
+        for event, _ in events_and_contexts:
+            token_id = getattr(event.internal_metadata, "token_id", None)
+            txn_id = getattr(event.internal_metadata, "txn_id", None)
+            if token_id and txn_id:
+                to_insert.append(
+                    {
+                        "event_id": event.event_id,
+                        "room_id": event.room_id,
+                        "user_id": event.sender,
+                        "token_id": token_id,
+                        "txn_id": txn_id,
+                        "inserted_ts": self._clock.time_msec(),
+                    }
+                )
+
+        if to_insert:
+            self.db_pool.simple_insert_many_txn(
+                txn, table="event_txn_id", values=to_insert,
+            )
+
     def _update_current_state_txn(
         self,
         txn: LoggingTransaction,

synapse/storage/databases/main/events_worker.py

@@ -12,7 +12,6 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
 import itertools
 import logging
 import threading
@@ -137,6 +136,15 @@ def __init__(self, database: DatabasePool, db_conn, hs):
                     db_conn, "events", "stream_ordering", step=-1
                 )
 
+        if not hs.config.worker.worker_app:
+            # We periodically clean out old transaction ID mappings
+            self._clock.looping_call(
+                run_as_background_process,
+                5 * 60 * 1000,
+                "_cleanup_old_transaction_ids",
+                self._cleanup_old_transaction_ids,
+            )
+
         self._get_event_cache = Cache(
             "*getEvent*",
             keylen=3,
@@ -1304,3 +1312,76 @@ def get_next_event_to_expire_txn(txn):
         return await self.db_pool.runInteraction(
             desc="get_next_event_to_expire", func=get_next_event_to_expire_txn
         )
+
+    async def get_event_id_from_transaction_id(
+        self, room_id: str, user_id: str, token_id: int, txn_id: str
+    ) -> Optional[str]:
+        """Look up if we have already persisted an event for the transaction ID,
+        returning the event ID if so.
+        """
+        return await self.db_pool.simple_select_one_onecol(
+            table="event_txn_id",
+            keyvalues={
+                "room_id": room_id,
+                "user_id": user_id,
+                "token_id": token_id,
+                "txn_id": txn_id,
+            },
+            retcol="event_id",
+            allow_none=True,
+            desc="get_event_id_from_transaction_id",
+        )
+
+    async def get_already_persisted_events(
+        self, events: Iterable[EventBase]
+    ) -> Dict[str, str]:
+        """Look up if we have already persisted an event for the transaction ID,
+        returning a mapping from event ID in the given list to the event ID of
+        an existing event.
+
+        Also checks if there are duplicates in the given events, if there are
+        will map duplicates to the *first* event.
+        """
+
+        mapping = {}
+        txn_id_to_event = {}  # type: Dict[Tuple[str, int, str], str]
+
+        for event in events:
+            token_id = getattr(event.internal_metadata, "token_id", None)
+            txn_id = getattr(event.internal_metadata, "txn_id", None)
+
+            if token_id and txn_id:
+                # Check if this is a duplicate of an event in the given events.
+                existing = txn_id_to_event.get((event.room_id, token_id, txn_id))
+                if existing:
+                    mapping[event.event_id] = existing
+                    continue
+
+                # Check if this is a duplicate of an event we've already
+                # persisted.
+                existing = await self.get_event_id_from_transaction_id(
+                    event.room_id, event.sender, token_id, txn_id
+                )
+                if existing:
+                    mapping[event.event_id] = existing
+                    txn_id_to_event[(event.room_id, token_id, txn_id)] = existing
+                else:
+                    txn_id_to_event[(event.room_id, token_id, txn_id)] = event.event_id
+
+        return mapping
+
+    async def _cleanup_old_transaction_ids(self):
+        """Cleans out transaction id mappings older than 24hrs.
+        """
+
+        def _cleanup_old_transaction_ids_txn(txn):
+            sql = """
+                DELETE FROM event_txn_id
+                WHERE inserted_ts < ?
+            """
+            one_day_ago = self._clock.time_msec() - 24 * 60 * 60 * 1000
+            txn.execute(sql, (one_day_ago,))
+
+        return await self.db_pool.runInteraction(
+            "_cleanup_old_transaction_ids", _cleanup_old_transaction_ids_txn,
+        )

synapse/storage/databases/main/registration.py

@@ -939,7 +939,7 @@ async def add_access_token_to_user(
         token: str,
         device_id: Optional[str],
         valid_until_ms: Optional[int],
-    ) -> None:
+    ) -> int:
         """Adds an access token for the given user.
 
         Args:
@@ -949,6 +949,8 @@ async def add_access_token_to_user(
             valid_until_ms: when the token is valid until. None for no expiry.
         Raises:
             StoreError if there was a problem adding this.
+        Returns:
+            The token ID
         """
         next_id = self._access_tokens_id_gen.get_next()
 
@@ -964,6 +966,8 @@ async def add_access_token_to_user(
             desc="add_access_token_to_user",
         )
 
+        return next_id
+
     def _set_device_for_access_token_txn(self, txn, token: str, device_id: str) -> str:
         old_device_id = self.db_pool.simple_select_one_onecol_txn(
             txn, "access_tokens", {"token": token}, "device_id"

synapse/storage/databases/main/schema/delta/58/19txn_id.sql

@@ -0,0 +1,40 @@
+/* Copyright 2020 The Matrix.org Foundation C.I.C
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+-- A map of recent events persisted with transaction IDs. Used to deduplicate
+-- send event requests with the same transaction ID.
+--
+-- Note: transaction IDs are scoped to the room ID/user ID/access token that was
+-- used to make the request.
+--
+-- Note: The foreign key constraints are ON DELETE CASCADE, as if we delete the
+-- events or access token we don't want to try and de-duplicate the event.
+CREATE TABLE IF NOT EXISTS event_txn_id (
+    event_id TEXT NOT NULL,
+    room_id TEXT NOT NULL,
+    user_id TEXT NOT NULL,
+    token_id BIGINT NOT NULL,
+    txn_id TEXT NOT NULL,
+    inserted_ts BIGINT NOT NULL,
+    FOREIGN KEY (event_id)
+        REFERENCES events (event_id) ON DELETE CASCADE,
+    FOREIGN KEY (token_id)
+        REFERENCES access_tokens (id) ON DELETE CASCADE
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS event_txn_id_event_id ON event_txn_id(event_id);
+CREATE UNIQUE INDEX IF NOT EXISTS event_txn_id_txn_id ON event_txn_id(room_id, user_id, token_id, txn_id);
+CREATE INDEX IF NOT EXISTS event_txn_id_ts ON event_txn_id(inserted_ts);