Experimental support for MSC3970: per-device transaction IDs

changelog.d/15318.feature

@@ -0,0 +1 @@
+Experimental support for MSC3970: Scope transaction IDs to devices.

synapse/config/experimental.py

@@ -191,3 +191,6 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
 
         # MSC2659: Application service ping endpoint
         self.msc2659_enabled = experimental.get("msc2659_enabled", False)
+
+        # MSC3970: Scope transaction IDs to devices
+        self.msc3970_enabled = experimental.get("msc3970_enabled", False)

synapse/events/__init__.py

@@ -198,9 +198,16 @@ def __init__(self, internal_metadata_dict: JsonDict):
     soft_failed: DictProperty[bool] = DictProperty("soft_failed")
     proactively_send: DictProperty[bool] = DictProperty("proactively_send")
     redacted: DictProperty[bool] = DictProperty("redacted")
+    historical: DictProperty[bool] = DictProperty("historical")
+
     txn_id: DictProperty[str] = DictProperty("txn_id")
+    """The transaction ID, if it was set when the event was created."""
+
     token_id: DictProperty[int] = DictProperty("token_id")
-    historical: DictProperty[bool] = DictProperty("historical")
+    """The access token ID of the user who sent this event, if any."""
+
+    device_id: DictProperty[str] = DictProperty("device_id")
+    """The device ID of the user who sent this event, if any."""
 
     # XXX: These are set by StreamWorkerStore._set_before_and_after.
     # I'm pretty sure that these are never persisted to the database, so shouldn't

synapse/events/utils.py

@@ -339,13 +339,16 @@ def serialize_event(
     time_now_ms: int,
     *,
     config: SerializeEventConfig = _DEFAULT_SERIALIZE_EVENT_CONFIG,
+    msc3970_enabled: bool = False,
 ) -> JsonDict:
     """Serialize event for clients
 
     Args:
         e
         time_now_ms
         config: Event serialization config
+        msc3970_enabled: Whether MSC3970 is enabled. It changes whether we should
+            include the `transaction_id` in the event's `unsigned` section.
 
     Returns:
         The serialized event dictionary.
@@ -368,27 +371,43 @@ def serialize_event(
 
     if "redacted_because" in e.unsigned:
         d["unsigned"]["redacted_because"] = serialize_event(
-            e.unsigned["redacted_because"], time_now_ms, config=config
+            e.unsigned["redacted_because"],
+            time_now_ms,
+            config=config,
+            msc3970_enabled=msc3970_enabled,
         )
 
     # If we have a txn_id saved in the internal_metadata, we should include it in the
     # unsigned section of the event if it was sent by the same session as the one
     # requesting the event.
-    # There is a special case for guests, because they only have one access token
-    # without associated access_token_id, so we always include the txn_id for events
-    # they sent.
-    txn_id = getattr(e.internal_metadata, "txn_id", None)
+    txn_id: Optional[str] = getattr(e.internal_metadata, "txn_id", None)
     if txn_id is not None and config.requester is not None:
-        event_token_id = getattr(e.internal_metadata, "token_id", None)
-        if config.requester.user.to_string() == e.sender and (
-            (
-                event_token_id is not None
-                and config.requester.access_token_id is not None
-                and event_token_id == config.requester.access_token_id
+        # For the MSC3970 rules to be applied, we *need* to have the device ID in the
+        # event internal metadata. Since we were not recording them before, if it hasn't
+        # been recorded, we fallback to the old behaviour.
+        event_device_id: Optional[str] = getattr(e.internal_metadata, "device_id", None)
+        if msc3970_enabled and event_device_id is not None:
+            if event_device_id == config.requester.device_id:
+                d["unsigned"]["transaction_id"] = txn_id
+
+        else:
+            # The pre-MSC3970 behaviour is to only include the transaction ID if the
+            # event was sent from the same access token. For regular users, we can use
+            # the access token ID to determine this. For guests, we can't, but since
+            # each guest only has one access token, we can just check that the event was
+            # sent by the same user as the one requesting the event.
+            event_token_id: Optional[int] = getattr(
+                e.internal_metadata, "token_id", None
             )
-            or config.requester.is_guest
-        ):
-            d["unsigned"]["transaction_id"] = txn_id
+            if config.requester.user.to_string() == e.sender and (
+                (
+                    event_token_id is not None
+                    and config.requester.access_token_id is not None
+                    and event_token_id == config.requester.access_token_id
+                )
+                or config.requester.is_guest
+            ):
+                d["unsigned"]["transaction_id"] = txn_id
 
     # invite_room_state and knock_room_state are a list of stripped room state events
     # that are meant to provide metadata about a room to an invitee/knocker. They are
@@ -419,6 +438,9 @@ class EventClientSerializer:
     clients.
     """
 
+    def __init__(self, *, msc3970_enabled: bool = False):
+        self._msc3970_enabled = msc3970_enabled
+
     def serialize_event(
         self,
         event: Union[JsonDict, EventBase],
@@ -443,7 +465,9 @@ def serialize_event(
         if not isinstance(event, EventBase):
             return event
 
-        serialized_event = serialize_event(event, time_now, config=config)
+        serialized_event = serialize_event(
+            event, time_now, config=config, msc3970_enabled=self._msc3970_enabled
+        )
 
         # Check if there are any bundled aggregations to include with the event.
         if bundle_aggregations:
@@ -501,7 +525,9 @@ def _inject_bundled_aggregations(
             # `sender` of the edit; however MSC3925 proposes extending it to the whole
             # of the edit, which is what we do here.
             serialized_aggregations[RelationTypes.REPLACE] = self.serialize_event(
-                event_aggregations.replace, time_now, config=config
+                event_aggregations.replace,
+                time_now,
+                config=config,
             )
 
         # Include any threaded replies to this event.

synapse/handlers/message.py

@@ -561,6 +561,8 @@ def __init__(self, hs: "HomeServer"):
                 expiry_ms=30 * 60 * 1000,
             )
 
+        self._msc3970_enabled = hs.config.experimental.msc3970_enabled
+
     async def create_event(
         self,
         requester: Requester,
@@ -701,9 +703,16 @@ async def create_event(
         if require_consent and not is_exempt:
             await self.assert_accepted_privacy_policy(requester)
 
+        # Save the access token ID, the device ID and the transaction ID in the event
+        # internal metadata. This is useful to determine if we should echo the
+        # transaction_id in events.
+        # See `synapse.events.utils.EventClientSerializer.serialize_event`
         if requester.access_token_id is not None:
             builder.internal_metadata.token_id = requester.access_token_id
 
+        if requester.device_id is not None:
+            builder.internal_metadata.device_id = requester.device_id
+
         if txn_id is not None:
             builder.internal_metadata.txn_id = txn_id
 
@@ -897,12 +906,31 @@ async def get_event_from_transaction(
         Returns:
             An event if one could be found, None otherwise.
         """
+
+        if self._msc3970_enabled and requester.device_id:
+            # When MSC3970 is enabled, we lookup for events sent by the same device first,
+            # and fallback to the old behaviour if none were found.
+            existing_event_id = (
+                await self.store.get_event_id_from_transaction_id_and_device_id(
+                    room_id,
+                    requester.user.to_string(),
+                    requester.device_id,
+                    txn_id,
+                )
+            )
+            if existing_event_id:
+                return await self.store.get_event(existing_event_id)
+
+        # Pre-MSC3970, we looked up for events that were sent by the same session by
+        # using the access token ID.
         if 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,
+            existing_event_id = (
+                await self.store.get_event_id_from_transaction_id_and_token_id(
+                    room_id,
+                    requester.user.to_string(),
+                    requester.access_token_id,
+                    txn_id,
+                )
             )
             if existing_event_id:
                 return await self.store.get_event(existing_event_id)

synapse/handlers/room_member.py

@@ -169,6 +169,8 @@ def __init__(self, hs: "HomeServer"):
         self.request_ratelimiter = hs.get_request_ratelimiter()
         hs.get_notifier().add_new_join_in_room_callback(self._on_user_joined_room)
 
+        self._msc3970_enabled = hs.config.experimental.msc3970_enabled
+
     def _on_user_joined_room(self, event_id: str, room_id: str) -> None:
         """Notify the rate limiter that a room join has occurred.
 
@@ -399,13 +401,30 @@ async def _local_membership_update(
         # 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 txn_id:
+            existing_event_id = None
+            if self._msc3970_enabled and requester.device_id:
+                # When MSC3970 is enabled, we lookup for events sent by the same device
+                # first, and fallback to the old behaviour if none were found.
+                existing_event_id = (
+                    await self.store.get_event_id_from_transaction_id_and_device_id(
+                        room_id,
+                        requester.user.to_string(),
+                        requester.device_id,
+                        txn_id,
+                    )
+                )
+
+            if requester.access_token_id and not existing_event_id:
+                existing_event_id = (
+                    await self.store.get_event_id_from_transaction_id_and_token_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

synapse/rest/client/transactions.py

@@ -50,6 +50,8 @@ def __init__(self, hs: "HomeServer"):
         # for at *LEAST* 30 mins, and at *MOST* 60 mins.
         self.cleaner = self.clock.looping_call(self._cleanup, CLEANUP_PERIOD_MS)
 
+        self._msc3970_enabled = hs.config.experimental.msc3970_enabled
+
     def _get_transaction_key(self, request: IRequest, requester: Requester) -> Hashable:
         """A helper function which returns a transaction key that can be used
         with TransactionCache for idempotent requests.
@@ -58,6 +60,7 @@ def _get_transaction_key(self, request: IRequest, requester: Requester) -> Hasha
         requests to the same endpoint. The key is formed from the HTTP request
         path and attributes from the requester: the access_token_id for regular users,
         the user ID for guest users, and the appservice ID for appservice users.
+        With MSC3970, for regular users, the key is based on the user ID and device ID.
 
         Args:
             request: The incoming request.
@@ -67,11 +70,21 @@ def _get_transaction_key(self, request: IRequest, requester: Requester) -> Hasha
         """
         assert request.path is not None
         path: str = request.path.decode("utf8")
+
         if requester.is_guest:
             assert requester.user is not None, "Guest requester must have a user ID set"
             return (path, "guest", requester.user)
+
         elif requester.app_service is not None:
             return (path, "appservice", requester.app_service.id)
+
+        # With MSC3970, we use the user ID and device ID as the transaction key
+        elif self._msc3970_enabled:
+            assert requester.user, "Requester must have a user"
+            assert requester.device_id, "Requester must have a device_id"
+            return (path, "user", requester.user, requester.device_id)
+
+        # Otherwise, the pre-MSC3970 behaviour is to use the access token ID
         else:
             assert (
                 requester.access_token_id is not None

synapse/server.py

@@ -762,7 +762,9 @@ def get_oidc_handler(self) -> "OidcHandler":
 
     @cache_in_self
     def get_event_client_serializer(self) -> EventClientSerializer:
-        return EventClientSerializer()
+        return EventClientSerializer(
+            msc3970_enabled=self.config.experimental.msc3970_enabled
+        )
 
     @cache_in_self
     def get_password_policy_handler(self) -> PasswordPolicyHandler:

synapse/storage/databases/main/events.py

@@ -127,6 +127,8 @@ def __init__(
         self._backfill_id_gen: AbstractStreamIdGenerator = self.store._backfill_id_gen
         self._stream_id_gen: AbstractStreamIdGenerator = self.store._stream_id_gen
 
+        self._msc3970_enabled = hs.config.experimental.msc3970_enabled
+
     @trace
     async def _persist_events_and_state_updates(
         self,
@@ -977,23 +979,43 @@ def _persist_transaction_ids_txn(
     ) -> None:
         """Persist the mapping from transaction IDs to event IDs (if defined)."""
 
-        to_insert = []
+        inserted_ts = self._clock.time_msec()
+        to_insert_token_id: List[Tuple[str, str, str, int, str, int]] = []
+        to_insert_device_id: List[Tuple[str, str, str, str, str, int]] = []
         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.event_id,
-                        event.room_id,
-                        event.sender,
-                        token_id,
-                        txn_id,
-                        self._clock.time_msec(),
+            token_id = getattr(event.internal_metadata, "token_id", None)
+            device_id = getattr(event.internal_metadata, "device_id", None)
+
+            if txn_id is not None:
+                if token_id is not None:
+                    to_insert_token_id.append(
+                        (
+                            event.event_id,
+                            event.room_id,
+                            event.sender,
+                            token_id,
+                            txn_id,
+                            inserted_ts,
+                        )
                     )
-                )
 
-        if to_insert:
+                if device_id is not None:
+                    to_insert_device_id.append(
+                        (
+                            event.event_id,
+                            event.room_id,
+                            event.sender,
+                            device_id,
+                            txn_id,
+                            inserted_ts,
+                        )
+                    )
+
+        # Pre-MSC3970, we rely on the access_token_id to scope the txn_id for events.
+        # Since this is an experimental flag, we still store the mapping even if the
+        # flag is disabled.
+        if to_insert_token_id:
             self.db_pool.simple_insert_many_txn(
                 txn,
                 table="event_txn_id",
@@ -1005,7 +1027,25 @@ def _persist_transaction_ids_txn(
                     "txn_id",
                     "inserted_ts",
                 ),
-                values=to_insert,
+                values=to_insert_token_id,
+            )
+
+        # With MSC3970, we rely on the device_id instead to scope the txn_id for events.
+        # We're only inserting if MSC3970 is *enabled*, because else the pre-MSC3970
+        # behaviour would allow for a UNIQUE constraint violation on this table
+        if to_insert_device_id and self._msc3970_enabled:
+            self.db_pool.simple_insert_many_txn(
+                txn,
+                table="event_txn_id_device_id",
+                keys=(
+                    "event_id",
+                    "room_id",
+                    "user_id",
+                    "device_id",
+                    "txn_id",
+                    "inserted_ts",
+                ),
+                values=to_insert_device_id,
             )
 
     async def update_current_state(