to_device updates could be dropped when consuming the replication stream

synapse/storage/databases/main/deviceinbox.py

@@ -639,10 +639,12 @@ def get_all_new_device_messages_txn(
             # Order by ascending stream ordering
             updates.sort()
 
-            limited = False
-            upto_token = current_id
+            upto_token = upper_pos
             if len(updates) >= limit:
                 upto_token = updates[-1][0]
+
+            limited = False
+            if upto_token < current_id:
                 limited = True
 
             return updates, upto_token, limited

tests/replication/tcp/streams/test_account_data.py

@@ -37,11 +37,6 @@ def test_update_function_room_account_data_limit(self) -> None:
         # also one global update
         self.get_success(store.add_account_data_for_user("test_user", "m.global", {}))
 
-        # tell the notifier to catch up to avoid duplicate rows.
-        # workaround for https://github.com/matrix-org/synapse/issues/7360
-        # FIXME remove this when the above is fixed
-        self.replicate()
-
         # check we're testing what we think we are: no rows should yet have been
         # received
         self.assertEqual([], self.test_handler.received_rdata_rows)

tests/replication/tcp/streams/test_to_device.py

@@ -0,0 +1,89 @@
+# Copyright 2023 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.
+import logging
+
+import synapse
+from synapse.replication.tcp.streams._base import _STREAM_UPDATE_TARGET_ROW_COUNT
+from synapse.types import JsonDict
+
+from tests.replication._base import BaseStreamTestCase
+
+logger = logging.getLogger(__name__)
+
+
+class ToDeviceStreamTestCase(BaseStreamTestCase):
+    servlets = [
+        synapse.rest.admin.register_servlets,
+        synapse.rest.client.login.register_servlets,
+    ]
+
+    def test_to_device_stream(self) -> None:
+        store = self.hs.get_datastores().main
+
+        user1 = self.register_user("user1", "pass")
+        self.login("user1", "pass", "device")
+        user2 = self.register_user("user2", "pass")
+        self.login("user2", "pass", "device")
+
+        # connect to pull the updates related to users creation/login
+        self.reconnect()
+        self.replicate()
+        self.test_handler.received_rdata_rows.clear()
+        # disconnect so we can accumulate the updates without pulling them
+        self.disconnect()
+
+        msg: JsonDict = {}
+        msg["sender"] = "@sender:example.org"
+        msg["type"] = "m.new_device"
+
+        # add messages to the device inbox for user1 up until the
+        # limit defined for a stream update batch
+        for i in range(0, _STREAM_UPDATE_TARGET_ROW_COUNT):
+            msg["content"] = {"device": {"device_id": f"{i}"}}
+            messages = {user1: {"device": msg}}
+
+            self.get_success(
+                store.add_messages_from_remote_to_device_inbox(
+                    "example.org",
+                    f"{i}",
+                    messages,
+                )
+            )
+
+        # add one more message, for user2 this time
+        # this message would be dropped before fixing #15335
+        msg["content"] = {"device": {"device_id": "1"}}
+        messages = {user2: {"device": msg}}
+
+        self.get_success(
+            store.add_messages_from_remote_to_device_inbox(
+                "example.org",
+                f"{_STREAM_UPDATE_TARGET_ROW_COUNT}",
+                messages,
+            )
+        )
+
+        # replication is disconnected so we shouldn't get any updates yet
+        self.assertEqual([], self.test_handler.received_rdata_rows)
+
+        # now reconnect to pull the updates
+        self.reconnect()
+        self.replicate()
+
+        # we should receive the fact that we have to_device updates
+        # for user1 and user2
+        received_rows = self.test_handler.received_rdata_rows
+        self.assertEqual(len(received_rows), 2)
+        self.assertEqual(received_rows[0][2].entity, user1)
+        self.assertEqual(received_rows[1][2].entity, user2)