Fix message duplication if something goes wrong after persisting the event (#8476)

Should fix #3365.

1 files changed, 157 insertions, 0 deletions

diff --git a/tests/handlers/test_message.py b/tests/handlers/test_message.py
new file mode 100644
index 0000000000..64e28bc639
--- /dev/null
+++ b/tests/handlers/test_message.py
@@ -0,0 +1,157 @@
+# -*- coding: utf-8 -*-
+# 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.
+import logging
+from typing import Tuple
+
+from synapse.api.constants import EventTypes
+from synapse.events import EventBase
+from synapse.events.snapshot import EventContext
+from synapse.rest import admin
+from synapse.rest.client.v1 import login, room
+from synapse.types import create_requester
+from synapse.util.stringutils import random_string
+
+from tests import unittest
+
+logger = logging.getLogger(__name__)
+
+
+class EventCreationTestCase(unittest.HomeserverTestCase):
+    servlets = [
+        admin.register_servlets,
+        login.register_servlets,
+        room.register_servlets,
+    ]
+
+    def prepare(self, reactor, clock, hs):
+        self.handler = self.hs.get_event_creation_handler()
+        self.persist_event_storage = self.hs.get_storage().persistence
+
+        self.user_id = self.register_user("tester", "foobar")
+        self.access_token = self.login("tester", "foobar")
+        self.room_id = self.helper.create_room_as(self.user_id, tok=self.access_token)
+
+        self.info = self.get_success(
+            self.hs.get_datastore().get_user_by_access_token(self.access_token,)
+        )
+        self.token_id = self.info["token_id"]
+
+        self.requester = create_requester(self.user_id, access_token_id=self.token_id)
+
+    def _create_duplicate_event(self, txn_id: str) -> Tuple[EventBase, EventContext]:
+        """Create a new event with the given transaction ID. All events produced
+        by this method will be considered duplicates.
+        """
+
+        # We create a new event with a random body, as otherwise we'll produce
+        # *exactly* the same event with the same hash, and so same event ID.
+        return self.get_success(
+            self.handler.create_event(
+                self.requester,
+                {
+                    "type": EventTypes.Message,
+                    "room_id": self.room_id,
+                    "sender": self.requester.user.to_string(),
+                    "content": {"msgtype": "m.text", "body": random_string(5)},
+                },
+                token_id=self.token_id,
+                txn_id=txn_id,
+            )
+        )
+
+    def test_duplicated_txn_id(self):
+        """Test that attempting to handle/persist an event with a transaction ID
+        that has already been persisted correctly returns the old event and does
+        *not* produce duplicate messages.
+        """
+
+        txn_id = "something_suitably_random"
+
+        event1, context = self._create_duplicate_event(txn_id)
+
+        ret_event1 = self.get_success(
+            self.handler.handle_new_client_event(self.requester, event1, context)
+        )
+        stream_id1 = ret_event1.internal_metadata.stream_ordering
+
+        self.assertEqual(event1.event_id, ret_event1.event_id)
+
+        event2, context = self._create_duplicate_event(txn_id)
+
+        # We want to test that the deduplication at the persit event end works,
+        # so we want to make sure we test with different events.
+        self.assertNotEqual(event1.event_id, event2.event_id)
+
+        ret_event2 = self.get_success(
+            self.handler.handle_new_client_event(self.requester, event2, context)
+        )
+        stream_id2 = ret_event2.internal_metadata.stream_ordering
+
+        # Assert that the returned values match those from the initial event
+        # rather than the new one.
+        self.assertEqual(ret_event1.event_id, ret_event2.event_id)
+        self.assertEqual(stream_id1, stream_id2)
+
+        # Let's test that calling `persist_event` directly also does the right
+        # thing.
+        event3, context = self._create_duplicate_event(txn_id)
+        self.assertNotEqual(event1.event_id, event3.event_id)
+
+        ret_event3, event_pos3, _ = self.get_success(
+            self.persist_event_storage.persist_event(event3, context)
+        )
+
+        # Assert that the returned values match those from the initial event
+        # rather than the new one.
+        self.assertEqual(ret_event1.event_id, ret_event3.event_id)
+        self.assertEqual(stream_id1, event_pos3.stream)
+
+        # Let's test that calling `persist_events` directly also does the right
+        # thing.
+        event4, context = self._create_duplicate_event(txn_id)
+        self.assertNotEqual(event1.event_id, event3.event_id)
+
+        events, _ = self.get_success(
+            self.persist_event_storage.persist_events([(event3, context)])
+        )
+        ret_event4 = events[0]
+
+        # Assert that the returned values match those from the initial event
+        # rather than the new one.
+        self.assertEqual(ret_event1.event_id, ret_event4.event_id)
+
+    def test_duplicated_txn_id_one_call(self):
+        """Test that we correctly handle duplicates that we try and persist at
+        the same time.
+        """
+
+        txn_id = "something_else_suitably_random"
+
+        # Create two duplicate events to persist at the same time
+        event1, context1 = self._create_duplicate_event(txn_id)
+        event2, context2 = self._create_duplicate_event(txn_id)
+
+        # Ensure their event IDs are different to start with
+        self.assertNotEqual(event1.event_id, event2.event_id)
+
+        events, _ = self.get_success(
+            self.persist_event_storage.persist_events(
+                [(event1, context1), (event2, context2)]
+            )
+        )
+
+        # Check that we've deduplicated the events.
+        self.assertEqual(len(events), 2)
+        self.assertEqual(events[0].event_id, events[1].event_id)