Fix dummy event insertion consent bug (#6053)

Fixes #5905

5 files changed, 266 insertions, 39 deletions

diff --git a/changelog.d/6053.bugfix b/changelog.d/6053.bugfix
new file mode 100644
index 0000000000..6311157bf6
--- /dev/null
+++ b/changelog.d/6053.bugfix
@@ -0,0 +1 @@
+Prevent exceptions being logged when extremity-cleanup events fail due to lack of user consent to the terms of service.
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 1f8272784e..0f8cce8ffe 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -222,6 +222,13 @@ class MessageHandler(object):
         }
 
 
+# The duration (in ms) after which rooms should be removed
+# `_rooms_to_exclude_from_dummy_event_insertion` (with the effect that we will try
+# to generate a dummy event for them once more)
+#
+_DUMMY_EVENT_ROOM_EXCLUSION_EXPIRY = 7 * 24 * 60 * 60 * 1000
+
+
 class EventCreationHandler(object):
     def __init__(self, hs):
         self.hs = hs
@@ -258,6 +265,13 @@ class EventCreationHandler(object):
             self.config.block_events_without_consent_error
         )
 
+        # Rooms which should be excluded from dummy insertion. (For instance,
+        # those without local users who can send events into the room).
+        #
+        # map from room id to time-of-last-attempt.
+        #
+        self._rooms_to_exclude_from_dummy_event_insertion = {}  # type: dict[str, int]
+
         # we need to construct a ConsentURIBuilder here, as it checks that the necessary
         # config options, but *only* if we have a configuration for which we are
         # going to need it.
@@ -888,9 +902,11 @@ class EventCreationHandler(object):
         """Background task to send dummy events into rooms that have a large
         number of extremities
         """
-
+        self._expire_rooms_to_exclude_from_dummy_event_insertion()
         room_ids = yield self.store.get_rooms_with_many_extremities(
-            min_count=10, limit=5
+            min_count=10,
+            limit=5,
+            room_id_filter=self._rooms_to_exclude_from_dummy_event_insertion.keys(),
         )
 
         for room_id in room_ids:
@@ -904,32 +920,61 @@ class EventCreationHandler(object):
             members = yield self.state.get_current_users_in_room(
                 room_id, latest_event_ids=latest_event_ids
             )
+            dummy_event_sent = False
+            for user_id in members:
+                if not self.hs.is_mine_id(user_id):
+                    continue
+                requester = create_requester(user_id)
+                try:
+                    event, context = yield self.create_event(
+                        requester,
+                        {
+                            "type": "org.matrix.dummy_event",
+                            "content": {},
+                            "room_id": room_id,
+                            "sender": user_id,
+                        },
+                        prev_events_and_hashes=prev_events_and_hashes,
+                    )
 
-            user_id = None
-            for member in members:
-                if self.hs.is_mine_id(member):
-                    user_id = member
-                    break
-
-            if not user_id:
-                # We don't have a joined user.
-                # TODO: We should do something here to stop the room from
-                # appearing next time.
-                continue
+                    event.internal_metadata.proactively_send = False
 
-            requester = create_requester(user_id)
+                    yield self.send_nonmember_event(
+                        requester, event, context, ratelimit=False
+                    )
+                    dummy_event_sent = True
+                    break
+                except ConsentNotGivenError:
+                    logger.info(
+                        "Failed to send dummy event into room %s for user %s due to "
+                        "lack of consent. Will try another user" % (room_id, user_id)
+                    )
+                except AuthError:
+                    logger.info(
+                        "Failed to send dummy event into room %s for user %s due to "
+                        "lack of power. Will try another user" % (room_id, user_id)
+                    )
 
-            event, context = yield self.create_event(
-                requester,
-                {
-                    "type": "org.matrix.dummy_event",
-                    "content": {},
-                    "room_id": room_id,
-                    "sender": user_id,
-                },
-                prev_events_and_hashes=prev_events_and_hashes,
+            if not dummy_event_sent:
+                # Did not find a valid user in the room, so remove from future attempts
+                # Exclusion is time limited, so the room will be rechecked in the future
+                # dependent on _DUMMY_EVENT_ROOM_EXCLUSION_EXPIRY
+                logger.info(
+                    "Failed to send dummy event into room %s. Will exclude it from "
+                    "future attempts until cache expires" % (room_id,)
+                )
+                now = self.clock.time_msec()
+                self._rooms_to_exclude_from_dummy_event_insertion[room_id] = now
+
+    def _expire_rooms_to_exclude_from_dummy_event_insertion(self):
+        expire_before = self.clock.time_msec() - _DUMMY_EVENT_ROOM_EXCLUSION_EXPIRY
+        to_expire = set()
+        for room_id, time in self._rooms_to_exclude_from_dummy_event_insertion.items():
+            if time < expire_before:
+                to_expire.add(room_id)
+        for room_id in to_expire:
+            logger.debug(
+                "Expiring room id %s from dummy event insertion exclusion cache",
+                room_id,
             )
-
-            event.internal_metadata.proactively_send = False
-
-            yield self.send_nonmember_event(requester, event, context, ratelimit=False)
+            del self._rooms_to_exclude_from_dummy_event_insertion[room_id]
diff --git a/synapse/storage/event_federation.py b/synapse/storage/event_federation.py
index 4f500d893e..f5e8c39262 100644
--- a/synapse/storage/event_federation.py
+++ b/synapse/storage/event_federation.py
@@ -12,6 +12,7 @@
 # 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 random
 
@@ -190,12 +191,13 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore, SQLBas
             room_id,
         )
 
-    def get_rooms_with_many_extremities(self, min_count, limit):
+    def get_rooms_with_many_extremities(self, min_count, limit, room_id_filter):
         """Get the top rooms with at least N extremities.
 
         Args:
             min_count (int): The minimum number of extremities
             limit (int): The maximum number of rooms to return.
+            room_id_filter (iterable[str]): room_ids to exclude from the results
 
         Returns:
             Deferred[list]: At most `limit` room IDs that have at least
@@ -203,15 +205,25 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore, SQLBas
         """
 
         def _get_rooms_with_many_extremities_txn(txn):
+            where_clause = "1=1"
+            if room_id_filter:
+                where_clause = "room_id NOT IN (%s)" % (
+                    ",".join("?" for _ in room_id_filter),
+                )
+
             sql = """
                 SELECT room_id FROM event_forward_extremities
+                WHERE %s
                 GROUP BY room_id
                 HAVING count(*) > ?
                 ORDER BY count(*) DESC
                 LIMIT ?
-            """
+            """ % (
+                where_clause,
+            )
 
-            txn.execute(sql, (min_count, limit))
+            query_args = list(itertools.chain(room_id_filter, [min_count, limit]))
+            txn.execute(sql, query_args)
             return [room_id for room_id, in txn]
 
         return self.runInteraction(
diff --git a/tests/storage/test_cleanup_extrems.py b/tests/storage/test_cleanup_extrems.py
index e9e2d5337c..34f9c72709 100644
--- a/tests/storage/test_cleanup_extrems.py
+++ b/tests/storage/test_cleanup_extrems.py
@@ -14,7 +14,13 @@
 # limitations under the License.
 
 import os.path
+from unittest.mock import patch
 
+from mock import Mock
+
+import synapse.rest.admin
+from synapse.api.constants import EventTypes
+from synapse.rest.client.v1 import login, room
 from synapse.storage import prepare_database
 from synapse.types import Requester, UserID
 
@@ -225,6 +231,14 @@ class CleanupExtremBackgroundUpdateStoreTestCase(HomeserverTestCase):
 
 
 class CleanupExtremDummyEventsTestCase(HomeserverTestCase):
+    CONSENT_VERSION = "1"
+    EXTREMITIES_COUNT = 50
+    servlets = [
+        synapse.rest.admin.register_servlets_for_client_rest_resource,
+        login.register_servlets,
+        room.register_servlets,
+    ]
+
     def make_homeserver(self, reactor, clock):
         config = self.default_config()
         config["cleanup_extremities_with_dummy_events"] = True
@@ -233,28 +247,39 @@ class CleanupExtremDummyEventsTestCase(HomeserverTestCase):
     def prepare(self, reactor, clock, homeserver):
         self.store = homeserver.get_datastore()
         self.room_creator = homeserver.get_room_creation_handler()
+        self.event_creator_handler = homeserver.get_event_creation_handler()
 
         # Create a test user and room
-        self.user = UserID("alice", "test")
+        self.user = UserID.from_string(self.register_user("user1", "password"))
+        self.token1 = self.login("user1", "password")
         self.requester = Requester(self.user, None, False, None, None)
         info = self.get_success(self.room_creator.create_room(self.requester, {}))
         self.room_id = info["room_id"]
+        self.event_creator = homeserver.get_event_creation_handler()
+        homeserver.config.user_consent_version = self.CONSENT_VERSION
 
     def test_send_dummy_event(self):
-        # Create a bushy graph with 50 extremities.
-
-        event_id_start = self.create_and_send_event(self.room_id, self.user)
+        self._create_extremity_rich_graph()
 
-        for _ in range(50):
-            self.create_and_send_event(
-                self.room_id, self.user, prev_event_ids=[event_id_start]
-            )
+        # Pump the reactor repeatedly so that the background updates have a
+        # chance to run.
+        self.pump(10 * 60)
 
         latest_event_ids = self.get_success(
             self.store.get_latest_event_ids_in_room(self.room_id)
         )
-        self.assertEqual(len(latest_event_ids), 50)
+        self.assertTrue(len(latest_event_ids) < 10, len(latest_event_ids))
 
+    @patch("synapse.handlers.message._DUMMY_EVENT_ROOM_EXCLUSION_EXPIRY", new=0)
+    def test_send_dummy_events_when_insufficient_power(self):
+        self._create_extremity_rich_graph()
+        # Criple power levels
+        self.helper.send_state(
+            self.room_id,
+            EventTypes.PowerLevels,
+            body={"users": {str(self.user): -1}},
+            tok=self.token1,
+        )
         # Pump the reactor repeatedly so that the background updates have a
         # chance to run.
         self.pump(10 * 60)
@@ -262,4 +287,108 @@ class CleanupExtremDummyEventsTestCase(HomeserverTestCase):
         latest_event_ids = self.get_success(
             self.store.get_latest_event_ids_in_room(self.room_id)
         )
+        # Check that the room has not been pruned
+        self.assertTrue(len(latest_event_ids) > 10)
+
+        # New user with regular levels
+        user2 = self.register_user("user2", "password")
+        token2 = self.login("user2", "password")
+        self.helper.join(self.room_id, user2, tok=token2)
+        self.pump(10 * 60)
+
+        latest_event_ids = self.get_success(
+            self.store.get_latest_event_ids_in_room(self.room_id)
+        )
+        self.assertTrue(len(latest_event_ids) < 10, len(latest_event_ids))
+
+    @patch("synapse.handlers.message._DUMMY_EVENT_ROOM_EXCLUSION_EXPIRY", new=0)
+    def test_send_dummy_event_without_consent(self):
+        self._create_extremity_rich_graph()
+        self._enable_consent_checking()
+
+        # Pump the reactor repeatedly so that the background updates have a
+        # chance to run. Attempt to add dummy event with user that has not consented
+        # Check that dummy event send fails.
+        self.pump(10 * 60)
+        latest_event_ids = self.get_success(
+            self.store.get_latest_event_ids_in_room(self.room_id)
+        )
+        self.assertTrue(len(latest_event_ids) == self.EXTREMITIES_COUNT)
+
+        # Create new user, and add consent
+        user2 = self.register_user("user2", "password")
+        token2 = self.login("user2", "password")
+        self.get_success(
+            self.store.user_set_consent_version(user2, self.CONSENT_VERSION)
+        )
+        self.helper.join(self.room_id, user2, tok=token2)
+
+        # Background updates should now cause a dummy event to be added to the graph
+        self.pump(10 * 60)
+
+        latest_event_ids = self.get_success(
+            self.store.get_latest_event_ids_in_room(self.room_id)
+        )
         self.assertTrue(len(latest_event_ids) < 10, len(latest_event_ids))
+
+    @patch("synapse.handlers.message._DUMMY_EVENT_ROOM_EXCLUSION_EXPIRY", new=250)
+    def test_expiry_logic(self):
+        """Simple test to ensure that _expire_rooms_to_exclude_from_dummy_event_insertion()
+        expires old entries correctly.
+        """
+        self.event_creator_handler._rooms_to_exclude_from_dummy_event_insertion[
+            "1"
+        ] = 100000
+        self.event_creator_handler._rooms_to_exclude_from_dummy_event_insertion[
+            "2"
+        ] = 200000
+        self.event_creator_handler._rooms_to_exclude_from_dummy_event_insertion[
+            "3"
+        ] = 300000
+        self.event_creator_handler._expire_rooms_to_exclude_from_dummy_event_insertion()
+        # All entries within time frame
+        self.assertEqual(
+            len(
+                self.event_creator_handler._rooms_to_exclude_from_dummy_event_insertion
+            ),
+            3,
+        )
+        # Oldest room to expire
+        self.pump(1)
+        self.event_creator_handler._expire_rooms_to_exclude_from_dummy_event_insertion()
+        self.assertEqual(
+            len(
+                self.event_creator_handler._rooms_to_exclude_from_dummy_event_insertion
+            ),
+            2,
+        )
+        # All rooms to expire
+        self.pump(2)
+        self.assertEqual(
+            len(
+                self.event_creator_handler._rooms_to_exclude_from_dummy_event_insertion
+            ),
+            0,
+        )
+
+    def _create_extremity_rich_graph(self):
+        """Helper method to create bushy graph on demand"""
+
+        event_id_start = self.create_and_send_event(self.room_id, self.user)
+
+        for _ in range(self.EXTREMITIES_COUNT):
+            self.create_and_send_event(
+                self.room_id, self.user, prev_event_ids=[event_id_start]
+            )
+
+        latest_event_ids = self.get_success(
+            self.store.get_latest_event_ids_in_room(self.room_id)
+        )
+        self.assertEqual(len(latest_event_ids), 50)
+
+    def _enable_consent_checking(self):
+        """Helper method to enable consent checking"""
+        self.event_creator._block_events_without_consent_error = "No consent from user"
+        consent_uri_builder = Mock()
+        consent_uri_builder.build_user_consent_uri.return_value = "http://example.com"
+        self.event_creator._consent_uri_builder = consent_uri_builder
diff --git a/tests/storage/test_event_federation.py b/tests/storage/test_event_federation.py
index 86c7ac350d..b58386994e 100644
--- a/tests/storage/test_event_federation.py
+++ b/tests/storage/test_event_federation.py
@@ -75,3 +75,43 @@ class EventFederationWorkerStoreTestCase(tests.unittest.TestCase):
             el = r[i]
             depth = el[2]
             self.assertLessEqual(5, depth)
+
+    @defer.inlineCallbacks
+    def test_get_rooms_with_many_extremities(self):
+        room1 = "#room1"
+        room2 = "#room2"
+        room3 = "#room3"
+
+        def insert_event(txn, i, room_id):
+            event_id = "$event_%i:local" % i
+            txn.execute(
+                (
+                    "INSERT INTO event_forward_extremities (room_id, event_id) "
+                    "VALUES (?, ?)"
+                ),
+                (room_id, event_id),
+            )
+
+        for i in range(0, 20):
+            yield self.store.runInteraction("insert", insert_event, i, room1)
+            yield self.store.runInteraction("insert", insert_event, i, room2)
+            yield self.store.runInteraction("insert", insert_event, i, room3)
+
+        # Test simple case
+        r = yield self.store.get_rooms_with_many_extremities(5, 5, [])
+        self.assertEqual(len(r), 3)
+
+        # Does filter work?
+
+        r = yield self.store.get_rooms_with_many_extremities(5, 5, [room1])
+        self.assertTrue(room2 in r)
+        self.assertTrue(room3 in r)
+        self.assertEqual(len(r), 2)
+
+        r = yield self.store.get_rooms_with_many_extremities(5, 5, [room1, room2])
+        self.assertEqual(r, [room3])
+
+        # Does filter and limit work?
+
+        r = yield self.store.get_rooms_with_many_extremities(5, 1, [room1])
+        self.assertTrue(r == [room2] or r == [room3])