Censor redactions in DB after a month

synapse/storage/events.py

@@ -23,7 +23,7 @@ from functools import wraps
 from six import iteritems, text_type
 from six.moves import range
 
-from canonicaljson import json
+from canonicaljson import encode_canonical_json, json
 from prometheus_client import Counter, Histogram
 
 from twisted.internet import defer
@@ -33,6 +33,7 @@ from synapse.api.constants import EventTypes
 from synapse.api.errors import SynapseError
 from synapse.events import EventBase  # noqa: F401
 from synapse.events.snapshot import EventContext  # noqa: F401
+from synapse.events.utils import prune_event_dict
 from synapse.logging.context import PreserveLoggingContext, make_deferred_yieldable
 from synapse.logging.utils import log_function
 from synapse.metrics import BucketCollector
@@ -262,6 +263,13 @@ class EventsStore(
 
         hs.get_clock().looping_call(read_forward_extremities, 60 * 60 * 1000)
 
+        def _censor_redactions():
+            return run_as_background_process(
+                "_censor_redactions", self._censor_redactions
+            )
+
+        hs.get_clock().looping_call(_censor_redactions, 10 * 60 * 1000)
+
     @defer.inlineCallbacks
     def _read_forward_extremities(self):
         def fetch(txn):
@@ -1548,6 +1556,84 @@ class EventsStore(
             (event.event_id, event.redacts),
         )
 
+    @defer.inlineCallbacks
+    def _censor_redactions(self):
+        """Censors all redactions older than a month that haven't been censored.
+
+        By censor we mean update the event_json table with the redacted event.
+
+        Returns:
+            Deferred
+        """
+
+        if self.stream_ordering_month_ago is None:
+            return
+
+        max_pos = self.stream_ordering_month_ago
+
+        # We fetch all redactions that point to an event that we have that has
+        # a stream ordering from over a month ago, that we haven't yet censored
+        # in the DB.
+        sql = """
+            SELECT er.event_id, redacts FROM redactions
+            INNER JOIN events AS er USING (event_id)
+            INNER JOIN events AS eb ON (er.room_id = eb.room_id AND redacts = eb.event_id)
+            WHERE NOT have_censored
+            AND ? <= er.stream_ordering AND er.stream_ordering <= ?
+            ORDER BY er.stream_ordering ASC
+            LIMIT ?
+        """
+
+        rows = yield self._execute(
+            "_censor_redactions_fetch", None, sql, -max_pos, max_pos, 100
+        )
+
+        updates = []
+
+        for redaction_id, event_id in rows:
+            redaction_event = yield self.get_event(redaction_id, allow_none=True)
+            original_event = yield self.get_event(
+                event_id, allow_rejected=True, allow_none=True
+            )
+
+            # The SQL above ensures that we have both the redaction and
+            # original event, so if the `get_event` calls return None it
+            # means that the redaction wasn't allowed. Either way we know that
+            # the result won't change so we mark the fact that we've checked.
+            if (
+                redaction_event
+                and original_event
+                and original_event.internal_metadata.is_redacted()
+            ):
+                # Redaction was allowed
+                pruned_json = encode_canonical_json(
+                    prune_event_dict(original_event.get_dict())
+                )
+            else:
+                # Redaction wasn't allowed
+                pruned_json = None
+
+            updates.append((redaction_id, event_id, pruned_json))
+
+        def _update_censor_txn(txn):
+            for redaction_id, event_id, pruned_json in updates:
+                if pruned_json:
+                    self._simple_update_one_txn(
+                        txn,
+                        table="event_json",
+                        keyvalues={"event_id": event_id},
+                        updatevalues={"json": pruned_json},
+                    )
+
+                self._simple_update_one_txn(
+                    txn,
+                    table="redactions",
+                    keyvalues={"event_id": redaction_id},
+                    updatevalues={"have_censored": True},
+                )
+
+        yield self.runInteraction("_update_censor_txn", _update_censor_txn)
+
     @defer.inlineCallbacks
     def count_daily_messages(self):
         """

synapse/storage/schema/delta/56/redaction_censor.sql

@@ -0,0 +1,17 @@
+/* Copyright 2019 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.
+ */
+
+ALTER TABLE redactions ADD COLUMN have_censored BOOL NOT NULL DEFAULT false;
+CREATE INDEX redactions_have_censored ON redactions(event_id) WHERE not have_censored;

tests/storage/test_redaction.py

@@ -17,6 +17,8 @@
 
 from mock import Mock
 
+from canonicaljson import json
+
 from twisted.internet import defer
 
 from synapse.api.constants import EventTypes, Membership
@@ -286,3 +288,72 @@ class RedactionTestCase(unittest.HomeserverTestCase):
         self.assertEqual(
             fetched.unsigned["redacted_because"].event_id, redaction_event_id2
         )
+
+    def test_redact_censor(self):
+        """Test that a redacted event gets censored in the DB after a month
+        """
+
+        self.get_success(
+            self.inject_room_member(self.room1, self.u_alice, Membership.JOIN)
+        )
+
+        msg_event = self.get_success(self.inject_message(self.room1, self.u_alice, "t"))
+
+        # Check event has not been redacted:
+        event = self.get_success(self.store.get_event(msg_event.event_id))
+
+        self.assertObjectHasAttributes(
+            {
+                "type": EventTypes.Message,
+                "user_id": self.u_alice.to_string(),
+                "content": {"body": "t", "msgtype": "message"},
+            },
+            event,
+        )
+
+        self.assertFalse("redacted_because" in event.unsigned)
+
+        # Redact event
+        reason = "Because I said so"
+        self.get_success(
+            self.inject_redaction(self.room1, msg_event.event_id, self.u_alice, reason)
+        )
+
+        event = self.get_success(self.store.get_event(msg_event.event_id))
+
+        self.assertTrue("redacted_because" in event.unsigned)
+
+        self.assertObjectHasAttributes(
+            {
+                "type": EventTypes.Message,
+                "user_id": self.u_alice.to_string(),
+                "content": {},
+            },
+            event,
+        )
+
+        event_json = self.get_success(
+            self.store._simple_select_one_onecol(
+                table="event_json",
+                keyvalues={"event_id": msg_event.event_id},
+                retcol="json",
+            )
+        )
+
+        self.assert_dict(
+            {"content": {"body": "t", "msgtype": "message"}}, json.loads(event_json)
+        )
+
+        # Advance by 30 days
+        self.reactor.advance(60 * 60 * 24 * 31)
+        self.reactor.advance(60 * 60 * 2)
+
+        event_json = self.get_success(
+            self.store._simple_select_one_onecol(
+                table="event_json",
+                keyvalues={"event_id": msg_event.event_id},
+                retcol="json",
+            )
+        )
+
+        self.assert_dict({"content": {}}, json.loads(event_json))