Merge pull request #5934 from matrix-org/erikj/censor_redactions

Censor redactions in DB after a month

3 files changed, 136 insertions, 1 deletions

diff --git a/synapse/config/server.py b/synapse/config/server.py
index 2abdef0971..c8b9fe2d0f 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -162,6 +162,16 @@ class ServerConfig(Config):
 
         self.mau_trial_days = config.get("mau_trial_days", 0)
 
+        # How long to keep redacted events in the database in unredacted form
+        # before redacting them.
+        redaction_retention_period = config.get("redaction_retention_period", "7d")
+        if redaction_retention_period is not None:
+            self.redaction_retention_period = self.parse_duration(
+                redaction_retention_period
+            )
+        else:
+            self.redaction_retention_period = None
+
         # Options to disable HS
         self.hs_disabled = config.get("hs_disabled", False)
         self.hs_disabled_message = config.get("hs_disabled_message", "")
@@ -718,6 +728,13 @@ class ServerConfig(Config):
         # Defaults to 'true'.
         #
         #allow_per_room_profiles: false
+
+        # How long to keep redacted events in unredacted form in the database. After
+        # this period redacted events get replaced with their redacted form in the DB.
+        #
+        # Defaults to `7d`. Set to `null` to disable.
+        #
+        redaction_retention_period: 7d
         """
             % locals()
         )
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 1958afe1d7..ddf7ab6479 100644
--- a/synapse/storage/events.py
+++ b/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 +263,14 @@ 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
+            )
+
+        if self.hs.config.redaction_retention_period is not None:
+            hs.get_clock().looping_call(_censor_redactions, 5 * 60 * 1000)
+
     @defer.inlineCallbacks
     def _read_forward_extremities(self):
         def fetch(txn):
@@ -1549,6 +1558,98 @@ class EventsStore(
         )
 
     @defer.inlineCallbacks
+    def _censor_redactions(self):
+        """Censors all redactions older than the configured period that haven't
+        been censored yet.
+
+        By censor we mean update the event_json table with the redacted event.
+
+        Returns:
+            Deferred
+        """
+
+        if self.hs.config.redaction_retention_period is None:
+            return
+
+        max_pos = yield self.find_first_stream_ordering_after_ts(
+            self._clock.time_msec() - self.hs.config.redaction_retention_period
+        )
+
+        # We fetch all redactions that:
+        #   1. point to an event we have,
+        #   2. has a stream ordering from before the cut off, and
+        #   3. we haven't yet censored.
+        #
+        # This is limited to 100 events to ensure that we don't try and do too
+        # much at once. We'll get called again so this should eventually catch
+        # up.
+        #
+        # We use the range [-max_pos, max_pos] to handle backfilled events,
+        # which are given negative stream ordering.
+        sql = """
+            SELECT redact_event.event_id, redacts FROM redactions
+            INNER JOIN events AS redact_event USING (event_id)
+            INNER JOIN events AS original_event ON (
+                redact_event.room_id = original_event.room_id
+                AND redacts = original_event.event_id
+            )
+            WHERE NOT have_censored
+            AND ? <= redact_event.stream_ordering AND redact_event.stream_ordering <= ?
+            ORDER BY redact_event.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):
         """
         Returns an estimate of the number of messages sent in the last day.
diff --git a/synapse/storage/schema/delta/56/redaction_censor.sql b/synapse/storage/schema/delta/56/redaction_censor.sql
new file mode 100644
index 0000000000..fe51b02309
--- /dev/null
+++ b/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;