Add basic editing support

synapse/events/utils.py

@@ -346,7 +346,7 @@ class EventClientSerializer(object):
             defer.returnValue(event)
 
         event_id = event.event_id
-        event = serialize_event(event, time_now, **kwargs)
+        serialized_event = serialize_event(event, time_now, **kwargs)
 
         # If MSC1849 is enabled then we need to look if thre are any relations
         # we need to bundle in with the event
@@ -359,14 +359,36 @@ class EventClientSerializer(object):
             )
 
             if annotations.chunk:
-                r = event["unsigned"].setdefault("m.relations", {})
+                r = serialized_event["unsigned"].setdefault("m.relations", {})
                 r[RelationTypes.ANNOTATION] = annotations.to_dict()
 
             if references.chunk:
-                r = event["unsigned"].setdefault("m.relations", {})
+                r = serialized_event["unsigned"].setdefault("m.relations", {})
                 r[RelationTypes.REFERENCES] = references.to_dict()
 
-        defer.returnValue(event)
+            edit = None
+            if event.type == EventTypes.Message:
+                edit = yield self.store.get_applicable_edit(
+                    event.event_id, event.type, event.sender,
+                )
+
+            if edit:
+                # If there is an edit replace the content, preserving existing
+                # relations.
+
+                relations = event.content.get("m.relates_to")
+                serialized_event["content"] = edit.content.get("m.new_content", {})
+                if relations:
+                    serialized_event["content"]["m.relates_to"] = relations
+                else:
+                    serialized_event["content"].pop("m.relates_to", None)
+
+                r = serialized_event["unsigned"].setdefault("m.relations", {})
+                r[RelationTypes.REPLACES] = {
+                    "event_id": edit.event_id,
+                }
+
+        defer.returnValue(serialized_event)
 
     def serialize_events(self, events, time_now, **kwargs):
         """Serializes multiple events.

synapse/replication/slave/storage/events.py

@@ -143,3 +143,4 @@ class SlavedEventStore(EventFederationWorkerStore,
         if relates_to:
             self.get_relations_for_event.invalidate_many((relates_to,))
             self.get_aggregation_groups_for_event.invalidate_many((relates_to,))
+            self.get_applicable_edit.invalidate_many((relates_to,))

synapse/storage/relations.py

@@ -17,11 +17,13 @@ import logging
 
 import attr
 
-from synapse.api.constants import RelationTypes
+from twisted.internet import defer
+
+from synapse.api.constants import EventTypes, RelationTypes
 from synapse.api.errors import SynapseError
 from synapse.storage._base import SQLBaseStore
 from synapse.storage.stream import generate_pagination_where_clause
-from synapse.util.caches.descriptors import cached
+from synapse.util.caches.descriptors import cached, cachedInlineCallbacks
 
 logger = logging.getLogger(__name__)
 
@@ -312,6 +314,59 @@ class RelationsWorkerStore(SQLBaseStore):
             "get_aggregation_groups_for_event", _get_aggregation_groups_for_event_txn
         )
 
+    @cachedInlineCallbacks(tree=True)
+    def get_applicable_edit(self, event_id, event_type, sender):
+        """Get the most recent edit (if any) that has happened for the given
+        event.
+
+        Correctly handles checking whether edits were allowed to happen.
+
+        Args:
+            event_id (str): The original event ID
+            event_type (str): The original event type
+            sender (str): The original event sender
+
+        Returns:
+            Deferred[EventBase|None]: Returns the most recent edit, if any.
+        """
+
+        # We only allow edits for `m.room.message` events that have the same sender
+        # and event type. We can't assert these things during regular event auth so
+        # we have to do the post hoc.
+
+        if event_type != EventTypes.Message:
+            return
+
+        sql = """
+            SELECT event_id, origin_server_ts FROM events
+            INNER JOIN event_relations USING (event_id)
+            WHERE
+                relates_to_id = ?
+                AND relation_type = ?
+                AND type = ?
+                AND sender = ?
+            ORDER by origin_server_ts DESC, event_id DESC
+            LIMIT 1
+        """
+
+        def _get_applicable_edit_txn(txn):
+            txn.execute(
+                sql, (event_id, RelationTypes.REPLACES, event_type, sender)
+            )
+            row = txn.fetchone()
+            if row:
+                return row[0]
+
+        edit_id = yield self.runInteraction(
+            "get_applicable_edit", _get_applicable_edit_txn
+        )
+
+        if not edit_id:
+            return
+
+        edit_event = yield self.get_event(edit_id, allow_none=True)
+        defer.returnValue(edit_event)
+
 
 class RelationsStore(RelationsWorkerStore):
     def _handle_event_relations(self, txn, event):
@@ -357,3 +412,4 @@ class RelationsStore(RelationsWorkerStore):
         txn.call_after(
             self.get_aggregation_groups_for_event.invalidate_many, (parent_id,)
         )
+        txn.call_after(self.get_applicable_edit.invalidate_many, (parent_id,))