Implement MSC2174: move redacts to a content property.

changelog.d/15395.misc

@@ -0,0 +1 @@
+Implement [MSC2174](https://github.com/matrix-org/matrix-spec-proposals/pull/2174) to move the `redacts` key to a `content` property.

synapse/api/room_versions.py

@@ -80,7 +80,8 @@ class RoomVersion:
     limit_notifications_power_levels: bool
     # MSC2175: No longer include the creator in m.room.create events.
     msc2175_implicit_room_creator: bool
-    # MSC2174/MSC2176: Apply updated redaction rules algorithm.
+    # MSC2174/MSC2176: Apply updated redaction rules algorithm, move redacts to
+    # content property.
     msc2176_redaction_rules: bool
     # MSC3083: Support the 'restricted' join_rule.
     msc3083_join_rules: bool

synapse/event_auth.py

@@ -793,7 +793,7 @@ def check_redaction(
     """Check whether the event sender is allowed to redact the target event.
 
     Returns:
-        True if the the sender is allowed to redact the target event if the
+        True if the sender is allowed to redact the target event if the
         target event was created by them.
         False if the sender is allowed to redact the target event with no
         further checks.

synapse/events/__init__.py

@@ -326,7 +326,6 @@ def __init__(
     hashes: DictProperty[Dict[str, str]] = DictProperty("hashes")
     origin: DictProperty[str] = DictProperty("origin")
     origin_server_ts: DictProperty[int] = DictProperty("origin_server_ts")
-    redacts: DefaultDictProperty[Optional[str]] = DefaultDictProperty("redacts", None)
     room_id: DictProperty[str] = DictProperty("room_id")
     sender: DictProperty[str] = DictProperty("sender")
     # TODO state_key should be Optional[str]. This is generally asserted in Synapse
@@ -346,6 +345,13 @@ def event_id(self) -> str:
     def membership(self) -> str:
         return self.content["membership"]
 
+    @property
+    def redacts(self) -> Optional[str]:
+        """MSC2176 moved the redacts field into the content."""
+        if self.room_version.msc2176_redaction_rules:
+            return self.content.get("redacts")
+        return self.get("redacts")
+
     def is_state(self) -> bool:
         return self.get_state_key() is not None
 

synapse/events/builder.py

@@ -173,7 +173,9 @@ async def build(
         if self.is_state():
             event_dict["state_key"] = self._state_key
 
-        if self._redacts is not None:
+        # MSC2174 moves the redacts property to the content, it is invalid to
+        # provide it as a top-level property.
+        if self._redacts is not None and not self.room_version.msc2176_redaction_rules:
             event_dict["redacts"] = self._redacts
 
         if self._origin_server_ts is not None:

synapse/rest/client/room.py

@@ -1096,6 +1096,7 @@ def __init__(self, hs: "HomeServer"):
         super().__init__(hs)
         self.event_creation_handler = hs.get_event_creation_handler()
         self.auth = hs.get_auth()
+        self._store = hs.get_datastores().main
         self._relation_handler = hs.get_relations_handler()
         self._msc3912_enabled = hs.config.experimental.msc3912_enabled
 
@@ -1113,6 +1114,15 @@ async def _do(
     ) -> Tuple[int, JsonDict]:
         content = parse_json_object_from_request(request)
 
+        # Ensure the redacts property in the content matches the one provided in
+        # the URL.
+        room_version = await self._store.get_room_version(room_id)
+        if room_version.msc2176_redaction_rules:
+            if "redacts" in content and content["redacts"] != event_id:
+                raise SynapseError(400, "Cannot provide", Codes.INVALID_PARAM)
+            else:
+                content["redacts"] = event_id
+
         try:
             with_relations = None
             if self._msc3912_enabled and "org.matrix.msc3912.with_relations" in content:
@@ -1128,20 +1138,23 @@ async def _do(
                     requester, txn_id, room_id
                 )
 
+            # Event is not yet redacted, create a new event to redact it.
             if event is None:
+                event_dict = {
+                    "type": EventTypes.Redaction,
+                    "content": content,
+                    "room_id": room_id,
+                    "sender": requester.user.to_string(),
+                }
+                # Earlier room versions had a top-level redacts property.
+                if not room_version.msc2176_redaction_rules:
+                    event_dict["redacts"] = event_id
+
                 (
                     event,
                     _,
                 ) = await self.event_creation_handler.create_and_send_nonmember_event(
-                    requester,
-                    {
-                        "type": EventTypes.Redaction,
-                        "content": content,
-                        "room_id": room_id,
-                        "sender": requester.user.to_string(),
-                        "redacts": event_id,
-                    },
-                    txn_id=txn_id,
+                    requester, event_dict, txn_id=txn_id
                 )
 
                 if with_relations:

tests/events/test_utils.py

@@ -318,7 +318,11 @@ def test_redacts(self) -> None:
         """Redaction events have no special behaviour until MSC2174/MSC2176."""
 
         self.run_test(
-            {"type": "m.room.redaction", "content": {"redacts": "$test2:domain"}},
+            {
+                "type": "m.room.redaction",
+                "content": {"redacts": "$test2:domain"},
+                "redacts": "$test2:domain",
+            },
             {
                 "type": "m.room.redaction",
                 "content": {},
@@ -330,7 +334,11 @@ def test_redacts(self) -> None:
 
         # After MSC2174, redaction events keep the redacts content key.
         self.run_test(
-            {"type": "m.room.redaction", "content": {"redacts": "$test2:domain"}},
+            {
+                "type": "m.room.redaction",
+                "content": {"redacts": "$test2:domain"},
+                "redacts": "$test2:domain",
+            },
             {
                 "type": "m.room.redaction",
                 "content": {"redacts": "$test2:domain"},

tests/rest/client/test_redactions.py

@@ -16,6 +16,7 @@
 from twisted.test.proto_helpers import MemoryReactor
 
 from synapse.api.constants import EventTypes, RelationTypes
+from synapse.api.room_versions import RoomVersions
 from synapse.rest import admin
 from synapse.rest.client import login, room, sync
 from synapse.server import HomeServer
@@ -74,14 +75,15 @@ def _redact_event(
         event_id: str,
         expect_code: int = 200,
         with_relations: Optional[List[str]] = None,
+        content: Optional[JsonDict] = None,
     ) -> JsonDict:
         """Helper function to send a redaction event.
 
         Returns the json body.
         """
         path = "/_matrix/client/r0/rooms/%s/redact/%s" % (room_id, event_id)
 
-        request_content = {}
+        request_content = content or {}
         if with_relations:
             request_content["org.matrix.msc3912.with_relations"] = with_relations
 
@@ -92,7 +94,7 @@ def _redact_event(
         return channel.json_body
 
     def _sync_room_timeline(self, access_token: str, room_id: str) -> List[JsonDict]:
-        channel = self.make_request("GET", "sync", access_token=self.mod_access_token)
+        channel = self.make_request("GET", "sync", access_token=access_token)
         self.assertEqual(channel.code, 200)
         room_sync = channel.json_body["rooms"]["join"][room_id]
         return room_sync["timeline"]["events"]
@@ -466,3 +468,36 @@ def test_redact_relations_txn_id_reuse(self) -> None:
         )
         self.assertIn("body", event_dict["content"], event_dict)
         self.assertEqual("I'm in a thread!", event_dict["content"]["body"])
+
+    def test_content_redaction(self) -> None:
+        """MSC2174 moved the redacts property to the content."""
+        # Create a room with the newer room version.
+        room_id = self.helper.create_room_as(
+            self.mod_user_id,
+            tok=self.mod_access_token,
+            room_version=RoomVersions.MSC2176.identifier,
+        )
+
+        # Create an event.
+        b = self.helper.send(room_id=room_id, tok=self.mod_access_token)
+        event_id = b["event_id"]
+
+        # Attempt to redact it with a bogus event ID.
+        self._redact_event(
+            self.mod_access_token,
+            room_id,
+            event_id,
+            expect_code=400,
+            content={"redacts": "foo"},
+        )
+
+        # Redact it for real.
+        self._redact_event(self.mod_access_token, room_id, event_id)
+
+        # Sync the room, to get the id of the create event
+        timeline = self._sync_room_timeline(self.mod_access_token, room_id)
+        redact_event = timeline[-1]
+        self.assertEqual(redact_event["type"], EventTypes.Redaction)
+        # The redacts key should be in the content.
+        self.assertNotIn("redacts", redact_event)
+        self.assertEquals(redact_event["content"]["redacts"], event_id)