Implement MSC3989 to redact the origin field. (#15393)

This will be done in a future room version, for now an unstable
room version is added which redacts the origin field.

4 files changed, 49 insertions, 1 deletions

diff --git a/changelog.d/15393.misc b/changelog.d/15393.misc
new file mode 100644
index 0000000000..24483c8d78
--- /dev/null
+++ b/changelog.d/15393.misc
@@ -0,0 +1 @@
+Implement [MSC3989](https://github.com/matrix-org/matrix-spec-proposals/pull/3989) redaction algorithm.
diff --git a/synapse/api/room_versions.py b/synapse/api/room_versions.py
index c397920fe5..bc15f2d063 100644
--- a/synapse/api/room_versions.py
+++ b/synapse/api/room_versions.py
@@ -104,6 +104,8 @@ class RoomVersion:
     # support the flag. Unknown flags are ignored by the evaluator, making conditions
     # fail if used.
     msc3931_push_features: Tuple[str, ...]  # values from PushRuleRoomFlag
+    # MSC3989: Redact the origin field.
+    msc3989_redaction_rules: bool
 
 
 class RoomVersions:
@@ -125,6 +127,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=False,
         msc3667_int_only_power_levels=False,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     V2 = RoomVersion(
         "2",
@@ -144,6 +147,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=False,
         msc3667_int_only_power_levels=False,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     V3 = RoomVersion(
         "3",
@@ -163,6 +167,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=False,
         msc3667_int_only_power_levels=False,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     V4 = RoomVersion(
         "4",
@@ -182,6 +187,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=False,
         msc3667_int_only_power_levels=False,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     V5 = RoomVersion(
         "5",
@@ -201,6 +207,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=False,
         msc3667_int_only_power_levels=False,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     V6 = RoomVersion(
         "6",
@@ -220,6 +227,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=False,
         msc3667_int_only_power_levels=False,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     MSC2176 = RoomVersion(
         "org.matrix.msc2176",
@@ -239,6 +247,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=False,
         msc3667_int_only_power_levels=False,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     V7 = RoomVersion(
         "7",
@@ -258,6 +267,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=False,
         msc3667_int_only_power_levels=False,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     V8 = RoomVersion(
         "8",
@@ -277,6 +287,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=False,
         msc3667_int_only_power_levels=False,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     V9 = RoomVersion(
         "9",
@@ -296,6 +307,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=False,
         msc3667_int_only_power_levels=False,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     MSC3787 = RoomVersion(
         "org.matrix.msc3787",
@@ -315,6 +327,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=True,
         msc3667_int_only_power_levels=False,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     V10 = RoomVersion(
         "10",
@@ -334,6 +347,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=True,
         msc3667_int_only_power_levels=True,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     MSC2716v4 = RoomVersion(
         "org.matrix.msc2716v4",
@@ -353,6 +367,7 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=False,
         msc3667_int_only_power_levels=False,
         msc3931_push_features=(),
+        msc3989_redaction_rules=False,
     )
     MSC1767v10 = RoomVersion(
         # MSC1767 (Extensible Events) based on room version "10"
@@ -373,6 +388,27 @@ class RoomVersions:
         msc3787_knock_restricted_join_rule=True,
         msc3667_int_only_power_levels=True,
         msc3931_push_features=(PushRuleRoomFlag.EXTENSIBLE_EVENTS,),
+        msc3989_redaction_rules=False,
+    )
+    MSC3989 = RoomVersion(
+        "org.matrix.msc3989",
+        RoomDisposition.UNSTABLE,
+        EventFormatVersions.ROOM_V4_PLUS,
+        StateResolutionVersions.V2,
+        enforce_key_validity=True,
+        special_case_aliases_auth=False,
+        strict_canonicaljson=True,
+        limit_notifications_power_levels=True,
+        msc2176_redaction_rules=False,
+        msc3083_join_rules=True,
+        msc3375_redaction_rules=True,
+        msc2403_knocking=True,
+        msc2716_historical=False,
+        msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=True,
+        msc3667_int_only_power_levels=True,
+        msc3931_push_features=(),
+        msc3989_redaction_rules=True,
     )
 
 
@@ -392,6 +428,7 @@ KNOWN_ROOM_VERSIONS: Dict[str, RoomVersion] = {
         RoomVersions.MSC3787,
         RoomVersions.V10,
         RoomVersions.MSC2716v4,
+        RoomVersions.MSC3989,
     )
 }
 
diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index c14c7791db..1d5d7491cd 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -106,7 +106,6 @@ def prune_event_dict(room_version: RoomVersion, event_dict: JsonDict) -> JsonDic
         "depth",
         "prev_events",
         "auth_events",
-        "origin",
         "origin_server_ts",
     ]
 
@@ -114,6 +113,10 @@ def prune_event_dict(room_version: RoomVersion, event_dict: JsonDict) -> JsonDic
     if not room_version.msc2176_redaction_rules:
         allowed_keys.extend(["prev_state", "membership"])
 
+    # Room versions before MSC3989 kept the origin field.
+    if not room_version.msc3989_redaction_rules:
+        allowed_keys.append("origin")
+
     event_type = event_dict["type"]
 
     new_content = {}
diff --git a/tests/events/test_utils.py b/tests/events/test_utils.py
index 4174a237ec..c35f58f462 100644
--- a/tests/events/test_utils.py
+++ b/tests/events/test_utils.py
@@ -143,6 +143,13 @@ class PruneEventTestCase(stdlib_unittest.TestCase):
             room_version=RoomVersions.MSC2176,
         )
 
+        # As of MSC3989 we now redact the origin key.
+        self.run_test(
+            {"type": "A", "origin": "example.com"},
+            {"type": "A", "content": {}, "signatures": {}, "unsigned": {}},
+            room_version=RoomVersions.MSC3989,
+        )
+
     def test_unsigned(self) -> None:
         """Ensure that unsigned properties get stripped (except age_ts and replaces_state)."""
         self.run_test(