Put MSC2666 endpoint behind an experimental flag (#19219)

changelog.d/19219.misc

@@ -0,0 +1 @@
+Require an experimental feature flag to be enabled in order for the unstable [MSC2666](https://github.com/matrix-org/matrix-spec-proposals/pull/2666) endpoint (`/_matrix/client/unstable/uk.half-shot.msc2666/user/mutual_rooms`) to be available.

docs/upgrade.md

@@ -117,6 +117,17 @@ each upgrade are complete before moving on to the next upgrade, to avoid
 stacking them up. You can monitor the currently running background updates with
 [the Admin API](usage/administration/admin_api/background_updates.html#status).
 
+# Upgrading to v1.144.0
+
+## Unstable mutual rooms endpoint is now behind an experimental feature flag
+
+The unstable mutual rooms endpoint from
+[MSC2666](https://github.com/matrix-org/matrix-spec-proposals/pull/2666)
+(`/_matrix/client/unstable/uk.half-shot.msc2666/user/mutual_rooms`) is now
+disabled by default.  If you rely on this unstable endpoint, you must now set
+`experimental_features.msc2666_enabled: true` in your configuration to keep
+using it.
+
 # Upgrading to v1.143.0
 
 ## Dropping support for PostgreSQL 13

synapse/config/experimental.py

@@ -438,6 +438,9 @@ class ExperimentalConfig(Config):
         # previously calculated push actions.
         self.msc2654_enabled: bool = experimental.get("msc2654_enabled", False)
 
+        # MSC2666: Query mutual rooms between two users.
+        self.msc2666_enabled: bool = experimental.get("msc2666_enabled", False)
+
         # MSC2815 (allow room moderators to view redacted event content)
         self.msc2815_enabled: bool = experimental.get("msc2815_enabled", False)
 

synapse/rest/client/mutual_rooms.py

@@ -90,4 +90,5 @@ class UserMutualRoomsServlet(RestServlet):
 
 
 def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
-    UserMutualRoomsServlet(hs).register(http_server)
+    if hs.config.experimental.msc2666_enabled:
+        UserMutualRoomsServlet(hs).register(http_server)

synapse/rest/client/versions.py

@@ -124,7 +124,7 @@ class VersionsRestServlet(RestServlet):
                     # Implements additional endpoints as described in MSC2432
                     "org.matrix.msc2432": True,
                     # Implements additional endpoints as described in MSC2666
-                    "uk.half-shot.msc2666.query_mutual_rooms": True,
+                    "uk.half-shot.msc2666.query_mutual_rooms": self.config.experimental.msc2666_enabled,
                     # Whether new rooms will be set to encrypted or not (based on presets).
                     "io.element.e2ee_forced.public": self.e2ee_forced_public,
                     "io.element.e2ee_forced.private": self.e2ee_forced_private,

tests/rest/client/test_mutual_rooms.py

@@ -43,6 +43,12 @@ class UserMutualRoomsTest(unittest.HomeserverTestCase):
         mutual_rooms.register_servlets,
     ]
 
+    def default_config(self) -> dict:
+        config = super().default_config()
+        experimental = config.setdefault("experimental_features", {})
+        experimental.setdefault("msc2666_enabled", True)
+        return config
+
     def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         config = self.default_config()
         return self.setup_test_homeserver(config=config)
@@ -58,6 +64,21 @@ class UserMutualRoomsTest(unittest.HomeserverTestCase):
             access_token=token,
         )
 
+    @unittest.override_config({"experimental_features": {"msc2666_enabled": False}})
+    def test_mutual_rooms_no_experimental_flag(self) -> None:
+        """
+        The endpoint should 404 if the experimental flag is not enabled.
+        """
+        # Register a user.
+        u1 = self.register_user("user1", "pass")
+        u1_token = self.login(u1, "pass")
+
+        # Check that we're unable to query the endpoint due to the endpoint
+        # being unrecognised.
+        channel = self._get_mutual_rooms(u1_token, "@not-used:test")
+        self.assertEqual(404, channel.code, channel.result)
+        self.assertEqual("M_UNRECOGNIZED", channel.json_body["errcode"], channel.result)
+
     def test_shared_room_list_public(self) -> None:
         """
         A room should show up in the shared list of rooms between two users