MSC3244 room capabilities implementation (#10283)

3 files changed, 46 insertions, 3 deletions

diff --git a/synapse/api/room_versions.py b/synapse/api/room_versions.py
index a20abc5a65..8dd33dcb83 100644
--- a/synapse/api/room_versions.py
+++ b/synapse/api/room_versions.py
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import Dict
+from typing import Callable, Dict, Optional
 
 import attr
 
@@ -208,5 +208,39 @@ KNOWN_ROOM_VERSIONS: Dict[str, RoomVersion] = {
         RoomVersions.MSC3083,
         RoomVersions.V7,
     )
-    # Note that we do not include MSC2043 here unless it is enabled in the config.
+}
+
+
+@attr.s(slots=True, frozen=True, auto_attribs=True)
+class RoomVersionCapability:
+    """An object which describes the unique attributes of a room version."""
+
+    identifier: str  # the identifier for this capability
+    preferred_version: Optional[RoomVersion]
+    support_check_lambda: Callable[[RoomVersion], bool]
+
+
+MSC3244_CAPABILITIES = {
+    cap.identifier: {
+        "preferred": cap.preferred_version.identifier
+        if cap.preferred_version is not None
+        else None,
+        "support": [
+            v.identifier
+            for v in KNOWN_ROOM_VERSIONS.values()
+            if cap.support_check_lambda(v)
+        ],
+    }
+    for cap in (
+        RoomVersionCapability(
+            "knock",
+            RoomVersions.V7,
+            lambda room_version: room_version.msc2403_knocking,
+        ),
+        RoomVersionCapability(
+            "restricted",
+            None,
+            lambda room_version: room_version.msc3083_join_rules,
+        ),
+    )
 }
diff --git a/synapse/config/experimental.py b/synapse/config/experimental.py
index e25ccba9ac..040c4504d8 100644
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -32,3 +32,6 @@ class ExperimentalConfig(Config):
 
         # MSC2716 (backfill existing history)
         self.msc2716_enabled: bool = experimental.get("msc2716_enabled", False)
+
+        # MSC3244 (room version capabilities)
+        self.msc3244_enabled: bool = experimental.get("msc3244_enabled", False)
diff --git a/synapse/rest/client/v2_alpha/capabilities.py b/synapse/rest/client/v2_alpha/capabilities.py
index 6a24021484..88e3aac797 100644
--- a/synapse/rest/client/v2_alpha/capabilities.py
+++ b/synapse/rest/client/v2_alpha/capabilities.py
@@ -14,7 +14,7 @@
 import logging
 from typing import TYPE_CHECKING, Tuple
 
-from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, MSC3244_CAPABILITIES
 from synapse.http.servlet import RestServlet
 from synapse.http.site import SynapseRequest
 from synapse.types import JsonDict
@@ -55,6 +55,12 @@ class CapabilitiesRestServlet(RestServlet):
                 "m.change_password": {"enabled": change_password},
             }
         }
+
+        if self.config.experimental.msc3244_enabled:
+            response["capabilities"]["m.room_versions"][
+                "org.matrix.msc3244.room_capabilities"
+            ] = MSC3244_CAPABILITIES
+
         return 200, response