3 files changed, 44 insertions, 0 deletions
diff --git a/changelog.d/13428.feature b/changelog.d/13428.feature
new file mode 100644
index 0000000000..085b61483f
--- /dev/null
+++ b/changelog.d/13428.feature
@@ -0,0 +1 @@
+Add a module API method to translate a room alias into a room ID.
diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index 6d8bf54083..18d6d1058a 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -1452,6 +1452,30 @@ class ModuleApi:
             start_timestamp, end_timestamp
         )
 
+    async def lookup_room_alias(self, room_alias: str) -> Tuple[str, List[str]]:
+        """
+        Get the room ID associated with a room alias.
+
+        Added in Synapse v1.65.0.
+
+        Args:
+            room_alias: The alias to look up.
+
+        Returns:
+            A tuple of:
+                The room ID (str).
+                Hosts likely to be participating in the room ([str]).
+
+        Raises:
+            SynapseError if room alias is invalid or could not be found.
+        """
+        alias = RoomAlias.from_string(room_alias)
+        (room_id, hosts) = await self._hs.get_room_member_handler().lookup_room_alias(
+            alias
+        )
+
+        return room_id.to_string(), hosts
+
 
 class PublicRoomListManager:
     """Contains methods for adding to, removing from and querying whether a room
diff --git a/tests/module_api/test_api.py b/tests/module_api/test_api.py
index 169e29b590..8e05590230 100644
--- a/tests/module_api/test_api.py
+++ b/tests/module_api/test_api.py
@@ -635,6 +635,25 @@ class ModuleApiTestCase(HomeserverTestCase):
             [{"set_tweak": "sound", "value": "default"}]
         )
 
+    def test_lookup_room_alias(self) -> None:
+        """Test that modules can resolve a room alias to a room ID."""
+        password = "password"
+        user_id = self.register_user("user", password)
+        access_token = self.login(user_id, password)
+        room_alias = "my-alias"
+        reference_room_id = self.helper.create_room_as(
+            tok=access_token, extra_content={"room_alias_name": room_alias}
+        )
+        self.assertIsNotNone(reference_room_id)
+
+        (room_id, _) = self.get_success(
+            self.module_api.lookup_room_alias(
+                f"#{room_alias}:{self.module_api.server_name}"
+            )
+        )
+
+        self.assertEqual(room_id, reference_room_id)
+
 
 class ModuleApiWorkerTestCase(BaseMultiWorkerStreamTestCase):
     """For testing ModuleApi functionality in a multi-worker setup"""