Allow ThirdPartyEventRules modules to manipulate public room state (#8292)

This PR allows `ThirdPartyEventRules` modules to view, manipulate and block changes to the state of whether a room is published in the public rooms directory.

While the idea of whether a room is in the public rooms list is not kept within an event in the room, `ThirdPartyEventRules` generally deal with controlling which modifications can happen to a room. Public rooms fits within that idea, even if its toggle state isn't controlled through a state event.

synapse/module_api/__init__.py

@@ -14,13 +14,18 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
+from typing import TYPE_CHECKING
 
 from twisted.internet import defer
 
+from synapse.http.client import SimpleHttpClient
 from synapse.http.site import SynapseRequest
 from synapse.logging.context import make_deferred_yieldable, run_in_background
 from synapse.types import UserID
 
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
 """
 This package defines the 'stable' API which can be used by extension modules which
 are loaded into Synapse.
@@ -43,6 +48,27 @@ class ModuleApi:
         self._auth = hs.get_auth()
         self._auth_handler = auth_handler
 
+        # We expose these as properties below in order to attach a helpful docstring.
+        self._http_client = hs.get_simple_http_client()  # type: SimpleHttpClient
+        self._public_room_list_manager = PublicRoomListManager(hs)
+
+    @property
+    def http_client(self):
+        """Allows making outbound HTTP requests to remote resources.
+
+        An instance of synapse.http.client.SimpleHttpClient
+        """
+        return self._http_client
+
+    @property
+    def public_room_list_manager(self):
+        """Allows adding to, removing from and checking the status of rooms in the
+        public room list.
+
+        An instance of synapse.module_api.PublicRoomListManager
+        """
+        return self._public_room_list_manager
+
     def get_user_by_req(self, req, allow_guest=False):
         """Check the access_token provided for a request
 
@@ -266,3 +292,44 @@ class ModuleApi:
         await self._auth_handler.complete_sso_login(
             registered_user_id, request, client_redirect_url,
         )
+
+
+class PublicRoomListManager:
+    """Contains methods for adding to, removing from and querying whether a room
+    is in the public room list.
+    """
+
+    def __init__(self, hs: "HomeServer"):
+        self._store = hs.get_datastore()
+
+    async def room_is_in_public_room_list(self, room_id: str) -> bool:
+        """Checks whether a room is in the public room list.
+
+        Args:
+            room_id: The ID of the room.
+
+        Returns:
+            Whether the room is in the public room list. Returns False if the room does
+            not exist.
+        """
+        room = await self._store.get_room(room_id)
+        if not room:
+            return False
+
+        return room.get("is_public", False)
+
+    async def add_room_to_public_room_list(self, room_id: str) -> None:
+        """Publishes a room to the public room list.
+
+        Args:
+            room_id: The ID of the room.
+        """
+        await self._store.set_room_is_public(room_id, True)
+
+    async def remove_room_from_public_room_list(self, room_id: str) -> None:
+        """Removes a room from the public room list.
+
+        Args:
+            room_id: The ID of the room.
+        """
+        await self._store.set_room_is_public(room_id, False)