Add a spamchecker callback to allow or deny room creation based on invites (#10898)

This is in the context of creating new module callbacks that modules in https://github.com/matrix-org/synapse-dinsic can use, in an effort to reconcile the spam checker API in synapse-dinsic with the one in mainline.

This adds a callback that's fairly similar to user_may_create_room except it also allows processing based on the invites sent at room creation.

synapse/events/spamcheck.py

@@ -46,6 +46,9 @@ CHECK_EVENT_FOR_SPAM_CALLBACK = Callable[
 ]
 USER_MAY_INVITE_CALLBACK = Callable[[str, str, str], Awaitable[bool]]
 USER_MAY_CREATE_ROOM_CALLBACK = Callable[[str], Awaitable[bool]]
+USER_MAY_CREATE_ROOM_WITH_INVITES_CALLBACK = Callable[
+    [str, List[str], List[Dict[str, str]]], Awaitable[bool]
+]
 USER_MAY_CREATE_ROOM_ALIAS_CALLBACK = Callable[[str, RoomAlias], Awaitable[bool]]
 USER_MAY_PUBLISH_ROOM_CALLBACK = Callable[[str, str], Awaitable[bool]]
 CHECK_USERNAME_FOR_SPAM_CALLBACK = Callable[[Dict[str, str]], Awaitable[bool]]
@@ -164,6 +167,9 @@ class SpamChecker:
         self._check_event_for_spam_callbacks: List[CHECK_EVENT_FOR_SPAM_CALLBACK] = []
         self._user_may_invite_callbacks: List[USER_MAY_INVITE_CALLBACK] = []
         self._user_may_create_room_callbacks: List[USER_MAY_CREATE_ROOM_CALLBACK] = []
+        self._user_may_create_room_with_invites_callbacks: List[
+            USER_MAY_CREATE_ROOM_WITH_INVITES_CALLBACK
+        ] = []
         self._user_may_create_room_alias_callbacks: List[
             USER_MAY_CREATE_ROOM_ALIAS_CALLBACK
         ] = []
@@ -183,6 +189,9 @@ class SpamChecker:
         check_event_for_spam: Optional[CHECK_EVENT_FOR_SPAM_CALLBACK] = None,
         user_may_invite: Optional[USER_MAY_INVITE_CALLBACK] = None,
         user_may_create_room: Optional[USER_MAY_CREATE_ROOM_CALLBACK] = None,
+        user_may_create_room_with_invites: Optional[
+            USER_MAY_CREATE_ROOM_WITH_INVITES_CALLBACK
+        ] = None,
         user_may_create_room_alias: Optional[
             USER_MAY_CREATE_ROOM_ALIAS_CALLBACK
         ] = None,
@@ -203,6 +212,11 @@ class SpamChecker:
         if user_may_create_room is not None:
             self._user_may_create_room_callbacks.append(user_may_create_room)
 
+        if user_may_create_room_with_invites is not None:
+            self._user_may_create_room_with_invites_callbacks.append(
+                user_may_create_room_with_invites,
+            )
+
         if user_may_create_room_alias is not None:
             self._user_may_create_room_alias_callbacks.append(
                 user_may_create_room_alias,
@@ -283,6 +297,34 @@ class SpamChecker:
 
         return True
 
+    async def user_may_create_room_with_invites(
+        self,
+        userid: str,
+        invites: List[str],
+        threepid_invites: List[Dict[str, str]],
+    ) -> bool:
+        """Checks if a given user may create a room with invites
+
+        If this method returns false, the creation request will be rejected.
+
+        Args:
+            userid: The ID of the user attempting to create a room
+            invites: The IDs of the Matrix users to be invited if the room creation is
+                allowed.
+            threepid_invites: The threepids to be invited if the room creation is allowed,
+                as a dict including a "medium" key indicating the threepid's medium (e.g.
+                "email") and an "address" key indicating the threepid's address (e.g.
+                "alice@example.com")
+
+        Returns:
+            True if the user may create the room, otherwise False
+        """
+        for callback in self._user_may_create_room_with_invites_callbacks:
+            if await callback(userid, invites, threepid_invites) is False:
+                return False
+
+        return True
+
     async def user_may_create_room_alias(
         self, userid: str, room_alias: RoomAlias
     ) -> bool:

synapse/handlers/room.py

@@ -649,8 +649,16 @@ class RoomCreationHandler(BaseHandler):
             requester, config, is_requester_admin=is_requester_admin
         )
 
-        if not is_requester_admin and not await self.spam_checker.user_may_create_room(
-            user_id
+        invite_3pid_list = config.get("invite_3pid", [])
+        invite_list = config.get("invite", [])
+
+        if not is_requester_admin and not (
+            await self.spam_checker.user_may_create_room(user_id)
+            and await self.spam_checker.user_may_create_room_with_invites(
+                user_id,
+                invite_list,
+                invite_3pid_list,
+            )
         ):
             raise SynapseError(403, "You are not permitted to create rooms")
 
@@ -684,8 +692,6 @@ class RoomCreationHandler(BaseHandler):
             if mapping:
                 raise SynapseError(400, "Room alias already taken", Codes.ROOM_IN_USE)
 
-        invite_3pid_list = config.get("invite_3pid", [])
-        invite_list = config.get("invite", [])
         for i in invite_list:
             try:
                 uid = UserID.from_string(i)