Allow admins to proactively block rooms

changelog.d/11228.feature

@@ -0,0 +1 @@
+Allow the admin [Delete Room API](https://matrix-org.github.io/synapse/latest/admin_api/rooms.html#delete-room-api) to block a room without the need to join it.

docs/admin_api/rooms.md

@@ -391,13 +391,16 @@ The new room will be created with the user specified by the `new_room_user_id` p
 as room administrator and will contain a message explaining what happened. Users invited
 to the new room will have power level `-10` by default, and thus be unable to speak.
 
-If `block` is `True` it prevents new joins to the old room.
+If `block` is `true`, users will be prevented from joining the old room.
+This option can also be used to pre-emptively block a room, even if it's unknown
+to this homeserver. (If `block` is `false`, attempting to delete an unknown room
+is invalid and will be rejected as a bad request.)
 
 This API will remove all trace of the old room from your database after removing
 all local users. If `purge` is `true` (the default), all traces of the old room will
 be removed from your database after removing all local users. If you do not want
 this to happen, set `purge` to `false`.
-Depending on the amount of history being purged a call to the API may take
+Depending on the amount of history being purged, a call to the API may take
 several minutes or longer.
 
 The local server will only have the power to move local user and room aliases to
@@ -459,8 +462,9 @@ The following JSON body parameters are available:
  `new_room_user_id` in the new room. Ideally this will clearly convey why the
  original room was shut down. Defaults to `Sharing illegal content on this server
  is not permitted and rooms in violation will be blocked.`
-* `block` - Optional. If set to `true`, this room will be added to a blocking list, preventing
- future attempts to join the room. Defaults to `false`.
+* `block` - Optional. If set to `true`, this room will be added to a blocking list,
+ preventing future attempts to join the room. Rooms can be blocked
+ even if they're not yet known to the homeserver. Defaults to `false`.
 * `purge` - Optional. If set to `true`, it will remove all traces of the room from your database.
  Defaults to `true`.
 * `force_purge` - Optional, and ignored unless `purge` is `true`. If set to `true`, it
@@ -478,7 +482,8 @@ The following fields are returned in the JSON response body:
 * `failed_to_kick_users` - An array of users (`user_id`) that that were not kicked.
 * `local_aliases` - An array of strings representing the local aliases that were migrated from
  the old room to the new.
-* `new_room_id` - A string representing the room ID of the new room.
+* `new_room_id` - A string representing the room ID of the new room, or `null` if
+ no such room was created.
 
 
 ## Undoing room deletions

synapse/handlers/room.py

@@ -12,8 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-"""Contains functions for performing events on rooms."""
-
+"""Contains functions for performing actions on rooms."""
 import itertools
 import logging
 import math
@@ -31,6 +30,8 @@
  Tuple,
 )
 
+from typing_extensions import TypedDict
+
 from synapse.api.constants import (
  EventContentFields,
  EventTypes,
@@ -1275,6 +1276,13 @@ def get_current_key_for_room(self, room_id: str) -> Awaitable[str]:
  return self.store.get_room_events_max_id(room_id)
 
 
+class ShutdownRoomResponse(TypedDict):
+ kicked_users: List[str]
+ failed_to_kick_users: List[str]
+ local_aliases: List[str]
+ new_room_id: Optional[str]
+
+
 class RoomShutdownHandler:
 
  DEFAULT_MESSAGE = (
@@ -1300,7 +1308,7 @@ async def shutdown_room(
  new_room_name: Optional[str] = None,
  message: Optional[str] = None,
  block: bool = False,
- ) -> dict:
+ ) -> ShutdownRoomResponse:
  """
  Shuts down a room. Moves all local users and room aliases automatically
  to a new room if `new_room_user_id` is set. Otherwise local users only
@@ -1334,8 +1342,10 @@ async def shutdown_room(
  Defaults to `Sharing illegal content on this server is not
  permitted and rooms in violation will be blocked.`
  block:
- If set to `true`, this room will be added to a blocking list,
- preventing future attempts to join the room. Defaults to `false`.
+ If set to `True`, this room will be added to a blocking list,
+ preventing future attempts to join the room. Rooms can be blocked
+ even if they're not yet known to the homeserver. Defaults to
+ `False`.
 
  Returns: a dict containing the following keys:
  kicked_users: An array of users (`user_id`) that were kicked.
@@ -1344,7 +1354,9 @@ async def shutdown_room(
  local_aliases:
  An array of strings representing the local aliases that were
  migrated from the old room to the new.
- new_room_id: A string representing the room ID of the new room.
+ new_room_id:
+ A string representing the room ID of the new room, or None if
+ no such room was created.
  """
 
  if not new_room_name:
@@ -1355,14 +1367,28 @@ async def shutdown_room(
  if not RoomID.is_valid(room_id):
  raise SynapseError(400, "%s is not a legal room ID" % (room_id,))
 
- if not await self.store.get_room(room_id):
- raise NotFoundError("Unknown room id %s" % (room_id,))
-
- # This will work even if the room is already blocked, but that is
- # desirable in case the first attempt at blocking the room failed below.
+ # Action the block first (even if the room doesn't exist yet)
  if block:
+ # This will work even if the room is already blocked, but that is
+ # desirable in case the first attempt at blocking the room failed below.
  await self.store.block_room(room_id, requester_user_id)
 
+ if not await self.store.get_room(room_id):
+ if block:
+ # We allow you to block an unknown room.
+ return {
+ "kicked_users": [],
+ "failed_to_kick_users": [],
+ "local_aliases": [],
+ "new_room_id": None,
+ }
+ else:
+ # But if you don't want to preventatively block another room,
+ # this function can't do anything useful.
+ raise NotFoundError(
+ "Cannot shut down room: unknown room id %s" % (room_id,)
+ )
+
  if new_room_user_id is not None:
  if not self.hs.is_mine_id(new_room_user_id):
  raise SynapseError(

synapse/rest/admin/rooms.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 import logging
 from http import HTTPStatus
-from typing import TYPE_CHECKING, List, Optional, Tuple
+from typing import TYPE_CHECKING, List, Optional, Tuple, cast
 from urllib import parse as urlparse
 
 from synapse.api.constants import EventTypes, JoinRules, Membership
@@ -239,9 +239,22 @@ async def _delete_room(
 
  # Purge room
  if purge:
- await pagination_handler.purge_room(room_id, force=force_purge)
-
- return 200, ret
+ try:
+ await pagination_handler.purge_room(room_id, force=force_purge)
+ except NotFoundError:
+ if block:
+ # We can block unknown rooms with this endpoint, in which case
+ # a failed purge is expected.
+ pass
+ else:
+ # But otherwise, we expect this purge to have succeeded.
+ raise
+
+ # Cast safety: cast away the knowledge that this is a TypedDict.
+ # See https://github.com/python/mypy/issues/4976#issuecomment-579883622
+ # for some discussion on why this is necessary. Either way,
+ # `ret` is an opaque dictionary blob as far as the rest of the app cares.
+ return 200, cast(JsonDict, ret)
 
 
 class RoomMembersRestServlet(RestServlet):

synapse/storage/databases/main/room.py

@@ -1744,7 +1744,12 @@ def _get_event_reports_paginate_txn(txn):
  )
 
  async def block_room(self, room_id: str, user_id: str) -> None:
- """Marks the room as blocked. Can be called multiple times.
+ """Marks the room as blocked.
+
+ Can be called multiple times (though we'll only track the last user to
+ block this room).
+
+ Can be called on a room unknown to this homeserver.
 
  Args:
  room_id: Room to block

tests/rest/admin/test_room.py

@@ -14,9 +14,12 @@
 
 import json
 import urllib.parse
+from http import HTTPStatus
 from typing import List, Optional
 from unittest.mock import Mock
 
+from parameterized import parameterized
+
 import synapse.rest.admin
 from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import Codes
@@ -281,6 +284,31 @@ def test_block_room_and_not_purge(self):
  self._is_blocked(self.room_id, expect=True)
  self._has_no_members(self.room_id)
 
+ @parameterized.expand([(True,), (False,)])
+ def test_block_unknown_room(self, purge: bool) -> None:
+ """
+ We can block an unknown room. In this case, the `purge` argument
+ should be ignored.
+ """
+ room_id = "!unknown:test"
+
+ # The room isn't already in the blocked rooms table
+ self._is_blocked(room_id, expect=False)
+
+ # Request the room be blocked.
+ channel = self.make_request(
+ "DELETE",
+ f"/_synapse/admin/v1/rooms/{room_id}",
+ {"block": True, "purge": purge},
+ access_token=self.admin_user_tok,
+ )
+
+ # The room is now blocked.
+ self.assertEqual(
+ HTTPStatus.OK, int(channel.result["code"]), msg=channel.result["body"]
+ )
+ self._is_blocked(room_id)
+
  def test_shutdown_room_consent(self):
  """Test that we can shutdown rooms with local users who have not
  yet accepted the privacy policy. This used to fail when we tried to