Add admin API to remove a local user from a space

changelog.d/11358.feature

@@ -0,0 +1 @@
+Add an admin API endpoint to force a local user to leave all non-public rooms in a space.

docs/SUMMARY.md

@@ -60,6 +60,7 @@
       - [Registration Tokens](usage/administration/admin_api/registration_tokens.md)
       - [Manipulate Room Membership](admin_api/room_membership.md)
       - [Rooms](admin_api/rooms.md)
+      - [Spaces](usage/administration/admin_api/spaces.md)
       - [Server Notices](admin_api/server_notices.md)
       - [Statistics](admin_api/statistics.md)
       - [Users](admin_api/user_admin_api.md)

docs/usage/administration/admin_api/spaces.md

@@ -0,0 +1,57 @@
+# Spaces API
+
+This API allows a server administrator to manage spaces.
+
+## Remove local user
+
+This API forces a local user to leave all non-public rooms in a space.
+
+The space itself is always left, regardless of whether it is public.
+
+May succeed partially if the user fails to leave some rooms.
+
+The API is:
+
+```
+DELETE /_synapse/admin/v1/rooms/<room_id>/hierarchy/members/<user_id>
+```
+
+with an optional body of:
+
+```json
+{
+  "include_remote_spaces": true,
+}
+```
+
+`include_remote_spaces` controls whether to process subspaces that the
+local homeserver is not participating in. The listings of such subspaces
+have to be retrieved over federation and their accuracy cannot be
+guaranteed.
+
+Returning:
+
+```json
+{
+    "left_rooms": ["!room1:example.net", "!room2:example.net", ...],
+    "inaccessible_rooms": ["!subspace1:example.net", ...],
+    "failed_rooms": {
+        "!room4:example.net": "Failed to leave room.",
+        ...
+    }
+}
+```
+
+`left_rooms`: A list of rooms that the user has been made to leave.
+
+`inaccessible_rooms`: A list of rooms and spaces that the local
+homeserver is not in, and may have not been fully processed. Rooms may
+appear here if:
+  * The room is a space that the local homeserver is not in, and so its
+    full list of child rooms could not be determined.
+  * The room is inaccessible to the local homeserver, and it is not
+    known whether the room is a subspace containing further rooms.
+
+`failed_rooms`: A dictionary of errors encountered when leaving rooms.
+The keys of the dictionary are room IDs and the values of the dictionary
+are error messages.

synapse/handlers/room_summary.py

@@ -1045,7 +1045,7 @@ async def _get_child_events(self, room_id: str) -> Iterable[EventBase]:
 
         # filter out any events without a "via" (which implies it has been redacted),
         # and order to ensure we return stable results.
-        return sorted(filter(_has_valid_via, events), key=_child_events_comparison_key)
+        return sorted(filter(has_valid_via, events), key=child_events_comparison_key)
 
     async def get_room_summary(
         self,
@@ -1139,7 +1139,7 @@ def as_json(self) -> JsonDict:
         return result
 
 
-def _has_valid_via(e: EventBase) -> bool:
+def has_valid_via(e: EventBase) -> bool:
     via = e.content.get("via")
     if not via or not isinstance(via, Sequence):
         return False
@@ -1162,7 +1162,7 @@ def _is_suggested_child_event(edge_event: EventBase) -> bool:
 _INVALID_ORDER_CHARS_RE = re.compile(r"[^\x20-\x7E]")
 
 
-def _child_events_comparison_key(
+def child_events_comparison_key(
     child: EventBase,
 ) -> Tuple[bool, Optional[str], int, str]:
     """

synapse/handlers/space_hierarchy.py

@@ -0,0 +1,294 @@
+# Copyright 2021 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+from typing import (
+    TYPE_CHECKING,
+    Dict,
+    Iterable,
+    List,
+    Mapping,
+    Optional,
+    Sequence,
+    Tuple,
+)
+
+from synapse.api.constants import EventContentFields, EventTypes, RoomTypes
+from synapse.api.errors import SynapseError
+from synapse.handlers.room_summary import child_events_comparison_key, has_valid_via
+from synapse.storage.state import StateFilter
+from synapse.types import JsonDict
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+
+logger = logging.getLogger(__name__)
+
+
+class SpaceHierarchyHandler:
+    """Provides methods for walking over space hierarchies.
+
+    Also see `RoomSummaryHandler`, which has similar functionality.
+    """
+
+    def __init__(self, hs: "HomeServer"):
+        self._store = hs.get_datastore()
+        self._federation_client = hs.get_federation_client()
+
+        self._server_name = hs.hostname
+
+    async def get_space_descendants(
+        self,
+        space_id: str,
+        via: Optional[Iterable[str]] = None,
+        enable_federation: Optional[bool] = True,
+    ) -> Tuple[Sequence[Tuple[str, Iterable[str]]], Sequence[str]]:
+        """Gets the children of a space, recursively.
+
+        Args:
+            space_id: The room ID of the space.
+            via: A list of servers which may know about the space.
+            enable_federation: A boolean controlling whether children of unknown rooms
+                should be fetched over federation. Defaults to `True`.
+
+        Returns:
+            A tuple containing:
+             * A list of (room ID, via) tuples, representing the descendants of the
+               space. `space_id` is included in the list.
+             * A list of room IDs whose children could not be fully listed.
+               Rooms in this list are either spaces not known locally, and thus require
+               listing over federation, or are unknown rooms or subspaces completely
+               inaccessible to the local homeserver which may contain further rooms.
+               Subspaces requiring listing over federation are always included here,
+               regardless of the value of the `enable_federation` flag.
+
+               This list is a subset of the previous list, except it may include
+               `space_id`.
+        """
+        via = via or []
+
+        # (room ID, via, federation room chunks)
+        todo: List[Tuple[str, Iterable[str], Mapping[str, Optional[JsonDict]]]] = [
+            (space_id, via, {})
+        ]
+        # [(room ID, via)]
+        descendants: List[Tuple[str, Iterable[str]]] = []
+
+        seen = {space_id}
+
+        inaccessible_room_ids: List[str] = []
+
+        while todo:
+            space_id, via, federation_room_chunks = todo.pop()
+            descendants.append((space_id, via))
+            try:
+                (
+                    is_in_room,
+                    children,
+                    federation_room_chunks,
+                ) = await self._get_space_children(
+                    space_id,
+                    via,
+                    federation_room_chunks,
+                    enable_federation=enable_federation,
+                )
+            except SynapseError:
+                # Could not list children over federation
+                inaccessible_room_ids.append(space_id)
+                continue
+
+            # Children were retrieved over federation, which is not guaranteed to be
+            # the full list.
+            if not is_in_room:
+                inaccessible_room_ids.append(space_id)
+
+            for child_room_id, child_via in reversed(children):
+                if child_room_id in seen:
+                    continue
+
+                seen.add(child_room_id)
+
+                # Queue up the child for processing.
+                # The child may not actually be a space, but that's checked by
+                # `_get_space_children`.
+                todo.append((child_room_id, child_via, federation_room_chunks))
+
+        return descendants, inaccessible_room_ids
+
+    async def _get_space_children(
+        self,
+        space_id: str,
+        via: Optional[Iterable[str]] = None,
+        federation_room_chunks: Optional[Mapping[str, Optional[JsonDict]]] = None,
+        enable_federation: Optional[bool] = True,
+    ) -> Tuple[
+        bool, Sequence[Tuple[str, Iterable[str]]], Mapping[str, Optional[JsonDict]]
+    ]:
+        """Gets the direct children of a space.
+
+        Args:
+            space_id: The room ID of the space.
+            via: A list of servers which may know about the space.
+            federation_room_chunks: A cache of room chunks previously returned by
+               `_get_space_children` that may be used to skip federation requests for
+               inaccessible or non-space rooms.
+
+        Returns:
+            A tuple containing:
+             * A boolean indicating whether `space_id` is known to the local homeserver.
+             * A list of (room ID, via) tuples, representing the children of the space,
+               if `space_id` refers to a space; an empty list otherwise.
+             * A dictionary of child room ID: `PublicRoomsChunk`s returned over
+               federation:
+               https://spec.matrix.org/latest/client-server-api/#get_matrixclientv3publicrooms
+               These are supposed to include extra `room_type` and `allowed_room_ids`
+               fields, as described in MSC2946.
+
+               Contains `None` for rooms to which the remote homeserver thinks we do not
+               have access.
+
+               Local information about rooms should be trusted over data in this
+               dictionary.
+
+        Raises:
+            SynapseError: if `space_id` is not known locally and its children could not
+                be retrieved over federation or `enable_federation` is `False`.
+        """
+        via = via or []
+        federation_room_chunks = federation_room_chunks or {}
+
+        is_in_room = await self._store.is_host_joined(space_id, self._server_name)
+        if is_in_room:
+            children = await self._get_space_children_local(space_id)
+            return True, children, {}
+        else:
+            # Check the room chunks previously returned over federation to see if we
+            # should really make a request.
+            # `federation_room_chunks` is intentionally not used earlier since we want
+            # to trust local data over data from federation.
+            if space_id in federation_room_chunks:
+                room_chunk = federation_room_chunks[space_id]
+                if room_chunk is None:
+                    # `space_id` is inaccessible to the local homeserver according to
+                    # federation.
+                    raise SynapseError(
+                        502, f"{space_id} is not accessible to the local homeserver"
+                    )
+                elif room_chunk.get("room_type") != RoomTypes.SPACE:
+                    # `space_id` is not a space according to federation.
+                    return False, [], {}
+
+            if not enable_federation:
+                raise SynapseError(
+                    502, f"{space_id} is not accessible to the local homeserver"
+                )
+
+            children, room_chunks = await self._get_space_children_remote(space_id, via)
+            return False, children, room_chunks
+
+    async def _get_space_children_local(
+        self, space_id: str
+    ) -> Sequence[Tuple[str, Iterable[str]]]:
+        """Gets the direct children of a space that the local homeserver is in.
+
+        Args:
+            space_id: The room ID of the space.
+
+        Returns:
+            A list of (room ID, via) tuples, representing the children of the space,
+            if `space_id` refers to a space; an empty list otherwise.
+
+        Raises:
+            ValueError: if `space_id` is not known locally.
+        """
+        # Fetch the `m.room.create` and `m.space.child` events for `space_id`
+        state_filter = StateFilter.from_types(
+            [(EventTypes.Create, ""), (EventTypes.SpaceChild, None)]
+        )
+        current_state_ids = await self._store.get_filtered_current_state_ids(
+            space_id, state_filter
+        )
+        state_events = await self._store.get_events_as_list(current_state_ids.values())
+        assert len(state_events) == len(current_state_ids)
+
+        create_event_id = current_state_ids.get((EventTypes.Create, ""))
+        if create_event_id is None:
+            # The local homeserver is not in this room
+            raise ValueError(f"{space_id} is not a room known locally.")
+
+        create_event = next(
+            event for event in state_events if event.event_id == create_event_id
+        )
+        if create_event.content.get(EventContentFields.ROOM_TYPE) != RoomTypes.SPACE:
+            # `space_id` is a regular room and not a space.
+            # Ignore any `m.space.child` events.
+            return []
+
+        child_events = [
+            event
+            for event in state_events
+            # Ignore events with a missing or non-array `via`, as per MSC1772
+            if event.event_id != create_event_id and has_valid_via(event)
+        ]
+        child_events.sort(key=child_events_comparison_key)
+        return [(event.state_key, event.content["via"]) for event in child_events]
+
+    async def _get_space_children_remote(
+        self, space_id: str, via: Iterable[str]
+    ) -> Tuple[Sequence[Tuple[str, Iterable[str]]], Mapping[str, Optional[JsonDict]]]:
+        """Gets the direct children of a space over federation.
+
+        Args:
+            space_id: The room ID of the space.
+            via: A list of servers which may know about the space.
+
+        Returns:
+            A tuple containing:
+             * A list of (room ID, via) tuples, representing the children of the space,
+               if `space_id` refers to a space; an empty list otherwise.
+             * A dictionary of child room ID: `PublicRoomsChunk`s returned over
+               federation:
+               https://spec.matrix.org/latest/client-server-api/#get_matrixclientv3publicrooms
+               These are supposed to include extra `room_type` and `allowed_room_ids`
+               fields, as described in MSC2946.
+
+               Contains `None` for rooms to which the remote homeserver thinks we do not
+               have access.
+
+        Raises:
+            SynapseError: if none of the remote servers provided us with the space's
+                children.
+        """
+        (
+            room,
+            children_chunks,
+            inaccessible_children,
+        ) = await self._federation_client.get_room_hierarchy(
+            via, space_id, suggested_only=False
+        )
+
+        child_events: List[JsonDict] = room["children_state"]
+        children = [
+            (child_event["room_id"], child_event["content"]["via"])
+            for child_event in child_events
+        ]
+
+        room_chunks: Dict[str, Optional[JsonDict]] = {}
+        room_chunks.update((room_id, None) for room_id in inaccessible_children)
+        room_chunks.update(
+            (room_chunk["room_id"], room_chunk) for room_chunk in children_chunks
+        )
+
+        return children, room_chunks