New API /_synapse/admin/v1/rooms/{roomId}/context/{eventId}

changelog.d/9150.feature

@@ -0,0 +1 @@
+New API /_synapse/admin/rooms/{roomId}/context/{eventId}.

docs/admin_api/rooms.md

@@ -10,6 +10,7 @@
   * [Undoing room shutdowns](#undoing-room-shutdowns)
 - [Make Room Admin API](#make-room-admin-api)
 - [Forward Extremities Admin API](#forward-extremities-admin-api)
+- [Event Context API](#event-context-api)
 
 # List Room API
 
@@ -564,3 +565,121 @@ that were deleted.
   "deleted": 1
 }
 ```
+
+# Event Context API
+
+This API lets a client find the context of an event. This is designed primarily to investigate abuse reports.
+
+```
+GET /_synapse/admin/v1/rooms/<room_id>/context/<event_id>
+```
+
+This API mimmicks [GET /_matrix/client/r0/rooms/{roomId}/context/{eventId}](https://matrix.org/docs/spec/client_server/r0.6.1#get-matrix-client-r0-rooms-roomid-context-eventid). Please refer to the link for all details on parameters and reseponse.
+
+Example response:
+
+```json
+{
+  "end": "t29-57_2_0_2",
+  "events_after": [
+    {
+      "content": {
+        "body": "This is an example text message",
+        "msgtype": "m.text",
+        "format": "org.matrix.custom.html",
+        "formatted_body": "<b>This is an example text message</b>"
+      },
+      "type": "m.room.message",
+      "event_id": "$143273582443PhrSn:example.org",
+      "room_id": "!636q39766251:example.com",
+      "sender": "@example:example.org",
+      "origin_server_ts": 1432735824653,
+      "unsigned": {
+        "age": 1234
+      }
+    }
+  ],
+  "event": {
+    "content": {
+      "body": "filename.jpg",
+      "info": {
+        "h": 398,
+        "w": 394,
+        "mimetype": "image/jpeg",
+        "size": 31037
+      },
+      "url": "mxc://example.org/JWEIFJgwEIhweiWJE",
+      "msgtype": "m.image"
+    },
+    "type": "m.room.message",
+    "event_id": "$f3h4d129462ha:example.com",
+    "room_id": "!636q39766251:example.com",
+    "sender": "@example:example.org",
+    "origin_server_ts": 1432735824653,
+    "unsigned": {
+      "age": 1234
+    }
+  },
+  "events_before": [
+    {
+      "content": {
+        "body": "something-important.doc",
+        "filename": "something-important.doc",
+        "info": {
+          "mimetype": "application/msword",
+          "size": 46144
+        },
+        "msgtype": "m.file",
+        "url": "mxc://example.org/FHyPlCeYUSFFxlgbQYZmoEoe"
+      },
+      "type": "m.room.message",
+      "event_id": "$143273582443PhrSn:example.org",
+      "room_id": "!636q39766251:example.com",
+      "sender": "@example:example.org",
+      "origin_server_ts": 1432735824653,
+      "unsigned": {
+        "age": 1234
+      }
+    }
+  ],
+  "start": "t27-54_2_0_2",
+  "state": [
+    {
+      "content": {
+        "creator": "@example:example.org",
+        "room_version": "1",
+        "m.federate": true,
+        "predecessor": {
+          "event_id": "$something:example.org",
+          "room_id": "!oldroom:example.org"
+        }
+      },
+      "type": "m.room.create",
+      "event_id": "$143273582443PhrSn:example.org",
+      "room_id": "!636q39766251:example.com",
+      "sender": "@example:example.org",
+      "origin_server_ts": 1432735824653,
+      "unsigned": {
+        "age": 1234
+      },
+      "state_key": ""
+    },
+    {
+      "content": {
+        "membership": "join",
+        "avatar_url": "mxc://example.org/SEsfnsuifSDFSSEF",
+        "displayname": "Alice Margatroid"
+      },
+      "type": "m.room.member",
+      "event_id": "$143273582443PhrSn:example.org",
+      "room_id": "!636q39766251:example.com",
+      "sender": "@example:example.org",
+      "origin_server_ts": 1432735824653,
+      "unsigned": {
+        "age": 1234
+      },
+      "state_key": "@alice:example.org"
+    }
+  ]
+}
+```

synapse/handlers/room.py

@@ -38,6 +38,7 @@
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersion
 from synapse.events import EventBase
 from synapse.events.utils import copy_power_levels_contents
+from synapse.rest.admin._base import assert_user_is_admin
 from synapse.storage.state import StateFilter
 from synapse.types import (
     JsonDict,
@@ -997,41 +998,51 @@ async def _generate_room_id(
 class RoomContextHandler:
     def __init__(self, hs: "HomeServer"):
         self.hs = hs
+        self.auth = hs.get_auth()
         self.store = hs.get_datastore()
         self.storage = hs.get_storage()
         self.state_store = self.storage.state
 
     async def get_event_context(
         self,
-        user: UserID,
+        requester: Requester,
         room_id: str,
         event_id: str,
         limit: int,
         event_filter: Optional[Filter],
+        use_admin_priviledge: bool = False,
     ) -> Optional[JsonDict]:
         """Retrieves events, pagination tokens and state around a given event
         in a room.
 
         Args:
-            user
+            requester
             room_id
             event_id
             limit: The maximum number of events to return in total
                 (excluding state).
             event_filter: the filter to apply to the events returned
                 (excluding the target event_id)
-
+            use_admin_priviledge: if `True`, return all events, regardless
+                of whether `user` has access to them. To be used **ONLY**
+                from the admin API.
         Returns:
             dict, or None if the event isn't found
         """
+        user = requester.user
+        if use_admin_priviledge:
+            await assert_user_is_admin(self.auth, requester.user)
+
         before_limit = math.floor(limit / 2.0)
         after_limit = limit - before_limit
 
         users = await self.store.get_users_in_room(room_id)
         is_peeking = user.to_string() not in users
 
-        def filter_evts(events):
-            return filter_events_for_client(
+        async def filter_evts(events):
+            if use_admin_priviledge:
+                return events
+            return await filter_events_for_client(
                 self.storage, user.to_string(), events, is_peeking=is_peeking
             )
 

synapse/rest/admin/__init__.py

@@ -42,6 +42,7 @@
     JoinRoomAliasServlet,
     ListRoomRestServlet,
     MakeRoomAdminRestServlet,
+    RoomEventContextServlet,
     RoomMembersRestServlet,
     RoomRestServlet,
     ShutdownRoomRestServlet,
@@ -236,6 +237,7 @@ def register_servlets(hs, http_server):
     MakeRoomAdminRestServlet(hs).register(http_server)
     ShadowBanRestServlet(hs).register(http_server)
     ForwardExtremitiesRestServlet(hs).register(http_server)
+    RoomEventContextServlet(hs).register(http_server)
 
 
 def register_servlets_for_client_rest_resource(hs, http_server):

synapse/rest/admin/rooms.py

@@ -15,9 +15,11 @@
 import logging
 from http import HTTPStatus
 from typing import TYPE_CHECKING, List, Optional, Tuple
+from urllib import parse as urlparse
 
 from synapse.api.constants import EventTypes, JoinRules, Membership
 from synapse.api.errors import AuthError, Codes, NotFoundError, SynapseError
+from synapse.api.filtering import Filter
 from synapse.http.servlet import (
     RestServlet,
     assert_params_in_dict,
@@ -33,6 +35,7 @@
 )
 from synapse.storage.databases.main.room import RoomSortOrder
 from synapse.types import JsonDict, RoomAlias, RoomID, UserID, create_requester
+from synapse.util import json_decoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -566,3 +569,65 @@ async def on_GET(self, request, room_identifier):
 
         extremities = await self.store.get_forward_extremities_for_room(room_id)
         return 200, {"count": len(extremities), "results": extremities}
+
+
+class RoomEventContextServlet(RestServlet):
+    """
+    Provide the context for an event.
+    This API is designed to be used when system administrators wish to look at
+    an abuse report and understand what happened during and immediately prior
+    to this event.
+    """
+
+    PATTERNS = admin_patterns("/rooms/(?P<room_id>[^/]*)/context/(?P<event_id>[^/]*)$")
+
+    def __init__(self, hs):
+        super().__init__()
+        self.clock = hs.get_clock()
+        self.room_context_handler = hs.get_room_context_handler()
+        self._event_serializer = hs.get_event_client_serializer()
+        self.auth = hs.get_auth()
+
+    async def on_GET(self, request, room_id, event_id):
+        requester = await self.auth.get_user_by_req(request, allow_guest=False)
+        await assert_user_is_admin(self.auth, requester.user)
+
+        limit = parse_integer(request, "limit", default=10)
+
+        # picking the API shape for symmetry with /messages
+        filter_str = parse_string(request, b"filter", encoding="utf-8")
+        if filter_str:
+            filter_json = urlparse.unquote(filter_str)
+            event_filter = Filter(
+                json_decoder.decode(filter_json)
+            )  # type: Optional[Filter]
+        else:
+            event_filter = None
+
+        results = await self.room_context_handler.get_event_context(
+            requester,
+            room_id,
+            event_id,
+            limit,
+            event_filter,
+            use_admin_priviledge=True,
+        )
+
+        if not results:
+            raise SynapseError(404, "Event not found.", errcode=Codes.NOT_FOUND)
+
+        time_now = self.clock.time_msec()
+        results["events_before"] = await self._event_serializer.serialize_events(
+            results["events_before"], time_now
+        )
+        results["event"] = await self._event_serializer.serialize_event(
+            results["event"], time_now
+        )
+        results["events_after"] = await self._event_serializer.serialize_events(
+            results["events_after"], time_now
+        )
+        results["state"] = await self._event_serializer.serialize_events(
+            results["state"], time_now
+        )
+
+        return 200, results

synapse/rest/client/v1/room.py

@@ -650,7 +650,7 @@ async def on_GET(self, request, room_id, event_id):
             event_filter = None
 
         results = await self.room_context_handler.get_event_context(
-            requester.user, room_id, event_id, limit, event_filter
+            requester, room_id, event_id, limit, event_filter
         )
 
         if not results:

synapse/visibility.py

@@ -80,6 +80,7 @@ async def filter_events_for_client(
     events = [e for e in events if not e.internal_metadata.is_soft_failed()]
 
     types = ((EventTypes.RoomHistoryVisibility, ""), (EventTypes.Member, user_id))
+
     event_id_to_state = await storage.state.get_state_for_events(
         frozenset(e.event_id for e in events),
         state_filter=StateFilter.from_types(types),