diff --git a/changelog.d/15200.misc b/changelog.d/15200.misc new file mode 100644 index 000000000..dc6617222 --- /dev/null +++ b/changelog.d/15200.misc @@ -0,0 +1 @@ +Make the `HttpTransactionCache` use the `Requester` in addition of the just the `Request` to build the transaction key. diff --git a/synapse/rest/admin/server_notice_servlet.py b/synapse/rest/admin/server_notice_servlet.py index 15da9cd88..7dd1c10b9 100644 --- a/synapse/rest/admin/server_notice_servlet.py +++ b/synapse/rest/admin/server_notice_servlet.py @@ -12,7 +12,7 @@ # See the License for the specific language governing permissions and # limitations under the License. from http import HTTPStatus -from typing import TYPE_CHECKING, Awaitable, Optional, Tuple +from typing import TYPE_CHECKING, Optional, Tuple from synapse.api.constants import EventTypes from synapse.api.errors import NotFoundError, SynapseError @@ -23,10 +23,10 @@ from synapse.http.servlet import ( parse_json_object_from_request, ) from synapse.http.site import SynapseRequest -from synapse.rest.admin import assert_requester_is_admin -from synapse.rest.admin._base import admin_patterns +from synapse.logging.opentracing import set_tag +from synapse.rest.admin._base import admin_patterns, assert_user_is_admin from synapse.rest.client.transactions import HttpTransactionCache -from synapse.types import JsonDict, UserID +from synapse.types import JsonDict, Requester, UserID if TYPE_CHECKING: from synapse.server import HomeServer @@ -70,10 +70,13 @@ class SendServerNoticeServlet(RestServlet): self.__class__.__name__, ) - async def on_POST( - self, request: SynapseRequest, txn_id: Optional[str] = None + async def _do( + self, + request: SynapseRequest, + requester: Requester, + txn_id: Optional[str], ) -> Tuple[int, JsonDict]: - await assert_requester_is_admin(self.auth, request) + await assert_user_is_admin(self.auth, requester) body = parse_json_object_from_request(request) assert_params_in_dict(body, ("user_id", "content")) event_type = body.get("type", EventTypes.Message) @@ -106,9 +109,18 @@ class SendServerNoticeServlet(RestServlet): return HTTPStatus.OK, {"event_id": event.event_id} - def on_PUT( + async def on_POST( + self, + request: SynapseRequest, + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request) + return await self._do(request, requester, None) + + async def on_PUT( self, request: SynapseRequest, txn_id: str - ) -> Awaitable[Tuple[int, JsonDict]]: - return self.txns.fetch_or_execute_request( - request, self.on_POST, request, txn_id + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request) + set_tag("txn_id", txn_id) + return await self.txns.fetch_or_execute_request( + request, requester, self._do, request, requester, txn_id ) diff --git a/synapse/rest/client/room.py b/synapse/rest/client/room.py index 61e4cf021..129b6fe6b 100644 --- a/synapse/rest/client/room.py +++ b/synapse/rest/client/room.py @@ -57,7 +57,7 @@ from synapse.metrics.background_process_metrics import run_as_background_process from synapse.rest.client._base import client_patterns from synapse.rest.client.transactions import HttpTransactionCache from synapse.streams.config import PaginationConfig -from synapse.types import JsonDict, StreamToken, ThirdPartyInstanceID, UserID +from synapse.types import JsonDict, Requester, StreamToken, ThirdPartyInstanceID, UserID from synapse.types.state import StateFilter from synapse.util import json_decoder from synapse.util.cancellation import cancellable @@ -151,15 +151,22 @@ class RoomCreateRestServlet(TransactionRestServlet): PATTERNS = "/createRoom" register_txn_path(self, PATTERNS, http_server) - def on_PUT( + async def on_PUT( self, request: SynapseRequest, txn_id: str - ) -> Awaitable[Tuple[int, JsonDict]]: + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request) set_tag("txn_id", txn_id) - return self.txns.fetch_or_execute_request(request, self.on_POST, request) + return await self.txns.fetch_or_execute_request( + request, requester, self._do, request, requester + ) async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]: requester = await self.auth.get_user_by_req(request) + return await self._do(request, requester) + async def _do( + self, request: SynapseRequest, requester: Requester + ) -> Tuple[int, JsonDict]: room_id, _, _ = await self._room_creation_handler.create_room( requester, self.get_room_config(request) ) @@ -172,9 +179,9 @@ class RoomCreateRestServlet(TransactionRestServlet): # TODO: Needs unit testing for generic events -class RoomStateEventRestServlet(TransactionRestServlet): +class RoomStateEventRestServlet(RestServlet): def __init__(self, hs: "HomeServer"): - super().__init__(hs) + super().__init__() self.event_creation_handler = hs.get_event_creation_handler() self.room_member_handler = hs.get_room_member_handler() self.message_handler = hs.get_message_handler() @@ -324,16 +331,16 @@ class RoomSendEventRestServlet(TransactionRestServlet): def register(self, http_server: HttpServer) -> None: # /rooms/$roomid/send/$event_type[/$txn_id] PATTERNS = "/rooms/(?P[^/]*)/send/(?P[^/]*)" - register_txn_path(self, PATTERNS, http_server, with_get=True) + register_txn_path(self, PATTERNS, http_server) - async def on_POST( + async def _do( self, request: SynapseRequest, + requester: Requester, room_id: str, event_type: str, - txn_id: Optional[str] = None, + txn_id: Optional[str], ) -> Tuple[int, JsonDict]: - requester = await self.auth.get_user_by_req(request, allow_guest=True) content = parse_json_object_from_request(request) event_dict: JsonDict = { @@ -362,18 +369,30 @@ class RoomSendEventRestServlet(TransactionRestServlet): set_tag("event_id", event_id) return 200, {"event_id": event_id} - def on_GET( - self, request: SynapseRequest, room_id: str, event_type: str, txn_id: str - ) -> Tuple[int, str]: - return 200, "Not implemented" + async def on_POST( + self, + request: SynapseRequest, + room_id: str, + event_type: str, + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request, allow_guest=True) + return await self._do(request, requester, room_id, event_type, None) - def on_PUT( + async def on_PUT( self, request: SynapseRequest, room_id: str, event_type: str, txn_id: str - ) -> Awaitable[Tuple[int, JsonDict]]: + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request, allow_guest=True) set_tag("txn_id", txn_id) - return self.txns.fetch_or_execute_request( - request, self.on_POST, request, room_id, event_type, txn_id + return await self.txns.fetch_or_execute_request( + request, + requester, + self._do, + request, + requester, + room_id, + event_type, + txn_id, ) @@ -389,14 +408,13 @@ class JoinRoomAliasServlet(ResolveRoomIdMixin, TransactionRestServlet): PATTERNS = "/join/(?P[^/]*)" register_txn_path(self, PATTERNS, http_server) - async def on_POST( + async def _do( self, request: SynapseRequest, + requester: Requester, room_identifier: str, - txn_id: Optional[str] = None, + txn_id: Optional[str], ) -> Tuple[int, JsonDict]: - requester = await self.auth.get_user_by_req(request, allow_guest=True) - content = parse_json_object_from_request(request, allow_empty_body=True) # twisted.web.server.Request.args is incorrectly defined as Optional[Any] @@ -420,22 +438,31 @@ class JoinRoomAliasServlet(ResolveRoomIdMixin, TransactionRestServlet): return 200, {"room_id": room_id} - def on_PUT( + async def on_POST( + self, + request: SynapseRequest, + room_identifier: str, + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request, allow_guest=True) + return await self._do(request, requester, room_identifier, None) + + async def on_PUT( self, request: SynapseRequest, room_identifier: str, txn_id: str - ) -> Awaitable[Tuple[int, JsonDict]]: + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request, allow_guest=True) set_tag("txn_id", txn_id) - return self.txns.fetch_or_execute_request( - request, self.on_POST, request, room_identifier, txn_id + return await self.txns.fetch_or_execute_request( + request, requester, self._do, request, requester, room_identifier, txn_id ) # TODO: Needs unit testing -class PublicRoomListRestServlet(TransactionRestServlet): +class PublicRoomListRestServlet(RestServlet): PATTERNS = client_patterns("/publicRooms$", v1=True) def __init__(self, hs: "HomeServer"): - super().__init__(hs) + super().__init__() self.hs = hs self.auth = hs.get_auth() @@ -907,22 +934,25 @@ class RoomForgetRestServlet(TransactionRestServlet): PATTERNS = "/rooms/(?P[^/]*)/forget" register_txn_path(self, PATTERNS, http_server) - async def on_POST( - self, request: SynapseRequest, room_id: str, txn_id: Optional[str] = None - ) -> Tuple[int, JsonDict]: - requester = await self.auth.get_user_by_req(request, allow_guest=False) - + async def _do(self, requester: Requester, room_id: str) -> Tuple[int, JsonDict]: await self.room_member_handler.forget(user=requester.user, room_id=room_id) return 200, {} - def on_PUT( + async def on_POST( + self, request: SynapseRequest, room_id: str + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request, allow_guest=False) + return await self._do(requester, room_id) + + async def on_PUT( self, request: SynapseRequest, room_id: str, txn_id: str - ) -> Awaitable[Tuple[int, JsonDict]]: + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request, allow_guest=False) set_tag("txn_id", txn_id) - return self.txns.fetch_or_execute_request( - request, self.on_POST, request, room_id, txn_id + return await self.txns.fetch_or_execute_request( + request, requester, self._do, requester, room_id ) @@ -941,15 +971,14 @@ class RoomMembershipRestServlet(TransactionRestServlet): ) register_txn_path(self, PATTERNS, http_server) - async def on_POST( + async def _do( self, request: SynapseRequest, + requester: Requester, room_id: str, membership_action: str, - txn_id: Optional[str] = None, + txn_id: Optional[str], ) -> Tuple[int, JsonDict]: - requester = await self.auth.get_user_by_req(request, allow_guest=True) - if requester.is_guest and membership_action not in { Membership.JOIN, Membership.LEAVE, @@ -1014,13 +1043,30 @@ class RoomMembershipRestServlet(TransactionRestServlet): return 200, return_value - def on_PUT( + async def on_POST( + self, + request: SynapseRequest, + room_id: str, + membership_action: str, + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request, allow_guest=True) + return await self._do(request, requester, room_id, membership_action, None) + + async def on_PUT( self, request: SynapseRequest, room_id: str, membership_action: str, txn_id: str - ) -> Awaitable[Tuple[int, JsonDict]]: + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request, allow_guest=True) set_tag("txn_id", txn_id) - return self.txns.fetch_or_execute_request( - request, self.on_POST, request, room_id, membership_action, txn_id + return await self.txns.fetch_or_execute_request( + request, + requester, + self._do, + request, + requester, + room_id, + membership_action, + txn_id, ) @@ -1036,14 +1082,14 @@ class RoomRedactEventRestServlet(TransactionRestServlet): PATTERNS = "/rooms/(?P[^/]*)/redact/(?P[^/]*)" register_txn_path(self, PATTERNS, http_server) - async def on_POST( + async def _do( self, request: SynapseRequest, + requester: Requester, room_id: str, event_id: str, - txn_id: Optional[str] = None, + txn_id: Optional[str], ) -> Tuple[int, JsonDict]: - requester = await self.auth.get_user_by_req(request) content = parse_json_object_from_request(request) try: @@ -1094,13 +1140,23 @@ class RoomRedactEventRestServlet(TransactionRestServlet): set_tag("event_id", event_id) return 200, {"event_id": event_id} - def on_PUT( + async def on_POST( + self, + request: SynapseRequest, + room_id: str, + event_id: str, + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request) + return await self._do(request, requester, room_id, event_id, None) + + async def on_PUT( self, request: SynapseRequest, room_id: str, event_id: str, txn_id: str - ) -> Awaitable[Tuple[int, JsonDict]]: + ) -> Tuple[int, JsonDict]: + requester = await self.auth.get_user_by_req(request) set_tag("txn_id", txn_id) - return self.txns.fetch_or_execute_request( - request, self.on_POST, request, room_id, event_id, txn_id + return await self.txns.fetch_or_execute_request( + request, requester, self._do, request, requester, room_id, event_id, txn_id ) @@ -1224,7 +1280,6 @@ def register_txn_path( servlet: RestServlet, regex_string: str, http_server: HttpServer, - with_get: bool = False, ) -> None: """Registers a transaction-based path. @@ -1236,7 +1291,6 @@ def register_txn_path( regex_string: The regex string to register. Must NOT have a trailing $ as this string will be appended to. http_server: The http_server to register paths with. - with_get: True to also register respective GET paths for the PUTs. """ on_POST = getattr(servlet, "on_POST", None) on_PUT = getattr(servlet, "on_PUT", None) @@ -1254,18 +1308,6 @@ def register_txn_path( on_PUT, servlet.__class__.__name__, ) - on_GET = getattr(servlet, "on_GET", None) - if with_get: - if on_GET is None: - raise RuntimeError( - "register_txn_path called with with_get = True, but no on_GET method exists" - ) - http_server.register_paths( - "GET", - client_patterns(regex_string + "/(?P[^/]*)$", v1=True), - on_GET, - servlet.__class__.__name__, - ) class TimestampLookupRestServlet(RestServlet): diff --git a/synapse/rest/client/sendtodevice.py b/synapse/rest/client/sendtodevice.py index 55d52f0b2..110af6df4 100644 --- a/synapse/rest/client/sendtodevice.py +++ b/synapse/rest/client/sendtodevice.py @@ -13,7 +13,7 @@ # limitations under the License. import logging -from typing import TYPE_CHECKING, Awaitable, Tuple +from typing import TYPE_CHECKING, Tuple from synapse.http import servlet from synapse.http.server import HttpServer @@ -21,7 +21,7 @@ from synapse.http.servlet import assert_params_in_dict, parse_json_object_from_r from synapse.http.site import SynapseRequest from synapse.logging.opentracing import set_tag from synapse.rest.client.transactions import HttpTransactionCache -from synapse.types import JsonDict +from synapse.types import JsonDict, Requester from ._base import client_patterns @@ -43,19 +43,26 @@ class SendToDeviceRestServlet(servlet.RestServlet): self.txns = HttpTransactionCache(hs) self.device_message_handler = hs.get_device_message_handler() - def on_PUT( - self, request: SynapseRequest, message_type: str, txn_id: str - ) -> Awaitable[Tuple[int, JsonDict]]: - set_tag("txn_id", txn_id) - return self.txns.fetch_or_execute_request( - request, self._put, request, message_type, txn_id - ) - - async def _put( + async def on_PUT( self, request: SynapseRequest, message_type: str, txn_id: str ) -> Tuple[int, JsonDict]: requester = await self.auth.get_user_by_req(request, allow_guest=True) + set_tag("txn_id", txn_id) + return await self.txns.fetch_or_execute_request( + request, + requester, + self._put, + request, + requester, + message_type, + ) + async def _put( + self, + request: SynapseRequest, + requester: Requester, + message_type: str, + ) -> Tuple[int, JsonDict]: content = parse_json_object_from_request(request) assert_params_in_dict(content, ("messages",)) diff --git a/synapse/rest/client/transactions.py b/synapse/rest/client/transactions.py index 3f40f1874..f2aaab622 100644 --- a/synapse/rest/client/transactions.py +++ b/synapse/rest/client/transactions.py @@ -15,16 +15,16 @@ """This module contains logic for storing HTTP PUT transactions. This is used to ensure idempotency when performing PUTs using the REST API.""" import logging -from typing import TYPE_CHECKING, Awaitable, Callable, Dict, Tuple +from typing import TYPE_CHECKING, Awaitable, Callable, Dict, Hashable, Tuple from typing_extensions import ParamSpec from twisted.internet.defer import Deferred from twisted.python.failure import Failure -from twisted.web.server import Request +from twisted.web.iweb import IRequest from synapse.logging.context import make_deferred_yieldable, run_in_background -from synapse.types import JsonDict +from synapse.types import JsonDict, Requester from synapse.util.async_helpers import ObservableDeferred if TYPE_CHECKING: @@ -41,53 +41,47 @@ P = ParamSpec("P") class HttpTransactionCache: def __init__(self, hs: "HomeServer"): self.hs = hs - self.auth = self.hs.get_auth() self.clock = self.hs.get_clock() # $txn_key: (ObservableDeferred<(res_code, res_json_body)>, timestamp) self.transactions: Dict[ - str, Tuple[ObservableDeferred[Tuple[int, JsonDict]], int] + Hashable, Tuple[ObservableDeferred[Tuple[int, JsonDict]], int] ] = {} # Try to clean entries every 30 mins. This means entries will exist # for at *LEAST* 30 mins, and at *MOST* 60 mins. self.cleaner = self.clock.looping_call(self._cleanup, CLEANUP_PERIOD_MS) - def _get_transaction_key(self, request: Request) -> str: + def _get_transaction_key(self, request: IRequest, requester: Requester) -> Hashable: """A helper function which returns a transaction key that can be used with TransactionCache for idempotent requests. Idempotency is based on the returned key being the same for separate requests to the same endpoint. The key is formed from the HTTP request - path and the access_token for the requesting user. + path and attributes from the requester: the access_token_id for regular users, + the user ID for guest users, and the appservice ID for appservice users. Args: - request: The incoming request. Must contain an access_token. + request: The incoming request. + requester: The requester doing the request. Returns: A transaction key """ assert request.path is not None - token = self.auth.get_access_token_from_request(request) - return request.path.decode("utf8") + "/" + token + path: str = request.path.decode("utf8") + if requester.is_guest: + assert requester.user is not None, "Guest requester must have a user ID set" + return (path, "guest", requester.user) + elif requester.app_service is not None: + return (path, "appservice", requester.app_service.id) + else: + assert ( + requester.access_token_id is not None + ), "Requester must have an access_token_id" + return (path, "user", requester.access_token_id) def fetch_or_execute_request( self, - request: Request, - fn: Callable[P, Awaitable[Tuple[int, JsonDict]]], - *args: P.args, - **kwargs: P.kwargs, - ) -> Awaitable[Tuple[int, JsonDict]]: - """A helper function for fetch_or_execute which extracts - a transaction key from the given request. - - See: - fetch_or_execute - """ - return self.fetch_or_execute( - self._get_transaction_key(request), fn, *args, **kwargs - ) - - def fetch_or_execute( - self, - txn_key: str, + request: IRequest, + requester: Requester, fn: Callable[P, Awaitable[Tuple[int, JsonDict]]], *args: P.args, **kwargs: P.kwargs, @@ -96,14 +90,15 @@ class HttpTransactionCache: to produce a response for this transaction. Args: - txn_key: A key to ensure idempotency should fetch_or_execute be - called again at a later point in time. + request: + requester: fn: A function which returns a tuple of (response_code, response_dict). *args: Arguments to pass to fn. **kwargs: Keyword arguments to pass to fn. Returns: Deferred which resolves to a tuple of (response_code, response_dict). """ + txn_key = self._get_transaction_key(request, requester) if txn_key in self.transactions: observable = self.transactions[txn_key][0] else: diff --git a/tests/rest/client/test_transactions.py b/tests/rest/client/test_transactions.py index 3086e1b56..d8dc56261 100644 --- a/tests/rest/client/test_transactions.py +++ b/tests/rest/client/test_transactions.py @@ -39,15 +39,23 @@ class HttpTransactionCacheTestCase(unittest.TestCase): self.cache = HttpTransactionCache(self.hs) self.mock_http_response = (HTTPStatus.OK, {"result": "GOOD JOB!"}) - self.mock_key = "foo" + + # Here we make sure that we're setting all the fields that HttpTransactionCache + # uses to build the transaction key. + self.mock_request = Mock() + self.mock_request.path = b"/foo/bar" + self.mock_requester = Mock() + self.mock_requester.app_service = None + self.mock_requester.is_guest = False + self.mock_requester.access_token_id = 1234 @defer.inlineCallbacks def test_executes_given_function( self, ) -> Generator["defer.Deferred[Any]", object, None]: cb = Mock(return_value=make_awaitable(self.mock_http_response)) - res = yield self.cache.fetch_or_execute( - self.mock_key, cb, "some_arg", keyword="arg" + res = yield self.cache.fetch_or_execute_request( + self.mock_request, self.mock_requester, cb, "some_arg", keyword="arg" ) cb.assert_called_once_with("some_arg", keyword="arg") self.assertEqual(res, self.mock_http_response) @@ -58,8 +66,13 @@ class HttpTransactionCacheTestCase(unittest.TestCase): ) -> Generator["defer.Deferred[Any]", object, None]: cb = Mock(return_value=make_awaitable(self.mock_http_response)) for i in range(3): # invoke multiple times - res = yield self.cache.fetch_or_execute( - self.mock_key, cb, "some_arg", keyword="arg", changing_args=i + res = yield self.cache.fetch_or_execute_request( + self.mock_request, + self.mock_requester, + cb, + "some_arg", + keyword="arg", + changing_args=i, ) self.assertEqual(res, self.mock_http_response) # expect only a single call to do the work @@ -77,7 +90,9 @@ class HttpTransactionCacheTestCase(unittest.TestCase): @defer.inlineCallbacks def test() -> Generator["defer.Deferred[Any]", object, None]: with LoggingContext("c") as c1: - res = yield self.cache.fetch_or_execute(self.mock_key, cb) + res = yield self.cache.fetch_or_execute_request( + self.mock_request, self.mock_requester, cb + ) self.assertIs(current_context(), c1) self.assertEqual(res, (1, {})) @@ -106,12 +121,16 @@ class HttpTransactionCacheTestCase(unittest.TestCase): with LoggingContext("test") as test_context: try: - yield self.cache.fetch_or_execute(self.mock_key, cb) + yield self.cache.fetch_or_execute_request( + self.mock_request, self.mock_requester, cb + ) except Exception as e: self.assertEqual(e.args[0], "boo") self.assertIs(current_context(), test_context) - res = yield self.cache.fetch_or_execute(self.mock_key, cb) + res = yield self.cache.fetch_or_execute_request( + self.mock_request, self.mock_requester, cb + ) self.assertEqual(res, self.mock_http_response) self.assertIs(current_context(), test_context) @@ -134,29 +153,39 @@ class HttpTransactionCacheTestCase(unittest.TestCase): with LoggingContext("test") as test_context: try: - yield self.cache.fetch_or_execute(self.mock_key, cb) + yield self.cache.fetch_or_execute_request( + self.mock_request, self.mock_requester, cb + ) except Exception as e: self.assertEqual(e.args[0], "boo") self.assertIs(current_context(), test_context) - res = yield self.cache.fetch_or_execute(self.mock_key, cb) + res = yield self.cache.fetch_or_execute_request( + self.mock_request, self.mock_requester, cb + ) self.assertEqual(res, self.mock_http_response) self.assertIs(current_context(), test_context) @defer.inlineCallbacks def test_cleans_up(self) -> Generator["defer.Deferred[Any]", object, None]: cb = Mock(return_value=make_awaitable(self.mock_http_response)) - yield self.cache.fetch_or_execute(self.mock_key, cb, "an arg") + yield self.cache.fetch_or_execute_request( + self.mock_request, self.mock_requester, cb, "an arg" + ) # should NOT have cleaned up yet self.clock.advance_time_msec(CLEANUP_PERIOD_MS / 2) - yield self.cache.fetch_or_execute(self.mock_key, cb, "an arg") + yield self.cache.fetch_or_execute_request( + self.mock_request, self.mock_requester, cb, "an arg" + ) # still using cache cb.assert_called_once_with("an arg") self.clock.advance_time_msec(CLEANUP_PERIOD_MS) - yield self.cache.fetch_or_execute(self.mock_key, cb, "an arg") + yield self.cache.fetch_or_execute_request( + self.mock_request, self.mock_requester, cb, "an arg" + ) # no longer using cache self.assertEqual(cb.call_count, 2) self.assertEqual(cb.call_args_list, [call("an arg"), call("an arg")])