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Generalise the @cancellable annotation so it can be used on functions other than just servlet methods. (#13662)

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reivilibre 2022-08-31 11:16:05 +00:00 committed by GitHub
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10 changed files with 75 additions and 75 deletions
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1
changelog.d/13662.misc Normal file
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@ -0,0 +1 @@
Generalise the `@cancellable` annotation so it can be used on functions other than just servlet methods.

5
synapse/federation/transport/server/_base.py
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@ -21,7 +21,7 @@ from typing import TYPE_CHECKING, Any, Awaitable, Callable, Dict, Optional, Tupl
from synapse.api.errors import Codes, FederationDeniedError, SynapseError
from synapse.api.urls import FEDERATION_V1_PREFIX
from synapse.http.server import HttpServer, ServletCallback, is_method_cancellable
from synapse.http.server import HttpServer, ServletCallback
from synapse.http.servlet import parse_json_object_from_request
from synapse.http.site import SynapseRequest
from synapse.logging.context import run_in_background
@ -34,6 +34,7 @@ from synapse.logging.opentracing import (
whitelisted_homeserver,
)
from synapse.types import JsonDict
from synapse.util.cancellation import is_function_cancellable
from synapse.util.ratelimitutils import FederationRateLimiter
from synapse.util.stringutils import parse_and_validate_server_name
@ -375,7 +376,7 @@ class BaseFederationServlet:
if code is None:
continue
if is_method_cancellable(code):
if is_function_cancellable(code):
# The wrapper added by `self._wrap` will inherit the cancellable flag,
# but the wrapper itself does not support cancellation yet.
# Once resolved, the cancellation tests in

68
synapse/http/server.py
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@ -33,7 +33,6 @@ from typing import (
Optional,
Pattern,
Tuple,
TypeVar,
Union,
)
@ -64,6 +63,7 @@ from synapse.logging.context import defer_to_thread, preserve_fn, run_in_backgro
from synapse.logging.opentracing import active_span, start_active_span, trace_servlet
from synapse.util import json_encoder
from synapse.util.caches import intern_dict
from synapse.util.cancellation import is_function_cancellable
from synapse.util.iterutils import chunk_seq
if TYPE_CHECKING:
@ -94,68 +94,6 @@ HTML_ERROR_TEMPLATE = """<!DOCTYPE html>
HTTP_STATUS_REQUEST_CANCELLED = 499
F = TypeVar("F", bound=Callable[..., Any])
_cancellable_method_names = frozenset(
{
# `RestServlet`, `BaseFederationServlet` and `BaseFederationServerServlet`
# methods
"on_GET",
"on_PUT",
"on_POST",
"on_DELETE",
# `_AsyncResource`, `DirectServeHtmlResource` and `DirectServeJsonResource`
# methods
"_async_render_GET",
"_async_render_PUT",
"_async_render_POST",
"_async_render_DELETE",
"_async_render_OPTIONS",
# `ReplicationEndpoint` methods
"_handle_request",
}
)
def cancellable(method: F) -> F:
"""Marks a servlet method as cancellable.
Methods with this decorator will be cancelled if the client disconnects before we
finish processing the request.
During cancellation, `Deferred.cancel()` will be invoked on the `Deferred` wrapping
the method. The `cancel()` call will propagate down to the `Deferred` that is
currently being waited on. That `Deferred` will raise a `CancelledError`, which will
propagate up, as per normal exception handling.
Before applying this decorator to a new endpoint, you MUST recursively check
that all `await`s in the function are on `async` functions or `Deferred`s that
handle cancellation cleanly, otherwise a variety of bugs may occur, ranging from
premature logging context closure, to stuck requests, to database corruption.
Usage:
class SomeServlet(RestServlet):
@cancellable
async def on_GET(self, request: SynapseRequest) -> ...:
...
"""
if method.__name__ not in _cancellable_method_names and not any(
method.__name__.startswith(prefix) for prefix in _cancellable_method_names
):
raise ValueError(
"@cancellable decorator can only be applied to servlet methods."
)
method.cancellable = True # type: ignore[attr-defined]
return method
def is_method_cancellable(method: Callable[..., Any]) -> bool:
"""Checks whether a servlet method has the `@cancellable` flag."""
return getattr(method, "cancellable", False)
def return_json_error(
f: failure.Failure, request: SynapseRequest, config: Optional[HomeServerConfig]
) -> None:
@ -389,7 +327,7 @@ class _AsyncResource(resource.Resource, metaclass=abc.ABCMeta):
method_handler = getattr(self, "_async_render_%s" % (request_method,), None)
if method_handler:
request.is_render_cancellable = is_method_cancellable(method_handler)
request.is_render_cancellable = is_function_cancellable(method_handler)
raw_callback_return = method_handler(request)
@ -551,7 +489,7 @@ class JsonResource(DirectServeJsonResource):
async def _async_render(self, request: SynapseRequest) -> Tuple[int, Any]:
callback, servlet_classname, group_dict = self._get_handler_for_request(request)
request.is_render_cancellable = is_method_cancellable(callback)
request.is_render_cancellable = is_function_cancellable(callback)
# Make sure we have an appropriate name for this handler in prometheus
# (rather than the default of JsonResource).

7
synapse/replication/http/_base.py
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@ -26,12 +26,13 @@ from twisted.web.server import Request
from synapse.api.errors import HttpResponseException, SynapseError
from synapse.http import RequestTimedOutError
from synapse.http.server import HttpServer, is_method_cancellable
from synapse.http.server import HttpServer
from synapse.http.site import SynapseRequest
from synapse.logging import opentracing
from synapse.logging.opentracing import trace_with_opname
from synapse.types import JsonDict
from synapse.util.caches.response_cache import ResponseCache
from synapse.util.cancellation import is_function_cancellable
from synapse.util.stringutils import random_string
if TYPE_CHECKING:
@ -311,7 +312,7 @@ class ReplicationEndpoint(metaclass=abc.ABCMeta):
url_args = list(self.PATH_ARGS)
method = self.METHOD
if self.CACHE and is_method_cancellable(self._handle_request):
if self.CACHE and is_function_cancellable(self._handle_request):
raise Exception(
f"{self.__class__.__name__} has been marked as cancellable, but CACHE "
"is set. The cancellable flag would have no effect."
@ -359,6 +360,6 @@ class ReplicationEndpoint(metaclass=abc.ABCMeta):
# The `@cancellable` decorator may be applied to `_handle_request`. But we
# told `HttpServer.register_paths` that our handler is `_check_auth_and_handle`,
# so we have to set up the cancellable flag ourselves.
request.is_render_cancellable = is_method_cancellable(self._handle_request)
request.is_render_cancellable = is_function_cancellable(self._handle_request)
return await self._handle_request(request, **kwargs)

3
synapse/rest/client/room.py
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@ -37,7 +37,7 @@ from synapse.api.errors import (
)
from synapse.api.filtering import Filter
from synapse.events.utils import format_event_for_client_v2
from synapse.http.server import HttpServer, cancellable
from synapse.http.server import HttpServer
from synapse.http.servlet import (
ResolveRoomIdMixin,
RestServlet,
@ -57,6 +57,7 @@ from synapse.storage.state import StateFilter
from synapse.streams.config import PaginationConfig
from synapse.types import JsonDict, StreamToken, ThirdPartyInstanceID, UserID
from synapse.util import json_decoder
from synapse.util.cancellation import cancellable
from synapse.util.stringutils import parse_and_validate_server_name, random_string
if TYPE_CHECKING:

56
synapse/util/cancellation.py Normal file
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@ -0,0 +1,56 @@
# Copyright 2022 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.
from typing import Any, Callable, TypeVar
F = TypeVar("F", bound=Callable[..., Any])
def cancellable(function: F) -> F:
"""Marks a function as cancellable.
Servlet methods with this decorator will be cancelled if the client disconnects before we
finish processing the request.
Although this annotation is particularly useful for servlet methods, it's also
useful for intermediate functions, where it documents the fact that the function has
been audited for cancellation safety and needs to preserve that.
This then simplifies auditing new functions that call those same intermediate
functions.
During cancellation, `Deferred.cancel()` will be invoked on the `Deferred` wrapping
the method. The `cancel()` call will propagate down to the `Deferred` that is
currently being waited on. That `Deferred` will raise a `CancelledError`, which will
propagate up, as per normal exception handling.
Before applying this decorator to a new function, you MUST recursively check
that all `await`s in the function are on `async` functions or `Deferred`s that
handle cancellation cleanly, otherwise a variety of bugs may occur, ranging from
premature logging context closure, to stuck requests, to database corruption.
See the documentation page on Cancellation for more information.
Usage:
class SomeServlet(RestServlet):
@cancellable
async def on_GET(self, request: SynapseRequest) -> ...:
...
"""
function.cancellable = True # type: ignore[attr-defined]
return function
def is_function_cancellable(function: Callable[..., Any]) -> bool:
"""Checks whether a servlet method has the `@cancellable` flag."""
return getattr(function, "cancellable", False)

3
tests/federation/transport/server/test__base.py
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@ -18,9 +18,10 @@ from typing import Dict, List, Tuple
from synapse.api.errors import Codes
from synapse.federation.transport.server import BaseFederationServlet
from synapse.federation.transport.server._base import Authenticator, _parse_auth_header
from synapse.http.server import JsonResource, cancellable
from synapse.http.server import JsonResource
from synapse.server import HomeServer
from synapse.types import JsonDict
from synapse.util.cancellation import cancellable
from synapse.util.ratelimitutils import FederationRateLimiter
from tests import unittest

2
tests/http/test_servlet.py
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@ -18,7 +18,6 @@ from typing import Tuple
from unittest.mock import Mock
from synapse.api.errors import Codes, SynapseError
from synapse.http.server import cancellable
from synapse.http.servlet import (
RestServlet,
parse_json_object_from_request,
@ -28,6 +27,7 @@ from synapse.http.site import SynapseRequest
from synapse.rest.client._base import client_patterns
from synapse.server import HomeServer
from synapse.types import JsonDict
from synapse.util.cancellation import cancellable
from tests import unittest
from tests.http.server._base import test_disconnect

3
tests/replication/http/test__base.py
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@ -18,11 +18,12 @@ from typing import Tuple
from twisted.web.server import Request
from synapse.api.errors import Codes
from synapse.http.server import JsonResource, cancellable
from synapse.http.server import JsonResource
from synapse.replication.http import REPLICATION_PREFIX
from synapse.replication.http._base import ReplicationEndpoint
from synapse.server import HomeServer
from synapse.types import JsonDict
from synapse.util.cancellation import cancellable
from tests import unittest
from tests.http.server._base import test_disconnect

2
tests/test_server.py
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@ -26,12 +26,12 @@ from synapse.http.server import (
DirectServeJsonResource,
JsonResource,
OptionsResource,
cancellable,
)
from synapse.http.site import SynapseRequest, SynapseSite
from synapse.logging.context import make_deferred_yieldable
from synapse.types import JsonDict
from synapse.util import Clock
from synapse.util.cancellation import cancellable
from tests import unittest
from tests.http.server._base import test_disconnect