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#
# This file is licensed under the Affero General Public License (AGPL) version 3.
#
# Copyright (C) 2023 New Vector, Ltd
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# See the GNU Affero General Public License for more details:
# <https://www.gnu.org/licenses/agpl-3.0.html>.
#
# Originally licensed under the Apache License, Version 2.0:
# <http://www.apache.org/licenses/LICENSE-2.0>.
#
# [This file includes modifications made by New Vector Limited]
#
#
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)
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