forked from MirrorHub/synapse
Add @cancellable
decorator, for use on request handlers (#12586)
Signed-off-by: Sean Quah <seanq@element.io>
This commit is contained in:
parent
2aad0ae57f
commit
5c00151c28
2 changed files with 62 additions and 0 deletions
1
changelog.d/12586.misc
Normal file
1
changelog.d/12586.misc
Normal file
|
@ -0,0 +1 @@
|
|||
Add `@cancellable` decorator, for use on endpoint methods that can be cancelled when clients disconnect.
|
|
@ -33,6 +33,7 @@ from typing import (
|
|||
Optional,
|
||||
Pattern,
|
||||
Tuple,
|
||||
TypeVar,
|
||||
Union,
|
||||
)
|
||||
|
||||
|
@ -92,6 +93,66 @@ 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:
|
||||
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) -> None:
|
||||
"""Sends a JSON error response to clients."""
|
||||
|
||||
|
|
Loading…
Reference in a new issue