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Allow background tasks to run with custom BaseHTTPMiddleware's #1441

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Allow background tasks to run with custom BaseHTTPMiddleware's #1441

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149aa7c
Allow background tasks to run with custom `BaseHTTPMiddleware`'s
Kludex Jan 28, 2022
e161bae
Ignore coverage for now
Kludex Jan 28, 2022
e1af17b
Merge branch 'master' into fix/remove-cancel-scope
Kludex Jan 28, 2022
3011702
Merge branch 'master' into fix/remove-cancel-scope
Kludex Feb 8, 2022
20406e7
Merge branch 'master' into fix/remove-cancel-scope
Kludex Feb 19, 2022
8e6063d
Merge branch 'master' into fix/remove-cancel-scope
Kludex Apr 4, 2022
5843a57
Merge branch 'master' into fix/remove-cancel-scope
Kludex Apr 24, 2022
346f893
Merge branch 'master' into fix/remove-cancel-scope
Kludex May 8, 2022
470b31c
Merge branch 'master' into fix/remove-cancel-scope
adriangb May 12, 2022
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17 changes: 12 additions & 5 deletions starlette/middleware/base.py
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Original file line number Diff line number Diff line change
Expand Up @@ -24,9 +24,11 @@ async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
await self.app(scope, receive, send)
return

call_next_response = None
send_stream, recv_stream = anyio.create_memory_object_stream()

async def call_next(request: Request) -> Response:
app_exc: typing.Optional[Exception] = None
send_stream, recv_stream = anyio.create_memory_object_stream()

async def coro() -> None:
nonlocal app_exc
Expand Down Expand Up @@ -61,17 +63,22 @@ async def body_stream() -> typing.AsyncGenerator[bytes, None]:
if app_exc is not None:
raise app_exc

response = StreamingResponse(
nonlocal call_next_response

call_next_response = StreamingResponse(
status_code=message["status"], content=body_stream()
)
response.raw_headers = message["headers"]
return response
call_next_response.raw_headers = message["headers"]
return call_next_response

async with anyio.create_task_group() as task_group:
request = Request(scope, receive=receive)
response = await self.dispatch_func(request, call_next)
if call_next_response and response is not call_next_response:
async with recv_stream:
async for _ in recv_stream:
... # pragma: no cover
Comment on lines +78 to +80
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I can create a function that performs this logic, if wanted.

await response(scope, receive, send)
Comment on lines +77 to 81
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@jhominal jhominal Jan 30, 2022 •
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It seems to me that we will wait for app to make all of its calls to send_stream.send before actually processing the response returned by dispatch_func. If that is the case, and given that all the messages from app are being discarded, I think it would be preferable, either to call await response(scope, receive, send) before draining recv_stream, or to put draining of recv_stream in another task of task_group.

Of course, I do not know the relevant technologies (ASGI/the server implementations/Starlette) as well as you do, so there could very well be a reason that either my analysis is wrong, or that my suggestions are unworkable.

Suggested change
if call_next_response and response is not call_next_response:
async with recv_stream:
async for _ in recv_stream:
... # pragma: no cover
await response(scope, receive, send)
if call_next_response and response is not call_next_response:
async def drain_stream():
async with recv_stream:
async for _ in recv_stream:
... # pragma: no cover
task_group.start_soon(drain_stream)
await response(scope, receive, send)

task_group.cancel_scope.cancel()

async def dispatch(
self, request: Request, call_next: RequestResponseEndpoint
Expand Down