Why middleware waits for all scheduled tasks to finish?

Description

I schedule tasks to event loop like this:

    async def wait_to_finish():
        time.sleep(5)
        print('finished')

    @router.get("/async/background")
    async def get() -> bool:
        asyncio.create_task(wait_to_finish())
        return True

And it works well. True returned as response without waiting wait_to_finish() function to finish. And wait_to_finish() function runs in the event loop and prints “finished”. Everything works well until here.

But when I add a middleware like this:

async def catch_exceptions_middleware(request: Request, call_next):
    try:
        return await call_next(request)
    except Exception as exc:
        logger.exception("Exception")
        return JSONResponse(status_code=getattr(exc, "status_code", 500),
                                    content={"message": f"Unexpected error occured."})

app.middleware('http')(catch_exceptions_middleware)

It waits to finish all tasks I created in the event loop before sending response. Thus it takes 5+ secs. to send response, in this example. Why middlewares force the event loop to finish all the tasks? How can I avoid this ? (Without using background-tasks. There are many reason I don’t use it. And remember, this works pretty well until I add a middleware as shown above).

Environment

• OS: macOS
• FastAPI Version : 0.61.0
• Python version: 3.8.5

[Kludex]

That’s pretty disappointing… Thank you @ycd

[ycd]

@Kludex doesn’t using a Middleware that inherits BaseHTTPMiddleware brokes the BackgroundTasks?

See Starlette Issues 919