Fastapi: [QUESTION] Background Task with websocket

[DrPyser]

Description

Is it possible to use BackgroundTasks with websockets?

I tried with a simple case:

def test():
   print('test')


@router.post("/test")
async def send_notification(background_tasks: BackgroundTasks):
   background_tasks.add_task(test)
   return {"message": "Notification sent in the background"}


@router.websocket("/ws")
async def listen(websocket: WebSocket, background_tasks: BackgroundTasks):
   await websocket.accept()
   background_tasks.add_task(test)

The send_notification http endpoint example works, but the listen websocket endpoint doesn't.

Thanks!

[tiangolo]

Background tasks internally depend on a Request, and they are executed after returning the request to the client. In the case of a WebSocket, as the WebSocket is not really "finished" but is an ongoing connection, it wouldn't be a background task.

Nevertheless, you can make sure an async function is executed with asyncio.ensure_future: https://docs.python.org/3/library/asyncio-future.html#asyncio.ensure_future

[DrPyser]

Okay, got it, thanks.

[tiangolo]

Cool! I'll close this issue now then.