Request.is_disconnected could consume request body

[msdrigg]

For some background, I got here looking for a way to cancel costly actions if the client disconnects. I checked the source of Request.is_disconnected:

    async def is_disconnected(self) -> bool:
        if not self._is_disconnected:
            message: Message = {}

            # If message isn't immediately available, move on
            with anyio.CancelScope() as cs:
                cs.cancel()
                message = await self._receive()

            if message.get("type") == "http.disconnect":
                self._is_disconnected = True

        return self._is_disconnected

Here we see that is_disconnected calls self._receive() (which consumes a asgi message). I believe that this could possibly consume and discard a http.request message containing the request body.

If this is actually a possible side effect, I believe that it should be avoided (or at least documented somewhere).

If this is not possible to fix, is there any way to listen for disconnection (ideally create an Event that signals disconnection) without consuming the request? I read the spec, but unless I buffer arbitrarily many messages from receive, I don't know how I would do this.

I am relatively new to async python web frameworks, so I may be missing something obvious (or asking in the right place), but I wanted to reach out to see if anyone here could help me

[msdrigg]

Linking tiangolo/fastapi#8805 for context

[aeb-dev]

We are also searching for a way to implement this

[hari01584]

Can you try and see if tiangolo/fastapi#11360 fix your problem?