Cannot receive streaming response and SSE API data when serve behind caddy

[hermeschen1116]

As mentioned in the title, I currently serve my FastAPI application with Granian behind Caddy. However, I am unable to receive data when calling the streaming response and SSE API while a connection appears to have been established. These APIs function correctly when served without Caddy. Is additional setup required to resolve this issue?

[gi0baro]

Hard to make guesses without further information (like the caddy configuration)

[hermeschen1116]

Oh, sorry. Below is my Caddy (version 2.11.2) configuration.

:8000 {
    reverse_proxy tlpr-server:8000 {
    	header_up Connection "keep-alive"
        header_up Cache-Control "no-cache"
        flush_interval -1
        transport http {
            versions 1.1
        }
    }
}

And one of my API.

@router.get(
	"/vehicleEvent/bbox",
	response_class=StreamingResponse,
	description="即時顯示偵測結果",
	responses={200: {"description": "成功建立串流"}, 422: {"description": "錯誤的 UUID 格式"}},
)
async def stream_bbox(
	request: Request,
	_: typing.Annotated[UserInfo, Security(check_permission())],
	channel: typing.Annotated[int, Query(description="Channel No.", ge=0)],
) -> StreamingResponse:

	async def bbox_streamer() -> AsyncGenerator[bytes]:
		try:
			while True:
				overlay = await _get_bbox_overlay_for_channel(CHANNEL(channel), app=request.app)
				if not overlay:
					await anyio.sleep(0.05)
					continue

				if check_if_service_is_shutdown(app=request.app) or (await request.is_disconnected()):
					break

				yield (b"--frame\r\nContent-Type: image/webp\r\n\r\n" + overlay + b"\r\n")
				await anyio.lowlevel.checkpoint()
		except (KeyboardInterrupt, SystemExit, anyio.get_cancelled_exc_class()):
			await anyio.sleep(0.01)
			await LOGGER.awarning(f"BBox Client（{request.client}）disconnected", channel=channel)
			return
		except Exception:  # noqa: BLE001
			await anyio.sleep(0.01)
			await LOGGER.aexception("Unexpected error occurred when streaming frame")
			return

	return StreamingResponse(
		bbox_streamer(), media_type="multipart/x-mixed-replace; boundary=frame", headers={"Cache-Control": "no-cache"}
	)
	

[gi0baro]

and what happens on the client side? timeouts, hanging, disconnect.. Do you receive the response headers?

[hermeschen1116]

It shows 200 and there are some logs appearing on the server side. But there's no data stream received.

[hermeschen1116]

@gi0baro Hello, I have identified the cause of the issue. It is related to a previous issue I raised. The same issue causes my API to fail when served by Docker on Linux (while it functions correctly on macOS). Removing the actual cause await request.is_disconnected() resolves the problem.

[hermeschen1116]

@gi0baro Sorry for bothering you again. But I'm wondering if it's normal that request.is_disconnected() causes the error mentioned in issue 698 when serving fastapi with granian. Or is it possible to know the cause?