ASGI 'lifespan' protocol appears unsupported

Question

I have an asynchronous code running on fastapi & aiofiles i'm trying to load and save my info from a .json file but every time I shut down the program, it save only the keys of the dict and showing me "ASGI 'lifespan' protocol appears unsupported" massage

this is my turn on/off part:

@app.on_event("startup")
async def startup_event():
    global beers
    try:
        async with aiofiles.open("data.json", mode='r+', json=True) as file:
            beers = await file.read()
    except:
        beers = {}


@app.on_event("shutdown")
async def on_exit_app():
    async with aiofiles.open("data.json", "w+") as outfile:
        await outfile.write(beers)

any ideas where is the problem?

Answer 1

This 99% means that something in the on_event("shutdown") function throws an error that isn't caught by the server (FastAPI/Starlette), and the app crashes, instead of ending properly. This leads uvicorn to believe that the server doesn't support the livespan part of the ASGI protocol.

If you run uvicorn with additional option --lifespan on , the error will be shown and you can debug it.

See Starlette bug report .

Answer 2

It is just an assertion you can omit that, as far as I understand you are using Uvicorn as an HTTP server, since FastAPI is built top on an ASGI framework and Uvicorn is an ASGI HTTP server, there are some protocols on it. ASGI protocol has support for http, websocket.

Uvicorn sets lifespan's value to auto and the assertion comes from there.

if self.config.lifespan == "auto":
    msg = "ASGI 'lifespan' protocol appears unsupported."

But you can use --lifespan on to fix that.