How to respond to WebSocket Ping message?

[otsuka]

When a WebSocket Ping message (data frame) is sent to a FastAPI WebSocket server, how can I receive it and return a Pong message?

Sending Ping using aiohttp as below, it doesn't seem that FastAPI WebSocket connection receives anything.

Sending Ping

async with aiohttp.ClientSession() as sess:
    async with sess.ws_connect(WS_ENDPOINT) as ws:
        await ws.ping()

Receiving Ping

@app.websocket("/ws")
async def websocket_endpoint(ws: WebSocket):
    await ws.accept()
    data = await ws.receive()

[euri10]

imho the simplest is not to use FastAPI decorator but subclassing Starlette WebSocketEndpoint and sending your pong in the on_receive method

Oo that ping... 😄

[tiangolo]

Ping events are defined in the WebSocket spec: https://tools.ietf.org/html/rfc6455#section-5.5.2 and are handled automatically by Uvicorn, not by FastAPI.

[otsuka]

@tiangolo
Thank you for your response.
I found the code that handles a Ping message in Uvicorn.
https://github.com/encode/uvicorn/blob/master/uvicorn/protocols/websockets/wsproto_impl.py#L186-L187