FastAPI: WebSocket connection close after ~40s

Question

I try to ping/pong json packages between a FastAPI websocket endpoint and a client using the websocket library from Zephyr RTOS. Unfortunately the connection is closed by the FastAPI server after ~40 seconds. This time seems to be constant. My guess is, that there must occur a timeout event due to a missing/wrong condition.

This post seems to address my issue. Unfortunately my code is not running with a newer uvicorn version which would support --ws-ping-interval or --ws-ping-timeout.

For a simple test I did the following:

Server side:

@app.websocket("/ws/update_status")
async def websocket_endpoint(websocket: WebSocket, db: Session = Depends(get_db)):
    await websocket.accept()
    while True:
        data = await websocket.receive_json()
        await websocket.send_json('{"status":"ok"}')  

Client side (C code running on Zephyr-RTOS):

// some code to define JSON package

while(1)
{
    websocket_send_msg(sock, send_buffer, json_length, WEBSOCKET_OPCODE_DATA_TEXT, true, true, SYS_FOREVER_MS);
    websocket_recv_msg(sock, receive_buffer, sizeof(receive_buffer), &message_type, 0, SYS_FOREVER_MS);
}

I use the following package versions:

uvicorn=='0.13.4'
fastapi=='0.68.2'

Does anyone know why the connection aborts after 40 seconds and how it can be avoided?