subscription_handler is the callback to my websockets server:

    server = await websockets.serve(subscription_handler, host=websocket_host, port=websocket_port)

The original version does not work:

async def subscription_handler(websocket, path):
    logger.info("New WebSocket connection")
    try:
        async for message in websocket:
            response = await prepare_response(message)
            logger.info("Sending response")
            await websocket.send(response)
            logger.info(f"Response sent: {response}")
    except ConnectionClosedOK:
        logger.info("WebSocket connection closed normally by the client.")
    except ConnectionClosedError as e:
        logger.warning(f"WebSocket connection closed unexpectedly: {e}")
    except Exception as e:
        logger.error(f"Error in subscription handler: {e}", exc_info=True)
    finally:
        logger.info("Subscription handler finished")

When sending the response, it throws ConnectionClosedOK but the client does not receive the message.

Using websocket.broadcast instead of websocket.send fixes this:

async def subscription_handler(websocket, path):
    logger.info("New WebSocket connection")
    connected.add(websocket)
    try:
        async for message in websocket:
            response = await prepare_response(message)
            logger.info("Sending response")
            websockets.broadcast(connected, response)
            logger.info(f"Response sent: {response}")
    except ConnectionClosedOK:
        logger.info("WebSocket connection closed normally by the client.")
    except ConnectionClosedError as e:
        logger.warning(f"WebSocket connection closed unexpectedly: {e}")
    except Exception as e:
        logger.error(f"Error in subscription handler: {e}", exc_info=True)
    finally:
        logger.info("Subscription handler finished")

The client receives the message and f"Response set: {response}" is logged.

My question is why doesn’t send work while broadcast does work?