将数据发送到 Pub/Sub 主题时 Firebase Cloud 函数会创建错误消息

Question

我正在做一个物联网项目，需要物联网设备将数据发送到网关设备，网关设备然后通过 mqtt 桥将此数据发布到 Google Pub/Sub 主题。 mqtt 桥代码是用 python 编写的，但我希望使用 Firebase Cloud Functions 将此数据存储在 Firebase Store 中。但是，每当将数据发布到 pub/sub 主题时，每当云函数尝试提取此数据时，我都会收到“语法错误：JSON.parse 位置 0 处的 JSON 中的意外标记 R”错误。 MQTT 代码使用函数调用客户端，如下所示：

def get_client(
        project_id, cloud_region, registry_id, gateway_id, private_key_file,
        algorithm, ca_certs, mqtt_bridge_hostname, mqtt_bridge_port,
        jwt_expires_minutes):
    """Create our MQTT client. The client_id is a unique string that identifies
    this device. For Google Cloud IoT Core, it must be in the format below."""
    client = mqtt.Client(
        client_id=('projects/{}/locations/{}/registries/{}/devices/{}'.format(
            project_id,
            cloud_region,
            registry_id,
            gateway_id)))

    # With Google Cloud IoT Core, the username field is ignored, and the
    # password field is used to transmit a JWT to authorize the device.
    client.username_pw_set(
        username='unused',
        password=create_jwt(
            project_id, private_key_file, algorithm, jwt_expires_minutes))

    # Enable SSL/TLS support.
    client.tls_set(ca_certs=ca_certs, tls_version=ssl.PROTOCOL_TLSv1_2)

    # Register callbacks. https://eclipse.org/paho/clients/python/docs/
    # describes additional callbacks that Paho supports. In this example,
    # the callbacks just print to standard out.
    client.on_connect = on_connect
    client.on_publish = on_publish
    client.on_disconnect = on_disconnect
    client.on_message = on_message
    client.on_subscribe = on_subscribe

    # Connect to the Google MQTT bridge.
    client.connect(mqtt_bridge_hostname, mqtt_bridge_port)

    mqtt_topic = '/devices/{}/events'.format(gateway_id)
    client.publish(mqtt_topic, 'RPI Gateway started.', qos=0)

    return client

此代码在将数据发布到云发布/订阅主题的 main 函数中执行：

client = get_client(
        args.project_id, args.cloud_region, args.registry_id, args.gateway_id,
        args.private_key_file, args.algorithm, args.ca_certs,
        args.mqtt_bridge_hostname, args.mqtt_bridge_port,
        args.jwt_expires_minutes)

    while True:
        client.loop()
        if gateway_state.connected is False:
            print('connect status {}'.format(gateway_state.connected))
            time.sleep(1)
            continue

        try:
            data, client_addr = udpSerSock.recvfrom(BUFSIZE)
        except socket.error:
            continue
        print('[{}]: From Address {}:{} receive data: {}'.format(
                ctime(), client_addr[0], client_addr[1], data.decode("utf-8")))

        command = json.loads(data.decode('utf-8'))
        if not command:
            print('invalid json command {}'.format(data))
            continue

        action = command["action"]
        device_id = command["device"]
        template = '{{ "device": "{}", "command": "{}", "status" : "ok" }}'

        if action == 'event':
            print('Sending telemetry event for device {}'.format(device_id))
            payload = command["data"]

            mqtt_topic = '/devices/{}/events'.format(device_id)
            print('Publishing message to topic {} with payload \'{}\''.format(
                    mqtt_topic, payload))
            _, event_mid = client.publish(mqtt_topic, payload, qos=0)

            message = template.format(device_id, 'event')
            udpSerSock.sendto(message.encode('utf8'), client_addr)
 
           
        elif action == 'attach':
            print('Sending telemetry event for device {}'.format(device_id))
            attach_topic = '/devices/{}/attach'.format(device_id)
            auth = ''  # TODO:    auth = command["jwt"]
            attach_payload = '{{"authorization" : "{}"}}'.format(auth)

            print('Attaching device {}'.format(device_id))
            print(attach_topic)
            response, attach_mid = client.publish(
                    attach_topic, attach_payload, qos=1)

            message = template.format(device_id, 'attach')
            udpSerSock.sendto(message.encode('utf8'), client_addr)
        elif action == 'detach':
            detach_topic = '/devices/{}/detach'.format(device_id)
            print(detach_topic)

            res, mid = client.publish(detach_topic, "{}", qos=1)

            message = template.format(res, mid)
            print('sending data over UDP {} {}'.format(client_addr, message))
            udpSerSock.sendto(message.encode('utf8'), client_addr)

        elif action == "subscribe":
            print('subscribe config for {}'.format(device_id))
            subscribe_topic = '/devices/{}/config'.format(device_id)
            skip_next_sub = True

            _, mid = client.subscribe(subscribe_topic, qos=1)
            message = template.format(device_id, 'subscribe')
            gateway_state.subscriptions[subscribe_topic] = client_addr

            udpSerSock.sendto(message.encode('utf8'), client_addr)

        else:
            print('undefined action: {}'.format(action))

    print('Finished.')

如何修改此代码，以便从发布/订阅主题中提取的数据采用适用于 Firebase Cloud Funciton 的正确 JSON 格式？