Dynamically get topic type for rosbag

edit

Hello,

I want to create a service, which records multiple different topics into a rosbag-file. The problem is, that I need the data type of the topic that is going to be recorded to subscribe to the topic. I start the service with the command line

rosservice call /start_data_recorder "topics: ['scan','map','imu/data']

to collect the three topics.

    def on_start_recording(self, msg):

        # Initialize new Rosbag
        PATH = "../catkin_ws/src/robolab_base/data_recorder/recordings"
        self.bag = rosbag.Bag(f'{PATH}/Rec.bag', 'w') 

        for topic in msg.topics:

            # Initialize new datawriter class
            subscriber = DataWriter(topic, self.bag, self.shutdown_recording)

            # Collect topic data
            data_type = rostopic.get_topic_type("/" + topic, blocking = False)[0]

            Sub = self._ros_api.Subscriber(topic, ros_msg_type, subscriber.callback)
            self.subscribers.append(Sub)

        return StartDataRecordingResponse()

with my DataWriter class writing the data to the bag file and a service (StartDataRecording.srv)

However, I get an error message, when initialising the Subscriber Sub:

Error processing request: data_class [sensor_msgs/LaserScan] is not a class

I suppose that data_type is not a valid output, but I am not sure how to proceed from here to get each topic recorded with the rosbag.

Edit:

I fixed it, by using rostopic.get_topic_class() instead of rostopic.get_topic_type() which provided the type of data needed for the Subscriber.