Internal method that will be called when receiving message.

def _callback(self, ch, method, properties, body):
        """Internal method that will be called when receiving message."""

        get_logger().info("Message received! Calling listeners...")

        topic = method.routing_key
        dct = json.loads(body.decode('utf-8'))

        for listener in self.listeners:
            listener(self, topic, dct)