mqtt-kafka源连接器:有趣的字节字符

我在跟随 https://github.com/kaiwaehner/kafka-connect-iot-mqtt-connector-example 用于将mosquitto和kafka与mqtt源连接器连接。我正在将mosquitto发行商发送的数据发送到mosquitto订户和kafka消费者。但是Kafka Consumer的ConsumerRecord对象中的key和value字段有一些预先准备好的字节字符。 下面是我得到的代码片段和输出。

mqttpublisher.py版

while v3 < 3:
             data3 = {
                      "time": str(datetime.datetime.now().time()),
                       "val": v3
                      }
             client.publish("sensor/dist", json.dumps(data3), qos=2)

             v3 += 1
             time.sleep(2)

mqtt订阅服务器.py

def on_message_print(client, userdata, message):
            print(message.topic,message.payload)

subscribe.callback(on_message_print, "sensor/#", hostname="localhost")

卡夫卡消费者.py

consumer = KafkaConsumer('mqtt.',
                     bootstrap_servers=['localhost:9092'])

for message in consumer:
   print(message)

输出:mqttsubscriber.py

传感器/距离b'“时间”:“12:44:30.817462”,“val”:0”

传感器/距离b'“时间”:“12:44:32.820040”,“val”:1”

传感器/距离b'“时间”:“12:44:34.822657”,“val”:2”

输出:kafkaconsumer.py

ConsumerRecord(topic='mqtt'',partition=0,offset=225,timestamp=1545117270870,timestamp_type=0, key=b'\x00\x00\x00\x00\x01\x16传感器/距离' , 值=b'\x00\x00\x00\x00\x02j“time”:“12:44:30.817462”,“val”:0 ,headers=[('mqtt.message.id',b'0'),('mqtt.qos',b'0'),('mqtt.retained',b'false'),('mqtt.duplicate',b'false')],checksum=none,serialized_key_size=17,serialized_value_size=43,serialized_header_size=62)

ConsumerRecord(topic='mqtt'',partition=0,offset=226,timestamp=1545117272821,timestamp_type=0, key=b'\x00\x00\x00\x00\x01\x16传感器/距离' , 值=b'\x00\x00\x00\x00\x02j“time”:“12:44:32.820040”,“val”:1” ,headers=[('mqtt.message.id',b'0'),('mqtt.qos',b'0'),('mqtt.retained',b'false'),('mqtt.duplicate',b'false')],checksum=none,serialized_key_size=17,serialized_value_size=43,serialized_header_size=62)

ConsumerRecord(topic='mqtt'',partition=0,offset=227,timestamp=1545117274824,timestamp_type=0, key=b'\x00\x00\x00\x00\x01\x16传感器/距离' , 值=b'\x00\x00\x00\x00\x02j“time”:“12:44:34.822657”,“val”:2” ,headers=[('mqtt.message.id',b'0'),('mqtt.qos',b'0'),('mqtt.retained',b'false'),('mqtt.duplicate',b'false')],checksum=none,serialized_key_size=17,serialized_value_size=43,serialized_header_size=62)

是什么导致了卡夫卡消费者在上面预先准备了额外的字节? 事先谢谢。