Paho-MQTT连接每90秒断开，协议版本遭拒问题求助

问题描述 #

使用Python的paho-mqtt库编写温度传感器数据上报脚本，数据能按预期每15分钟发布，但日志显示MQTT连接每隔约90秒意外断开，尽管已将keepalive值设置为930秒（15分30秒）。日志报错如下：

INFO:root:Unexpected disconnection. Reason: Connection Refused: unacceptable protocol version.

脚本代码 #

import paho.mqtt.client as mqtt
import Adafruit_DHT
import time
import ssl
import logging

logging.basicConfig(level=logging.DEBUG, filename='/home/pi/Documents/mqtt.log', encoding='utf-8')

# Set up DHT22 sensor
dht_sensor = Adafruit_DHT.DHT22
dht_pin = 4  # GPIO pin number the sensor is connected to

username = 'master:mqttuser_karlsruhe'
secret = 'ifYsftrjtzktzkfDSc'
host = '192.168.0.52'
port = 8883
clientID = 'raspi_ka'
assetID = '3ndhrtjtz55rrGa'


def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))
    logging.info("Connected with result code "+str(rc))


def on_publish(client, userdata, msg):
    print(msg.topic+" "+str(msg.payload))
    logging.info(msg.topic+" "+str(msg.payload))


def on_disconnect(client, userdata, rc):
    if rc != 0:
        print("Unexpected disconnection.")
        logging.info(f"Unexpected disconnection. Reason: {mqtt.connack_string(rc)}")


def on_log(client, userdata, level, buf):
    print("log: ", buf)
    logging.info("log: ", buf)


mqtt_client = mqtt.Client(clientID)
mqtt_client.username_pw_set(username, password=secret)
context = ssl.SSLContext(ssl.PROTOCOL_TLSv1_2)
mqtt_client.tls_set_context(context)
mqtt_client.on_connect = on_connect
mqtt_client.on_disconnect = on_disconnect
mqtt_client.on_publish = on_publish
mqtt_client.on_log = on_log
mqtt_client.connect(host, port=port, keepalive=930)
mqtt_client.loop_start()

# Continuously read and send temperature values
while True:
    humidity, temperature = Adafruit_DHT.read_retry(dht_sensor, dht_pin)
    if humidity is not None and temperature is not None:
        mqtt_client.publish(f"master/{clientID}/writeattributevalue/temperature/{assetID}", temperature)
        mqtt_client.publish(f"master/{clientID}/writeattributevalue/humidity/{assetID}", humidity)
    else:
        print("Failed to read temperature sensor data")
    print(temperature)
    print("")
    time.sleep(900)

# Disconnect MQTT client
mqtt_client.disconnect()
mqtt_client.loop_stop()

问题原因与解决方法 #

核心原因 #

报错Connection Refused: unacceptable protocol version明确指向客户端与MQTT服务器的协议版本不匹配。paho-mqtt库的mqtt.Client()默认使用MQTT 3.1版本，而多数现代MQTT服务器（如Mosquitto、EMQX）默认仅支持MQTT 3.1.1或更高版本（如5.0），导致连接被服务器拒绝，进而触发重复重连-断开的循环。

解决步骤 #

1. 指定兼容的MQTT协议版本
   在创建Client实例时，显式指定服务器支持的协议版本，推荐使用MQTT 3.1.1：

   # 替换原创建Client的代码，指定MQTT 3.1.1协议
   mqtt_client = mqtt.Client(clientID, protocol=mqtt.MQTTv311)
   

   若服务器支持MQTT 5.0，也可使用protocol=mqtt.MQTTv5。

2. 验证服务器协议支持
   检查MQTT服务器的配置文件，确认其允许的协议版本。例如Mosquitto的配置中，protocol字段可设置为mqtt（默认支持3.1.1）或明确指定版本。

3. 额外注意点
   脚本中loop_start()已开启后台线程处理MQTT网络事件（包括心跳），time.sleep(900)的阻塞逻辑本身不会导致连接问题，解决协议版本匹配后，keepalive设置即可正常生效。

内容的提问来源于stack exchange，提问作者deputy-chief-hardy