Ubuntu、mosquitto 和 paho-mqtt 出现 MQTT“协议版本无效”错误

Question

我目前正在使用运行 Ubuntu 18.04 的 NVIDIA Jetson 开发 MQTT 项目。我已安装 mosquitto（版本 2.0.15）作为我的 MQTT 代理，并为我的 Python MQTT 客户端安装 paho-mqtt（版本 1.6.1）。

我遇到一个问题，在尝试向 MQTT 代理发布消息时，我始终收到“mid”（消息标识符）代码为 1 的“协议版本无效”错误。我已经仔细检查了我的代码和配置，并且我相信我在 Python MQTT 客户端中指定了正确的协议版本 (MQTTv5)，因为 mosquitto v2.0.15 支持 MQTTv5 和 MQTTv3.1。

代理服务器和发布客户端在同一设备/网络上运行。

MQTT 代理确实正在运行：

gabe@gabe-desktop:~$ systemctl status mosquitto

mosquitto.service - Mosquitto MQTT Broker
   Loaded: loaded (/lib/systemd/system/mosquitto.service; enabled; vendor preset: enabled)
   Active: active (running) since Sat 2024-01-06 19:10:01 CET; 1h 35min ago
     Docs: man:mosquitto.conf(5)
           man:mosquitto(8)
 Main PID: 22604 (mosquitto)
    Tasks: 1 (limit: 4180)
   CGroup: /system.slice/mosquitto.service
           └─22604 /usr/sbin/mosquitto -c /etc/mosquitto/mosquitto.conf

Jan 06 19:10:01 gabe-desktop systemd[1]: Starting Mosquitto MQTT Broker...
Jan 06 19:10:01 gabe-desktop systemd[1]: Started Mosquitto MQTT Broker.

并且端口 1883 正在侦听地址：

localhost:1883

和

ip6-localhost:1883

。

gabe@gabe-desktop:~$ netstat -at

Proto Recv-Q Send-Q Local Address           Foreign Address         State      
tcp        0      0 0.0.0.0:sunrpc          0.0.0.0:*               LISTEN     
tcp        0      0 localhost:domain        0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:ssh             0.0.0.0:*               LISTEN     
tcp        0      0 localhost:1883          0.0.0.0:*               LISTEN     
tcp        0      0 localhost:40283         0.0.0.0:*               LISTEN     
tcp        0      0 localhost:42269         0.0.0.0:*               LISTEN     
tcp        0      0 localhost:34941         0.0.0.0:*               LISTEN     
tcp        0      0 localhost:40451         0.0.0.0:*               LISTEN     
tcp        0      0 localhost:gpsd          0.0.0.0:*               LISTEN     
tcp        0      0 localhost:40283         localhost:47786         ESTABLISHED
tcp        0      0 gabe-desktop:35130      13.107.5.93:https       ESTABLISHED
tcp        0    108 gabe-desktop:ssh        Gabes-MBP:53006         ESTABLISHED
tcp        0      0 gabe-desktop:35140      13.107.5.93:https       ESTABLISHED
tcp        0      0 localhost:40283         localhost:47788         ESTABLISHED
tcp        0      0 localhost:47786         localhost:40283         ESTABLISHED
tcp        0      0 localhost:47788         localhost:40283         ESTABLISHED
tcp        0      0 localhost:40283         localhost:47272         CLOSE_WAIT 
tcp6       0      0 [::]:sunrpc             [::]:*                  LISTEN     
tcp6       0      0 [::]:ssh                [::]:*                  LISTEN     
tcp6       0      0 ip6-localhost:1883      [::]:*                  LISTEN     
tcp6       0      0 ip6-localhost:gpsd      [::]:*                  LISTEN

以下是尝试创建发布连接时的 Python 代码和错误：

import paho.mqtt.client as mqtt


# MQTT broker information
BROKER_ADDRESS = "localhost"
PORT = 1883
TOPIC = "testing"
RESPONSE = {
    0: "connection succeeded",
    1: "connection failed - incorrect protocol version",
    2: "connection failed - invalid client identifier",
    3: "connection failed - the broker is not available",
    4: "connection failed - wrong username or password",
    5: "connection failed - unauthorized"
}


def on_publish(client, data, mid):
    print(f"Connected to broker with status: {mid}: {RESPONSE.get(mid, 'Unknown')}")


def main():

    client = mqtt.Client(client_id="jetson", protocol=mqtt.MQTTv5)
    # Set the callback function for when the publisher connects to the broker
    client.on_publish = on_publish
    # Connect to the broker
    client.connect(BROKER_ADDRESS, PORT)

    # Publish a message to the "testing" topic
    message = "Hello, world!"
    client.publish(TOPIC, message)

    # Keep client running "forever"
    client.loop_forever()


if __name__ == '__main__':
    main()

Connected to broker with status: 1: connection failed - incorrect protocol version

我也尝试了协议版本

mqtt.MQTTv31

并收到了相同的错误。

所有在线资源都必须确保正确配置 mosquitto 配置文件。不过，我仔细检查过，情况似乎确实如此。

为了确保 MQTT 代理服务器确实正确运行，我在两个单独的终端中执行了以下测试

1号航站楼：

gabe@gabe-desktop:~$ mosquitto_sub -h localhost -t test

2号航站楼：

gabe@gabe-desktop:~$ mosquitto_pub -h localhost -t test -m "hello world"

我在终端 1 中得到“hello world”输出。

Answer 1

def on_publish(client, data, mid):
    print(f"Connected to broker with status: {mid}: {RESPONSE.get(mid, 'Unknown')}")

on_publish

是“当要使用 publish() 调用已完成向代理的传输。”并且已通过:

client：此回调的客户端实例
userdata：在Client()或userdata_set()中设置的私有用户数据
mid：匹配从相应的publish()调用返回的mid变量，以允许跟踪传出消息。

您似乎假设

mid

指示连接是否成功（根据上面复制的文档；事实并非如此）。 .

所以发生的事情（好吧，当我测试你的代码时会发生什么）是你成功连接到代理，然后成功发布消息。然而，一旦消息被传输，您的

on_publish

就会被调用（这会错误地打印错误消息）。

我认为你的意图是这样的：

def on_connect(client, userdata, flags, reasonCode, properties):
    print(f"Connected to broker with status: {reasonCode}")

def on_publish(client, data, mid):
    print(f"Publish completed: {mid}")


def main():
    client = mqtt.Client(client_id="jetson", protocol=mqtt.MQTTv5)
    # Set the callback function for when the publisher connects to the broker
    client.on_connect = on_connect
    client.on_publish = on_publish
...