如何检查我与mqtt代理的连接是否断开？

分配一个自定义项OnConnectionLostHandler来捕获连接丢失事件，以便您可以在客户端断开连接时执行其他操作。如果将AutoReconnect选项设置为true（这是默认行为），则客户端将在连接断开后自动重新连接到代理。请注意，连接断开后，代理可能不会保存您的订阅状态/信息，因此您将无法收到任何消息。要解决此问题，请将主题订阅移至OnConnect处理程序。下面是一个示例实现：

package main

import (
    "fmt"
    "os"
    "time"

    mqtt "github.com/eclipse/paho.mqtt.golang"
)

func messageHandler(c mqtt.Client, msg mqtt.Message) {
    fmt.Printf("TOPIC: %s\n", msg.Topic())
    fmt.Printf("MSG: %s\n", msg.Payload())
}

func connLostHandler(c mqtt.Client, err error) {
    fmt.Printf("Connection lost, reason: %v\n", err)

    //Perform additional action...
}

func main() {
    //create a ClientOptions
    opts := mqtt.NewClientOptions().
        AddBroker("tcp://localhost:1883").
        SetClientID("group-one").
        SetDefaultPublishHandler(messageHandler).
        SetConnectionLostHandler(connLostHandler)

    //set OnConnect handler as anonymous function
    //after connected, subscribe to topic
    opts.OnConnect= func(c mqtt.Client) {
        fmt.Printf("Client connected, subscribing to: test/topic\n")

        //Subscribe here, otherwise after connection lost, 
        //you may not receive any message
        if token := c.Subscribe("test/topic", 0, nil); token.Wait() && token.Error() != nil {
            fmt.Println(token.Error())
            os.Exit(1)
        }
    }

    //create and start a client using the above ClientOptions
    c := mqtt.NewClient(opts)
    if token := c.Connect(); token.Wait() && token.Error() != nil {
        panic(token.Error())
    }

    for {
        //Lazy...
        time.Sleep(500 * time.Millisecond)
    }
}