Paho MQTT Golang way to loop forever

Question

In the python version, you can "listen" for messages forever but I'm lost with the golang version. How can I have something similar to client.loop_forever()?

Answer 1

As per the comments to your question, you need to set up the Paho client with callbacks to handle the connected and disconnected events and received messages, and then wait-until-exit. For a v3 client, the code looks something like this:

func main() {
    if client,err := subscribe(); err != nil {
       fmt.Printf("error subscribing to MQTT broker (%v)",err)
    } else {
       exit := make(chan os.Signal)

       signal.Notify(exit, syscall.SIGINT, syscall.SIGTERM)

       <-exit

       client.Disconnect(250)
    }
}

func subscribe() (paho.Client, error) {
    topic := "allthethings/#"

    var handler paho.MessageHandler = func(client paho.Client, msg paho.Message) {
        // (process received message)
    }

    var connected paho.OnConnectHandler = func(client paho.Client) {
        for _, url := range client.OptionsReader().Servers() {
            fmt.Printf("connected to %s", url)
        }

        token := client.Subscribe(topic, 0, handler)
        if err := token.Error(); err != nil {
            fmt.Printf("error subscribing to topic %s (%v)", topic, err)
        }
    }

    var disconnected paho.ConnectionLostHandler = func(client paho.Client, err error) {
        fmt.Printf("connection to MQTT broker lost (%v)", err)

        go func() {
            time.Sleep(10 * time.Second)
            token := client.Connect()
            if err := token.Error(); err != nil {
                fmt.Printf("error reconnecting to broker (%v)", err)
            }
        }()
    }

    options := paho.
        NewClientOptions().
        AddBroker(broker).
        SetClientID(clientID).
        SetUsername(uid).
        SetPassword(pwd).
        SetTLSConfig(TLS).
        SetCleanSession(false).
        SetAutoReconnect(false).
        SetConnectRetry(true).
        SetConnectRetryInterval(30 * time.Second).
        SetOnConnectHandler(connected).
        SetConnectionLostHandler(disconnected)

    client := paho.NewClient(options)
    token := client.Connect()
    if err := token.Error(); err != nil {
        return nil, err
    }

    return client, nil
}