how to implement client listener in Android using golang object?

Question

Problem description:

I am working on a small project in which i need to port the existing mqtt client library from Golang to Android. I found using gomobile repository as an option to prevent duplicating the same functionality in different programming languages (GO and Java).

To use this library we have two different options:

1. Design the android app purely in Go and use "gomobile -build" to generate an APK file. An APK file then can be loaded to android device or emulator using adb tool.
2. Implement some functionality and then bind them into existing Android project using "gomobile -bind". With this option there are some restriction for conversion and building Golang objects.

For my case I plan to pick the second option. Also trying to convert the following small sample GO implementation to Android (borrowed from here).

package main

import (
    "fmt"
    mqtt "github.com/eclipse/paho.mqtt.golang"
    "log"
    "time"
)

var messagePubHandler mqtt.MessageHandler = func(client mqtt.Client, msg mqtt.Message) {
    fmt.Printf("Received message: %s from topic: %s\n", msg.Payload(), msg.Topic())
}

var connectHandler mqtt.OnConnectHandler = func(client mqtt.Client) {
    fmt.Println("Connected")
}

var connectLostHandler mqtt.ConnectionLostHandler = func(client mqtt.Client, err error) {
    fmt.Printf("Connect lost: %v", err)
}

func main() {
    var broker = "broker.emqx.io"
    var port = 1883
    opts := mqtt.NewClientOptions()
    opts.AddBroker(fmt.Sprintf("tcp://%s:%d", broker, port))
    opts.SetClientID("go_mqtt_client")
    opts.SetUsername("emqx")
    opts.SetPassword("public")
    opts.SetDefaultPublishHandler(messagePubHandler)
    opts.OnConnect = connectHandler
    opts.OnConnectionLost = connectLostHandler
    client := mqtt.NewClient(opts)
    if token := client.Connect(); token.Wait() && token.Error() != nil {
        panic(token.Error())
    }

    sub(client)
    publish(client)

    client.Disconnect(250)
}

func publish(client mqtt.Client) {
    num := 10
    for i := 0; i < num; i++ {
        text := fmt.Sprintf("Message %d", i)
        token := client.Publish("topic/test", 0, false, text)
        token.Wait()
        time.Sleep(time.Second)
    }
}

func sub(client mqtt.Client) {
    topic := "topic/test"
    token := client.Subscribe(topic, 1, nil)
    token.Wait()
  fmt.Printf("Subscribed to topic: %s", topic)
}

My Question:

After converting the sample code, i am not sure how i can implement the listener side. the probelm is that "gomobile -bind" cannot convert all user data types (i.e client into Java). I can implement the connect, subscribe, and publish, but not the listener one (in other words, the "opts.SetDefaultPublishHandler(messagePubHandler)" is not repeatedly working when i call the corresponding method in Android)

Any suggestion?

This is what is tried, but it does not work

var Options *mqtt.ClientOptions
var ReceivedMsg string

func AddBroker(broker string, port int) {
    Options = mqtt.NewClientOptions()
    Options.AddBroker(fmt.Sprintf("tcp://%s:%d", broker, port))
}
var MessagePubHandler mqtt.MessageHandler = func(client mqtt.Client, msg mqtt.Message) {
    ReceivedMsg = " Message " + string(msg.Payload()) + " received on topic" + msg.Topic()
    fmt.Printf(ReceivedMsg)
}

 
func Listener(clientId string) {
    Options.SetClientID(clientId)
    Options.SetDefaultPublishHandler(MessagePubHandler)
    Options.OnConnect = ConnectHandler
    Options.OnConnectionLost = ConnectionLostHandler
}