# MQTT Go Client library

Eclipse Paho MQTT Go Client (opens new window) is the Go language client library under the Eclipse Paho project, which can connect to the MQTT Broker to publish messages, subscribe to topics and receive the published message. It supports asynchronous operation mode completely.

The client depends on Google's software Package of proxy (opens new window) and websockets (opens new window), which can be installed with the following command:

go get github.com/eclipse/paho.mqtt.golang
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# MQTT Go usage example

This example contains the complete code for Paho MQTT in Go language connecting to EMQ X Broker, sending and receiving messages:

package main

import (
	"fmt"
	"log"
	"os"
	"time"

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

var f mqtt.MessageHandler = func(client mqtt.Client, msg mqtt.Message) {
	fmt.Printf("TOPIC: %s\n", msg.Topic())
	fmt.Printf("MSG: %s\n", msg.Payload())
}

func main() {
	mqtt.DEBUG = log.New(os.Stdout, "", 0)
	mqtt.ERROR = log.New(os.Stdout, "", 0)
	opts := mqtt.NewClientOptions().AddBroker("tcp://broker.emqx.io:1883").SetClientID("emqx_test_client")
	
	opts.SetKeepAlive(60 * time.Second)
	// Set the message callback handler
	opts.SetDefaultPublishHandler(f)
	opts.SetPingTimeout(1 * time.Second)

	c := mqtt.NewClient(opts)
	if token := c.Connect(); token.Wait() && token.Error() != nil {
		panic(token.Error())
	}

	// Subscribe to a topic
	if token := c.Subscribe("testtopic/#", 0, nil); token.Wait() && token.Error() != nil {
		fmt.Println(token.Error())
		os.Exit(1)
	}
	
	// Publish a message
	token := c.Publish("testtopic/1", 0, false, "Hello World")
	token.Wait()

	time.Sleep(6 * time.Second)

	// Unscribe
	if token := c.Unsubscribe("testtopic/#"); token.Wait() && token.Error() != nil {
		fmt.Println(token.Error())
		os.Exit(1)
	}
  
  // Disconnect
	c.Disconnect(250)
	time.Sleep(1 * time.Second)
}
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# Paho Golang MQTT 5.0 support

Currently, Paho Golang is still adapting to MQTT 5.0 and has not yet fully supported it.