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Go Paho MQTT Client

Victoria Harbour, Hongkong

I want to create a Go MQTT client that can connect to the INSTAR MQTT Broker on an IN-8015 FHD camera on local IP 192.168.2.77. I want to be able to add topic subscriptions as well as publishing MQTT updates to the broker.

Project initialization​

This project uses paho.mqtt.golang as MQTT client library, install:

go mod init go/paho-mqtt
go get github.com/eclipse/paho.mqtt.golang

Connect to the MQTT broker​

./src/client/main.go

package main

import (
	"fmt"

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

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

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 = "192.168.2.70"
    var port = 1883
    opts := mqtt.NewClientOptions()
    opts.AddBroker(fmt.Sprintf("tcp://%s:%d", broker, port))
    opts.SetClientID("go_mqtt_client")
    opts.SetUsername("admin")
    opts.SetPassword("instar")
    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())
  }
}
  • messagePubHandler: global MQTT pub message processing
  • connectHandler: callback for the connection
  • connectLostHandler: callback for connection loss
  • ClientOptions: used to set broker, port, client id, username, password and other options.

Topic Subscription​

func sub(client mqtt.Client) {
    // Subscribe to the LWT connection status
    topic := "cameras/77/status/connection"
    token := client.Subscribe(topic, 1, nil)
    token.Wait()
    fmt.Printf("Subscribed to LWT %s", topic)
}

Topic Update​

func publish(client mqtt.Client) {
    // Go to PTZ preset 2 and return to 1 after 15s
    nums := []int{2, 1}
    for _, num := range nums {
        value := fmt.Sprintf("%d", num)
        token := client.Publish("cameras/77/features/ptz/preset/raw", 0, false, value)
        token.Wait()
        time.Sleep(15 * time.Second)
    }
}

Testing​

Now bringing it all together:

package main

import (
	"fmt"
	"time"

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

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

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 = "192.168.2.77"
    var port = 1883
    opts := mqtt.NewClientOptions()
    opts.AddBroker(fmt.Sprintf("tcp://%s:%d", broker, port))
    opts.SetClientID("go_mqtt_client")
    opts.SetUsername("admin")
    opts.SetPassword("instar")
    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) {
    // Go to PTZ preset 2 and return to 1 after 15s
    nums := []int{2, 1}
    for _, num := range nums {
        value := fmt.Sprintf("%d", num)
        token := client.Publish("cameras/77/features/ptz/preset/raw", 0, false, value)
        token.Wait()
        time.Sleep(15 * time.Second)
    }
}

func sub(client mqtt.Client) {
    // Subscribe to the LWT connection status
    topic := "cameras/77/status/connection"
    token := client.Subscribe(topic, 1, nil)
    token.Wait()
    fmt.Println("Subscribed to LWT", topic)
}

Running the Program​

go run .\main.go
Connected
Subscribed to LWT cameras/77/status/connection        
Topic: cameras/77/status/connection | {"val":"online"}

The program will pan your camera to preset position 2, return it to preset 1 and then stop running.