go get github.com/eclipse/paho.golang


package main

import (
    "context"
    "fmt"
    "net/url"
    "os"
    "os/signal"
    "strconv"
    "syscall"
    "time"

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

// Access point, obtained from the console
const accessPoint = "mqtt://mqtt-xxx-sh-public.mqtt.tencenttdmq.com:1883"

// Change this to something random if using a public test server
const clientID = "PahoGoClient"

const topic = "PahoGoTestTopic"

// User name, obtained from the console
const username = "YOUR_USERNAME"

// Password, obtained from the console
var password = []byte("YOUR_PASSWORD")

func main() {
    // App will run until cancelled by user (e.g. ctrl-c)
    ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
    defer stop()

    // We will connect to the Eclipse test server (note that you may see messages that other users publish)
    u, err := url.Parse(accessPoint)
    if err != nil {
        panic(err)
    }

    cliCfg := autopaho.ClientConfig{
        ServerUrls:      []*url.URL{u},
        ConnectUsername: username,
        ConnectPassword: password,

        // Keepalive message should be sent every 60 seconds
        KeepAlive: 60,

        // CleanStartOnInitialConnection defaults to false. Setting this to true will clear the session on the first connection.
        CleanStartOnInitialConnection: false,

        // SessionExpiryInterval - Seconds that a session will survive after disconnection.
        // It is important to set this because otherwise, any queued messages will be lost if the connection drops and
        // the server will not queue messages while it is down. The specific setting will depend upon your needs
        // (60 = 1 minute, 3600 = 1 hour, 86400 = one day, 259200 = 3 days)
        // MQTT server permits expiry interval up to 3 days
        SessionExpiryInterval: 60,
        OnConnectionUp: func(cm *autopaho.ConnectionManager, connAck *paho.Connack) {
            fmt.Println("mqtt connection up")
            // Subscribing in the OnConnectionUp callback is recommended (ensures the subscription is reestablished if
            // the connection drops)
            if _, err := cm.Subscribe(context.Background(), &paho.Subscribe{
                Subscriptions: []paho.SubscribeOptions{
                    {Topic: topic, QoS: 1},
                },
            }); err != nil {
                fmt.Printf("failed to subscribe (%s). This is likely to mean no messages will be received.", err)
            }
            fmt.Println("mqtt subscription made")
        },
        OnConnectError: func(err error) { fmt.Printf("error whilst attempting connection: %s\\n", err) },
        // eclipse/paho.golang/paho provides base mqtt functionality, the below config will be passed in for each connection
        ClientConfig: paho.ClientConfig{
            // If you are using QOS 1/2, then it's important to specify a client id (which must be unique)
            ClientID: clientID,
            // OnPublishReceived is a slice of functions that will be called when a message is received.
            // You can write the function(s) yourself or use the supplied Router
            OnPublishReceived: []func(paho.PublishReceived) (bool, error){
                func(pr paho.PublishReceived) (bool, error) {
                    fmt.Printf("received message on topic %s; body: %s (retain: %t)\\n", pr.Packet.Topic, pr.Packet.Payload, pr.Packet.Retain)
                    return true, nil
                }},
            OnClientError: func(err error) { fmt.Printf("client error: %s\\n", err) },
            OnServerDisconnect: func(d *paho.Disconnect) {
                if d.Properties != nil {
                    fmt.Printf("server requested disconnect: %s\\n", d.Properties.ReasonString)
                } else {
                    fmt.Printf("server requested disconnect; reason code: %d\\n", d.ReasonCode)
                }
            },
        },
    }

    c, err := autopaho.NewConnection(ctx, cliCfg) // starts process; will reconnect until context cancelled
    if err != nil {
        panic(err)
    }
    // Wait for the connection to come up
    if err = c.AwaitConnection(ctx); err != nil {
        panic(err)
    }

    ticker := time.NewTicker(time.Second)
    msgCount := 0
    defer ticker.Stop()
    for {
        select {
        case <-ticker.C:
            msgCount++
            // Publish a test message (use PublishViaQueue if you don't want to wait for a response)
            if _, err = c.Publish(ctx, &paho.Publish{
                QoS:     1,
                Topic:   topic,
                Payload: []byte("TestMessage: " + strconv.Itoa(msgCount)),
            }); err != nil {
                if ctx.Err() == nil {
                    panic(err) // Publish will exit when context cancelled or if something went wrong
                }
            }
            continue
        case <-ctx.Done():
        }
        break
    }

    fmt.Println("signal caught - exiting")
    <-c.Done() // Wait for clean shutdown (cancelling the context triggered the shutdown)
}