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example.go
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example.go
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/*
* Copyright 2021 HiveMQ GmbH
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package main
import (
"fmt"
"time"
mqtt "github.com/eclipse/paho.mqtt.golang"
)
// this callback triggers when a message is received, it then prints the message (in the payload) and topic
var messagePubHandler mqtt.MessageHandler = func(client mqtt.Client, msg mqtt.Message) {
fmt.Printf("Received message: %s from topic: %s\n", msg.Payload(), msg.Topic())
}
// upon connection to the client, this is called
var connectHandler mqtt.OnConnectHandler = func(client mqtt.Client) {
fmt.Println("Connected")
}
// this is called when the connection to the client is lost, it prints "Connection lost" and the corresponding error
var connectLostHandler mqtt.ConnectionLostHandler = func(client mqtt.Client, err error) {
fmt.Printf("Connection lost: %v", err)
}
func main() {
var broker = "<host_name>" // find the host name in the Overview of your cluster (see readme)
var port = 8883 // find the port right under the host name, standard is 8883
opts := mqtt.NewClientOptions()
opts.AddBroker(fmt.Sprintf("tls://%s:%d", broker, port))
opts.SetClientID("<client_name>") // set a name as you desire
opts.SetUsername("<username>") // these are the credentials that you declare for your cluster (see readme)
opts.SetPassword("<password>")
// (optionally) configure callback handlers that get called on certain events
opts.SetDefaultPublishHandler(messagePubHandler)
opts.OnConnect = connectHandler
opts.OnConnectionLost = connectLostHandler
// create the client using the options above
client := mqtt.NewClient(opts)
// throw an error if the connection isn't successfull
if token := client.Connect(); token.Wait() && token.Error() != nil {
panic(token.Error())
}
subscribe(client)
publish(client)
client.Disconnect(250)
}
func subscribe(client mqtt.Client) {
// subscribe to the same topic, that was published to, to receive the messages
topic := "topic/test"
token := client.Subscribe(topic, 1, nil)
token.Wait()
// Check for errors during subscribe (More on error reporting https://pkg.go.dev/github.com/eclipse/paho.mqtt.golang#readme-error-handling)
if token.Error() != nil {
fmt.Printf("Failed to subscribe to topic")
panic(token.Error())
}
fmt.Printf("Subscribed to topic: %s", topic)
}
func publish(client mqtt.Client) {
// publish the message "Message" to the topic "topic/test" 10 times in a for loop
num := 10
for i := 0; i < num; i++ {
text := fmt.Sprintf("Message %d", i)
token := client.Publish("topic/test", 0, false, text)
token.Wait()
// Check for errors during publishing (More on error reporting https://pkg.go.dev/github.com/eclipse/paho.mqtt.golang#readme-error-handling)
if token.Error() != nil {
fmt.Printf("Failed to publish to topic")
panic(token.Error())
}
time.Sleep(time.Second)
}
}