Subscribing MQTT using Goroutine not printing messages

I currently have Go code that subscribes to a topic and prints out sensor data. The part that prints out the sensor data is in a Goroutine, however, nothing is printing out currently. This is my code:

package main

import (
"fmt"
MQTT "github.com/eclipse/paho.mqtt.golang"
"os"
"os/signal"
"syscall"
"sync"
)



var wg sync.WaitGroup

func subscriber(client MQTT.Client, message MQTT.Message) {
wg.Add(1)
go func() {
defer wg.Done()
fmt.Printf("%sn", message.Payload())
}()
}

func main() {

c := make(chan os.Signal, 1)
signal.Notify(c, os.Interrupt, syscall.SIGTERM)

opts := MQTT.NewClientOptions().AddBroker("tcp://test.mosquitto.org:1883")

//opts.SetDefaultPublishHandler(f)
// Topic to subscribe to for sensor data
topic := "sensor/data"
client := MQTT.NewClient(opts)
if token := client.Connect(); token.Wait() && token.Error() != nil {
panic(token.Error())
} else {
fmt.Printf("Connected to servern")
}
opts.OnConnect = func(c MQTT.Client) {
//if token := c.Subscribe(topic, 0, f); token.Wait() && token.Error() != nil {
if token := c.Subscribe(topic, 0, subscriber); token.Wait() && token.Error() != nil {

panic(token.Error())

}
}

wg.Wait()

<-c

}


I'm wondering if it has to do with the way I coded the sync.WaitGroup? Any ideas are appreciated.

I believe you'll need to send your goroutine the message in order for this to work. go func(msg MQTT.Message) { fmt.Println(msg.Payload) }(message)
– Fishdigger
2 days ago

go func(msg MQTT.Message) { fmt.Println(msg.Payload) }(message)

@Fishdigger That doesn't seem to work. message is already passed into the function as a parameter.
– Melissa
2 days ago

message

1 Answer
1

I managed to fix it Here is my new code:

var wg sync.WaitGroup
// All messages are handled here - printing published messages and publishing new messages
var f MQTT.MessageHandler = func(client MQTT.Client, msg MQTT.Message) {

wg.Add(1)
go func() {
defer wg.Done()
fmt.Printf("%sn", msg.Payload())
}()

}


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