Handle reconnecting after MQTT broker is down

mqtt.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"log/slog"
+	"time"
 
 	mqtt "github.com/eclipse/paho.mqtt.golang"
 )
@@ -14,19 +15,35 @@ func MQTTSetup(cfg *Config, publishHandler mqtt.MessageHandler) mqtt.Client {
 	opts := mqtt.NewClientOptions().
 		AddBroker(fmt.Sprintf("tcp://%s:%d", cfg.brokerHost, cfg.brokerPort)).
 		SetClientID(mqttClientID).
-		SetDefaultPublishHandler(publishHandler).SetAutoReconnect(true)
+		SetDefaultPublishHandler(publishHandler).
+		SetConnectionLostHandler(MQTTLostCnx).
+		SetMaxReconnectInterval(time.Minute * 2)
+
+	opts = opts.SetOnConnectHandler(func(client mqtt.Client) {
+		MQTTSubscribe(client, cfg)
+	})
 
 	client := mqtt.NewClient(opts)
 	if token := client.Connect(); token.Wait() && token.Error() != nil {
-		panic(token.Error())
-	}
-	slog.Debug("Connected to", "Broker", cfg.brokerHost, "Port", cfg.brokerPort, "Client", mqttClientID)
-	if token := client.Subscribe(cfg.topic+"/#", 0, nil); token.Wait() && token.Error() != nil {
-		panic(token.Error())
+		// panic(token.Error())
+		slog.Warn("MQTTSetup failed", "err", token.Error())
 	}
 	return client
 }
 
+func MQTTSubscribe(client mqtt.Client, cfg *Config) error {
+	token := client.Subscribe(cfg.topic+"/#", 0, nil)
+	if err := token.Wait(); token.Error() != nil {
+		return fmt.Errorf("failed to subscribe to topic '%s/#': %v", cfg.topic, err)
+	}
+	slog.Debug("Subscribed to", "Topic", cfg.topic+"/#")
+	return nil
+}
+
+func MQTTLostCnx(client mqtt.Client, err error) {
+	slog.Warn("MQTT connection lost")
+}
+
 // MQTTDumpMsg displays the MQTT message
 func MQTTDumpMsg(msg mqtt.Message) {
 	var data map[string]interface{}