<slide style="title">
<blurb class="large">Step 4: Make Stream Deck Listen for Incoming MQTT Messages</blurb>
<break/>
<example inline="2">
import (
  mqtt "github.com/eclipse/paho.mqtt.golang"
  "github.com/spf13/viper"
)

type MqttThing struct {
  SD          *streamdeck.StreamDeck
  Brightness  *Brightness
  mqtt_client mqtt.Client
  actions     []MqttAction
}

type MqttSubscription struct {
  Topic string `mapstructure:"topic"`
}

type MqttAction struct {
  Topic           string `mapstructure:"topic"`
  Value           string `mapstructure:"value"`
  Type            string `mapstructure:"type"`
  BrightnessLevel *int   `mapstructure:"brightnessLevel"`
}

func (p *MqttThing) onMqttMessageReceived(client mqtt.Client, message mqtt.Message) {
  payload := string(message.Payload()[:])

  for _, topic := range p.actions {
    if topic.Topic == message.Topic() &amp;&amp; topic.Value == payload {
      if topic.Type == "brightness" &amp;&amp; topic.BrightnessLevel != nil {
        p.Brightness.SetBrightnessLevel(*topic.BrightnessLevel)
      }
    }
  }
}

func (p *MqttThing) Init() {
  opts := mqtt.NewClientOptions().
    AddBroker(viper.GetString("mqtt.broker")).
    SetClientID(viper.GetString("mqtt.clientid")).
    SetUsername(viper.GetString("mqtt.username")).
    SetPassword(viper.GetString("mqtt.password"))

  viper.UnmarshalKey("mqtt.actions", &amp;p.actions)

  opts.OnConnect = func(c mqtt.Client) {
    var subscriptions []MqttSubscription
    viper.UnmarshalKey("mqtt.subscriptions", &amp;subscriptions)

    for _, topic := range subscriptions {
      if token := p.mqtt_client.Subscribe(topic.Topic, byte(0), p.onMqttMessageReceived);
       token.Wait() &amp;&amp; token.Error() != nil {
        panic(token.Error())
      }
    }
  }

  p.mqtt_client = mqtt.NewClient(opts)
  if conn_token := p.mqtt_client.Connect(); conn_token.Wait() &amp;&amp; conn_token.Error() != nil {
    log.Warn().Err(conn_token.Error()).Msg("Cannot connect to MQTT")
  }
}
</example>
</slide>