Add initial MQTT scrubber service scaffold

internal/mqtt/subscriber.go

@@ -0,0 +1,95 @@
+package mqtt
+
+import (
+	"log/slog"
+	"time"
+
+	paho "github.com/eclipse/paho.mqtt.golang"
+
+	"mqqt-scrubber/internal/config"
+	"mqqt-scrubber/internal/model"
+)
+
+type Subscriber struct {
+	config  config.MQTTConfig
+	handle  func(model.RawMessage)
+	client  paho.Client
+	started bool
+}
+
+func NewSubscriber(cfg config.MQTTConfig, handle func(model.RawMessage)) *Subscriber {
+	return &Subscriber{
+		config: cfg,
+		handle: handle,
+	}
+}
+
+func (subscriber *Subscriber) Start() error {
+	options := paho.NewClientOptions()
+	options.AddBroker(subscriber.config.Broker)
+	options.SetClientID(subscriber.config.ClientID)
+	options.SetAutoReconnect(true)
+	options.SetConnectRetry(true)
+	options.SetConnectRetryInterval(5 * time.Second)
+	options.SetKeepAlive(30 * time.Second)
+	options.SetPingTimeout(10 * time.Second)
+	options.SetOrderMatters(false)
+
+	if subscriber.config.Username != "" {
+		options.SetUsername(subscriber.config.Username)
+	}
+	if subscriber.config.Password != "" {
+		options.SetPassword(subscriber.config.Password)
+	}
+
+	callback := func(_ paho.Client, message paho.Message) {
+		subscriber.handle(model.RawMessage{
+			Topic:      message.Topic(),
+			Payload:    append([]byte(nil), message.Payload()...),
+			ReceivedAt: time.Now().UTC(),
+		})
+	}
+
+	options.SetOnConnectHandler(func(client paho.Client) {
+		filters := make(map[string]byte, len(subscriber.config.Topics))
+		for _, topic := range subscriber.config.Topics {
+			filters[topic] = subscriber.config.QoS
+		}
+
+		token := client.SubscribeMultiple(filters, callback)
+		token.Wait()
+		if err := token.Error(); err != nil {
+			slog.Error("failed to subscribe after connect", "error", err)
+			return
+		}
+
+		slog.Info("subscribed to mqtt topics", "topics", subscriber.config.Topics)
+	})
+
+	options.SetConnectionLostHandler(func(_ paho.Client, err error) {
+		slog.Warn("mqtt connection lost", "error", err)
+	})
+
+	options.SetReconnectingHandler(func(_ paho.Client, _ *paho.ClientOptions) {
+		slog.Info("mqtt reconnecting")
+	})
+
+	subscriber.client = paho.NewClient(options)
+	token := subscriber.client.Connect()
+	token.Wait()
+	if err := token.Error(); err != nil {
+		return err
+	}
+
+	subscriber.started = true
+	return nil
+}
+
+func (subscriber *Subscriber) Stop() {
+	if !subscriber.started || subscriber.client == nil {
+		return
+	}
+
+	subscriber.client.Disconnect(250)
+	subscriber.started = false
+}