snapshot of https://github.com/ThreeDotsLabs/watermill.git (master, 2026-09-15; blobs > 131072B omitted)

_examples/real-world-examples/server-sent-events/server/event_handlers.go

@@ -0,0 +1,180 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"time"
+
+	"github.com/ThreeDotsLabs/watermill"
+	"github.com/ThreeDotsLabs/watermill-nats/pkg/nats"
+	"github.com/ThreeDotsLabs/watermill/message"
+	"github.com/ThreeDotsLabs/watermill/message/router/middleware"
+	"github.com/nats-io/stan.go"
+)
+
+const (
+	PostCreatedTopic = "post-created"
+	PostUpdatedTopic = "post-updated"
+	FeedUpdatedTopic = "feed-updated"
+)
+
+func SetupMessageRouter(
+	feedsStorage FeedsStorage,
+	logger watermill.LoggerAdapter,
+) (message.Publisher, message.Subscriber, error) {
+	router, err := message.NewRouter(message.RouterConfig{}, logger)
+	if err != nil {
+		return nil, nil, err
+	}
+	router.AddMiddleware(middleware.Recoverer)
+
+	natsURL := stan.NatsURL("nats://nats-streaming:4222")
+	pub, err := nats.NewStreamingPublisher(nats.StreamingPublisherConfig{
+		ClusterID:   "test-cluster",
+		ClientID:    "publisher",
+		StanOptions: []stan.Option{natsURL},
+		Marshaler:   nats.GobMarshaler{},
+	}, logger)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	sub, err := nats.NewStreamingSubscriber(nats.StreamingSubscriberConfig{
+		ClusterID:   "test-cluster",
+		ClientID:    "subscriber",
+		StanOptions: []stan.Option{natsURL},
+		Unmarshaler: nats.GobMarshaler{},
+	}, logger)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	router.AddHandler(
+		"update-feeds-on-post-created",
+		PostCreatedTopic,
+		sub,
+		FeedUpdatedTopic,
+		pub,
+		func(msg *message.Message) (messages []*message.Message, err error) {
+			defer func() {
+				if err == nil {
+					logger.Info("Successfully updated feeds on new post created", nil)
+				} else {
+					logger.Error("Error while updating feeds on new post created", err, nil)
+				}
+			}()
+
+			event := PostCreated{}
+			err = json.Unmarshal(msg.Payload, &event)
+			if err != nil {
+				return nil, err
+			}
+
+			logger.Info("Adding post", watermill.LogFields{"post": event.Post})
+
+			if len(event.Post.Tags) > 0 {
+				for _, tag := range event.Post.Tags {
+					logger.Info("Adding tag", watermill.LogFields{"tag": tag})
+					err = feedsStorage.Add(msg.Context(), tag)
+					if err != nil {
+						return nil, err
+					}
+
+				}
+
+				err = feedsStorage.AppendPost(msg.Context(), event.Post)
+				if err != nil {
+					return nil, err
+				}
+			}
+
+			return createFeedUpdatedEvents(event.Post.Tags)
+		},
+	)
+
+	router.AddHandler(
+		"update-feeds-on-post-updated",
+		PostUpdatedTopic,
+		sub,
+		FeedUpdatedTopic,
+		pub,
+		func(msg *message.Message) (messages []*message.Message, err error) {
+			defer func() {
+				if err == nil {
+					logger.Info("Successfully updated feeds on post updated", nil)
+				} else {
+					logger.Error("Error while updating feeds on post updated", err, nil)
+				}
+			}()
+
+			event := PostUpdated{}
+			err = json.Unmarshal(msg.Payload, &event)
+			if err != nil {
+				return nil, err
+			}
+
+			for _, tag := range event.NewPost.Tags {
+				logger.Info("Adding tag", watermill.LogFields{"tag": tag})
+				err = feedsStorage.Add(msg.Context(), tag)
+				if err != nil {
+					return nil, err
+				}
+			}
+
+			err = feedsStorage.UpdatePost(msg.Context(), event.NewPost)
+			if err != nil {
+				return nil, err
+			}
+
+			return createFeedUpdatedEvents(append(event.NewPost.Tags, event.OriginalPost.Tags...))
+		},
+	)
+
+	go func() {
+		err = router.Run(context.Background())
+		if err != nil {
+			panic(err)
+		}
+	}()
+
+	<-router.Running()
+
+	return pub, sub, nil
+}
+
+func createFeedUpdatedEvents(tags []string) ([]*message.Message, error) {
+	var messages []*message.Message
+
+	for _, tag := range tags {
+		event := FeedUpdated{
+			Name:       tag,
+			OccurredAt: time.Now().UTC(),
+		}
+
+		payload, err := json.Marshal(event)
+		if err != nil {
+			return nil, err
+		}
+
+		msg := message.NewMessage(watermill.NewUUID(), payload)
+
+		messages = append(messages, msg)
+	}
+
+	return messages, nil
+}
+
+type Publisher struct {
+	publisher message.Publisher
+}
+
+func (p Publisher) Publish(topic string, event interface{}) error {
+	payload, err := json.Marshal(event)
+	if err != nil {
+		return err
+	}
+
+	msg := message.NewMessage(watermill.NewUUID(), payload)
+
+	return p.publisher.Publish(topic, msg)
+}