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

components/forwarder/publisher.go

@@ -0,0 +1,73 @@
+package forwarder
+
+import (
+	"github.com/ThreeDotsLabs/watermill/message"
+	"github.com/pkg/errors"
+)
+
+// PublisherConfig configures the decorating Publisher returned by NewPublisher.
+type PublisherConfig struct {
+	// ForwarderTopic is a topic which the forwarder is listening to. Publisher will send enveloped messages to this topic.
+	// Defaults to `forwarder_topic`.
+	ForwarderTopic string
+
+	// Marshaler is used to serialize envelopes sent to ForwarderTopic.
+	// It must match the Marshaler used by the Forwarder consuming the topic.
+	// Defaults to DefaultMarshaler, which uses encoding/json.
+	Marshaler Marshaler
+}
+
+func (c *PublisherConfig) setDefaults() {
+	if c.ForwarderTopic == "" {
+		c.ForwarderTopic = defaultForwarderTopic
+	}
+	if c.Marshaler == nil {
+		c.Marshaler = DefaultMarshaler{}
+	}
+}
+
+func (c *PublisherConfig) Validate() error {
+	if c.ForwarderTopic == "" {
+		return errors.New("empty forwarder topic")
+	}
+
+	return nil
+}
+
+// Publisher changes `Publish` method behavior so it wraps a sent message in an envelope
+// and sends it to the forwarder topic provided in the config.
+type Publisher struct {
+	wrappedPublisher message.Publisher
+	config           PublisherConfig
+}
+
+func NewPublisher(publisher message.Publisher, config PublisherConfig) *Publisher {
+	config.setDefaults()
+
+	return &Publisher{
+		wrappedPublisher: publisher,
+		config:           config,
+	}
+}
+
+func (p *Publisher) Publish(topic string, messages ...*message.Message) error {
+	envelopedMessages := make([]*message.Message, 0, len(messages))
+	for _, msg := range messages {
+		envelopedMsg, err := wrapMessageInEnvelope(topic, msg, p.config.Marshaler)
+		if err != nil {
+			return errors.Wrapf(err, "cannot wrap message, target topic: '%s', uuid: '%s'", topic, msg.UUID)
+		}
+
+		envelopedMessages = append(envelopedMessages, envelopedMsg)
+	}
+
+	if err := p.wrappedPublisher.Publish(p.config.ForwarderTopic, envelopedMessages...); err != nil {
+		return errors.Wrapf(err, "cannot publish messages to forwarder topic: '%s'", p.config.ForwarderTopic)
+	}
+
+	return nil
+}
+
+func (p *Publisher) Close() error {
+	return p.wrappedPublisher.Close()
+}