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

components/forwarder/envelope.go

@@ -0,0 +1,80 @@
+package forwarder
+
+import (
+	"github.com/ThreeDotsLabs/watermill"
+	"github.com/ThreeDotsLabs/watermill/message"
+	"github.com/pkg/errors"
+)
+
+// messageEnvelope wraps Watermill message and contains destination topic.
+type messageEnvelope struct {
+	DestinationTopic string `json:"destination_topic"`
+
+	UUID     string            `json:"uuid"`
+	Payload  []byte            `json:"payload"`
+	Metadata map[string]string `json:"metadata"`
+}
+
+func newMessageEnvelope(destTopic string, msg *message.Message) (*messageEnvelope, error) {
+	e := &messageEnvelope{
+		DestinationTopic: destTopic,
+		UUID:             msg.UUID,
+		Payload:          msg.Payload,
+		Metadata:         msg.Metadata,
+	}
+
+	if err := e.validate(); err != nil {
+		return nil, errors.Wrap(err, "cannot create a message envelope")
+	}
+
+	return e, nil
+}
+
+func (e *messageEnvelope) validate() error {
+	if e.DestinationTopic == "" {
+		return errors.New("unknown destination topic")
+	}
+
+	return nil
+}
+
+func wrapMessageInEnvelope(
+	destinationTopic string,
+	msg *message.Message,
+	marshaler Marshaler,
+) (*message.Message, error) {
+	envelope, err := newMessageEnvelope(destinationTopic, msg)
+	if err != nil {
+		return nil, errors.Wrap(err, "cannot envelope a message")
+	}
+
+	envelopedMessage, err := marshaler.Marshal(envelope)
+	if err != nil {
+		return nil, errors.Wrap(err, "cannot marshal a message")
+	}
+
+	wrappedMsg := message.NewMessage(watermill.NewUUID(), envelopedMessage)
+	wrappedMsg.SetContext(msg.Context())
+
+	return wrappedMsg, nil
+}
+
+func unwrapMessageFromEnvelope(
+	msg *message.Message,
+	marshaler Marshaler,
+) (destinationTopic string, unwrappedMsg *message.Message, err error) {
+	envelopedMsg := messageEnvelope{}
+	if err := marshaler.Unmarshal(msg.Payload, &envelopedMsg); err != nil {
+		return "", nil, errors.Wrap(err, "cannot unmarshal message wrapped in an envelope")
+	}
+
+	if err := envelopedMsg.validate(); err != nil {
+		return "", nil, errors.Wrap(err, "an unmarshalled message envelope is invalid")
+	}
+
+	watermillMessage := message.NewMessage(envelopedMsg.UUID, envelopedMsg.Payload)
+	watermillMessage.Metadata = envelopedMsg.Metadata
+	watermillMessage.SetContext(msg.Context())
+
+	return envelopedMsg.DestinationTopic, watermillMessage, nil
+}