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

message/router/middleware/duplicator.go

@@ -0,0 +1,22 @@
+package middleware
+
+import (
+	"github.com/ThreeDotsLabs/watermill/message"
+)
+
+// Duplicator is processing messages twice, to ensure that the endpoint is idempotent.
+func Duplicator(h message.HandlerFunc) message.HandlerFunc {
+	return func(msg *message.Message) ([]*message.Message, error) {
+		firstProducedMessages, firstErr := h(msg)
+		if firstErr != nil {
+			return nil, firstErr
+		}
+
+		secondProducedMessages, secondErr := h(msg)
+		if secondErr != nil {
+			return nil, secondErr
+		}
+
+		return append(firstProducedMessages, secondProducedMessages...), nil
+	}
+}