Added WithMessageKey to add the key to a producer message

protocol/kafka_sarama/v2/sender.go

@@ -53,6 +53,10 @@ func (s *Sender) Send(ctx context.Context, m binding.Message, transformers ...bi
 
 	kafkaMessage := sarama.ProducerMessage{Topic: s.topic}
 
+	if k := ctx.Value(withMessageKey{}); k != nil {
+		kafkaMessage.Key = k.(sarama.Encoder)
+	}
+
 	if err = WriteProducerMessage(ctx, m, &kafkaMessage, transformers...); err != nil {
 		return err
 	}
@@ -70,3 +74,10 @@ func (s *Sender) Close(ctx context.Context) error {
 	// otherwise it will close the whole client
 	return s.syncProducer.Close()
 }
+
+type withMessageKey struct{}
+
+// WithMessageKey allows to set the key used when sending the producer message
+func WithMessageKey(ctx context.Context, key sarama.Encoder) context.Context {
+	return context.WithValue(ctx, withMessageKey{}, key)
+}

protocol/kafka_sarama/v2/sender_test.go

@@ -0,0 +1,51 @@
+package kafka_sarama
+
+import (
+	"context"
+	"sync"
+	"testing"
+
+	"github.com/Shopify/sarama"
+	"github.com/stretchr/testify/require"
+
+	"github.com/cloudevents/sdk-go/v2/test"
+)
+
+type syncProducerMock struct {
+	lock sync.Mutex
+	sent []*sarama.ProducerMessage
+}
+
+func (s *syncProducerMock) SendMessage(msg *sarama.ProducerMessage) (partition int32, offset int64, err error) {
+	s.lock.Lock()
+	defer s.lock.Unlock()
+	s.sent = append(s.sent, msg)
+	return 0, int64(len(s.sent) - 1), err
+}
+
+func (s *syncProducerMock) SendMessages(msgs []*sarama.ProducerMessage) error {
+	s.lock.Lock()
+	defer s.lock.Unlock()
+	s.sent = append(s.sent, msgs...)
+	return nil
+}
+
+func (s *syncProducerMock) Close() error {
+	return nil
+}
+
+func TestSenderWithKey(t *testing.T) {
+	syncProducerMock := &syncProducerMock{}
+	topic := "aaa"
+
+	sender := &Sender{topic: topic, syncProducer: syncProducerMock}
+	require.NoError(t, sender.Send(
+		WithMessageKey(context.TODO(), sarama.StringEncoder("hello")),
+		test.FullMessage(),
+	))
+
+	require.Len(t, syncProducerMock.sent, 1)
+	kafkaMsg := syncProducerMock.sent[0]
+	require.Equal(t, kafkaMsg.Topic, topic)
+	require.Equal(t, kafkaMsg.Key, sarama.StringEncoder("hello"))
+}

samples/kafka/sender/main.go

@@ -5,6 +5,7 @@ import (
 	"log"
 
 	"github.com/Shopify/sarama"
+	"github.com/google/uuid"
 
 	"github.com/cloudevents/sdk-go/protocol/kafka_sarama/v2"
 	cloudevents "github.com/cloudevents/sdk-go/v2"
@@ -32,14 +33,19 @@ func main() {
 
 	for i := 0; i < count; i++ {
 		e := cloudevents.NewEvent()
+		e.SetID(uuid.New().String())
 		e.SetType("com.cloudevents.sample.sent")
 		e.SetSource("https://github.com/cloudevents/sdk-go/v2/samples/kafka/sender")
 		_ = e.SetData(cloudevents.ApplicationJSON, map[string]interface{}{
 			"id":      i,
 			"message": "Hello, World!",
 		})
 
-		if result := c.Send(context.Background(), e); cloudevents.IsUndelivered(result) {
+		if result := c.Send(
+			// Set the producer message key
+			kafka_sarama.WithMessageKey(context.Background(), sarama.StringEncoder(e.ID())),
+			e,
+		); cloudevents.IsUndelivered(result) {
 			log.Printf("failed to send: %v", err)
 		} else {
 			log.Printf("sent: %d, accepted: %t", i, cloudevents.IsACK(result))

v2/test/event_mocks.go

@@ -6,6 +6,7 @@ import (
 	"net/url"
 	"time"
 
+	"github.com/cloudevents/sdk-go/v2/binding"
 	"github.com/cloudevents/sdk-go/v2/binding/spec"
 	"github.com/cloudevents/sdk-go/v2/event"
 	"github.com/cloudevents/sdk-go/v2/types"
@@ -56,6 +57,18 @@ func MinEvent() event.Event {
 	}
 }
 
+// FullMessage returns the same event of FullEvent but wrapped as Message.
+func FullMessage() binding.Message {
+	ev := FullEvent()
+	return binding.ToMessage(&ev)
+}
+
+// MinMessage returns the same event of MinEvent but wrapped as Message.
+func MinMessage() binding.Message {
+	ev := MinEvent()
+	return binding.ToMessage(&ev)
+}
+
 // AllVersions returns all versions of each event in events.
 // ID gets a -number suffix so IDs are unique.
 func AllVersions(events []event.Event) []event.Event {