SyncProducer batch support

Provide a `SyncProducer.SendMessages` method which produces a given *batch* of
messages (though does not guarantee they will end up in a single batch on the
wire).

sync_producer.go

@@ -16,6 +16,12 @@ type SyncProducer interface {
 	// of the produced message, or an error if the message failed to produce.
 	SendMessage(msg *ProducerMessage) (partition int32, offset int64, err error)
 
+	// SendMessages produces a given set of messages, and returns only when all
+	// messages in the set have either succeeded or failed. Note that messages
+	// can succeed and fail individually; if some succeed and some fail,
+	// SendMessages will return an error.
+	SendMessages(msgs []*ProducerMessage) error
+
 	// Close shuts down the producer and flushes any messages it may have buffered.
 	// You must call this function before a producer object passes out of scope, as
 	// it may otherwise leak memory. You must call this before calling Close on the
@@ -65,21 +71,56 @@ func (sp *syncProducer) SendMessage(msg *ProducerMessage) (partition int32, offs
 		msg.Metadata = oldMetadata
 	}()
 
-	expectation := make(chan error, 1)
+	expectation := make(chan *ProducerError, 1)
 	msg.Metadata = expectation
 	sp.producer.Input() <- msg
 
 	if err := <-expectation; err != nil {
-		return -1, -1, err
+		return -1, -1, err.Err
 	}
 
 	return msg.Partition, msg.Offset, nil
 }
 
+func (sp *syncProducer) SendMessages(msgs []*ProducerMessage) error {
+	savedMetadata := make([]interface{}, len(msgs))
+	for i := range msgs {
+		savedMetadata[i] = msgs[i].Metadata
+	}
+	defer func() {
+		for i := range msgs {
+			msgs[i].Metadata = savedMetadata[i]
+		}
+	}()
+
+	expectations := make(chan chan *ProducerError, len(msgs))
+	go func() {
+		for _, msg := range msgs {
+			expectation := make(chan *ProducerError, 1)
+			msg.Metadata = expectation
+			sp.producer.Input() <- msg
+			expectations <- expectation
+		}
+		close(expectations)
+	}()
+
+	var errors ProducerErrors
+	for expectation := range expectations {
+		if err := <-expectation; err != nil {
+			errors = append(errors, err)
+		}
+	}
+
+	if len(errors) > 0 {
+		return errors
+	}
+	return nil
+}
+
 func (sp *syncProducer) handleSuccesses() {
 	defer sp.wg.Done()
 	for msg := range sp.producer.Successes() {
-		expectation := msg.Metadata.(chan error)
+		expectation := msg.Metadata.(chan *ProducerError)
 		expectation <- nil
 	}
 }
@@ -87,8 +128,8 @@ func (sp *syncProducer) handleSuccesses() {
 func (sp *syncProducer) handleErrors() {
 	defer sp.wg.Done()
 	for err := range sp.producer.Errors() {
-		expectation := err.Msg.Metadata.(chan error)
-		expectation <- err.Err
+		expectation := err.Msg.Metadata.(chan *ProducerError)
+		expectation <- err
 	}
 }
 

sync_producer_test.go

@@ -54,6 +54,53 @@ func TestSyncProducer(t *testing.T) {
 	seedBroker.Close()
 }
 
+func TestSyncProducerBatch(t *testing.T) {
+	seedBroker := NewMockBroker(t, 1)
+	leader := NewMockBroker(t, 2)
+
+	metadataResponse := new(MetadataResponse)
+	metadataResponse.AddBroker(leader.Addr(), leader.BrokerID())
+	metadataResponse.AddTopicPartition("my_topic", 0, leader.BrokerID(), nil, nil, ErrNoError)
+	seedBroker.Returns(metadataResponse)
+
+	prodSuccess := new(ProduceResponse)
+	prodSuccess.AddTopicPartition("my_topic", 0, ErrNoError)
+	leader.Returns(prodSuccess)
+
+	config := NewConfig()
+	config.Producer.Flush.Messages = 3
+	producer, err := NewSyncProducer([]string{seedBroker.Addr()}, config)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = producer.SendMessages([]*ProducerMessage{
+		&ProducerMessage{
+			Topic:    "my_topic",
+			Value:    StringEncoder(TestMessage),
+			Metadata: "test",
+		},
+		&ProducerMessage{
+			Topic:    "my_topic",
+			Value:    StringEncoder(TestMessage),
+			Metadata: "test",
+		},
+		&ProducerMessage{
+			Topic:    "my_topic",
+			Value:    StringEncoder(TestMessage),
+			Metadata: "test",
+		},
+	})
+
+	if err != nil {
+		t.Error(err)
+	}
+
+	safeClose(t, producer)
+	leader.Close()
+	seedBroker.Close()
+}
+
 func TestConcurrentSyncProducer(t *testing.T) {
 	seedBroker := NewMockBroker(t, 1)
 	leader := NewMockBroker(t, 2)