Writer: ensure batching logic factors in message headers

message.go

@@ -49,6 +49,17 @@ func (msg *Message) size() int32 {
 	return 4 + 1 + 1 + sizeofBytes(msg.Key) + sizeofBytes(msg.Value) + timestampSize
 }
 
+func (msg *Message) headerSize() int {
+	return varArrayLen(len(msg.Headers), func(i int) int {
+		h := &msg.Headers[i]
+		return varStringLen(h.Key) + varBytesLen(h.Value)
+	})
+}
+
+func (msg *Message) totalSize() int32 {
+	return int32(msg.headerSize()) + msg.size()
+}
+
 type message struct {
 	CRC        int32
 	MagicByte  int8

writer.go

@@ -621,7 +621,7 @@ func (w *Writer) WriteMessages(ctx context.Context, msgs ...Message) error {
 	batchBytes := w.batchBytes()
 
 	for i := range msgs {
-		n := int64(msgs[i].size())
+		n := int64(msgs[i].totalSize())
 		if n > batchBytes {
 			// This error is left for backward compatibility with historical
 			// behavior, but it can yield O(N^2) behaviors. The expectations
@@ -1216,7 +1216,7 @@ func newWriteBatch(now time.Time, timeout time.Duration) *writeBatch {
 }
 
 func (b *writeBatch) add(msg Message, maxSize int, maxBytes int64) bool {
-	bytes := int64(msg.size())
+	bytes := int64(msg.totalSize())
 
 	if b.size > 0 && (b.bytes+bytes) > maxBytes {
 		return false

writer_test.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"math"
 	"strconv"
+	"strings"
 	"sync"
 	"testing"
 	"time"
@@ -134,6 +135,10 @@ func TestWriter(t *testing.T) {
 			scenario: "writing messages with a small batch byte size",
 			function: testWriterSmallBatchBytes,
 		},
+		{
+			scenario: "writing messages with headers",
+			function: testWriterBatchBytesHeaders,
+		},
 		{
 			scenario: "setting a non default balancer on the writer",
 			function: testWriterSetsRightBalancer,
@@ -449,7 +454,7 @@ func testWriterBatchBytes(t *testing.T) {
 
 	w := newTestWriter(WriterConfig{
 		Topic:        topic,
-		BatchBytes:   48,
+		BatchBytes:   50,
 		BatchTimeout: math.MaxInt32 * time.Second,
 		Balancer:     &RoundRobin{},
 	})
@@ -458,10 +463,10 @@ func testWriterBatchBytes(t *testing.T) {
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()
 	if err := w.WriteMessages(ctx, []Message{
-		{Value: []byte("M0")}, // 24 Bytes
-		{Value: []byte("M1")}, // 24 Bytes
-		{Value: []byte("M2")}, // 24 Bytes
-		{Value: []byte("M3")}, // 24 Bytes
+		{Value: []byte("M0")}, // 25 Bytes
+		{Value: []byte("M1")}, // 25 Bytes
+		{Value: []byte("M2")}, // 25 Bytes
+		{Value: []byte("M3")}, // 25 Bytes
 	}...); err != nil {
 		t.Error(err)
 		return
@@ -592,6 +597,67 @@ func testWriterSmallBatchBytes(t *testing.T) {
 	}
 }
 
+func testWriterBatchBytesHeaders(t *testing.T) {
+	topic := makeTopic()
+	createTopic(t, topic, 1)
+	defer deleteTopic(t, topic)
+
+	offset, err := readOffset(topic, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	w := newTestWriter(WriterConfig{
+		Topic:        topic,
+		BatchBytes:   100,
+		BatchTimeout: 50 * time.Millisecond,
+		Balancer:     &RoundRobin{},
+	})
+	defer w.Close()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	if err := w.WriteMessages(ctx, []Message{
+		{
+			Value: []byte("Hello World 1"),
+			Headers: []Header{
+				{Key: "User-Agent", Value: []byte("abc/xyz")},
+			},
+		},
+		{
+			Value: []byte("Hello World 2"),
+			Headers: []Header{
+				{Key: "User-Agent", Value: []byte("abc/xyz")},
+			},
+		},
+	}...); err != nil {
+		t.Error(err)
+		return
+	}
+	ws := w.Stats()
+	if ws.Writes != 2 {
+		t.Error("didn't batch messages; Writes: ", ws.Writes)
+		return
+	}
+	msgs, err := readPartition(topic, 0, offset)
+	if err != nil {
+		t.Error("error reading partition", err)
+		return
+	}
+
+	if len(msgs) != 2 {
+		t.Error("bad messages in partition", msgs)
+		return
+	}
+
+	for _, m := range msgs {
+		if strings.HasPrefix(string(m.Value), "Hello World") {
+			continue
+		}
+		t.Error("bad messages in partition", msgs)
+	}
+}
+
 func testWriterMultipleTopics(t *testing.T) {
 	topic1 := makeTopic()
 	createTopic(t, topic1, 1)