fix: move produce tagged fields inside partition loop

pkg/protocol/request.go

@@ -505,16 +505,16 @@ func ParseRequest(b []byte) (*RequestHeader, Request, error) {
 				if err != nil {
 					return nil, nil, fmt.Errorf("read produce records: %w", err)
 				}
+				if flexible {
+					if err := reader.SkipTaggedFields(); err != nil {
+						return nil, nil, fmt.Errorf("skip partition tags: %w", err)
+					}
+				}
 				partitions = append(partitions, ProducePartition{
 					Partition: index,
 					Records:   records,
 				})
 			}
-			if flexible {
-				if err := reader.SkipTaggedFields(); err != nil {
-					return nil, nil, fmt.Errorf("skip partition tags: %w", err)
-				}
-			}
 			if flexible {
 				if err := reader.SkipTaggedFields(); err != nil {
 					return nil, nil, fmt.Errorf("skip topic tags: %w", err)
@@ -1931,14 +1931,12 @@ func EncodeProduceRequest(header *RequestHeader, req *ProduceRequest, version in
 			} else {
 				w.BytesWithLength(part.Records)
 			}
+			if flexible {
+				w.WriteTaggedFields(0)
+			}
 		}
-		// Match the parser: two tagged-field blocks after the partition array.
-		// The Kafka protocol spec places per-partition tags inside the partition
-		// loop, but our parser (ParseRequest) reads them outside. Since the
-		// broker is always KafScale (not vanilla Kafka), this is intentional.
 		if flexible {
 			w.WriteTaggedFields(0)
-			w.WriteTaggedFields(0)
 		}
 	}
 	if flexible {

pkg/protocol/request_test.go

@@ -1033,3 +1033,113 @@ func TestEncodeFetchRequest_KmsgValidation(t *testing.T) {
 		t.Fatalf("fetch offset: got %d, want 42", kmsgReq.Topics[0].Partitions[0].FetchOffset)
 	}
 }
+
+// TestProduceMultiPartitionFranzCompat tests byte-level compatibility with
+// franz-go for multi-partition produce requests in both directions:
+//   - franz-go encodes → KafScale parses
+//   - KafScale encodes → franz-go decodes
+func TestProduceMultiPartitionFranzCompat(t *testing.T) {
+	t.Run("franz-encode-kafscale-parse", func(t *testing.T) {
+		req := kmsg.NewPtrProduceRequest()
+		req.Version = 9
+		req.Acks = -1
+		req.TimeoutMillis = 3000
+		topic := kmsg.NewProduceRequestTopic()
+		topic.Topic = "orders"
+		for _, pi := range []int32{0, 1, 2} {
+			part := kmsg.NewProduceRequestTopicPartition()
+			part.Partition = pi
+			part.Records = []byte{byte(pi + 1), byte(pi + 2)}
+			topic.Partitions = append(topic.Partitions, part)
+		}
+		req.Topics = append(req.Topics, topic)
+		body := req.AppendTo(nil)
+
+		w := newByteWriter(len(body) + 32)
+		w.Int16(APIKeyProduce)
+		w.Int16(9)
+		w.Int32(55)
+		clientID := "kgo"
+		w.NullableString(&clientID)
+		w.WriteTaggedFields(0)
+		w.write(body)
+
+		_, parsed, err := ParseRequest(w.Bytes())
+		if err != nil {
+			t.Fatalf("ParseRequest: %v", err)
+		}
+		got, ok := parsed.(*ProduceRequest)
+		if !ok {
+			t.Fatalf("expected *ProduceRequest, got %T", parsed)
+		}
+		if len(got.Topics) != 1 {
+			t.Fatalf("topic count: got %d want 1", len(got.Topics))
+		}
+		if len(got.Topics[0].Partitions) != 3 {
+			t.Fatalf("partition count: got %d want 3", len(got.Topics[0].Partitions))
+		}
+		for pi, part := range got.Topics[0].Partitions {
+			if part.Partition != int32(pi) {
+				t.Fatalf("part[%d] index: got %d want %d", pi, part.Partition, pi)
+			}
+			want := []byte{byte(pi + 1), byte(pi + 2)}
+			if string(part.Records) != string(want) {
+				t.Fatalf("part[%d] records: got %x want %x", pi, part.Records, want)
+			}
+		}
+	})
+
+	t.Run("kafscale-encode-franz-parse", func(t *testing.T) {
+		header := &RequestHeader{
+			APIKey:        APIKeyProduce,
+			APIVersion:    9,
+			CorrelationID: 66,
+			ClientID:      strPtr("test"),
+		}
+		req := &ProduceRequest{
+			Acks:      -1,
+			TimeoutMs: 3000,
+			Topics: []ProduceTopic{
+				{
+					Name: "orders",
+					Partitions: []ProducePartition{
+						{Partition: 0, Records: []byte{1, 2}},
+						{Partition: 1, Records: []byte{3, 4}},
+						{Partition: 2, Records: []byte{5, 6}},
+					},
+				},
+			},
+		}
+		encoded, err := EncodeProduceRequest(header, req, 9)
+		if err != nil {
+			t.Fatalf("encode: %v", err)
+		}
+
+		_, reader, err := ParseRequestHeader(encoded)
+		if err != nil {
+			t.Fatalf("ParseRequestHeader: %v", err)
+		}
+		bodyStart := len(encoded) - reader.remaining()
+
+		kmsgReq := kmsg.NewPtrProduceRequest()
+		kmsgReq.Version = 9
+		if err := kmsgReq.ReadFrom(encoded[bodyStart:]); err != nil {
+			t.Fatalf("kmsg.ReadFrom: %v", err)
+		}
+		if len(kmsgReq.Topics) != 1 {
+			t.Fatalf("topic count: got %d want 1", len(kmsgReq.Topics))
+		}
+		if len(kmsgReq.Topics[0].Partitions) != 3 {
+			t.Fatalf("partition count: got %d want 3", len(kmsgReq.Topics[0].Partitions))
+		}
+		for pi, part := range kmsgReq.Topics[0].Partitions {
+			if part.Partition != int32(pi) {
+				t.Fatalf("part[%d] index: got %d want %d", pi, part.Partition, pi)
+			}
+			want := []byte{byte(pi*2 + 1), byte(pi*2 + 2)}
+			if string(part.Records) != string(want) {
+				t.Fatalf("part[%d] records: got %x want %x", pi, part.Records, want)
+			}
+		}
+	})
+}

pkg/protocol/response_test.go

@@ -1518,77 +1518,65 @@ func TestParseProduceResponseRoundTrip(t *testing.T) {
 }
 
 func TestEncodeProduceRequestRoundTrip(t *testing.T) {
-	header := &RequestHeader{
-		APIKey:        APIKeyProduce,
-		APIVersion:    9,
-		CorrelationID: 77,
-		ClientID:      strPtr("test-client"),
-	}
 	req := &ProduceRequest{
 		Acks:      -1,
 		TimeoutMs: 5000,
 		Topics: []ProduceTopic{
 			{
 				Name: "orders",
 				Partitions: []ProducePartition{
-					{Partition: 0, Records: []byte{1, 2, 3, 4}},
-					{Partition: 1, Records: []byte{5, 6}},
+					{Partition: 0, Records: []byte{1, 2, 3}},
+					{Partition: 1, Records: []byte{4, 5}},
+					{Partition: 2, Records: []byte{6, 7, 8, 9}},
 				},
 			},
 			{
 				Name: "events",
 				Partitions: []ProducePartition{
-					{Partition: 0, Records: []byte{7, 8, 9}},
+					{Partition: 0, Records: []byte{10}},
+					{Partition: 3, Records: []byte{11, 12}},
 				},
 			},
 		},
 	}
 	for _, version := range []int16{3, 5, 7, 8, 9, 10} {
 		t.Run(fmt.Sprintf("v%d", version), func(t *testing.T) {
-			h := &RequestHeader{
+			header := &RequestHeader{
 				APIKey:        APIKeyProduce,
 				APIVersion:    version,
-				CorrelationID: header.CorrelationID,
-				ClientID:      header.ClientID,
+				CorrelationID: 77,
+				ClientID:      strPtr("test-client"),
 			}
-			encoded, err := EncodeProduceRequest(h, req, version)
+			encoded, err := EncodeProduceRequest(header, req, version)
 			if err != nil {
 				t.Fatalf("encode: %v", err)
 			}
-			parsedHeader, parsedReq, err := ParseRequest(encoded)
+			_, parsedReq, err := ParseRequest(encoded)
 			if err != nil {
 				t.Fatalf("parse: %v", err)
 			}
-			if parsedHeader.CorrelationID != h.CorrelationID {
-				t.Fatalf("correlation id: got %d want %d", parsedHeader.CorrelationID, h.CorrelationID)
-			}
-			produceReq, ok := parsedReq.(*ProduceRequest)
+			got, ok := parsedReq.(*ProduceRequest)
 			if !ok {
 				t.Fatalf("expected *ProduceRequest, got %T", parsedReq)
 			}
-			if produceReq.Acks != req.Acks {
-				t.Fatalf("acks: got %d want %d", produceReq.Acks, req.Acks)
+			if len(got.Topics) != len(req.Topics) {
+				t.Fatalf("topic count: got %d want %d", len(got.Topics), len(req.Topics))
 			}
-			if produceReq.TimeoutMs != req.TimeoutMs {
-				t.Fatalf("timeout: got %d want %d", produceReq.TimeoutMs, req.TimeoutMs)
-			}
-			if len(produceReq.Topics) != len(req.Topics) {
-				t.Fatalf("topic count: got %d want %d", len(produceReq.Topics), len(req.Topics))
-			}
-			for ti, topic := range produceReq.Topics {
-				if topic.Name != req.Topics[ti].Name {
-					t.Fatalf("topic[%d] name: got %q want %q", ti, topic.Name, req.Topics[ti].Name)
+			for ti, topic := range got.Topics {
+				want := req.Topics[ti]
+				if topic.Name != want.Name {
+					t.Fatalf("topic[%d] name: got %q want %q", ti, topic.Name, want.Name)
 				}
-				if len(topic.Partitions) != len(req.Topics[ti].Partitions) {
-					t.Fatalf("topic[%d] partition count: got %d want %d", ti, len(topic.Partitions), len(req.Topics[ti].Partitions))
+				if len(topic.Partitions) != len(want.Partitions) {
+					t.Fatalf("topic[%d] partition count: got %d want %d", ti, len(topic.Partitions), len(want.Partitions))
 				}
 				for pi, part := range topic.Partitions {
-					want := req.Topics[ti].Partitions[pi]
-					if part.Partition != want.Partition {
-						t.Fatalf("topic[%d].part[%d] index: got %d want %d", ti, pi, part.Partition, want.Partition)
+					wantPart := want.Partitions[pi]
+					if part.Partition != wantPart.Partition {
+						t.Fatalf("topic[%d].part[%d] index: got %d want %d", ti, pi, part.Partition, wantPart.Partition)
 					}
-					if string(part.Records) != string(want.Records) {
-						t.Fatalf("topic[%d].part[%d] records: got %v want %v", ti, pi, part.Records, want.Records)
+					if string(part.Records) != string(wantPart.Records) {
+						t.Fatalf("topic[%d].part[%d] records: got %x want %x", ti, pi, part.Records, wantPart.Records)
 					}
 				}
 			}