fix: make fetchInitialOffset use correct protocol

The `fetchInitialOffset` func in offsetManager was hardcoded to send a
Version 1 OffsetFetchRequest rather than sending the appropriate version
based on the config KafkaVersion. As discussed in #2694 this meant that
LeaderEpoch was always being decoded as the default value '0' (because
it was only returned in Version >= 5 OffsetFetchRequest). However, other
areas of the offsetManager code were sending the newer protocol
versions, so for example the OffsetCommitRequest would include a leader
epoch value of 0 rather than an accurate one.

Correct this bug by sending the correct protocol version in
fetchInitialOffset and also ensure we default to `-1` when we decode an
OffsetFetchResponse of a Version < 5

Fixes #2694

Signed-off-by: Dominic Evans <dominic.evans@uk.ibm.com>

admin.go

@@ -1018,35 +1018,7 @@ func (ca *clusterAdmin) ListConsumerGroupOffsets(group string, topicPartitions m
 		return nil, err
 	}
 
-	request := &OffsetFetchRequest{
-		ConsumerGroup: group,
-		partitions:    topicPartitions,
-	}
-
-	if ca.conf.Version.IsAtLeast(V2_5_0_0) {
-		// Version 7 is adding the require stable flag.
-		request.Version = 7
-	} else if ca.conf.Version.IsAtLeast(V2_4_0_0) {
-		// Version 6 is the first flexible version.
-		request.Version = 6
-	} else if ca.conf.Version.IsAtLeast(V2_1_0_0) {
-		// Version 3, 4, and 5 are the same as version 2.
-		request.Version = 5
-	} else if ca.conf.Version.IsAtLeast(V2_0_0_0) {
-		request.Version = 4
-	} else if ca.conf.Version.IsAtLeast(V0_11_0_0) {
-		request.Version = 3
-	} else if ca.conf.Version.IsAtLeast(V0_10_2_0) {
-		// Starting in version 2, the request can contain a null topics array to indicate that offsets
-		// for all topics should be fetched. It also returns a top level error code
-		// for group or coordinator level errors.
-		request.Version = 2
-	} else if ca.conf.Version.IsAtLeast(V0_8_2_0) {
-		// In version 0, the request read offsets from ZK.
-		//
-		// Starting in version 1, the broker supports fetching offsets from the internal __consumer_offsets topic.
-		request.Version = 1
-	}
+	request := NewOffsetFetchRequest(ca.conf.Version, group, topicPartitions)
 
 	return coordinator.FetchOffset(request)
 }

offset_fetch_request.go

@@ -7,6 +7,43 @@ type OffsetFetchRequest struct {
 	partitions    map[string][]int32
 }
 
+func NewOffsetFetchRequest(
+	version KafkaVersion,
+	group string,
+	partitions map[string][]int32,
+) *OffsetFetchRequest {
+	request := &OffsetFetchRequest{
+		ConsumerGroup: group,
+		partitions:    partitions,
+	}
+	if version.IsAtLeast(V2_5_0_0) {
+		// Version 7 is adding the require stable flag.
+		request.Version = 7
+	} else if version.IsAtLeast(V2_4_0_0) {
+		// Version 6 is the first flexible version.
+		request.Version = 6
+	} else if version.IsAtLeast(V2_1_0_0) {
+		// Version 3, 4, and 5 are the same as version 2.
+		request.Version = 5
+	} else if version.IsAtLeast(V2_0_0_0) {
+		request.Version = 4
+	} else if version.IsAtLeast(V0_11_0_0) {
+		request.Version = 3
+	} else if version.IsAtLeast(V0_10_2_0) {
+		// Starting in version 2, the request can contain a null topics array to indicate that offsets
+		// for all topics should be fetched. It also returns a top level error code
+		// for group or coordinator level errors.
+		request.Version = 2
+	} else if version.IsAtLeast(V0_8_2_0) {
+		// In version 0, the request read offsets from ZK.
+		//
+		// Starting in version 1, the broker supports fetching offsets from the internal __consumer_offsets topic.
+		request.Version = 1
+	}
+
+	return request
+}
+
 func (r *OffsetFetchRequest) encode(pe packetEncoder) (err error) {
 	if r.Version < 0 || r.Version > 7 {
 		return PacketEncodingError{"invalid or unsupported OffsetFetchRequest version field"}

offset_fetch_response.go

@@ -22,6 +22,8 @@ func (b *OffsetFetchResponseBlock) decode(pd packetDecoder, version int16) (err
 		if err != nil {
 			return err
 		}
+	} else {
+		b.LeaderEpoch = -1
 	}
 
 	if isFlexible {

offset_fetch_response_test.go

@@ -44,19 +44,19 @@ func TestNormalOffsetFetchResponse(t *testing.T) {
 
 	for version := 0; version <= 1; version++ {
 		response := OffsetFetchResponse{Version: int16(version)}
-		response.AddBlock("t", 0, &OffsetFetchResponseBlock{0, 0, "md", ErrRequestTimedOut})
+		response.AddBlock("t", 0, &OffsetFetchResponseBlock{0, -1, "md", ErrRequestTimedOut})
 		response.Blocks["m"] = nil
 		testResponse(t, fmt.Sprintf("Normal v%d", version), &response, nil)
 	}
 
 	responseV2 := OffsetFetchResponse{Version: 2, Err: ErrInvalidRequest}
-	responseV2.AddBlock("t", 0, &OffsetFetchResponseBlock{0, 0, "md", ErrRequestTimedOut})
+	responseV2.AddBlock("t", 0, &OffsetFetchResponseBlock{0, -1, "md", ErrRequestTimedOut})
 	responseV2.Blocks["m"] = nil
 	testResponse(t, "normal V2", &responseV2, nil)
 
 	for version := 3; version <= 4; version++ {
 		responseV3 := OffsetFetchResponse{Version: int16(version), Err: ErrInvalidRequest, ThrottleTimeMs: 9}
-		responseV3.AddBlock("t", 0, &OffsetFetchResponseBlock{0, 0, "md", ErrRequestTimedOut})
+		responseV3.AddBlock("t", 0, &OffsetFetchResponseBlock{0, -1, "md", ErrRequestTimedOut})
 		responseV3.Blocks["m"] = nil
 		testResponse(t, fmt.Sprintf("Normal v%d", version), &responseV3, nil)
 	}

offset_manager.go

@@ -153,11 +153,8 @@ func (om *offsetManager) fetchInitialOffset(topic string, partition int32, retri
 		return om.fetchInitialOffset(topic, partition, retries-1)
 	}
 
-	req := new(OffsetFetchRequest)
-	req.Version = 1
-	req.ConsumerGroup = om.group
-	req.AddPartition(topic, partition)
-
+	partitions := map[string][]int32{topic: {partition}}
+	req := NewOffsetFetchRequest(om.conf.Version, om.group, partitions)
 	resp, err := broker.FetchOffset(req)
 	if err != nil {
 		if retries <= 0 {