Allow BalanceStrategy to provide custom assignment data

balance_strategy.go

@@ -47,6 +47,10 @@ type BalanceStrategy interface {
 	// Plan accepts a map of `memberID -> metadata` and a map of `topic -> partitions`
 	// and returns a distribution plan.
 	Plan(members map[string]ConsumerGroupMemberMetadata, topics map[string][]int32) (BalanceStrategyPlan, error)
+
+	// AssignmentData returns the serialized assignment data for the specified
+	// memberID
+	AssignmentData(memberID string, topics map[string][]int32, generationID int32) ([]byte, error)
 }
 
 // --------------------------------------------------------------------
@@ -132,6 +136,11 @@ func (s *balanceStrategy) Plan(members map[string]ConsumerGroupMemberMetadata, t
 	return plan, nil
 }
 
+// AssignmentData simple strategies do not require any shared assignment data
+func (s *balanceStrategy) AssignmentData(memberID string, topics map[string][]int32, generationID int32) ([]byte, error) {
+	return nil, nil
+}
+
 type balanceStrategySortable struct {
 	topic     string
 	memberIDs []string
@@ -268,6 +277,15 @@ func (s *stickyBalanceStrategy) Plan(members map[string]ConsumerGroupMemberMetad
 	return plan, nil
 }
 
+// AssignmentData serializes the set of topics currently assigned to the
+// specified member as part of the supplied balance plan
+func (s *stickyBalanceStrategy) AssignmentData(memberID string, topics map[string][]int32, generationID int32) ([]byte, error) {
+	return encode(&StickyAssignorUserDataV1{
+		Topics:     topics,
+		Generation: generationID,
+	}, nil)
+}
+
 func strsContains(s []string, value string) bool {
 	for _, entry := range s {
 		if entry == value {

balance_strategy_test.go

@@ -1,6 +1,7 @@
 package sarama
 
 import (
+	"bytes"
 	"fmt"
 	"math"
 	"math/rand"
@@ -62,6 +63,27 @@ func TestBalanceStrategyRange(t *testing.T) {
 	}
 }
 
+func TestBalanceStrategyRangeAssignmentData(t *testing.T) {
+
+	strategy := BalanceStrategyRange
+
+	members := make(map[string]ConsumerGroupMemberMetadata, 2)
+	members["consumer1"] = ConsumerGroupMemberMetadata{
+		Topics: []string{"topic1"},
+	}
+	members["consumer2"] = ConsumerGroupMemberMetadata{
+		Topics: []string{"topic1"},
+	}
+
+	actual, err := strategy.AssignmentData("consumer1", map[string][]int32{"topic1": {0, 1}}, 1)
+	if err != nil {
+		t.Errorf("Error building assignment data: %v", err)
+	}
+	if actual != nil {
+		t.Error("Invalid assignment data returned from AssignmentData")
+	}
+}
+
 func TestBalanceStrategyRoundRobin(t *testing.T) {
 	tests := []struct {
 		members  map[string][]string
@@ -191,6 +213,27 @@ func Test_deserializeTopicPartitionAssignment(t *testing.T) {
 	}
 }
 
+func TestBalanceStrategyRoundRobinAssignmentData(t *testing.T) {
+
+	strategy := BalanceStrategyRoundRobin
+
+	members := make(map[string]ConsumerGroupMemberMetadata, 2)
+	members["consumer1"] = ConsumerGroupMemberMetadata{
+		Topics: []string{"topic1"},
+	}
+	members["consumer2"] = ConsumerGroupMemberMetadata{
+		Topics: []string{"topic1"},
+	}
+
+	actual, err := strategy.AssignmentData("consumer1", map[string][]int32{"topic1": {0, 1}}, 1)
+	if err != nil {
+		t.Errorf("Error building assignment data: %v", err)
+	}
+	if actual != nil {
+		t.Error("Invalid assignment data returned from AssignmentData")
+	}
+}
+
 func Test_prepopulateCurrentAssignments(t *testing.T) {
 	type args struct {
 		members map[string]ConsumerGroupMemberMetadata
@@ -1950,6 +1993,29 @@ func Test_stickyBalanceStrategy_Plan_ConflictingPreviousAssignments(t *testing.T
 	verifyFullyBalanced(t, plan)
 }
 
+func Test_stickyBalanceStrategy_Plan_AssignmentData(t *testing.T) {
+
+	s := &stickyBalanceStrategy{}
+
+	members := make(map[string]ConsumerGroupMemberMetadata, 2)
+	members["consumer1"] = ConsumerGroupMemberMetadata{
+		Topics: []string{"topic1"},
+	}
+	members["consumer2"] = ConsumerGroupMemberMetadata{
+		Topics: []string{"topic1"},
+	}
+
+	expected := encodeSubscriberPlanWithGeneration(t, map[string][]int32{"topic1": {0, 1}}, 1)
+
+	actual, err := s.AssignmentData("consumer1", map[string][]int32{"topic1": {0, 1}}, 1)
+	if err != nil {
+		t.Errorf("Error building assignment data: %v", err)
+	}
+	if bytes.Compare(expected, actual) != 0 {
+		t.Error("Invalid assignment data returned from AssignmentData")
+	}
+}
+
 func BenchmarkStickAssignmentWithLargeNumberOfConsumersAndTopics(b *testing.B) {
 	s := &stickyBalanceStrategy{}
 	r := rand.New(rand.NewSource(time.Now().UnixNano()))

consumer_group.go

@@ -331,20 +331,14 @@ func (c *consumerGroup) syncGroupRequest(coordinator *Broker, plan BalanceStrate
 		MemberId:     c.memberID,
 		GenerationId: generationID,
 	}
+	strategy := c.config.Consumer.Group.Rebalance.Strategy
 	for memberID, topics := range plan {
 		assignment := &ConsumerGroupMemberAssignment{Topics: topics}
-
-		// Include topic assignments in group-assignment userdata for each consumer-group member
-		if c.config.Consumer.Group.Rebalance.Strategy.Name() == StickyBalanceStrategyName {
-			userDataBytes, err := encode(&StickyAssignorUserDataV1{
-				Topics:     topics,
-				Generation: generationID,
-			}, nil)
-			if err != nil {
-				return nil, err
-			}
-			assignment.UserData = userDataBytes
+		userDataBytes, err := strategy.AssignmentData(memberID, topics, generationID)
+		if err != nil {
+			return nil, err
 		}
+		assignment.UserData = userDataBytes
 		if err := req.AddGroupAssignmentMember(memberID, assignment); err != nil {
 			return nil, err
 		}