consumer.go

package cluster

import (
	"sort"
	"sync"
	"sync/atomic"
	"time"

	"github.com/IBM/sarama"
)

// Consumer is a cluster group consumer
type Consumer struct {
	client    *Client
	ownClient bool

	consumer sarama.Consumer
	subs     *partitionMap

	consumerID string
	groupID    string

	memberID     string
	generationID int32
	membershipMu sync.RWMutex

	coreTopics  []string
	extraTopics []string

	dying, dead chan none
	closeOnce   sync.Once

	consuming     int32
	messages      chan *sarama.ConsumerMessage
	errors        chan error
	partitions    chan PartitionConsumer
	notifications chan *Notification

	commitMu sync.Mutex
}

// NewConsumer initializes a new consumer
func NewConsumer(addrs []string, groupID string, topics []string, config *Config) (*Consumer, error) {
	client, err := NewClient(addrs, config)
	if err != nil {
		return nil, err
	}

	consumer, err := NewConsumerFromClient(client, groupID, topics)
	if err != nil {
		return nil, err
	}
	consumer.ownClient = true
	return consumer, nil
}

// NewConsumerFromClient initializes a new consumer from an existing client.
//
// Please note that clients cannot be shared between consumers (due to Kafka internals),
// they can only be re-used which requires the user to call Close() on the first consumer
// before using this method again to initialize another one. Attempts to use a client with
// more than one consumer at a time will return errors.
func NewConsumerFromClient(client *Client, groupID string, topics []string) (*Consumer, error) {
	if !client.claim() {
		return nil, errClientInUse
	}

	consumer, err := sarama.NewConsumerFromClient(client.Client)
	if err != nil {
		client.release()
		return nil, err
	}

	sort.Strings(topics)
	c := &Consumer{
		client:   client,
		consumer: consumer,
		subs:     newPartitionMap(),
		groupID:  groupID,

		coreTopics: topics,

		dying: make(chan none),
		dead:  make(chan none),

		messages:      make(chan *sarama.ConsumerMessage),
		errors:        make(chan error, client.config.ChannelBufferSize),
		partitions:    make(chan PartitionConsumer, 1),
		notifications: make(chan *Notification),
	}
	if err := c.client.RefreshCoordinator(groupID); err != nil {
		client.release()
		return nil, err
	}

	go c.mainLoop()
	return c, nil
}

// Messages returns the read channel for the messages that are returned by
// the broker.
//
// This channel will only return if Config.Group.Mode option is set to
// ConsumerModeMultiplex (default).
func (c *Consumer) Messages() <-chan *sarama.ConsumerMessage { return c.messages }

// Partitions returns the read channels for individual partitions of this broker.
//
// This will channel will only return if Config.Group.Mode option is set to
// ConsumerModePartitions.
//
// The Partitions() channel must be listened to for the life of this consumer;
// when a rebalance happens old partitions will be closed (naturally come to
// completion) and new ones will be emitted. The returned channel will only close
// when the consumer is completely shut down.
func (c *Consumer) Partitions() <-chan PartitionConsumer { return c.partitions }

// Errors returns a read channel of errors that occur during offset management, if
// enabled. By default, errors are logged and not returned over this channel. If
// you want to implement any custom error handling, set your config's
// Consumer.Return.Errors setting to true, and read from this channel.
func (c *Consumer) Errors() <-chan error { return c.errors }

// Notifications returns a channel of Notifications that occur during consumer
// rebalancing. Notifications will only be emitted over this channel, if your config's
// Group.Return.Notifications setting to true.
func (c *Consumer) Notifications() <-chan *Notification { return c.notifications }

// HighWaterMarks returns the current high water marks for each topic and partition
// Consistency between partitions is not guaranteed since high water marks are updated separately.
func (c *Consumer) HighWaterMarks() map[string]map[int32]int64 { return c.consumer.HighWaterMarks() }

// MarkOffset marks the provided message as processed, alongside a metadata string
// that represents the state of the partition consumer at that point in time. The
// metadata string can be used by another consumer to restore that state, so it
// can resume consumption.
//
// Note: calling MarkOffset does not necessarily commit the offset to the backend
// store immediately for efficiency reasons, and it may never be committed if
// your application crashes. This means that you may end up processing the same
// message twice, and your processing should ideally be idempotent.
func (c *Consumer) MarkOffset(msg *sarama.ConsumerMessage, metadata string) {
	if sub := c.subs.Fetch(msg.Topic, msg.Partition); sub != nil {
		sub.MarkOffset(msg.Offset, metadata)
	}
}

// MarkPartitionOffset marks an offset of the provided topic/partition as processed.
// See MarkOffset for additional explanation.
func (c *Consumer) MarkPartitionOffset(topic string, partition int32, offset int64, metadata string) {
	if sub := c.subs.Fetch(topic, partition); sub != nil {
		sub.MarkOffset(offset, metadata)
	}
}

// MarkOffsets marks stashed offsets as processed.
// See MarkOffset for additional explanation.
func (c *Consumer) MarkOffsets(s *OffsetStash) {
	s.mu.Lock()
	defer s.mu.Unlock()

	for tp, info := range s.offsets {
		if sub := c.subs.Fetch(tp.Topic, tp.Partition); sub != nil {
			sub.MarkOffset(info.Offset, info.Metadata)
		}
		delete(s.offsets, tp)
	}
}

// ResetOffsets marks the provided message as processed, alongside a metadata string
// that represents the state of the partition consumer at that point in time. The
// metadata string can be used by another consumer to restore that state, so it
// can resume consumption.
//
// Difference between ResetOffset and MarkOffset is that it allows to rewind to an earlier offset
func (c *Consumer) ResetOffset(msg *sarama.ConsumerMessage, metadata string) {
	if sub := c.subs.Fetch(msg.Topic, msg.Partition); sub != nil {
		sub.ResetOffset(msg.Offset, metadata)
	}
}

// ResetPartitionOffset marks an offset of the provided topic/partition as processed.
// See ResetOffset for additional explanation.
func (c *Consumer) ResetPartitionOffset(topic string, partition int32, offset int64, metadata string) {
	sub := c.subs.Fetch(topic, partition)
	if sub != nil {
		sub.ResetOffset(offset, metadata)
	}
}

// ResetOffsets marks stashed offsets as processed.
// See ResetOffset for additional explanation.
func (c *Consumer) ResetOffsets(s *OffsetStash) {
	s.mu.Lock()
	defer s.mu.Unlock()

	for tp, info := range s.offsets {
		if sub := c.subs.Fetch(tp.Topic, tp.Partition); sub != nil {
			sub.ResetOffset(info.Offset, info.Metadata)
		}
		delete(s.offsets, tp)
	}
}

// Subscriptions returns the consumed topics and partitions
func (c *Consumer) Subscriptions() map[string][]int32 {
	return c.subs.Info()
}

// CommitOffsets allows to manually commit previously marked offsets. By default there is no
// need to call this function as the consumer will commit offsets automatically
// using the Config.Consumer.Offsets.CommitInterval setting.
//
// Please be aware that calling this function during an internal rebalance cycle may return
// broker errors (e.g. sarama.ErrUnknownMemberId or sarama.ErrIllegalGeneration).
func (c *Consumer) CommitOffsets() error {
	c.commitMu.Lock()
	defer c.commitMu.Unlock()

	memberID, generationID := c.membership()
	req := &sarama.OffsetCommitRequest{
		Version:                 2,
		ConsumerGroup:           c.groupID,
		ConsumerGroupGeneration: generationID,
		ConsumerID:              memberID,
		RetentionTime:           -1,
	}

	if ns := c.client.config.Consumer.Offsets.Retention; ns != 0 {
		req.RetentionTime = int64(ns / time.Millisecond)
	}

	snap := c.subs.Snapshot()
	dirty := false
	for tp, state := range snap {
		if state.Dirty {
			dirty = true
			req.AddBlock(tp.Topic, tp.Partition, state.Info.Offset, 0, state.Info.Metadata)
		}
	}
	if !dirty {
		return nil
	}

	broker, err := c.client.Coordinator(c.groupID)
	if err != nil {
		c.closeCoordinator(broker, err)
		return err
	}

	resp, err := broker.CommitOffset(req)
	if err != nil {
		c.closeCoordinator(broker, err)
		return err
	}

	for topic, errs := range resp.Errors {
		for partition, kerr := range errs {
			if kerr != sarama.ErrNoError {
				err = kerr
			} else if state, ok := snap[topicPartition{topic, partition}]; ok {
				if sub := c.subs.Fetch(topic, partition); sub != nil {
					sub.markCommitted(state.Info.Offset)
				}
			}
		}
	}
	return err
}

// Close safely closes the consumer and releases all resources
func (c *Consumer) Close() (err error) {
	c.closeOnce.Do(func() {
		close(c.dying)
		<-c.dead

		if e := c.release(); e != nil {
			err = e
		}
		if e := c.consumer.Close(); e != nil {
			err = e
		}
		close(c.messages)
		close(c.errors)

		if e := c.leaveGroup(); e != nil {
			err = e
		}
		close(c.partitions)
		close(c.notifications)

		// drain
		for range c.messages {
		}
		for range c.errors {
		}
		for p := range c.partitions {
			_ = p.Close()
		}
		for range c.notifications {
		}

		c.client.release()
		if c.ownClient {
			if e := c.client.Close(); e != nil {
				err = e
			}
		}
	})
	return
}

func (c *Consumer) mainLoop() {
	defer close(c.dead)
	defer atomic.StoreInt32(&c.consuming, 0)

	for {
		atomic.StoreInt32(&c.consuming, 0)

		// Check if close was requested
		select {
		case <-c.dying:
			return
		default:
		}

		// Start next consume cycle
		c.nextTick()
	}
}

func (c *Consumer) nextTick() {
	// Remember previous subscriptions
	var notification *Notification
	if c.client.config.Group.Return.Notifications {
		notification = newNotification(c.subs.Info())
	}

	// Refresh coordinator
	if err := c.refreshCoordinator(); err != nil {
		c.rebalanceError(err, nil)
		return
	}

	// Release subscriptions
	if err := c.release(); err != nil {
		c.rebalanceError(err, nil)
		return
	}

	// Issue rebalance start notification
	if c.client.config.Group.Return.Notifications {
		c.handleNotification(notification)
	}

	// Rebalance, fetch new subscriptions
	subs, err := c.rebalance()
	if err != nil {
		c.rebalanceError(err, notification)
		return
	}

	// Coordinate loops, make sure everything is
	// stopped on exit
	tomb := newLoopTomb()
	defer tomb.Close()

	// Start the heartbeat
	tomb.Go(c.hbLoop)

	// Subscribe to topic/partitions
	if err := c.subscribe(tomb, subs); err != nil {
		c.rebalanceError(err, notification)
		return
	}

	// Update/issue notification with new claims
	if c.client.config.Group.Return.Notifications {
		notification = notification.success(subs)
		c.handleNotification(notification)
	}

	// Start topic watcher loop
	tomb.Go(c.twLoop)

	// Start consuming and committing offsets
	tomb.Go(c.cmLoop)
	atomic.StoreInt32(&c.consuming, 1)

	// Wait for signals
	select {
	case <-tomb.Dying():
	case <-c.dying:
	}
}

// heartbeat loop, triggered by the mainLoop
func (c *Consumer) hbLoop(stopped <-chan none) {
	ticker := time.NewTicker(c.client.config.Group.Heartbeat.Interval)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			switch err := c.heartbeat(); err {
			case nil, sarama.ErrNoError:
			case sarama.ErrNotCoordinatorForConsumer, sarama.ErrRebalanceInProgress:
				return
			default:
				c.handleError(&Error{Ctx: "heartbeat", error: err})
				return
			}
		case <-stopped:
			return
		case <-c.dying:
			return
		}
	}
}

// topic watcher loop, triggered by the mainLoop
func (c *Consumer) twLoop(stopped <-chan none) {
	ticker := time.NewTicker(c.client.config.Metadata.RefreshFrequency / 2)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			topics, err := c.client.Topics()
			if err != nil {
				c.handleError(&Error{Ctx: "topics", error: err})
				return
			}

			for _, topic := range topics {
				if !c.isKnownCoreTopic(topic) &&
					!c.isKnownExtraTopic(topic) &&
					c.isPotentialExtraTopic(topic) {
					return
				}
			}
		case <-stopped:
			return
		case <-c.dying:
			return
		}
	}
}

// commit loop, triggered by the mainLoop
func (c *Consumer) cmLoop(stopped <-chan none) {
	ticker := time.NewTicker(c.client.config.Consumer.Offsets.CommitInterval)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			if err := c.commitOffsetsWithRetry(c.client.config.Group.Offsets.Retry.Max); err != nil {
				c.handleError(&Error{Ctx: "commit", error: err})
				return
			}
		case <-stopped:
			return
		case <-c.dying:
			return
		}
	}
}

func (c *Consumer) rebalanceError(err error, n *Notification) {
	if n != nil {
		n.Type = RebalanceError
		c.handleNotification(n)
	}

	switch err {
	case sarama.ErrRebalanceInProgress:
	default:
		c.handleError(&Error{Ctx: "rebalance", error: err})
	}

	select {
	case <-c.dying:
	case <-time.After(c.client.config.Metadata.Retry.Backoff):
	}
}

func (c *Consumer) handleNotification(n *Notification) {
	if c.client.config.Group.Return.Notifications {
		select {
		case c.notifications <- n:
		case <-c.dying:
			return
		}
	}
}

func (c *Consumer) handleError(e *Error) {
	if c.client.config.Consumer.Return.Errors {
		select {
		case c.errors <- e:
		case <-c.dying:
			return
		}
	} else {
		sarama.Logger.Printf("%s error: %s\n", e.Ctx, e.Error())
	}
}

// Releases the consumer and commits offsets, called from rebalance() and Close()
func (c *Consumer) release() (err error) {
	// Stop all consumers
	c.subs.Stop()

	// Clear subscriptions on exit
	defer c.subs.Clear()

	// Wait for messages to be processed
	timeout := time.NewTimer(c.client.config.Group.Offsets.Synchronization.DwellTime)
	defer timeout.Stop()

	select {
	case <-c.dying:
	case <-timeout.C:
	}

	// Commit offsets, continue on errors
	if e := c.commitOffsetsWithRetry(c.client.config.Group.Offsets.Retry.Max); e != nil {
		err = e
	}

	return
}

// --------------------------------------------------------------------

// Performs a heartbeat, part of the mainLoop()
func (c *Consumer) heartbeat() error {
	broker, err := c.client.Coordinator(c.groupID)
	if err != nil {
		c.closeCoordinator(broker, err)
		return err
	}

	memberID, generationID := c.membership()
	resp, err := broker.Heartbeat(&sarama.HeartbeatRequest{
		GroupId:      c.groupID,
		MemberId:     memberID,
		GenerationId: generationID,
	})
	if err != nil {
		c.closeCoordinator(broker, err)
		return err
	}
	return resp.Err
}

// Performs a rebalance, part of the mainLoop()
func (c *Consumer) rebalance() (map[string][]int32, error) {
	memberID, _ := c.membership()
	sarama.Logger.Printf("cluster/consumer %s rebalance\n", memberID)

	allTopics, err := c.client.Topics()
	if err != nil {
		return nil, err
	}
	c.extraTopics = c.selectExtraTopics(allTopics)
	sort.Strings(c.extraTopics)

	// Re-join consumer group
	strategy, err := c.joinGroup()
	switch {
	case err == sarama.ErrUnknownMemberId:
		c.membershipMu.Lock()
		c.memberID = ""
		c.membershipMu.Unlock()
		return nil, err
	case err != nil:
		return nil, err
	}

	// Sync consumer group state, fetch subscriptions
	subs, err := c.syncGroup(strategy)
	switch {
	case err == sarama.ErrRebalanceInProgress:
		return nil, err
	case err != nil:
		_ = c.leaveGroup()
		return nil, err
	}
	return subs, nil
}

// Performs the subscription, part of the mainLoop()
func (c *Consumer) subscribe(tomb *loopTomb, subs map[string][]int32) error {
	// fetch offsets
	offsets, err := c.fetchOffsets(subs)
	if err != nil {
		_ = c.leaveGroup()
		return err
	}

	// create consumers in parallel
	var mu sync.Mutex
	var wg sync.WaitGroup

	for topic, partitions := range subs {
		for _, partition := range partitions {
			wg.Add(1)

			info := offsets[topic][partition]
			go func(topic string, partition int32) {
				if e := c.createConsumer(tomb, topic, partition, info); e != nil {
					mu.Lock()
					err = e
					mu.Unlock()
				}
				wg.Done()
			}(topic, partition)
		}
	}
	wg.Wait()

	if err != nil {
		_ = c.release()
		_ = c.leaveGroup()
	}
	return err
}

// --------------------------------------------------------------------

// Send a request to the broker to join group on rebalance()
func (c *Consumer) joinGroup() (*balancer, error) {
	memberID, _ := c.membership()
	req := &sarama.JoinGroupRequest{
		GroupId:        c.groupID,
		MemberId:       memberID,
		SessionTimeout: int32(c.client.config.Group.Session.Timeout / time.Millisecond),
		ProtocolType:   "consumer",
	}

	meta := &sarama.ConsumerGroupMemberMetadata{
		Version:  1,
		Topics:   append(c.coreTopics, c.extraTopics...),
		UserData: c.client.config.Group.Member.UserData,
	}
	err := req.AddGroupProtocolMetadata(string(StrategyRange), meta)
	if err != nil {
		return nil, err
	}
	err = req.AddGroupProtocolMetadata(string(StrategyRoundRobin), meta)
	if err != nil {
		return nil, err
	}

	broker, err := c.client.Coordinator(c.groupID)
	if err != nil {
		c.closeCoordinator(broker, err)
		return nil, err
	}

	resp, err := broker.JoinGroup(req)
	if err != nil {
		c.closeCoordinator(broker, err)
		return nil, err
	} else if resp.Err != sarama.ErrNoError {
		c.closeCoordinator(broker, resp.Err)
		return nil, resp.Err
	}

	var strategy *balancer
	if resp.LeaderId == resp.MemberId {
		members, err := resp.GetMembers()
		if err != nil {
			return nil, err
		}

		strategy, err = newBalancerFromMeta(c.client, members)
		if err != nil {
			return nil, err
		}
	}

	c.membershipMu.Lock()
	c.memberID = resp.MemberId
	c.generationID = resp.GenerationId
	c.membershipMu.Unlock()

	return strategy, nil
}

// Send a request to the broker to sync the group on rebalance().
// Returns a list of topics and partitions to consume.
func (c *Consumer) syncGroup(strategy *balancer) (map[string][]int32, error) {
	memberID, generationID := c.membership()
	req := &sarama.SyncGroupRequest{
		GroupId:      c.groupID,
		MemberId:     memberID,
		GenerationId: generationID,
	}

	if strategy != nil {
		for memberID, topics := range strategy.Perform(c.client.config.Group.PartitionStrategy) {
			if err := req.AddGroupAssignmentMember(memberID, &sarama.ConsumerGroupMemberAssignment{
				Topics: topics,
			}); err != nil {
				return nil, err
			}
		}
	}

	broker, err := c.client.Coordinator(c.groupID)
	if err != nil {
		c.closeCoordinator(broker, err)
		return nil, err
	}

	resp, err := broker.SyncGroup(req)
	if err != nil {
		c.closeCoordinator(broker, err)
		return nil, err
	} else if resp.Err != sarama.ErrNoError {
		c.closeCoordinator(broker, resp.Err)
		return nil, resp.Err
	}

	// Return if there is nothing to subscribe to
	if len(resp.MemberAssignment) == 0 {
		return nil, nil
	}

	// Get assigned subscriptions
	members, err := resp.GetMemberAssignment()
	if err != nil {
		return nil, err
	}

	// Sort partitions, for each topic
	for topic := range members.Topics {
		sort.Sort(int32Slice(members.Topics[topic]))
	}
	return members.Topics, nil
}

// Fetches latest committed offsets for all subscriptions
func (c *Consumer) fetchOffsets(subs map[string][]int32) (map[string]map[int32]offsetInfo, error) {
	offsets := make(map[string]map[int32]offsetInfo, len(subs))
	req := &sarama.OffsetFetchRequest{
		Version:       1,
		ConsumerGroup: c.groupID,
	}

	for topic, partitions := range subs {
		offsets[topic] = make(map[int32]offsetInfo, len(partitions))
		for _, partition := range partitions {
			offsets[topic][partition] = offsetInfo{Offset: -1}
			req.AddPartition(topic, partition)
		}
	}

	broker, err := c.client.Coordinator(c.groupID)
	if err != nil {
		c.closeCoordinator(broker, err)
		return nil, err
	}

	resp, err := broker.FetchOffset(req)
	if err != nil {
		c.closeCoordinator(broker, err)
		return nil, err
	}

	for topic, partitions := range subs {
		for _, partition := range partitions {
			block := resp.GetBlock(topic, partition)
			if block == nil {
				return nil, sarama.ErrIncompleteResponse
			}

			if block.Err == sarama.ErrNoError {
				offsets[topic][partition] = offsetInfo{Offset: block.Offset, Metadata: block.Metadata}
			} else {
				return nil, block.Err
			}
		}
	}
	return offsets, nil
}

// Send a request to the broker to leave the group on failes rebalance() and on Close()
func (c *Consumer) leaveGroup() error {
	broker, err := c.client.Coordinator(c.groupID)
	if err != nil {
		c.closeCoordinator(broker, err)
		return err
	}

	memberID, _ := c.membership()
	if _, err = broker.LeaveGroup(&sarama.LeaveGroupRequest{
		GroupId:  c.groupID,
		MemberId: memberID,
	}); err != nil {
		c.closeCoordinator(broker, err)
	}
	return err
}

// --------------------------------------------------------------------

func (c *Consumer) createConsumer(tomb *loopTomb, topic string, partition int32, info offsetInfo) error {
	memberID, _ := c.membership()
	sarama.Logger.Printf("cluster/consumer %s consume %s/%d from %d\n", memberID, topic, partition, info.NextOffset(c.client.config.Consumer.Offsets.Initial))

	// Create partitionConsumer
	pc, err := newPartitionConsumer(c.consumer, topic, partition, info, c.client.config.Consumer.Offsets.Initial)
	if err != nil {
		return err
	}

	// Store in subscriptions
	c.subs.Store(topic, partition, pc)

	// Start partition consumer goroutine
	tomb.Go(func(stopper <-chan none) {
		if c.client.config.Group.Mode == ConsumerModePartitions {
			pc.waitFor(stopper, c.errors)
		} else {
			pc.multiplex(stopper, c.messages, c.errors)
		}
	})

	if c.client.config.Group.Mode == ConsumerModePartitions {
		c.partitions <- pc
	}
	return nil
}

func (c *Consumer) commitOffsetsWithRetry(retries int) error {
	err := c.CommitOffsets()
	if err != nil && retries > 0 {
		return c.commitOffsetsWithRetry(retries - 1)
	}
	return err
}

func (c *Consumer) closeCoordinator(broker *sarama.Broker, err error) {
	if broker != nil {
		_ = broker.Close()
	}

	switch err {
	case sarama.ErrConsumerCoordinatorNotAvailable, sarama.ErrNotCoordinatorForConsumer:
		_ = c.client.RefreshCoordinator(c.groupID)
	}
}

func (c *Consumer) selectExtraTopics(allTopics []string) []string {
	extra := allTopics[:0]
	for _, topic := range allTopics {
		if !c.isKnownCoreTopic(topic) && c.isPotentialExtraTopic(topic) {
			extra = append(extra, topic)
		}
	}
	return extra
}

func (c *Consumer) isKnownCoreTopic(topic string) bool {
	pos := sort.SearchStrings(c.coreTopics, topic)
	return pos < len(c.coreTopics) && c.coreTopics[pos] == topic
}

func (c *Consumer) isKnownExtraTopic(topic string) bool {
	pos := sort.SearchStrings(c.extraTopics, topic)
	return pos < len(c.extraTopics) && c.extraTopics[pos] == topic
}

func (c *Consumer) isPotentialExtraTopic(topic string) bool {
	rx := c.client.config.Group.Topics
	if rx.Blacklist != nil && rx.Blacklist.MatchString(topic) {
		return false
	}
	if rx.Whitelist != nil && rx.Whitelist.MatchString(topic) {
		return true
	}
	return false
}

func (c *Consumer) refreshCoordinator() error {
	if err := c.refreshMetadata(); err != nil {
		return err
	}
	return c.client.RefreshCoordinator(c.groupID)
}

func (c *Consumer) refreshMetadata() (err error) {
	if c.client.config.Metadata.Full {
		err = c.client.RefreshMetadata()
	} else {
		var topics []string
		if topics, err = c.client.Topics(); err == nil && len(topics) != 0 {
			err = c.client.RefreshMetadata(topics...)
		}
	}

	// maybe we didn't have authorization to describe all topics
	switch err {
	case sarama.ErrTopicAuthorizationFailed:
		err = c.client.RefreshMetadata(c.coreTopics...)
	}
	return
}

func (c *Consumer) membership() (memberID string, generationID int32) {
	c.membershipMu.RLock()
	memberID, generationID = c.memberID, c.generationID
	c.membershipMu.RUnlock()
	return
}