sarama/client.go

package sarama

import (
	"sort"
	"sync"
	"time"
)

// ClientConfig is used to pass multiple configuration options to NewClient.
type ClientConfig struct {
	MetadataRetries   int           // How many times to retry a metadata request when a partition is in the middle of leader election.
	WaitForElection   time.Duration // How long to wait for leader election to finish between retries.
	DefaultBrokerConf *BrokerConfig // Default configuration for broker connections created by this client.
}

// Client is a generic Kafka client. It manages connections to one or more Kafka brokers.
// You MUST call Close() on a client to avoid leaks, it will not be garbage-collected
// automatically when it passes out of scope. A single client can be safely shared by
// multiple concurrent Producers and Consumers.
type Client struct {
	id     string
	config ClientConfig

	// the broker addresses given to us through the constructor are not guaranteed to be returned in
	// the cluster metadata (I *think* it only returns brokers who are currently leading partitions?)
	// so we store them separately
	extraBrokerAddrs []string
	extraBroker      *Broker
	deadBrokerAddrs  []string

	brokers map[int32]*Broker          // maps broker ids to brokers
	leaders map[string]map[int32]int32 // maps topics to partition ids to broker ids
	lock    sync.RWMutex               // protects access to the maps, only one since they're always written together
}

// NewClient creates a new Client with the given client ID. It connects to one of the given broker addresses
// and uses that broker to automatically fetch metadata on the rest of the kafka cluster. If metadata cannot
// be retrieved from any of the given broker addresses, the client is not created.
func NewClient(id string, addrs []string, config *ClientConfig) (*Client, error) {
	Logger.Println("Initializing new client")

	if config == nil {
		config = NewClientConfig()
	}

	if err := config.Validate(); err != nil {
		return nil, err
	}

	if len(addrs) < 1 {
		return nil, ConfigurationError("You must provide at least one broker address")
	}

	client := &Client{
		id:               id,
		config:           *config,
		extraBrokerAddrs: addrs,
		extraBroker:      NewBroker(addrs[0]),
		brokers:          make(map[int32]*Broker),
		leaders:          make(map[string]map[int32]int32),
	}
	client.extraBroker.Open(config.DefaultBrokerConf)

	// do an initial fetch of all cluster metadata by specifing an empty list of topics
	err := client.RefreshAllMetadata()
	if err != nil {
		client.Close() // this closes tmp, since it's still in the brokers hash
		return nil, err
	}

	Logger.Println("Successfully initialized new client")

	return client, nil
}

// Close shuts down all broker connections managed by this client. It is required to call this function before
// a client object passes out of scope, as it will otherwise leak memory. You must close any Producers or Consumers
// using a client before you close the client.
func (client *Client) Close() error {
	client.lock.Lock()
	defer client.lock.Unlock()
	Logger.Println("Closing Client")

	for _, broker := range client.brokers {
		myBroker := broker // NB: block-local prevents clobbering
		go withRecover(func() { myBroker.Close() })
	}
	client.brokers = nil
	client.leaders = nil

	if client.extraBroker != nil {
		go withRecover(func() { client.extraBroker.Close() })
	}

	return nil
}

// Partitions returns the sorted list of available partition IDs for the given topic.
func (client *Client) Partitions(topic string) ([]int32, error) {
	partitions := client.cachedPartitions(topic)

	// len==0 catches when it's nil (no such topic) and the odd case when every single
	// partition is undergoing leader election simultaneously. Callers have to be able to handle
	// this function returning an empty slice (which is a valid return value) but catching it
	// here the first time (note we *don't* catch it below where we return NoSuchTopic) triggers
	// a metadata refresh as a nicety so callers can just try again and don't have to manually
	// trigger a refresh (otherwise they'd just keep getting a stale cached copy).
	if len(partitions) == 0 {
		err := client.RefreshTopicMetadata(topic)
		if err != nil {
			return nil, err
		}
		partitions = client.cachedPartitions(topic)
	}

	if partitions == nil {
		return nil, NoSuchTopic
	}

	return partitions, nil
}

// Topics returns the set of available topics as retrieved from the cluster metadata.
func (client *Client) Topics() ([]string, error) {
	client.lock.RLock()
	defer client.lock.RUnlock()

	ret := make([]string, 0, len(client.leaders))
	for topic := range client.leaders {
		ret = append(ret, topic)
	}

	return ret, nil
}

// Leader returns the broker object that is the leader of the current topic/partition, as
// determined by querying the cluster metadata.
func (client *Client) Leader(topic string, partitionID int32) (*Broker, error) {
	leader := client.cachedLeader(topic, partitionID)

	if leader == nil {
		err := client.RefreshTopicMetadata(topic)
		if err != nil {
			return nil, err
		}
		leader = client.cachedLeader(topic, partitionID)
	}

	if leader == nil {
		return nil, UnknownTopicOrPartition
	}

	return leader, nil
}

// RefreshTopicMetadata takes a list of topics and queries the cluster to refresh the
// available metadata for those topics.
func (client *Client) RefreshTopicMetadata(topics ...string) error {
	return client.refreshMetadata(topics, client.config.MetadataRetries)
}

// RefreshAllMetadata queries the cluster to refresh the available metadata for all topics.
func (client *Client) RefreshAllMetadata() error {
	// Kafka refreshes all when you encode it an empty array...
	return client.refreshMetadata(make([]string, 0), client.config.MetadataRetries)
}

// misc private helper functions

// XXX: see https://github.com/Shopify/sarama/issues/15
//      and https://github.com/Shopify/sarama/issues/23
// disconnectBroker is a bad hacky way to accomplish broker management. It should be replaced with
// something sane and the replacement should be made part of the public Client API
func (client *Client) disconnectBroker(broker *Broker) {
	client.lock.Lock()
	defer client.lock.Unlock()
	Logger.Printf("Disconnecting Broker %d\n", broker.ID())

	client.deadBrokerAddrs = append(client.deadBrokerAddrs, broker.addr)

	if broker == client.extraBroker {
		client.extraBrokerAddrs = client.extraBrokerAddrs[1:]
		if len(client.extraBrokerAddrs) > 0 {
			client.extraBroker = NewBroker(client.extraBrokerAddrs[0])
			client.extraBroker.Open(client.config.DefaultBrokerConf)
		} else {
			client.extraBroker = nil
		}
	} else {
		// we don't need to update the leaders hash, it will automatically get refreshed next time because
		// the broker lookup will return nil
		delete(client.brokers, broker.ID())
	}

	myBroker := broker // NB: block-local prevents clobbering
	go withRecover(func() { myBroker.Close() })
}

func (client *Client) refreshMetadata(topics []string, retries int) error {
	// Kafka will throw exceptions on an empty topic and not return a proper
	// error. This handles the case by returning an error instead of sending it
	// off to Kafka. See: https://github.com/Shopify/sarama/pull/38#issuecomment-26362310
	for _, topic := range topics {
		if len(topic) == 0 {
			return NoSuchTopic
		}
	}

	for broker := client.any(); broker != nil; broker = client.any() {
		Logger.Printf("Fetching metadata from broker %s\n", broker.addr)
		response, err := broker.GetMetadata(client.id, &MetadataRequest{Topics: topics})

		switch err {
		case nil:
			// valid response, use it
			retry, err := client.update(response)
			switch {
			case err != nil:
				return err
			case len(retry) == 0:
				return nil
			default:
				if retries <= 0 {
					return LeaderNotAvailable
				}
				Logger.Printf("Failed to fetch metadata from broker %s, waiting %dms... (%d retries remaining)\n", broker.addr, client.config.WaitForElection/time.Millisecond, retries)
				time.Sleep(client.config.WaitForElection) // wait for leader election
				return client.refreshMetadata(retry, retries-1)
			}
		case EncodingError:
			// didn't even send, return the error
			return err
		}

		// some other error, remove that broker and try again
		Logger.Println("Unexpected error from GetMetadata, closing broker:", err)
		client.disconnectBroker(broker)
	}

	if retries > 0 {
		Logger.Printf("Out of available brokers. Resurrecting dead brokers after %dms... (%d retries remaining)\n", client.config.WaitForElection/time.Millisecond, retries)
		time.Sleep(client.config.WaitForElection)
		client.resurrectDeadBrokers()
		return client.refreshMetadata(topics, retries-1)
	} else {
		Logger.Printf("Out of available brokers.\n")
	}

	return OutOfBrokers
}

func (client *Client) resurrectDeadBrokers() {
	client.lock.Lock()
	defer client.lock.Unlock()

	brokers := make(map[string]struct{})
	for _, addr := range client.deadBrokerAddrs {
		brokers[addr] = struct{}{}
	}
	for _, addr := range client.extraBrokerAddrs {
		brokers[addr] = struct{}{}
	}

	client.deadBrokerAddrs = []string{}
	client.extraBrokerAddrs = []string{}
	for addr := range brokers {
		client.extraBrokerAddrs = append(client.extraBrokerAddrs, addr)
	}

	client.extraBroker = NewBroker(client.extraBrokerAddrs[0])
	client.extraBroker.Open(client.config.DefaultBrokerConf)
}

func (client *Client) any() *Broker {
	client.lock.RLock()
	defer client.lock.RUnlock()

	for _, broker := range client.brokers {
		return broker
	}

	return client.extraBroker
}

func (client *Client) cachedLeader(topic string, partitionID int32) *Broker {
	client.lock.RLock()
	defer client.lock.RUnlock()

	partitions := client.leaders[topic]
	if partitions != nil {
		leader, ok := partitions[partitionID]
		if ok {
			return client.brokers[leader]
		}
	}

	return nil
}

func (client *Client) cachedPartitions(topic string) []int32 {
	client.lock.RLock()
	defer client.lock.RUnlock()

	partitions := client.leaders[topic]
	if partitions == nil {
		return nil
	}

	ret := make([]int32, 0, len(partitions))
	for id := range partitions {
		ret = append(ret, id)
	}

	sort.Sort(int32Slice(ret))
	return ret
}

// if no fatal error, returns a list of topics that need retrying due to LeaderNotAvailable
func (client *Client) update(data *MetadataResponse) ([]string, error) {
	client.lock.Lock()
	defer client.lock.Unlock()

	// For all the brokers we received:
	// - if it is a new ID, save it
	// - if it is an existing ID, but the address we have is stale, discard the old one and save it
	// - otherwise ignore it, replacing our existing one would just bounce the connection
	// We asynchronously try to open connections to the new brokers. We don't care if they
	// fail, since maybe that broker is unreachable but doesn't have a topic we care about.
	// If it fails and we do care, whoever tries to use it will get the connection error.
	for _, broker := range data.Brokers {
		if client.brokers[broker.ID()] == nil {
			broker.Open(client.config.DefaultBrokerConf)
			client.brokers[broker.ID()] = broker
			Logger.Printf("Registered new broker #%d at %s", broker.ID(), broker.Addr())
		} else if broker.Addr() != client.brokers[broker.ID()].Addr() {
			myBroker := client.brokers[broker.ID()] // use block-local to prevent clobbering `broker` for Gs
			go withRecover(func() { myBroker.Close() })
			broker.Open(client.config.DefaultBrokerConf)
			client.brokers[broker.ID()] = broker
			Logger.Printf("Replaced registered broker #%d with %s", broker.ID(), broker.Addr())
		}
	}

	toRetry := make(map[string]bool)

	for _, topic := range data.Topics {
		switch topic.Err {
		case NoError:
			break
		case LeaderNotAvailable:
			toRetry[topic.Name] = true
		default:
			return nil, topic.Err
		}
		client.leaders[topic.Name] = make(map[int32]int32, len(topic.Partitions))
		for _, partition := range topic.Partitions {
			switch partition.Err {
			case LeaderNotAvailable:
				toRetry[topic.Name] = true
				delete(client.leaders[topic.Name], partition.ID)
			case NoError:
				client.leaders[topic.Name][partition.ID] = partition.Leader
			default:
				return nil, partition.Err
			}
		}
	}

	ret := make([]string, 0, len(toRetry))
	for topic := range toRetry {
		ret = append(ret, topic)
	}
	return ret, nil
}

// Creates a new ClientConfig instance with sensible defaults
func NewClientConfig() *ClientConfig {
	return &ClientConfig{
		MetadataRetries: 3,
		WaitForElection: 250 * time.Millisecond,
	}
}

// Validates a ClientConfig instance. This will return a
// ConfigurationError if the specified values don't make sense.
func (config *ClientConfig) Validate() error {
	if config.MetadataRetries <= 0 {
		return ConfigurationError("Invalid MetadataRetries. Try 10")
	}

	if config.WaitForElection <= time.Duration(0) {
		return ConfigurationError("Invalid WaitForElection. Try 250*time.Millisecond")
	}

	if config.DefaultBrokerConf != nil {
		if err := config.DefaultBrokerConf.Validate(); err != nil {
			return err
		}
	}

	return nil
}