sarama/broker.go

package sarama

import (
	"crypto/tls"
	"encoding/binary"
	"fmt"
	"io"
	"net"
	"sort"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	metrics "github.com/rcrowley/go-metrics"
)

// Broker represents a single Kafka broker connection. All operations on this object are entirely concurrency-safe.
type Broker struct {
	conf *Config
	rack *string

	id            int32
	addr          string
	correlationID int32
	conn          net.Conn
	connErr       error
	lock          sync.Mutex
	opened        int32
	responses     chan responsePromise
	done          chan bool

	registeredMetrics []string

	incomingByteRate       metrics.Meter
	requestRate            metrics.Meter
	requestSize            metrics.Histogram
	requestLatency         metrics.Histogram
	outgoingByteRate       metrics.Meter
	responseRate           metrics.Meter
	responseSize           metrics.Histogram
	brokerIncomingByteRate metrics.Meter
	brokerRequestRate      metrics.Meter
	brokerRequestSize      metrics.Histogram
	brokerRequestLatency   metrics.Histogram
	brokerOutgoingByteRate metrics.Meter
	brokerResponseRate     metrics.Meter
	brokerResponseSize     metrics.Histogram
}

// SASLMechanism specifies the SASL mechanism the client uses to authenticate with the broker
type SASLMechanism string

const (
	// SASLTypeOAuth represents the SASL/OAUTHBEARER mechanism (Kafka 2.0.0+)
	SASLTypeOAuth = "OAUTHBEARER"
	// SASLTypePlaintext represents the SASL/PLAIN mechanism
	SASLTypePlaintext = "PLAIN"
	// SASLTypeSCRAMSHA256 represents the SCRAM-SHA-256 mechanism.
	SASLTypeSCRAMSHA256 = "SCRAM-SHA-256"
	// SASLTypeSCRAMSHA512 represents the SCRAM-SHA-512 mechanism.
	SASLTypeSCRAMSHA512 = "SCRAM-SHA-512"
	// SASLHandshakeV0 is v0 of the Kafka SASL handshake protocol. Client and
	// server negotiate SASL auth using opaque packets.
	SASLHandshakeV0 = int16(0)
	// SASLHandshakeV1 is v1 of the Kafka SASL handshake protocol. Client and
	// server negotiate SASL by wrapping tokens with Kafka protocol headers.
	SASLHandshakeV1 = int16(1)
	// SASLExtKeyAuth is the reserved extension key name sent as part of the
	// SASL/OAUTHBEARER intial client response
	SASLExtKeyAuth = "auth"
)

// AccessToken contains an access token used to authenticate a
// SASL/OAUTHBEARER client along with associated metadata.
type AccessToken struct {
	// Token is the access token payload.
	Token string
	// Extensions is a optional map of arbitrary key-value pairs that can be
	// sent with the SASL/OAUTHBEARER initial client response. These values are
	// ignored by the SASL server if they are unexpected. This feature is only
	// supported by Kafka >= 2.1.0.
	Extensions map[string]string
}

// AccessTokenProvider is the interface that encapsulates how implementors
// can generate access tokens for Kafka broker authentication.
type AccessTokenProvider interface {
	// Token returns an access token. The implementation should ensure token
	// reuse so that multiple calls at connect time do not create multiple
	// tokens. The implementation should also periodically refresh the token in
	// order to guarantee that each call returns an unexpired token.  This
	// method should not block indefinitely--a timeout error should be returned
	// after a short period of inactivity so that the broker connection logic
	// can log debugging information and retry.
	Token() (*AccessToken, error)
}

// SCRAMClient is a an interface to a SCRAM
// client implementation.
type SCRAMClient interface {
	// Begin prepares the client for the SCRAM exchange
	// with the server with a user name and a password
	Begin(userName, password, authzID string) error
	// Step steps client through the SCRAM exchange. It is
	// called repeatedly until it errors or `Done` returns true.
	Step(challenge string) (response string, err error)
	// Done should return true when the SCRAM conversation
	// is over.
	Done() bool
}

type responsePromise struct {
	requestTime   time.Time
	correlationID int32
	packets       chan []byte
	errors        chan error
}

// NewBroker creates and returns a Broker targeting the given host:port address.
// This does not attempt to actually connect, you have to call Open() for that.
func NewBroker(addr string) *Broker {
	return &Broker{id: -1, addr: addr}
}

// Open tries to connect to the Broker if it is not already connected or connecting, but does not block
// waiting for the connection to complete. This means that any subsequent operations on the broker will
// block waiting for the connection to succeed or fail. To get the effect of a fully synchronous Open call,
// follow it by a call to Connected(). The only errors Open will return directly are ConfigurationError or
// AlreadyConnected. If conf is nil, the result of NewConfig() is used.
func (b *Broker) Open(conf *Config) error {
	if !atomic.CompareAndSwapInt32(&b.opened, 0, 1) {
		return ErrAlreadyConnected
	}

	if conf == nil {
		conf = NewConfig()
	}

	err := conf.Validate()
	if err != nil {
		return err
	}

	b.lock.Lock()

	go withRecover(func() {
		defer b.lock.Unlock()

		dialer := net.Dialer{
			Timeout:   conf.Net.DialTimeout,
			KeepAlive: conf.Net.KeepAlive,
			LocalAddr: conf.Net.LocalAddr,
		}

		if conf.Net.TLS.Enable {
			b.conn, b.connErr = tls.DialWithDialer(&dialer, "tcp", b.addr, conf.Net.TLS.Config)
		} else if conf.Net.Proxy.Enable {
			b.conn, b.connErr = conf.Net.Proxy.Dialer.Dial("tcp", b.addr)
		} else {
			b.conn, b.connErr = dialer.Dial("tcp", b.addr)
		}
		if b.connErr != nil {
			Logger.Printf("Failed to connect to broker %s: %s\n", b.addr, b.connErr)
			b.conn = nil
			atomic.StoreInt32(&b.opened, 0)
			return
		}
		b.conn = newBufConn(b.conn)

		b.conf = conf

		// Create or reuse the global metrics shared between brokers
		b.incomingByteRate = metrics.GetOrRegisterMeter("incoming-byte-rate", conf.MetricRegistry)
		b.requestRate = metrics.GetOrRegisterMeter("request-rate", conf.MetricRegistry)
		b.requestSize = getOrRegisterHistogram("request-size", conf.MetricRegistry)
		b.requestLatency = getOrRegisterHistogram("request-latency-in-ms", conf.MetricRegistry)
		b.outgoingByteRate = metrics.GetOrRegisterMeter("outgoing-byte-rate", conf.MetricRegistry)
		b.responseRate = metrics.GetOrRegisterMeter("response-rate", conf.MetricRegistry)
		b.responseSize = getOrRegisterHistogram("response-size", conf.MetricRegistry)
		// Do not gather metrics for seeded broker (only used during bootstrap) because they share
		// the same id (-1) and are already exposed through the global metrics above
		if b.id >= 0 {
			b.registerMetrics()
		}

		if conf.Net.SASL.Enable {

			b.connErr = b.authenticateViaSASL()

			if b.connErr != nil {
				err = b.conn.Close()
				if err == nil {
					Logger.Printf("Closed connection to broker %s\n", b.addr)
				} else {
					Logger.Printf("Error while closing connection to broker %s: %s\n", b.addr, err)
				}
				b.conn = nil
				atomic.StoreInt32(&b.opened, 0)
				return
			}
		}

		b.done = make(chan bool)
		b.responses = make(chan responsePromise, b.conf.Net.MaxOpenRequests-1)

		if b.id >= 0 {
			Logger.Printf("Connected to broker at %s (registered as #%d)\n", b.addr, b.id)
		} else {
			Logger.Printf("Connected to broker at %s (unregistered)\n", b.addr)
		}
		go withRecover(b.responseReceiver)
	})

	return nil
}

// Connected returns true if the broker is connected and false otherwise. If the broker is not
// connected but it had tried to connect, the error from that connection attempt is also returned.
func (b *Broker) Connected() (bool, error) {
	b.lock.Lock()
	defer b.lock.Unlock()

	return b.conn != nil, b.connErr
}

//Close closes the broker resources
func (b *Broker) Close() error {
	b.lock.Lock()
	defer b.lock.Unlock()

	if b.conn == nil {
		return ErrNotConnected
	}

	close(b.responses)
	<-b.done

	err := b.conn.Close()

	b.conn = nil
	b.connErr = nil
	b.done = nil
	b.responses = nil

	b.unregisterMetrics()

	if err == nil {
		Logger.Printf("Closed connection to broker %s\n", b.addr)
	} else {
		Logger.Printf("Error while closing connection to broker %s: %s\n", b.addr, err)
	}

	atomic.StoreInt32(&b.opened, 0)

	return err
}

// ID returns the broker ID retrieved from Kafka's metadata, or -1 if that is not known.
func (b *Broker) ID() int32 {
	return b.id
}

// Addr returns the broker address as either retrieved from Kafka's metadata or passed to NewBroker.
func (b *Broker) Addr() string {
	return b.addr
}

// Rack returns the broker's rack as retrieved from Kafka's metadata or the
// empty string if it is not known.  The returned value corresponds to the
// broker's broker.rack configuration setting.  Requires protocol version to be
// at least v0.10.0.0.
func (b *Broker) Rack() string {
	if b.rack == nil {
		return ""
	}
	return *b.rack
}

//GetMetadata send a metadata request and returns a metadata response or error
func (b *Broker) GetMetadata(request *MetadataRequest) (*MetadataResponse, error) {
	response := new(MetadataResponse)

	err := b.sendAndReceive(request, response)

	if err != nil {
		return nil, err
	}

	return response, nil
}

//GetConsumerMetadata send a consumer metadata request and returns a consumer metadata response or error
func (b *Broker) GetConsumerMetadata(request *ConsumerMetadataRequest) (*ConsumerMetadataResponse, error) {
	response := new(ConsumerMetadataResponse)

	err := b.sendAndReceive(request, response)

	if err != nil {
		return nil, err
	}

	return response, nil
}

//FindCoordinator sends a find coordinate request and returns a response or error
func (b *Broker) FindCoordinator(request *FindCoordinatorRequest) (*FindCoordinatorResponse, error) {
	response := new(FindCoordinatorResponse)

	err := b.sendAndReceive(request, response)

	if err != nil {
		return nil, err
	}

	return response, nil
}

//GetAvailableOffsets return an offset response or error
func (b *Broker) GetAvailableOffsets(request *OffsetRequest) (*OffsetResponse, error) {
	response := new(OffsetResponse)

	err := b.sendAndReceive(request, response)

	if err != nil {
		return nil, err
	}

	return response, nil
}

//Produce returns a produce response or error
func (b *Broker) Produce(request *ProduceRequest) (*ProduceResponse, error) {
	var (
		response *ProduceResponse
		err      error
	)

	if request.RequiredAcks == NoResponse {
		err = b.sendAndReceive(request, nil)
	} else {
		response = new(ProduceResponse)
		err = b.sendAndReceive(request, response)
	}

	if err != nil {
		return nil, err
	}

	return response, nil
}

//Fetch returns a FetchResponse or error
func (b *Broker) Fetch(request *FetchRequest) (*FetchResponse, error) {
	response := new(FetchResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//CommitOffset return an Offset commit reponse or error
func (b *Broker) CommitOffset(request *OffsetCommitRequest) (*OffsetCommitResponse, error) {
	response := new(OffsetCommitResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//FetchOffset returns an offset fetch response or error
func (b *Broker) FetchOffset(request *OffsetFetchRequest) (*OffsetFetchResponse, error) {
	response := new(OffsetFetchResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//JoinGroup returns a join group response or error
func (b *Broker) JoinGroup(request *JoinGroupRequest) (*JoinGroupResponse, error) {
	response := new(JoinGroupResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//SyncGroup returns a sync group response or error
func (b *Broker) SyncGroup(request *SyncGroupRequest) (*SyncGroupResponse, error) {
	response := new(SyncGroupResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//LeaveGroup return a leave group response or error
func (b *Broker) LeaveGroup(request *LeaveGroupRequest) (*LeaveGroupResponse, error) {
	response := new(LeaveGroupResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//Heartbeat returns a heartbeat response or error
func (b *Broker) Heartbeat(request *HeartbeatRequest) (*HeartbeatResponse, error) {
	response := new(HeartbeatResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//ListGroups return a list group response or error
func (b *Broker) ListGroups(request *ListGroupsRequest) (*ListGroupsResponse, error) {
	response := new(ListGroupsResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//DescribeGroups return describe group response or error
func (b *Broker) DescribeGroups(request *DescribeGroupsRequest) (*DescribeGroupsResponse, error) {
	response := new(DescribeGroupsResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//ApiVersions return api version response or error
func (b *Broker) ApiVersions(request *ApiVersionsRequest) (*ApiVersionsResponse, error) {
	response := new(ApiVersionsResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//CreateTopics send a create topic request and returns create topic response
func (b *Broker) CreateTopics(request *CreateTopicsRequest) (*CreateTopicsResponse, error) {
	response := new(CreateTopicsResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//DeleteTopics sends a delete topic request and returns delete topic response
func (b *Broker) DeleteTopics(request *DeleteTopicsRequest) (*DeleteTopicsResponse, error) {
	response := new(DeleteTopicsResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//CreatePartitions sends a create partition request and returns create
//partitions response or error
func (b *Broker) CreatePartitions(request *CreatePartitionsRequest) (*CreatePartitionsResponse, error) {
	response := new(CreatePartitionsResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//DeleteRecords send a request to delete records and return delete record
//response or error
func (b *Broker) DeleteRecords(request *DeleteRecordsRequest) (*DeleteRecordsResponse, error) {
	response := new(DeleteRecordsResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//DescribeAcls sends a describe acl request and returns a response or error
func (b *Broker) DescribeAcls(request *DescribeAclsRequest) (*DescribeAclsResponse, error) {
	response := new(DescribeAclsResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//CreateAcls sends a create acl request and returns a response or error
func (b *Broker) CreateAcls(request *CreateAclsRequest) (*CreateAclsResponse, error) {
	response := new(CreateAclsResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//DeleteAcls sends a delete acl request and returns a response or error
func (b *Broker) DeleteAcls(request *DeleteAclsRequest) (*DeleteAclsResponse, error) {
	response := new(DeleteAclsResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//InitProducerID sends an init producer request and returns a response or error
func (b *Broker) InitProducerID(request *InitProducerIDRequest) (*InitProducerIDResponse, error) {
	response := new(InitProducerIDResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//AddPartitionsToTxn send a request to add partition to txn and returns
//a response or error
func (b *Broker) AddPartitionsToTxn(request *AddPartitionsToTxnRequest) (*AddPartitionsToTxnResponse, error) {
	response := new(AddPartitionsToTxnResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//AddOffsetsToTxn sends a request to add offsets to txn and returns a response
//or error
func (b *Broker) AddOffsetsToTxn(request *AddOffsetsToTxnRequest) (*AddOffsetsToTxnResponse, error) {
	response := new(AddOffsetsToTxnResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//EndTxn sends a request to end txn and returns a response or error
func (b *Broker) EndTxn(request *EndTxnRequest) (*EndTxnResponse, error) {
	response := new(EndTxnResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//TxnOffsetCommit sends a request to commit transaction offsets and returns
//a response or error
func (b *Broker) TxnOffsetCommit(request *TxnOffsetCommitRequest) (*TxnOffsetCommitResponse, error) {
	response := new(TxnOffsetCommitResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//DescribeConfigs sends a request to describe config and returns a response or
//error
func (b *Broker) DescribeConfigs(request *DescribeConfigsRequest) (*DescribeConfigsResponse, error) {
	response := new(DescribeConfigsResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//AlterConfigs sends a request to alter config and return a response or error
func (b *Broker) AlterConfigs(request *AlterConfigsRequest) (*AlterConfigsResponse, error) {
	response := new(AlterConfigsResponse)

	err := b.sendAndReceive(request, response)
	if err != nil {
		return nil, err
	}

	return response, nil
}

//DeleteGroups sends a request to delete groups and returns a response or error
func (b *Broker) DeleteGroups(request *DeleteGroupsRequest) (*DeleteGroupsResponse, error) {
	response := new(DeleteGroupsResponse)

	if err := b.sendAndReceive(request, response); err != nil {
		return nil, err
	}

	return response, nil
}

func (b *Broker) send(rb protocolBody, promiseResponse bool) (*responsePromise, error) {
	b.lock.Lock()
	defer b.lock.Unlock()

	if b.conn == nil {
		if b.connErr != nil {
			return nil, b.connErr
		}
		return nil, ErrNotConnected
	}

	if !b.conf.Version.IsAtLeast(rb.requiredVersion()) {
		return nil, ErrUnsupportedVersion
	}

	req := &request{correlationID: b.correlationID, clientID: b.conf.ClientID, body: rb}
	buf, err := encode(req, b.conf.MetricRegistry)
	if err != nil {
		return nil, err
	}

	err = b.conn.SetWriteDeadline(time.Now().Add(b.conf.Net.WriteTimeout))
	if err != nil {
		return nil, err
	}

	requestTime := time.Now()
	bytes, err := b.conn.Write(buf)
	b.updateOutgoingCommunicationMetrics(bytes) //TODO: should it be after error check
	if err != nil {
		return nil, err
	}
	b.correlationID++

	if !promiseResponse {
		// Record request latency without the response
		b.updateRequestLatencyMetrics(time.Since(requestTime))
		return nil, nil
	}

	promise := responsePromise{requestTime, req.correlationID, make(chan []byte), make(chan error)}
	b.responses <- promise

	return &promise, nil
}

func (b *Broker) sendAndReceive(req protocolBody, res versionedDecoder) error {
	promise, err := b.send(req, res != nil)
	if err != nil {
		return err
	}

	if promise == nil {
		return nil
	}

	select {
	case buf := <-promise.packets:
		return versionedDecode(buf, res, req.version())
	case err = <-promise.errors:
		return err
	}
}

func (b *Broker) decode(pd packetDecoder, version int16) (err error) {
	b.id, err = pd.getInt32()
	if err != nil {
		return err
	}

	host, err := pd.getString()
	if err != nil {
		return err
	}

	port, err := pd.getInt32()
	if err != nil {
		return err
	}

	if version >= 1 {
		b.rack, err = pd.getNullableString()
		if err != nil {
			return err
		}
	}

	b.addr = net.JoinHostPort(host, fmt.Sprint(port))
	if _, _, err := net.SplitHostPort(b.addr); err != nil {
		return err
	}

	return nil
}

func (b *Broker) encode(pe packetEncoder, version int16) (err error) {
	host, portstr, err := net.SplitHostPort(b.addr)
	if err != nil {
		return err
	}

	port, err := strconv.Atoi(portstr)
	if err != nil {
		return err
	}

	pe.putInt32(b.id)

	err = pe.putString(host)
	if err != nil {
		return err
	}

	pe.putInt32(int32(port))

	if version >= 1 {
		err = pe.putNullableString(b.rack)
		if err != nil {
			return err
		}
	}

	return nil
}

func (b *Broker) responseReceiver() {
	var dead error
	header := make([]byte, 8)

	for response := range b.responses {
		if dead != nil {
			response.errors <- dead
			continue
		}

		err := b.conn.SetReadDeadline(time.Now().Add(b.conf.Net.ReadTimeout))
		if err != nil {
			dead = err
			response.errors <- err
			continue
		}

		bytesReadHeader, err := io.ReadFull(b.conn, header)
		requestLatency := time.Since(response.requestTime)
		if err != nil {
			b.updateIncomingCommunicationMetrics(bytesReadHeader, requestLatency)
			dead = err
			response.errors <- err
			continue
		}

		decodedHeader := responseHeader{}
		err = decode(header, &decodedHeader)
		if err != nil {
			b.updateIncomingCommunicationMetrics(bytesReadHeader, requestLatency)
			dead = err
			response.errors <- err
			continue
		}
		if decodedHeader.correlationID != response.correlationID {
			b.updateIncomingCommunicationMetrics(bytesReadHeader, requestLatency)
			// TODO if decoded ID < cur ID, discard until we catch up
			// TODO if decoded ID > cur ID, save it so when cur ID catches up we have a response
			dead = PacketDecodingError{fmt.Sprintf("correlation ID didn't match, wanted %d, got %d", response.correlationID, decodedHeader.correlationID)}
			response.errors <- dead
			continue
		}

		buf := make([]byte, decodedHeader.length-4)
		bytesReadBody, err := io.ReadFull(b.conn, buf)
		b.updateIncomingCommunicationMetrics(bytesReadHeader+bytesReadBody, requestLatency)
		if err != nil {
			dead = err
			response.errors <- err
			continue
		}

		response.packets <- buf
	}
	close(b.done)
}

func (b *Broker) authenticateViaSASL() error {
	switch b.conf.Net.SASL.Mechanism {
	case SASLTypeOAuth:
		return b.sendAndReceiveSASLOAuth(b.conf.Net.SASL.TokenProvider)
	case SASLTypeSCRAMSHA256, SASLTypeSCRAMSHA512:
		return b.sendAndReceiveSASLSCRAMv1()
	default:
		return b.sendAndReceiveSASLPlainAuth()
	}
}

func (b *Broker) sendAndReceiveSASLHandshake(saslType SASLMechanism, version int16) error {
	rb := &SaslHandshakeRequest{Mechanism: string(saslType), Version: version}

	req := &request{correlationID: b.correlationID, clientID: b.conf.ClientID, body: rb}
	buf, err := encode(req, b.conf.MetricRegistry)
	if err != nil {
		return err
	}

	err = b.conn.SetWriteDeadline(time.Now().Add(b.conf.Net.WriteTimeout))
	if err != nil {
		return err
	}

	requestTime := time.Now()
	bytes, err := b.conn.Write(buf)
	b.updateOutgoingCommunicationMetrics(bytes)
	if err != nil {
		Logger.Printf("Failed to send SASL handshake %s: %s\n", b.addr, err.Error())
		return err
	}
	b.correlationID++
	//wait for the response
	header := make([]byte, 8) // response header
	_, err = io.ReadFull(b.conn, header)
	if err != nil {
		Logger.Printf("Failed to read SASL handshake header : %s\n", err.Error())
		return err
	}

	length := binary.BigEndian.Uint32(header[:4])
	payload := make([]byte, length-4)
	n, err := io.ReadFull(b.conn, payload)
	if err != nil {
		Logger.Printf("Failed to read SASL handshake payload : %s\n", err.Error())
		return err
	}

	b.updateIncomingCommunicationMetrics(n+8, time.Since(requestTime))
	res := &SaslHandshakeResponse{}

	err = versionedDecode(payload, res, 0)
	if err != nil {
		Logger.Printf("Failed to parse SASL handshake : %s\n", err.Error())
		return err
	}

	if res.Err != ErrNoError {
		Logger.Printf("Invalid SASL Mechanism : %s\n", res.Err.Error())
		return res.Err
	}

	Logger.Print("Successful SASL handshake. Available mechanisms: ", res.EnabledMechanisms)
	return nil
}

// Kafka 0.10.x supported SASL PLAIN/Kerberos via KAFKA-3149 (KIP-43).
// Kafka 1.x.x onward added a SaslAuthenticate request/response message which
// wraps the SASL flow in the Kafka protocol, which allows for returning
// meaningful errors on authentication failure.
//
// In SASL Plain, Kafka expects the auth header to be in the following format
// Message format (from https://tools.ietf.org/html/rfc4616):
//
//   message   = [authzid] UTF8NUL authcid UTF8NUL passwd
//   authcid   = 1*SAFE ; MUST accept up to 255 octets
//   authzid   = 1*SAFE ; MUST accept up to 255 octets
//   passwd    = 1*SAFE ; MUST accept up to 255 octets
//   UTF8NUL   = %x00 ; UTF-8 encoded NUL character
//
//   SAFE      = UTF1 / UTF2 / UTF3 / UTF4
//                  ;; any UTF-8 encoded Unicode character except NUL
//
// With SASL v0 handshake and auth then:
// When credentials are valid, Kafka returns a 4 byte array of null characters.
// When credentials are invalid, Kafka closes the connection.
//
// With SASL v1 handshake and auth then:
// When credentials are invalid, Kafka replies with a SaslAuthenticate response
// containing an error code and message detailing the authentication failure.
func (b *Broker) sendAndReceiveSASLPlainAuth() error {
	// default to V0 to allow for backward compatability when SASL is enabled
	// but not the handshake
	saslHandshake := SASLHandshakeV0
	if b.conf.Net.SASL.Handshake {
		if b.conf.Version.IsAtLeast(V1_0_0_0) {
			saslHandshake = SASLHandshakeV1
		}
		handshakeErr := b.sendAndReceiveSASLHandshake(SASLTypePlaintext, saslHandshake)
		if handshakeErr != nil {
			Logger.Printf("Error while performing SASL handshake %s\n", b.addr)
			return handshakeErr
		}
	}

	if saslHandshake == SASLHandshakeV1 {
		return b.sendAndReceiveV1SASLPlainAuth()
	}
	return b.sendAndReceiveV0SASLPlainAuth()
}

// sendAndReceiveV0SASLPlainAuth flows the v0 sasl auth NOT wrapped in the kafka protocol
func (b *Broker) sendAndReceiveV0SASLPlainAuth() error {

	length := 1 + len(b.conf.Net.SASL.User) + 1 + len(b.conf.Net.SASL.Password)
	authBytes := make([]byte, length+4) //4 byte length header + auth data
	binary.BigEndian.PutUint32(authBytes, uint32(length))
	copy(authBytes[4:], []byte("\x00"+b.conf.Net.SASL.User+"\x00"+b.conf.Net.SASL.Password))

	err := b.conn.SetWriteDeadline(time.Now().Add(b.conf.Net.WriteTimeout))
	if err != nil {
		Logger.Printf("Failed to set write deadline when doing SASL auth with broker %s: %s\n", b.addr, err.Error())
		return err
	}

	requestTime := time.Now()
	bytesWritten, err := b.conn.Write(authBytes)
	b.updateOutgoingCommunicationMetrics(bytesWritten)
	if err != nil {
		Logger.Printf("Failed to write SASL auth header to broker %s: %s\n", b.addr, err.Error())
		return err
	}

	header := make([]byte, 4)
	n, err := io.ReadFull(b.conn, header)
	b.updateIncomingCommunicationMetrics(n, time.Since(requestTime))
	// If the credentials are valid, we would get a 4 byte response filled with null characters.
	// Otherwise, the broker closes the connection and we get an EOF
	if err != nil {
		Logger.Printf("Failed to read response while authenticating with SASL to broker %s: %s\n", b.addr, err.Error())
		return err
	}

	Logger.Printf("SASL authentication successful with broker %s:%v - %v\n", b.addr, n, header)
	return nil
}

// sendAndReceiveV1SASLPlainAuth flows the v1 sasl authentication using the kafka protocol
func (b *Broker) sendAndReceiveV1SASLPlainAuth() error {
	correlationID := b.correlationID

	requestTime := time.Now()

	bytesWritten, err := b.sendSASLPlainAuthClientResponse(correlationID)

	b.updateOutgoingCommunicationMetrics(bytesWritten)

	if err != nil {
		Logger.Printf("Failed to write SASL auth header to broker %s: %s\n", b.addr, err.Error())
		return err
	}

	b.correlationID++

	bytesRead, err := b.receiveSASLServerResponse(correlationID)
	b.updateIncomingCommunicationMetrics(bytesRead, time.Since(requestTime))

	// With v1 sasl we get an error message set in the response we can return
	if err != nil {
		Logger.Printf("Error returned from broker during SASL flow %s: %s\n", b.addr, err.Error())
		return err
	}

	return nil
}

// sendAndReceiveSASLOAuth performs the authentication flow as described by KIP-255
// https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=75968876
func (b *Broker) sendAndReceiveSASLOAuth(provider AccessTokenProvider) error {
	if err := b.sendAndReceiveSASLHandshake(SASLTypeOAuth, SASLHandshakeV1); err != nil {
		return err
	}

	token, err := provider.Token()
	if err != nil {
		return err
	}

	requestTime := time.Now()
	correlationID := b.correlationID

	bytesWritten, err := b.sendSASLOAuthBearerClientResponse(token, correlationID)
	if err != nil {
		return err
	}

	b.updateOutgoingCommunicationMetrics(bytesWritten)
	b.correlationID++

	bytesRead, err := b.receiveSASLServerResponse(correlationID)
	if err != nil {
		return err
	}

	requestLatency := time.Since(requestTime)
	b.updateIncomingCommunicationMetrics(bytesRead, requestLatency)

	return nil
}

func (b *Broker) sendAndReceiveSASLSCRAMv1() error {
	if err := b.sendAndReceiveSASLHandshake(b.conf.Net.SASL.Mechanism, SASLHandshakeV1); err != nil {
		return err
	}

	scramClient := b.conf.Net.SASL.SCRAMClientGeneratorFunc()
	if err := scramClient.Begin(b.conf.Net.SASL.User, b.conf.Net.SASL.Password, b.conf.Net.SASL.SCRAMAuthzID); err != nil {
		return fmt.Errorf("failed to start SCRAM exchange with the server: %s", err.Error())
	}

	msg, err := scramClient.Step("")
	if err != nil {
		return fmt.Errorf("failed to advance the SCRAM exchange: %s", err.Error())

	}

	for !scramClient.Done() {
		requestTime := time.Now()
		correlationID := b.correlationID
		bytesWritten, err := b.sendSaslAuthenticateRequest(correlationID, []byte(msg))
		if err != nil {
			Logger.Printf("Failed to write SASL auth header to broker %s: %s\n", b.addr, err.Error())
			return err
		}

		b.updateOutgoingCommunicationMetrics(bytesWritten)
		b.correlationID++
		challenge, err := b.receiveSaslAuthenticateResponse(correlationID)
		if err != nil {
			Logger.Printf("Failed to read response while authenticating with SASL to broker %s: %s\n", b.addr, err.Error())
			return err
		}

		b.updateIncomingCommunicationMetrics(len(challenge), time.Since(requestTime))
		msg, err = scramClient.Step(string(challenge))
		if err != nil {
			Logger.Println("SASL authentication failed", err)
			return err
		}
	}

	Logger.Println("SASL authentication succeeded")
	return nil
}

func (b *Broker) sendSaslAuthenticateRequest(correlationID int32, msg []byte) (int, error) {
	rb := &SaslAuthenticateRequest{msg}
	req := &request{correlationID: correlationID, clientID: b.conf.ClientID, body: rb}
	buf, err := encode(req, b.conf.MetricRegistry)
	if err != nil {
		return 0, err
	}

	if err := b.conn.SetWriteDeadline(time.Now().Add(b.conf.Net.WriteTimeout)); err != nil {
		return 0, err
	}

	return b.conn.Write(buf)
}

func (b *Broker) receiveSaslAuthenticateResponse(correlationID int32) ([]byte, error) {
	buf := make([]byte, responseLengthSize+correlationIDSize)
	_, err := io.ReadFull(b.conn, buf)
	if err != nil {
		return nil, err
	}

	header := responseHeader{}
	err = decode(buf, &header)
	if err != nil {
		return nil, err
	}

	if header.correlationID != correlationID {
		return nil, fmt.Errorf("correlation ID didn't match, wanted %d, got %d", b.correlationID, header.correlationID)
	}

	buf = make([]byte, header.length-correlationIDSize)
	_, err = io.ReadFull(b.conn, buf)
	if err != nil {
		return nil, err
	}

	res := &SaslAuthenticateResponse{}
	if err := versionedDecode(buf, res, 0); err != nil {
		return nil, err
	}
	if res.Err != ErrNoError {
		return nil, res.Err
	}
	return res.SaslAuthBytes, nil
}

// Build SASL/OAUTHBEARER initial client response as described by RFC-7628
// https://tools.ietf.org/html/rfc7628
func buildClientInitialResponse(token *AccessToken) ([]byte, error) {
	var ext string

	if token.Extensions != nil && len(token.Extensions) > 0 {
		if _, ok := token.Extensions[SASLExtKeyAuth]; ok {
			return []byte{}, fmt.Errorf("the extension `%s` is invalid", SASLExtKeyAuth)
		}
		ext = "\x01" + mapToString(token.Extensions, "=", "\x01")
	}

	resp := []byte(fmt.Sprintf("n,,\x01auth=Bearer %s%s\x01\x01", token.Token, ext))

	return resp, nil
}

// mapToString returns a list of key-value pairs ordered by key.
// keyValSep separates the key from the value. elemSep separates each pair.
func mapToString(extensions map[string]string, keyValSep string, elemSep string) string {
	buf := make([]string, 0, len(extensions))

	for k, v := range extensions {
		buf = append(buf, k+keyValSep+v)
	}

	sort.Strings(buf)

	return strings.Join(buf, elemSep)
}

func (b *Broker) sendSASLPlainAuthClientResponse(correlationID int32) (int, error) {
	authBytes := []byte("\x00" + b.conf.Net.SASL.User + "\x00" + b.conf.Net.SASL.Password)
	rb := &SaslAuthenticateRequest{authBytes}
	req := &request{correlationID: correlationID, clientID: b.conf.ClientID, body: rb}
	buf, err := encode(req, b.conf.MetricRegistry)
	if err != nil {
		return 0, err
	}

	err = b.conn.SetWriteDeadline(time.Now().Add(b.conf.Net.WriteTimeout))
	if err != nil {
		Logger.Printf("Failed to set write deadline when doing SASL auth with broker %s: %s\n", b.addr, err.Error())
		return 0, err
	}
	return b.conn.Write(buf)
}

func (b *Broker) sendSASLOAuthBearerClientResponse(token *AccessToken, correlationID int32) (int, error) {
	initialResp, err := buildClientInitialResponse(token)
	if err != nil {
		return 0, err
	}

	rb := &SaslAuthenticateRequest{initialResp}

	req := &request{correlationID: correlationID, clientID: b.conf.ClientID, body: rb}

	buf, err := encode(req, b.conf.MetricRegistry)
	if err != nil {
		return 0, err
	}

	if err := b.conn.SetWriteDeadline(time.Now().Add(b.conf.Net.WriteTimeout)); err != nil {
		return 0, err
	}

	return b.conn.Write(buf)
}

func (b *Broker) receiveSASLServerResponse(correlationID int32) (int, error) {

	buf := make([]byte, responseLengthSize+correlationIDSize)

	bytesRead, err := io.ReadFull(b.conn, buf)
	if err != nil {
		return bytesRead, err
	}

	header := responseHeader{}

	err = decode(buf, &header)
	if err != nil {
		return bytesRead, err
	}

	if header.correlationID != correlationID {
		return bytesRead, fmt.Errorf("correlation ID didn't match, wanted %d, got %d", b.correlationID, header.correlationID)
	}

	buf = make([]byte, header.length-correlationIDSize)

	c, err := io.ReadFull(b.conn, buf)
	bytesRead += c
	if err != nil {
		return bytesRead, err
	}

	res := &SaslAuthenticateResponse{}

	if err := versionedDecode(buf, res, 0); err != nil {
		return bytesRead, err
	}

	if res.Err != ErrNoError {
		return bytesRead, res.Err
	}

	if len(res.SaslAuthBytes) > 0 {
		Logger.Printf("Received SASL auth response: %s", res.SaslAuthBytes)
	}

	return bytesRead, nil
}

func (b *Broker) updateIncomingCommunicationMetrics(bytes int, requestLatency time.Duration) {
	b.updateRequestLatencyMetrics(requestLatency)
	b.responseRate.Mark(1)

	if b.brokerResponseRate != nil {
		b.brokerResponseRate.Mark(1)
	}

	responseSize := int64(bytes)
	b.incomingByteRate.Mark(responseSize)
	if b.brokerIncomingByteRate != nil {
		b.brokerIncomingByteRate.Mark(responseSize)
	}

	b.responseSize.Update(responseSize)
	if b.brokerResponseSize != nil {
		b.brokerResponseSize.Update(responseSize)
	}
}

func (b *Broker) updateRequestLatencyMetrics(requestLatency time.Duration) {
	requestLatencyInMs := int64(requestLatency / time.Millisecond)
	b.requestLatency.Update(requestLatencyInMs)

	if b.brokerRequestLatency != nil {
		b.brokerRequestLatency.Update(requestLatencyInMs)
	}

}

func (b *Broker) updateOutgoingCommunicationMetrics(bytes int) {
	b.requestRate.Mark(1)
	if b.brokerRequestRate != nil {
		b.brokerRequestRate.Mark(1)
	}

	requestSize := int64(bytes)
	b.outgoingByteRate.Mark(requestSize)
	if b.brokerOutgoingByteRate != nil {
		b.brokerOutgoingByteRate.Mark(requestSize)
	}

	b.requestSize.Update(requestSize)
	if b.brokerRequestSize != nil {
		b.brokerRequestSize.Update(requestSize)
	}

}

func (b *Broker) registerMetrics() {
	b.brokerIncomingByteRate = b.registerMeter("incoming-byte-rate")
	b.brokerRequestRate = b.registerMeter("request-rate")
	b.brokerRequestSize = b.registerHistogram("request-size")
	b.brokerRequestLatency = b.registerHistogram("request-latency-in-ms")
	b.brokerOutgoingByteRate = b.registerMeter("outgoing-byte-rate")
	b.brokerResponseRate = b.registerMeter("response-rate")
	b.brokerResponseSize = b.registerHistogram("response-size")
}

func (b *Broker) unregisterMetrics() {
	for _, name := range b.registeredMetrics {
		b.conf.MetricRegistry.Unregister(name)
	}
}

func (b *Broker) registerMeter(name string) metrics.Meter {
	nameForBroker := getMetricNameForBroker(name, b)
	b.registeredMetrics = append(b.registeredMetrics, nameForBroker)
	return metrics.GetOrRegisterMeter(nameForBroker, b.conf.MetricRegistry)
}

func (b *Broker) registerHistogram(name string) metrics.Histogram {
	nameForBroker := getMetricNameForBroker(name, b)
	b.registeredMetrics = append(b.registeredMetrics, nameForBroker)
	return getOrRegisterHistogram(nameForBroker, b.conf.MetricRegistry)
}