pkg/db/kvstore/etcdclient.go - voltha-lib-go - Gitiles

 /*
  * Copyright 2018-present Open Networking Foundation

  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at

  * http://www.apache.org/licenses/LICENSE-2.0

  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 package kvstore

 import (
 	"context"
 	"errors"
 	"fmt"
 	"sync"

 	"github.com/opencord/voltha-lib-go/v3/pkg/log"
 	v3Client "go.etcd.io/etcd/clientv3"
 	v3Concurrency "go.etcd.io/etcd/clientv3/concurrency"
 	v3rpcTypes "go.etcd.io/etcd/etcdserver/api/v3rpc/rpctypes"
 )

 // EtcdClient represents the Etcd KV store client
 type EtcdClient struct {
 	ectdAPI             *v3Client.Client
 	keyReservations     map[string]*v3Client.LeaseID
 	watchedChannels     sync.Map
 	keyReservationsLock sync.RWMutex
 	lockToMutexMap      map[string]*v3Concurrency.Mutex
 	lockToSessionMap    map[string]*v3Concurrency.Session
 	lockToMutexLock     sync.Mutex
 }

 // NewEtcdClient returns a new client for the Etcd KV store
 func NewEtcdClient(addr string, timeout int, level log.LogLevel) (*EtcdClient, error) {
 	duration := GetDuration(timeout)
 	logconfig := log.ConstructZapConfig(log.JSON, level, log.Fields{})

 	c, err := v3Client.New(v3Client.Config{
 		Endpoints:   []string{addr},
 		DialTimeout: duration,
 		LogConfig:   &logconfig,
 	})
 	if err != nil {
 		logger.Error(err)
 		return nil, err
 	}

 	reservations := make(map[string]*v3Client.LeaseID)
 	lockMutexMap := make(map[string]*v3Concurrency.Mutex)
 	lockSessionMap := make(map[string]*v3Concurrency.Session)

 	return &EtcdClient{ectdAPI: c, keyReservations: reservations, lockToMutexMap: lockMutexMap,
 		lockToSessionMap: lockSessionMap}, nil
 }

 // IsConnectionUp returns whether the connection to the Etcd KV store is up.  If a timeout occurs then
 // it is assumed the connection is down or unreachable.
 func (c *EtcdClient) IsConnectionUp(ctx context.Context) bool {
 	// Let's try to get a non existent key.  If the connection is up then there will be no error returned.
 	if _, err := c.Get(ctx, "non-existent-key"); err != nil {
 		return false
 	}
 	//cancel()
 	return true
 }

 // List returns an array of key-value pairs with key as a prefix.  Timeout defines how long the function will
 // wait for a response
 func (c *EtcdClient) List(ctx context.Context, key string) (map[string]*KVPair, error) {
 	resp, err := c.ectdAPI.Get(ctx, key, v3Client.WithPrefix())
 	if err != nil {
 		logger.Error(err)
 		return nil, err
 	}
 	m := make(map[string]*KVPair)
 	for _, ev := range resp.Kvs {
 		m[string(ev.Key)] = NewKVPair(string(ev.Key), ev.Value, "", ev.Lease, ev.Version)
 	}
 	return m, nil
 }

 // Get returns a key-value pair for a given key. Timeout defines how long the function will
 // wait for a response
 func (c *EtcdClient) Get(ctx context.Context, key string) (*KVPair, error) {

 	resp, err := c.ectdAPI.Get(ctx, key)

 	if err != nil {
 		logger.Error(err)
 		return nil, err
 	}
 	for _, ev := range resp.Kvs {
 		// Only one value is returned
 		return NewKVPair(string(ev.Key), ev.Value, "", ev.Lease, ev.Version), nil
 	}
 	return nil, nil
 }

 // Put writes a key-value pair to the KV store.  Value can only be a string or []byte since the etcd API
 // accepts only a string as a value for a put operation. Timeout defines how long the function will
 // wait for a response
 func (c *EtcdClient) Put(ctx context.Context, key string, value interface{}) error {

 	// Validate that we can convert value to a string as etcd API expects a string
 	var val string
 	var er error
 	if val, er = ToString(value); er != nil {
 		return fmt.Errorf("unexpected-type-%T", value)
 	}

 	var err error
 	// Check if there is already a lease for this key - if there is then use it, otherwise a PUT will make
 	// that KV key permanent instead of automatically removing it after a lease expiration
 	c.keyReservationsLock.RLock()
 	leaseID, ok := c.keyReservations[key]
 	c.keyReservationsLock.RUnlock()
 	if ok {
 		_, err = c.ectdAPI.Put(ctx, key, val, v3Client.WithLease(*leaseID))
 	} else {
 		_, err = c.ectdAPI.Put(ctx, key, val)
 	}

 	if err != nil {
 		switch err {
 		case context.Canceled:
 			logger.Warnw("context-cancelled", log.Fields{"error": err})
 		case context.DeadlineExceeded:
 			logger.Warnw("context-deadline-exceeded", log.Fields{"error": err})
 		case v3rpcTypes.ErrEmptyKey:
 			logger.Warnw("etcd-client-error", log.Fields{"error": err})
 		default:
 			logger.Warnw("bad-endpoints", log.Fields{"error": err})
 		}
 		return err
 	}
 	return nil
 }

 // Delete removes a key from the KV store. Timeout defines how long the function will
 // wait for a response
 func (c *EtcdClient) Delete(ctx context.Context, key string) error {

 	// delete the key
 	if _, err := c.ectdAPI.Delete(ctx, key); err != nil {
 		logger.Errorw("failed-to-delete-key", log.Fields{"key": key, "error": err})
 		return err
 	}
 	logger.Debugw("key(s)-deleted", log.Fields{"key": key})
 	return nil
 }

 // Reserve is invoked to acquire a key and set it to a given value. Value can only be a string or []byte since
 // the etcd API accepts only a string.  Timeout defines how long the function will wait for a response.  TTL
 // defines how long that reservation is valid.  When TTL expires the key is unreserved by the KV store itself.
 // If the key is acquired then the value returned will be the value passed in.  If the key is already acquired
 // then the value assigned to that key will be returned.
 func (c *EtcdClient) Reserve(ctx context.Context, key string, value interface{}, ttl int64) (interface{}, error) {
 	// Validate that we can convert value to a string as etcd API expects a string
 	var val string
 	var er error
 	if val, er = ToString(value); er != nil {
 		return nil, fmt.Errorf("unexpected-type%T", value)
 	}

 	resp, err := c.ectdAPI.Grant(ctx, ttl)
 	if err != nil {
 		logger.Error(err)
 		return nil, err
 	}
 	// Register the lease id
 	c.keyReservationsLock.Lock()
 	c.keyReservations[key] = &resp.ID
 	c.keyReservationsLock.Unlock()

 	// Revoke lease if reservation is not successful
 	reservationSuccessful := false
 	defer func() {
 		if !reservationSuccessful {
 			if err = c.ReleaseReservation(context.Background(), key); err != nil {
 				logger.Error("cannot-release-lease")
 			}
 		}
 	}()

 	// Try to grap the Key with the above lease
 	c.ectdAPI.Txn(context.Background())
 	txn := c.ectdAPI.Txn(context.Background())
 	txn = txn.If(v3Client.Compare(v3Client.Version(key), "=", 0))
 	txn = txn.Then(v3Client.OpPut(key, val, v3Client.WithLease(resp.ID)))
 	txn = txn.Else(v3Client.OpGet(key))
 	result, er := txn.Commit()
 	if er != nil {
 		return nil, er
 	}

 	if !result.Succeeded {
 		// Verify whether we are already the owner of that Key
 		if len(result.Responses) > 0 &&
 			len(result.Responses[0].GetResponseRange().Kvs) > 0 {
 			kv := result.Responses[0].GetResponseRange().Kvs[0]
 			if string(kv.Value) == val {
 				reservationSuccessful = true
 				return value, nil
 			}
 			return kv.Value, nil
 		}
 	} else {
 		// Read the Key to ensure this is our Key
 		m, err := c.Get(ctx, key)
 		if err != nil {
 			return nil, err
 		}
 		if m != nil {
 			if m.Key == key && isEqual(m.Value, value) {
 				// My reservation is successful - register it.  For now, support is only for 1 reservation per key
 				// per session.
 				reservationSuccessful = true
 				return value, nil
 			}
 			// My reservation has failed.  Return the owner of that key
 			return m.Value, nil
 		}
 	}
 	return nil, nil
 }

 // ReleaseAllReservations releases all key reservations previously made (using Reserve API)
 func (c *EtcdClient) ReleaseAllReservations(ctx context.Context) error {
 	c.keyReservationsLock.Lock()
 	defer c.keyReservationsLock.Unlock()

 	for key, leaseID := range c.keyReservations {
 		_, err := c.ectdAPI.Revoke(ctx, *leaseID)
 		if err != nil {
 			logger.Errorw("cannot-release-reservation", log.Fields{"key": key, "error": err})
 			return err
 		}
 		delete(c.keyReservations, key)
 	}
 	return nil
 }

 // ReleaseReservation releases reservation for a specific key.
 func (c *EtcdClient) ReleaseReservation(ctx context.Context, key string) error {
 	// Get the leaseid using the key
 	logger.Debugw("Release-reservation", log.Fields{"key": key})
 	var ok bool
 	var leaseID *v3Client.LeaseID
 	c.keyReservationsLock.Lock()
 	defer c.keyReservationsLock.Unlock()
 	if leaseID, ok = c.keyReservations[key]; !ok {
 		return nil
 	}

 	if leaseID != nil {
 		_, err := c.ectdAPI.Revoke(ctx, *leaseID)
 		if err != nil {
 			logger.Error(err)
 			return err
 		}
 		delete(c.keyReservations, key)
 	}
 	return nil
 }

 // RenewReservation renews a reservation.  A reservation will go stale after the specified TTL (Time To Live)
 // period specified when reserving the key
 func (c *EtcdClient) RenewReservation(ctx context.Context, key string) error {
 	// Get the leaseid using the key
 	var ok bool
 	var leaseID *v3Client.LeaseID
 	c.keyReservationsLock.RLock()
 	leaseID, ok = c.keyReservations[key]
 	c.keyReservationsLock.RUnlock()

 	if !ok {
 		return errors.New("key-not-reserved")
 	}

 	if leaseID != nil {
 		_, err := c.ectdAPI.KeepAliveOnce(ctx, *leaseID)
 		if err != nil {
 			logger.Errorw("lease-may-have-expired", log.Fields{"error": err})
 			return err
 		}
 	} else {
 		return errors.New("lease-expired")
 	}
 	return nil
 }

 // Watch provides the watch capability on a given key.  It returns a channel onto which the callee needs to
 // listen to receive Events.
 func (c *EtcdClient) Watch(ctx context.Context, key string, withPrefix bool) chan *Event {
 	w := v3Client.NewWatcher(c.ectdAPI)
 	ctx, cancel := context.WithCancel(ctx)
 	var channel v3Client.WatchChan
 	if withPrefix {
 		channel = w.Watch(ctx, key, v3Client.WithPrefix())
 	} else {
 		channel = w.Watch(ctx, key)
 	}

 	// Create a new channel
 	ch := make(chan *Event, maxClientChannelBufferSize)

 	// Keep track of the created channels so they can be closed when required
 	channelMap := make(map[chan *Event]v3Client.Watcher)
 	channelMap[ch] = w

 	channelMaps := c.addChannelMap(key, channelMap)

 	// Changing the log field (from channelMaps) as the underlying logger cannot format the map of channels into a
 	// json format.
 	logger.Debugw("watched-channels", log.Fields{"len": len(channelMaps)})
 	// Launch a go routine to listen for updates
 	go c.listenForKeyChange(channel, ch, cancel)

 	return ch

 }

 func (c *EtcdClient) addChannelMap(key string, channelMap map[chan *Event]v3Client.Watcher) []map[chan *Event]v3Client.Watcher {
 	var channels interface{}
 	var exists bool

 	if channels, exists = c.watchedChannels.Load(key); exists {
 		channels = append(channels.([]map[chan *Event]v3Client.Watcher), channelMap)
 	} else {
 		channels = []map[chan *Event]v3Client.Watcher{channelMap}
 	}
 	c.watchedChannels.Store(key, channels)

 	return channels.([]map[chan *Event]v3Client.Watcher)
 }

 func (c *EtcdClient) removeChannelMap(key string, pos int) []map[chan *Event]v3Client.Watcher {
 	var channels interface{}
 	var exists bool

 	if channels, exists = c.watchedChannels.Load(key); exists {
 		channels = append(channels.([]map[chan *Event]v3Client.Watcher)[:pos], channels.([]map[chan *Event]v3Client.Watcher)[pos+1:]...)
 		c.watchedChannels.Store(key, channels)
 	}

 	return channels.([]map[chan *Event]v3Client.Watcher)
 }

 func (c *EtcdClient) getChannelMaps(key string) ([]map[chan *Event]v3Client.Watcher, bool) {
 	var channels interface{}
 	var exists bool

 	channels, exists = c.watchedChannels.Load(key)

 	if channels == nil {
 		return nil, exists
 	}

 	return channels.([]map[chan *Event]v3Client.Watcher), exists
 }

 // CloseWatch closes a specific watch. Both the key and the channel are required when closing a watch as there
 // may be multiple listeners on the same key.  The previously created channel serves as a key
 func (c *EtcdClient) CloseWatch(key string, ch chan *Event) {
 	// Get the array of channels mapping
 	var watchedChannels []map[chan *Event]v3Client.Watcher
 	var ok bool

 	if watchedChannels, ok = c.getChannelMaps(key); !ok {
 		logger.Warnw("key-has-no-watched-channels", log.Fields{"key": key})
 		return
 	}
 	// Look for the channels
 	var pos = -1
 	for i, chMap := range watchedChannels {
 		if t, ok := chMap[ch]; ok {
 			logger.Debug("channel-found")
 			// Close the etcd watcher before the client channel.  This should close the etcd channel as well
 			if err := t.Close(); err != nil {
 				logger.Errorw("watcher-cannot-be-closed", log.Fields{"key": key, "error": err})
 			}
 			pos = i
 			break
 		}
 	}

 	channelMaps, _ := c.getChannelMaps(key)
 	// Remove that entry if present
 	if pos >= 0 {
 		channelMaps = c.removeChannelMap(key, pos)
 	}
 	logger.Infow("watcher-channel-exiting", log.Fields{"key": key, "channel": channelMaps})
 }

 func (c *EtcdClient) listenForKeyChange(channel v3Client.WatchChan, ch chan<- *Event, cancel context.CancelFunc) {
 	logger.Debug("start-listening-on-channel ...")
 	defer cancel()
 	defer close(ch)
 	for resp := range channel {
 		for _, ev := range resp.Events {
 			ch <- NewEvent(getEventType(ev), ev.Kv.Key, ev.Kv.Value, ev.Kv.Version)
 		}
 	}
 	logger.Debug("stop-listening-on-channel ...")
 }

 func getEventType(event *v3Client.Event) int {
 	switch event.Type {
 	case v3Client.EventTypePut:
 		return PUT
 	case v3Client.EventTypeDelete:
 		return DELETE
 	}
 	return UNKNOWN
 }

 // Close closes the KV store client
 func (c *EtcdClient) Close() {
 	if err := c.ectdAPI.Close(); err != nil {
 		logger.Errorw("error-closing-client", log.Fields{"error": err})
 	}
 }

 func (c *EtcdClient) addLockName(lockName string, lock *v3Concurrency.Mutex, session *v3Concurrency.Session) {
 	c.lockToMutexLock.Lock()
 	defer c.lockToMutexLock.Unlock()
 	c.lockToMutexMap[lockName] = lock
 	c.lockToSessionMap[lockName] = session
 }

 func (c *EtcdClient) deleteLockName(lockName string) {
 	c.lockToMutexLock.Lock()
 	defer c.lockToMutexLock.Unlock()
 	delete(c.lockToMutexMap, lockName)
 	delete(c.lockToSessionMap, lockName)
 }

 func (c *EtcdClient) getLock(lockName string) (*v3Concurrency.Mutex, *v3Concurrency.Session) {
 	c.lockToMutexLock.Lock()
 	defer c.lockToMutexLock.Unlock()
 	var lock *v3Concurrency.Mutex
 	var session *v3Concurrency.Session
 	if l, exist := c.lockToMutexMap[lockName]; exist {
 		lock = l
 	}
 	if s, exist := c.lockToSessionMap[lockName]; exist {
 		session = s
 	}
 	return lock, session
 }

 func (c *EtcdClient) AcquireLock(ctx context.Context, lockName string, timeout int) error {
 	session, _ := v3Concurrency.NewSession(c.ectdAPI, v3Concurrency.WithContext(ctx))
 	mu := v3Concurrency.NewMutex(session, "/devicelock_"+lockName)
 	if err := mu.Lock(context.Background()); err != nil {
 		//cancel()
 		return err
 	}
 	c.addLockName(lockName, mu, session)
 	return nil
 }

 func (c *EtcdClient) ReleaseLock(lockName string) error {
 	lock, session := c.getLock(lockName)
 	var err error
 	if lock != nil {
 		if e := lock.Unlock(context.Background()); e != nil {
 			err = e
 		}
 	}
 	if session != nil {
 		if e := session.Close(); e != nil {
 			err = e
 		}
 	}
 	c.deleteLockName(lockName)

 	return err
 }
	/*
	* Copyright 2018-present Open Networking Foundation

	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at

	* http://www.apache.org/licenses/LICENSE-2.0

	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	package kvstore

	import (
	"context"
	"errors"
	"fmt"
	"sync"

	"github.com/opencord/voltha-lib-go/v3/pkg/log"
	v3Client "go.etcd.io/etcd/clientv3"
	v3Concurrency "go.etcd.io/etcd/clientv3/concurrency"
	v3rpcTypes "go.etcd.io/etcd/etcdserver/api/v3rpc/rpctypes"
	)

	// EtcdClient represents the Etcd KV store client
	type EtcdClient struct {
	ectdAPI *v3Client.Client
	keyReservations map[string]*v3Client.LeaseID
	watchedChannels sync.Map
	keyReservationsLock sync.RWMutex
	lockToMutexMap map[string]*v3Concurrency.Mutex
	lockToSessionMap map[string]*v3Concurrency.Session
	lockToMutexLock sync.Mutex
	}

	// NewEtcdClient returns a new client for the Etcd KV store
	func NewEtcdClient(addr string, timeout int, level log.LogLevel) (*EtcdClient, error) {
	duration := GetDuration(timeout)
	logconfig := log.ConstructZapConfig(log.JSON, level, log.Fields{})

	c, err := v3Client.New(v3Client.Config{
	Endpoints: []string{addr},
	DialTimeout: duration,
	LogConfig: &logconfig,
	})
	if err != nil {
	logger.Error(err)
	return nil, err
	}

	reservations := make(map[string]*v3Client.LeaseID)
	lockMutexMap := make(map[string]*v3Concurrency.Mutex)
	lockSessionMap := make(map[string]*v3Concurrency.Session)

	return &EtcdClient{ectdAPI: c, keyReservations: reservations, lockToMutexMap: lockMutexMap,
	lockToSessionMap: lockSessionMap}, nil
	}

	// IsConnectionUp returns whether the connection to the Etcd KV store is up. If a timeout occurs then
	// it is assumed the connection is down or unreachable.
	func (c *EtcdClient) IsConnectionUp(ctx context.Context) bool {
	// Let's try to get a non existent key. If the connection is up then there will be no error returned.
	if _, err := c.Get(ctx, "non-existent-key"); err != nil {
	return false
	}
	//cancel()
	return true
	}

	// List returns an array of key-value pairs with key as a prefix. Timeout defines how long the function will
	// wait for a response
	func (c EtcdClient) List(ctx context.Context, key string) (map[string]KVPair, error) {
	resp, err := c.ectdAPI.Get(ctx, key, v3Client.WithPrefix())
	if err != nil {
	logger.Error(err)
	return nil, err
	}
	m := make(map[string]*KVPair)
	for _, ev := range resp.Kvs {
	m[string(ev.Key)] = NewKVPair(string(ev.Key), ev.Value, "", ev.Lease, ev.Version)
	}
	return m, nil
	}

	// Get returns a key-value pair for a given key. Timeout defines how long the function will
	// wait for a response
	func (c EtcdClient) Get(ctx context.Context, key string) (KVPair, error) {

	resp, err := c.ectdAPI.Get(ctx, key)

	if err != nil {
	logger.Error(err)
	return nil, err
	}
	for _, ev := range resp.Kvs {
	// Only one value is returned
	return NewKVPair(string(ev.Key), ev.Value, "", ev.Lease, ev.Version), nil
	}
	return nil, nil
	}

	// Put writes a key-value pair to the KV store. Value can only be a string or []byte since the etcd API
	// accepts only a string as a value for a put operation. Timeout defines how long the function will
	// wait for a response
	func (c *EtcdClient) Put(ctx context.Context, key string, value interface{}) error {

	// Validate that we can convert value to a string as etcd API expects a string
	var val string
	var er error
	if val, er = ToString(value); er != nil {
	return fmt.Errorf("unexpected-type-%T", value)
	}

	var err error
	// Check if there is already a lease for this key - if there is then use it, otherwise a PUT will make
	// that KV key permanent instead of automatically removing it after a lease expiration
	c.keyReservationsLock.RLock()
	leaseID, ok := c.keyReservations[key]
	c.keyReservationsLock.RUnlock()
	if ok {
	_, err = c.ectdAPI.Put(ctx, key, val, v3Client.WithLease(*leaseID))
	} else {
	_, err = c.ectdAPI.Put(ctx, key, val)
	}

	if err != nil {
	switch err {
	case context.Canceled:
	logger.Warnw("context-cancelled", log.Fields{"error": err})
	case context.DeadlineExceeded:
	logger.Warnw("context-deadline-exceeded", log.Fields{"error": err})
	case v3rpcTypes.ErrEmptyKey:
	logger.Warnw("etcd-client-error", log.Fields{"error": err})
	default:
	logger.Warnw("bad-endpoints", log.Fields{"error": err})
	}
	return err
	}
	return nil
	}

	// Delete removes a key from the KV store. Timeout defines how long the function will
	// wait for a response
	func (c *EtcdClient) Delete(ctx context.Context, key string) error {

	// delete the key
	if _, err := c.ectdAPI.Delete(ctx, key); err != nil {
	logger.Errorw("failed-to-delete-key", log.Fields{"key": key, "error": err})
	return err
	}
	logger.Debugw("key(s)-deleted", log.Fields{"key": key})
	return nil
	}

	// Reserve is invoked to acquire a key and set it to a given value. Value can only be a string or []byte since
	// the etcd API accepts only a string. Timeout defines how long the function will wait for a response. TTL
	// defines how long that reservation is valid. When TTL expires the key is unreserved by the KV store itself.
	// If the key is acquired then the value returned will be the value passed in. If the key is already acquired
	// then the value assigned to that key will be returned.
	func (c *EtcdClient) Reserve(ctx context.Context, key string, value interface{}, ttl int64) (interface{}, error) {
	// Validate that we can convert value to a string as etcd API expects a string
	var val string
	var er error
	if val, er = ToString(value); er != nil {
	return nil, fmt.Errorf("unexpected-type%T", value)
	}

	resp, err := c.ectdAPI.Grant(ctx, ttl)
	if err != nil {
	logger.Error(err)
	return nil, err
	}
	// Register the lease id
	c.keyReservationsLock.Lock()
	c.keyReservations[key] = &resp.ID
	c.keyReservationsLock.Unlock()

	// Revoke lease if reservation is not successful
	reservationSuccessful := false
	defer func() {
	if !reservationSuccessful {
	if err = c.ReleaseReservation(context.Background(), key); err != nil {
	logger.Error("cannot-release-lease")
	}
	}
	}()

	// Try to grap the Key with the above lease
	c.ectdAPI.Txn(context.Background())
	txn := c.ectdAPI.Txn(context.Background())
	txn = txn.If(v3Client.Compare(v3Client.Version(key), "=", 0))
	txn = txn.Then(v3Client.OpPut(key, val, v3Client.WithLease(resp.ID)))
	txn = txn.Else(v3Client.OpGet(key))
	result, er := txn.Commit()
	if er != nil {
	return nil, er
	}

	if !result.Succeeded {
	// Verify whether we are already the owner of that Key
	if len(result.Responses) > 0 &&
	len(result.Responses[0].GetResponseRange().Kvs) > 0 {
	kv := result.Responses[0].GetResponseRange().Kvs[0]
	if string(kv.Value) == val {
	reservationSuccessful = true
	return value, nil
	}
	return kv.Value, nil
	}
	} else {
	// Read the Key to ensure this is our Key
	m, err := c.Get(ctx, key)
	if err != nil {
	return nil, err
	}
	if m != nil {
	if m.Key == key && isEqual(m.Value, value) {
	// My reservation is successful - register it. For now, support is only for 1 reservation per key
	// per session.
	reservationSuccessful = true
	return value, nil
	}
	// My reservation has failed. Return the owner of that key
	return m.Value, nil
	}
	}
	return nil, nil
	}

	// ReleaseAllReservations releases all key reservations previously made (using Reserve API)
	func (c *EtcdClient) ReleaseAllReservations(ctx context.Context) error {
	c.keyReservationsLock.Lock()
	defer c.keyReservationsLock.Unlock()

	for key, leaseID := range c.keyReservations {
	_, err := c.ectdAPI.Revoke(ctx, *leaseID)
	if err != nil {
	logger.Errorw("cannot-release-reservation", log.Fields{"key": key, "error": err})
	return err
	}
	delete(c.keyReservations, key)
	}
	return nil
	}

	// ReleaseReservation releases reservation for a specific key.
	func (c *EtcdClient) ReleaseReservation(ctx context.Context, key string) error {
	// Get the leaseid using the key
	logger.Debugw("Release-reservation", log.Fields{"key": key})
	var ok bool
	var leaseID *v3Client.LeaseID
	c.keyReservationsLock.Lock()
	defer c.keyReservationsLock.Unlock()
	if leaseID, ok = c.keyReservations[key]; !ok {
	return nil
	}

	if leaseID != nil {
	_, err := c.ectdAPI.Revoke(ctx, *leaseID)
	if err != nil {
	logger.Error(err)
	return err
	}
	delete(c.keyReservations, key)
	}
	return nil
	}

	// RenewReservation renews a reservation. A reservation will go stale after the specified TTL (Time To Live)
	// period specified when reserving the key
	func (c *EtcdClient) RenewReservation(ctx context.Context, key string) error {
	// Get the leaseid using the key
	var ok bool
	var leaseID *v3Client.LeaseID
	c.keyReservationsLock.RLock()
	leaseID, ok = c.keyReservations[key]
	c.keyReservationsLock.RUnlock()

	if !ok {
	return errors.New("key-not-reserved")
	}

	if leaseID != nil {
	_, err := c.ectdAPI.KeepAliveOnce(ctx, *leaseID)
	if err != nil {
	logger.Errorw("lease-may-have-expired", log.Fields{"error": err})
	return err
	}
	} else {
	return errors.New("lease-expired")
	}
	return nil
	}

	// Watch provides the watch capability on a given key. It returns a channel onto which the callee needs to
	// listen to receive Events.
	func (c EtcdClient) Watch(ctx context.Context, key string, withPrefix bool) chan Event {
	w := v3Client.NewWatcher(c.ectdAPI)
	ctx, cancel := context.WithCancel(ctx)
	var channel v3Client.WatchChan
	if withPrefix {
	channel = w.Watch(ctx, key, v3Client.WithPrefix())
	} else {
	channel = w.Watch(ctx, key)
	}

	// Create a new channel
	ch := make(chan *Event, maxClientChannelBufferSize)

	// Keep track of the created channels so they can be closed when required
	channelMap := make(map[chan *Event]v3Client.Watcher)
	channelMap[ch] = w

	channelMaps := c.addChannelMap(key, channelMap)

	// Changing the log field (from channelMaps) as the underlying logger cannot format the map of channels into a
	// json format.
	logger.Debugw("watched-channels", log.Fields{"len": len(channelMaps)})
	// Launch a go routine to listen for updates
	go c.listenForKeyChange(channel, ch, cancel)

	return ch

	}

	func (c EtcdClient) addChannelMap(key string, channelMap map[chan Event]v3Client.Watcher) []map[chan *Event]v3Client.Watcher {
	var channels interface{}
	var exists bool

	if channels, exists = c.watchedChannels.Load(key); exists {
	channels = append(channels.([]map[chan *Event]v3Client.Watcher), channelMap)
	} else {
	channels = []map[chan *Event]v3Client.Watcher{channelMap}
	}
	c.watchedChannels.Store(key, channels)

	return channels.([]map[chan *Event]v3Client.Watcher)
	}

	func (c EtcdClient) removeChannelMap(key string, pos int) []map[chan Event]v3Client.Watcher {
	var channels interface{}
	var exists bool

	if channels, exists = c.watchedChannels.Load(key); exists {
	channels = append(channels.([]map[chan Event]v3Client.Watcher)[:pos], channels.([]map[chan Event]v3Client.Watcher)[pos+1:]...)
	c.watchedChannels.Store(key, channels)
	}

	return channels.([]map[chan *Event]v3Client.Watcher)
	}

	func (c EtcdClient) getChannelMaps(key string) ([]map[chan Event]v3Client.Watcher, bool) {
	var channels interface{}
	var exists bool

	channels, exists = c.watchedChannels.Load(key)

	if channels == nil {
	return nil, exists
	}

	return channels.([]map[chan *Event]v3Client.Watcher), exists
	}

	// CloseWatch closes a specific watch. Both the key and the channel are required when closing a watch as there
	// may be multiple listeners on the same key. The previously created channel serves as a key
	func (c EtcdClient) CloseWatch(key string, ch chan Event) {
	// Get the array of channels mapping
	var watchedChannels []map[chan *Event]v3Client.Watcher
	var ok bool

	if watchedChannels, ok = c.getChannelMaps(key); !ok {
	logger.Warnw("key-has-no-watched-channels", log.Fields{"key": key})
	return
	}
	// Look for the channels
	var pos = -1
	for i, chMap := range watchedChannels {
	if t, ok := chMap[ch]; ok {
	logger.Debug("channel-found")
	// Close the etcd watcher before the client channel. This should close the etcd channel as well
	if err := t.Close(); err != nil {
	logger.Errorw("watcher-cannot-be-closed", log.Fields{"key": key, "error": err})
	}
	pos = i
	break
	}
	}

	channelMaps, _ := c.getChannelMaps(key)
	// Remove that entry if present
	if pos >= 0 {
	channelMaps = c.removeChannelMap(key, pos)
	}
	logger.Infow("watcher-channel-exiting", log.Fields{"key": key, "channel": channelMaps})
	}

	func (c EtcdClient) listenForKeyChange(channel v3Client.WatchChan, ch chan<- Event, cancel context.CancelFunc) {
	logger.Debug("start-listening-on-channel ...")
	defer cancel()
	defer close(ch)
	for resp := range channel {
	for _, ev := range resp.Events {
	ch <- NewEvent(getEventType(ev), ev.Kv.Key, ev.Kv.Value, ev.Kv.Version)
	}
	}
	logger.Debug("stop-listening-on-channel ...")
	}

	func getEventType(event *v3Client.Event) int {
	switch event.Type {
	case v3Client.EventTypePut:
	return PUT
	case v3Client.EventTypeDelete:
	return DELETE
	}
	return UNKNOWN
	}

	// Close closes the KV store client
	func (c *EtcdClient) Close() {
	if err := c.ectdAPI.Close(); err != nil {
	logger.Errorw("error-closing-client", log.Fields{"error": err})
	}
	}

	func (c EtcdClient) addLockName(lockName string, lock v3Concurrency.Mutex, session *v3Concurrency.Session) {
	c.lockToMutexLock.Lock()
	defer c.lockToMutexLock.Unlock()
	c.lockToMutexMap[lockName] = lock
	c.lockToSessionMap[lockName] = session
	}

	func (c *EtcdClient) deleteLockName(lockName string) {
	c.lockToMutexLock.Lock()
	defer c.lockToMutexLock.Unlock()
	delete(c.lockToMutexMap, lockName)
	delete(c.lockToSessionMap, lockName)
	}

	func (c EtcdClient) getLock(lockName string) (v3Concurrency.Mutex, *v3Concurrency.Session) {
	c.lockToMutexLock.Lock()
	defer c.lockToMutexLock.Unlock()
	var lock *v3Concurrency.Mutex
	var session *v3Concurrency.Session
	if l, exist := c.lockToMutexMap[lockName]; exist {
	lock = l
	}
	if s, exist := c.lockToSessionMap[lockName]; exist {
	session = s
	}
	return lock, session
	}

	func (c *EtcdClient) AcquireLock(ctx context.Context, lockName string, timeout int) error {
	session, _ := v3Concurrency.NewSession(c.ectdAPI, v3Concurrency.WithContext(ctx))
	mu := v3Concurrency.NewMutex(session, "/devicelock_"+lockName)
	if err := mu.Lock(context.Background()); err != nil {
	//cancel()
	return err
	}
	c.addLockName(lockName, mu, session)
	return nil
	}

	func (c *EtcdClient) ReleaseLock(lockName string) error {
	lock, session := c.getLock(lockName)
	var err error
	if lock != nil {
	if e := lock.Unlock(context.Background()); e != nil {
	err = e
	}
	}
	if session != nil {
	if e := session.Close(); e != nil {
	err = e
	}
	}
	c.deleteLockName(lockName)

	return err
	}