[VOL-3860] redis client support in voltha-lib-go

redis client support has been added in this patch. There are two
types client `redis` and `redis-sentinel` to connect a redis instance.
redis-sentinel is required to be able to find the master redis
instance from a redis-sentinel process. See redis-sentinel usage
https://redis.io/topics/sentinel and
https://pkg.go.dev/github.com/go-redis/redis/v8#NewFailoverClient
for more information. If there is no need to have any failover
mechanism then the redis client type is the option to choose.

Change-Id: I997ed92115a9d565df632c6dd8184b9bab77b991
diff --git a/pkg/db/kvstore/redisclient.go b/pkg/db/kvstore/redisclient.go
new file mode 100644
index 0000000..decb0a4
--- /dev/null
+++ b/pkg/db/kvstore/redisclient.go
@@ -0,0 +1,417 @@
+/*
+ * 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"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/go-redis/redis/v8"
+	"github.com/opencord/voltha-lib-go/v7/pkg/log"
+)
+
+type RedisClient struct {
+	redisAPI            *redis.Client
+	keyReservations     map[string]time.Duration
+	watchedChannels     sync.Map
+	writeLock           sync.Mutex
+	keyReservationsLock sync.RWMutex
+}
+
+func NewRedisClient(addr string, timeout time.Duration, useSentinel bool) (*RedisClient, error) {
+	var r *redis.Client
+	if !useSentinel {
+		r = redis.NewClient(&redis.Options{Addr: addr})
+	} else {
+		// Redis Master-Replicas with Sentinel, sentinel masterSet config
+		//  should be set to sebaRedis
+		r = redis.NewFailoverClient(&redis.FailoverOptions{
+			MasterName:    "sebaRedis",
+			SentinelAddrs: []string{addr},
+		})
+	}
+
+	reservations := make(map[string]time.Duration)
+	return &RedisClient{redisAPI: r, keyReservations: reservations}, nil
+}
+
+func (c *RedisClient) Get(ctx context.Context, key string) (*KVPair, error) {
+
+	val, err := c.redisAPI.Get(ctx, key).Result()
+	valBytes, _ := ToByte(val)
+	if err != nil {
+		return nil, nil
+	}
+	return NewKVPair(key, valBytes, "", 0, 0), nil
+}
+
+func (c *RedisClient) 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)
+	}
+
+	// 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
+	setErr := c.redisAPI.Set(ctx, key, val, 0)
+	err := setErr.Err()
+
+	if err != nil {
+		switch setErr.Err() {
+		case context.Canceled:
+			logger.Warnw(ctx, "context-cancelled", log.Fields{"error": err})
+		case context.DeadlineExceeded:
+			logger.Warnw(ctx, "context-deadline-exceeded", log.Fields{"error": err})
+		default:
+			logger.Warnw(ctx, "bad-endpoints", log.Fields{"error": err})
+		}
+		return err
+	}
+	return nil
+}
+
+func (c *RedisClient) scanAllKeysWithPrefix(ctx context.Context, key string) ([]string, error) {
+	var err error
+	allkeys := []string{}
+	cont := true
+	cursor := uint64(0)
+	matchPrefix := key + "*"
+
+	for cont {
+		// search in the first 10000 entries starting from the point indicated by the cursor
+		logger.Debugw(ctx, "redis-scan", log.Fields{"matchPrefix": matchPrefix, "cursor": cursor})
+		var keys []string
+		keys, cursor, err = c.redisAPI.Scan(context.Background(), cursor, matchPrefix, 10000).Result()
+		if err != nil {
+			return nil, err
+		}
+		if cursor == 0 {
+			// all data searched. break the loop
+			logger.Debugw(ctx, "redis-scan-ended", log.Fields{"matchPrefix": matchPrefix, "cursor": cursor})
+			cont = false
+		}
+		if len(keys) == 0 {
+			// no matched data found in this cycle. Continue to search
+			logger.Debugw(ctx, "redis-scan-no-data-found-continue", log.Fields{"matchPrefix": matchPrefix, "cursor": cursor})
+			continue
+		}
+		allkeys = append(allkeys, keys...)
+	}
+	return allkeys, nil
+}
+
+func (c *RedisClient) List(ctx context.Context, key string) (map[string]*KVPair, error) {
+	var err error
+	var keys []string
+	m := make(map[string]*KVPair)
+	var values []interface{}
+
+	if keys, err = c.scanAllKeysWithPrefix(ctx, key); err != nil {
+		return nil, err
+	}
+
+	if len(keys) != 0 {
+		values, err = c.redisAPI.MGet(ctx, keys...).Result()
+		if err != nil {
+			return nil, err
+		}
+	}
+	for i, key := range keys {
+		if valBytes, err := ToByte(values[i]); err == nil {
+			m[key] = NewKVPair(key, interface{}(valBytes), "", 0, 0)
+		}
+	}
+	return m, nil
+}
+
+func (c *RedisClient) Delete(ctx context.Context, key string) error {
+	// delete the key
+	if _, err := c.redisAPI.Del(ctx, key).Result(); err != nil {
+		logger.Errorw(ctx, "failed-to-delete-key", log.Fields{"key": key, "error": err})
+		return err
+	}
+	logger.Debugw(ctx, "key(s)-deleted", log.Fields{"key": key})
+	return nil
+}
+
+func (c *RedisClient) DeleteWithPrefix(ctx context.Context, prefixKey string) error {
+	var keys []string
+	var err error
+	if keys, err = c.scanAllKeysWithPrefix(ctx, prefixKey); err != nil {
+		return err
+	}
+	if len(keys) == 0 {
+		logger.Warn(ctx, "nothing-to-delete-from-kv", log.Fields{"key": prefixKey})
+		return nil
+	}
+	//call delete for keys
+	entryCount := int64(0)
+	start := 0
+	pageSize := 5000
+	length := len(keys)
+	for start < length {
+		end := start + pageSize
+		if end >= length {
+			end = length
+		}
+		keysToDelete := keys[start:end]
+		count := int64(0)
+		if count, err = c.redisAPI.Del(ctx, keysToDelete...).Result(); err != nil {
+			logger.Errorw(ctx, "DeleteWithPrefix method failed", log.Fields{"prefixKey": prefixKey, "numOfMatchedKeys": len(keysToDelete), "err": err})
+			return err
+		}
+		entryCount += count
+		start = end
+	}
+	logger.Debugf(ctx, "%d entries matching with the key prefix %s have been deleted successfully", entryCount, prefixKey)
+	return nil
+}
+
+func (c *RedisClient) Reserve(ctx context.Context, key string, value interface{}, ttl time.Duration) (interface{}, error) {
+	var val string
+	var er error
+	if val, er = ToString(value); er != nil {
+		return nil, fmt.Errorf("unexpected-type%T", value)
+	}
+
+	// SetNX -- Only set the key if it does not already exist.
+	c.redisAPI.SetNX(ctx, key, value, ttl)
+
+	// Check if set is successful
+	redisVal := c.redisAPI.Get(ctx, key).Val()
+	if redisVal == "" {
+		println("NULL")
+		return nil, nil
+	}
+
+	if val == redisVal {
+		// set is successful, return new reservation value
+		c.keyReservationsLock.Lock()
+		c.keyReservations[key] = ttl
+		c.keyReservationsLock.Unlock()
+		bytes, _ := ToByte(val)
+		return bytes, nil
+	} else {
+		// set is not successful, return existing reservation value
+		bytes, _ := ToByte(redisVal)
+		return bytes, nil
+	}
+
+}
+
+func (c *RedisClient) ReleaseReservation(ctx context.Context, key string) error {
+
+	redisVal := c.redisAPI.Get(ctx, key).Val()
+	if redisVal == "" {
+		return nil
+	}
+
+	// Override SetNX value with no TTL
+	_, err := c.redisAPI.Set(ctx, key, redisVal, 0).Result()
+	if err != nil {
+		delete(c.keyReservations, key)
+	} else {
+		return err
+	}
+	return nil
+
+}
+
+func (c *RedisClient) ReleaseAllReservations(ctx context.Context) error {
+	c.writeLock.Lock()
+	defer c.writeLock.Unlock()
+	for key := range c.keyReservations {
+		err := c.ReleaseReservation(ctx, key)
+		if err != nil {
+			logger.Errorw(ctx, "cannot-release-reservation", log.Fields{"key": key, "error": err})
+			return err
+		}
+	}
+	return nil
+}
+
+func (c *RedisClient) RenewReservation(ctx context.Context, key string) error {
+	c.writeLock.Lock()
+	defer c.writeLock.Unlock()
+
+	// Verify the key was reserved
+	ttl, ok := c.keyReservations[key]
+	if !ok {
+		return errors.New("key-not-reserved. Key not found")
+	}
+
+	redisVal := c.redisAPI.Get(ctx, key).Val()
+	if redisVal != "" {
+		c.redisAPI.Set(ctx, key, redisVal, ttl)
+	}
+	return nil
+}
+
+func (c *RedisClient) listenForKeyChange(ctx context.Context, redisCh <-chan *redis.Message, ch chan<- *Event, cancel context.CancelFunc) {
+	logger.Debug(ctx, "start-listening-on-channel ...")
+	defer cancel()
+	defer close(ch)
+	for msg := range redisCh {
+		words := strings.Split(msg.Channel, ":")
+		key := words[1]
+		msgType := getMessageType(msg.Payload)
+		var valBytes []byte
+		if msgType == PUT {
+			ev, _ := c.Get(ctx, key)
+			valBytes, _ = ToByte(ev.Value)
+		}
+		ch <- NewEvent(getMessageType(msg.Payload), []byte(key), valBytes, 0)
+	}
+	logger.Debug(ctx, "stop-listening-on-channel ...")
+}
+
+func getMessageType(msg string) int {
+	isPut := strings.HasSuffix(msg, "set")
+	isDel := strings.HasSuffix(msg, "del")
+	if isPut {
+		return PUT
+	} else if isDel {
+		return DELETE
+	} else {
+		return UNKNOWN
+	}
+}
+
+func (c *RedisClient) addChannelMap(key string, channelMap map[chan *Event]*redis.PubSub) []map[chan *Event]*redis.PubSub {
+
+	var channels interface{}
+	var exists bool
+
+	if channels, exists = c.watchedChannels.Load(key); exists {
+		channels = append(channels.([]map[chan *Event]*redis.PubSub), channelMap)
+	} else {
+		channels = []map[chan *Event]*redis.PubSub{channelMap}
+	}
+	c.watchedChannels.Store(key, channels)
+
+	return channels.([]map[chan *Event]*redis.PubSub)
+}
+
+func (c *RedisClient) removeChannelMap(key string, pos int) []map[chan *Event]*redis.PubSub {
+	var channels interface{}
+	var exists bool
+
+	if channels, exists = c.watchedChannels.Load(key); exists {
+		channels = append(channels.([]map[chan *Event]*redis.PubSub)[:pos], channels.([]map[chan *Event]*redis.PubSub)[pos+1:]...)
+		c.watchedChannels.Store(key, channels)
+	}
+
+	return channels.([]map[chan *Event]*redis.PubSub)
+}
+
+func (c *RedisClient) getChannelMaps(key string) ([]map[chan *Event]*redis.PubSub, bool) {
+	var channels interface{}
+	var exists bool
+
+	channels, exists = c.watchedChannels.Load(key)
+
+	if channels == nil {
+		return nil, exists
+	}
+
+	return channels.([]map[chan *Event]*redis.PubSub), exists
+}
+
+func (c *RedisClient) Watch(ctx context.Context, key string, withPrefix bool) chan *Event {
+
+	ctx, cancel := context.WithCancel(ctx)
+
+	var subscribePath string
+	subscribePath = "__key*__:" + key
+	if withPrefix {
+		subscribePath += "*"
+	}
+	pubsub := c.redisAPI.PSubscribe(ctx, subscribePath)
+	redisCh := pubsub.Channel()
+
+	// Create 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]*redis.PubSub)
+	channelMap[ch] = pubsub
+
+	channelMaps := c.addChannelMap(key, channelMap)
+	logger.Debugw(ctx, "watched-channels", log.Fields{"len": len(channelMaps)})
+
+	// Launch a go routine to listen for updates
+	go c.listenForKeyChange(ctx, redisCh, ch, cancel)
+	return ch
+}
+
+func (c *RedisClient) CloseWatch(ctx context.Context, key string, ch chan *Event) {
+	// Get the array of channels mapping
+	var watchedChannels []map[chan *Event]*redis.PubSub
+	var ok bool
+
+	if watchedChannels, ok = c.getChannelMaps(key); !ok {
+		logger.Warnw(ctx, "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(ctx, "channel-found")
+			// Close the Redis watcher before the client channel.  This should close the etcd channel as well
+			if err := t.Close(); err != nil {
+				logger.Errorw(ctx, "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(ctx, "watcher-channel-exiting", log.Fields{"key": key, "channel": channelMaps})
+}
+func (c *RedisClient) AcquireLock(ctx context.Context, lockName string, timeout time.Duration) error {
+	return nil
+}
+
+func (c *RedisClient) ReleaseLock(lockName string) error {
+	return nil
+}
+
+func (c *RedisClient) IsConnectionUp(ctx context.Context) bool {
+	if _, err := c.redisAPI.Set(ctx, "connection-check", "1", 0).Result(); err != nil {
+		return false
+	}
+	return true
+
+}
+
+func (c *RedisClient) Close(ctx context.Context) {
+	if err := c.redisAPI.Close(); err != nil {
+		logger.Errorw(ctx, "error-closing-client", log.Fields{"error": err})
+	}
+}