minio/cmd/event-notifier.go

/*
 * Minio Cloud Storage, (C) 2016, 2017 Minio, Inc.
 *
 * 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 cmd

import (
	"bytes"
	"encoding/json"
	"encoding/xml"
	"fmt"
	"net"
	"net/url"
	"path"
	"sync"

	"github.com/Sirupsen/logrus"
)

const (
	minioEventSource = "minio:s3"
)

type externalNotifier struct {
	// Per-bucket notification config. This is updated via
	// PutBucketNotification API.
	notificationConfigs map[string]*notificationConfig

	// An external target keeps a connection to an external
	// service to which events are to be sent. It is a mapping
	// from an ARN to a log object
	targets map[string]*logrus.Logger

	rwMutex *sync.RWMutex
}

type internalNotifier struct {
	// per-bucket listener configuration. This is updated
	// when listeners connect or disconnect.
	listenerConfigs map[string][]listenerConfig

	// An internal target is a peer Minio server, that is
	// connected to a listening client. Here, targets is a map of
	// listener ARN to log object.
	targets map[string]*listenerLogger

	// Connected listeners is a map of listener ARNs to channels
	// on which the ListenBucket API handler go routine is waiting
	// for events to send to a client.
	connectedListeners map[string]chan []NotificationEvent

	rwMutex *sync.RWMutex
}

// Global event notification configuration. This structure has state
// about configured external notifications, and run-time configuration
// for listener notifications.
type eventNotifier struct {

	// `external` here refers to notification configuration to
	// send events to supported external systems
	external externalNotifier

	// `internal` refers to notification configuration for live
	// listening clients. Events for a client are send from all
	// servers, internally to a particular server that is
	// connected to the client.
	internal internalNotifier
}

// Represents data to be sent with notification event.
type eventData struct {
	Type      EventName
	Bucket    string
	ObjInfo   ObjectInfo
	ReqParams map[string]string
	Host      string
	Port      string
	UserAgent string
}

// New notification event constructs a new notification event message from
// input request metadata which completed successfully.
func newNotificationEvent(event eventData) NotificationEvent {
	// Fetch the region.
	region := serverConfig.GetRegion()

	// Fetch the credentials.
	creds := serverConfig.GetCredential()

	// Time when Minio finished processing the request.
	eventTime := UTCNow()

	// API endpoint is captured here to be returned back
	// to the client for it to differentiate from which
	// server the request came from.
	var apiEndpoint string
	if len(globalAPIEndpoints) >= 1 {
		apiEndpoint = globalAPIEndpoints[0]
	}

	// Fetch a hexadecimal representation of event time in nano seconds.
	uniqueID := mustGetRequestID(eventTime)

	/// Construct a new object created event.

	// Following blocks fills in all the necessary details of s3
	// event message structure.
	// http://docs.aws.amazon.com/AmazonS3/latest/dev/notification-content-structure.html
	nEvent := NotificationEvent{
		EventVersion:      eventVersion,
		EventSource:       minioEventSource,
		AwsRegion:         region,
		EventTime:         eventTime.Format(timeFormatAMZ),
		EventName:         event.Type.String(),
		UserIdentity:      identity{creds.AccessKey},
		RequestParameters: event.ReqParams,
		ResponseElements: map[string]string{
			responseRequestIDKey: uniqueID,
			// Following is a custom response element to indicate
			// event origin server endpoint.
			responseOriginEndpointKey: apiEndpoint,
		},
		S3: eventMeta{
			SchemaVersion:   eventSchemaVersion,
			ConfigurationID: eventConfigID,
			Bucket: bucketMeta{
				Name:          event.Bucket,
				OwnerIdentity: identity{creds.AccessKey},
				ARN:           bucketARNPrefix + event.Bucket,
			},
		},
		Source: sourceInfo{
			Host:      event.Host,
			Port:      event.Port,
			UserAgent: event.UserAgent,
		},
	}

	// Escape the object name. For example "red flower.jpg" becomes "red+flower.jpg".
	escapedObj := url.QueryEscape(event.ObjInfo.Name)

	// For delete object event type, we do not need to set ETag and Size.
	if event.Type == ObjectRemovedDelete {
		nEvent.S3.Object = objectMeta{
			Key:       escapedObj,
			VersionID: "1",
			Sequencer: uniqueID,
		}
		return nEvent
	}

	// For all other events we should set ETag and Size.
	nEvent.S3.Object = objectMeta{
		Key:         escapedObj,
		ETag:        event.ObjInfo.MD5Sum,
		Size:        event.ObjInfo.Size,
		ContentType: event.ObjInfo.ContentType,
		UserDefined: event.ObjInfo.UserDefined,
		VersionID:   "1",
		Sequencer:   uniqueID,
	}

	// Success.
	return nEvent
}

// Fetch all external targets. This returns a copy of the current map of
// external notification targets.
func (en eventNotifier) GetAllExternalTargets() map[string]*logrus.Logger {
	en.external.rwMutex.RLock()
	defer en.external.rwMutex.RUnlock()
	targetsCopy := make(map[string]*logrus.Logger)
	for k, v := range en.external.targets {
		targetsCopy[k] = v
	}
	return targetsCopy
}

// Fetch the external target.
func (en eventNotifier) GetExternalTarget(queueARN string) *logrus.Logger {
	en.external.rwMutex.RLock()
	defer en.external.rwMutex.RUnlock()
	return en.external.targets[queueARN]
}

func (en eventNotifier) GetInternalTarget(arn string) *listenerLogger {
	en.internal.rwMutex.RLock()
	defer en.internal.rwMutex.RUnlock()
	return en.internal.targets[arn]
}

// Set a new sns target for an input sns ARN.
func (en *eventNotifier) AddListenerChan(snsARN string, listenerCh chan []NotificationEvent) error {
	if listenerCh == nil {
		return errInvalidArgument
	}
	en.internal.rwMutex.Lock()
	defer en.internal.rwMutex.Unlock()
	en.internal.connectedListeners[snsARN] = listenerCh
	return nil
}

// Remove sns target for an input sns ARN.
func (en *eventNotifier) RemoveListenerChan(snsARN string) {
	en.internal.rwMutex.Lock()
	defer en.internal.rwMutex.Unlock()
	if en.internal.connectedListeners != nil {
		delete(en.internal.connectedListeners, snsARN)
	}
}

func (en *eventNotifier) SendListenerEvent(arn string, event []NotificationEvent) error {
	en.internal.rwMutex.Lock()
	defer en.internal.rwMutex.Unlock()

	ch, ok := en.internal.connectedListeners[arn]
	if ok {
		ch <- event
	}
	// If the channel is not present we ignore the event.
	return nil
}

// Fetch bucket notification config for an input bucket.
func (en eventNotifier) GetBucketNotificationConfig(bucket string) *notificationConfig {
	en.external.rwMutex.RLock()
	defer en.external.rwMutex.RUnlock()
	return en.external.notificationConfigs[bucket]
}

func (en *eventNotifier) SetBucketNotificationConfig(bucket string, ncfg *notificationConfig) {
	en.external.rwMutex.Lock()
	if ncfg == nil {
		delete(en.external.notificationConfigs, bucket)
	} else {
		en.external.notificationConfigs[bucket] = ncfg
	}
	en.external.rwMutex.Unlock()
}

func (en *eventNotifier) GetBucketListenerConfig(bucket string) []listenerConfig {
	en.internal.rwMutex.RLock()
	defer en.internal.rwMutex.RUnlock()
	return en.internal.listenerConfigs[bucket]
}

func (en *eventNotifier) SetBucketListenerConfig(bucket string, lcfg []listenerConfig) error {
	en.internal.rwMutex.Lock()
	defer en.internal.rwMutex.Unlock()
	if len(lcfg) == 0 {
		delete(en.internal.listenerConfigs, bucket)
	} else {
		en.internal.listenerConfigs[bucket] = lcfg
	}
	for _, elcArr := range en.internal.listenerConfigs {
		for _, elcElem := range elcArr {
			currArn := elcElem.TopicConfig.TopicARN
			logger, err := newListenerLogger(currArn, elcElem.TargetServer)
			if err != nil {
				return err
			}
			en.internal.targets[currArn] = logger
		}
	}
	return nil
}

func eventNotifyForBucketNotifications(eventType, objectName, bucketName string, nEvent []NotificationEvent) {
	nConfig := globalEventNotifier.GetBucketNotificationConfig(bucketName)
	if nConfig == nil {
		return
	}
	// Validate if the event and object match the queue configs.
	for _, qConfig := range nConfig.QueueConfigs {
		eventMatch := eventMatch(eventType, qConfig.Events)
		ruleMatch := filterRuleMatch(objectName, qConfig.Filter.Key.FilterRules)
		if eventMatch && ruleMatch {
			targetLog := globalEventNotifier.GetExternalTarget(qConfig.QueueARN)
			if targetLog != nil {
				targetLog.WithFields(logrus.Fields{
					"Key":       path.Join(bucketName, objectName),
					"EventType": eventType,
					"Records":   nEvent,
				}).Info()
			}
		}
	}
}

func eventNotifyForBucketListeners(eventType, objectName, bucketName string,
	nEvent []NotificationEvent) {
	lCfgs := globalEventNotifier.GetBucketListenerConfig(bucketName)
	if lCfgs == nil {
		return
	}
	// Validate if the event and object match listener configs
	for _, lcfg := range lCfgs {
		ruleMatch := filterRuleMatch(objectName, lcfg.TopicConfig.Filter.Key.FilterRules)
		eventMatch := eventMatch(eventType, lcfg.TopicConfig.Events)
		if eventMatch && ruleMatch {
			targetLog := globalEventNotifier.GetInternalTarget(
				lcfg.TopicConfig.TopicARN)
			if targetLog != nil && targetLog.log != nil {
				targetLog.log.WithFields(logrus.Fields{
					"Key":       path.Join(bucketName, objectName),
					"EventType": eventType,
					"Records":   nEvent,
				}).Info()
			}
		}
	}

}

// eventNotify notifies an event to relevant targets based on their
// bucket configuration (notifications and listeners).
func eventNotify(event eventData) {
	if globalEventNotifier == nil {
		return
	}
	// Notifies a new event.
	// List of events reported through this function are
	//  - s3:ObjectCreated:Put
	//  - s3:ObjectCreated:Post
	//  - s3:ObjectCreated:Copy
	//  - s3:ObjectCreated:CompleteMultipartUpload
	//  - s3:ObjectRemoved:Delete

	// Event type.
	eventType := event.Type.String()

	// Object name.
	objectName := event.ObjInfo.Name

	// Save the notification event to be sent.
	notificationEvent := []NotificationEvent{newNotificationEvent(event)}

	// Notify external targets.
	eventNotifyForBucketNotifications(eventType, objectName, event.Bucket, notificationEvent)

	// Notify internal targets.
	eventNotifyForBucketListeners(eventType, objectName, event.Bucket, notificationEvent)
}

// loads notification config if any for a given bucket, returns
// structured notification config.
func loadNotificationConfig(bucket string, objAPI ObjectLayer) (*notificationConfig, error) {
	// Construct the notification config path.
	ncPath := path.Join(bucketConfigPrefix, bucket, bucketNotificationConfig)

	// Acquire a write lock on notification config before modifying.
	objLock := globalNSMutex.NewNSLock(minioMetaBucket, ncPath)
	objLock.RLock()
	defer objLock.RUnlock()

	var buffer bytes.Buffer
	err := objAPI.GetObject(minioMetaBucket, ncPath, 0, -1, &buffer) // Read everything.
	if err != nil {
		// 'notification.xml' not found return
		// 'errNoSuchNotifications'.  This is default when no
		// bucket notifications are found on the bucket.
		if isErrObjectNotFound(err) || isErrIncompleteBody(err) {
			return nil, errNoSuchNotifications
		}
		errorIf(err, "Unable to load bucket-notification for bucket %s", bucket)
		// Returns error for other errors.
		return nil, err
	}

	// Unmarshal notification bytes.
	notificationConfigBytes := buffer.Bytes()
	notificationCfg := &notificationConfig{}
	if err = xml.Unmarshal(notificationConfigBytes, &notificationCfg); err != nil {
		return nil, err
	}

	// Return success.
	return notificationCfg, nil
}

// loads notification config if any for a given bucket, returns
// structured notification config.
func loadListenerConfig(bucket string, objAPI ObjectLayer) ([]listenerConfig, error) {
	// in single node mode, there are no peers, so in this case
	// there is no configuration to load, as any previously
	// connected listen clients have been disconnected
	if !globalIsDistXL {
		return nil, nil
	}

	// Construct the notification config path.
	lcPath := path.Join(bucketConfigPrefix, bucket, bucketListenerConfig)

	// Acquire a write lock on notification config before modifying.
	objLock := globalNSMutex.NewNSLock(minioMetaBucket, lcPath)
	objLock.RLock()
	defer objLock.RUnlock()

	var buffer bytes.Buffer
	err := objAPI.GetObject(minioMetaBucket, lcPath, 0, -1, &buffer)
	if err != nil {
		// 'notification.xml' not found return
		// 'errNoSuchNotifications'.  This is default when no
		// bucket listeners are found on the bucket.
		if isErrObjectNotFound(err) {
			return nil, errNoSuchNotifications
		}
		errorIf(err, "Unable to load bucket-listeners for bucket %s", bucket)
		// Returns error for other errors.
		return nil, err
	}

	// Unmarshal notification bytes.
	var lCfg []listenerConfig
	lConfigBytes := buffer.Bytes()
	if err = json.Unmarshal(lConfigBytes, &lCfg); err != nil {
		errorIf(err, "Unable to unmarshal listener config from JSON.")
		return nil, err
	}

	// Return success.
	return lCfg, nil
}

func persistNotificationConfig(bucket string, ncfg *notificationConfig, obj ObjectLayer) error {
	// marshal to xml
	buf, err := xml.Marshal(ncfg)
	if err != nil {
		errorIf(err, "Unable to marshal notification configuration into XML")
		return err
	}

	// build path
	ncPath := path.Join(bucketConfigPrefix, bucket, bucketNotificationConfig)
	// Acquire a write lock on notification config before modifying.
	objLock := globalNSMutex.NewNSLock(minioMetaBucket, ncPath)
	objLock.Lock()
	defer objLock.Unlock()

	// write object to path
	sha256Sum := getSHA256Hash(buf)
	_, err = obj.PutObject(minioMetaBucket, ncPath, int64(len(buf)), bytes.NewReader(buf), nil, sha256Sum)
	if err != nil {
		errorIf(err, "Unable to write bucket notification configuration.")
		return err
	}
	return nil
}

// Persists validated listener config to object layer.
func persistListenerConfig(bucket string, lcfg []listenerConfig, obj ObjectLayer) error {
	buf, err := json.Marshal(lcfg)
	if err != nil {
		errorIf(err, "Unable to marshal listener config to JSON.")
		return err
	}

	// build path
	lcPath := path.Join(bucketConfigPrefix, bucket, bucketListenerConfig)
	// Acquire a write lock on notification config before modifying.
	objLock := globalNSMutex.NewNSLock(minioMetaBucket, lcPath)
	objLock.Lock()
	defer objLock.Unlock()

	// write object to path
	sha256Sum := getSHA256Hash(buf)
	_, err = obj.PutObject(minioMetaBucket, lcPath, int64(len(buf)), bytes.NewReader(buf), nil, sha256Sum)
	if err != nil {
		errorIf(err, "Unable to write bucket listener configuration to object layer.")
	}
	return err
}

// Removes notification.xml for a given bucket, only used during DeleteBucket.
func removeNotificationConfig(bucket string, objAPI ObjectLayer) error {
	// Verify bucket is valid.
	if !IsValidBucketName(bucket) {
		return BucketNameInvalid{Bucket: bucket}
	}

	ncPath := path.Join(bucketConfigPrefix, bucket, bucketNotificationConfig)

	// Acquire a write lock on notification config before modifying.
	objLock := globalNSMutex.NewNSLock(minioMetaBucket, ncPath)
	objLock.Lock()
	err := objAPI.DeleteObject(minioMetaBucket, ncPath)
	objLock.Unlock()
	return err
}

// Remove listener configuration from storage layer. Used when a bucket is deleted.
func removeListenerConfig(bucket string, objAPI ObjectLayer) error {
	// make the path
	lcPath := path.Join(bucketConfigPrefix, bucket, bucketListenerConfig)

	// Acquire a write lock on notification config before modifying.
	objLock := globalNSMutex.NewNSLock(minioMetaBucket, lcPath)
	objLock.Lock()
	err := objAPI.DeleteObject(minioMetaBucket, lcPath)
	objLock.Unlock()
	return err
}

// Loads both notification and listener config.
func loadNotificationAndListenerConfig(bucketName string, objAPI ObjectLayer) (nCfg *notificationConfig, lCfg []listenerConfig, err error) {
	// Loads notification config if any.
	nCfg, err = loadNotificationConfig(bucketName, objAPI)
	if err != nil && !isErrIgnored(err, errDiskNotFound, errNoSuchNotifications) {
		return nil, nil, err
	}

	// Loads listener config if any.
	lCfg, err = loadListenerConfig(bucketName, objAPI)
	if err != nil && !isErrIgnored(err, errDiskNotFound, errNoSuchNotifications) {
		return nil, nil, err
	}
	return nCfg, lCfg, nil
}

// loads all bucket notifications if present.
func loadAllBucketNotifications(objAPI ObjectLayer) (map[string]*notificationConfig, map[string][]listenerConfig, error) {
	// List buckets to proceed loading all notification configuration.
	buckets, err := objAPI.ListBuckets()
	if err != nil {
		return nil, nil, err
	}

	nConfigs := make(map[string]*notificationConfig)
	lConfigs := make(map[string][]listenerConfig)

	// Loads all bucket notifications.
	for _, bucket := range buckets {
		// Load persistent notification and listener configurations
		// a given bucket name.
		nConfigs[bucket.Name], lConfigs[bucket.Name], err = loadNotificationAndListenerConfig(bucket.Name, objAPI)
		if err != nil {
			return nil, nil, err
		}
	}

	// Success.
	return nConfigs, lConfigs, nil
}

// addQueueTarget - calls newTargetFunc function and adds its returned value to queueTargets
func addQueueTarget(queueTargets map[string]*logrus.Logger,
	accountID, queueType string,
	newTargetFunc func(string) (*logrus.Logger, error)) (string, error) {

	// Construct the queue ARN for AMQP.
	queueARN := minioSqs + serverConfig.GetRegion() + ":" + accountID + ":" + queueType

	// Queue target if already initialized we move to the next ARN.
	if _, ok := queueTargets[queueARN]; ok {
		return queueARN, nil
	}

	// Using accountID we can now initialize a new AMQP logrus instance.
	logger, err := newTargetFunc(accountID)
	if err == nil {
		queueTargets[queueARN] = logger
	}

	return queueARN, err
}

// Loads all queue targets, initializes each queueARNs depending on their config.
// Each instance of queueARN registers its own logrus to communicate with the
// queue service. QueueARN once initialized is not initialized again for the
// same queueARN, instead previous connection is used.
func loadAllQueueTargets() (map[string]*logrus.Logger, error) {
	queueTargets := make(map[string]*logrus.Logger)
	// Load all amqp targets, initialize their respective loggers.
	for accountID, amqpN := range serverConfig.Notify.GetAMQP() {
		if !amqpN.Enable {
			continue
		}

		if queueARN, err := addQueueTarget(queueTargets, accountID, queueTypeAMQP, newAMQPNotify); err != nil {
			if _, ok := err.(net.Error); ok {
				err = &net.OpError{
					Op:  "Connecting to " + queueARN,
					Net: "tcp",
					Err: err,
				}
			}

			return nil, err
		}
	}

	// Load all nats targets, initialize their respective loggers.
	for accountID, natsN := range serverConfig.Notify.GetNATS() {
		if !natsN.Enable {
			continue
		}

		if queueARN, err := addQueueTarget(queueTargets, accountID, queueTypeNATS, newNATSNotify); err != nil {
			if _, ok := err.(net.Error); ok {
				err = &net.OpError{
					Op:  "Connecting to " + queueARN,
					Net: "tcp",
					Err: err,
				}
			}

			return nil, err
		}
	}

	// Load redis targets, initialize their respective loggers.
	for accountID, redisN := range serverConfig.Notify.GetRedis() {
		if !redisN.Enable {
			continue
		}

		if queueARN, err := addQueueTarget(queueTargets, accountID, queueTypeRedis, newRedisNotify); err != nil {
			if _, ok := err.(net.Error); ok {
				err = &net.OpError{
					Op:  "Connecting to " + queueARN,
					Net: "tcp",
					Err: err,
				}
			}

			return nil, err
		}
	}

	// Load Webhook targets, initialize their respective loggers.
	for accountID, webhookN := range serverConfig.Notify.GetWebhook() {
		if !webhookN.Enable {
			continue
		}

		if _, err := addQueueTarget(queueTargets, accountID, queueTypeWebhook, newWebhookNotify); err != nil {
			return nil, err
		}
	}

	// Load elastic targets, initialize their respective loggers.
	for accountID, elasticN := range serverConfig.Notify.GetElasticSearch() {
		if !elasticN.Enable {
			continue
		}

		if queueARN, err := addQueueTarget(queueTargets, accountID, queueTypeElastic, newElasticNotify); err != nil {
			if _, ok := err.(net.Error); ok {
				err = &net.OpError{
					Op:  "Connecting to " + queueARN,
					Net: "tcp",
					Err: err,
				}
			}

			return nil, err
		}
	}

	// Load PostgreSQL targets, initialize their respective loggers.
	for accountID, pgN := range serverConfig.Notify.GetPostgreSQL() {
		if !pgN.Enable {
			continue
		}

		if queueARN, err := addQueueTarget(queueTargets, accountID, queueTypePostgreSQL, newPostgreSQLNotify); err != nil {
			if _, ok := err.(net.Error); ok {
				err = &net.OpError{
					Op:  "Connecting to " + queueARN,
					Net: "tcp",
					Err: err,
				}
			}

			return nil, err
		}
	}

	// Load MySQL targets, initialize their respective loggers.
	for accountID, msqlN := range serverConfig.Notify.GetMySQL() {
		if !msqlN.Enable {
			continue
		}

		if queueARN, err := addQueueTarget(queueTargets, accountID, queueTypeMySQL, newMySQLNotify); err != nil {
			if _, ok := err.(net.Error); ok {
				err = &net.OpError{
					Op:  "Connecting to " + queueARN,
					Net: "tcp",
					Err: err,
				}
			}

			return nil, err
		}
	}

	// Load Kafka targets, initialize their respective loggers.
	for accountID, kafkaN := range serverConfig.Notify.GetKafka() {
		if !kafkaN.Enable {
			continue
		}

		if queueARN, err := addQueueTarget(queueTargets, accountID, queueTypeKafka, newKafkaNotify); err != nil {
			if _, ok := err.(net.Error); ok {
				err = &net.OpError{
					Op:  "Connecting to " + queueARN,
					Net: "tcp",
					Err: err,
				}
			}

			return nil, err
		}
	}

	// Successfully initialized queue targets.
	return queueTargets, nil
}

// Global instance of event notification queue.
var globalEventNotifier *eventNotifier

// Initialize event notifier.
func initEventNotifier(objAPI ObjectLayer) error {
	if objAPI == nil {
		return errInvalidArgument
	}

	// Read all saved bucket notifications.
	nConfigs, lConfigs, err := loadAllBucketNotifications(objAPI)
	if err != nil {
		errorIf(err, "Error loading bucket notifications - %v", err)
		return err
	}

	// Initializes all queue targets.
	queueTargets, err := loadAllQueueTargets()
	if err != nil {
		return err
	}

	// Initialize internal listener targets
	listenTargets := make(map[string]*listenerLogger)
	for _, listeners := range lConfigs {
		for _, listener := range listeners {
			ln, err := newListenerLogger(
				listener.TopicConfig.TopicARN,
				listener.TargetServer,
			)
			if err != nil {
				errorIf(err, "Unable to initialize listener target logger.")
				//TODO: improve error
				return fmt.Errorf("Error initializing listner target logger - %v", err)
			}
			listenTargets[listener.TopicConfig.TopicARN] = ln
		}
	}

	// Initialize event notifier queue.
	globalEventNotifier = &eventNotifier{
		external: externalNotifier{
			notificationConfigs: nConfigs,
			targets:             queueTargets,
			rwMutex:             &sync.RWMutex{},
		},
		internal: internalNotifier{
			rwMutex:            &sync.RWMutex{},
			targets:            listenTargets,
			listenerConfigs:    lConfigs,
			connectedListeners: make(map[string]chan []NotificationEvent),
		},
	}

	return nil
}