rename all remaining packages to internal/ (#12418)

This is to ensure that there are no projects
that try to import `minio/minio/pkg` into
their own repo. Any such common packages should
go to `https://github.com/minio/pkg`

internal/event/target/amqp.go

@@ -0,0 +1,311 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"net"
+	"net/url"
+	"os"
+	"path/filepath"
+	"sync"
+
+	"github.com/minio/minio/internal/event"
+	xnet "github.com/minio/minio/internal/net"
+	"github.com/streadway/amqp"
+)
+
+// AMQPArgs - AMQP target arguments.
+type AMQPArgs struct {
+	Enable       bool     `json:"enable"`
+	URL          xnet.URL `json:"url"`
+	Exchange     string   `json:"exchange"`
+	RoutingKey   string   `json:"routingKey"`
+	ExchangeType string   `json:"exchangeType"`
+	DeliveryMode uint8    `json:"deliveryMode"`
+	Mandatory    bool     `json:"mandatory"`
+	Immediate    bool     `json:"immediate"`
+	Durable      bool     `json:"durable"`
+	Internal     bool     `json:"internal"`
+	NoWait       bool     `json:"noWait"`
+	AutoDeleted  bool     `json:"autoDeleted"`
+	QueueDir     string   `json:"queueDir"`
+	QueueLimit   uint64   `json:"queueLimit"`
+}
+
+//lint:file-ignore ST1003 We cannot change these exported names.
+
+// AMQP input constants.
+const (
+	AmqpQueueDir   = "queue_dir"
+	AmqpQueueLimit = "queue_limit"
+
+	AmqpURL               = "url"
+	AmqpExchange          = "exchange"
+	AmqpRoutingKey        = "routing_key"
+	AmqpExchangeType      = "exchange_type"
+	AmqpDeliveryMode      = "delivery_mode"
+	AmqpMandatory         = "mandatory"
+	AmqpImmediate         = "immediate"
+	AmqpDurable           = "durable"
+	AmqpInternal          = "internal"
+	AmqpNoWait            = "no_wait"
+	AmqpAutoDeleted       = "auto_deleted"
+	AmqpArguments         = "arguments"
+	AmqpPublishingHeaders = "publishing_headers"
+
+	EnvAMQPEnable            = "MINIO_NOTIFY_AMQP_ENABLE"
+	EnvAMQPURL               = "MINIO_NOTIFY_AMQP_URL"
+	EnvAMQPExchange          = "MINIO_NOTIFY_AMQP_EXCHANGE"
+	EnvAMQPRoutingKey        = "MINIO_NOTIFY_AMQP_ROUTING_KEY"
+	EnvAMQPExchangeType      = "MINIO_NOTIFY_AMQP_EXCHANGE_TYPE"
+	EnvAMQPDeliveryMode      = "MINIO_NOTIFY_AMQP_DELIVERY_MODE"
+	EnvAMQPMandatory         = "MINIO_NOTIFY_AMQP_MANDATORY"
+	EnvAMQPImmediate         = "MINIO_NOTIFY_AMQP_IMMEDIATE"
+	EnvAMQPDurable           = "MINIO_NOTIFY_AMQP_DURABLE"
+	EnvAMQPInternal          = "MINIO_NOTIFY_AMQP_INTERNAL"
+	EnvAMQPNoWait            = "MINIO_NOTIFY_AMQP_NO_WAIT"
+	EnvAMQPAutoDeleted       = "MINIO_NOTIFY_AMQP_AUTO_DELETED"
+	EnvAMQPArguments         = "MINIO_NOTIFY_AMQP_ARGUMENTS"
+	EnvAMQPPublishingHeaders = "MINIO_NOTIFY_AMQP_PUBLISHING_HEADERS"
+	EnvAMQPQueueDir          = "MINIO_NOTIFY_AMQP_QUEUE_DIR"
+	EnvAMQPQueueLimit        = "MINIO_NOTIFY_AMQP_QUEUE_LIMIT"
+)
+
+// Validate AMQP arguments
+func (a *AMQPArgs) Validate() error {
+	if !a.Enable {
+		return nil
+	}
+	if _, err := amqp.ParseURI(a.URL.String()); err != nil {
+		return err
+	}
+	if a.QueueDir != "" {
+		if !filepath.IsAbs(a.QueueDir) {
+			return errors.New("queueDir path should be absolute")
+		}
+	}
+
+	return nil
+}
+
+// AMQPTarget - AMQP target
+type AMQPTarget struct {
+	id         event.TargetID
+	args       AMQPArgs
+	conn       *amqp.Connection
+	connMutex  sync.Mutex
+	store      Store
+	loggerOnce func(ctx context.Context, err error, id interface{}, errKind ...interface{})
+}
+
+// ID - returns TargetID.
+func (target *AMQPTarget) ID() event.TargetID {
+	return target.id
+}
+
+// IsActive - Return true if target is up and active
+func (target *AMQPTarget) IsActive() (bool, error) {
+	ch, err := target.channel()
+	if err != nil {
+		return false, err
+	}
+	defer func() {
+		ch.Close()
+	}()
+	return true, nil
+}
+
+// HasQueueStore - Checks if the queueStore has been configured for the target
+func (target *AMQPTarget) HasQueueStore() bool {
+	return target.store != nil
+}
+
+func (target *AMQPTarget) channel() (*amqp.Channel, error) {
+	var err error
+	var conn *amqp.Connection
+	var ch *amqp.Channel
+
+	isAMQPClosedErr := func(err error) bool {
+		if err == amqp.ErrClosed {
+			return true
+		}
+
+		if nerr, ok := err.(*net.OpError); ok {
+			return (nerr.Err.Error() == "use of closed network connection")
+		}
+
+		return false
+	}
+
+	target.connMutex.Lock()
+	defer target.connMutex.Unlock()
+
+	if target.conn != nil {
+		ch, err = target.conn.Channel()
+		if err == nil {
+			return ch, nil
+		}
+
+		if !isAMQPClosedErr(err) {
+			return nil, err
+		}
+	}
+
+	conn, err = amqp.Dial(target.args.URL.String())
+	if err != nil {
+		if IsConnRefusedErr(err) {
+			return nil, errNotConnected
+		}
+		return nil, err
+	}
+
+	ch, err = conn.Channel()
+	if err != nil {
+		return nil, err
+	}
+
+	target.conn = conn
+
+	return ch, nil
+}
+
+// send - sends an event to the AMQP.
+func (target *AMQPTarget) send(eventData event.Event, ch *amqp.Channel) error {
+	objectName, err := url.QueryUnescape(eventData.S3.Object.Key)
+	if err != nil {
+		return err
+	}
+	key := eventData.S3.Bucket.Name + "/" + objectName
+
+	data, err := json.Marshal(event.Log{EventName: eventData.EventName, Key: key, Records: []event.Event{eventData}})
+	if err != nil {
+		return err
+	}
+
+	if err = ch.ExchangeDeclare(target.args.Exchange, target.args.ExchangeType, target.args.Durable,
+		target.args.AutoDeleted, target.args.Internal, target.args.NoWait, nil); err != nil {
+		return err
+	}
+
+	return ch.Publish(target.args.Exchange, target.args.RoutingKey, target.args.Mandatory,
+		target.args.Immediate, amqp.Publishing{
+			ContentType:  "application/json",
+			DeliveryMode: target.args.DeliveryMode,
+			Body:         data,
+		})
+}
+
+// Save - saves the events to the store which will be replayed when the amqp connection is active.
+func (target *AMQPTarget) Save(eventData event.Event) error {
+	if target.store != nil {
+		return target.store.Put(eventData)
+	}
+	ch, err := target.channel()
+	if err != nil {
+		return err
+	}
+	defer func() {
+		cErr := ch.Close()
+		target.loggerOnce(context.Background(), cErr, target.ID())
+	}()
+
+	return target.send(eventData, ch)
+}
+
+// Send - sends event to AMQP.
+func (target *AMQPTarget) Send(eventKey string) error {
+	ch, err := target.channel()
+	if err != nil {
+		return err
+	}
+	defer func() {
+		cErr := ch.Close()
+		target.loggerOnce(context.Background(), cErr, target.ID())
+	}()
+
+	eventData, eErr := target.store.Get(eventKey)
+	if eErr != nil {
+		// The last event key in a successful batch will be sent in the channel atmost once by the replayEvents()
+		// Such events will not exist and wouldve been already been sent successfully.
+		if os.IsNotExist(eErr) {
+			return nil
+		}
+		return eErr
+	}
+
+	if err := target.send(eventData, ch); err != nil {
+		return err
+	}
+
+	// Delete the event from store.
+	return target.store.Del(eventKey)
+}
+
+// Close - does nothing and available for interface compatibility.
+func (target *AMQPTarget) Close() error {
+	if target.conn != nil {
+		return target.conn.Close()
+	}
+	return nil
+}
+
+// NewAMQPTarget - creates new AMQP target.
+func NewAMQPTarget(id string, args AMQPArgs, doneCh <-chan struct{}, loggerOnce func(ctx context.Context, err error, id interface{}, errKind ...interface{}), test bool) (*AMQPTarget, error) {
+	var conn *amqp.Connection
+	var err error
+
+	var store Store
+
+	target := &AMQPTarget{
+		id:         event.TargetID{ID: id, Name: "amqp"},
+		args:       args,
+		loggerOnce: loggerOnce,
+	}
+
+	if args.QueueDir != "" {
+		queueDir := filepath.Join(args.QueueDir, storePrefix+"-amqp-"+id)
+		store = NewQueueStore(queueDir, args.QueueLimit)
+		if oErr := store.Open(); oErr != nil {
+			target.loggerOnce(context.Background(), oErr, target.ID())
+			return target, oErr
+		}
+		target.store = store
+	}
+
+	conn, err = amqp.Dial(args.URL.String())
+	if err != nil {
+		if store == nil || !(IsConnRefusedErr(err) || IsConnResetErr(err)) {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+	}
+	target.conn = conn
+
+	if target.store != nil && !test {
+		// Replays the events from the store.
+		eventKeyCh := replayEvents(target.store, doneCh, target.loggerOnce, target.ID())
+
+		// Start replaying events from the store.
+		go sendEvents(target, eventKeyCh, doneCh, target.loggerOnce)
+	}
+
+	return target, nil
+}

internal/event/target/common.go

@@ -0,0 +1,29 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import "github.com/google/uuid"
+
+func getNewUUID() (string, error) {
+	u, err := uuid.NewRandom()
+	if err != nil {
+		return "", err
+	}
+
+	return u.String(), nil
+}

internal/event/target/elasticsearch.go

@@ -0,0 +1,649 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"bytes"
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/minio/minio/internal/event"
+	xnet "github.com/minio/minio/internal/net"
+	"github.com/pkg/errors"
+
+	elasticsearch7 "github.com/elastic/go-elasticsearch/v7"
+	"github.com/minio/highwayhash"
+	"github.com/olivere/elastic/v7"
+)
+
+// Elastic constants
+const (
+	ElasticFormat     = "format"
+	ElasticURL        = "url"
+	ElasticIndex      = "index"
+	ElasticQueueDir   = "queue_dir"
+	ElasticQueueLimit = "queue_limit"
+	ElasticUsername   = "username"
+	ElasticPassword   = "password"
+
+	EnvElasticEnable     = "MINIO_NOTIFY_ELASTICSEARCH_ENABLE"
+	EnvElasticFormat     = "MINIO_NOTIFY_ELASTICSEARCH_FORMAT"
+	EnvElasticURL        = "MINIO_NOTIFY_ELASTICSEARCH_URL"
+	EnvElasticIndex      = "MINIO_NOTIFY_ELASTICSEARCH_INDEX"
+	EnvElasticQueueDir   = "MINIO_NOTIFY_ELASTICSEARCH_QUEUE_DIR"
+	EnvElasticQueueLimit = "MINIO_NOTIFY_ELASTICSEARCH_QUEUE_LIMIT"
+	EnvElasticUsername   = "MINIO_NOTIFY_ELASTICSEARCH_USERNAME"
+	EnvElasticPassword   = "MINIO_NOTIFY_ELASTICSEARCH_PASSWORD"
+)
+
+// ESSupportStatus is a typed string representing the support status for
+// Elasticsearch
+type ESSupportStatus string
+
+const (
+	// ESSUnknown is default value
+	ESSUnknown ESSupportStatus = "ESSUnknown"
+	// ESSDeprecated -> support will be removed in future
+	ESSDeprecated ESSupportStatus = "ESSDeprecated"
+	// ESSUnsupported -> we wont work with this ES server
+	ESSUnsupported ESSupportStatus = "ESSUnsupported"
+	// ESSSupported -> all good!
+	ESSSupported ESSupportStatus = "ESSSupported"
+)
+
+func getESVersionSupportStatus(version string) (res ESSupportStatus, err error) {
+	parts := strings.Split(version, ".")
+	if len(parts) < 1 {
+		err = fmt.Errorf("bad ES version string: %s", version)
+		return
+	}
+
+	majorVersion, err := strconv.Atoi(parts[0])
+	if err != nil {
+		err = fmt.Errorf("bad ES version string: %s", version)
+		return
+	}
+
+	switch {
+	case majorVersion <= 4:
+		res = ESSUnsupported
+	case majorVersion <= 6:
+		res = ESSDeprecated
+	default:
+		res = ESSSupported
+	}
+	return
+}
+
+// magic HH-256 key as HH-256 hash of the first 100 decimals of π as utf-8 string with a zero key.
+var magicHighwayHash256Key = []byte("\x4b\xe7\x34\xfa\x8e\x23\x8a\xcd\x26\x3e\x83\xe6\xbb\x96\x85\x52\x04\x0f\x93\x5d\xa3\x9f\x44\x14\x97\xe0\x9d\x13\x22\xde\x36\xa0")
+
+// Interface for elasticsearch client objects
+type esClient interface {
+	isAtleastV7() bool
+	createIndex(ElasticsearchArgs) error
+	ping(context.Context, ElasticsearchArgs) (bool, error)
+	stop()
+
+	entryExists(context.Context, string, string) (bool, error)
+	removeEntry(context.Context, string, string) error
+	updateEntry(context.Context, string, string, event.Event) error
+	addEntry(context.Context, string, event.Event) error
+}
+
+// ElasticsearchArgs - Elasticsearch target arguments.
+type ElasticsearchArgs struct {
+	Enable     bool            `json:"enable"`
+	Format     string          `json:"format"`
+	URL        xnet.URL        `json:"url"`
+	Index      string          `json:"index"`
+	QueueDir   string          `json:"queueDir"`
+	QueueLimit uint64          `json:"queueLimit"`
+	Transport  *http.Transport `json:"-"`
+	Username   string          `json:"username"`
+	Password   string          `json:"password"`
+}
+
+// Validate ElasticsearchArgs fields
+func (a ElasticsearchArgs) Validate() error {
+	if !a.Enable {
+		return nil
+	}
+	if a.URL.IsEmpty() {
+		return errors.New("empty URL")
+	}
+	if a.Format != "" {
+		f := strings.ToLower(a.Format)
+		if f != event.NamespaceFormat && f != event.AccessFormat {
+			return errors.New("format value unrecognized")
+		}
+	}
+	if a.Index == "" {
+		return errors.New("empty index value")
+	}
+
+	if (a.Username == "" && a.Password != "") || (a.Username != "" && a.Password == "") {
+		return errors.New("username and password should be set in pairs")
+	}
+
+	return nil
+}
+
+// ElasticsearchTarget - Elasticsearch target.
+type ElasticsearchTarget struct {
+	id         event.TargetID
+	args       ElasticsearchArgs
+	client     esClient
+	store      Store
+	loggerOnce func(ctx context.Context, err error, id interface{}, errKind ...interface{})
+}
+
+// ID - returns target ID.
+func (target *ElasticsearchTarget) ID() event.TargetID {
+	return target.id
+}
+
+// HasQueueStore - Checks if the queueStore has been configured for the target
+func (target *ElasticsearchTarget) HasQueueStore() bool {
+	return target.store != nil
+}
+
+// IsActive - Return true if target is up and active
+func (target *ElasticsearchTarget) IsActive() (bool, error) {
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	err := target.checkAndInitClient(ctx)
+	if err != nil {
+		return false, err
+	}
+	return target.client.ping(ctx, target.args)
+}
+
+// Save - saves the events to the store if queuestore is configured, which will be replayed when the elasticsearch connection is active.
+func (target *ElasticsearchTarget) Save(eventData event.Event) error {
+	if target.store != nil {
+		return target.store.Put(eventData)
+	}
+	err := target.send(eventData)
+	if elastic.IsConnErr(err) || elastic.IsContextErr(err) || xnet.IsNetworkOrHostDown(err, false) {
+		return errNotConnected
+	}
+	return err
+}
+
+// send - sends the event to the target.
+func (target *ElasticsearchTarget) send(eventData event.Event) error {
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	if target.args.Format == event.NamespaceFormat {
+		objectName, err := url.QueryUnescape(eventData.S3.Object.Key)
+		if err != nil {
+			return err
+		}
+
+		// Calculate a hash of the key for the id of the ES document.
+		// Id's are limited to 512 bytes in V7+, so we need to do this.
+		var keyHash string
+		{
+			key := eventData.S3.Bucket.Name + "/" + objectName
+			if target.client.isAtleastV7() {
+				hh, _ := highwayhash.New(magicHighwayHash256Key) // New will never return error since key is 256 bit
+				hh.Write([]byte(key))
+				hashBytes := hh.Sum(nil)
+				keyHash = base64.URLEncoding.EncodeToString(hashBytes)
+			} else {
+				keyHash = key
+			}
+		}
+
+		if eventData.EventName == event.ObjectRemovedDelete {
+			err = target.client.removeEntry(ctx, target.args.Index, keyHash)
+		} else {
+			err = target.client.updateEntry(ctx, target.args.Index, keyHash, eventData)
+		}
+		return err
+	}
+
+	if target.args.Format == event.AccessFormat {
+		return target.client.addEntry(ctx, target.args.Index, eventData)
+	}
+
+	return nil
+}
+
+// Send - reads an event from store and sends it to Elasticsearch.
+func (target *ElasticsearchTarget) Send(eventKey string) error {
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	err := target.checkAndInitClient(ctx)
+	if err != nil {
+		return err
+	}
+
+	eventData, eErr := target.store.Get(eventKey)
+	if eErr != nil {
+		// The last event key in a successful batch will be sent in the channel atmost once by the replayEvents()
+		// Such events will not exist and wouldve been already been sent successfully.
+		if os.IsNotExist(eErr) {
+			return nil
+		}
+		return eErr
+	}
+
+	if err := target.send(eventData); err != nil {
+		if elastic.IsConnErr(err) || elastic.IsContextErr(err) || xnet.IsNetworkOrHostDown(err, false) {
+			return errNotConnected
+		}
+		return err
+	}
+
+	// Delete the event from store.
+	return target.store.Del(eventKey)
+}
+
+// Close - does nothing and available for interface compatibility.
+func (target *ElasticsearchTarget) Close() error {
+	if target.client != nil {
+		// Stops the background processes that the client is running.
+		target.client.stop()
+	}
+	return nil
+}
+
+func (target *ElasticsearchTarget) checkAndInitClient(ctx context.Context) error {
+	if target.client != nil {
+		return nil
+	}
+
+	clientV7, err := newClientV7(target.args)
+	if err != nil {
+		return err
+	}
+
+	// Check es version to confirm if it is supported.
+	serverSupportStatus, version, err := clientV7.getServerSupportStatus(ctx)
+	if err != nil {
+		return err
+	}
+
+	switch serverSupportStatus {
+	case ESSUnknown:
+		return errors.New("unable to determine support status of ES (should not happen)")
+
+	case ESSDeprecated:
+		fmt.Printf("DEPRECATION WARNING: Support for Elasticsearch version '%s' will be dropped in a future release. Please upgrade to a version >= 7.x.", version)
+		target.client, err = newClientV56(target.args)
+		if err != nil {
+			return err
+		}
+
+	case ESSSupported:
+		target.client = clientV7
+
+	default:
+		// ESSUnsupported case
+		return fmt.Errorf("Elasticsearch version '%s' is not supported! Please use at least version 7.x.", version)
+	}
+
+	target.client.createIndex(target.args)
+	return nil
+}
+
+// NewElasticsearchTarget - creates new Elasticsearch target.
+func NewElasticsearchTarget(id string, args ElasticsearchArgs, doneCh <-chan struct{}, loggerOnce func(ctx context.Context, err error, id interface{}, kind ...interface{}), test bool) (*ElasticsearchTarget, error) {
+	target := &ElasticsearchTarget{
+		id:         event.TargetID{ID: id, Name: "elasticsearch"},
+		args:       args,
+		loggerOnce: loggerOnce,
+	}
+
+	if args.QueueDir != "" {
+		queueDir := filepath.Join(args.QueueDir, storePrefix+"-elasticsearch-"+id)
+		target.store = NewQueueStore(queueDir, args.QueueLimit)
+		if err := target.store.Open(); err != nil {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	err := target.checkAndInitClient(ctx)
+	if err != nil {
+		if target.store == nil || err != errNotConnected {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+	}
+
+	if target.store != nil && !test {
+		// Replays the events from the store.
+		eventKeyCh := replayEvents(target.store, doneCh, target.loggerOnce, target.ID())
+		// Start replaying events from the store.
+		go sendEvents(target, eventKeyCh, doneCh, target.loggerOnce)
+	}
+
+	return target, nil
+}
+
+// ES Client definitions and methods
+
+type esClientV7 struct {
+	*elasticsearch7.Client
+}
+
+func newClientV7(args ElasticsearchArgs) (*esClientV7, error) {
+	// Client options
+	elasticConfig := elasticsearch7.Config{
+		Addresses:  []string{args.URL.String()},
+		Transport:  args.Transport,
+		MaxRetries: 10,
+	}
+	// Set basic auth
+	if args.Username != "" && args.Password != "" {
+		elasticConfig.Username = args.Username
+		elasticConfig.Password = args.Password
+	}
+	// Create a client
+	client, err := elasticsearch7.NewClient(elasticConfig)
+	if err != nil {
+		return nil, err
+	}
+	clientV7 := &esClientV7{client}
+	return clientV7, nil
+}
+
+func (c *esClientV7) getServerSupportStatus(ctx context.Context) (ESSupportStatus, string, error) {
+	resp, err := c.Info(
+		c.Info.WithContext(ctx),
+	)
+	if err != nil {
+		return ESSUnknown, "", errNotConnected
+	}
+
+	defer resp.Body.Close()
+
+	m := make(map[string]interface{})
+	err = json.NewDecoder(resp.Body).Decode(&m)
+	if err != nil {
+		return ESSUnknown, "", fmt.Errorf("unable to get ES Server version - json parse error: %v", err)
+	}
+
+	if v, ok := m["version"].(map[string]interface{}); ok {
+		if ver, ok := v["number"].(string); ok {
+			status, err := getESVersionSupportStatus(ver)
+			return status, ver, err
+		}
+	}
+	return ESSUnknown, "", fmt.Errorf("Unable to get ES Server Version - got INFO response: %v", m)
+
+}
+
+func (c *esClientV7) isAtleastV7() bool {
+	return true
+}
+
+// createIndex - creates the index if it does not exist.
+func (c *esClientV7) createIndex(args ElasticsearchArgs) error {
+	res, err := c.Indices.ResolveIndex([]string{args.Index})
+	if err != nil {
+		return err
+	}
+	defer res.Body.Close()
+
+	var v map[string]interface{}
+	found := false
+	if err := json.NewDecoder(res.Body).Decode(&v); err != nil {
+		return fmt.Errorf("Error parsing response body: %v", err)
+	}
+
+	indices := v["indices"].([]interface{})
+	for _, index := range indices {
+		name := index.(map[string]interface{})["name"]
+		if name == args.Index {
+			found = true
+			break
+		}
+	}
+
+	if !found {
+		resp, err := c.Indices.Create(args.Index)
+		if err != nil {
+			return err
+		}
+		defer resp.Body.Close()
+		if resp.IsError() {
+			err := fmt.Errorf("Create index err: %s", res.String())
+			return err
+		}
+		io.Copy(ioutil.Discard, resp.Body)
+		return nil
+	}
+	return nil
+}
+
+func (c *esClientV7) ping(ctx context.Context, _ ElasticsearchArgs) (bool, error) {
+	resp, err := c.Ping(
+		c.Ping.WithContext(ctx),
+	)
+	if err != nil {
+		return false, errNotConnected
+	}
+	io.Copy(ioutil.Discard, resp.Body)
+	resp.Body.Close()
+	return !resp.IsError(), nil
+}
+
+func (c *esClientV7) entryExists(ctx context.Context, index string, key string) (bool, error) {
+	res, err := c.Exists(
+		index,
+		key,
+		c.Exists.WithContext(ctx),
+	)
+	if err != nil {
+		return false, err
+	}
+	io.Copy(ioutil.Discard, res.Body)
+	res.Body.Close()
+	return !res.IsError(), nil
+}
+
+func (c *esClientV7) removeEntry(ctx context.Context, index string, key string) error {
+	exists, err := c.entryExists(ctx, index, key)
+	if err == nil && exists {
+		res, err := c.Delete(
+			index,
+			key,
+			c.Delete.WithContext(ctx),
+		)
+		if err != nil {
+			return err
+		}
+		defer res.Body.Close()
+		if res.IsError() {
+			err := fmt.Errorf("Delete err: %s", res.String())
+			return err
+		}
+		io.Copy(ioutil.Discard, res.Body)
+		return nil
+	}
+	return err
+}
+
+func (c *esClientV7) updateEntry(ctx context.Context, index string, key string, eventData event.Event) error {
+	doc := map[string]interface{}{
+		"Records": []event.Event{eventData},
+	}
+	var buf bytes.Buffer
+	enc := json.NewEncoder(&buf)
+	err := enc.Encode(doc)
+	if err != nil {
+		return err
+	}
+	res, err := c.Index(
+		index,
+		&buf,
+		c.Index.WithDocumentID(key),
+		c.Index.WithContext(ctx),
+	)
+	if err != nil {
+		return err
+	}
+	defer res.Body.Close()
+	if res.IsError() {
+		err := fmt.Errorf("Update err: %s", res.String())
+		return err
+	}
+	io.Copy(ioutil.Discard, res.Body)
+	return nil
+}
+
+func (c *esClientV7) addEntry(ctx context.Context, index string, eventData event.Event) error {
+	doc := map[string]interface{}{
+		"Records": []event.Event{eventData},
+	}
+	var buf bytes.Buffer
+	enc := json.NewEncoder(&buf)
+	err := enc.Encode(doc)
+	if err != nil {
+		return err
+	}
+	res, err := c.Index(
+		index,
+		&buf,
+		c.Index.WithContext(ctx),
+	)
+	if err != nil {
+		return err
+	}
+	defer res.Body.Close()
+	if res.IsError() {
+		err := fmt.Errorf("Add err: %s", res.String())
+		return err
+	}
+	io.Copy(ioutil.Discard, res.Body)
+	return nil
+}
+
+func (c *esClientV7) stop() {
+}
+
+// For versions under 7
+type esClientV56 struct {
+	*elastic.Client
+}
+
+func newClientV56(args ElasticsearchArgs) (*esClientV56, error) {
+	// Client options
+	options := []elastic.ClientOptionFunc{elastic.SetURL(args.URL.String()),
+		elastic.SetMaxRetries(10),
+		elastic.SetSniff(false),
+		elastic.SetHttpClient(&http.Client{Transport: args.Transport})}
+	// Set basic auth
+	if args.Username != "" && args.Password != "" {
+		options = append(options, elastic.SetBasicAuth(args.Username, args.Password))
+	}
+	// Create a client
+	client, err := elastic.NewClient(options...)
+	if err != nil {
+		// https://github.com/olivere/elastic/wiki/Connection-Errors
+		if elastic.IsConnErr(err) || elastic.IsContextErr(err) || xnet.IsNetworkOrHostDown(err, false) {
+			return nil, errNotConnected
+		}
+		return nil, err
+	}
+	return &esClientV56{client}, nil
+}
+
+func (c *esClientV56) isAtleastV7() bool {
+	return false
+}
+
+// createIndex - creates the index if it does not exist.
+func (c *esClientV56) createIndex(args ElasticsearchArgs) error {
+	exists, err := c.IndexExists(args.Index).Do(context.Background())
+	if err != nil {
+		return err
+	}
+	if !exists {
+		var createIndex *elastic.IndicesCreateResult
+		if createIndex, err = c.CreateIndex(args.Index).Do(context.Background()); err != nil {
+			return err
+		}
+
+		if !createIndex.Acknowledged {
+			return fmt.Errorf("index %v not created", args.Index)
+		}
+	}
+	return nil
+}
+
+func (c *esClientV56) ping(ctx context.Context, args ElasticsearchArgs) (bool, error) {
+	_, code, err := c.Ping(args.URL.String()).HttpHeadOnly(true).Do(ctx)
+	if err != nil {
+		if elastic.IsConnErr(err) || elastic.IsContextErr(err) || xnet.IsNetworkOrHostDown(err, false) {
+			return false, errNotConnected
+		}
+		return false, err
+	}
+	return !(code >= http.StatusBadRequest), nil
+
+}
+
+func (c *esClientV56) entryExists(ctx context.Context, index string, key string) (bool, error) {
+	return c.Exists().Index(index).Type("event").Id(key).Do(ctx)
+}
+
+func (c *esClientV56) removeEntry(ctx context.Context, index string, key string) error {
+	exists, err := c.entryExists(ctx, index, key)
+	if err == nil && exists {
+		_, err = c.Delete().Index(index).Type("event").Id(key).Do(ctx)
+	}
+	return err
+
+}
+
+func (c *esClientV56) updateEntry(ctx context.Context, index string, key string, eventData event.Event) error {
+	_, err := c.Index().Index(index).Type("event").BodyJson(map[string]interface{}{"Records": []event.Event{eventData}}).Id(key).Do(ctx)
+	return err
+}
+
+func (c *esClientV56) addEntry(ctx context.Context, index string, eventData event.Event) error {
+	_, err := c.Index().Index(index).Type("event").BodyJson(map[string]interface{}{"Records": []event.Event{eventData}}).Do(ctx)
+	return err
+
+}
+
+func (c *esClientV56) stop() {
+	c.Stop()
+}

internal/event/target/kafka.go

@@ -0,0 +1,331 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"context"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/json"
+	"errors"
+	"net"
+	"net/url"
+	"os"
+	"path/filepath"
+
+	"github.com/minio/minio/internal/event"
+	xnet "github.com/minio/minio/internal/net"
+
+	sarama "github.com/Shopify/sarama"
+	saramatls "github.com/Shopify/sarama/tools/tls"
+)
+
+// Kafka input constants
+const (
+	KafkaBrokers       = "brokers"
+	KafkaTopic         = "topic"
+	KafkaQueueDir      = "queue_dir"
+	KafkaQueueLimit    = "queue_limit"
+	KafkaTLS           = "tls"
+	KafkaTLSSkipVerify = "tls_skip_verify"
+	KafkaTLSClientAuth = "tls_client_auth"
+	KafkaSASL          = "sasl"
+	KafkaSASLUsername  = "sasl_username"
+	KafkaSASLPassword  = "sasl_password"
+	KafkaSASLMechanism = "sasl_mechanism"
+	KafkaClientTLSCert = "client_tls_cert"
+	KafkaClientTLSKey  = "client_tls_key"
+	KafkaVersion       = "version"
+
+	EnvKafkaEnable        = "MINIO_NOTIFY_KAFKA_ENABLE"
+	EnvKafkaBrokers       = "MINIO_NOTIFY_KAFKA_BROKERS"
+	EnvKafkaTopic         = "MINIO_NOTIFY_KAFKA_TOPIC"
+	EnvKafkaQueueDir      = "MINIO_NOTIFY_KAFKA_QUEUE_DIR"
+	EnvKafkaQueueLimit    = "MINIO_NOTIFY_KAFKA_QUEUE_LIMIT"
+	EnvKafkaTLS           = "MINIO_NOTIFY_KAFKA_TLS"
+	EnvKafkaTLSSkipVerify = "MINIO_NOTIFY_KAFKA_TLS_SKIP_VERIFY"
+	EnvKafkaTLSClientAuth = "MINIO_NOTIFY_KAFKA_TLS_CLIENT_AUTH"
+	EnvKafkaSASLEnable    = "MINIO_NOTIFY_KAFKA_SASL"
+	EnvKafkaSASLUsername  = "MINIO_NOTIFY_KAFKA_SASL_USERNAME"
+	EnvKafkaSASLPassword  = "MINIO_NOTIFY_KAFKA_SASL_PASSWORD"
+	EnvKafkaSASLMechanism = "MINIO_NOTIFY_KAFKA_SASL_MECHANISM"
+	EnvKafkaClientTLSCert = "MINIO_NOTIFY_KAFKA_CLIENT_TLS_CERT"
+	EnvKafkaClientTLSKey  = "MINIO_NOTIFY_KAFKA_CLIENT_TLS_KEY"
+	EnvKafkaVersion       = "MINIO_NOTIFY_KAFKA_VERSION"
+)
+
+// KafkaArgs - Kafka target arguments.
+type KafkaArgs struct {
+	Enable     bool        `json:"enable"`
+	Brokers    []xnet.Host `json:"brokers"`
+	Topic      string      `json:"topic"`
+	QueueDir   string      `json:"queueDir"`
+	QueueLimit uint64      `json:"queueLimit"`
+	Version    string      `json:"version"`
+	TLS        struct {
+		Enable        bool               `json:"enable"`
+		RootCAs       *x509.CertPool     `json:"-"`
+		SkipVerify    bool               `json:"skipVerify"`
+		ClientAuth    tls.ClientAuthType `json:"clientAuth"`
+		ClientTLSCert string             `json:"clientTLSCert"`
+		ClientTLSKey  string             `json:"clientTLSKey"`
+	} `json:"tls"`
+	SASL struct {
+		Enable    bool   `json:"enable"`
+		User      string `json:"username"`
+		Password  string `json:"password"`
+		Mechanism string `json:"mechanism"`
+	} `json:"sasl"`
+}
+
+// Validate KafkaArgs fields
+func (k KafkaArgs) Validate() error {
+	if !k.Enable {
+		return nil
+	}
+	if len(k.Brokers) == 0 {
+		return errors.New("no broker address found")
+	}
+	for _, b := range k.Brokers {
+		if _, err := xnet.ParseHost(b.String()); err != nil {
+			return err
+		}
+	}
+	if k.QueueDir != "" {
+		if !filepath.IsAbs(k.QueueDir) {
+			return errors.New("queueDir path should be absolute")
+		}
+	}
+	if k.Version != "" {
+		if _, err := sarama.ParseKafkaVersion(k.Version); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// KafkaTarget - Kafka target.
+type KafkaTarget struct {
+	id         event.TargetID
+	args       KafkaArgs
+	producer   sarama.SyncProducer
+	config     *sarama.Config
+	store      Store
+	loggerOnce func(ctx context.Context, err error, id interface{}, errKind ...interface{})
+}
+
+// ID - returns target ID.
+func (target *KafkaTarget) ID() event.TargetID {
+	return target.id
+}
+
+// HasQueueStore - Checks if the queueStore has been configured for the target
+func (target *KafkaTarget) HasQueueStore() bool {
+	return target.store != nil
+}
+
+// IsActive - Return true if target is up and active
+func (target *KafkaTarget) IsActive() (bool, error) {
+	if !target.args.pingBrokers() {
+		return false, errNotConnected
+	}
+	return true, nil
+}
+
+// Save - saves the events to the store which will be replayed when the Kafka connection is active.
+func (target *KafkaTarget) Save(eventData event.Event) error {
+	if target.store != nil {
+		return target.store.Put(eventData)
+	}
+	_, err := target.IsActive()
+	if err != nil {
+		return err
+	}
+	return target.send(eventData)
+}
+
+// send - sends an event to the kafka.
+func (target *KafkaTarget) send(eventData event.Event) error {
+	if target.producer == nil {
+		return errNotConnected
+	}
+	objectName, err := url.QueryUnescape(eventData.S3.Object.Key)
+	if err != nil {
+		return err
+	}
+	key := eventData.S3.Bucket.Name + "/" + objectName
+
+	data, err := json.Marshal(event.Log{EventName: eventData.EventName, Key: key, Records: []event.Event{eventData}})
+	if err != nil {
+		return err
+	}
+
+	msg := sarama.ProducerMessage{
+		Topic: target.args.Topic,
+		Key:   sarama.StringEncoder(key),
+		Value: sarama.ByteEncoder(data),
+	}
+
+	_, _, err = target.producer.SendMessage(&msg)
+
+	return err
+}
+
+// Send - reads an event from store and sends it to Kafka.
+func (target *KafkaTarget) Send(eventKey string) error {
+	var err error
+	_, err = target.IsActive()
+	if err != nil {
+		return err
+	}
+
+	if target.producer == nil {
+		brokers := []string{}
+		for _, broker := range target.args.Brokers {
+			brokers = append(brokers, broker.String())
+		}
+		target.producer, err = sarama.NewSyncProducer(brokers, target.config)
+		if err != nil {
+			if err != sarama.ErrOutOfBrokers {
+				return err
+			}
+			return errNotConnected
+		}
+	}
+
+	eventData, eErr := target.store.Get(eventKey)
+	if eErr != nil {
+		// The last event key in a successful batch will be sent in the channel atmost once by the replayEvents()
+		// Such events will not exist and wouldve been already been sent successfully.
+		if os.IsNotExist(eErr) {
+			return nil
+		}
+		return eErr
+	}
+
+	err = target.send(eventData)
+	if err != nil {
+		// Sarama opens the ciruit breaker after 3 consecutive connection failures.
+		if err == sarama.ErrLeaderNotAvailable || err.Error() == "circuit breaker is open" {
+			return errNotConnected
+		}
+		return err
+	}
+
+	// Delete the event from store.
+	return target.store.Del(eventKey)
+}
+
+// Close - closes underneath kafka connection.
+func (target *KafkaTarget) Close() error {
+	if target.producer != nil {
+		return target.producer.Close()
+	}
+	return nil
+}
+
+// Check if atleast one broker in cluster is active
+func (k KafkaArgs) pingBrokers() bool {
+
+	for _, broker := range k.Brokers {
+		_, dErr := net.Dial("tcp", broker.String())
+		if dErr == nil {
+			return true
+		}
+	}
+	return false
+}
+
+// NewKafkaTarget - creates new Kafka target with auth credentials.
+func NewKafkaTarget(id string, args KafkaArgs, doneCh <-chan struct{}, loggerOnce func(ctx context.Context, err error, id interface{}, kind ...interface{}), test bool) (*KafkaTarget, error) {
+	config := sarama.NewConfig()
+
+	target := &KafkaTarget{
+		id:         event.TargetID{ID: id, Name: "kafka"},
+		args:       args,
+		loggerOnce: loggerOnce,
+	}
+
+	if args.Version != "" {
+		kafkaVersion, err := sarama.ParseKafkaVersion(args.Version)
+		if err != nil {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+		config.Version = kafkaVersion
+	}
+
+	config.Net.SASL.User = args.SASL.User
+	config.Net.SASL.Password = args.SASL.Password
+	initScramClient(args, config) // initializes configured scram client.
+	config.Net.SASL.Enable = args.SASL.Enable
+
+	tlsConfig, err := saramatls.NewConfig(args.TLS.ClientTLSCert, args.TLS.ClientTLSKey)
+
+	if err != nil {
+		target.loggerOnce(context.Background(), err, target.ID())
+		return target, err
+	}
+
+	config.Net.TLS.Enable = args.TLS.Enable
+	config.Net.TLS.Config = tlsConfig
+	config.Net.TLS.Config.InsecureSkipVerify = args.TLS.SkipVerify
+	config.Net.TLS.Config.ClientAuth = args.TLS.ClientAuth
+	config.Net.TLS.Config.RootCAs = args.TLS.RootCAs
+
+	config.Producer.RequiredAcks = sarama.WaitForAll
+	config.Producer.Retry.Max = 10
+	config.Producer.Return.Successes = true
+
+	target.config = config
+
+	brokers := []string{}
+	for _, broker := range args.Brokers {
+		brokers = append(brokers, broker.String())
+	}
+
+	var store Store
+
+	if args.QueueDir != "" {
+		queueDir := filepath.Join(args.QueueDir, storePrefix+"-kafka-"+id)
+		store = NewQueueStore(queueDir, args.QueueLimit)
+		if oErr := store.Open(); oErr != nil {
+			target.loggerOnce(context.Background(), oErr, target.ID())
+			return target, oErr
+		}
+		target.store = store
+	}
+
+	producer, err := sarama.NewSyncProducer(brokers, config)
+	if err != nil {
+		if store == nil || err != sarama.ErrOutOfBrokers {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+	}
+	target.producer = producer
+
+	if target.store != nil && !test {
+		// Replays the events from the store.
+		eventKeyCh := replayEvents(target.store, doneCh, target.loggerOnce, target.ID())
+		// Start replaying events from the store.
+		go sendEvents(target, eventKeyCh, doneCh, target.loggerOnce)
+	}
+
+	return target, nil
+}

internal/event/target/kafka_scram_client_contrib.go

@@ -0,0 +1,83 @@
+/*
+ * MinIO Object Storage (c) 2021 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 target
+
+import (
+	"crypto/sha256"
+	"crypto/sha512"
+
+	"github.com/Shopify/sarama"
+	"github.com/xdg/scram"
+)
+
+func initScramClient(args KafkaArgs, config *sarama.Config) {
+	if args.SASL.Mechanism == "sha512" {
+		config.Net.SASL.SCRAMClientGeneratorFunc = func() sarama.SCRAMClient { return &XDGSCRAMClient{HashGeneratorFcn: KafkaSHA512} }
+		config.Net.SASL.Mechanism = sarama.SASLMechanism(sarama.SASLTypeSCRAMSHA512)
+	} else if args.SASL.Mechanism == "sha256" {
+		config.Net.SASL.SCRAMClientGeneratorFunc = func() sarama.SCRAMClient { return &XDGSCRAMClient{HashGeneratorFcn: KafkaSHA256} }
+		config.Net.SASL.Mechanism = sarama.SASLMechanism(sarama.SASLTypeSCRAMSHA256)
+	} else {
+		// default to PLAIN
+		config.Net.SASL.Mechanism = sarama.SASLMechanism(sarama.SASLTypePlaintext)
+	}
+}
+
+// KafkaSHA256 is a function that returns a crypto/sha256 hasher and should be used
+// to create Client objects configured for SHA-256 hashing.
+var KafkaSHA256 scram.HashGeneratorFcn = sha256.New
+
+// KafkaSHA512 is a function that returns a crypto/sha512 hasher and should be used
+// to create Client objects configured for SHA-512 hashing.
+var KafkaSHA512 scram.HashGeneratorFcn = sha512.New
+
+// XDGSCRAMClient implements the client-side of an authentication
+// conversation with a server.  A new conversation must be created for
+// each authentication attempt.
+type XDGSCRAMClient struct {
+	*scram.Client
+	*scram.ClientConversation
+	scram.HashGeneratorFcn
+}
+
+// Begin constructs a SCRAM client component based on a given hash.Hash
+// factory receiver.  This constructor will normalize the username, password
+// and authzID via the SASLprep algorithm, as recommended by RFC-5802.  If
+// SASLprep fails, the method returns an error.
+func (x *XDGSCRAMClient) Begin(userName, password, authzID string) (err error) {
+	x.Client, err = x.HashGeneratorFcn.NewClient(userName, password, authzID)
+	if err != nil {
+		return err
+	}
+	x.ClientConversation = x.Client.NewConversation()
+	return nil
+}
+
+// Step takes a string provided from a server (or just an empty string for the
+// very first conversation step) and attempts to move the authentication
+// conversation forward.  It returns a string to be sent to the server or an
+// error if the server message is invalid.  Calling Step after a conversation
+// completes is also an error.
+func (x *XDGSCRAMClient) Step(challenge string) (response string, err error) {
+	response, err = x.ClientConversation.Step(challenge)
+	return
+}
+
+// Done returns true if the conversation is completed or has errored.
+func (x *XDGSCRAMClient) Done() bool {
+	return x.ClientConversation.Done()
+}

internal/event/target/mqtt.go

@@ -0,0 +1,281 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"context"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/url"
+	"os"
+	"path/filepath"
+	"time"
+
+	mqtt "github.com/eclipse/paho.mqtt.golang"
+	"github.com/minio/minio/internal/event"
+	xnet "github.com/minio/minio/internal/net"
+)
+
+const (
+	reconnectInterval = 5 // In Seconds
+	storePrefix       = "minio"
+)
+
+// MQTT input constants
+const (
+	MqttBroker            = "broker"
+	MqttTopic             = "topic"
+	MqttQoS               = "qos"
+	MqttUsername          = "username"
+	MqttPassword          = "password"
+	MqttReconnectInterval = "reconnect_interval"
+	MqttKeepAliveInterval = "keep_alive_interval"
+	MqttQueueDir          = "queue_dir"
+	MqttQueueLimit        = "queue_limit"
+
+	EnvMQTTEnable            = "MINIO_NOTIFY_MQTT_ENABLE"
+	EnvMQTTBroker            = "MINIO_NOTIFY_MQTT_BROKER"
+	EnvMQTTTopic             = "MINIO_NOTIFY_MQTT_TOPIC"
+	EnvMQTTQoS               = "MINIO_NOTIFY_MQTT_QOS"
+	EnvMQTTUsername          = "MINIO_NOTIFY_MQTT_USERNAME"
+	EnvMQTTPassword          = "MINIO_NOTIFY_MQTT_PASSWORD"
+	EnvMQTTReconnectInterval = "MINIO_NOTIFY_MQTT_RECONNECT_INTERVAL"
+	EnvMQTTKeepAliveInterval = "MINIO_NOTIFY_MQTT_KEEP_ALIVE_INTERVAL"
+	EnvMQTTQueueDir          = "MINIO_NOTIFY_MQTT_QUEUE_DIR"
+	EnvMQTTQueueLimit        = "MINIO_NOTIFY_MQTT_QUEUE_LIMIT"
+)
+
+// MQTTArgs - MQTT target arguments.
+type MQTTArgs struct {
+	Enable               bool           `json:"enable"`
+	Broker               xnet.URL       `json:"broker"`
+	Topic                string         `json:"topic"`
+	QoS                  byte           `json:"qos"`
+	User                 string         `json:"username"`
+	Password             string         `json:"password"`
+	MaxReconnectInterval time.Duration  `json:"reconnectInterval"`
+	KeepAlive            time.Duration  `json:"keepAliveInterval"`
+	RootCAs              *x509.CertPool `json:"-"`
+	QueueDir             string         `json:"queueDir"`
+	QueueLimit           uint64         `json:"queueLimit"`
+}
+
+// Validate MQTTArgs fields
+func (m MQTTArgs) Validate() error {
+	if !m.Enable {
+		return nil
+	}
+	u, err := xnet.ParseURL(m.Broker.String())
+	if err != nil {
+		return err
+	}
+	switch u.Scheme {
+	case "ws", "wss", "tcp", "ssl", "tls", "tcps":
+	default:
+		return errors.New("unknown protocol in broker address")
+	}
+	if m.QueueDir != "" {
+		if !filepath.IsAbs(m.QueueDir) {
+			return errors.New("queueDir path should be absolute")
+		}
+		if m.QoS == 0 {
+			return errors.New("qos should be set to 1 or 2 if queueDir is set")
+		}
+	}
+
+	return nil
+}
+
+// MQTTTarget - MQTT target.
+type MQTTTarget struct {
+	id         event.TargetID
+	args       MQTTArgs
+	client     mqtt.Client
+	store      Store
+	quitCh     chan struct{}
+	loggerOnce func(ctx context.Context, err error, id interface{}, kind ...interface{})
+}
+
+// ID - returns target ID.
+func (target *MQTTTarget) ID() event.TargetID {
+	return target.id
+}
+
+// HasQueueStore - Checks if the queueStore has been configured for the target
+func (target *MQTTTarget) HasQueueStore() bool {
+	return target.store != nil
+}
+
+// IsActive - Return true if target is up and active
+func (target *MQTTTarget) IsActive() (bool, error) {
+	if !target.client.IsConnectionOpen() {
+		return false, errNotConnected
+	}
+	return true, nil
+}
+
+// send - sends an event to the mqtt.
+func (target *MQTTTarget) send(eventData event.Event) error {
+	objectName, err := url.QueryUnescape(eventData.S3.Object.Key)
+	if err != nil {
+		return err
+	}
+	key := eventData.S3.Bucket.Name + "/" + objectName
+
+	data, err := json.Marshal(event.Log{EventName: eventData.EventName, Key: key, Records: []event.Event{eventData}})
+	if err != nil {
+		return err
+	}
+
+	token := target.client.Publish(target.args.Topic, target.args.QoS, false, string(data))
+	if !token.WaitTimeout(reconnectInterval * time.Second) {
+		return errNotConnected
+	}
+	return token.Error()
+}
+
+// Send - reads an event from store and sends it to MQTT.
+func (target *MQTTTarget) Send(eventKey string) error {
+	// Do not send if the connection is not active.
+	_, err := target.IsActive()
+	if err != nil {
+		return err
+	}
+
+	eventData, err := target.store.Get(eventKey)
+	if err != nil {
+		// The last event key in a successful batch will be sent in the channel atmost once by the replayEvents()
+		// Such events will not exist and wouldve been already been sent successfully.
+		if os.IsNotExist(err) {
+			return nil
+		}
+		return err
+	}
+
+	if err = target.send(eventData); err != nil {
+		return err
+	}
+
+	// Delete the event from store.
+	return target.store.Del(eventKey)
+}
+
+// Save - saves the events to the store if queuestore is configured, which will
+// be replayed when the mqtt connection is active.
+func (target *MQTTTarget) Save(eventData event.Event) error {
+	if target.store != nil {
+		return target.store.Put(eventData)
+	}
+
+	// Do not send if the connection is not active.
+	_, err := target.IsActive()
+	if err != nil {
+		return err
+	}
+
+	return target.send(eventData)
+}
+
+// Close - does nothing and available for interface compatibility.
+func (target *MQTTTarget) Close() error {
+	target.client.Disconnect(100)
+	close(target.quitCh)
+	return nil
+}
+
+// NewMQTTTarget - creates new MQTT target.
+func NewMQTTTarget(id string, args MQTTArgs, doneCh <-chan struct{}, loggerOnce func(ctx context.Context, err error, id interface{}, kind ...interface{}), test bool) (*MQTTTarget, error) {
+	if args.MaxReconnectInterval == 0 {
+		// Default interval
+		// https://github.com/eclipse/paho.mqtt.golang/blob/master/options.go#L115
+		args.MaxReconnectInterval = 10 * time.Minute
+	}
+
+	options := mqtt.NewClientOptions().
+		SetClientID("").
+		SetCleanSession(true).
+		SetUsername(args.User).
+		SetPassword(args.Password).
+		SetMaxReconnectInterval(args.MaxReconnectInterval).
+		SetKeepAlive(args.KeepAlive).
+		SetTLSConfig(&tls.Config{RootCAs: args.RootCAs}).
+		AddBroker(args.Broker.String())
+
+	client := mqtt.NewClient(options)
+
+	target := &MQTTTarget{
+		id:         event.TargetID{ID: id, Name: "mqtt"},
+		args:       args,
+		client:     client,
+		quitCh:     make(chan struct{}),
+		loggerOnce: loggerOnce,
+	}
+
+	token := client.Connect()
+	retryRegister := func() {
+		for {
+		retry:
+			select {
+			case <-doneCh:
+				return
+			case <-target.quitCh:
+				return
+			default:
+				ok := token.WaitTimeout(reconnectInterval * time.Second)
+				if ok && token.Error() != nil {
+					target.loggerOnce(context.Background(),
+						fmt.Errorf("Previous connect failed with %w attempting a reconnect",
+							token.Error()),
+						target.ID())
+					time.Sleep(reconnectInterval * time.Second)
+					token = client.Connect()
+					goto retry
+				}
+				if ok {
+					// Successfully connected.
+					return
+				}
+			}
+		}
+	}
+
+	if args.QueueDir != "" {
+		queueDir := filepath.Join(args.QueueDir, storePrefix+"-mqtt-"+id)
+		target.store = NewQueueStore(queueDir, args.QueueLimit)
+		if err := target.store.Open(); err != nil {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+
+		if !test {
+			go retryRegister()
+			// Replays the events from the store.
+			eventKeyCh := replayEvents(target.store, doneCh, target.loggerOnce, target.ID())
+			// Start replaying events from the store.
+			go sendEvents(target, eventKeyCh, doneCh, target.loggerOnce)
+		}
+	} else {
+		if token.Wait() && token.Error() != nil {
+			return target, token.Error()
+		}
+	}
+	return target, nil
+}

internal/event/target/mysql.go

@@ -0,0 +1,401 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/go-sql-driver/mysql"
+	"github.com/minio/minio/internal/event"
+	xnet "github.com/minio/minio/internal/net"
+)
+
+const (
+	mysqlTableExists          = `SELECT 1 FROM %s;`
+	mysqlCreateNamespaceTable = `CREATE TABLE %s (key_name VARCHAR(2048), value JSON, PRIMARY KEY (key_name));`
+	mysqlCreateAccessTable    = `CREATE TABLE %s (event_time DATETIME NOT NULL, event_data JSON);`
+
+	mysqlUpdateRow = `INSERT INTO %s (key_name, value) VALUES (?, ?) ON DUPLICATE KEY UPDATE value=VALUES(value);`
+	mysqlDeleteRow = `DELETE FROM %s WHERE key_name = ?;`
+	mysqlInsertRow = `INSERT INTO %s (event_time, event_data) VALUES (?, ?);`
+)
+
+// MySQL related constants
+const (
+	MySQLFormat             = "format"
+	MySQLDSNString          = "dsn_string"
+	MySQLTable              = "table"
+	MySQLHost               = "host"
+	MySQLPort               = "port"
+	MySQLUsername           = "username"
+	MySQLPassword           = "password"
+	MySQLDatabase           = "database"
+	MySQLQueueLimit         = "queue_limit"
+	MySQLQueueDir           = "queue_dir"
+	MySQLMaxOpenConnections = "max_open_connections"
+
+	EnvMySQLEnable             = "MINIO_NOTIFY_MYSQL_ENABLE"
+	EnvMySQLFormat             = "MINIO_NOTIFY_MYSQL_FORMAT"
+	EnvMySQLDSNString          = "MINIO_NOTIFY_MYSQL_DSN_STRING"
+	EnvMySQLTable              = "MINIO_NOTIFY_MYSQL_TABLE"
+	EnvMySQLHost               = "MINIO_NOTIFY_MYSQL_HOST"
+	EnvMySQLPort               = "MINIO_NOTIFY_MYSQL_PORT"
+	EnvMySQLUsername           = "MINIO_NOTIFY_MYSQL_USERNAME"
+	EnvMySQLPassword           = "MINIO_NOTIFY_MYSQL_PASSWORD"
+	EnvMySQLDatabase           = "MINIO_NOTIFY_MYSQL_DATABASE"
+	EnvMySQLQueueLimit         = "MINIO_NOTIFY_MYSQL_QUEUE_LIMIT"
+	EnvMySQLQueueDir           = "MINIO_NOTIFY_MYSQL_QUEUE_DIR"
+	EnvMySQLMaxOpenConnections = "MINIO_NOTIFY_MYSQL_MAX_OPEN_CONNECTIONS"
+)
+
+// MySQLArgs - MySQL target arguments.
+type MySQLArgs struct {
+	Enable             bool     `json:"enable"`
+	Format             string   `json:"format"`
+	DSN                string   `json:"dsnString"`
+	Table              string   `json:"table"`
+	Host               xnet.URL `json:"host"`
+	Port               string   `json:"port"`
+	User               string   `json:"user"`
+	Password           string   `json:"password"`
+	Database           string   `json:"database"`
+	QueueDir           string   `json:"queueDir"`
+	QueueLimit         uint64   `json:"queueLimit"`
+	MaxOpenConnections int      `json:"maxOpenConnections"`
+}
+
+// Validate MySQLArgs fields
+func (m MySQLArgs) Validate() error {
+	if !m.Enable {
+		return nil
+	}
+
+	if m.Format != "" {
+		f := strings.ToLower(m.Format)
+		if f != event.NamespaceFormat && f != event.AccessFormat {
+			return fmt.Errorf("unrecognized format")
+		}
+	}
+
+	if m.Table == "" {
+		return fmt.Errorf("table unspecified")
+	}
+
+	if m.DSN != "" {
+		if _, err := mysql.ParseDSN(m.DSN); err != nil {
+			return err
+		}
+	} else {
+		// Some fields need to be specified when DSN is unspecified
+		if m.Port == "" {
+			return fmt.Errorf("unspecified port")
+		}
+		if _, err := strconv.Atoi(m.Port); err != nil {
+			return fmt.Errorf("invalid port")
+		}
+		if m.Database == "" {
+			return fmt.Errorf("database unspecified")
+		}
+	}
+
+	if m.QueueDir != "" {
+		if !filepath.IsAbs(m.QueueDir) {
+			return errors.New("queueDir path should be absolute")
+		}
+	}
+
+	if m.MaxOpenConnections < 0 {
+		return errors.New("maxOpenConnections cannot be less than zero")
+	}
+
+	return nil
+}
+
+// MySQLTarget - MySQL target.
+type MySQLTarget struct {
+	id         event.TargetID
+	args       MySQLArgs
+	updateStmt *sql.Stmt
+	deleteStmt *sql.Stmt
+	insertStmt *sql.Stmt
+	db         *sql.DB
+	store      Store
+	firstPing  bool
+	loggerOnce func(ctx context.Context, err error, id interface{}, errKind ...interface{})
+}
+
+// ID - returns target ID.
+func (target *MySQLTarget) ID() event.TargetID {
+	return target.id
+}
+
+// HasQueueStore - Checks if the queueStore has been configured for the target
+func (target *MySQLTarget) HasQueueStore() bool {
+	return target.store != nil
+}
+
+// IsActive - Return true if target is up and active
+func (target *MySQLTarget) IsActive() (bool, error) {
+	if target.db == nil {
+		db, sErr := sql.Open("mysql", target.args.DSN)
+		if sErr != nil {
+			return false, sErr
+		}
+		target.db = db
+		if target.args.MaxOpenConnections > 0 {
+			// Set the maximum connections limit
+			target.db.SetMaxOpenConns(target.args.MaxOpenConnections)
+		}
+	}
+	if err := target.db.Ping(); err != nil {
+		if IsConnErr(err) {
+			return false, errNotConnected
+		}
+		return false, err
+	}
+	return true, nil
+}
+
+// Save - saves the events to the store which will be replayed when the SQL connection is active.
+func (target *MySQLTarget) Save(eventData event.Event) error {
+	if target.store != nil {
+		return target.store.Put(eventData)
+	}
+	_, err := target.IsActive()
+	if err != nil {
+		return err
+	}
+	return target.send(eventData)
+}
+
+// send - sends an event to the mysql.
+func (target *MySQLTarget) send(eventData event.Event) error {
+	if target.args.Format == event.NamespaceFormat {
+		objectName, err := url.QueryUnescape(eventData.S3.Object.Key)
+		if err != nil {
+			return err
+		}
+		key := eventData.S3.Bucket.Name + "/" + objectName
+
+		if eventData.EventName == event.ObjectRemovedDelete {
+			_, err = target.deleteStmt.Exec(key)
+		} else {
+			var data []byte
+			if data, err = json.Marshal(struct{ Records []event.Event }{[]event.Event{eventData}}); err != nil {
+				return err
+			}
+
+			_, err = target.updateStmt.Exec(key, data)
+		}
+
+		return err
+	}
+
+	if target.args.Format == event.AccessFormat {
+		eventTime, err := time.Parse(event.AMZTimeFormat, eventData.EventTime)
+		if err != nil {
+			return err
+		}
+
+		data, err := json.Marshal(struct{ Records []event.Event }{[]event.Event{eventData}})
+		if err != nil {
+			return err
+		}
+
+		_, err = target.insertStmt.Exec(eventTime, data)
+
+		return err
+	}
+
+	return nil
+}
+
+// Send - reads an event from store and sends it to MySQL.
+func (target *MySQLTarget) Send(eventKey string) error {
+
+	_, err := target.IsActive()
+	if err != nil {
+		return err
+	}
+
+	if !target.firstPing {
+		if err := target.executeStmts(); err != nil {
+			if IsConnErr(err) {
+				return errNotConnected
+			}
+			return err
+		}
+	}
+
+	eventData, eErr := target.store.Get(eventKey)
+	if eErr != nil {
+		// The last event key in a successful batch will be sent in the channel atmost once by the replayEvents()
+		// Such events will not exist and wouldve been already been sent successfully.
+		if os.IsNotExist(eErr) {
+			return nil
+		}
+		return eErr
+	}
+
+	if err := target.send(eventData); err != nil {
+		if IsConnErr(err) {
+			return errNotConnected
+		}
+		return err
+	}
+
+	// Delete the event from store.
+	return target.store.Del(eventKey)
+}
+
+// Close - closes underneath connections to MySQL database.
+func (target *MySQLTarget) Close() error {
+	if target.updateStmt != nil {
+		// FIXME: log returned error. ignore time being.
+		_ = target.updateStmt.Close()
+	}
+
+	if target.deleteStmt != nil {
+		// FIXME: log returned error. ignore time being.
+		_ = target.deleteStmt.Close()
+	}
+
+	if target.insertStmt != nil {
+		// FIXME: log returned error. ignore time being.
+		_ = target.insertStmt.Close()
+	}
+
+	return target.db.Close()
+}
+
+// Executes the table creation statements.
+func (target *MySQLTarget) executeStmts() error {
+
+	_, err := target.db.Exec(fmt.Sprintf(mysqlTableExists, target.args.Table))
+	if err != nil {
+		createStmt := mysqlCreateNamespaceTable
+		if target.args.Format == event.AccessFormat {
+			createStmt = mysqlCreateAccessTable
+		}
+
+		if _, dbErr := target.db.Exec(fmt.Sprintf(createStmt, target.args.Table)); dbErr != nil {
+			return dbErr
+		}
+	}
+
+	switch target.args.Format {
+	case event.NamespaceFormat:
+		// insert or update statement
+		if target.updateStmt, err = target.db.Prepare(fmt.Sprintf(mysqlUpdateRow, target.args.Table)); err != nil {
+			return err
+		}
+		// delete statement
+		if target.deleteStmt, err = target.db.Prepare(fmt.Sprintf(mysqlDeleteRow, target.args.Table)); err != nil {
+			return err
+		}
+	case event.AccessFormat:
+		// insert statement
+		if target.insertStmt, err = target.db.Prepare(fmt.Sprintf(mysqlInsertRow, target.args.Table)); err != nil {
+			return err
+		}
+	}
+
+	return nil
+
+}
+
+// NewMySQLTarget - creates new MySQL target.
+func NewMySQLTarget(id string, args MySQLArgs, doneCh <-chan struct{}, loggerOnce func(ctx context.Context, err error, id interface{}, kind ...interface{}), test bool) (*MySQLTarget, error) {
+	if args.DSN == "" {
+		config := mysql.Config{
+			User:                 args.User,
+			Passwd:               args.Password,
+			Net:                  "tcp",
+			Addr:                 args.Host.String() + ":" + args.Port,
+			DBName:               args.Database,
+			AllowNativePasswords: true,
+			CheckConnLiveness:    true,
+		}
+
+		args.DSN = config.FormatDSN()
+	}
+
+	target := &MySQLTarget{
+		id:         event.TargetID{ID: id, Name: "mysql"},
+		args:       args,
+		firstPing:  false,
+		loggerOnce: loggerOnce,
+	}
+
+	db, err := sql.Open("mysql", args.DSN)
+	if err != nil {
+		target.loggerOnce(context.Background(), err, target.ID())
+		return target, err
+	}
+	target.db = db
+
+	if args.MaxOpenConnections > 0 {
+		// Set the maximum connections limit
+		target.db.SetMaxOpenConns(args.MaxOpenConnections)
+	}
+
+	var store Store
+
+	if args.QueueDir != "" {
+		queueDir := filepath.Join(args.QueueDir, storePrefix+"-mysql-"+id)
+		store = NewQueueStore(queueDir, args.QueueLimit)
+		if oErr := store.Open(); oErr != nil {
+			target.loggerOnce(context.Background(), oErr, target.ID())
+			return target, oErr
+		}
+		target.store = store
+	}
+
+	err = target.db.Ping()
+	if err != nil {
+		if target.store == nil || !(IsConnRefusedErr(err) || IsConnResetErr(err)) {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+	} else {
+		if err = target.executeStmts(); err != nil {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+		target.firstPing = true
+	}
+
+	if target.store != nil && !test {
+		// Replays the events from the store.
+		eventKeyCh := replayEvents(target.store, doneCh, target.loggerOnce, target.ID())
+		// Start replaying events from the store.
+		go sendEvents(target, eventKeyCh, doneCh, target.loggerOnce)
+	}
+
+	return target, nil
+}

internal/event/target/mysql_test.go

@@ -0,0 +1,38 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"database/sql"
+	"testing"
+)
+
+// TestPostgreSQLRegistration checks if sql driver
+// is registered and fails otherwise.
+func TestMySQLRegistration(t *testing.T) {
+	var found bool
+	for _, drv := range sql.Drivers() {
+		if drv == "mysql" {
+			found = true
+			break
+		}
+	}
+	if !found {
+		t.Fatal("mysql driver not registered")
+	}
+}

internal/event/target/nats.go

@@ -0,0 +1,373 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"context"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/json"
+	"errors"
+	"net/url"
+	"os"
+	"path/filepath"
+
+	"github.com/minio/minio/internal/event"
+	xnet "github.com/minio/minio/internal/net"
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/stan.go"
+)
+
+// NATS related constants
+const (
+	NATSAddress       = "address"
+	NATSSubject       = "subject"
+	NATSUsername      = "username"
+	NATSPassword      = "password"
+	NATSToken         = "token"
+	NATSTLS           = "tls"
+	NATSTLSSkipVerify = "tls_skip_verify"
+	NATSPingInterval  = "ping_interval"
+	NATSQueueDir      = "queue_dir"
+	NATSQueueLimit    = "queue_limit"
+	NATSCertAuthority = "cert_authority"
+	NATSClientCert    = "client_cert"
+	NATSClientKey     = "client_key"
+
+	// Streaming constants
+	NATSStreaming                   = "streaming"
+	NATSStreamingClusterID          = "streaming_cluster_id"
+	NATSStreamingAsync              = "streaming_async"
+	NATSStreamingMaxPubAcksInFlight = "streaming_max_pub_acks_in_flight"
+
+	EnvNATSEnable        = "MINIO_NOTIFY_NATS_ENABLE"
+	EnvNATSAddress       = "MINIO_NOTIFY_NATS_ADDRESS"
+	EnvNATSSubject       = "MINIO_NOTIFY_NATS_SUBJECT"
+	EnvNATSUsername      = "MINIO_NOTIFY_NATS_USERNAME"
+	EnvNATSPassword      = "MINIO_NOTIFY_NATS_PASSWORD"
+	EnvNATSToken         = "MINIO_NOTIFY_NATS_TOKEN"
+	EnvNATSTLS           = "MINIO_NOTIFY_NATS_TLS"
+	EnvNATSTLSSkipVerify = "MINIO_NOTIFY_NATS_TLS_SKIP_VERIFY"
+	EnvNATSPingInterval  = "MINIO_NOTIFY_NATS_PING_INTERVAL"
+	EnvNATSQueueDir      = "MINIO_NOTIFY_NATS_QUEUE_DIR"
+	EnvNATSQueueLimit    = "MINIO_NOTIFY_NATS_QUEUE_LIMIT"
+	EnvNATSCertAuthority = "MINIO_NOTIFY_NATS_CERT_AUTHORITY"
+	EnvNATSClientCert    = "MINIO_NOTIFY_NATS_CLIENT_CERT"
+	EnvNATSClientKey     = "MINIO_NOTIFY_NATS_CLIENT_KEY"
+
+	// Streaming constants
+	EnvNATSStreaming                   = "MINIO_NOTIFY_NATS_STREAMING"
+	EnvNATSStreamingClusterID          = "MINIO_NOTIFY_NATS_STREAMING_CLUSTER_ID"
+	EnvNATSStreamingAsync              = "MINIO_NOTIFY_NATS_STREAMING_ASYNC"
+	EnvNATSStreamingMaxPubAcksInFlight = "MINIO_NOTIFY_NATS_STREAMING_MAX_PUB_ACKS_IN_FLIGHT"
+)
+
+// NATSArgs - NATS target arguments.
+type NATSArgs struct {
+	Enable        bool      `json:"enable"`
+	Address       xnet.Host `json:"address"`
+	Subject       string    `json:"subject"`
+	Username      string    `json:"username"`
+	Password      string    `json:"password"`
+	Token         string    `json:"token"`
+	TLS           bool      `json:"tls"`
+	TLSSkipVerify bool      `json:"tlsSkipVerify"`
+	Secure        bool      `json:"secure"`
+	CertAuthority string    `json:"certAuthority"`
+	ClientCert    string    `json:"clientCert"`
+	ClientKey     string    `json:"clientKey"`
+	PingInterval  int64     `json:"pingInterval"`
+	QueueDir      string    `json:"queueDir"`
+	QueueLimit    uint64    `json:"queueLimit"`
+	Streaming     struct {
+		Enable             bool   `json:"enable"`
+		ClusterID          string `json:"clusterID"`
+		Async              bool   `json:"async"`
+		MaxPubAcksInflight int    `json:"maxPubAcksInflight"`
+	} `json:"streaming"`
+
+	RootCAs *x509.CertPool `json:"-"`
+}
+
+// Validate NATSArgs fields
+func (n NATSArgs) Validate() error {
+	if !n.Enable {
+		return nil
+	}
+
+	if n.Address.IsEmpty() {
+		return errors.New("empty address")
+	}
+
+	if n.Subject == "" {
+		return errors.New("empty subject")
+	}
+
+	if n.ClientCert != "" && n.ClientKey == "" || n.ClientCert == "" && n.ClientKey != "" {
+		return errors.New("cert and key must be specified as a pair")
+	}
+
+	if n.Username != "" && n.Password == "" || n.Username == "" && n.Password != "" {
+		return errors.New("username and password must be specified as a pair")
+	}
+
+	if n.Streaming.Enable {
+		if n.Streaming.ClusterID == "" {
+			return errors.New("empty cluster id")
+		}
+	}
+
+	if n.QueueDir != "" {
+		if !filepath.IsAbs(n.QueueDir) {
+			return errors.New("queueDir path should be absolute")
+		}
+	}
+
+	return nil
+}
+
+// To obtain a nats connection from args.
+func (n NATSArgs) connectNats() (*nats.Conn, error) {
+	connOpts := []nats.Option{nats.Name("Minio Notification")}
+	if n.Username != "" && n.Password != "" {
+		connOpts = append(connOpts, nats.UserInfo(n.Username, n.Password))
+	}
+	if n.Token != "" {
+		connOpts = append(connOpts, nats.Token(n.Token))
+	}
+	if n.Secure || n.TLS && n.TLSSkipVerify {
+		connOpts = append(connOpts, nats.Secure(nil))
+	} else if n.TLS {
+		connOpts = append(connOpts, nats.Secure(&tls.Config{RootCAs: n.RootCAs}))
+	}
+	if n.CertAuthority != "" {
+		connOpts = append(connOpts, nats.RootCAs(n.CertAuthority))
+	}
+	if n.ClientCert != "" && n.ClientKey != "" {
+		connOpts = append(connOpts, nats.ClientCert(n.ClientCert, n.ClientKey))
+	}
+	return nats.Connect(n.Address.String(), connOpts...)
+}
+
+// To obtain a streaming connection from args.
+func (n NATSArgs) connectStan() (stan.Conn, error) {
+	scheme := "nats"
+	if n.Secure {
+		scheme = "tls"
+	}
+
+	var addressURL string
+	if n.Username != "" && n.Password != "" {
+		addressURL = scheme + "://" + n.Username + ":" + n.Password + "@" + n.Address.String()
+	} else if n.Token != "" {
+		addressURL = scheme + "://" + n.Token + "@" + n.Address.String()
+	} else {
+		addressURL = scheme + "://" + n.Address.String()
+	}
+
+	clientID, err := getNewUUID()
+	if err != nil {
+		return nil, err
+	}
+
+	connOpts := []stan.Option{stan.NatsURL(addressURL)}
+	if n.Streaming.MaxPubAcksInflight > 0 {
+		connOpts = append(connOpts, stan.MaxPubAcksInflight(n.Streaming.MaxPubAcksInflight))
+	}
+
+	return stan.Connect(n.Streaming.ClusterID, clientID, connOpts...)
+}
+
+// NATSTarget - NATS target.
+type NATSTarget struct {
+	id         event.TargetID
+	args       NATSArgs
+	natsConn   *nats.Conn
+	stanConn   stan.Conn
+	store      Store
+	loggerOnce func(ctx context.Context, err error, id interface{}, errKind ...interface{})
+}
+
+// ID - returns target ID.
+func (target *NATSTarget) ID() event.TargetID {
+	return target.id
+}
+
+// HasQueueStore - Checks if the queueStore has been configured for the target
+func (target *NATSTarget) HasQueueStore() bool {
+	return target.store != nil
+}
+
+// IsActive - Return true if target is up and active
+func (target *NATSTarget) IsActive() (bool, error) {
+	var connErr error
+	if target.args.Streaming.Enable {
+		if target.stanConn == nil || target.stanConn.NatsConn() == nil {
+			target.stanConn, connErr = target.args.connectStan()
+		} else {
+			if !target.stanConn.NatsConn().IsConnected() {
+				return false, errNotConnected
+			}
+		}
+	} else {
+		if target.natsConn == nil {
+			target.natsConn, connErr = target.args.connectNats()
+		} else {
+			if !target.natsConn.IsConnected() {
+				return false, errNotConnected
+			}
+		}
+	}
+
+	if connErr != nil {
+		if connErr.Error() == nats.ErrNoServers.Error() {
+			return false, errNotConnected
+		}
+		return false, connErr
+	}
+
+	return true, nil
+}
+
+// Save - saves the events to the store which will be replayed when the Nats connection is active.
+func (target *NATSTarget) Save(eventData event.Event) error {
+	if target.store != nil {
+		return target.store.Put(eventData)
+	}
+	_, err := target.IsActive()
+	if err != nil {
+		return err
+	}
+	return target.send(eventData)
+}
+
+// send - sends an event to the Nats.
+func (target *NATSTarget) send(eventData event.Event) error {
+	objectName, err := url.QueryUnescape(eventData.S3.Object.Key)
+	if err != nil {
+		return err
+	}
+	key := eventData.S3.Bucket.Name + "/" + objectName
+
+	data, err := json.Marshal(event.Log{EventName: eventData.EventName, Key: key, Records: []event.Event{eventData}})
+	if err != nil {
+		return err
+	}
+
+	if target.stanConn != nil {
+		if target.args.Streaming.Async {
+			_, err = target.stanConn.PublishAsync(target.args.Subject, data, nil)
+		} else {
+			err = target.stanConn.Publish(target.args.Subject, data)
+		}
+	} else {
+		err = target.natsConn.Publish(target.args.Subject, data)
+	}
+	return err
+}
+
+// Send - sends event to Nats.
+func (target *NATSTarget) Send(eventKey string) error {
+	_, err := target.IsActive()
+	if err != nil {
+		return err
+	}
+
+	eventData, eErr := target.store.Get(eventKey)
+	if eErr != nil {
+		// The last event key in a successful batch will be sent in the channel atmost once by the replayEvents()
+		// Such events will not exist and wouldve been already been sent successfully.
+		if os.IsNotExist(eErr) {
+			return nil
+		}
+		return eErr
+	}
+
+	if err := target.send(eventData); err != nil {
+		return err
+	}
+
+	return target.store.Del(eventKey)
+}
+
+// Close - closes underneath connections to NATS server.
+func (target *NATSTarget) Close() (err error) {
+	if target.stanConn != nil {
+		// closing the streaming connection does not close the provided NATS connection.
+		if target.stanConn.NatsConn() != nil {
+			target.stanConn.NatsConn().Close()
+		}
+		err = target.stanConn.Close()
+	}
+
+	if target.natsConn != nil {
+		target.natsConn.Close()
+	}
+
+	return err
+}
+
+// NewNATSTarget - creates new NATS target.
+func NewNATSTarget(id string, args NATSArgs, doneCh <-chan struct{}, loggerOnce func(ctx context.Context, err error, id interface{}, kind ...interface{}), test bool) (*NATSTarget, error) {
+	var natsConn *nats.Conn
+	var stanConn stan.Conn
+
+	var err error
+
+	var store Store
+
+	target := &NATSTarget{
+		id:         event.TargetID{ID: id, Name: "nats"},
+		args:       args,
+		loggerOnce: loggerOnce,
+	}
+
+	if args.QueueDir != "" {
+		queueDir := filepath.Join(args.QueueDir, storePrefix+"-nats-"+id)
+		store = NewQueueStore(queueDir, args.QueueLimit)
+		if oErr := store.Open(); oErr != nil {
+			target.loggerOnce(context.Background(), oErr, target.ID())
+			return target, oErr
+		}
+		target.store = store
+	}
+
+	if args.Streaming.Enable {
+		stanConn, err = args.connectStan()
+		target.stanConn = stanConn
+	} else {
+		natsConn, err = args.connectNats()
+		target.natsConn = natsConn
+	}
+
+	if err != nil {
+		if store == nil || err.Error() != nats.ErrNoServers.Error() {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+	}
+
+	if target.store != nil && !test {
+		// Replays the events from the store.
+		eventKeyCh := replayEvents(target.store, doneCh, target.loggerOnce, target.ID())
+		// Start replaying events from the store.
+		go sendEvents(target, eventKeyCh, doneCh, target.loggerOnce)
+	}
+
+	return target, nil
+}

internal/event/target/nats_contrib_test.go

@@ -0,0 +1,92 @@
+/*
+ * MinIO Object Storage (c) 2021 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 target
+
+import (
+	"testing"
+
+	xnet "github.com/minio/minio/internal/net"
+	natsserver "github.com/nats-io/nats-server/v2/test"
+)
+
+func TestNatsConnPlain(t *testing.T) {
+	opts := natsserver.DefaultTestOptions
+	opts.Port = 14222
+	s := natsserver.RunServer(&opts)
+	defer s.Shutdown()
+
+	clientConfig := &NATSArgs{
+		Enable: true,
+		Address: xnet.Host{Name: "localhost",
+			Port:      (xnet.Port(opts.Port)),
+			IsPortSet: true},
+		Subject: "test",
+	}
+	con, err := clientConfig.connectNats()
+	if err != nil {
+		t.Errorf("Could not connect to nats: %v", err)
+	}
+	defer con.Close()
+}
+
+func TestNatsConnUserPass(t *testing.T) {
+	opts := natsserver.DefaultTestOptions
+	opts.Port = 14223
+	opts.Username = "testminio"
+	opts.Password = "miniotest"
+	s := natsserver.RunServer(&opts)
+	defer s.Shutdown()
+
+	clientConfig := &NATSArgs{
+		Enable: true,
+		Address: xnet.Host{Name: "localhost",
+			Port:      (xnet.Port(opts.Port)),
+			IsPortSet: true},
+		Subject:  "test",
+		Username: opts.Username,
+		Password: opts.Password,
+	}
+
+	con, err := clientConfig.connectNats()
+	if err != nil {
+		t.Errorf("Could not connect to nats: %v", err)
+	}
+	defer con.Close()
+}
+
+func TestNatsConnToken(t *testing.T) {
+	opts := natsserver.DefaultTestOptions
+	opts.Port = 14223
+	opts.Authorization = "s3cr3t"
+	s := natsserver.RunServer(&opts)
+	defer s.Shutdown()
+
+	clientConfig := &NATSArgs{
+		Enable: true,
+		Address: xnet.Host{Name: "localhost",
+			Port:      (xnet.Port(opts.Port)),
+			IsPortSet: true},
+		Subject: "test",
+		Token:   opts.Authorization,
+	}
+
+	con, err := clientConfig.connectNats()
+	if err != nil {
+		t.Errorf("Could not connect to nats: %v", err)
+	}
+	defer con.Close()
+}

internal/event/target/nats_tls_contrib_test.go

@@ -0,0 +1,70 @@
+/*
+ * MinIO Object Storage (c) 2021 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 target
+
+import (
+	"path"
+	"path/filepath"
+	"testing"
+
+	xnet "github.com/minio/minio/internal/net"
+	natsserver "github.com/nats-io/nats-server/v2/test"
+)
+
+func TestNatsConnTLSCustomCA(t *testing.T) {
+	s, opts := natsserver.RunServerWithConfig(filepath.Join("testdata", "contrib", "nats_tls.conf"))
+	defer s.Shutdown()
+
+	clientConfig := &NATSArgs{
+		Enable: true,
+		Address: xnet.Host{Name: "localhost",
+			Port:      (xnet.Port(opts.Port)),
+			IsPortSet: true},
+		Subject:       "test",
+		Secure:        true,
+		CertAuthority: path.Join("testdata", "contrib", "certs", "root_ca_cert.pem"),
+	}
+
+	con, err := clientConfig.connectNats()
+	if err != nil {
+		t.Errorf("Could not connect to nats: %v", err)
+	}
+	defer con.Close()
+}
+
+func TestNatsConnTLSClientAuthorization(t *testing.T) {
+	s, opts := natsserver.RunServerWithConfig(filepath.Join("testdata", "contrib", "nats_tls_client_cert.conf"))
+	defer s.Shutdown()
+
+	clientConfig := &NATSArgs{
+		Enable: true,
+		Address: xnet.Host{Name: "localhost",
+			Port:      (xnet.Port(opts.Port)),
+			IsPortSet: true},
+		Subject:       "test",
+		Secure:        true,
+		CertAuthority: path.Join("testdata", "contrib", "certs", "root_ca_cert.pem"),
+		ClientCert:    path.Join("testdata", "contrib", "certs", "nats_client_cert.pem"),
+		ClientKey:     path.Join("testdata", "contrib", "certs", "nats_client_key.pem"),
+	}
+
+	con, err := clientConfig.connectNats()
+	if err != nil {
+		t.Errorf("Could not connect to nats: %v", err)
+	}
+	defer con.Close()
+}

internal/event/target/nsq.go

@@ -0,0 +1,242 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"context"
+	"crypto/tls"
+	"encoding/json"
+	"errors"
+	"net/url"
+	"os"
+	"path/filepath"
+
+	"github.com/nsqio/go-nsq"
+
+	"github.com/minio/minio/internal/event"
+	xnet "github.com/minio/minio/internal/net"
+)
+
+// NSQ constants
+const (
+	NSQAddress       = "nsqd_address"
+	NSQTopic         = "topic"
+	NSQTLS           = "tls"
+	NSQTLSSkipVerify = "tls_skip_verify"
+	NSQQueueDir      = "queue_dir"
+	NSQQueueLimit    = "queue_limit"
+
+	EnvNSQEnable        = "MINIO_NOTIFY_NSQ_ENABLE"
+	EnvNSQAddress       = "MINIO_NOTIFY_NSQ_NSQD_ADDRESS"
+	EnvNSQTopic         = "MINIO_NOTIFY_NSQ_TOPIC"
+	EnvNSQTLS           = "MINIO_NOTIFY_NSQ_TLS"
+	EnvNSQTLSSkipVerify = "MINIO_NOTIFY_NSQ_TLS_SKIP_VERIFY"
+	EnvNSQQueueDir      = "MINIO_NOTIFY_NSQ_QUEUE_DIR"
+	EnvNSQQueueLimit    = "MINIO_NOTIFY_NSQ_QUEUE_LIMIT"
+)
+
+// NSQArgs - NSQ target arguments.
+type NSQArgs struct {
+	Enable      bool      `json:"enable"`
+	NSQDAddress xnet.Host `json:"nsqdAddress"`
+	Topic       string    `json:"topic"`
+	TLS         struct {
+		Enable     bool `json:"enable"`
+		SkipVerify bool `json:"skipVerify"`
+	} `json:"tls"`
+	QueueDir   string `json:"queueDir"`
+	QueueLimit uint64 `json:"queueLimit"`
+}
+
+// Validate NSQArgs fields
+func (n NSQArgs) Validate() error {
+	if !n.Enable {
+		return nil
+	}
+
+	if n.NSQDAddress.IsEmpty() {
+		return errors.New("empty nsqdAddress")
+	}
+
+	if n.Topic == "" {
+		return errors.New("empty topic")
+	}
+	if n.QueueDir != "" {
+		if !filepath.IsAbs(n.QueueDir) {
+			return errors.New("queueDir path should be absolute")
+		}
+	}
+
+	return nil
+}
+
+// NSQTarget - NSQ target.
+type NSQTarget struct {
+	id         event.TargetID
+	args       NSQArgs
+	producer   *nsq.Producer
+	store      Store
+	config     *nsq.Config
+	loggerOnce func(ctx context.Context, err error, id interface{}, errKind ...interface{})
+}
+
+// ID - returns target ID.
+func (target *NSQTarget) ID() event.TargetID {
+	return target.id
+}
+
+// HasQueueStore - Checks if the queueStore has been configured for the target
+func (target *NSQTarget) HasQueueStore() bool {
+	return target.store != nil
+}
+
+// IsActive - Return true if target is up and active
+func (target *NSQTarget) IsActive() (bool, error) {
+	if target.producer == nil {
+		producer, err := nsq.NewProducer(target.args.NSQDAddress.String(), target.config)
+		if err != nil {
+			return false, err
+		}
+		target.producer = producer
+	}
+
+	if err := target.producer.Ping(); err != nil {
+		// To treat "connection refused" errors as errNotConnected.
+		if IsConnRefusedErr(err) {
+			return false, errNotConnected
+		}
+		return false, err
+	}
+	return true, nil
+}
+
+// Save - saves the events to the store which will be replayed when the nsq connection is active.
+func (target *NSQTarget) Save(eventData event.Event) error {
+	if target.store != nil {
+		return target.store.Put(eventData)
+	}
+	_, err := target.IsActive()
+	if err != nil {
+		return err
+	}
+	return target.send(eventData)
+}
+
+// send - sends an event to the NSQ.
+func (target *NSQTarget) send(eventData event.Event) error {
+	objectName, err := url.QueryUnescape(eventData.S3.Object.Key)
+	if err != nil {
+		return err
+	}
+	key := eventData.S3.Bucket.Name + "/" + objectName
+
+	data, err := json.Marshal(event.Log{EventName: eventData.EventName, Key: key, Records: []event.Event{eventData}})
+	if err != nil {
+		return err
+	}
+
+	return target.producer.Publish(target.args.Topic, data)
+}
+
+// Send - reads an event from store and sends it to NSQ.
+func (target *NSQTarget) Send(eventKey string) error {
+	_, err := target.IsActive()
+	if err != nil {
+		return err
+	}
+
+	eventData, eErr := target.store.Get(eventKey)
+	if eErr != nil {
+		// The last event key in a successful batch will be sent in the channel atmost once by the replayEvents()
+		// Such events will not exist and wouldve been already been sent successfully.
+		if os.IsNotExist(eErr) {
+			return nil
+		}
+		return eErr
+	}
+
+	if err := target.send(eventData); err != nil {
+		return err
+	}
+
+	// Delete the event from store.
+	return target.store.Del(eventKey)
+}
+
+// Close - closes underneath connections to NSQD server.
+func (target *NSQTarget) Close() (err error) {
+	if target.producer != nil {
+		// this blocks until complete:
+		target.producer.Stop()
+	}
+	return nil
+}
+
+// NewNSQTarget - creates new NSQ target.
+func NewNSQTarget(id string, args NSQArgs, doneCh <-chan struct{}, loggerOnce func(ctx context.Context, err error, id interface{}, kind ...interface{}), test bool) (*NSQTarget, error) {
+	config := nsq.NewConfig()
+	if args.TLS.Enable {
+		config.TlsV1 = true
+		config.TlsConfig = &tls.Config{
+			InsecureSkipVerify: args.TLS.SkipVerify,
+		}
+	}
+
+	var store Store
+
+	target := &NSQTarget{
+		id:         event.TargetID{ID: id, Name: "nsq"},
+		args:       args,
+		config:     config,
+		loggerOnce: loggerOnce,
+	}
+
+	if args.QueueDir != "" {
+		queueDir := filepath.Join(args.QueueDir, storePrefix+"-nsq-"+id)
+		store = NewQueueStore(queueDir, args.QueueLimit)
+		if oErr := store.Open(); oErr != nil {
+			target.loggerOnce(context.Background(), oErr, target.ID())
+			return target, oErr
+		}
+		target.store = store
+	}
+
+	producer, err := nsq.NewProducer(args.NSQDAddress.String(), config)
+	if err != nil {
+		target.loggerOnce(context.Background(), err, target.ID())
+		return target, err
+	}
+	target.producer = producer
+
+	if err := target.producer.Ping(); err != nil {
+		// To treat "connection refused" errors as errNotConnected.
+		if target.store == nil || !(IsConnRefusedErr(err) || IsConnResetErr(err)) {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+	}
+
+	if target.store != nil && !test {
+		// Replays the events from the store.
+		eventKeyCh := replayEvents(target.store, doneCh, target.loggerOnce, target.ID())
+		// Start replaying events from the store.
+		go sendEvents(target, eventKeyCh, doneCh, target.loggerOnce)
+	}
+
+	return target, nil
+}

internal/event/target/nsq_test.go

@@ -0,0 +1,98 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"testing"
+
+	xnet "github.com/minio/minio/internal/net"
+)
+
+func TestNSQArgs_Validate(t *testing.T) {
+	type fields struct {
+		Enable      bool
+		NSQDAddress xnet.Host
+		Topic       string
+		TLS         struct {
+			Enable     bool
+			SkipVerify bool
+		}
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		wantErr bool
+	}{
+		{
+			name: "test1_missing_topic",
+			fields: fields{
+				Enable: true,
+				NSQDAddress: xnet.Host{
+					Name:      "127.0.0.1",
+					Port:      4150,
+					IsPortSet: true,
+				},
+				Topic: "",
+			},
+			wantErr: true,
+		},
+		{
+			name: "test2_disabled",
+			fields: fields{
+				Enable:      false,
+				NSQDAddress: xnet.Host{},
+				Topic:       "topic",
+			},
+			wantErr: false,
+		},
+		{
+			name: "test3_OK",
+			fields: fields{
+				Enable: true,
+				NSQDAddress: xnet.Host{
+					Name:      "127.0.0.1",
+					Port:      4150,
+					IsPortSet: true,
+				},
+				Topic: "topic",
+			},
+			wantErr: false,
+		},
+		{
+			name: "test4_emptynsqdaddr",
+			fields: fields{
+				Enable:      true,
+				NSQDAddress: xnet.Host{},
+				Topic:       "topic",
+			},
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			n := NSQArgs{
+				Enable:      tt.fields.Enable,
+				NSQDAddress: tt.fields.NSQDAddress,
+				Topic:       tt.fields.Topic,
+			}
+			if err := n.Validate(); (err != nil) != tt.wantErr {
+				t.Errorf("NSQArgs.Validate() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}

internal/event/target/postgresql.go

@@ -0,0 +1,408 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
+
+	_ "github.com/lib/pq" // Register postgres driver
+
+	"github.com/minio/minio/internal/event"
+	xnet "github.com/minio/minio/internal/net"
+)
+
+const (
+	psqlTableExists          = `SELECT 1 FROM %s;`
+	psqlCreateNamespaceTable = `CREATE TABLE %s (key VARCHAR PRIMARY KEY, value JSONB);`
+	psqlCreateAccessTable    = `CREATE TABLE %s (event_time TIMESTAMP WITH TIME ZONE NOT NULL, event_data JSONB);`
+
+	psqlUpdateRow = `INSERT INTO %s (key, value) VALUES ($1, $2) ON CONFLICT (key) DO UPDATE SET value = EXCLUDED.value;`
+	psqlDeleteRow = `DELETE FROM %s WHERE key = $1;`
+	psqlInsertRow = `INSERT INTO %s (event_time, event_data) VALUES ($1, $2);`
+)
+
+// Postgres constants
+const (
+	PostgresFormat             = "format"
+	PostgresConnectionString   = "connection_string"
+	PostgresTable              = "table"
+	PostgresHost               = "host"
+	PostgresPort               = "port"
+	PostgresUsername           = "username"
+	PostgresPassword           = "password"
+	PostgresDatabase           = "database"
+	PostgresQueueDir           = "queue_dir"
+	PostgresQueueLimit         = "queue_limit"
+	PostgresMaxOpenConnections = "max_open_connections"
+
+	EnvPostgresEnable             = "MINIO_NOTIFY_POSTGRES_ENABLE"
+	EnvPostgresFormat             = "MINIO_NOTIFY_POSTGRES_FORMAT"
+	EnvPostgresConnectionString   = "MINIO_NOTIFY_POSTGRES_CONNECTION_STRING"
+	EnvPostgresTable              = "MINIO_NOTIFY_POSTGRES_TABLE"
+	EnvPostgresHost               = "MINIO_NOTIFY_POSTGRES_HOST"
+	EnvPostgresPort               = "MINIO_NOTIFY_POSTGRES_PORT"
+	EnvPostgresUsername           = "MINIO_NOTIFY_POSTGRES_USERNAME"
+	EnvPostgresPassword           = "MINIO_NOTIFY_POSTGRES_PASSWORD"
+	EnvPostgresDatabase           = "MINIO_NOTIFY_POSTGRES_DATABASE"
+	EnvPostgresQueueDir           = "MINIO_NOTIFY_POSTGRES_QUEUE_DIR"
+	EnvPostgresQueueLimit         = "MINIO_NOTIFY_POSTGRES_QUEUE_LIMIT"
+	EnvPostgresMaxOpenConnections = "MINIO_NOTIFY_POSTGRES_MAX_OPEN_CONNECTIONS"
+)
+
+// PostgreSQLArgs - PostgreSQL target arguments.
+type PostgreSQLArgs struct {
+	Enable             bool      `json:"enable"`
+	Format             string    `json:"format"`
+	ConnectionString   string    `json:"connectionString"`
+	Table              string    `json:"table"`
+	Host               xnet.Host `json:"host"`     // default: localhost
+	Port               string    `json:"port"`     // default: 5432
+	Username           string    `json:"username"` // default: user running minio
+	Password           string    `json:"password"` // default: no password
+	Database           string    `json:"database"` // default: same as user
+	QueueDir           string    `json:"queueDir"`
+	QueueLimit         uint64    `json:"queueLimit"`
+	MaxOpenConnections int       `json:"maxOpenConnections"`
+}
+
+// Validate PostgreSQLArgs fields
+func (p PostgreSQLArgs) Validate() error {
+	if !p.Enable {
+		return nil
+	}
+	if p.Table == "" {
+		return fmt.Errorf("empty table name")
+	}
+	if p.Format != "" {
+		f := strings.ToLower(p.Format)
+		if f != event.NamespaceFormat && f != event.AccessFormat {
+			return fmt.Errorf("unrecognized format value")
+		}
+	}
+
+	if p.ConnectionString != "" {
+		// No pq API doesn't help to validate connection string
+		// prior connection, so no validation for now.
+	} else {
+		// Some fields need to be specified when ConnectionString is unspecified
+		if p.Port == "" {
+			return fmt.Errorf("unspecified port")
+		}
+		if _, err := strconv.Atoi(p.Port); err != nil {
+			return fmt.Errorf("invalid port")
+		}
+		if p.Database == "" {
+			return fmt.Errorf("database unspecified")
+		}
+	}
+
+	if p.QueueDir != "" {
+		if !filepath.IsAbs(p.QueueDir) {
+			return errors.New("queueDir path should be absolute")
+		}
+	}
+
+	if p.MaxOpenConnections < 0 {
+		return errors.New("maxOpenConnections cannot be less than zero")
+	}
+
+	return nil
+}
+
+// PostgreSQLTarget - PostgreSQL target.
+type PostgreSQLTarget struct {
+	id         event.TargetID
+	args       PostgreSQLArgs
+	updateStmt *sql.Stmt
+	deleteStmt *sql.Stmt
+	insertStmt *sql.Stmt
+	db         *sql.DB
+	store      Store
+	firstPing  bool
+	connString string
+	loggerOnce func(ctx context.Context, err error, id interface{}, errKind ...interface{})
+}
+
+// ID - returns target ID.
+func (target *PostgreSQLTarget) ID() event.TargetID {
+	return target.id
+}
+
+// HasQueueStore - Checks if the queueStore has been configured for the target
+func (target *PostgreSQLTarget) HasQueueStore() bool {
+	return target.store != nil
+}
+
+// IsActive - Return true if target is up and active
+func (target *PostgreSQLTarget) IsActive() (bool, error) {
+	if target.db == nil {
+		db, err := sql.Open("postgres", target.connString)
+		if err != nil {
+			return false, err
+		}
+		target.db = db
+		if target.args.MaxOpenConnections > 0 {
+			// Set the maximum connections limit
+			target.db.SetMaxOpenConns(target.args.MaxOpenConnections)
+		}
+	}
+	if err := target.db.Ping(); err != nil {
+		if IsConnErr(err) {
+			return false, errNotConnected
+		}
+		return false, err
+	}
+	return true, nil
+}
+
+// Save - saves the events to the store if questore is configured, which will be replayed when the PostgreSQL connection is active.
+func (target *PostgreSQLTarget) Save(eventData event.Event) error {
+	if target.store != nil {
+		return target.store.Put(eventData)
+	}
+	_, err := target.IsActive()
+	if err != nil {
+		return err
+	}
+	return target.send(eventData)
+}
+
+// IsConnErr - To detect a connection error.
+func IsConnErr(err error) bool {
+	return IsConnRefusedErr(err) || err.Error() == "sql: database is closed" || err.Error() == "sql: statement is closed" || err.Error() == "invalid connection"
+}
+
+// send - sends an event to the PostgreSQL.
+func (target *PostgreSQLTarget) send(eventData event.Event) error {
+	if target.args.Format == event.NamespaceFormat {
+		objectName, err := url.QueryUnescape(eventData.S3.Object.Key)
+		if err != nil {
+			return err
+		}
+		key := eventData.S3.Bucket.Name + "/" + objectName
+
+		if eventData.EventName == event.ObjectRemovedDelete {
+			_, err = target.deleteStmt.Exec(key)
+		} else {
+			var data []byte
+			if data, err = json.Marshal(struct{ Records []event.Event }{[]event.Event{eventData}}); err != nil {
+				return err
+			}
+
+			_, err = target.updateStmt.Exec(key, data)
+		}
+		return err
+	}
+
+	if target.args.Format == event.AccessFormat {
+		eventTime, err := time.Parse(event.AMZTimeFormat, eventData.EventTime)
+		if err != nil {
+			return err
+		}
+
+		data, err := json.Marshal(struct{ Records []event.Event }{[]event.Event{eventData}})
+		if err != nil {
+			return err
+		}
+
+		if _, err = target.insertStmt.Exec(eventTime, data); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// Send - reads an event from store and sends it to PostgreSQL.
+func (target *PostgreSQLTarget) Send(eventKey string) error {
+	_, err := target.IsActive()
+	if err != nil {
+		return err
+	}
+	if !target.firstPing {
+		if err := target.executeStmts(); err != nil {
+			if IsConnErr(err) {
+				return errNotConnected
+			}
+			return err
+		}
+	}
+
+	eventData, eErr := target.store.Get(eventKey)
+	if eErr != nil {
+		// The last event key in a successful batch will be sent in the channel atmost once by the replayEvents()
+		// Such events will not exist and wouldve been already been sent successfully.
+		if os.IsNotExist(eErr) {
+			return nil
+		}
+		return eErr
+	}
+
+	if err := target.send(eventData); err != nil {
+		if IsConnErr(err) {
+			return errNotConnected
+		}
+		return err
+	}
+
+	// Delete the event from store.
+	return target.store.Del(eventKey)
+}
+
+// Close - closes underneath connections to PostgreSQL database.
+func (target *PostgreSQLTarget) Close() error {
+	if target.updateStmt != nil {
+		// FIXME: log returned error. ignore time being.
+		_ = target.updateStmt.Close()
+	}
+
+	if target.deleteStmt != nil {
+		// FIXME: log returned error. ignore time being.
+		_ = target.deleteStmt.Close()
+	}
+
+	if target.insertStmt != nil {
+		// FIXME: log returned error. ignore time being.
+		_ = target.insertStmt.Close()
+	}
+
+	return target.db.Close()
+}
+
+// Executes the table creation statements.
+func (target *PostgreSQLTarget) executeStmts() error {
+
+	_, err := target.db.Exec(fmt.Sprintf(psqlTableExists, target.args.Table))
+	if err != nil {
+		createStmt := psqlCreateNamespaceTable
+		if target.args.Format == event.AccessFormat {
+			createStmt = psqlCreateAccessTable
+		}
+
+		if _, dbErr := target.db.Exec(fmt.Sprintf(createStmt, target.args.Table)); dbErr != nil {
+			return dbErr
+		}
+	}
+
+	switch target.args.Format {
+	case event.NamespaceFormat:
+		// insert or update statement
+		if target.updateStmt, err = target.db.Prepare(fmt.Sprintf(psqlUpdateRow, target.args.Table)); err != nil {
+			return err
+		}
+		// delete statement
+		if target.deleteStmt, err = target.db.Prepare(fmt.Sprintf(psqlDeleteRow, target.args.Table)); err != nil {
+			return err
+		}
+	case event.AccessFormat:
+		// insert statement
+		if target.insertStmt, err = target.db.Prepare(fmt.Sprintf(psqlInsertRow, target.args.Table)); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// NewPostgreSQLTarget - creates new PostgreSQL target.
+func NewPostgreSQLTarget(id string, args PostgreSQLArgs, doneCh <-chan struct{}, loggerOnce func(ctx context.Context, err error, id interface{}, kind ...interface{}), test bool) (*PostgreSQLTarget, error) {
+	params := []string{args.ConnectionString}
+	if args.ConnectionString == "" {
+		params = []string{}
+		if !args.Host.IsEmpty() {
+			params = append(params, "host="+args.Host.String())
+		}
+		if args.Port != "" {
+			params = append(params, "port="+args.Port)
+		}
+		if args.Username != "" {
+			params = append(params, "username="+args.Username)
+		}
+		if args.Password != "" {
+			params = append(params, "password="+args.Password)
+		}
+		if args.Database != "" {
+			params = append(params, "dbname="+args.Database)
+		}
+	}
+	connStr := strings.Join(params, " ")
+
+	target := &PostgreSQLTarget{
+		id:         event.TargetID{ID: id, Name: "postgresql"},
+		args:       args,
+		firstPing:  false,
+		connString: connStr,
+		loggerOnce: loggerOnce,
+	}
+
+	db, err := sql.Open("postgres", connStr)
+	if err != nil {
+		return target, err
+	}
+	target.db = db
+
+	if args.MaxOpenConnections > 0 {
+		// Set the maximum connections limit
+		target.db.SetMaxOpenConns(args.MaxOpenConnections)
+	}
+
+	var store Store
+
+	if args.QueueDir != "" {
+		queueDir := filepath.Join(args.QueueDir, storePrefix+"-postgresql-"+id)
+		store = NewQueueStore(queueDir, args.QueueLimit)
+		if oErr := store.Open(); oErr != nil {
+			target.loggerOnce(context.Background(), oErr, target.ID())
+			return target, oErr
+		}
+		target.store = store
+	}
+
+	err = target.db.Ping()
+	if err != nil {
+		if target.store == nil || !(IsConnRefusedErr(err) || IsConnResetErr(err)) {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+	} else {
+		if err = target.executeStmts(); err != nil {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+		target.firstPing = true
+	}
+
+	if target.store != nil && !test {
+		// Replays the events from the store.
+		eventKeyCh := replayEvents(target.store, doneCh, target.loggerOnce, target.ID())
+		// Start replaying events from the store.
+		go sendEvents(target, eventKeyCh, doneCh, target.loggerOnce)
+	}
+
+	return target, nil
+}

internal/event/target/postgresql_test.go

@@ -0,0 +1,38 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"database/sql"
+	"testing"
+)
+
+// TestPostgreSQLRegistration checks if postgres driver
+// is registered and fails otherwise.
+func TestPostgreSQLRegistration(t *testing.T) {
+	var found bool
+	for _, drv := range sql.Drivers() {
+		if drv == "postgres" {
+			found = true
+			break
+		}
+	}
+	if !found {
+		t.Fatal("postgres driver not registered")
+	}
+}

internal/event/target/queuestore.go

@@ -0,0 +1,207 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"math"
+	"os"
+	"path/filepath"
+	"sort"
+	"sync"
+
+	"github.com/minio/minio/internal/event"
+	"github.com/minio/pkg/sys"
+)
+
+const (
+	defaultLimit = 100000 // Default store limit.
+	eventExt     = ".event"
+)
+
+// QueueStore - Filestore for persisting events.
+type QueueStore struct {
+	sync.RWMutex
+	currentEntries uint64
+	entryLimit     uint64
+	directory      string
+}
+
+// NewQueueStore - Creates an instance for QueueStore.
+func NewQueueStore(directory string, limit uint64) Store {
+	if limit == 0 {
+		limit = defaultLimit
+		_, maxRLimit, err := sys.GetMaxOpenFileLimit()
+		if err == nil {
+			// Limit the maximum number of entries
+			// to maximum open file limit
+			if maxRLimit < limit {
+				limit = maxRLimit
+			}
+		}
+	}
+
+	return &QueueStore{
+		directory:  directory,
+		entryLimit: limit,
+	}
+}
+
+// Open - Creates the directory if not present.
+func (store *QueueStore) Open() error {
+	store.Lock()
+	defer store.Unlock()
+
+	if err := os.MkdirAll(store.directory, os.FileMode(0770)); err != nil {
+		return err
+	}
+
+	names, err := store.list()
+	if err != nil {
+		return err
+	}
+
+	currentEntries := uint64(len(names))
+	if currentEntries >= store.entryLimit {
+		return errLimitExceeded
+	}
+
+	store.currentEntries = currentEntries
+
+	return nil
+}
+
+// write - writes event to the directory.
+func (store *QueueStore) write(key string, e event.Event) error {
+
+	// Marshalls the event.
+	eventData, err := json.Marshal(e)
+	if err != nil {
+		return err
+	}
+
+	path := filepath.Join(store.directory, key+eventExt)
+	if err := ioutil.WriteFile(path, eventData, os.FileMode(0770)); err != nil {
+		return err
+	}
+
+	// Increment the event count.
+	store.currentEntries++
+
+	return nil
+}
+
+// Put - puts a event to the store.
+func (store *QueueStore) Put(e event.Event) error {
+	store.Lock()
+	defer store.Unlock()
+	if store.currentEntries >= store.entryLimit {
+		return errLimitExceeded
+	}
+	key, err := getNewUUID()
+	if err != nil {
+		return err
+	}
+	return store.write(key, e)
+}
+
+// Get - gets a event from the store.
+func (store *QueueStore) Get(key string) (event event.Event, err error) {
+	store.RLock()
+
+	defer func(store *QueueStore) {
+		store.RUnlock()
+		if err != nil {
+			// Upon error we remove the entry.
+			store.Del(key)
+		}
+	}(store)
+
+	var eventData []byte
+	eventData, err = ioutil.ReadFile(filepath.Join(store.directory, key+eventExt))
+	if err != nil {
+		return event, err
+	}
+
+	if len(eventData) == 0 {
+		return event, os.ErrNotExist
+	}
+
+	if err = json.Unmarshal(eventData, &event); err != nil {
+		return event, err
+	}
+
+	return event, nil
+}
+
+// Del - Deletes an entry from the store.
+func (store *QueueStore) Del(key string) error {
+	store.Lock()
+	defer store.Unlock()
+	return store.del(key)
+}
+
+// lockless call
+func (store *QueueStore) del(key string) error {
+	if err := os.Remove(filepath.Join(store.directory, key+eventExt)); err != nil {
+		return err
+	}
+
+	// Decrement the current entries count.
+	store.currentEntries--
+
+	// Current entries can underflow, when multiple
+	// events are being pushed in parallel, this code
+	// is needed to ensure that we don't underflow.
+	//
+	// queueStore replayEvents is not serialized,
+	// this code is needed to protect us under
+	// such situations.
+	if store.currentEntries == math.MaxUint64 {
+		store.currentEntries = 0
+	}
+	return nil
+}
+
+// List - lists all files from the directory.
+func (store *QueueStore) List() ([]string, error) {
+	store.RLock()
+	defer store.RUnlock()
+	return store.list()
+}
+
+// list lock less.
+func (store *QueueStore) list() ([]string, error) {
+	var names []string
+	files, err := ioutil.ReadDir(store.directory)
+	if err != nil {
+		return names, err
+	}
+
+	// Sort the dentries.
+	sort.Slice(files, func(i, j int) bool {
+		return files[i].ModTime().Before(files[j].ModTime())
+	})
+
+	for _, file := range files {
+		names = append(names, file.Name())
+	}
+
+	return names, nil
+}

internal/event/target/queuestore_test.go

@@ -0,0 +1,214 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"os"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"testing"
+
+	"github.com/minio/minio/internal/event"
+)
+
+// TestDir
+var queueDir = filepath.Join(os.TempDir(), "minio_test")
+
+// Sample test event.
+var testEvent = event.Event{EventVersion: "1.0", EventSource: "test_source", AwsRegion: "test_region", EventTime: "test_time", EventName: event.ObjectAccessedGet}
+
+// Initialize the store.
+func setUpStore(directory string, limit uint64) (Store, error) {
+	store := NewQueueStore(queueDir, limit)
+	if oErr := store.Open(); oErr != nil {
+		return nil, oErr
+	}
+	return store, nil
+}
+
+// Tear down store
+func tearDownStore() error {
+	return os.RemoveAll(queueDir)
+}
+
+// TestQueueStorePut - tests for store.Put
+func TestQueueStorePut(t *testing.T) {
+	defer func() {
+		if err := tearDownStore(); err != nil {
+			t.Fatal("Failed to tear down store ", err)
+		}
+	}()
+	store, err := setUpStore(queueDir, 100)
+	if err != nil {
+		t.Fatal("Failed to create a queue store ", err)
+
+	}
+	// Put 100 events.
+	for i := 0; i < 100; i++ {
+		if err := store.Put(testEvent); err != nil {
+			t.Fatal("Failed to put to queue store ", err)
+		}
+	}
+	// Count the events.
+	names, err := store.List()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(names) != 100 {
+		t.Fatalf("List() Expected: 100, got %d", len(names))
+	}
+}
+
+// TestQueueStoreGet - tests for store.Get
+func TestQueueStoreGet(t *testing.T) {
+	defer func() {
+		if err := tearDownStore(); err != nil {
+			t.Fatal("Failed to tear down store ", err)
+		}
+	}()
+	store, err := setUpStore(queueDir, 10)
+	if err != nil {
+		t.Fatal("Failed to create a queue store ", err)
+	}
+	// Put 10 events
+	for i := 0; i < 10; i++ {
+		if err := store.Put(testEvent); err != nil {
+			t.Fatal("Failed to put to queue store ", err)
+		}
+	}
+	eventKeys, err := store.List()
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Get 10 events.
+	if len(eventKeys) == 10 {
+		for _, key := range eventKeys {
+			event, eErr := store.Get(strings.TrimSuffix(key, eventExt))
+			if eErr != nil {
+				t.Fatal("Failed to Get the event from the queue store ", eErr)
+			}
+			if !reflect.DeepEqual(testEvent, event) {
+				t.Fatalf("Failed to read the event: error: expected = %v, got = %v", testEvent, event)
+			}
+		}
+	} else {
+		t.Fatalf("List() Expected: 10, got %d", len(eventKeys))
+	}
+}
+
+// TestQueueStoreDel - tests for store.Del
+func TestQueueStoreDel(t *testing.T) {
+	defer func() {
+		if err := tearDownStore(); err != nil {
+			t.Fatal("Failed to tear down store ", err)
+		}
+	}()
+	store, err := setUpStore(queueDir, 20)
+	if err != nil {
+		t.Fatal("Failed to create a queue store ", err)
+	}
+	// Put 20 events.
+	for i := 0; i < 20; i++ {
+		if err := store.Put(testEvent); err != nil {
+			t.Fatal("Failed to put to queue store ", err)
+		}
+	}
+	eventKeys, err := store.List()
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Remove all the events.
+	if len(eventKeys) == 20 {
+		for _, key := range eventKeys {
+			err := store.Del(strings.TrimSuffix(key, eventExt))
+			if err != nil {
+				t.Fatal("queue store Del failed with ", err)
+			}
+		}
+	} else {
+		t.Fatalf("List() Expected: 20, got %d", len(eventKeys))
+	}
+
+	names, err := store.List()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(names) != 0 {
+		t.Fatalf("List() Expected: 0, got %d", len(names))
+	}
+}
+
+// TestQueueStoreLimit - tests the event limit for the store.
+func TestQueueStoreLimit(t *testing.T) {
+	defer func() {
+		if err := tearDownStore(); err != nil {
+			t.Fatal("Failed to tear down store ", err)
+		}
+	}()
+	// The max limit is set to 5.
+	store, err := setUpStore(queueDir, 5)
+	if err != nil {
+		t.Fatal("Failed to create a queue store ", err)
+	}
+	for i := 0; i < 5; i++ {
+		if err := store.Put(testEvent); err != nil {
+			t.Fatal("Failed to put to queue store ", err)
+		}
+	}
+	// Should not allow 6th Put.
+	if err := store.Put(testEvent); err == nil {
+		t.Fatalf("Expected to fail with %s, but passes", errLimitExceeded)
+	}
+}
+
+// TestQueueStoreLimit - tests for store.LimitN.
+func TestQueueStoreListN(t *testing.T) {
+	defer func() {
+		if err := tearDownStore(); err != nil {
+			t.Fatal("Failed to tear down store ", err)
+		}
+	}()
+	store, err := setUpStore(queueDir, 10)
+	if err != nil {
+		t.Fatal("Failed to create a queue store ", err)
+	}
+	for i := 0; i < 10; i++ {
+		if err := store.Put(testEvent); err != nil {
+			t.Fatal("Failed to put to queue store ", err)
+		}
+	}
+	// Should return all the event keys in the store.
+	names, err := store.List()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if len(names) != 10 {
+		t.Fatalf("List() Expected: 10, got %d", len(names))
+	}
+
+	if err = os.RemoveAll(queueDir); err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = store.List()
+	if !os.IsNotExist(err) {
+		t.Fatalf("Expected List() to fail with os.ErrNotExist, %s", err)
+	}
+}

internal/event/target/redis.go

@@ -0,0 +1,343 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"github.com/gomodule/redigo/redis"
+	"github.com/minio/minio/internal/event"
+	xnet "github.com/minio/minio/internal/net"
+)
+
+// Redis constants
+const (
+	RedisFormat     = "format"
+	RedisAddress    = "address"
+	RedisPassword   = "password"
+	RedisKey        = "key"
+	RedisQueueDir   = "queue_dir"
+	RedisQueueLimit = "queue_limit"
+
+	EnvRedisEnable     = "MINIO_NOTIFY_REDIS_ENABLE"
+	EnvRedisFormat     = "MINIO_NOTIFY_REDIS_FORMAT"
+	EnvRedisAddress    = "MINIO_NOTIFY_REDIS_ADDRESS"
+	EnvRedisPassword   = "MINIO_NOTIFY_REDIS_PASSWORD"
+	EnvRedisKey        = "MINIO_NOTIFY_REDIS_KEY"
+	EnvRedisQueueDir   = "MINIO_NOTIFY_REDIS_QUEUE_DIR"
+	EnvRedisQueueLimit = "MINIO_NOTIFY_REDIS_QUEUE_LIMIT"
+)
+
+// RedisArgs - Redis target arguments.
+type RedisArgs struct {
+	Enable     bool      `json:"enable"`
+	Format     string    `json:"format"`
+	Addr       xnet.Host `json:"address"`
+	Password   string    `json:"password"`
+	Key        string    `json:"key"`
+	QueueDir   string    `json:"queueDir"`
+	QueueLimit uint64    `json:"queueLimit"`
+}
+
+// RedisAccessEvent holds event log data and timestamp
+type RedisAccessEvent struct {
+	Event     []event.Event
+	EventTime string
+}
+
+// Validate RedisArgs fields
+func (r RedisArgs) Validate() error {
+	if !r.Enable {
+		return nil
+	}
+
+	if r.Format != "" {
+		f := strings.ToLower(r.Format)
+		if f != event.NamespaceFormat && f != event.AccessFormat {
+			return fmt.Errorf("unrecognized format")
+		}
+	}
+
+	if r.Key == "" {
+		return fmt.Errorf("empty key")
+	}
+
+	if r.QueueDir != "" {
+		if !filepath.IsAbs(r.QueueDir) {
+			return errors.New("queueDir path should be absolute")
+		}
+	}
+
+	return nil
+}
+
+func (r RedisArgs) validateFormat(c redis.Conn) error {
+	typeAvailable, err := redis.String(c.Do("TYPE", r.Key))
+	if err != nil {
+		return err
+	}
+
+	if typeAvailable != "none" {
+		expectedType := "hash"
+		if r.Format == event.AccessFormat {
+			expectedType = "list"
+		}
+
+		if typeAvailable != expectedType {
+			return fmt.Errorf("expected type %v does not match with available type %v", expectedType, typeAvailable)
+		}
+	}
+
+	return nil
+}
+
+// RedisTarget - Redis target.
+type RedisTarget struct {
+	id         event.TargetID
+	args       RedisArgs
+	pool       *redis.Pool
+	store      Store
+	firstPing  bool
+	loggerOnce func(ctx context.Context, err error, id interface{}, errKind ...interface{})
+}
+
+// ID - returns target ID.
+func (target *RedisTarget) ID() event.TargetID {
+	return target.id
+}
+
+// HasQueueStore - Checks if the queueStore has been configured for the target
+func (target *RedisTarget) HasQueueStore() bool {
+	return target.store != nil
+}
+
+// IsActive - Return true if target is up and active
+func (target *RedisTarget) IsActive() (bool, error) {
+	conn := target.pool.Get()
+	defer func() {
+		cErr := conn.Close()
+		target.loggerOnce(context.Background(), cErr, target.ID())
+	}()
+	_, pingErr := conn.Do("PING")
+	if pingErr != nil {
+		if IsConnRefusedErr(pingErr) {
+			return false, errNotConnected
+		}
+		return false, pingErr
+	}
+	return true, nil
+}
+
+// Save - saves the events to the store if questore is configured, which will be replayed when the redis connection is active.
+func (target *RedisTarget) Save(eventData event.Event) error {
+	if target.store != nil {
+		return target.store.Put(eventData)
+	}
+	_, err := target.IsActive()
+	if err != nil {
+		return err
+	}
+	return target.send(eventData)
+}
+
+// send - sends an event to the redis.
+func (target *RedisTarget) send(eventData event.Event) error {
+	conn := target.pool.Get()
+	defer func() {
+		cErr := conn.Close()
+		target.loggerOnce(context.Background(), cErr, target.ID())
+	}()
+
+	if target.args.Format == event.NamespaceFormat {
+		objectName, err := url.QueryUnescape(eventData.S3.Object.Key)
+		if err != nil {
+			return err
+		}
+		key := eventData.S3.Bucket.Name + "/" + objectName
+
+		if eventData.EventName == event.ObjectRemovedDelete {
+			_, err = conn.Do("HDEL", target.args.Key, key)
+		} else {
+			var data []byte
+			if data, err = json.Marshal(struct{ Records []event.Event }{[]event.Event{eventData}}); err != nil {
+				return err
+			}
+
+			_, err = conn.Do("HSET", target.args.Key, key, data)
+		}
+		if err != nil {
+			return err
+		}
+	}
+
+	if target.args.Format == event.AccessFormat {
+		data, err := json.Marshal([]RedisAccessEvent{{Event: []event.Event{eventData}, EventTime: eventData.EventTime}})
+		if err != nil {
+			return err
+		}
+		if _, err := conn.Do("RPUSH", target.args.Key, data); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// Send - reads an event from store and sends it to redis.
+func (target *RedisTarget) Send(eventKey string) error {
+	conn := target.pool.Get()
+	defer func() {
+		cErr := conn.Close()
+		target.loggerOnce(context.Background(), cErr, target.ID())
+	}()
+	_, pingErr := conn.Do("PING")
+	if pingErr != nil {
+		if IsConnRefusedErr(pingErr) {
+			return errNotConnected
+		}
+		return pingErr
+	}
+
+	if !target.firstPing {
+		if err := target.args.validateFormat(conn); err != nil {
+			if IsConnRefusedErr(err) {
+				return errNotConnected
+			}
+			return err
+		}
+		target.firstPing = true
+	}
+
+	eventData, eErr := target.store.Get(eventKey)
+	if eErr != nil {
+		// The last event key in a successful batch will be sent in the channel atmost once by the replayEvents()
+		// Such events will not exist and would've been already been sent successfully.
+		if os.IsNotExist(eErr) {
+			return nil
+		}
+		return eErr
+	}
+
+	if err := target.send(eventData); err != nil {
+		if IsConnRefusedErr(err) {
+			return errNotConnected
+		}
+		return err
+	}
+
+	// Delete the event from store.
+	return target.store.Del(eventKey)
+}
+
+// Close - releases the resources used by the pool.
+func (target *RedisTarget) Close() error {
+	return target.pool.Close()
+}
+
+// NewRedisTarget - creates new Redis target.
+func NewRedisTarget(id string, args RedisArgs, doneCh <-chan struct{}, loggerOnce func(ctx context.Context, err error, id interface{}, errKind ...interface{}), test bool) (*RedisTarget, error) {
+	pool := &redis.Pool{
+		MaxIdle:     3,
+		IdleTimeout: 2 * 60 * time.Second,
+		Dial: func() (redis.Conn, error) {
+			conn, err := redis.Dial("tcp", args.Addr.String())
+			if err != nil {
+				return nil, err
+			}
+
+			if args.Password != "" {
+				if _, err = conn.Do("AUTH", args.Password); err != nil {
+					cErr := conn.Close()
+					targetID := event.TargetID{ID: id, Name: "redis"}
+					loggerOnce(context.Background(), cErr, targetID)
+					return nil, err
+				}
+			}
+
+			// Must be done after AUTH
+			if _, err = conn.Do("CLIENT", "SETNAME", "MinIO"); err != nil {
+				cErr := conn.Close()
+				targetID := event.TargetID{ID: id, Name: "redis"}
+				loggerOnce(context.Background(), cErr, targetID)
+				return nil, err
+			}
+
+			return conn, nil
+		},
+		TestOnBorrow: func(c redis.Conn, t time.Time) error {
+			_, err := c.Do("PING")
+			return err
+		},
+	}
+
+	var store Store
+
+	target := &RedisTarget{
+		id:         event.TargetID{ID: id, Name: "redis"},
+		args:       args,
+		pool:       pool,
+		loggerOnce: loggerOnce,
+	}
+
+	if args.QueueDir != "" {
+		queueDir := filepath.Join(args.QueueDir, storePrefix+"-redis-"+id)
+		store = NewQueueStore(queueDir, args.QueueLimit)
+		if oErr := store.Open(); oErr != nil {
+			target.loggerOnce(context.Background(), oErr, target.ID())
+			return target, oErr
+		}
+		target.store = store
+	}
+
+	conn := target.pool.Get()
+	defer func() {
+		cErr := conn.Close()
+		target.loggerOnce(context.Background(), cErr, target.ID())
+	}()
+
+	_, pingErr := conn.Do("PING")
+	if pingErr != nil {
+		if target.store == nil || !(IsConnRefusedErr(pingErr) || IsConnResetErr(pingErr)) {
+			target.loggerOnce(context.Background(), pingErr, target.ID())
+			return target, pingErr
+		}
+	} else {
+		if err := target.args.validateFormat(conn); err != nil {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+		target.firstPing = true
+	}
+
+	if target.store != nil && !test {
+		// Replays the events from the store.
+		eventKeyCh := replayEvents(target.store, doneCh, target.loggerOnce, target.ID())
+		// Start replaying events from the store.
+		go sendEvents(target, eventKeyCh, doneCh, target.loggerOnce)
+	}
+
+	return target, nil
+}

internal/event/target/store.go

@@ -0,0 +1,144 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+	"syscall"
+	"time"
+
+	"github.com/minio/minio/internal/event"
+)
+
+const retryInterval = 3 * time.Second
+
+// errNotConnected - indicates that the target connection is not active.
+var errNotConnected = errors.New("not connected to target server/service")
+
+// errLimitExceeded error is sent when the maximum limit is reached.
+var errLimitExceeded = errors.New("the maximum store limit reached")
+
+// Store - To persist the events.
+type Store interface {
+	Put(event event.Event) error
+	Get(key string) (event.Event, error)
+	List() ([]string, error)
+	Del(key string) error
+	Open() error
+}
+
+// replayEvents - Reads the events from the store and replays.
+func replayEvents(store Store, doneCh <-chan struct{}, loggerOnce func(ctx context.Context, err error, id interface{}, kind ...interface{}), id event.TargetID) <-chan string {
+	eventKeyCh := make(chan string)
+
+	go func() {
+		retryTicker := time.NewTicker(retryInterval)
+		defer retryTicker.Stop()
+		defer close(eventKeyCh)
+		for {
+			names, err := store.List()
+			if err == nil {
+				for _, name := range names {
+					select {
+					case eventKeyCh <- strings.TrimSuffix(name, eventExt):
+						// Get next key.
+					case <-doneCh:
+						return
+					}
+				}
+			}
+
+			if len(names) < 2 {
+				select {
+				case <-retryTicker.C:
+					if err != nil {
+						loggerOnce(context.Background(),
+							fmt.Errorf("store.List() failed '%w'", err), id)
+					}
+				case <-doneCh:
+					return
+				}
+			}
+		}
+	}()
+
+	return eventKeyCh
+}
+
+// IsConnRefusedErr - To check fot "connection refused" error.
+func IsConnRefusedErr(err error) bool {
+	return errors.Is(err, syscall.ECONNREFUSED)
+}
+
+// IsConnResetErr - Checks for connection reset errors.
+func IsConnResetErr(err error) bool {
+	if strings.Contains(err.Error(), "connection reset by peer") {
+		return true
+	}
+	// incase if error message is wrapped.
+	return errors.Is(err, syscall.ECONNRESET)
+}
+
+// sendEvents - Reads events from the store and re-plays.
+func sendEvents(target event.Target, eventKeyCh <-chan string, doneCh <-chan struct{}, loggerOnce func(ctx context.Context, err error, id interface{}, kind ...interface{})) {
+	retryTicker := time.NewTicker(retryInterval)
+	defer retryTicker.Stop()
+
+	send := func(eventKey string) bool {
+		for {
+			err := target.Send(eventKey)
+			if err == nil {
+				break
+			}
+
+			if err != errNotConnected && !IsConnResetErr(err) {
+				loggerOnce(context.Background(),
+					fmt.Errorf("target.Send() failed with '%w'", err),
+					target.ID())
+			}
+
+			// Retrying after 3secs back-off
+
+			select {
+			case <-retryTicker.C:
+			case <-doneCh:
+				return false
+			}
+		}
+		return true
+	}
+
+	for {
+		select {
+		case eventKey, ok := <-eventKeyCh:
+			if !ok {
+				// closed channel.
+				return
+			}
+
+			if !send(eventKey) {
+				return
+			}
+		case <-doneCh:
+			return
+		}
+	}
+}

internal/event/target/testdata/contrib/certs/nats_client_cert.pem

@@ -0,0 +1,13 @@
+-----BEGIN CERTIFICATE-----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==
+-----END CERTIFICATE-----

internal/event/target/testdata/contrib/certs/nats_client_key.pem

@@ -0,0 +1,5 @@
+-----BEGIN EC PRIVATE KEY-----
+MHcCAQEEIBluB2BuspJcz1e58rnXpQEx48/ZwNmygNw06NbdTZDroAoGCCqGSM49
+AwEHoUQDQgAEQIWK0F2G83islUsPJ3+e4AaYcBT9aOUuwo8aBign4Ic3YRMSohJm
+4rCvhUktmLZbVO3DOy+wHbiyG7hJxhx2EA==
+-----END EC PRIVATE KEY-----

internal/event/target/testdata/contrib/certs/nats_server_cert.pem

@@ -0,0 +1,12 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

internal/event/target/testdata/contrib/certs/nats_server_key.pem

@@ -0,0 +1,5 @@
+-----BEGIN EC PRIVATE KEY-----
+MHcCAQEEILFuMS2xvsc/CsuqtSv3S2iSCcc28rZsg1wpR2kirXFloAoGCCqGSM49
+AwEHoUQDQgAEqJSlCOxVUgNk7PhklvwxwyjXMwzY33HCNhixE7KOonvG7r3jjg49
+SSC/X3+aUQzflOkL8MJQ5lxKodWulwSOBw==
+-----END EC PRIVATE KEY-----

internal/event/target/testdata/contrib/certs/root_ca_cert.pem

@@ -0,0 +1,11 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

internal/event/target/testdata/contrib/certs/root_ca_key.pem

@@ -0,0 +1,5 @@
+-----BEGIN EC PRIVATE KEY-----
+MHcCAQEEIB8tAGuc9FP4XbYqMP67TKgjL7OTrACGgEmTf+zMvYRhoAoGCCqGSM49
+AwEHoUQDQgAESvX1TRh3NYeQeX6TjMhHcoYdfMTTXDVBkOYhizve2dCrSub0ZQ3n
+hNSNEmiYKqaZvThB8N9iVNBzIuBQWYtkbA==
+-----END EC PRIVATE KEY-----

internal/event/target/testdata/contrib/nats_tls.conf

@@ -0,0 +1,7 @@
+port: 14225
+net: localhost
+
+tls {
+    cert_file:  "./testdata/contrib/certs/nats_server_cert.pem"
+    key_file:   "./testdata/contrib/certs/nats_server_key.pem"
+}

internal/event/target/testdata/contrib/nats_tls_client_cert.conf

@@ -0,0 +1,18 @@
+port: 14226
+net: localhost
+
+tls {
+    cert_file:  "./testdata/contrib/certs/nats_server_cert.pem"
+    key_file:   "./testdata/contrib/certs/nats_server_key.pem"
+    ca_file:   "./testdata/contrib/certs/root_ca_cert.pem"
+    verify_and_map: true
+}
+authorization {
+    ADMIN = {
+        publish = ">"
+        subscribe = ">"
+    }
+    users = [
+        {user: "CN=localhost,OU=Client,O=MinIO,C=CA", permissions: $ADMIN}
+    ]
+}

internal/event/target/webhook.go

@@ -0,0 +1,262 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package target
+
+import (
+	"bytes"
+	"context"
+	"crypto/tls"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/minio/minio/internal/event"
+	xnet "github.com/minio/minio/internal/net"
+	"github.com/minio/pkg/certs"
+)
+
+// Webhook constants
+const (
+	WebhookEndpoint   = "endpoint"
+	WebhookAuthToken  = "auth_token"
+	WebhookQueueDir   = "queue_dir"
+	WebhookQueueLimit = "queue_limit"
+	WebhookClientCert = "client_cert"
+	WebhookClientKey  = "client_key"
+
+	EnvWebhookEnable     = "MINIO_NOTIFY_WEBHOOK_ENABLE"
+	EnvWebhookEndpoint   = "MINIO_NOTIFY_WEBHOOK_ENDPOINT"
+	EnvWebhookAuthToken  = "MINIO_NOTIFY_WEBHOOK_AUTH_TOKEN"
+	EnvWebhookQueueDir   = "MINIO_NOTIFY_WEBHOOK_QUEUE_DIR"
+	EnvWebhookQueueLimit = "MINIO_NOTIFY_WEBHOOK_QUEUE_LIMIT"
+	EnvWebhookClientCert = "MINIO_NOTIFY_WEBHOOK_CLIENT_CERT"
+	EnvWebhookClientKey  = "MINIO_NOTIFY_WEBHOOK_CLIENT_KEY"
+)
+
+// WebhookArgs - Webhook target arguments.
+type WebhookArgs struct {
+	Enable     bool            `json:"enable"`
+	Endpoint   xnet.URL        `json:"endpoint"`
+	AuthToken  string          `json:"authToken"`
+	Transport  *http.Transport `json:"-"`
+	QueueDir   string          `json:"queueDir"`
+	QueueLimit uint64          `json:"queueLimit"`
+	ClientCert string          `json:"clientCert"`
+	ClientKey  string          `json:"clientKey"`
+}
+
+// Validate WebhookArgs fields
+func (w WebhookArgs) Validate() error {
+	if !w.Enable {
+		return nil
+	}
+	if w.Endpoint.IsEmpty() {
+		return errors.New("endpoint empty")
+	}
+	if w.QueueDir != "" {
+		if !filepath.IsAbs(w.QueueDir) {
+			return errors.New("queueDir path should be absolute")
+		}
+	}
+	if w.ClientCert != "" && w.ClientKey == "" || w.ClientCert == "" && w.ClientKey != "" {
+		return errors.New("cert and key must be specified as a pair")
+	}
+	return nil
+}
+
+// WebhookTarget - Webhook target.
+type WebhookTarget struct {
+	id         event.TargetID
+	args       WebhookArgs
+	httpClient *http.Client
+	store      Store
+	loggerOnce func(ctx context.Context, err error, id interface{}, errKind ...interface{})
+}
+
+// ID - returns target ID.
+func (target WebhookTarget) ID() event.TargetID {
+	return target.id
+}
+
+// HasQueueStore - Checks if the queueStore has been configured for the target
+func (target *WebhookTarget) HasQueueStore() bool {
+	return target.store != nil
+}
+
+// IsActive - Return true if target is up and active
+func (target *WebhookTarget) IsActive() (bool, error) {
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodHead, target.args.Endpoint.String(), nil)
+	if err != nil {
+		if xnet.IsNetworkOrHostDown(err, false) {
+			return false, errNotConnected
+		}
+		return false, err
+	}
+
+	resp, err := target.httpClient.Do(req)
+	if err != nil {
+		if xnet.IsNetworkOrHostDown(err, false) || errors.Is(err, context.DeadlineExceeded) {
+			return false, errNotConnected
+		}
+		return false, err
+	}
+	io.Copy(ioutil.Discard, resp.Body)
+	resp.Body.Close()
+	// No network failure i.e response from the target means its up
+	return true, nil
+}
+
+// Save - saves the events to the store if queuestore is configured, which will be replayed when the wenhook connection is active.
+func (target *WebhookTarget) Save(eventData event.Event) error {
+	if target.store != nil {
+		return target.store.Put(eventData)
+	}
+	err := target.send(eventData)
+	if err != nil {
+		if xnet.IsNetworkOrHostDown(err, false) {
+			return errNotConnected
+		}
+	}
+	return err
+}
+
+// send - sends an event to the webhook.
+func (target *WebhookTarget) send(eventData event.Event) error {
+	objectName, err := url.QueryUnescape(eventData.S3.Object.Key)
+	if err != nil {
+		return err
+	}
+	key := eventData.S3.Bucket.Name + "/" + objectName
+
+	data, err := json.Marshal(event.Log{EventName: eventData.EventName, Key: key, Records: []event.Event{eventData}})
+	if err != nil {
+		return err
+	}
+
+	req, err := http.NewRequest("POST", target.args.Endpoint.String(), bytes.NewReader(data))
+	if err != nil {
+		return err
+	}
+
+	if target.args.AuthToken != "" {
+		req.Header.Set("Authorization", "Bearer "+target.args.AuthToken)
+	}
+
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := target.httpClient.Do(req)
+	if err != nil {
+		target.Close()
+		return err
+	}
+	defer resp.Body.Close()
+	io.Copy(ioutil.Discard, resp.Body)
+
+	if resp.StatusCode < 200 || resp.StatusCode > 299 {
+		target.Close()
+		return fmt.Errorf("sending event failed with %v", resp.Status)
+	}
+
+	return nil
+}
+
+// Send - reads an event from store and sends it to webhook.
+func (target *WebhookTarget) Send(eventKey string) error {
+	eventData, eErr := target.store.Get(eventKey)
+	if eErr != nil {
+		// The last event key in a successful batch will be sent in the channel atmost once by the replayEvents()
+		// Such events will not exist and would've been already been sent successfully.
+		if os.IsNotExist(eErr) {
+			return nil
+		}
+		return eErr
+	}
+
+	if err := target.send(eventData); err != nil {
+		if xnet.IsNetworkOrHostDown(err, false) {
+			return errNotConnected
+		}
+		return err
+	}
+
+	// Delete the event from store.
+	return target.store.Del(eventKey)
+}
+
+// Close - does nothing and available for interface compatibility.
+func (target *WebhookTarget) Close() error {
+	// Close idle connection with "keep-alive" states
+	target.httpClient.CloseIdleConnections()
+	return nil
+}
+
+// NewWebhookTarget - creates new Webhook target.
+func NewWebhookTarget(ctx context.Context, id string, args WebhookArgs, loggerOnce func(ctx context.Context, err error, id interface{}, kind ...interface{}), transport *http.Transport, test bool) (*WebhookTarget, error) {
+	var store Store
+	target := &WebhookTarget{
+		id:         event.TargetID{ID: id, Name: "webhook"},
+		args:       args,
+		loggerOnce: loggerOnce,
+	}
+
+	if target.args.ClientCert != "" && target.args.ClientKey != "" {
+		manager, err := certs.NewManager(ctx, target.args.ClientCert, target.args.ClientKey, tls.LoadX509KeyPair)
+		if err != nil {
+			return target, err
+		}
+		transport.TLSClientConfig.GetClientCertificate = manager.GetClientCertificate
+	}
+	target.httpClient = &http.Client{Transport: transport}
+
+	if args.QueueDir != "" {
+		queueDir := filepath.Join(args.QueueDir, storePrefix+"-webhook-"+id)
+		store = NewQueueStore(queueDir, args.QueueLimit)
+		if err := store.Open(); err != nil {
+			target.loggerOnce(context.Background(), err, target.ID())
+			return target, err
+		}
+		target.store = store
+	}
+
+	_, err := target.IsActive()
+	if err != nil {
+		if target.store == nil || err != errNotConnected {
+			target.loggerOnce(ctx, err, target.ID())
+			return target, err
+		}
+	}
+
+	if target.store != nil && !test {
+		// Replays the events from the store.
+		eventKeyCh := replayEvents(target.store, ctx.Done(), target.loggerOnce, target.ID())
+		// Start replaying events from the store.
+		go sendEvents(target, eventKeyCh, ctx.Done(), target.loggerOnce)
+	}
+
+	return target, nil
+}