api: Add new ListenBucketNotificationHandler. (#2336)

This API is precursor before implementing `minio lambda` and `mc` continous replication.

This new api is an extention to BucketNofication APIs.

// Request
```
GET /bucket?notificationARN=arn:minio:lambda:us-east-1:10:minio HTTP/1.1
...
...
```

// Response
```

{"Records": ...}
...
...
...
{"Records": ...}
```

config-v6.go

@@ -0,0 +1,255 @@
+/*
+ * Minio Cloud Storage, (C) 2016 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 main
+
+import (
+	"os"
+	"sync"
+
+	"github.com/minio/minio/pkg/quick"
+)
+
+// serverConfigV6 server configuration version '5'.
+type serverConfigV6 struct {
+	Version string `json:"version"`
+
+	// S3 API configuration.
+	Credential credential `json:"credential"`
+	Region     string     `json:"region"`
+
+	// Additional error logging configuration.
+	Logger logger `json:"logger"`
+
+	// Notification queue configuration.
+	Notify notifier `json:"notify"`
+
+	// Read Write mutex.
+	rwMutex *sync.RWMutex
+}
+
+// initConfig - initialize server config. config version (called only once).
+func initConfig() error {
+	if !isConfigFileExists() {
+		// Initialize server config.
+		srvCfg := &serverConfigV6{}
+		srvCfg.Version = globalMinioConfigVersion
+		srvCfg.Region = "us-east-1"
+		srvCfg.Credential = mustGenAccessKeys()
+
+		// Enable console logger by default on a fresh run.
+		srvCfg.Logger.Console = consoleLogger{
+			Enable: true,
+			Level:  "fatal",
+		}
+		srvCfg.rwMutex = &sync.RWMutex{}
+
+		// Create config path.
+		err := createConfigPath()
+		if err != nil {
+			return err
+		}
+
+		// Save the new config globally.
+		serverConfig = srvCfg
+
+		// Save config into file.
+		return serverConfig.Save()
+	}
+	configFile, err := getConfigFile()
+	if err != nil {
+		return err
+	}
+	if _, err = os.Stat(configFile); err != nil {
+		return err
+	}
+	srvCfg := &serverConfigV6{}
+	srvCfg.Version = globalMinioConfigVersion
+	srvCfg.rwMutex = &sync.RWMutex{}
+	qc, err := quick.New(srvCfg)
+	if err != nil {
+		return err
+	}
+	if err := qc.Load(configFile); err != nil {
+		return err
+	}
+	// Save the loaded config globally.
+	serverConfig = srvCfg
+	// Set the version properly after the unmarshalled json is loaded.
+	serverConfig.Version = globalMinioConfigVersion
+
+	return nil
+}
+
+// serverConfig server config.
+var serverConfig *serverConfigV6
+
+// GetVersion get current config version.
+func (s serverConfigV6) GetVersion() string {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+	return s.Version
+}
+
+/// Logger related.
+
+func (s *serverConfigV6) SetAMQPNotifyByID(accountID string, amqpn amqpNotify) {
+	s.rwMutex.Lock()
+	defer s.rwMutex.Unlock()
+	s.Notify.AMQP[accountID] = amqpn
+}
+
+func (s serverConfigV6) GetAMQP() map[string]amqpNotify {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+	return s.Notify.AMQP
+}
+
+// GetAMQPNotify get current AMQP logger.
+func (s serverConfigV6) GetAMQPNotifyByID(accountID string) amqpNotify {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+	return s.Notify.AMQP[accountID]
+}
+
+func (s *serverConfigV6) SetElasticSearchNotifyByID(accountID string, esNotify elasticSearchNotify) {
+	s.rwMutex.Lock()
+	defer s.rwMutex.Unlock()
+	s.Notify.ElasticSearch[accountID] = esNotify
+}
+
+func (s serverConfigV6) GetElasticSearch() map[string]elasticSearchNotify {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+	return s.Notify.ElasticSearch
+}
+
+// GetElasticSearchNotify get current ElasicSearch logger.
+func (s serverConfigV6) GetElasticSearchNotifyByID(accountID string) elasticSearchNotify {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+	return s.Notify.ElasticSearch[accountID]
+}
+
+func (s *serverConfigV6) SetRedisNotifyByID(accountID string, rNotify redisNotify) {
+	s.rwMutex.Lock()
+	defer s.rwMutex.Unlock()
+	s.Notify.Redis[accountID] = rNotify
+}
+
+func (s serverConfigV6) GetRedis() map[string]redisNotify {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+	return s.Notify.Redis
+}
+
+// GetRedisNotify get current Redis logger.
+func (s serverConfigV6) GetRedisNotifyByID(accountID string) redisNotify {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+	return s.Notify.Redis[accountID]
+}
+
+// SetFileLogger set new file logger.
+func (s *serverConfigV6) SetFileLogger(flogger fileLogger) {
+	s.rwMutex.Lock()
+	defer s.rwMutex.Unlock()
+	s.Logger.File = flogger
+}
+
+// GetFileLogger get current file logger.
+func (s serverConfigV6) GetFileLogger() fileLogger {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+	return s.Logger.File
+}
+
+// SetConsoleLogger set new console logger.
+func (s *serverConfigV6) SetConsoleLogger(clogger consoleLogger) {
+	s.rwMutex.Lock()
+	defer s.rwMutex.Unlock()
+	s.Logger.Console = clogger
+}
+
+// GetConsoleLogger get current console logger.
+func (s serverConfigV6) GetConsoleLogger() consoleLogger {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+	return s.Logger.Console
+}
+
+// SetSyslogLogger set new syslog logger.
+func (s *serverConfigV6) SetSyslogLogger(slogger syslogLogger) {
+	s.rwMutex.Lock()
+	defer s.rwMutex.Unlock()
+	s.Logger.Syslog = slogger
+}
+
+// GetSyslogLogger get current syslog logger.
+func (s *serverConfigV6) GetSyslogLogger() syslogLogger {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+	return s.Logger.Syslog
+}
+
+// SetRegion set new region.
+func (s *serverConfigV6) SetRegion(region string) {
+	s.rwMutex.Lock()
+	defer s.rwMutex.Unlock()
+	s.Region = region
+}
+
+// GetRegion get current region.
+func (s serverConfigV6) GetRegion() string {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+	return s.Region
+}
+
+// SetCredentials set new credentials.
+func (s *serverConfigV6) SetCredential(creds credential) {
+	s.rwMutex.Lock()
+	defer s.rwMutex.Unlock()
+	s.Credential = creds
+}
+
+// GetCredentials get current credentials.
+func (s serverConfigV6) GetCredential() credential {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+	return s.Credential
+}
+
+// Save config.
+func (s serverConfigV6) Save() error {
+	s.rwMutex.RLock()
+	defer s.rwMutex.RUnlock()
+
+	// get config file.
+	configFile, err := getConfigFile()
+	if err != nil {
+		return err
+	}
+
+	// initialize quick.
+	qc, err := quick.New(&s)
+	if err != nil {
+		return err
+	}
+
+	// Save config file.
+	return qc.Save(configFile)
+}