Add support for MQTT server as a notification target (#4474)

This implementation is similar to AMQP notifications:

* Notifications are published on a single topic as a JSON feed
* Topic is configurable, as is the QoS. Uses the paho.mqtt.golang
  library for the mqtt connection, and supports connections over tcp
  and websockets, with optional secure tls support.
* Additionally the minio server configuration has been bumped up
  so mqtt configuration can be added.
* Configuration migration code is added with tests.

MQTT is an ISO standard M2M/IoT messaging protocol and was
originally designed for applications for limited bandwidth
networks. Today it's use is growing in the IoT space.

cmd/notify-mqtt.go

@@ -0,0 +1,123 @@
+/*
+ * 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 cmd
+
+import (
+	"crypto/tls"
+	"io/ioutil"
+	"time"
+
+	"github.com/Sirupsen/logrus"
+	MQTT "github.com/eclipse/paho.mqtt.golang"
+)
+
+type mqttNotify struct {
+	Enable   bool   `json:"enable"`
+	Broker   string `json:"broker"`
+	Topic    string `json:"topic"`
+	QoS      int    `json:"qos"`
+	ClientID string `json:"clientId"`
+	User     string `json:"username"`
+	Password string `json:"password"`
+}
+
+func (m *mqttNotify) Validate() error {
+	if !m.Enable {
+		return nil
+	}
+	if _, err := checkURL(m.Broker); err != nil {
+		return err
+	}
+	return nil
+}
+
+type mqttConn struct {
+	params mqttNotify
+	Client MQTT.Client
+}
+
+func dialMQTT(mqttL mqttNotify) (mqttConn, error) {
+	if !mqttL.Enable {
+		return mqttConn{}, errNotifyNotEnabled
+	}
+	connOpts := &MQTT.ClientOptions{
+		ClientID:             mqttL.ClientID,
+		CleanSession:         true,
+		Username:             mqttL.User,
+		Password:             mqttL.Password,
+		MaxReconnectInterval: 1 * time.Second,
+		KeepAlive:            30 * time.Second,
+		TLSConfig:            tls.Config{RootCAs: globalRootCAs},
+	}
+	connOpts.AddBroker(mqttL.Broker)
+	client := MQTT.NewClient(connOpts)
+	if token := client.Connect(); token.Wait() && token.Error() != nil {
+		return mqttConn{}, token.Error()
+	}
+	return mqttConn{Client: client, params: mqttL}, nil
+}
+
+func newMQTTNotify(accountID string) (*logrus.Logger, error) {
+	mqttL := serverConfig.Notify.GetMQTTByID(accountID)
+
+	//connect to MQTT Server
+	mqttC, err := dialMQTT(mqttL)
+	if err != nil {
+		return nil, err
+	}
+
+	mqttLog := logrus.New()
+
+	// Disable writing to console.
+	mqttLog.Out = ioutil.Discard
+
+	// Add a mqtt hook.
+	mqttLog.Hooks.Add(mqttC)
+
+	// Set default JSON formatter
+	mqttLog.Formatter = new(logrus.JSONFormatter)
+
+	// successfully enabled all MQTTs
+	return mqttLog, nil
+}
+
+// Fire if called when an event should be sent to the message broker.
+func (q mqttConn) Fire(entry *logrus.Entry) error {
+	body, err := entry.String()
+	if err != nil {
+		return err
+	}
+
+	if !q.Client.IsConnected() {
+		if token := q.Client.Connect(); token.Wait() && token.Error() != nil {
+			return token.Error()
+		}
+	}
+	token := q.Client.Publish(q.params.Topic, byte(q.params.QoS), false, body)
+	if token.Wait() && token.Error() != nil {
+		return token.Error()
+	}
+
+	return nil
+}
+
+// Levels is available logging levels.
+func (q mqttConn) Levels() []logrus.Level {
+	return []logrus.Level{
+		logrus.InfoLevel,
+	}
+}