Peer RPCs for bucket notifications (#2877)

* Implements a Peer RPC router that sends info to all Minio servers in the cluster.
* Bucket notifications are propagated to all nodes via this RPC router.
* Bucket listener configuration is persisted to separate object layer
  file (`listener.json`) and peer RPCs are used to communicate changes
  throughout the cluster.
* When events are generated, RPC calls to send them to other servers
  where bucket listeners may be connected is implemented.
* Some bucket notification tests are now disabled as they cannot work in
  the new design.
* Minor fix in `funcFromPC` to use `path.Join`

cmd/notify-listener.go

@@ -0,0 +1,82 @@
+/*
+ * 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 (
+	"fmt"
+	"io/ioutil"
+
+	"github.com/Sirupsen/logrus"
+)
+
+type listenerConn struct {
+	Client      *AuthRPCClient
+	ListenerARN string
+}
+
+type listenerLogger struct {
+	log   *logrus.Logger
+	lconn listenerConn
+}
+
+func newListenerLogger(listenerArn, targetAddr string) (*listenerLogger, error) {
+	client := globalS3Peers.GetPeerClient(targetAddr)
+	if client == nil {
+		return nil, fmt.Errorf("Peer %s was not initialized - bug!",
+			targetAddr)
+	}
+	lc := listenerConn{
+		Client:      client,
+		ListenerARN: listenerArn,
+	}
+
+	lcLog := logrus.New()
+
+	lcLog.Out = ioutil.Discard
+
+	lcLog.Formatter = new(logrus.JSONFormatter)
+
+	lcLog.Hooks.Add(lc)
+
+	return &listenerLogger{lcLog, lc}, nil
+}
+
+func (lc listenerConn) Close() {
+	// ignore closing errors
+	_ = lc.Client.Close()
+}
+
+// send event to target server via rpc client calls.
+func (lc listenerConn) Fire(entry *logrus.Entry) error {
+	notificationEvent, ok := entry.Data["Records"].([]NotificationEvent)
+	if !ok {
+		// If the record is not of the expected type, silently
+		// discard.
+		return nil
+	}
+
+	evArgs := EventArgs{Event: notificationEvent, Arn: lc.ListenerARN}
+	reply := GenericReply{}
+	err := lc.Client.Call("S3.Event", &evArgs, &reply)
+	return err
+}
+
+func (lc listenerConn) Levels() []logrus.Level {
+	return []logrus.Level{
+		logrus.InfoLevel,
+	}
+}