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/s3-peer-router.go

@@ -0,0 +1,43 @@
+/*
+ * Minio Cloud Storage, (C) 2014-2016 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 (
+	"net/rpc"
+
+	router "github.com/gorilla/mux"
+)
+
+const (
+	s3Path = "/s3/remote"
+)
+
+type s3PeerAPIHandlers struct {
+	ObjectAPI func() ObjectLayer
+}
+
+func registerS3PeerRPCRouter(mux *router.Router) {
+	s3PeerHandlers := &s3PeerAPIHandlers{
+		ObjectAPI: newObjectLayerFn,
+	}
+
+	s3PeerRPCServer := rpc.NewServer()
+	s3PeerRPCServer.RegisterName("S3", s3PeerHandlers)
+
+	s3PeerRouter := mux.NewRoute().PathPrefix(reservedBucket).Subrouter()
+	s3PeerRouter.Path(s3Path).Handler(s3PeerRPCServer)
+}