Implement HTTP POST based RPC (#5840)

Added support for new RPC support using HTTP POST.  RPC's 
arguments and reply are Gob encoded and sent as HTTP 
request/response body.

This patch also removes Go RPC based implementation.

cmd/local-admin-client.go

@@ -0,0 +1,123 @@
+/*
+ * Minio Cloud Storage, (C) 2018 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 (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/minio/minio/cmd/logger"
+)
+
+// localAdminClient - represents admin operation to be executed locally.
+type localAdminClient struct{}
+
+// SignalService - sends a restart or stop signal to the local server
+func (lc localAdminClient) SignalService(s serviceSignal) error {
+	switch s {
+	case serviceRestart, serviceStop:
+		globalServiceSignalCh <- s
+	default:
+		return errUnsupportedSignal
+	}
+	return nil
+}
+
+// ReInitFormat - re-initialize disk format.
+func (lc localAdminClient) ReInitFormat(dryRun bool) error {
+	objectAPI := newObjectLayerFn()
+	if objectAPI == nil {
+		return errServerNotInitialized
+	}
+	return objectAPI.ReloadFormat(context.Background(), dryRun)
+}
+
+// ListLocks - Fetches lock information from local lock instrumentation.
+func (lc localAdminClient) ListLocks(bucket, prefix string, duration time.Duration) ([]VolumeLockInfo, error) {
+	objectAPI := newObjectLayerFn()
+	if objectAPI == nil {
+		return nil, errServerNotInitialized
+	}
+
+	return objectAPI.ListLocks(context.Background(), bucket, prefix, duration)
+}
+
+// ServerInfo - Returns the server info of this server.
+func (lc localAdminClient) ServerInfo() (sid ServerInfoData, e error) {
+	if globalBootTime.IsZero() {
+		return sid, errServerNotInitialized
+	}
+
+	// Build storage info
+	objLayer := newObjectLayerFn()
+	if objLayer == nil {
+		return sid, errServerNotInitialized
+	}
+	storage := objLayer.StorageInfo(context.Background())
+
+	return ServerInfoData{
+		StorageInfo: storage,
+		ConnStats:   globalConnStats.toServerConnStats(),
+		HTTPStats:   globalHTTPStats.toServerHTTPStats(),
+		Properties: ServerProperties{
+			Uptime:   UTCNow().Sub(globalBootTime),
+			Version:  Version,
+			CommitID: CommitID,
+			SQSARN:   globalNotificationSys.GetARNList(),
+			Region:   globalServerConfig.GetRegion(),
+		},
+	}, nil
+}
+
+// GetConfig - returns config.json of the local server.
+func (lc localAdminClient) GetConfig() ([]byte, error) {
+	if globalServerConfig == nil {
+		return nil, fmt.Errorf("config not present")
+	}
+
+	return json.Marshal(globalServerConfig)
+}
+
+// WriteTmpConfig - writes config file content to a temporary file on
+// the local server.
+func (lc localAdminClient) WriteTmpConfig(tmpFileName string, configBytes []byte) error {
+	tmpConfigFile := filepath.Join(getConfigDir(), tmpFileName)
+	err := ioutil.WriteFile(tmpConfigFile, configBytes, 0666)
+	reqInfo := (&logger.ReqInfo{}).AppendTags("tmpConfigFile", tmpConfigFile)
+	ctx := logger.SetReqInfo(context.Background(), reqInfo)
+	logger.LogIf(ctx, err)
+	return err
+}
+
+// CommitConfig - Move the new config in tmpFileName onto config.json
+// on a local node.
+func (lc localAdminClient) CommitConfig(tmpFileName string) error {
+	configFile := getConfigFile()
+	tmpConfigFile := filepath.Join(getConfigDir(), tmpFileName)
+
+	err := os.Rename(tmpConfigFile, configFile)
+	reqInfo := (&logger.ReqInfo{}).AppendTags("tmpConfigFile", tmpConfigFile)
+	reqInfo.AppendTags("configFile", configFile)
+	ctx := logger.SetReqInfo(context.Background(), reqInfo)
+	logger.LogIf(ctx, err)
+	return err
+}