Move admin APIs to new path and add redesigned heal APIs (#5351)

- Changes related to moving admin APIs
   - admin APIs now have an endpoint under /minio/admin
   - admin APIs are now versioned - a new API to server the version is
     added at "GET /minio/admin/version" and all API operations have the
     path prefix /minio/admin/v1/<operation>
   - new service stop API added
   - credentials change API is moved to /minio/admin/v1/config/credential
   - credentials change API and configuration get/set API now require TLS
     so that credentials are protected
   - all API requests now receive JSON
   - heal APIs are disabled as they will be changed substantially

- Heal API changes
   Heal API is now provided at a single endpoint with the ability for a
   client to start a heal sequence on all the data in the server, a
   single bucket, or under a prefix within a bucket.

   When a heal sequence is started, the server returns a unique token
   that needs to be used for subsequent 'status' requests to fetch heal
   results.

   On each status request from the client, the server returns heal result
   records that it has accumulated since the previous status request. The
   server accumulates upto 1000 records and pauses healing further
   objects until the client requests for status. If the client does not
   request any further records for a long time, the server aborts the
   heal sequence automatically.

   A heal result record is returned for each entity healed on the server,
   such as system metadata, object metadata, buckets and objects, and has
   information about the before and after states on each disk.

   A client may request to force restart a heal sequence - this causes
   the running heal sequence to be aborted at the next safe spot and
   starts a new heal sequence.

cmd/admin-rpc-client.go

@@ -34,7 +34,7 @@ import (
 
 const (
 	// Admin service names
-	serviceRestartRPC = "Admin.Restart"
+	signalServiceRPC  = "Admin.SignalService"
 	listLocksRPC      = "Admin.ListLocks"
 	reInitDisksRPC    = "Admin.ReInitDisks"
 	serverInfoDataRPC = "Admin.ServerInfoData"
@@ -56,7 +56,7 @@ type remoteAdminClient struct {
 // adminCmdRunner - abstracts local and remote execution of admin
 // commands like service stop and service restart.
 type adminCmdRunner interface {
-	Restart() error
+	SignalService(s serviceSignal) error
 	ListLocks(bucket, prefix string, duration time.Duration) ([]VolumeLockInfo, error)
 	ReInitDisks() error
 	ServerInfoData() (ServerInfoData, error)
@@ -65,10 +65,16 @@ type adminCmdRunner interface {
 	CommitConfig(tmpFileName string) error
 }
 
-// Restart - Sends a message over channel to the go-routine
-// responsible for restarting the process.
-func (lc localAdminClient) Restart() error {
-	globalServiceSignalCh <- serviceRestart
+var errUnsupportedSignal = fmt.Errorf("unsupported signal: only restart and stop signals are supported")
+
+// 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
 }
 
@@ -77,25 +83,31 @@ func (lc localAdminClient) ListLocks(bucket, prefix string, duration time.Durati
 	return listLocksInfo(bucket, prefix, duration), nil
 }
 
-// Restart - Sends restart command to remote server via RPC.
-func (rc remoteAdminClient) Restart() error {
-	args := AuthRPCArgs{}
-	reply := AuthRPCReply{}
-	return rc.Call(serviceRestartRPC, &args, &reply)
+func (rc remoteAdminClient) SignalService(s serviceSignal) (err error) {
+	switch s {
+	case serviceRestart, serviceStop:
+		reply := AuthRPCReply{}
+		err = rc.Call(signalServiceRPC, &SignalServiceArgs{Sig: s},
+			&reply)
+	default:
+		err = errUnsupportedSignal
+	}
+	return err
+
 }
 
 // ListLocks - Sends list locks command to remote server via RPC.
 func (rc remoteAdminClient) ListLocks(bucket, prefix string, duration time.Duration) ([]VolumeLockInfo, error) {
 	listArgs := ListLocksQuery{
-		bucket:   bucket,
-		prefix:   prefix,
-		duration: duration,
+		Bucket:   bucket,
+		Prefix:   prefix,
+		Duration: duration,
 	}
 	var reply ListLocksReply
 	if err := rc.Call(listLocksRPC, &listArgs, &reply); err != nil {
 		return nil, err
 	}
-	return reply.volLocks, nil
+	return reply.VolLocks, nil
 }
 
 // ReInitDisks - There is nothing to do here, heal format REST API
@@ -225,7 +237,7 @@ func (rc remoteAdminClient) CommitConfig(tmpFileName string) error {
 	return nil
 }
 
-// adminPeer - represents an entity that implements Restart methods.
+// adminPeer - represents an entity that implements admin API RPCs.
 type adminPeer struct {
 	addr      string
 	cmdRunner adminCmdRunner
@@ -274,11 +286,11 @@ func initGlobalAdminPeers(endpoints EndpointList) {
 	globalAdminPeers = makeAdminPeers(endpoints)
 }
 
-// invokeServiceCmd - Invoke Restart command.
+// invokeServiceCmd - Invoke Restart/Stop command.
 func invokeServiceCmd(cp adminPeer, cmd serviceSignal) (err error) {
 	switch cmd {
-	case serviceRestart:
-		err = cp.cmdRunner.Restart()
+	case serviceRestart, serviceStop:
+		err = cp.cmdRunner.SignalService(cmd)
 	}
 	return err
 }