api: Allow reconnection of policy/notification rpc clients. (#3368)

Since we moved out reconnection logic from net-rpc-client.go
we should do it from the top-layer properly and bring back
the code to reconnect properly in-case the connection is lost.

cmd/bucket-metadata.go

@@ -16,7 +16,10 @@
 
 package cmd
 
-import "encoding/json"
+import (
+	"encoding/json"
+	"net/rpc"
+)
 
 // BucketMetaState - Interface to update bucket metadata in-memory
 // state.
@@ -104,26 +107,62 @@ type remoteBucketMetaState struct {
 // change to remote peer via RPC call.
 func (rc *remoteBucketMetaState) UpdateBucketNotification(args *SetBucketNotificationPeerArgs) error {
 	reply := GenericReply{}
-	return rc.Call("S3.SetBucketNotificationPeer", args, &reply)
+	err := rc.Call("S3.SetBucketNotificationPeer", args, &reply)
+	// Check for network error and retry once.
+	if err != nil && err == rpc.ErrShutdown {
+		// Close the underlying connection to attempt once more.
+		rc.Close()
+
+		// Attempt again and proceed.
+		err = rc.Call("S3.SetBucketNotificationPeer", args, &reply)
+	}
+	return err
 }
 
 // remoteBucketMetaState.UpdateBucketListener - sends bucket listener change to
 // remote peer via RPC call.
 func (rc *remoteBucketMetaState) UpdateBucketListener(args *SetBucketListenerPeerArgs) error {
 	reply := GenericReply{}
-	return rc.Call("S3.SetBucketListenerPeer", args, &reply)
+	err := rc.Call("S3.SetBucketListenerPeer", args, &reply)
+	// Check for network error and retry once.
+	if err != nil && err == rpc.ErrShutdown {
+		// Close the underlying connection to attempt once more.
+		rc.Close()
+
+		// Attempt again and proceed.
+		err = rc.Call("S3.SetBucketListenerPeer", args, &reply)
+	}
+	return err
 }
 
 // remoteBucketMetaState.UpdateBucketPolicy - sends bucket policy change to remote
 // peer via RPC call.
 func (rc *remoteBucketMetaState) UpdateBucketPolicy(args *SetBucketPolicyPeerArgs) error {
 	reply := GenericReply{}
-	return rc.Call("S3.SetBucketPolicyPeer", args, &reply)
+	err := rc.Call("S3.SetBucketPolicyPeer", args, &reply)
+	// Check for network error and retry once.
+	if err != nil && err == rpc.ErrShutdown {
+		// Close the underlying connection to attempt once more.
+		rc.Close()
+
+		// Attempt again and proceed.
+		err = rc.Call("S3.SetBucketPolicyPeer", args, &reply)
+	}
+	return err
 }
 
 // remoteBucketMetaState.SendEvent - sends event for bucket listener to remote
 // peer via RPC call.
 func (rc *remoteBucketMetaState) SendEvent(args *EventArgs) error {
 	reply := GenericReply{}
-	return rc.Call("S3.Event", args, &reply)
+	err := rc.Call("S3.Event", args, &reply)
+	// Check for network error and retry once.
+	if err != nil && err == rpc.ErrShutdown {
+		// Close the underlying connection to attempt once more.
+		rc.Close()
+
+		// Attempt again and proceed.
+		err = rc.Call("S3.Event", args, &reply)
+	}
+	return err
 }

cmd/s3-peer-client.go

@@ -71,8 +71,8 @@ func makeS3Peers(eps []*url.URL) s3Peers {
 			}
 
 			ret = append(ret, s3Peer{
-				ep.Host,
-				&remoteBucketMetaState{newAuthClient(&cfg)},
+				addr:      ep.Host,
+				bmsClient: &remoteBucketMetaState{newAuthClient(&cfg)},
 			})
 			seenAddr[ep.Host] = true
 		}