No `listener.json` for single-node mode (Fixes #3052) (#3108)

In FS or single-node XL mode, there is no need to save listener
configuration to persistent storage. As there is only one server, if it
is restarted, any connected listenBucketAPI clients were disconnected
and will have to reconnect - so there is nothing to actually store.

This incidentally solves #3052 by avoiding the problem.

cmd/bucket-notification-handlers.go

@@ -379,12 +379,14 @@ func AddBucketListenerConfig(bucket string, lcfg *listenerConfig, objAPI ObjectL
 	// Release lock after notifying peers
 	defer nsMutex.Unlock(bucket, "", opsID)
 
-	// update persistent config
+	// update persistent config if dist XL
+	if globalS3Peers.isDistXL {
 		err := persistListenerConfig(bucket, listenerCfgs, objAPI)
 		if err != nil {
 			errorIf(err, "Error persisting listener config when adding a listener.")
 			return err
 		}
+	}
 
 	// persistence success - now update in-memory globals on all
 	// peers (including local)
@@ -419,12 +421,14 @@ func RemoveBucketListenerConfig(bucket string, lcfg *listenerConfig, objAPI Obje
 	// Release lock after notifying peers
 	defer nsMutex.Unlock(bucket, "", opsID)
 
-	// update persistent config
+	// update persistent config if dist XL
+	if globalS3Peers.isDistXL {
 		err := persistListenerConfig(bucket, updatedLcfgs, objAPI)
 		if err != nil {
 			errorIf(err, "Error persisting listener config when removing a listener.")
 			return
 		}
+	}
 
 	// persistence success - now update in-memory globals on all
 	// peers (including local)

cmd/event-notifier.go

@@ -347,6 +347,13 @@ func loadNotificationConfig(bucket string, objAPI ObjectLayer) (*notificationCon
 // loads notification config if any for a given bucket, returns
 // structured notification config.
 func loadListenerConfig(bucket string, objAPI ObjectLayer) ([]listenerConfig, error) {
+	// in single node mode, there are no peers, so in this case
+	// there is no configuration to load, as any previously
+	// connected listen clients have been disconnected
+	if !globalS3Peers.isDistXL {
+		return nil, nil
+	}
+
 	// Construct the notification config path.
 	listenerConfigPath := path.Join(bucketConfigPrefix, bucket, bucketListenerConfig)
 	objInfo, err := objAPI.GetObjectInfo(minioMetaBucket, listenerConfigPath)

cmd/event-notifier_test.go

@@ -291,6 +291,11 @@ func TestInitEventNotifier(t *testing.T) {
 		t.Fatal("Unexpected error:", err)
 	}
 
+	// needed to load listener config from disk for testing (in
+	// single peer mode, the listener config is ingored, but here
+	// we want to test the loading from disk too.)
+	globalS3Peers.isDistXL = true
+
 	// test event notifier init
 	if err := initEventNotifier(obj); err != nil {
 		t.Fatal("Unexpected error:", err)
@@ -361,6 +366,11 @@ func TestListenBucketNotification(t *testing.T) {
 		t.Fatalf("Test Setup error: %v", err)
 	}
 
+	// needed to load listener config from disk for testing (in
+	// single peer mode, the listener config is ingored, but here
+	// we want to test the loading from disk too.)
+	globalS3Peers.isDistXL = true
+
 	// Init event notifier
 	if err := initEventNotifier(obj); err != nil {
 		t.Fatal("Unexpected error:", err)

cmd/s3-peer-client.go

@@ -32,6 +32,9 @@ type s3Peers struct {
 
 	mutex *sync.RWMutex
 
+	// Is single-node?
+	isDistXL bool
+
 	// Slice of all peer addresses (in `host:port` format).
 	peers []string
 }
@@ -53,6 +56,9 @@ func initGlobalS3Peers(eps []storageEndPoint) {
 
 	// Save new peers
 	globalS3Peers.peers = peers
+
+	// store if this is a distributed setup or not.
+	globalS3Peers.isDistXL = len(globalS3Peers.peers) > 1
 }
 
 func (s3p *s3Peers) GetPeers() []string {