Allow event notifications to work without region (#5119)

Fixes #5101

cmd/bucket-notification-handlers.go

@@ -150,6 +150,12 @@ func (api objectAPIHandlers) PutBucketNotificationHandler(w http.ResponseWriter,
 		return
 	}
 
+	// Convert the incoming ARNs properly to the GetRegion().
+	for i, queueConfig := range notificationCfg.QueueConfigs {
+		queueConfig.QueueARN = unmarshalSqsARN(queueConfig.QueueARN).String()
+		notificationCfg.QueueConfigs[i] = queueConfig
+	}
+
 	// Put bucket notification config.
 	err = PutBucketNotificationConfig(bucket, &notificationCfg, objectAPI)
 	if err != nil {

cmd/bucket-notification-utils.go

@@ -116,9 +116,13 @@ func checkARN(arn, arnType string) APIErrorCode {
 	if len(strs) != 6 {
 		return ErrARNNotification
 	}
-	if serverConfig.GetRegion() != "" {
+
+	// Server region is allowed to be empty by default,
+	// in such a scenario ARN region is not validating
+	// allowing all regions.
+	if sregion := serverConfig.GetRegion(); sregion != "" {
 		region := strs[3]
-		if region != serverConfig.GetRegion() {
+		if region != sregion {
 			return ErrRegionNotification
 		}
 	}
@@ -273,9 +277,13 @@ func unmarshalSqsARN(queueARN string) (mSqs arnSQS) {
 	if len(strs) != 6 {
 		return
 	}
-	if serverConfig.GetRegion() != "" {
+
+	// Server region is allowed to be empty by default,
+	// in such a scenario ARN region is not validating
+	// allowing all regions.
+	if sregion := serverConfig.GetRegion(); sregion != "" {
 		region := strs[3]
-		if region != serverConfig.GetRegion() {
+		if region != sregion {
 			return
 		}
 	}