Fix notification unmarshalling, unmarshal only when size is > 0 (#5087)

Fixes #5085

cmd/bucket-notification-handlers.go

@@ -63,13 +63,13 @@ func (api objectAPIHandlers) GetBucketNotificationHandler(w http.ResponseWriter,
 
 	// Attempt to successfully load notification config.
 	nConfig, err := loadNotificationConfig(bucket, objAPI)
-	if err != nil && err != errNoSuchNotifications {
+	if err != nil && errorCause(err) != errNoSuchNotifications {
 		errorIf(err, "Unable to read notification configuration.")
 		writeErrorResponse(w, toAPIErrorCode(err), r.URL)
 		return
 	}
 	// For no notifications we write a dummy XML.
-	if err == errNoSuchNotifications {
+	if errorCause(err) == errNoSuchNotifications {
 		// Complies with the s3 behavior in this regard.
 		nConfig = &notificationConfig{}
 	}

cmd/event-notifier.go

@@ -377,18 +377,24 @@ func loadNotificationConfig(bucket string, objAPI ObjectLayer) (*notificationCon
 		// 'errNoSuchNotifications'.  This is default when no
 		// bucket notifications are found on the bucket.
 		if isErrObjectNotFound(err) || isErrIncompleteBody(err) {
-			return nil, errNoSuchNotifications
+			return nil, traceError(errNoSuchNotifications)
 		}
 		errorIf(err, "Unable to load bucket-notification for bucket %s", bucket)
 		// Returns error for other errors.
 		return nil, err
 	}
 
+	// if `notifications.xml` is empty we should return NoSuchNotifications.
+	if buffer.Len() == 0 {
+		return nil, traceError(errNoSuchNotifications)
+	}
+
 	// Unmarshal notification bytes.
 	notificationConfigBytes := buffer.Bytes()
 	notificationCfg := &notificationConfig{}
-	if err = xml.Unmarshal(notificationConfigBytes, &notificationCfg); err != nil {
+	// Unmarshal notification bytes only if we read data.
-		return nil, err
+	if err = xml.Unmarshal(notificationConfigBytes, notificationCfg); err != nil {
+		return nil, traceError(err)
 	}
 
 	// Return success.
@@ -418,23 +424,27 @@ func loadListenerConfig(bucket string, objAPI ObjectLayer) ([]listenerConfig, er
 	var buffer bytes.Buffer
 	err := objAPI.GetObject(minioMetaBucket, lcPath, 0, -1, &buffer)
 	if err != nil {
-		// 'notification.xml' not found return
+		// 'listener.json' not found return
 		// 'errNoSuchNotifications'.  This is default when no
-		// bucket listeners are found on the bucket.
+		// bucket listeners are found on the bucket
-		if isErrObjectNotFound(err) {
+		if isErrObjectNotFound(err) || isErrIncompleteBody(err) {
-			return nil, errNoSuchNotifications
+			return nil, traceError(errNoSuchNotifications)
 		}
 		errorIf(err, "Unable to load bucket-listeners for bucket %s", bucket)
 		// Returns error for other errors.
 		return nil, err
 	}
 
-	// Unmarshal notification bytes.
+	// if `listener.json` is empty we should return NoSuchNotifications.
+	if buffer.Len() == 0 {
+		return nil, traceError(errNoSuchNotifications)
+	}
+
 	var lCfg []listenerConfig
 	lConfigBytes := buffer.Bytes()
 	if err = json.Unmarshal(lConfigBytes, &lCfg); err != nil {
 		errorIf(err, "Unable to unmarshal listener config from JSON.")
-		return nil, err
+		return nil, traceError(err)
 	}
 
 	// Return success.