listen bucket: Support empty events from the server

Ask the server to send empty events to clear the buffer scanner which
can be filled with whitespaces but without new lines when the bucket is
idle and without any events

api-bucket-notification.go

@@ -166,6 +166,7 @@ func (c *Client) ListenBucketNotification(ctx context.Context, bucketName, prefi
 
 		// Prepare urlValues to pass into the request on every loop
 		urlValues := make(url.Values)
+		urlValues.Set("ping", "true")
 		urlValues.Set("prefix", prefix)
 		urlValues.Set("suffix", suffix)
 		urlValues["events"] = events
@@ -224,6 +225,12 @@ func (c *Client) ListenBucketNotification(ctx context.Context, bucketName, prefi
 					closeResponse(resp)
 					continue
 				}
+
+				// Empty events pinged from the server
+				if len(notificationInfo.Records) == 0 && notificationInfo.Err == nil {
+					continue
+				}
+
 				// Send notificationInfo
 				select {
 				case notificationInfoCh <- notificationInfo: