[#644] Support keepalive during listing

Send whitespaces every time as new object in list is ready
to prevent client from context cancelling.

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

api/handler/util.go

@@ -45,6 +45,23 @@ func (h *handler) logAndSendError(ctx context.Context, w http.ResponseWriter, lo
 	h.reqLogger(ctx).Error(logs.RequestFailed, append(fields, logs.TagField(logs.TagDatapath))...)
 }
 
+func (h *handler) logAndSendErrorNoHeader(ctx context.Context, w http.ResponseWriter, logText string, reqInfo *middleware.ReqInfo, err error, additional ...zap.Field) {
+	err = handleDeleteMarker(w, err)
+	if wrErr := middleware.WriteErrorResponseNoHeader(w, reqInfo, apierr.TransformToS3Error(err)); wrErr != nil {
+		additional = append(additional, zap.NamedError("write_response_error", wrErr))
+	}
+	fields := []zap.Field{
+		zap.String("method", reqInfo.API),
+		zap.String("bucket", reqInfo.BucketName),
+		zap.String("object", reqInfo.ObjectName),
+		zap.String("description", logText),
+		zap.String("user", reqInfo.User),
+		zap.Error(err),
+	}
+	fields = append(fields, additional...)
+	h.reqLogger(ctx).Error(logs.RequestFailed, append(fields, logs.TagField(logs.TagDatapath))...)
+}
+
 func (h *handler) logError(ctx context.Context, logText string, reqInfo *middleware.ReqInfo, err error, additional ...zap.Field) {
 	fields := []zap.Field{
 		zap.String("method", reqInfo.API),