@Override public void onStart(JsonResponse response, boolean fullyApplied) throws IOException {
                if (streamed)
                    response.commit(Response.Status.OK, fullyApplied);

                response.writeDocumentsArrayStart();
            }
Called at the end of response rendering, before generic status data is written. Called from a dedicated thread pool.
vespaclient-container-plugin/src/main/java/com/yahoo/document/restapi/resource/DocumentV1ApiHandler.java