private Headers getHeaders() throws IOException {
    if (responseHeaders == null) {
      Response response = getResponse().getResponse();
      Headers headers = response.headers();

      responseHeaders = headers.newBuilder()
          .add(Platform.get().getPrefix() + "-Response-Source", responseSourceHeader(response))
          .build();
    }
    return responseHeaders;
  }
Returns an input stream from the server in the case of error such as the
requested file (txt, htm, html) is not found on the remote server.
gateway/platforms/servlet/src/main/java/io/apiman/gateway/platforms/servlet/connectors/ok/HttpURLConnectionImpl.java