code: public static StringBuilder computeMessageBuffer(HttpResponse response) {
      StringBuilder builder = new StringBuilder();
      int statusCode = response.getStatusCode();
      if (statusCode != 0) {
        builder.append(statusCode);
      }
      String statusMessage = response.getStatusMessage();
      if (statusMessage != null) {
        if (statusCode != 0) {
          builder.append(' ');
        }
        builder.append(statusMessage);
      }
      return builder;
    }
docs: Returns an exception message string builder to use for the given HTTP response.
  
  @since 1.7