Drupal → Как программно отдать пользователю данные в виде файла

/**
 * Export form.
 */
function mymodule_export_form($form, &$form_state) {
  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => 'Export',
  );
  return $form;
}
 
/**
 * Export form submit callback.
 */
function mymodule_export_form_submit($form, &$form_state) {
  drupal_add_http_header('Content-Disposition', 'attachment; filename=filename.txt');
  drupal_add_http_header('Content-Type', 'text/plain; charset=utf-8');
  echo 'Hello World!';
  drupal_exit();
}