/**
 * Implements hook_verify_update_archive().
 */
function {{ machine_name }}_verify_update_archive($project, $archive_file, $directory) {
  $errors = array();
  if (!file_exists($directory)) {
    $errors[] = t('The %directory does not exist.', array('%directory' => $directory));
  }
  // Add other checks on the archive integrity here.
  return $errors;
}