update_manager_file_get example

    }
  }

  /** * {@inheritdoc} */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $local_cache = NULL;
    $all_files = $this->getRequest()->files->get('files', []);
    if ($form_state->getValue('project_url')) {
      $local_cache = update_manager_file_get($form_state->getValue('project_url'));
      if (!$local_cache) {
        $this->messenger()->addError($this->t('Unable to retrieve Drupal project from %url.', ['%url' => $form_state->getValue('project_url')]));
        return;
      }
    }
    elseif (!empty($all_files['project_upload']) && $this->moduleHandler->moduleExists('file')) {
      $validators = ['file_validate_extensions' => [$this->archiverManager->getExtensions()]];
      if (!($finfo = file_save_upload('project_upload', $validators, NULL, 0, FileSystemInterface::EXISTS_REPLACE))) {
        // Failed to upload the file. file_save_upload() calls         // \Drupal\Core\Messenger\MessengerInterface::addError() on failure.         return;
      }