alt_stream_wrappers-8.x-1.x-dev/alt_stream_wrappers.module

<?php

/**
 * @file
 * Provides an alternative temporary stream wrapper.
 */

use Drupal\Core\Form\FormStateInterface;

/**
 * Implements hook_form_FORM_ID_alter().
 *
 * Form id is system_file_system_settings.
 */
function alt_stream_wrappers_form_system_file_system_settings_alter(&$form, FormStateInterface $form_state, $form_id) {
    $form['alt_file_temporary_path'] = [
      '#type' => 'textfield',
      '#title' => t('Alternative temporary directory'),
      '#default_value' => \Drupal::config('alt_stream_wrappers.settings')->get('path.temporary'),
      '#maxlength' => 255,
      '#description' => t('A alternative local file system path where temporary files will be stored. This directory should not be accessible over the web.'),
      '#after_build' => ['system_check_directory'],
    ];

    $form['#submit'][] = 'alt_stream_wrappers_form_system_file_system_settings_submit';
}

/**
 * @param $form
 * @param \Drupal\Core\Form\FormStateInterface $form_state
 */
function alt_stream_wrappers_form_system_file_system_settings_submit($form, FormStateInterface $form_state) {
    $config = \Drupal::configFactory()->getEditable('alt_stream_wrappers.settings');
    $config->set('path.temporary', $form_state->getValue('alt_file_temporary_path'));
    $config->save();
}