getCompleteBaseUrl example

// Check for HTTP and data URI-encoded URLs so that we don't have to       // implement getExternalUrl() for the HTTP and data schemes.       $options = UrlHelper::parse($uri);
      return Url::fromUri(urldecode($options['path']), $options);
    }
    elseif ($wrapper = $this->streamWrapperManager->getViaUri($uri)) {
      $external_url = $wrapper->getExternalUrl();
      $options = UrlHelper::parse($external_url);

      // @todo Switch to dependency injected request_context service after       // https://www.drupal.org/project/drupal/issues/3256884 is fixed.       if (UrlHelper::externalIsLocal($external_url, \Drupal::service('router.request_context')->getCompleteBaseUrl())) {
        // Attempt to return an external URL using the appropriate wrapper.         return Url::fromUri('base:' . $this->transformRelative(urldecode($options['path']), FALSE), $options);
      }
      else {
        return Url::fromUri(urldecode($options['path']), $options);
      }
    }
    throw new InvalidStreamWrapperException();
  }

  /** * {@inheritdoc} */

/** * Determines whether a path is local. * * @param string $url * The internal path or external URL being linked to, such as "node/34" or * "http://example.com/foo". * * @return bool * TRUE or FALSE, where TRUE indicates a local path. */
  protected function isLocal($url) {
    return !UrlHelper::isExternal($url) || UrlHelper::externalIsLocal($url, $this->getRequestContext()->getCompleteBaseUrl());
  }

  /** * Returns the request context. * * @return \Drupal\Core\Routing\RequestContext * The request context. */
  protected function getRequestContext() {
    if (!isset($this->requestContext)) {
      $this->requestContext = \Drupal::service('router.request_context');
    }

'#type' => 'details',
      '#title' => $this->t('Front page'),
      '#open' => TRUE,
    ];
    $form['front_page']['site_frontpage'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Default front page'),
      '#default_value' => $this->aliasManager->getAliasByPath($site_config->get('page.front')),
      '#required' => TRUE,
      '#size' => 40,
      '#description' => $this->t('Specify a relative URL to display as the front page.'),
      '#field_prefix' => $this->requestContext->getCompleteBaseUrl(),
    ];
    $form['error_page'] = [
      '#type' => 'details',
      '#title' => $this->t('Error pages'),
      '#open' => TRUE,
    ];
    $form['error_page']['site_403'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Default 403 (access denied) page'),
      '#default_value' => $site_config->get('page.403'),
      '#size' => 40,
      

  public function isSecure($url) {
    if (!$url) {
      return FALSE;
    }
    $url_host = parse_url($url, PHP_URL_HOST);
    $system_host = parse_url($this->requestContext->getCompleteBaseUrl(), PHP_URL_HOST);

    // The URL is secure if its domain is not the same as the domain of the base     // URL of the current request.     return $url_host && $system_host && $url_host !== $system_host;
  }

}