Pause redirect module

pause_redirect.info.yml

name: Pause redirect
type: module
description: Pause redirects
package: redirect
core: 8.x
core_version_requirement: ^8 || ^9
dependencies:
  - redirect

pause_redirect.links.task.yml

pause_redirect.settings:
  route_name: pause_redirect.settings
  base_route: redirect.list
  title: Pause
  weight: 60

pause_redirect.routing.yml

pause_redirect.settings:
  path: '/admin/config/search/redirect/pause'
  defaults:
    _form: 'Drupal\pause_redirect\Form\PauseRedirectSettingsForm'
    _title: 'Pause Redirect settings'
  requirements:
    _permission: 'administer redirects'

pause_redirect.services.yml

services:
  pause_redirect.event_subscriber:
    class: Drupal\pause_redirect\EventSubscriber\PauseRedirectRequestSubscriber
    decorates: redirect.request_subscriber
    arguments: ['@pause_redirect.event_subscriber.inner', '@messenger']

PauseRedirectRequestSubscriber.php

<?php

namespace Drupal\pause_redirect\EventSubscriber;

use Drupal\Core\Messenger\MessengerInterface;
use Drupal\pause_redirect\Form\PauseRedirectSettingsForm;
use Drupal\redirect\EventSubscriber\RedirectRequestSubscriber;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpFoundation\RedirectResponse;
use Symfony\Component\HttpKernel\Event\RequestEvent;
use Symfony\Component\HttpKernel\KernelEvents;

/**
 * Pause redirect event subscriber.
 */
class PauseRedirectRequestSubscriber implements EventSubscriberInterface {

  /**
   * Constructs event subscriber.
   *
   * @param \Drupal\redirect\EventSubscriber\RedirectRequestSubscriber $original
   *   The original redirect request subscriber.
   * @param \Drupal\Core\Messenger\MessengerInterface $messenger
   *   The messenger.
   */
  public function __construct(protected RedirectRequestSubscriber $original, protected MessengerInterface $messenger) {
  }

  public function onKernelRequestCheckRedirect(RequestEvent $original_event): void {
    $cloned_event = clone $original_event;
    $this->original->onKernelRequestCheckRedirect($cloned_event);
    if ($cloned_event->hasResponse()) {
      $response = $cloned_event->getResponse();
      if ($response instanceof RedirectResponse && PauseRedirectSettingsForm::isPaused($original_event->getRequest())) {
        $this->messenger->addWarning(t('This page redirects to <a href="@link">@link</a>.', ['@link' => $response->getTargetUrl()]));
      }
      else {
        $original_event->setResponse($response);
      }
    }
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents(): array {
    $events[KernelEvents::REQUEST][] = ['onKernelRequestCheckRedirect', 33];
    return $events;
  }

}

PauseRedirectSettingsForm.php

<?php

namespace Drupal\pause_redirect\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Symfony\Component\HttpFoundation\Request;

/**
 * Configure Redirect settings for this site.
 */
class PauseRedirectSettingsForm extends FormBase {

  const PAUSE_REDIRECT = 'pause_redirect';

  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'pause_redirect_settings';
  }

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $form[self::PAUSE_REDIRECT] = [
      '#type' => 'checkbox',
      '#title' => $this->t('Pause redirects'),
      '#default_value' => static::isPaused($this->getRequest()),
    ];
    $form['actions']['#type'] = 'actions';
    $form['actions']['submit'] = [
      '#type' => 'submit',
      '#value' => $this->t('Save'),
      '#button_type' => 'primary',
    ];

    return $form;
  }

  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $this->messenger()->addStatus($this->t('Saved.'));
    $this->getRequest()->getSession()->set(self::PAUSE_REDIRECT, (bool) $form_state->getValue(self::PAUSE_REDIRECT));
  }

  /**
   * @param \Symfony\Component\HttpFoundation\Request $request
   *   The request holding the session.
   *
   * @return bool
   *   Whether redirects are paused.
   */
  public static function isPaused(Request $request): bool {
    return $request->getSession()->get(self::PAUSE_REDIRECT, FALSE);
  }

}