How do I convert code implementing hook_init()?

Question

Looking on Drupal.org API, I noticed that hook_init() is not documented for Drupal 8. Looking at the change records, I found Bootstrap hooks no longer exist, which points to Get rid of all 'bootstrap' hooks, where the bootstrap hooks are said to be hook_boot() and hook_exit(); nothing is said about hook_init().

I searched for hook_init in Drupal 8 source, and I found the following code. The first one is a reference to hook_init() made in a comment; the other two seem a hook_init() implementation, but they both get a parameter I am not expecting.

function overlay_enable() {
  if (strpos(current_path(), 'admin/modules') === 0) {
    // Flag for a redirect to <front>#overlay=admin/modules on hook_init().
    $_SESSION['overlay_enable_redirect'] = 1;
  }
}

/**
 * Implements hook_init().
 */
function phptemplate_init($template) {
  $file = dirname($template->filename) . '/' . $template->name . '.theme';
  if (file_exists($file)) {
    include_once DRUPAL_ROOT . '/' . $file;
  }
}

/**
 * Implements hook_init().
 */
function twig_init($template) {
  $file = dirname($template->filename) . '/' . $template->name . '.theme';
  if (file_exists($file)) {
    include_once DRUPAL_ROOT . '/' . $file;
  }
}

I also looked for any function invoking hook_init() but I didn't find any.

How do I convert Drupal 7 code implementing hook_init() to code running on Drupal 8/9?

Answer 1

Perhaps this has changed since this question was last answered. But I think the preferred approach to replacing what is going on in hook_init is to create an event subscriber, and adding to the 'request'. Here is how you do that for those that may find it useful.

Example services.yml

services:
  init_subscriber:
    class:   Drupal\mymodule\EventSubscriber\MyModuleSubscriber
    arguments: ['@current_user'] // <- optional args
    tags:
      - {name: event_subscriber} // <- Required Tag

Then you would implement the EventSubscriberInterface (new file in the src/EventSubscriber directory) and in the implemented method getSubscribedEvents you can do something like...

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

And add the method accordingly

/**
 * MyModule
 *
 * @param \Symfony\Component\HttpKernel\Event\GetResponseEvent $event
 *   The event to process.
 */
public function initializeMyModule(GetResponseEvent $event) {
  $request = $event->getRequest();   
  ...
}

Answer 2

Yes, hook_init() is not used in Drupal 8. If you need drupal_add_js() or drupal_add_css() you can use hook_page_build() instead, which is also useful for that in Drupal 7.

For example, CSS styles and JavaScript code can be added to hook_page_build() using $page['#attached'].

$path = drupal_get_path('module', 'MY_MODULE');
$page['#attached']['js'][$path . '/my_module.js'] = array('scope' => 'footer');
$page['#attached']['css'][$path . '/my_module.base.css'] = array('every_page' => TRUE);

If you need to do more complex listening on the request/response, you can define an event listener as documented on hook_init() removed.

Answer 3

hook_page_build() has been deprecated in favor of hook_page_attachments() as documented on Added hook_page_attachments(_alter)() and removed hook_page_build/alter().

For example, to attach a library to every page, the hook implementation would be similar to the following one.

function mymodule_page_attachments(array &$attachments) {
  $attachments['#attached']['library'][] = 'modulename/libraryname';
}

libraryname is the name of the library, defined in your module's mymodule.libraries.yml.