class NodeViewController

class NodeViewController extends EntityViewController {
    
    /**
     * The current user.
     *
     * @var \Drupal\Core\Session\AccountInterface
     */
    protected $currentUser;
    
    /**
     * The entity repository service.
     *
     * @var \Drupal\Core\Entity\EntityRepositoryInterface
     */
    protected $entityRepository;
    
    /**
     * Creates an NodeViewController object.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\Core\Render\RendererInterface $renderer
     *   The renderer service.
     * @param \Drupal\Core\Session\AccountInterface $current_user
     *   The current user. For backwards compatibility this is optional, however
     *   this will be removed before Drupal 9.0.0.
     * @param \Drupal\Core\Entity\EntityRepositoryInterface $entity_repository
     *   The entity repository.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, RendererInterface $renderer, AccountInterface $current_user = NULL, EntityRepositoryInterface $entity_repository = NULL) {
        parent::__construct($entity_type_manager, $renderer);
        $this->currentUser = $current_user ?: \Drupal::currentUser();
        if (!$entity_repository) {
            @trigger_error('The entity.repository service must be passed to NodeViewController::__construct(), it is required before Drupal 9.0.0. See https://www.drupal.org/node/2549139.', E_USER_DEPRECATED);
            $entity_repository = \Drupal::service('entity.repository');
        }
        $this->entityRepository = $entity_repository;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager'), $container->get('renderer'), $container->get('current_user'), $container->get('entity.repository'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function view(EntityInterface $node, $view_mode = 'full', $langcode = NULL) {
        $build = parent::view($node, $view_mode, $langcode);
        foreach ($node->uriRelationships() as $rel) {
            $url = $node->toUrl($rel)
                ->setAbsolute(TRUE);
            // Add link relationships if the user is authenticated or if the anonymous
            // user has access. Access checking must be done for anonymous users to
            // avoid traffic to inaccessible pages from web crawlers. For
            // authenticated users, showing the links in HTML head does not impact
            // user experience or security, since the routes are access checked when
            // visited and only visible via view source. This prevents doing
            // potentially expensive and hard to cache access checks on every request.
            // This means that the page will vary by user.permissions. We also rely on
            // the access checking fallback to ensure the correct cacheability
            // metadata if we have to check access.
            if ($this->currentUser
                ->isAuthenticated() || $url->access($this->currentUser)) {
                // Set the node path as the canonical URL to prevent duplicate content.
                $build['#attached']['html_head_link'][] = [
                    [
                        'rel' => $rel,
                        'href' => $url->toString(),
                    ],
                    TRUE,
                ];
            }
            if ($rel == 'canonical') {
                // Set the non-aliased canonical path as a default shortlink.
                $build['#attached']['html_head_link'][] = [
                    [
                        'rel' => 'shortlink',
                        'href' => $url->setOption('alias', TRUE)
                            ->toString(),
                    ],
                    TRUE,
                ];
            }
        }
        // Since this generates absolute URLs, it can only be cached "per site".
        $build['#cache']['contexts'][] = 'url.site';
        // Given this varies by $this->currentUser->isAuthenticated(), add a cache
        // context based on the anonymous role.
        $build['#cache']['contexts'][] = 'user.roles:anonymous';
        return $build;
    }
    
    /**
     * The _title_callback for the page that renders a single node.
     *
     * @param \Drupal\Core\Entity\EntityInterface $node
     *   The current node.
     *
     * @return string
     *   The page title.
     */
    public function title(EntityInterface $node) {
        return $this->entityRepository
            ->getTranslationFromContext($node)
            ->label();
    }

}