NodeViewController::view

public NodeViewController::view(EntityInterface $node, $view_mode = 'full', $langcode = NULL)

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);
    // 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'][] = array(
        array(
          'rel' => $rel,
          'href' => $url->toString(),
        ),
        TRUE,
      );
    }

    if ($rel == 'canonical') {
      // Set the non-aliased canonical path as a default shortlink.
      $build['#attached']['html_head_link'][] = array(
        array(
          'rel' => 'shortlink',
          'href' => $url->setOption('alias', TRUE)->toString(),
        ),
        TRUE,
      );
    }
  }

  // Given this varies by $this->currentUser->isAuthenticated(), add a cache
  // context based on the anonymous role.
  $build['#cache']['contexts'][] = 'user.roles:anonymous';

  return $build;
}