function hook_file_url_alter

Alter the URL to a file.

This hook is called from \Drupal\Core\File\FileUrlGenerator::generate(), and is called fairly frequently (10+ times per page), depending on how many files there are in a given page. If CSS and JS aggregation are disabled, this can become very frequently (50+ times per page) so performance is critical.

This function should alter the URI, if it wants to rewrite the file URL.

Parameters

$uri: The URI to a file for which we need an external URL, or the path to a shipped file.

Related topics

File

core/lib/Drupal/Core/File/file.api.php, line 60

Hooks related to the File management system.

Code

function hook_file_url_alter(&$uri) {
  $user = \Drupal::currentUser();

  // User 1 will always see the local file in this example.
  if ($user
    ->id() == 1) {
    return;
  }
  $cdn1 = 'http://cdn1.example.com';
  $cdn2 = 'http://cdn2.example.com';
  $cdn_extensions = [
    'css',
    'js',
    'gif',
    'jpg',
    'jpeg',
    'png',
  ];

  // Most CDNs don't support private file transfers without a lot of hassle,
  // so don't support this in the common case.
  $schemes = [
    'public',
  ];

  /** @var \Drupal\Core\StreamWrapper\StreamWrapperManagerInterface $stream_wrapper_manager */
  $stream_wrapper_manager = \Drupal::service('stream_wrapper_manager');
  $scheme = $stream_wrapper_manager::getScheme($uri);

  // Only serve shipped files and public created files from the CDN.
  if (!$scheme || in_array($scheme, $schemes)) {

    // Shipped files.
    if (!$scheme) {
      $path = $uri;
    }
    else {
      $wrapper = $stream_wrapper_manager
        ->getViaScheme($scheme);
      $path = $wrapper
        ->getDirectoryPath() . '/' . $stream_wrapper_manager::getTarget($uri);
    }

    // Clean up Windows paths.
    $path = str_replace('\\', '/', $path);

    // Serve files with one of the CDN extensions from CDN 1, all others from
    // CDN 2.
    $pathinfo = pathinfo($path);
    if (isset($pathinfo['extension']) && in_array($pathinfo['extension'], $cdn_extensions)) {
      $uri = $cdn1 . '/' . $path;
    }
    else {
      $uri = $cdn2 . '/' . $path;
    }
  }
}