function hook_file_url_alter

Alter the URL to a file.

This hook is called from file_create_url(), 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.


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

Related topics

1 function implements hook_file_url_alter()

Note: this list is generated by pattern matching, so it may include some functions that are not actually implementations of this hook.

file_test_file_url_alter in drupal/modules/simpletest/tests/file_test.module
Implements hook_file_url_alter().
1 invocation of hook_file_url_alter()
file_create_url in drupal/includes/
Creates a web-accessible URL for a stream to an external or local file.


drupal/modules/system/system.api.php, line 3038
Hooks provided by Drupal core and the System module.


function hook_file_url_alter(&$uri) {
  global $user;

  // User 1 will always see the local file in this example.
  if ($user->uid == 1) {
  $cdn1 = '';
  $cdn2 = '';
  $cdn_extensions = array(

  // Most CDNs don't support private file transfers without a lot of hassle,
  // so don't support this in the common case.
  $schemes = array(
  $scheme = file_uri_scheme($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 {
      $wrapper = file_stream_wrapper_get_instance_by_scheme($scheme);
      $path = $wrapper
        ->getDirectoryPath() . '/' . file_uri_target($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;