file_create_url

file_create_url($uri)

function file_create_url($uri) {
  // Allow the URI to be altered, e.g. to serve a file from a CDN or static
  // file server.
  \Drupal::moduleHandler()->alter('file_url', $uri);

  $scheme = \Drupal::service('file_system')->uriScheme($uri);

  if (!$scheme) {
    // Allow for:
    // - root-relative URIs (e.g. /foo.jpg in http://example.com/foo.jpg)
    // - protocol-relative URIs (e.g. //bar.jpg, which is expanded to
    //   http://example.com/bar.jpg by the browser when viewing a page over
    //   HTTP and to https://example.com/bar.jpg when viewing a HTTPS page)
    // Both types of relative URIs are characterized by a leading slash, hence
    // we can use a single check.
    if (Unicode::substr($uri, 0, 1) == '/') {
      return $uri;
    }
    else {
      // If this is not a properly formatted stream, then it is a shipped file.
      // Therefore, return the urlencoded URI with the base URL prepended.
      $options = UrlHelper::parse($uri);
      $path = $GLOBALS['base_url'] . '/' . UrlHelper::encodePath($options['path']);
      // Append the query.
      if ($options['query']) {
        $path .= '?' . UrlHelper::buildQuery($options['query']);
      }

      // Append fragment.
      if ($options['fragment']) {
        $path .= '#' . $options['fragment'];
      }

      return $path;
    }
  }
  elseif ($scheme == 'http' || $scheme == 'https' || $scheme == 'data') {
    // Check for HTTP and data URI-encoded URLs so that we don't have to
    // implement getExternalUrl() for the HTTP and data schemes.
    return $uri;
  }
  else {
    // Attempt to return an external URL using the appropriate wrapper.
    if ($wrapper = \Drupal::service('stream_wrapper_manager')->getViaUri($uri)) {
      return $wrapper->getExternalUrl();
    }
    else {
      return FALSE;
    }
  }
}