Wrap html in link based on uri component of other field
I needed to use the drupal function file_create_url and PHP parse_url to accomplish this.

function newsletter_preprocess_node(&amp;$variables) {

  if ($variables['type'] === 'newsletter' &amp;&amp; $variables['view_mode']) {
    // Generate a path to the file based on the download uri
    $path = $variables['field_download'][0]['uri'];
    $path = file_create_url($path);
    $path = parse_url($path);
    $path = $path['path'];
    $variables['download_link'] = $path;
  }
}