WP redirect 404 .html urls

/**
 * Redirect .html URLs that cause 404
 */
add_action('template_redirect', function() {

  if (is_404()) {

    // get url without GET parameters
    $url = parse_url($_SERVER['REQUEST_URI'], PHP_URL_PATH);

    // check if current url ends with .html
    if (preg_match('/' . preg_quote('.html', '/') . '$/', $url)) {

      // remove .html and redirect
      if (function_exists('mb_substr') && function_exists('mb_strlen') && function_exists('mb_substr_count')) {

        // prevent making costly DoS requests with chaining extension
        if (mb_substr_count($url, '.html') > 2) {
          return;
        }

        $url = mb_substr($url, 0, mb_strlen($url) - 5);
        wp_redirect($url);
        exit();

      }

    }

  }

});