Piwik\Tracker\Request::getUserAgent PHP Method

    public function getUserAgent()
    {
        $default = false;
        if (array_key_exists('HTTP_USER_AGENT', $_SERVER)) {
            $default = $_SERVER['HTTP_USER_AGENT'];
        }
        return Common::getRequestVar('ua', $default, 'string', $this->params);
    }

 /**
  * Checks for DoNotTrack headers and if found, sets `$exclude` to `true`.
  */
 public function checkHeaderInTracker(&$exclude)
 {
     if ($exclude) {
         Common::printDebug("Visit is already excluded, no need to check DoNotTrack support.");
         return;
     }
     if (!$this->isActive()) {
         Common::printDebug("DoNotTrack support is not enabled, skip check");
         return;
     }
     if (isset($_SERVER['HTTP_X_DO_NOT_TRACK']) && $_SERVER['HTTP_X_DO_NOT_TRACK'] === '1' || isset($_SERVER['HTTP_DNT']) && substr($_SERVER['HTTP_DNT'], 0, 1) === '1') {
         $request = new Request($_REQUEST);
         $ua = $request->getUserAgent();
         if (strpos($ua, 'MSIE') !== false || strpos($ua, 'Trident') !== false) {
             Common::printDebug("INTERNET EXPLORER enable DoNotTrack by default; so Piwik ignores DNT IE browsers...");
             return;
         }
         Common::printDebug("DoNotTrack header found!");
         $exclude = true;
         $trackingCookie = IgnoreCookie::getTrackingCookie();
         $trackingCookie->delete();
         // this is an optional supplement to the site's tracking status resource at:
         //     /.well-known/dnt
         // per Tracking Preference Expression (draft)
         header('Tk: 1');
     } else {
         Common::printDebug("DoNotTrack header not found");
     }
 }