add support for SENDFILE_LINK_MODE=rewrite, fixes #174

exercises/Exercise.php

@@ -674,7 +674,10 @@ abstract class Exercise extends SimpleORMap
             }
         } else if (is_string($data) && Studip\Markup::isHtml($data)) {
             $data = preg_replace_callback('/"\Khttps?:[^"]*/', function($match) {
-                list($url, $query) = explode('?', html_entity_decode($match[0]));
+                $url = html_entity_decode($match[0]);
+                $url = preg_replace('%/download/(?:normal|force_download)/\d/(\w+)/.+%',
+                                    '/sendfile.php?file_id=$1', $url);
+                list($url, $query) = explode('?', $url);
 
                 if (is_internal_url($url) && basename($url) === 'sendfile.php') {
                     parse_str($query, $query_params);