/**
  * Json-decode any 'radix' parameter.
  */
 protected function decode_input()
 {
     parent::decode_input();
     if (isset($this->input_all['radix'])) {
         $r = $this->input_all['radix'];
         try {
             $this->input_radix = json_decode($r, true);
         } catch (Exception $err) {
             show_error("Json decode error: Bad record format in key 'radix'", 400);
         }
     }
     // TODO: how strict should RADIX checking be?
     // sanity check radix
     //$should_have_radix = $this->method == 'POST' || $this->method == 'PUT';
     //if ($should_have_radix && !$this->input_radix) {
     //    show_error("Error: Bad record format in key 'radix'", 400);
     //}
     // attach any "file input" to the radix, in the form of filepaths
     if (is_array($this->input_radix)) {
         foreach ($_FILES as $name => $def) {
             if (!isset($this->input_radix[$name])) {
                 $this->input_radix[$name] = $def;
             }
         }
     }
 }