PHP uses recursion to calculate folder size, _PHP tutorial

protected function dir_size($dir){
$ Dh = OpenDIR ($ dir); // Open the directory and return a directory
          $size = 0;                                                                                                                                                                                                      //The initial size is 0
While(false !== ($file = @readdir($dh))){ //Loop to read files in the directory
If($file!='.' and $file!='..'){
               $path = $dir.'/'.$file; If(is_dir($path)){
                      $size += $this->dir_size($path); //Recursive call, calculate directory size
                      }elseif(is_file($path)){
                             $size += filesize($path);                 }
                                                                                                                                              Closedir ($ dh); // Turn off the directors
          return $size;                                                                                                                                                                                                                                                    }