apache - php resume capability or download in chunks -

php $_server not return http_range key , without key how can perform "resume download" or download in chunks?

   if (isset($_server['http_range'])) {     echo "find";    } else{     echo "not find";    } 

i can't $_server['http_range'] server .......

there no key http_range when print $_server

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<?php      // file request, throw error if nothing supplied      // hide notices     @ini_set('error_reporting', e_all & ~ e_notice);      //- turn off compression on server     @apache_setenv('no-gzip', 1);     @ini_set('zlib.output_compression', 'off');      if(!isset($_request['file']) || empty($_request['file']))      {         header("http/1.0 400 bad request");         exit;     }      // sanitize file request, keep name , extension     // also, replaces file location preset 1 ('./myfiles/' in example)     $file_path  = $_request['file'];     $path_parts = pathinfo($file_path);     $file_name  = $path_parts['basename'];     $file_ext   = $path_parts['extension'];     $file_path  = './myfiles/' . $file_name;      // allow file streamed instead of sent attachment     $is_attachment = isset($_request['stream']) ? false : true;      // make sure file exists     if (is_file($file_path))     {         $file_size  = filesize($file_path);         $file = @fopen($file_path,"rb");         if ($file)         {             // set headers, prevent caching             header("pragma: public");             header("expires: -1");             header("cache-control: public, must-revalidate, post-check=0, pre-check=0");             header("content-disposition: attachment; filename=\"$file_name\"");              // set appropriate headers attachment or streamed file             if ($is_attachment) {                     header("content-disposition: attachment; filename=\"$file_name\"");             }             else {                     header('content-disposition: inline;');                     header('content-transfer-encoding: binary');             }              // set mime type based on extension, add yours if needed.             $ctype_default = "application/octet-stream";             $content_types = array(                     "exe" => "application/octet-stream",                     "zip" => "application/zip",                     "mp3" => "audio/mpeg",                     "mpg" => "video/mpeg",                     "avi" => "video/x-msvideo",             );             $ctype = isset($content_types[$file_ext]) ? $content_types[$file_ext] : $ctype_default;             header("content-type: " . $ctype);              //check if http_range sent browser (or download manager)             if(isset($_server['http_range']))             {                 list($size_unit, $range_orig) = explode('=', $_server['http_range'], 2);                 if ($size_unit == 'bytes')                 {                     //multiple ranges specified @ same time, simplicity serve first range                     //http://tools.ietf.org/id/draft-ietf-http-range-retrieval-00.txt                     list($range, $extra_ranges) = explode(',', $range_orig, 2);                 }                 else                 {                     $range = '';                     header('http/1.1 416 requested range not satisfiable');                     exit;                 }             }             else             {                 $range = '';             }              //figure out download piece range (if set)             list($seek_start, $seek_end) = explode('-', $range, 2);              //set start , end based on range (if set), else set defaults             //also check invalid ranges.             $seek_end   = (empty($seek_end)) ? ($file_size - 1) : min(abs(intval($seek_end)),($file_size - 1));             $seek_start = (empty($seek_start) || $seek_end < abs(intval($seek_start))) ? 0 : max(abs(intval($seek_start)),0);              //only send partial content header if downloading piece of file (ie workaround)             if ($seek_start > 0 || $seek_end < ($file_size - 1))             {                 header('http/1.1 206 partial content');                 header('content-range: bytes '.$seek_start.'-'.$seek_end.'/'.$file_size);                 header('content-length: '.($seek_end - $seek_start + 1));             }             else               header("content-length: $file_size");              header('accept-ranges: bytes');              set_time_limit(0);             fseek($file, $seek_start);              while(!feof($file))              {                 print(@fread($file, 1024*8));                 ob_flush();                 flush();                 if (connection_status()!=0)                  {                     @fclose($file);                     exit;                 }                        }              // file save success             @fclose($file);             exit;         }         else          {             // file couldn't opened             header("http/1.0 500 internal server error");             exit;         }     }     else     {         // file not exist         header("http/1.0 404 not found");         exit;     }     ?>