php控制文件下载速度的方法

<?php
 /
  set here a limit of downloading rate (e.g. 10.20 Kb/s)
 /
 $download_rate = 10.20;
 $download_file = 'download-file.zip'; 
 $target_file = 'target-file.zip';
 if(file_exists($download_file)){
  / headers /
  header('Last-Modified:'.gmdate('D, d M Y H:i:s').'GMT');
  header('Cache-control: private');
  header('Content-Type: application/octet-stream');
  header('Content-Length: '.filesize($download_file));
  header('Content-Disposition: filename='.$target_file);
  / flush content /
  flush();
  / open file /
  $fh = @fopen($download_file, 'r');
  while(!feof($fh)){
   / send only current part of the file to browser /
   print fread($fh, round($download_rate  1024));
   / flush the content to the browser /
   flush();
   / sleep for 1 sec /
   sleep(1);
  }
  / close file /
  @fclose($fh);
 }else{
  die('Fatal error: the '.$download_file.' file does not exist!');
 }
?>