用PHP实现文件下载

<?php

    /*
     * 最后修改： 2006-5-11
     * 修改人：redriver@263.net
     *
     * 创建日期： 2006-5-11
     * 创建人：redriver@263.net
     */
       
    $fileName = $_GET['fileName'];
   
    if (!file_exists($fileName))
    {
        exit('文件' . $fileName . '不存在。');
    }
   
    $fileSize = filesize($fileName);
   
    Header("Content-type: application/octet-stream");
    Header("Accept-Ranges: bytes");
    Header("Content-Length: " . $fileSize);
    Header("Content-Disposition: attachment; filename=" . $fileName);
   
    $fp = fopen($fileName, "r");
    $bufferSize = 1024;
    $curPos = 0;
   
    while((!feof($fp)) && (($fileSize - $curPos) > $bufferSize))
    {
        $buffer = fread($fp, $bufferSize);
        print($buffer);
        $curPos += $bufferSize;
    }
   
    $buffer = fread($fp, $fileSize - $curPos);
    print($buffer);
       
?>