php文件下载

<?php
/**  Author ZhangZhaoyu  2012-9-13 下午2:28:18 **/

/**
*
* @param unknown_type $file_name
* @param unknown_type $file_sub_path "xxx/xxx/"
*
*/
function down_file($file_name, $file_sub_dir) {

$file_path = $_SERVER["DOCUMENT_ROOT"] . $file_sub_dir . $file_name;


if (!file_exists($file_path)) {
echo "file not exist !";
echo $file_path;
return ;
}

$file = fopen($file_path, "r");
$file_size = filesize($file_path);
//the return file
Header("Content-type: application/octet-stream");
//return by bytes
Header("Accept-Ranges: bytes");
//return the size of the file
Header("Accept-Length: " . $file_size);
//return the name of the file 弹出的下载框对应的文件名
Header("Content-Disposition: attachment; filename=" . $file_name);
//向客户端会送数据

$buffer = 1024;
$file_count = 0;
while (!feof($file) && (($file_size - $file_count)) > 0) {
$file_data = fread($file, $buffer);
$file_count += $buffer;
echo $file_data;
}
fclose($file);
exit();

}
$file_name = $_REQUEST["filename"];
down_file($file_name, "/HelloWorld/project/up/");
?>