php下载功能

<?php
	$file_name = "57c79b825dbd8.jpg"; 
	$file_dir = "/Upload/download/"; 
	if (!file_exists($file_dir . $file_name)) { //检查文件是否存在 
		echo "文件找不到"; 
		exit;
	} else { 
		$file = fopen($file_dir . $file_name,"r"); // 打开文件 
		// 输入文件标签 
		Header("Content-type: application/octet-stream");
		Header("Accept-Ranges: bytes");
		Header("Accept-Length: ".filesize($file_dir . $file_name));
		Header("Content-Disposition: attachment; filename=" . $file_name);
		// 输出文件内容 
		echo fread($file,filesize($file_dir . $file_name));
		fclose($file);
		exit;
	} 

?>