php下载文件代码

一般的文件安全下载方法可以使用下面的代码:
1. <?php?
2.
3. $durl = 'file/phpcms2008_o2abf32efj883c91a.iso';
4. $filename = 'phpcms2008_o2abf32efj883c91a.iso';
5. $file = @fopen($durl, 'r');
6. header("Content-Type: application/octet-stream");
7. header("Accept-Ranges: bytes");
8. header("Accept-Length: ".filesize($durl));
9. header("Content-Disposition: attachment; filename=".$filename);
10. echo fread($file,filesize($durl));
11. fclose($file);
12. ?>
但是文件一大（超过php.ini配置的内存最大值），这里就出问题了，服务器会非常占用CPU资源，更重要的是文件不能正常下载，只能下载几十Kb的文件，明显不是预期想要的。
1. function download($url, $filename) {
2.
3. // 获得文件大小, 防止超过2G的文件, 用sprintf来读
4. $filesize = sprintf ( "%u", filesize ( $url ) );
5. if (! $filesize) {
6. return;
7. }
8. header ( "Content-type:application/octet-stream\n" ); //application/octet-stream
9. header ( "Content-type:unknown/unknown;" );
10. header ( "Content-disposition: attachment; filename=\"" . $filename . "\"" );
11. header ( 'Content-transfer-encoding: binary' );
12. if ($range = getenv ( 'HTTP_RANGE' )) { // 当有偏移量的时候，采用206的断点续传头
13. $range = explode ( '=', $range );
14. $range = $range [1];
15.
16. header ( "HTTP/1.1 206 Partial Content" );
17. header ( "Date: " . gmdate ( "D, d M Y H:i:s" ) . " GMT" );
18. header ( "Last-Modified: " . gmdate ( "D, d M Y H:i:s", filemtime ( $url ) ) . " GMT" );
19. header ( "Accept-Ranges: bytes" );
20. header ( "C