先来看下一般文件的安全下载方法： 代码示例:

php

/**

* 一般文件安全下载

* edit www.#

*/

$durl = 'file/phpcms2008_o2abf32efj883c91a.iso';

$filename = 'phpcms2008_o2abf32efj883c91a.iso';

$file = @fopen($durl, 'r');

header("Content-Type: application/octet-stream");

header("Accept-Ranges:    bytes");

header("Accept-Length:    ".filesize($durl));

header("Content-Disposition:    attachment;    filename=".$filename);

echo   fread($file,filesize($durl));

fclose($file);

?>

以上的代码，在遇到大文件时，超过php.ini配置的内存最大值的文件时，服务器会非常占用CPU资源，文件不能正常下载，只能下载几十Kb的文件。

可以用下面的代码来解决： 代码示例:

/**

* 大文件

安全下载的实现代码

* edit www.#

*/

function download($url, $filename) {

// 获得文件大小, 防止超过2G的文件, 用sprintf来读

$filesize = sprintf ( "%u", filesize ( $url ) );

if (! $filesize) {

return;

}

header ( "Content-type:application/octet-stream\n" ); //application/octet-stream

header ( "Content-type:unknown/unknown;" );

header ( "Content-disposition: attachment; filename=\"" . $filename . "\"" );

header ( 'Content-transfer-encoding: binary' );

if ($range = getenv ( 'HTTP_RANGE' )) { // 当有偏移量的时候，采用206的断点续传头

$range = explode ( '=', $range );

$range = $range [1];

header ( "HTTP/1.1 206 Partial Content" );

header ( "Date: " . gmdate ( "D, d M Y H:i:s" ) . " GMT" );

header ( "Last-Modified: " . gmdate ( "D, d M Y H:i:s", filemtime ( $url ) ) . " GMT" );

header ( "Accept-Ranges: bytes" );

header ( "Content-Length:" . ($filesize - $range) );

header ( "Content-Range: bytes " . $range . ($filesize - 1) . "/" . $filesize );

header ( "Connection: close" . "\n\n" );

} e

lse {

header ( "Content-Length:" . $filesize . "\n\n" );

$range = 0;

}

loadFile ( $url );

}

function loadFile($filename, $retbytes = true) {

$buffer = '';

$cnt = 0;

$handle = fopen ( $filename, 'rb' );

if ($handle === false) {

return false;

}

while ( ! feof ( $handle ) ) {

$buffer = fread ( $handle, 1024 * 1024 );

echo $buffer;

ob_flush ();

flush ();

if ($retbytes) {

$cnt += strlen ( $buffer );

}

}

$status = fclose ( $handle );

if ($retbytes && $status) {

return $cnt; // return num. bytes delivered like readfile() does.

}

return $status;

}

?>

调用示例： 代码示例:

//大文件的安全下载

dow

nload($url, $filename);