php安全下载大文件的实现代码

/**
* 一般文件安全下载
* edit bbs.it-home.org
*/
    $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：

/**
* 大文件安全下载的实现代码
* edit bbs.it-home.org
*/
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" );
 } else {
     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：

//大文件的安全下载
download($url, $filename);