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;}