PHP implementation code for safely downloading large files

/**
* Safe download of general files
* 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);
?>

When the above code encounters a large file that exceeds the maximum memory value configured in php.ini, the server will occupy a lot of CPU resources and the file cannot be downloaded normally, and only files of dozens of Kb can be downloaded. This can be solved with the following code:

/**
* Implementation code for safe downloading of large files
* edit bbs.it-home.org
*/
function download($url, $filename) {
// Get the file size, prevent files exceeding 2G, use sprintf to read
$filesize = sprintf ( "%u", filesize ( $url ) );
if (! $filesize) {
 return;
 }
 header ( "Content-type:application/octet-streamn" ); //application/octet- stream
 header ( "Content-type:unknown/unknown;" );
 header ( "Content-disposition: attachment; filename="" . $filename . """ );
 header ( 'Content-transfer-encoding: binary ' );
if ($range = getenv ( 'HTTP_RANGE' )) { // When there is an offset, use the breakpoint resume header of 206
 $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" . "nn" );
 } else {
 header ( "Content-Length:" . $filesize . "nn" );
 $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;
}
?>

Call example:

//Safe download of large files
download($url, $filename);