PHP forces file download (avoid files or images being opened directly in the browser)

/**
* The FLEA_Helper_SendFile class is used to send files to the browser
*
* Using FLEA_Helper_SendFile, applications can save important files in
* locations that are inaccessible to the browser. The file contents are then sent to the browser through the program.
* @site http://bbs.it-home.org
*/
class FLEA_Helper_SendFile
{
/**
* Send the file content to the browser
*
* @param string $serverPath The path of the file on the server (absolute or relative path)
* @param string $filename The file name sent to the browser (do not use Chinese if possible)
* @param string $mimeType indicates the file type
*/
function sendFile($serverPath, $filename, $mimeType = 'application/octet- stream')
{
header("Content-Type: {$mimeType}");
$filename = '"' . htmlspecialchars($filename) . '"';
$filesize = filesize($serverPath);
$ charset = FLEA::getAppInf('responseCharset');//According to the actual file encoding type, such as utf-8, gbk
header("Content-Disposition: attachment; filename={$filename}; charset={$charset}" );
header('Pragma: cache');
header('Cache-Control: public, must-revalidate, max-age=0');
header("Content-Length: {$filesize}");
 readfile($serverPath);
exit;
}
}