Download of text file is not possible

When clicking on the download link the file is displayed in the browser and not downloaded.

This snippet should do

// required for IE, otherwise Content-disposition is ignored
if(ini_get('zlib.output_compression')) { ini_set('zlib.output_compression', 'Off'); }

// build file headers
header("Pragma: public");
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: private",false);

// and some more headers
header("Content-Disposition: attachment; filename=\"".basename($filename)."\";" );
header("Content-Transfer-Encoding: binary");
header("Content-Length: ".filesize($filename));

// refer to file and exit
readfile("$filename");
exit();