After an hour long reading his frustrations over IM, I began google’ing on files served thru PHP but locks clicks in a client’s browser until download is finished. It is unresponsive until the download is complete.
// add this function before a readfile() or chunked with fopen() session_write_close(); // header goes here, content-type, filename, etc readfile($filepath);
And, also, I found this class to support downloading using a download manager.