write method produce a huge memory leak!
workaround: use getResource
==============8<===========================
$chunkSize = intval($f->file['chunkSize']);
//echo $chunkSize;
$stream = $f->getResource();
$outStream = fopen($tmp,'wb');
while (!feof($stream)) {
fwrite($outStream, fread($stream, $chunkSize));
}
fclose($stream);
fclose($outStream);
unset($stream);
unset($outStream);
==============8<===========================