The code itself is quite large so here is the boiled down version:
<?php
//set common headers
ob_start();
//generate the javascript source
$ret=ob_get_clean();
$handle=gzopen('cache/file.js.gz','wb');
gzwrite($handle,$ret);
gzclose($handle);
header('Content-Length: '.filesize('cache/file.js.gz'),true);
readfile('cache/file.js.gz');
The fun part. If cache/file.js.gz doesn't exist readfile('cache/file.js.gz'); reports the correct size. If it does exists then it reports the old size of the file.
I have tried adding fflush($handle) after the gzwrite with the same result. I have not tried unlinking the file before writing. Seems like a superfluous step.
The output files are generally pretty small. The largest being 5kB.
Server Info:
call clearstatcache() before getting file stats