Caching not working! Blank page. How does CI write a cache file? All I see is a timestamp.

[eluser]dtrenz[/eluser]
OK, I just walked the CI Output class and I can't find anywhere that they are writing the actual output of the page to the cache file!

All it does is write a timestamp to a file. Where is the actual output? Where is the content and the HTML? I'm so confused. could somebody please explain this to me

Code:

if ( ! $fp = @fopen($cache_path, 'wb'))
{
    log_message('error', "Unable to write cache file: ".$cache_path);
    return;
}

$expire = time() + ($this->cache_expiration * 60);

flock($fp, LOCK_EX);
fwrite($fp, $expire.'TS--->'.$output);
flock($fp, LOCK_UN);
fclose($fp);