Always send Content-Length in Apache?

Question

I'm loading a particularly large JSON string that is dynamically generated by PHP. To provide some feedback to the user, I want to show download progress.

I have the code figured out, and it works fine for static content such as images, JS files, etc. However, it doesn't seem to work for dynamic files.

This makes sense, since the dynamic files don't have predictable content length, but even if I add this in PHP:

ob_start(function($c) {
    header("Content-Length: ".strlen($c));
    return $c;
});

It still does not send the header (but if I add any other header it works fine).

Is there any way to force Apache to send the Content-Length header? Currently my only alternative is to save the output to a temporary file and redirect to it instead. This would work, but it's kind of messy so I'd rather avoid it if possible.

Answer 1

I had similar problem but in my case Content-Length header wasn't sent by Apache because the response was gzip compressed. When I disable compression the Content-Length was calculated and sent properly.

Below is htaccess setting to disable gzip compression for swf file only

<FilesMatch "\.swf$">
  SetEnv no-gzip 1
</FilesMatch>