Test if X-Sendfile header is working

I am looking for a way to confirm if X-Sendfile is properly handling requests handed back to the webserver by a script (PHP). Images are being served correctly but I thought I would see the header in curl requests.

$ curl -I http://blog2.stageserver.net/wp-includes/ms-files.php?file=/2011/05/amos-lee-feature.jpg
HTTP/1.1 200 OK
Date: Wed, 04 Jan 2012 17:19:45 GMT
Server: Cherokee/1.2.100 (Arch Linux)
ETag: "4dd2e306=9da0"
Last-Modified: Tue, 17 May 2011 21:05:10 GMT
Content-Type: image/jpeg
Content-Length: 40352
X-Powered-By: PHP/5.3.8
Content-Disposition: inline; filename="amos-lee-feature.jpg"

Configuration

Cherokee 1.2.100 with PHP-FPM 5.3.8 in FastCGI:
cherokee.conf: vserver!20!rule!500!handler!xsendfile = 1
(Set by vServer > Behavior > Extensions php > Handler: Allow X-Sendfile [check Enabled])

WordPress Network / WPMU 3.3.1:
define('WPMU_SENDFILE',true); is set in the wp-config.php the following just before wp-settings.php is included. This will trigger the following code to be executed in WP’s wp-includes/ms-files.php:50 serves up files for a particular blog:

header( 'X-Sendfile: ' . $file );
exit;

I have confirmed that the above snippet is executing by adding an additional header for disposition right before the exit(); call. That Content-Disposition is present with curl results above and not originally in the ms-files.php code. The code that was added is:
header('Content-Disposition: inline; filename="'.basename($file).'"');

Research

I have:

• Rebooted php-fpm / cherokee daemons after making configuration changes.
• Tried several tricks in the comments over at php.net/readfile and replaced the simple header in ms-files.php with more complete code from examples.
  • php.net/manual/en/function.readfile.php
  • www.jasny.net/articles/how-i-php-x-sendfile/
  • *codeutopia.net/blog/2009/03/06/sending-files-better-apache-mod_xsendfile-and-php/*
• Confirmed [cherokee support][5] and tested [with and without][6] compression even though I don’t think it would apply since my images are serving correctly. I also found a suspiciously similar problem from a lighttpd post.
  • *cherokee-project.com/doc/other_goodies.html*
  • code.google.com/p/cherokee/issues/detail?id=1228
  • webdevrefinery.com/forums/topic/4761-x-sendfile/
• Found a blurb here on SO that may indicate the header gets stripped
  • stackoverflow.com/questions/7296642/django-understanding-x-sendfile
• Tested that the headers above are consistent from curl, wget, Firefox, Chrome, and web-sniffer.net.
• Found out that I can’t post more than 2 links yet due to lack of reputation.

Questions

• Will X-Sendfile be present in the headers when it is working correctly or is it stripped out?
• Can the access logs be used to determine if X-Sendfile is working?

I am looking for general troubleshooting tips or information here, not necessarily specific to PHP / Cherokee.

Update

I have found a suitable way to confirm X-Sendfile or X-Accel-Redirect in a test or sandbox environment: Disable X-Sendfile and check the headers.

With Allow X-Sendfile disabled in Cherokee:

$ curl -I http://blog2.stageserver.net/wp-includes/ms-files.php?file=/2011/05/amos-lee-feature.jpg
HTTP/1.1 200 OK
Date: Fri, 06 Jan 2012 15:34:49 GMT
Server: Cherokee/1.2.101 (Ubuntu)
X-Powered-By: PHP/5.3.6-13ubuntu3.3
Content-Type: image/jpeg
X-Sendfile: /srv/http/wordpress/wp-content/blogs.dir/2/files/2011/05/amos-lee-feature.jpg
Content-Length: 40352

The image will not load in browsers but you can see that the header is present. After re-enabling Allow X-Sendfile the image loads and you can be confident that X-Sendfile is working.