How To Test Mod_Expires .htaccess Rules with Curl?

Confirming Mod_Expires is Installed

To be able to use the Expires header, mod_expires must be enabled in your Apache configuration. You can confirm this on CentOS using the following command,

httpd -M | grep -i expires

This module controls the Expires HTTP header settings and the Cache-Control HTTP header max-age directives. This should be installed by default on most servers.

Testing For the Expires Header Using Curl

If the current date is Mar 2, 2019, the following shows that the Expires headers for a .png resource is set for 4 months,

$ curl -LI https://domain.tld/wp-content/uploads/2018/12/img-023-144x144.png
HTTP/1.1 200 OK
Date: Sun, 03 Mar 2019 04:38:32 GMT
Server: Apache
Last-Modified: Tue, 25 Dec 2018 11:42:14 GMT
Accept-Ranges: bytes
Content-Length: 10603
Cache-Control: max-age=10368000, public
Expires: Mon, 01 Jul 2019 04:38:32 GMT
Vary: Accept-Encoding
Content-Type: image/png

Here is the .htaccess rule confirming this,

[root@host public_html]# grep png .htaccess  | grep -i expires
  ExpiresByType image/png                     "access plus 4 months"

This shows that Expires is working.

Occasionally, you may test your landing page on some 3rd-party tools and they will inform you that Expires are not working. What they should say is that Expires are not set and working for *all* resources used on the landing page.

If you instead curl a single resource from your site that you have explicitly set expiration rules for, then you can see the output like that shown above. The landing page is often returned as text/html Content-Type, but it usually doesn’t give the same headers that are given when testing a single resource.

You can go further and change the setting to make sure the change is detected when testing. Initially, html was set 0 for this one resource,

[root@host public_html]# grep -i expires .htaccess  | grep -i html
   ExpiresByType text/html                     "access plus 0 seconds"

If you change the expires time for html to something else, it should then be detected. I’ve tested this using the readme.html file by setting it to 10 days,

Before changing from 0, it shows the current date,

$ curl -I https://domain.com/readme.html
HTTP/1.1 200 OK
Date: Sun, 03 Mar 2019 04:37:07 GMT
Server: Apache
Accept-Ranges: bytes
Content-Length: 7425
Cache-Control: max-age=0, public
Expires: Sun, 03 Mar 2019 04:37:07 GMT
Vary: Accept-Encoding,User-Agent
X-Powered-By: WP Rocket/3.2.6
Content-Type: text/html; charset=UTF-8

After changing to 10 days, it shows 10 days from now,

$ curl -I https://domain.com/readme.html
HTTP/1.1 200 OK
Date: Sun, 03 Mar 2019 04:53:59 GMT
Server: Apache
Accept-Ranges: bytes
Content-Length: 7425
Cache-Control: max-age=864000, public
Expires: Wed, 13 Mar 2019 04:53:59 GMT
Vary: Accept-Encoding,User-Agent
X-Powered-By: WP Rocket/3.2.6
Content-Type: text/html; charset=UTF-8

If you want your landing page to show these headers as well, you may have to consult your developer for help in identifying what resources exist on the landing page but do not have expirations set in the .htaccess.

Conclusion

Now that we’ve gone over how to rest mod_expires .htaccess rules with curl. Mod_expires is used to set up the expiration on .htaccess rules along with the mod_rewrite apache module.

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