Title: Cache Validator / Last Modified Header Last modified: November 22, 2018 --- # Cache Validator / Last Modified Header * Resolved [mlepisto](https://wordpress.org/support/users/mlepisto/) * (@mlepisto) * [7 years, 6 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/) * Hi, * So I have the plugin working now and it seems to be doing well. However, one thing I noticed that is when the rewrites are enabled and I do a speed test with say Gtmetrics, all the images (jpg & png) that are being converted give a “specify cache validator” warning/error. When I remove the rules from the .htaccess file the plugin creates, these warnings/errors go away so I’m fairly certain it has to do with the plugin. * This is probably more a feature request than anything else, but I was wondering if you have any suggestions on how to handle this before I start hacking at things. * Thanks, Mika Viewing 11 replies - 1 through 11 (of 11 total) * Plugin Author [rosell.dk](https://wordpress.org/support/users/roselldk/) * (@roselldk) * [7 years, 6 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/#post-10916235) * Hi Mika, * Yes, it appears that performance can be improved if WebP Express adds a Last- Modified header to the image responses. It will be quite easily implemented. I will implement it in the WebP Convert library. I have created an issue for it here: [https://github.com/rosell-dk/webp-convert/issues/86](https://github.com/rosell-dk/webp-convert/issues/86) * Plugin Author [rosell.dk](https://wordpress.org/support/users/roselldk/) * (@roselldk) * [7 years, 6 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/#post-10972398) * Done. * A Last-Modified header has been implemented in 0.8.0, which has just been released * Thread Starter [mlepisto](https://wordpress.org/support/users/mlepisto/) * (@mlepisto) * [7 years, 6 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/#post-10977682) * Thanks [@roselldk](https://wordpress.org/support/users/roselldk/) ! * [mr_spock](https://wordpress.org/support/users/mr_spock/) * (@mr_spock) * [7 years, 3 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/#post-11290081) * Hi, I must be dumb – where is this set? * Plugin Author [rosell.dk](https://wordpress.org/support/users/roselldk/) * (@roselldk) * [7 years, 3 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/#post-11290114) * It is set by the converter (when an image is redirected to the converter). * When an image is redirected directly to an existing webp through the Apache rewrite rule, it will also be set automatically by Apache. Same goes for Nginx * [mr_spock](https://wordpress.org/support/users/mr_spock/) * (@mr_spock) * [7 years, 3 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/#post-11290226) * Sorry, but that’s not happening. Check it out at [https://www.abiquo.com](https://www.abiquo.com)– the htaccess rules (which I just forced the plugin to rewrite) are below. I’ve tried changing the expires header, that works fine. Any other ideas? * ``` # BEGIN WebP Express RewriteEngine On # Redirect to existing converted image in cache-dir (if browser supports webp) RewriteCond %{HTTP_ACCEPT} image/webp RewriteCond %{REQUEST_FILENAME} -f RewriteCond %{DOCUMENT_ROOT}/wp-content/webp-express/webp-images/doc-root/wp-content/$1.$2.webp -f RewriteRule ^/?(.+)\.(jpe?g|png)$ /wp-content/webp-express/webp-images/doc-root/wp-content/$1.$2.webp [NC,T=image/webp,E=EXISTING:1,L] # Set Cache-Control header so these direct redirections also get the header set # (and also webp-realizer.php) Header set Cache-Control "public, max-age=31536000" # Fall back to mod_expires if mod_headers is unavailable ExpiresActive On ExpiresByType image/webp "access plus 1 years" # WebP Realizer: Redirect non-existing webp images to webp-realizer.php, which will locate corresponding jpg/png, convert it, and deliver the webp (if possible) RewriteCond %{REQUEST_FILENAME} !-f RewriteRule ^/?(.+)\.(webp)$ /wp-content/plugins/webp-express/wod/webp-realizer.php?xdestination-rel=xwp-content/$1.$2&wp-content=wp-content [NC,L] # Redirect images to webp-on-demand.php (if browser supports webp) RewriteCond %{HTTP_ACCEPT} image/webp RewriteCond %{REQUEST_FILENAME} -f RewriteCond %{QUERY_STRING} (.*) RewriteRule ^/?(.+)\.(jpe?g|png)$ /wp-content/plugins/webp-express/wod/webp-on-demand.php?xsource-rel=xwp-content/$1.$2&wp-content=wp-content&%1 [NC,L] # Set Vary:Accept header for the image types handled by WebP Express. # The purpose is to make proxies and CDNs aware that the response varies with the Accept header. SetEnvIf Request_URI "\.(jpe?g|png)" ADDVARY Header append "Vary" "Accept" env=ADDVARY # Set X-WebP-Express header for diagnose purposes # Apache appends "REDIRECT_" in front of the environment variables defined in mod_rewrite, but LiteSpeed does not. # So, the next line is for Apache, in order to set environment variables without "REDIRECT_" SetEnvIf REDIRECT_EXISTING 1 EXISTING=1 Header set "X-WebP-Express" "Redirected directly to existing webp" env=EXISTING AddType image/webp .webp ``` * Plugin Author [rosell.dk](https://wordpress.org/support/users/roselldk/) * (@roselldk) * [7 years, 3 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/#post-11290323) * Just curious. Are you on version 0.12? * I can see that requesting [https://www.abiquo.com/wp-content/uploads/2018/02/abiquo_logo_224x94-2.jpg](https://www.abiquo.com/wp-content/uploads/2018/02/abiquo_logo_224x94-2.jpg) gives me the following headers (among others): * cache-control: public, max-age=31536000 content-type: image/webp date: Fri, 08 Mar 2019 12:47:58 GMT expires: Sat, 07 Mar 2020 12:47:58 GMT pragma: public server: Apache/2.4.37 (Amazon) x-webp-express: Redirected directly to existing webp * The x-webp-express header tells me that it was an internal redirect. And you are right, there are no Last-Modified header. * I’m thinking that it does not matter in your case, because the Last-Modified header is as far as I know only useful when other headers, such as cache-control or expires are missing. * But I’m curious. Does the server send the Last-Modified header when you unset Cache-Control? (it could be that the server does not care to set the Last-Modified header because it is superfluous) * [mr_spock](https://wordpress.org/support/users/mr_spock/) * (@mr_spock) * [7 years, 3 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/#post-11290930) * I don’t really care about it except some of the speed testing tools think it’s important so I’m concerned about search rank. * I’ll try the cache-control later… * Plugin Author [rosell.dk](https://wordpress.org/support/users/roselldk/) * (@roselldk) * [7 years, 3 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/#post-11291131) * Here is someone advocating (and showing how) to turn Last-Modified OFF for images: * [https://www.askapache.com/htaccess/apache-speed-last-modified/](https://www.askapache.com/htaccess/apache-speed-last-modified/) * It is commented on here: [https://webmasters.stackexchange.com/questions/27694/last-modified-etags-to-include-or-not](https://webmasters.stackexchange.com/questions/27694/last-modified-etags-to-include-or-not) * And here is more on the subject: [https://serverfault.com/questions/292070/how-to-setup-apache-2-2-3-to-send-last-modified-etc](https://serverfault.com/questions/292070/how-to-setup-apache-2-2-3-to-send-last-modified-etc) * [mr_spock](https://wordpress.org/support/users/mr_spock/) * (@mr_spock) * [6 years, 11 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/#post-11691586) * I eventually tested removing the cache control setting, and there’s still no last-modified. * Plugin Author [rosell.dk](https://wordpress.org/support/users/roselldk/) * (@roselldk) * [6 years, 10 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/#post-11790845) * [@mr_spock](https://wordpress.org/support/users/mr_spock/): Ok. This is not how it behaves on the Apache servers that I have access to (I get the Last-Modified header). I see from the “server” response header that you are on Amazon (it is“ Apache/2.4.37 (Amazon)”). It could perhaps be that they for some reason decided policy. * But wait, I just had a more careful look at the .htaccess rules that you posted. Here is an extract: * ``` # Set Cache-Control header so these direct redirections also get the header set # (and also webp-realizer.php) Header set Cache-Control "public, max-age=31536000" # Fall back to mod_expires if mod_headers is unavailable ExpiresActive On ExpiresByType image/webp "access plus 1 years" ``` * Removing the first block will is not enough as the second block is only going to have effect on systems where the mod_headers are unavailable. The above should be replaced with this: * ``` ExpiresActive On ExpiresByType image/webp "access plus 1 years" ``` * Or rather: You should place this outside the WebP Express section in the FAQ, in order for it not to be overridden later. * Does that work? Viewing 11 replies - 1 through 11 (of 11 total) The topic ‘Cache Validator / Last Modified Header’ is closed to new replies. * ![](https://ps.w.org/webp-express/assets/icon.svg?rev=1918288) * [WebP Express](https://wordpress.org/plugins/webp-express/) * [Frequently Asked Questions](https://wordpress.org/plugins/webp-express/#faq) * [Support Threads](https://wordpress.org/support/plugin/webp-express/) * [Active Topics](https://wordpress.org/support/plugin/webp-express/active/) * [Unresolved Topics](https://wordpress.org/support/plugin/webp-express/unresolved/) * [Reviews](https://wordpress.org/support/plugin/webp-express/reviews/) * 11 replies * 3 participants * Last reply from: [rosell.dk](https://wordpress.org/support/users/roselldk/) * Last activity: [6 years, 10 months ago](https://wordpress.org/support/topic/cache-validator-last-modified-header/#post-11790845) * Status: resolved