It is possible to use if-modified-Since with "304 not modified" without PHP

Question

Based on this solution used in this answer in SO-en i created a . htaccess and a PHP script

.htaccess:

RewriteEngine On

RewriteCond %{HTTP:if-modified-since} .
RewriteCond %{HTTP:if-none-match} .
RewriteRule . not_modified.php [L]

not_modified.php:

<?php
if (isset($_SERVER['REDIRECT_URL'])) {
    $file = $_SERVER['REDIRECT_URL'];
} else if (isset($_SERVER['REQUEST_URI'])) {
    $file = $_SERVER['REQUEST_URI'];
}

$last_modified_time = filemtime($file); 
$etag = md5_file($file);

header('Last-Modified: ' . gmdate('D, d M Y H:i:s', $last_modified_time) . ' GMT'); 

if (
    strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) === $last_modified_time ||
    trim($_SERVER['HTTP_IF_NONE_MATCH']) === $etag
) {
    if (isset($_SERVER['SERVER_PROTOCOL'])) {
        header($_SERVER['SERVER_PROTOCOL'] . ' 304 Not Modified');
    } else {
        header('HTTP/1.0 304 Not Modified');
    }
}

The script checks for changes in the file and if there are no changes then it sends the 304 code to the client response.

My question is the following, it is possible to do this without using PHP, ie using only .htaccess?

Answer 1

To use 304 Not Modified for static files it will be necessary to use the module mod_expires and "manipulate" the rule of FileETag:

1. mod_expires: Generates the HTTP headers Expires and Cache-Control according to criteria defined by the user
2. Fileetag Directive

mod_expires

This module is required to generate cache and use the 304 Not Modified, this module works the if-modified-since and the if-none-match. A simple example to set the image cache:

 #Cache de 1 mês a partir da data de acesso do arquivo
<FilesMatch "\.(?i:ico|gif|jpe?g|png|css|js|svg)$">
   ExpiresDefault "access plus 1 mouth"
</FilesMatch>

Note that the cache is generated from the image access date.

Fileetag Directive

When we use Etag instead of if-modified-since it sometimes does not work in an expected way, ie ignores that there are no "modifications" and sends the file again to the client response. In addition also according to the "Yahoo! Performance Rules - EN", disable the ETags can make pages load faster by decreasing server load and reducing bandwidth if your website is on multiple servers.

Example

A complete example of .htaccess, note that it was not necessary to use mod_rewrite:

# Trabalha o if-modified-since com arquivos de estáticos, como images, js, css, etc
<FilesMatch "\.(?i:ico|gif|jpe?g|png|css|js|svg)$">
    # Cache para um mês
    <IfModule mod_expires.c>
        ExpiresActive On
        ExpiresDefault "access plus 1 mouth"
    </IfModule>
    
    # Remove Etag para previnir o uso do mesmo
    # Pois iremos trabalhar com if-modified-since e last-modifed
    FileETag None
</FilesMatch>

Read also about:

• if-modified-since
• if-none-match