PHP 304 Last Modified Example

.htaccess

# Bitrix Example
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-l
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !/bitrix/urlrewrite.php$
RewriteRule ^(.*)$ /bitrix/urlrewrite.php [L]
#RewriteRule .* - [E=REMOTE_USER:%{HTTP:Authorization}]
RewriteRule .* - [E=REMOTE_USER:%{HTTP:Authorization},E=HTTP_IF_MODIFIED_SINCE:%{HTTP:If-Modified-Since}]

last_modified_example.php

<?php

$LastModifiedTime = 0; // < == SOME TIMESTAMP WHEN MODIFIED

$LastModified = date('D, d M Y H:i:s') . ' GMT';

$IfModifiedSince = isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])? $_SERVER['HTTP_IF_MODIFIED_SINCE'] : 0;

$IfModifiedSinceTime = strtotime($IfModifiedSince);

if ($IfModifiedSince && preg_match('/[0-9]{2,}\s+[a-z]{2,}\s+[0-9]{4}\s[0-9]{2}:[0-9]{2}:[0-9]{2}/i', $IfModifiedSince) && $LastModifiedTime > $IfModifiedSinceTime){

	$sapi_name = php_sapi_name();

	if (strrpos($sapi_name, 'cgi') === 0){
		header('Status: 304 Not Modified');
	}else{
		header('HTTP/1.1 304 Not Modified');
	}

	exit;
}

header('Last-Modified: ' . $LastModified);

/* ... contents of file ... */