Check the last modified date and Etag of a web page using PHP to optimize caching and improve performance.
<?php
$lastModified=filemtime(__FILE__);
$etagFile = md5_file(__FILE__);
$ifModifiedSince=(isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) ? $_SERVER['HTTP_IF_MODIFIED_SINCE'] : false);
$etagHeader=(isset($_SERVER['HTTP_IF_NONE_MATCH']) ? trim($_SERVER['HTTP_IF_NONE_MATCH']) : false);
header("Last-Modified: ".gmdate("D, d M Y H:i:s", $lastModified)." GMT");
header("Etag: $etagFile");
header('Cache-Control: public');
if (@strtotime($ifModifiedSince)==$lastModified || $etagHeader == $etagFile)
{
header("HTTP/1.1 304 Not Modified");
exit;
}
echo "This page was last modified: ".date("d.m.Y H:i:s",time());
?>
