This is really simple and great solution. I have made a little modification which I believe it is more efficient. It explodes whole content at current script. What I did is writing time to filename and getting from filename. It will be more robust I guess. Here it is:

$cache_dir = “/var/www/vhosts/domain.com/httpdocs/cache/”;
function getUrl () {
global $cache_dir;
if (!isset($_SERVER['REQUEST_URI'])) {
$url = $_SERVER['REQUEST_URI'];
} else {
$url = $_SERVER['SCRIPT_NAME'];
$url .= (!empty($_SERVER['QUERY_STRING']))? ‘?’ . $_SERVER[ 'QUERY_STRING' ] : ”;

}
return $url;
}

//getUrl gets the queried page with query string
function cache ($buffer) { //page’s content is $buffer
global $cache_dir;
$url = getUrl();
$filename = time().’-’.md5($url) . ‘.cache’;
$filew = fopen($cache_dir . $filename, ‘w’);
fwrite($filew, $buffer);
fclose($filew);
return $buffer;
}

function display () {
global $cache_dir;
$url = getUrl();
$filename = md5($url) . ‘.cache’;
if (!file_exists($cache_dir . $filename)) {
return false;
}
$filer = fopen($cache_dir . $filename, ‘r’);
$data = fread($filer, filesize($cache_dir . $filename));
fclose($filer);
$arr = explode(’-', $filename, 2);
if (count($arr)!= 2 OR !is_numeric($arr['0'])) {
return false;
}
if (time()-(100) > $arr['0']) { // 100 is the cache time here!!!
return false;
}
echo $data;
die();
}

// Display cache (if any)
display(); // if it is displayed, die function will end the program here.

// if no cache, callback cache
ob_start (’cache’);

Where is the send button by the way :)

PS. I had to use firebug to add a submit button to this form.