<?php
 
class SimpleCache
{
	private $cacheDir = 'cache';
	private $expiryInterval = 2592000; //30*24*60*60;
 
	public function setCacheDir($val) {  $this->cacheDir = $val; }
	public function setExpiryInterval($val) {  $this->expiryInterval = $val; }
 
	public function exists($key)
	{
		$filename_cache = $this->cacheDir . '/' . $key . '.cache'; //Cache filename
		$filename_info = $this->cacheDir . '/' . $key . '.info'; //Cache info
 
		if (file_exists($filename_cache) && file_exists($filename_info))
		{
			$cache_time = file_get_contents ($filename_info) + (int)$this->expiryInterval; //Last update time of the cache file
			$time = time(); //Current Time
 
			$expiry_time = (int)$time; //Expiry time for the cache
 
			if ((int)$cache_time >= (int)$expiry_time) //Compare last updated and current time
			{
				return true;
			}
		}
 
		return false;
	}
 
 
	public function get($key)
	{
		$filename_cache = $this->cacheDir . '/' . $key . '.cache'; //Cache filename
		$filename_info = $this->cacheDir . '/' . $key . '.info'; //Cache info
 
		if (file_exists($filename_cache) && file_exists($filename_info))
		{
			$cache_time = file_get_contents ($filename_info) + (int)$this->expiryInterval; //Last update time of the cache file
			$time = time(); //Current Time
 
			$expiry_time = (int)$time; //Expiry time for the cache
 
			if ((int)$cache_time >= (int)$expiry_time) //Compare last updated and current time
			{
				return file_get_contents ($filename_cache);   //Get contents from file
			}
		}
 
		return null;
	}
 
 
	public function put($key, $content)
	{
		$time = time(); //Current Time
 
		if (! file_exists($this->cacheDir))
			mkdir($this->cacheDir);
 
		$filename_cache = $this->cacheDir . '/' . $key . '.cache'; //Cache filename
		$filename_info = $this->cacheDir . '/' . $key . '.info'; //Cache info
 
		file_put_contents ($filename_cache ,  $content); // save the content
		file_put_contents ($filename_info , $time); // save the time of last cache update
	}
 
}

<?php
 
require_once "SimpleCache.php";
 
if (isset($_GET['url'])) {
	$cache = new SimpleCache();
 
	$url = $_GET['url'];
	$key = md5($url);
 
	if ( !$cache->exists($key)) {
		$value = file_get_contents($url);
		if ($value !== null) {
			$cache->put($key, $value);
		} else {
			exit();
		}
	}
 
	echo $cache->get($key);
 
}