Question

I want to give a url with curl..and fetch it based on its header attribute Expires.

I want to retrieve the page only if it was cached in the last 30 days.

Two things that I think arent right…

1) The gmmktime(0, 0, 0, 1, 1, 1998).. I am not sure how to set it to today – 30 days ago.
2) Whether it will return me google based on its headers? what the $page variable will be if the url has no cached headers with date older than 30 days

 function exractURl()
   {
       //How to convert gmmktime to the last 30 days from today
       $ts = gmdate("D, d M Y H:i:s", gmmktime(0, 0, 0, 1, 1, 1998)) . " GMT";
       $c=  curl_init('http://www.google.co.il/');
       curl_setopt($c, CURLOPT_RETURNTRANSFER, true);
       curl_setopt($c, CURLOPT_HTTPHEADER, array('Expires:'.$ts));
      //  What output will page give me..if the headers arent found
       $page= curl_exec($c);
       curl_close($c);
   }

UPDATE:

   function exractURl()
   {
       $ts = gmdate("D, d M Y H:i:s", strtotime("30 days ago")) . " GMT";
       $c=  curl_init('http://www.google.co.il/');
       curl_setopt($c, CURLOPT_RETURNTRANSFER, true);
       curl_setopt($c, CURLOPT_HTTPHEADER, array('If-Modified-Since:'.$ts));
       $page= curl_exec($c);
       curl_close($c);
       return $page;
   }

Answer 1

You can use the If-Modified-Since to ask the server to only return the content if it has changed (Otherwise you’ll get a 304 Not Modified response). Of course this relies on the server behaving. See here for more details: http://www.mnot.net/cache_docs/

And to answer your question on how to get the time as of 30 days ago, you can use the ever convenient strtotime:

$ts = gmdate("D, d M Y H:i:s", strtotime("30 days ago")) . " GMT";