C´est bon, j´y suis parvenu.
J´ai utilisé quand meme curl, qui m´a permis sous php de recuperer le header de la requete http.
function get_header($url){
$ch = curl_init(); // initialize curl handle
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_HEADER, true);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$result = curl_exec($ch); // run the whole process
curl_close($ch);
return $result;
}
function find_date($s){
$st = strpos($s,"Date") + 5;
$date = substr($s,$st);
$end = strpos($date,"\n") - 1;
$date = substr($date,0,$end);
return strtotime($date);
}