/**
* Calculates the total Time To Live based on the specification
* RFC 2616 cache lifetime rules.
*
* @param Response $response Response to evaluate
* @return mixed TTL value or false if the response should not be cached
*/
public function cache_lifetime(Response $response)
{
// Get out of here if this cannot be cached
if (!$this->set_cache($response)) {
return FALSE;
}
// Calculate apparent age
if ($date = $response->headers('date')) {
$apparent_age = max(0, $this->_response_time - strtotime((string) $date));
} else {
$apparent_age = max(0, $this->_response_time);
}
// Calculate corrected received age
if ($age = $response->headers('age')) {
$corrected_received_age = max($apparent_age, intval((string) $age));
} else {
$corrected_received_age = $apparent_age;
}
// Corrected initial age
$corrected_initial_age = $corrected_received_age + $this->request_execution_time();
// Resident time
$resident_time = time() - $this->_response_time;
// Current age
$current_age = $corrected_initial_age + $resident_time;
// Prepare the cache freshness lifetime
$ttl = NULL;
// Cache control overrides
if ($cache_control = $response->headers('cache-control')) {
// Parse the cache control header
$cache_control = Response::parse_cache_control((string) $cache_control);
if (isset($cache_control['max-age'])) {
$ttl = (int) $cache_control['max-age'];
}
if (isset($cache_control['s-maxage']) and isset($cache_control['private']) and $this->_allow_private_cache) {
$ttl = (int) $cache_control['s-maxage'];
}
if (isset($cache_control['max-stale']) and !isset($cache_control['must-revalidate'])) {
$ttl = $current_age + (int) $cache_control['max-stale'];
}
}
// If we have a TTL at this point, return
if ($ttl !== NULL) {
return $ttl;
}
if ($expires = $response->headers('expires')) {
return strtotime((string) $expires) - $current_age;
}
return FALSE;
}
