/**
* @static
* @param Google\Http\Request $resp
* @return bool True if the HTTP response is considered to be expired.
* False if it is considered to be fresh.
*/
public static function isExpired(Request $resp)
{
// HTTP/1.1 clients and caches MUST treat other invalid date formats,
// especially including the value “0”, as in the past.
$parsedExpires = false;
$responseHeaders = $resp->getResponseHeaders();
if (isset($responseHeaders['expires'])) {
$rawExpires = $responseHeaders['expires'];
// Check for a malformed expires header first.
if (empty($rawExpires) || is_numeric($rawExpires) && $rawExpires <= 0) {
return true;
}
// See if we can parse the expires header.
$parsedExpires = strtotime($rawExpires);
if (false == $parsedExpires || $parsedExpires <= 0) {
return true;
}
}
// Calculate the freshness of an http response.
$freshnessLifetime = false;
$cacheControl = $resp->getParsedCacheControl();
if (isset($cacheControl['max-age'])) {
$freshnessLifetime = $cacheControl['max-age'];
}
$rawDate = $resp->getResponseHeader('date');
$parsedDate = strtotime($rawDate);
if (empty($rawDate) || false == $parsedDate) {
// We can't default this to now, as that means future cache reads
// will always pass with the logic below, so we will require a
// date be injected if not supplied.
throw new Exception("All cacheable requests must have creation dates.");
}
if (false == $freshnessLifetime && isset($responseHeaders['expires'])) {
$freshnessLifetime = $parsedExpires - $parsedDate;
}
if (false == $freshnessLifetime) {
return true;
}
// Calculate the age of an http response.
$age = max(0, time() - $parsedDate);
if (isset($responseHeaders['age'])) {
$age = max($age, strtotime($responseHeaders['age']));
}
return $freshnessLifetime <= $age;
}