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<?php
/*
* This file is part of the Symfony package.
*
* (c) Fabien Potencier <fabien@symfony.com>
*
* For the full copyright and license information, please view the LICENSE
* file that was distributed with this source code.
*/
namespace Symfony\Component\HttpKernel\HttpCache;
use Symfony\Component\HttpFoundation\Response;
/**
* ResponseCacheStrategy knows how to compute the Response cache HTTP header
* based on the different response cache headers.
*
* This implementation changes the main response TTL to the smallest TTL received
* or force validation if one of the surrogates has validation cache strategy.
*
* @author Fabien Potencier <fabien@symfony.com>
*/
class ResponseCacheStrategy implements ResponseCacheStrategyInterface
{
/**
* Cache-Control headers that are sent to the final response if they appear in ANY of the responses.
*/
private const OVERRIDE_DIRECTIVES = ['private', 'no-cache', 'no-store', 'no-transform', 'must-revalidate', 'proxy-revalidate'];
/**
* Cache-Control headers that are sent to the final response if they appear in ALL of the responses.
*/
private const INHERIT_DIRECTIVES = ['public', 'immutable'];
private int $embeddedResponses = 0;
private bool $isNotCacheableResponseEmbedded = false;
private int $age = 0;
private \DateTimeInterface|false|null $lastModified = null;
private array $flagDirectives = [
'no-cache' => null,
'no-store' => null,
'no-transform' => null,
'must-revalidate' => null,
'proxy-revalidate' => null,
'public' => null,
'private' => null,
'immutable' => null,
];
private array $ageDirectives = [
'max-age' => null,
's-maxage' => null,
'expires' => false,
];
public function add(Response $response): void
{
++$this->embeddedResponses;
foreach (self::OVERRIDE_DIRECTIVES as $directive) {
if ($response->headers->hasCacheControlDirective($directive)) {
$this->flagDirectives[$directive] = true;
}
}
foreach (self::INHERIT_DIRECTIVES as $directive) {
if (false !== $this->flagDirectives[$directive]) {
$this->flagDirectives[$directive] = $response->headers->hasCacheControlDirective($directive);
}
}
$age = $response->getAge();
$this->age = max($this->age, $age);
if ($this->willMakeFinalResponseUncacheable($response)) {
$this->isNotCacheableResponseEmbedded = true;
return;
}
$maxAge = $response->headers->hasCacheControlDirective('max-age') ? (int) $response->headers->getCacheControlDirective('max-age') : null;
$sharedMaxAge = $response->headers->hasCacheControlDirective('s-maxage') ? (int) $response->headers->getCacheControlDirective('s-maxage') : $maxAge;
$expires = $response->getExpires();
$expires = null !== $expires ? (int) $expires->format('U') - (int) $response->getDate()->format('U') : null;
// See https://datatracker.ietf.org/doc/html/rfc7234#section-4.2.2
// If a response is "public" but does not have maximum lifetime, heuristics might be applied.
// Do not store NULL values so the final response can have more limiting value from other responses.
$isHeuristicallyCacheable = $response->headers->hasCacheControlDirective('public')
&& null === $maxAge
&& null === $sharedMaxAge
&& null === $expires;
if (!$isHeuristicallyCacheable || null !== $maxAge || null !== $expires) {
$this->storeRelativeAgeDirective('max-age', $maxAge, $expires, $age);
}
if (!$isHeuristicallyCacheable || null !== $sharedMaxAge || null !== $expires) {
$this->storeRelativeAgeDirective('s-maxage', $sharedMaxAge, $expires, $age);
}
if (null !== $expires) {
$this->ageDirectives['expires'] = true;
}
if (false !== $this->lastModified) {
$lastModified = $response->getLastModified();
$this->lastModified = $lastModified ? max($this->lastModified, $lastModified) : false;
}
}
public function update(Response $response): void
{
// if we have no embedded Response, do nothing
if (0 === $this->embeddedResponses) {
return;
}
// Remove Etag since it cannot be merged from embedded responses.
$response->setEtag(null);
$this->add($response);
$response->headers->set('Age', $this->age);
if ($this->isNotCacheableResponseEmbedded) {
$response->setLastModified(null);
if ($this->flagDirectives['no-store']) {
$response->headers->set('Cache-Control', 'no-cache, no-store, must-revalidate');
} else {
$response->headers->set('Cache-Control', 'no-cache, must-revalidate');
}
return;
}
$response->setLastModified($this->lastModified ?: null);
$flags = array_filter($this->flagDirectives);
if (isset($flags['must-revalidate'])) {
$flags['no-cache'] = true;
}
$response->headers->set('Cache-Control', implode(', ', array_keys($flags)));
$maxAge = null;
if (is_numeric($this->ageDirectives['max-age'])) {
$maxAge = $this->ageDirectives['max-age'] + $this->age;
$response->headers->addCacheControlDirective('max-age', $maxAge);
}
if (is_numeric($this->ageDirectives['s-maxage'])) {
$sMaxage = $this->ageDirectives['s-maxage'] + $this->age;
if ($maxAge !== $sMaxage) {
$response->headers->addCacheControlDirective('s-maxage', $sMaxage);
}
}
if ($this->ageDirectives['expires'] && null !== $maxAge) {
$date = clone $response->getDate();
$date = $date->modify('+'.$maxAge.' seconds');
$response->setExpires($date);
}
}
/**
* RFC2616, Section 13.4.
*
* @see https://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.4
*/
private function willMakeFinalResponseUncacheable(Response $response): bool
{
// RFC2616: A response received with a status code of 200, 203, 300, 301 or 410
// MAY be stored by a cache […] unless a cache-control directive prohibits caching.
if ($response->headers->hasCacheControlDirective('no-cache')
|| $response->headers->hasCacheControlDirective('no-store')
) {
return true;
}
// Etag headers cannot be merged, they render the response uncacheable
// by default (except if the response also has max-age etc.).
if (null === $response->getEtag() && \in_array($response->getStatusCode(), [200, 203, 300, 301, 410], true)) {
return false;
}
// RFC2616: A response received with any other status code (e.g. status codes 302 and 307)
// MUST NOT be returned in a reply to a subsequent request unless there are
// cache-control directives or another header(s) that explicitly allow it.
$cacheControl = ['max-age', 's-maxage', 'must-revalidate', 'proxy-revalidate', 'public', 'private'];
foreach ($cacheControl as $key) {
if ($response->headers->hasCacheControlDirective($key)) {
return false;
}
}
if ($response->headers->has('Expires')) {
return false;
}
return true;
}
/**
* Store lowest max-age/s-maxage/expires for the final response.
*
* The response might have been stored in cache a while ago. To keep things comparable,
* we have to subtract the age so that the value is normalized for an age of 0.
*
* If the value is lower than the currently stored value, we update the value, to keep a rolling
* minimal value of each instruction. If the value is NULL, the directive will not be set on the final response.
*/
private function storeRelativeAgeDirective(string $directive, ?int $value, ?int $expires, int $age): void
{
if (null === $value && null === $expires) {
$this->ageDirectives[$directive] = false;
}
if (false !== $this->ageDirectives[$directive]) {
$value = min($value ?? \PHP_INT_MAX, $expires ?? \PHP_INT_MAX);
$value -= $age;
$this->ageDirectives[$directive] = null !== $this->ageDirectives[$directive] ? min($this->ageDirectives[$directive], $value) : $value;
}
}
}