Classes List

Symfony\Component\HttpKernel\HttpCache\HttpCache

 1 
 2 
 3 
 4 
 5 
 6 
 7 
 8 
 9 
 10 
 11 
 12 
 13 
 14 
 15 
 16 
 17 
 18 
 19 
 20 
 21 
 22 
 23 
 24 
 25 
 26 
 27 
 28 
 29 
 30 
 31 
 32 
 33 
 34 
 35 
 36 
 37 
 38 
 39 
 40 
 41 
 42 
 43 
 44 
 45 
 46 
 47 
 48 
 49 
 50 
 51 
 52 
 53 
 54 
 55 
 56 
 57 
 58 
 59 
 60 
 61 
 62 
 63 
 64 
 65 
 66 
 67 
 68 
 69 
 70 
 71 
 72 
 73 
 74 
 75 
 76 
 77 
 78 
 79 
 80 
 81 
 82 
 83 
 84 
 85 
 86 
 87 
 88 
 89 
 90 
 91 
 92 
 93 
 94 
 95 
 96 
 97 
 98 
 99 
 100 
 101 
 102 
 103 
 104 
 105 
 106 
 107 
 108 
 109 
 110 
 111 
 112 
 113 
 114 
 115 
 116 
 117 
 118 
 119 
 120 
 121 
 122 
 123 
 124 
 125 
 126 
 127 
 128 
 129 
 130 
 131 
 132 
 133 
 134 
 135 
 136 
 137 
 138 
 139 
 140 
 141 
 142 
 143 
 144 
 145 
 146 
 147 
 148 
 149 
 150 
 151 
 152 
 153 
 154 
 155 
 156 
 157 
 158 
 159 
 160 
 161 
 162 
 163 
 164 
 165 
 166 
 167 
 168 
 169 
 170 
 171 
 172 
 173 
 174 
 175 
 176 
 177 
 178 
 179 
 180 
 181 
 182 
 183 
 184 
 185 
 186 
 187 
 188 
 189 
 190 
 191 
 192 
 193 
 194 
 195 
 196 
 197 
 198 
 199 
 200 
 201 
 202 
 203 
 204 
 205 
 206 
 207 
 208 
 209 
 210 
 211 
 212 
 213 
 214 
 215 
 216 
 217 
 218 
 219 
 220 
 221 
 222 
 223 
 224 
 225 
 226 
 227 
 228 
 229 
 230 
 231 
 232 
 233 
 234 
 235 
 236 
 237 
 238 
 239 
 240 
 241 
 242 
 243 
 244 
 245 
 246 
 247 
 248 
 249 
 250 
 251 
 252 
 253 
 254 
 255 
 256 
 257 
 258 
 259 
 260 
 261 
 262 
 263 
 264 
 265 
 266 
 267 
 268 
 269 
 270 
 271 
 272 
 273 
 274 
 275 
 276 
 277 
 278 
 279 
 280 
 281 
 282 
 283 
 284 
 285 
 286 
 287 
 288 
 289 
 290 
 291 
 292 
 293 
 294 
 295 
 296 
 297 
 298 
 299 
 300 
 301 
 302 
 303 
 304 
 305 
 306 
 307 
 308 
 309 
 310 
 311 
 312 
 313 
 314 
 315 
 316 
 317 
 318 
 319 
 320 
 321 
 322 
 323 
 324 
 325 
 326 
 327 
 328 
 329 
 330 
 331 
 332 
 333 
 334 
 335 
 336 
 337 
 338 
 339 
 340 
 341 
 342 
 343 
 344 
 345 
 346 
 347 
 348 
 349 
 350 
 351 
 352 
 353 
 354 
 355 
 356 
 357 
 358 
 359 
 360 
 361 
 362 
 363 
 364 
 365 
 366 
 367 
 368 
 369 
 370 
 371 
 372 
 373 
 374 
 375 
 376 
 377 
 378 
 379 
 380 
 381 
 382 
 383 
 384 
 385 
 386 
 387 
 388 
 389 
 390 
 391 
 392 
 393 
 394 
 395 
 396 
 397 
 398 
 399 
 400 
 401 
 402 
 403 
 404 
 405 
 406 
 407 
 408 
 409 
 410 
 411 
 412 
 413 
 414 
 415 
 416 
 417 
 418 
 419 
 420 
 421 
 422 
 423 
 424 
 425 
 426 
 427 
 428 
 429 
 430 
 431 
 432 
 433 
 434 
 435 
 436 
 437 
 438 
 439 
 440 
 441 
 442 
 443 
 444 
 445 
 446 
 447 
 448 
 449 
 450 
 451 
 452 
 453 
 454 
 455 
 456 
 457 
 458 
 459 
 460 
 461 
 462 
 463 
 464 
 465 
 466 
 467 
 468 
 469 
 470 
 471 
 472 
 473 
 474 
 475 
 476 
 477 
 478 
 479 
 480 
 481 
 482 
 483 
 484 
 485 
 486 
 487 
 488 
 489 
 490 
 491 
 492 
 493 
 494 
 495 
 496 
 497 
 498 
 499 
 500 
 501 
 502 
 503 
 504 
 505 
 506 
 507 
 508 
 509 
 510 
 511 
 512 
 513 
 514 
 515 
 516 
 517 
 518 
 519 
 520 
 521 
 522 
 523 
 524 
 525 
 526 
 527 
 528 
 529 
 530 
 531 
 532 
 533 
 534 
 535 
 536 
 537 
 538 
 539 
 540 
 541 
 542 
 543 
 544 
 545 
 546 
 547 
 548 
 549 
 550 
 551 
 552 
 553 
 554 
 555 
 556 
 557 
 558 
 559 
 560 
 561 
 562 
 563 
 564 
 565 
 566 
 567 
 568 
 569 
 570 
 571 
 572 
 573 
 574 
 575 
 576 
 577 
 578 
 579 
 580 
 581 
 582 
 583 
 584 
 585 
 586 
 587 
 588 
 589 
 590 
 591 
 592 
 593 
 594 
 595 
 596 
 597 
 598 
 599 
 600 
 601 
 602 
 603 
 604 
 605 
 606 
 607 
 608 
 609 
 610 
 611 
 612 
 613 
 614 
 615 
 616 
 617 
 618 
 619 
 620 
 621 
 622 
 623 
 624 
 625 
 626 
 627 
 628 
 629 
 630 
 631 
 632 
 633 
 634 
 635 
 636 
 637 
 638 
 639 
 640 
 641 
 642 
 643 
 644 
 645 
 646 
 647 
 648 
 649 
 650 
 651 
 652 
 653 
 654 
 655 
 656 
 657 
 658 
 659 
 660 
 661 
 662 
 663 
 664 
 665 
 666 
 667 
 668 
 669 
 670 
 671 
 672 
 673 
 674 
 675 
 676 
 677 
 678 
 679 
 680 
 681 
 682 
 683 
 684 
 685 
 686 
 687 
 688 
 689 
 690 
 691 
 692 
 693 
 694 
 695 
 696 
 697 
 698 
 699 
 700 
 701 
 702 
 703 
 704 
 705 
 706 
 707 
 708 
 709 
 710 
 711 
 712 
 713 
 714 
 715 
<?php

/* * This file is part of the Symfony package. * * (c) Fabien Potencier <fabien@symfony.com> * * This code is partially based on the Rack-Cache library by Ryan Tomayko, * which is released under the MIT license. * (based on commit 02d2b48d75bcb63cf1c0c7149c077ad256542801) * * 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\HttpKernel\HttpKernelInterface;
use Symfony\Component\HttpKernel\TerminableInterface;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;

/** * Cache provides HTTP caching. * * @author Fabien Potencier <fabien@symfony.com> */
class HttpCache implements HttpKernelInterfaceTerminableInterface
{
    private $kernel;
    private $store;
    private $request;
    private $surrogate;
    private $surrogateCacheStrategy;
    private $options = array();
    private $traces = array();

    /** * Constructor. * * The available options are: * * * debug: If true, the traces are added as a HTTP header to ease debugging * * * default_ttl The number of seconds that a cache entry should be considered * fresh when no explicit freshness information is provided in * a response. Explicit Cache-Control or Expires headers * override this value. (default: 0) * * * private_headers Set of request headers that trigger "private" cache-control behavior * on responses that don't explicitly state whether the response is * public or private via a Cache-Control directive. (default: Authorization and Cookie) * * * allow_reload Specifies whether the client can force a cache reload by including a * Cache-Control "no-cache" directive in the request. Set it to ``true`` * for compliance with RFC 2616. (default: false) * * * allow_revalidate Specifies whether the client can force a cache revalidate by including * a Cache-Control "max-age=0" directive in the request. Set it to ``true`` * for compliance with RFC 2616. (default: false) * * * stale_while_revalidate Specifies the default number of seconds (the granularity is the second as the * Response TTL precision is a second) during which the cache can immediately return * a stale response while it revalidates it in the background (default: 2). * This setting is overridden by the stale-while-revalidate HTTP Cache-Control * extension (see RFC 5861). * * * stale_if_error Specifies the default number of seconds (the granularity is the second) during which * the cache can serve a stale response when an error is encountered (default: 60). * This setting is overridden by the stale-if-error HTTP Cache-Control extension * (see RFC 5861). */
    public function __construct(HttpKernelInterface $kernelStoreInterface $storeSurrogateInterface $surrogate = nullarray $options = array())
    {
        $this->store = $store;
        $this->kernel = $kernel;
        $this->surrogate = $surrogate;

        // needed in case there is a fatal error because the backend is too slow to respond
        register_shutdown_function(array($this->store'cleanup'));

        $this->options = array_merge(array(
            'debug' => false,
            'default_ttl' => 0,
            'private_headers' => array('Authorization''Cookie'),
            'allow_reload' => false,
            'allow_revalidate' => false,
            'stale_while_revalidate' => 2,
            'stale_if_error' => 60,
        ), $options);
    }

    /** * Gets the current store. * * @return StoreInterface $store A StoreInterface instance */
    public function getStore()
    {
        return $this->store;
    }

    /** * Returns an array of events that took place during processing of the last request. * * @return array An array of events */
    public function getTraces()
    {
        return $this->traces;
    }

    /** * Returns a log message for the events of the last request processing. * * @return string A log message */
    public function getLog()
    {
        $log = array();
        foreach ($this->traces as $request => $traces) {
            $log[] = sprintf('%s: %s'$requestimplode(', '$traces));
        }

        return implode('; '$log);
    }

    /** * Gets the Request instance associated with the master request. * * @return Request A Request instance */
    public function getRequest()
    {
        return $this->request;
    }

    /** * Gets the Kernel instance. * * @return HttpKernelInterface An HttpKernelInterface instance */
    public function getKernel()
    {
        return $this->kernel;
    }

    /** * Gets the Surrogate instance. * * @return SurrogateInterface A Surrogate instance * * @throws \LogicException */
    public function getSurrogate()
    {
        return $this->surrogate;
    }

    /** * {@inheritdoc} */
    public function handle(Request $request$type = HttpKernelInterface::MASTER_REQUEST$catch = true)
    {
        // FIXME: catch exceptions and implement a 500 error page here? -> in Varnish, there is a built-in error page mechanism
        if (HttpKernelInterface::MASTER_REQUEST === $type) {
            $this->traces = array();
            $this->request = $request;
            if (null !== $this->surrogate) {
                $this->surrogateCacheStrategy = $this->surrogate->createCacheStrategy();
            }
        }

        $this->traces[$this->getTraceKey($request)] = array();

        if (!$request->isMethodSafe(false)) {
            $response = $this->invalidate($request$catch);
        } elseif ($request->headers->has('expect'|| !$request->isMethodCacheable()) {
            $response = $this->pass($request$catch);
        } elseif ($this->options['allow_reload'&& $request->isNoCache()) {
            /* If allow_reload is configured and the client requests "Cache-Control: no-cache", reload the cache by fetching a fresh response and caching it (if possible). */

            $this->record($request'reload');
            $response = $this->fetch($request$catch);
        } else {
            $response = $this->lookup($request$catch);
        }

        $this->restoreResponseBody($request$response);

        if (HttpKernelInterface::MASTER_REQUEST === $type && $this->options['debug']) {
            $response->headers->set('X-Symfony-Cache'$this->getLog());
        }

        if (null !== $this->surrogate) {
            if (HttpKernelInterface::MASTER_REQUEST === $type) {
                $this->surrogateCacheStrategy->update($response);
            } else {
                $this->surrogateCacheStrategy->add($response);
            }
        }

        $response->prepare($request);

        $response->isNotModified($request);

        return $response;
    }

    /** * {@inheritdoc} */
    public function terminate(Request $requestResponse $response)
    {
        if ($this->getKernel() instanceof TerminableInterface) {
            $this->getKernel()->terminate($request$response);
        }
    }

    /** * Forwards the Request to the backend without storing the Response in the cache. * * @param Request $request A Request instance * @param bool $catch Whether to process exceptions * * @return Response A Response instance */
    protected function pass(Request $request$catch = false)
    {
        $this->record($request'pass');

        return $this->forward($request$catch);
    }

    /** * Invalidates non-safe methods (like POST, PUT, and DELETE). * * @param Request $request A Request instance * @param bool $catch Whether to process exceptions * * @return Response A Response instance * * @throws \Exception * * @see RFC2616 13.10 */
    protected function invalidate(Request $request$catch = false)
    {
        $response = $this->pass($request$catch);

        // invalidate only when the response is successful
        if ($response->isSuccessful() || $response->isRedirect()) {
            try {
                $this->store->invalidate($request);

                // As per the RFC, invalidate Location and Content-Location URLs if present
                foreach (array('Location''Content-Location'as $header) {
                    if ($uri = $response->headers->get($header)) {
                        $subRequest = Request::create($uri'get'array(), array(), array(), $request->server->all());

                        $this->store->invalidate($subRequest);
                    }
                }

                $this->record($request'invalidate');
            } catch (\Exception $e) {
                $this->record($request'invalidate-failed');

                if ($this->options['debug']) {
                    throw $e;
                }
            }
        }

        return $response;
    }

    /** * Lookups a Response from the cache for the given Request. * * When a matching cache entry is found and is fresh, it uses it as the * response without forwarding any request to the backend. When a matching * cache entry is found but is stale, it attempts to "validate" the entry with * the backend using conditional GET. When no matching cache entry is found, * it triggers "miss" processing. * * @param Request $request A Request instance * @param bool $catch Whether to process exceptions * * @return Response A Response instance * * @throws \Exception */
    protected function lookup(Request $request$catch = false)
    {
        try {
            $entry = $this->store->lookup($request);
        } catch (\Exception $e) {
            $this->record($request'lookup-failed');

            if ($this->options['debug']) {
                throw $e;
            }

            return $this->pass($request$catch);
        }

        if (null === $entry) {
            $this->record($request'miss');

            return $this->fetch($request$catch);
        }

        if (!$this->isFreshEnough($request$entry)) {
            $this->record($request'stale');

            return $this->validate($request$entry$catch);
        }

        $this->record($request'fresh');

        $entry->headers->set('Age'$entry->getAge());

        return $entry;
    }

    /** * Validates that a cache entry is fresh. * * The original request is used as a template for a conditional * GET request with the backend. * * @param Request $request A Request instance * @param Response $entry A Response instance to validate * @param bool $catch Whether to process exceptions * * @return Response A Response instance */
    protected function validate(Request $requestResponse $entry$catch = false)
    {
        $subRequest = clone $request;

        // send no head requests because we want content
        if ('HEAD' === $request->getMethod()) {
            $subRequest->setMethod('GET');
        }

        // add our cached last-modified validator
        $subRequest->headers->set('if_modified_since'$entry->headers->get('Last-Modified'));

        // Add our cached etag validator to the environment.
        // We keep the etags from the client to handle the case when the client
        // has a different private valid entry which is not cached here.
        $cachedEtags = $entry->getEtag() ? array($entry->getEtag()) : array();
        $requestEtags = $request->getETags();
        if ($etags = array_unique(array_merge($cachedEtags$requestEtags))) {
            $subRequest->headers->set('if_none_match'implode(', '$etags));
        }

        $response = $this->forward($subRequest$catch$entry);

        if (304 == $response->getStatusCode()) {
            $this->record($request'valid');

            // return the response and not the cache entry if the response is valid but not cached
            $etag = $response->getEtag();
            if ($etag && in_array($etag$requestEtags&& !in_array($etag$cachedEtags)) {
                return $response;
            }

            $entry = clone $entry;
            $entry->headers->remove('Date');

            foreach (array('Date''Expires''Cache-Control''ETag''Last-Modified'as $name) {
                if ($response->headers->has($name)) {
                    $entry->headers->set($name$response->headers->get($name));
                }
            }

            $response = $entry;
        } else {
            $this->record($request'invalid');
        }

        if ($response->isCacheable()) {
            $this->store($request$response);
        }

        return $response;
    }

    /** * Unconditionally fetches a fresh response from the backend and * stores it in the cache if is cacheable. * * @param Request $request A Request instance * @param bool $catch Whether to process exceptions * * @return Response A Response instance */
    protected function fetch(Request $request$catch = false)
    {
        $subRequest = clone $request;

        // send no head requests because we want content
        if ('HEAD' === $request->getMethod()) {
            $subRequest->setMethod('GET');
        }

        // avoid that the backend sends no content
        $subRequest->headers->remove('if_modified_since');
        $subRequest->headers->remove('if_none_match');

        $response = $this->forward($subRequest$catch);

        if ($response->isCacheable()) {
            $this->store($request$response);
        }

        return $response;
    }

    /** * Forwards the Request to the backend and returns the Response. * * All backend requests (cache passes, fetches, cache validations) * run through this method. * * @param Request $request A Request instance * @param bool $catch Whether to catch exceptions or not * @param Response $entry A Response instance (the stale entry if present, null otherwise) * * @return Response A Response instance */
    protected function forward(Request $request$catch = falseResponse $entry = null)
    {
        if ($this->surrogate) {
            $this->surrogate->addSurrogateCapability($request);
        }

        // modify the X-Forwarded-For header if needed
        $forwardedFor = $request->headers->get('X-Forwarded-For');
        if ($forwardedFor) {
            $request->headers->set('X-Forwarded-For'$forwardedFor.', '.$request->server->get('REMOTE_ADDR'));
        } else {
            $request->headers->set('X-Forwarded-For'$request->server->get('REMOTE_ADDR'));
        }

        // fix the client IP address by setting it to 127.0.0.1 as HttpCache
        // is always called from the same process as the backend.
        $request->server->set('REMOTE_ADDR''127.0.0.1');

        // make sure HttpCache is a trusted proxy
        if (!in_array('127.0.0.1'$trustedProxies = Request::getTrustedProxies())) {
            $trustedProxies[] = '127.0.0.1';
            Request::setTrustedProxies($trustedProxiesRequest::HEADER_X_FORWARDED_ALL);
        }

        // always a "master" request (as the real master request can be in cache)
        $response = $this->kernel->handle($requestHttpKernelInterface::MASTER_REQUEST$catch);
        // FIXME: we probably need to also catch exceptions if raw === true

        // we don't implement the stale-if-error on Requests, which is nonetheless part of the RFC
        if (null !== $entry && in_array($response->getStatusCode(), array(500502503504))) {
            if (null === $age = $entry->headers->getCacheControlDirective('stale-if-error')) {
                $age = $this->options['stale_if_error'];
            }

            if (abs($entry->getTtl()) < $age) {
                $this->record($request'stale-if-error');

                return $entry;
            }
        }

        /* RFC 7231 Sect. 7.1.1.2 says that a server that does not have a reasonably accurate clock MUST NOT send a "Date" header, although it MUST send one in most other cases except for 1xx or 5xx responses where it MAY do so. Anyway, a client that received a message without a "Date" header MUST add it. */

        if (!$response->headers->has('Date')) {
            $response->setDate(\DateTime::createFromFormat('U'time()));
        }

        $this->processResponseBody($request$response);

        if ($this->isPrivateRequest($request&& !$response->headers->hasCacheControlDirective('public')) {
            $response->setPrivate();
        } elseif ($this->options['default_ttl'] > 0 && null === $response->getTtl() && !$response->headers->getCacheControlDirective('must-revalidate')) {
            $response->setTtl($this->options['default_ttl']);
        }

        return $response;
    }

    /** * Checks whether the cache entry is "fresh enough" to satisfy the Request. * * @return bool true if the cache entry if fresh enough, false otherwise */
    protected function isFreshEnough(Request $requestResponse $entry)
    {
        if (!$entry->isFresh()) {
            return $this->lock($request$entry);
        }

        if ($this->options['allow_revalidate'&& null !== $maxAge = $request->headers->getCacheControlDirective('max-age')) {
            return $maxAge > 0 && $maxAge >= $entry->getAge();
        }

        return true;
    }

    /** * Locks a Request during the call to the backend. * * @return bool true if the cache entry can be returned even if it is staled, false otherwise */
    protected function lock(Request $requestResponse $entry)
    {
        // try to acquire a lock to call the backend
        $lock = $this->store->lock($request);

        if (true === $lock) {
            // we have the lock, call the backend
            return false;
        }

        // there is already another process calling the backend

        // May we serve a stale response?
        if ($this->mayServeStaleWhileRevalidate($entry)) {
            $this->record($request'stale-while-revalidate');

            return true;
        }

        // wait for the lock to be released
        if ($this->waitForLock($request)) {
            // replace the current entry with the fresh one
            $new = $this->lookup($request);
            $entry->headers = $new->headers;
            $entry->setContent($new->getContent());
            $entry->setStatusCode($new->getStatusCode());
            $entry->setProtocolVersion($new->getProtocolVersion());
            foreach ($new->headers->getCookies() as $cookie) {
                $entry->headers->setCookie($cookie);
            }
        } else {
            // backend is slow as hell, send a 503 response (to avoid the dog pile effect)
            $entry->setStatusCode(503);
            $entry->setContent('503 Service Unavailable');
            $entry->headers->set('Retry-After'10);
        }

        return true;
    }

    /** * Writes the Response to the cache. * * @throws \Exception */
    protected function store(Request $requestResponse $response)
    {
        try {
            $this->store->write($request$response);

            $this->record($request'store');

            $response->headers->set('Age'$response->getAge());
        } catch (\Exception $e) {
            $this->record($request'store-failed');

            if ($this->options['debug']) {
                throw $e;
            }
        }

        // now that the response is cached, release the lock
        $this->store->unlock($request);
    }

    /** * Restores the Response body. */
    private function restoreResponseBody(Request $requestResponse $response)
    {
        if ($response->headers->has('X-Body-Eval')) {
            ob_start();

            if ($response->headers->has('X-Body-File')) {
                include $response->headers->get('X-Body-File');
            } else {
                eval('; ?>'.$response->getContent().'<?php ;');
            }

            $response->setContent(ob_get_clean());
            $response->headers->remove('X-Body-Eval');
            if (!$response->headers->has('Transfer-Encoding')) {
                $response->headers->set('Content-Length'strlen($response->getContent()));
            }
        } elseif ($response->headers->has('X-Body-File')) {
            // Response does not include possibly dynamic content (ESI, SSI), so we need
            // not handle the content for HEAD requests
            if (!$request->isMethod('HEAD')) {
                $response->setContent(file_get_contents($response->headers->get('X-Body-File')));
            }
        } else {
            return;
        }

        $response->headers->remove('X-Body-File');
    }

    protected function processResponseBody(Request $requestResponse $response)
    {
        if (null !== $this->surrogate && $this->surrogate->needsParsing($response)) {
            $this->surrogate->process($request$response);
        }
    }

    /** * Checks if the Request includes authorization or other sensitive information * that should cause the Response to be considered private by default. * * @return bool true if the Request is private, false otherwise */
    private function isPrivateRequest(Request $request)
    {
        foreach ($this->options['private_headers'as $key) {
            $key = strtolower(str_replace('HTTP_'''$key));

            if ('cookie' === $key) {
                if (count($request->cookies->all())) {
                    return true;
                }
            } elseif ($request->headers->has($key)) {
                return true;
            }
        }

        return false;
    }

    /** * Records that an event took place. * * @param Request $request A Request instance * @param string $event The event name */
    private function record(Request $request$event)
    {
        $this->traces[$this->getTraceKey($request)][] = $event;
    }

    /** * Calculates the key we use in the "trace" array for a given request. * * @param Request $request * * @return string */
    private function getTraceKey(Request $request)
    {
        $path = $request->getPathInfo();
        if ($qs = $request->getQueryString()) {
            $path .= '?'.$qs;
        }

        return $request->getMethod().' '.$path;
    }

    /** * Checks whether the given (cached) response may be served as "stale" when a revalidation * is currently in progress. * * @param Response $entry * * @return bool true when the stale response may be served, false otherwise */
    private function mayServeStaleWhileRevalidate(Response $entry)
    {
        $timeout = $entry->headers->getCacheControlDirective('stale-while-revalidate');

        if (null === $timeout) {
            $timeout = $this->options['stale_while_revalidate'];
        }

        return abs($entry->getTtl()) < $timeout;
    }

    /** * Waits for the store to release a locked entry. * * @param Request $request The request to wait for * * @return bool true if the lock was released before the internal timeout was hit; false if the wait timeout was exceeded */
    private function waitForLock(Request $request)
    {
        $wait = 0;
        while ($this->store->isLocked($request&& $wait < 100) {
            usleep(50000);
            ++$wait;
        }

        return $wait < 100;
    }
}