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Name	Type	Actions
AbstractSurrogate.php	File	Edit
Esi.php	File	Edit
HttpCache.php	File	Edit
ResponseCacheStrategy.php	File	Edit
ResponseCacheStrategyInterface.php	File	Edit
Ssi.php	File	Edit
Store.php	File	Edit
StoreInterface.php	File	Edit
SubRequestHandler.php	File	Edit
SurrogateInterface.php	File	Edit

Editing: HttpCache.php

<?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.
 */

/*
 * This code is partially based on the Rack-Cache library by Ryan Tomayko,
 * which is released under the MIT license.
 * (based on commit 02d2b48d75bcb63cf1c0c7149c077ad256542801)
 */

namespace Symfony\Component\HttpKernel\HttpCache;

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\HttpKernelInterface;
use Symfony\Component\HttpKernel\TerminableInterface;

/**
 * Cache provides HTTP caching.
 *
 * @author Fabien Potencier <fabien@symfony.com>
 */
class HttpCache implements HttpKernelInterface, TerminableInterface
{
    private HttpKernelInterface $kernel;
    private StoreInterface $store;
    private Request $request;
    private ?SurrogateInterface $surrogate;
    private ?ResponseCacheStrategyInterface $surrogateCacheStrategy = null;
    private array $options = [];
    private array $traces = [];

/**
     * Constructor.
     *
     * The available options are:
     *
     *   * debug                  If true, exceptions are thrown when things go wrong. Otherwise, the cache
     *                            will try to carry on and deliver a meaningful response.
     *
     *   * trace_level            May be one of 'none', 'short' and 'full'. For 'short', a concise trace of the
     *                            main request will be added as an HTTP header. 'full' will add traces for all
     *                            requests (including ESI subrequests). (default: 'full' if in debug; 'none' otherwise)
     *
     *   * trace_header           Header name to use for traces. (default: X-Symfony-Cache)
     *
     *   * 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).
     *
     *   * terminate_on_cache_hit Specifies if the kernel.terminate event should be dispatched even when the cache
     *                            was hit (default: true).
     *                            Unless your application needs to process events on cache hits, it is recommended
     *                            to set this to false to avoid having to bootstrap the Symfony framework on a cache hit.
     */
    public function __construct(HttpKernelInterface $kernel, StoreInterface $store, SurrogateInterface $surrogate = null, array $options = [])
    {
        $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($this->store->cleanup(...));

$this->options = array_merge([
            'debug' => false,
            'default_ttl' => 0,
            'private_headers' => ['Authorization', 'Cookie'],
            'allow_reload' => false,
            'allow_revalidate' => false,
            'stale_while_revalidate' => 2,
            'stale_if_error' => 60,
            'trace_level' => 'none',
            'trace_header' => 'X-Symfony-Cache',
            'terminate_on_cache_hit' => true,
        ], $options);

if (!isset($options['trace_level'])) {
            $this->options['trace_level'] = $this->options['debug'] ? 'full' : 'none';
        }
    }

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

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

private function addTraces(Response $response)
    {
        $traceString = null;

if ('full' === $this->options['trace_level']) {
            $traceString = $this->getLog();
        }

if ('short' === $this->options['trace_level'] && $masterId = array_key_first($this->traces)) {
            $traceString = implode('/', $this->traces[$masterId]);
        }

if (null !== $traceString) {
            $response->headers->add([$this->options['trace_header'] => $traceString]);
        }
    }

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

return implode('; ', $log);
    }

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

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

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

public function handle(Request $request, int $type = HttpKernelInterface::MAIN_REQUEST, bool $catch = true): Response
    {
        // FIXME: catch exceptions and implement a 500 error page here? -> in Varnish, there is a built-in error page mechanism
        if (HttpKernelInterface::MAIN_REQUEST === $type) {
            $this->traces = [];
            // Keep a clone of the original request for surrogates so they can access it.
            // We must clone here to get a separate instance because the application will modify the request during
            // the application flow (we know it always does because we do ourselves by setting REMOTE_ADDR to 127.0.0.1
            // and adding the X-Forwarded-For header, see HttpCache::forward()).
            $this->request = clone $request;
            if (null !== $this->surrogate) {
                $this->surrogateCacheStrategy = $this->surrogate->createCacheStrategy();
            }
        }

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

if (!$request->isMethodSafe()) {
            $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::MAIN_REQUEST === $type) {
            $this->addTraces($response);
        }

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

$response->prepare($request);

$response->isNotModified($request);

return $response;
    }

public function terminate(Request $request, Response $response)
    {
        // Do not call any listeners in case of a cache hit.
        // This ensures identical behavior as if you had a separate
        // reverse caching proxy such as Varnish and the like.
        if ($this->options['terminate_on_cache_hit']) {
            trigger_deprecation('symfony/http-kernel', '6.2', 'Setting "terminate_on_cache_hit" to "true" is deprecated and will be changed to "false" in Symfony 7.0.');
        } elseif (\in_array('fresh', $this->traces[$this->getTraceKey($request)] ?? [], true)) {
            return;
        }

if ($this->getKernel() instanceof TerminableInterface) {
            $this->getKernel()->terminate($request, $response);
        }
    }

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

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

/**
     * Invalidates non-safe methods (like POST, PUT, and DELETE).
     *
     * @param bool $catch Whether to process exceptions
     *
     * @throws \Exception
     *
     * @see RFC2616 13.10
     */
    protected function invalidate(Request $request, bool $catch = false): Response
    {
        $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 (['Location', 'Content-Location'] as $header) {
                    if ($uri = $response->headers->get($header)) {
                        $subRequest = Request::create($uri, 'get', [], [], [], $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 bool $catch Whether to process exceptions
     *
     * @throws \Exception
     */
    protected function lookup(Request $request, bool $catch = false): Response
    {
        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);
        }

if ($entry->headers->hasCacheControlDirective('no-cache')) {
            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 bool $catch Whether to process exceptions
     */
    protected function validate(Request $request, Response $entry, bool $catch = false): Response
    {
        $subRequest = clone $request;

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

// add our cached last-modified validator
        if ($entry->headers->has('Last-Modified')) {
            $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 = $entry->getEtag() ? [$entry->getEtag()] : [];
        $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 (['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 bool $catch Whether to process exceptions
     */
    protected function fetch(Request $request, bool $catch = false): Response
    {
        $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 bool          $catch Whether to catch exceptions or not
     * @param Response|null $entry A Response instance (the stale entry if present, null otherwise)
     *
     * @return Response
     */
    protected function forward(Request $request, bool $catch = false, Response $entry = null)
    {
        $this->surrogate?->addSurrogateCapability($request);

// always a "master" request (as the real master request can be in cache)
        $response = SubRequestHandler::handle($this->kernel, $request, HttpKernelInterface::MAIN_REQUEST, $catch);

/*
         * Support stale-if-error given on Responses or as a config option.
         * RFC 7234 summarizes in Section 4.2.4 (but also mentions with the individual
         * Cache-Control directives) that
         *
         *      A cache MUST NOT generate a stale response if it is prohibited by an
         *      explicit in-protocol directive (e.g., by a "no-store" or "no-cache"
         *      cache directive, a "must-revalidate" cache-response-directive, or an
         *      applicable "s-maxage" or "proxy-revalidate" cache-response-directive;
         *      see Section 5.2.2).
         *
         * https://tools.ietf.org/html/rfc7234#section-4.2.4
         *
         * We deviate from this in one detail, namely that we *do* serve entries in the
         * stale-if-error case even if they have a `s-maxage` Cache-Control directive.
         */
        if (null !== $entry
            && \in_array($response->getStatusCode(), [500, 502, 503, 504])
            && !$entry->headers->hasCacheControlDirective('no-cache')
            && !$entry->mustRevalidate()
        ) {
            if (null === $age = $entry->headers->getCacheControlDirective('stale-if-error')) {
                $age = $this->options['stale_if_error'];
            }

/*
             * stale-if-error gives the (extra) time that the Response may be used *after* it has become stale.
             * So we compare the time the $entry has been sitting in the cache already with the
             * time it was fresh plus the allowed grace period.
             */
            if ($entry->getAge() <= $entry->getMaxAge() + $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(\DateTimeImmutable::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.
     */
    protected function isFreshEnough(Request $request, Response $entry): bool
    {
        if (!$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 $request, Response $entry): bool
    {
        // 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 $request, Response $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 $request, Response $response)
    {
        if ($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 $request, Response $response)
    {
        if ($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.
     */
    private function isPrivateRequest(Request $request): bool
    {
        foreach ($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.
     */
    private function record(Request $request, string $event)
    {
        $this->traces[$this->getTraceKey($request)][] = $event;
    }

/**
     * Calculates the key we use in the "trace" array for a given request.
     */
    private function getTraceKey(Request $request): string
    {
        $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.
     */
    private function mayServeStaleWhileRevalidate(Response $entry): bool
    {
        $timeout = $entry->headers->getCacheControlDirective('stale-while-revalidate');
        $timeout ??= $this->options['stale_while_revalidate'];

return abs($entry->getTtl() ?? 0) < $timeout;
    }

/**
     * Waits for the store to release a locked entry.
     */
    private function waitForLock(Request $request): bool
    {
        $wait = 0;
        while ($this->store->isLocked($request) && $wait < 100) {
            usleep(50000);
            ++$wait;
        }

return $wait < 100;
    }
}

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Editing: HttpCache.php