Source/WebCore/loader/cache/CachedResource.cpp

/*
    Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
    Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
    Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
    Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
    Copyright (C) 2004-2011, 2014 Apple Inc. All rights reserved.

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public License
    along with this library; see the file COPYING.LIB.  If not, write to
    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
    Boston, MA 02110-1301, USA.
*/

#include "config.h"
#include "CachedResource.h"

#include "CachedResourceClient.h"
#include "CachedResourceClientWalker.h"
#include "CachedResourceHandle.h"
#include "CachedResourceLoader.h"
#include "CrossOriginAccessControl.h"
#include "DiagnosticLoggingClient.h"
#include "DiagnosticLoggingKeys.h"
#include "Document.h"
#include "DocumentLoader.h"
#include "FrameLoader.h"
#include "FrameLoaderClient.h"
#include "HTTPHeaderNames.h"
#include "InspectorInstrumentation.h"
#include "URL.h"
#include "LoaderStrategy.h"
#include "Logging.h"
#include "MainFrame.h"
#include "MemoryCache.h"
#include "Page.h"
#include "PlatformStrategies.h"
#include "ResourceHandle.h"
#include "SchemeRegistry.h"
#include "SecurityOrigin.h"
#include "SecurityPolicy.h"
#include "SubresourceLoader.h"
#include <wtf/CurrentTime.h>
#include <wtf/MathExtras.h>
#include <wtf/RefCountedLeakCounter.h>
#include <wtf/StdLibExtras.h>
#include <wtf/text/CString.h>
#include <wtf/Vector.h>

#if USE(QUICK_LOOK)
#include "QuickLook.h"
#endif

using namespace WTF;

#define RELEASE_LOG_IF_ALLOWED(fmt, ...) RELEASE_LOG_IF(cachedResourceLoader.isAlwaysOnLoggingAllowed(), Network, "%p - CachedResource::" fmt, this, ##__VA_ARGS__)

namespace WebCore {

ResourceLoadPriority CachedResource::defaultPriorityForResourceType(Type type)
{
    switch (type) {
    case CachedResource::MainResource:
        return ResourceLoadPriority::VeryHigh;
    case CachedResource::CSSStyleSheet:
        return ResourceLoadPriority::High;
    case CachedResource::Script:
#if ENABLE(SVG_FONTS)
    case CachedResource::SVGFontResource:
#endif
    case CachedResource::MediaResource:
    case CachedResource::FontResource:
    case CachedResource::RawResource:
        return ResourceLoadPriority::Medium;
    case CachedResource::ImageResource:
        return ResourceLoadPriority::Low;
#if ENABLE(XSLT)
    case CachedResource::XSLStyleSheet:
        return ResourceLoadPriority::High;
#endif
    case CachedResource::SVGDocumentResource:
        return ResourceLoadPriority::Low;
#if ENABLE(LINK_PREFETCH)
    case CachedResource::LinkPrefetch:
        return ResourceLoadPriority::VeryLow;
    case CachedResource::LinkSubresource:
        return ResourceLoadPriority::VeryLow;
#endif
#if ENABLE(VIDEO_TRACK)
    case CachedResource::TextTrackResource:
        return ResourceLoadPriority::Low;
#endif
    }
    ASSERT_NOT_REACHED();
    return ResourceLoadPriority::Low;
}

static std::chrono::milliseconds deadDecodedDataDeletionIntervalForResourceType(CachedResource::Type type)
{
    if (type == CachedResource::Script)
        return std::chrono::milliseconds { 0 };

    return MemoryCache::singleton().deadDecodedDataDeletionInterval();
}

DEFINE_DEBUG_ONLY_GLOBAL(RefCountedLeakCounter, cachedResourceLeakCounter, ("CachedResource"));

CachedResource::CachedResource(CachedResourceRequest&& request, Type type, SessionID sessionID)
    : m_resourceRequest(WTFMove(request.mutableResourceRequest()))
    , m_options(request.options())
    , m_decodedDataDeletionTimer(*this, &CachedResource::destroyDecodedData, deadDecodedDataDeletionIntervalForResourceType(type))
    , m_sessionID(sessionID)
    , m_loadPriority(defaultPriorityForResourceType(type))
    , m_responseTimestamp(std::chrono::system_clock::now())
    , m_origin(request.releaseOrigin())
    , m_type(type)
{
    ASSERT(sessionID.isValid());
    finishRequestInitialization();

    // FIXME: We should have a better way of checking for Navigation loads, maybe FetchMode::Options::Navigate.
    ASSERT(m_origin || m_type == CachedResource::MainResource);

    if (m_options.mode != FetchOptions::Mode::SameOrigin && m_origin
        && !(m_resourceRequest.url().protocolIsData() && m_options.sameOriginDataURLFlag == SameOriginDataURLFlag::Set)
        && !m_origin->canRequest(m_resourceRequest.url()))
        setCrossOrigin();
}

CachedResource::CachedResource(const URL& url, Type type, SessionID sessionID)
    : m_resourceRequest(url)
    , m_decodedDataDeletionTimer(*this, &CachedResource::destroyDecodedData, deadDecodedDataDeletionIntervalForResourceType(type))
    , m_sessionID(sessionID)
    , m_responseTimestamp(std::chrono::system_clock::now())
    , m_type(type)
    , m_status(Cached)
{
    ASSERT(sessionID.isValid());
    finishRequestInitialization();
}

void CachedResource::finishRequestInitialization()
{
#ifndef NDEBUG
    cachedResourceLeakCounter.increment();
#endif

    if (!m_resourceRequest.url().hasFragmentIdentifier())
        return;
    URL urlForCache = MemoryCache::removeFragmentIdentifierIfNeeded(m_resourceRequest.url());
    if (urlForCache.hasFragmentIdentifier())
        return;
    m_fragmentIdentifierForRequest = m_resourceRequest.url().fragmentIdentifier();
    m_resourceRequest.setURL(urlForCache);
}

CachedResource::~CachedResource()
{
    ASSERT(!m_resourceToRevalidate); // Should be true because canDelete() checks this.
    ASSERT(canDelete());
    ASSERT(!inCache());
    ASSERT(!m_deleted);
    ASSERT(url().isNull() || !allowsCaching() || MemoryCache::singleton().resourceForRequest(resourceRequest(), sessionID()) != this);

#ifndef NDEBUG
    m_deleted = true;
    cachedResourceLeakCounter.decrement();
#endif

    if (m_owningCachedResourceLoader)
        m_owningCachedResourceLoader->removeCachedResource(*this);
}

void CachedResource::failBeforeStarting()
{
    // FIXME: What if resources in other frames were waiting for this revalidation?
    LOG(ResourceLoading, "Cannot start loading '%s'", url().string().latin1().data());
    if (allowsCaching() && m_resourceToRevalidate)
        MemoryCache::singleton().revalidationFailed(*this);
    error(CachedResource::LoadError);
}

static void addAdditionalRequestHeadersToRequest(ResourceRequest& request, const CachedResourceLoader& cachedResourceLoader, CachedResource& resource)
{
    if (resource.type() == CachedResource::MainResource)
        return;
    // In some cases we may try to load resources in frameless documents. Such loads always fail.
    // FIXME: We shouldn't get this far.
    if (!cachedResourceLoader.frame())
        return;

    // Note: We skip the Content-Security-Policy check here because we check
    // the Content-Security-Policy at the CachedResourceLoader layer so we can
    // handle different resource types differently.
    FrameLoader& frameLoader = cachedResourceLoader.frame()->loader();
    String outgoingReferrer;
    String outgoingOrigin;
    if (request.httpReferrer().isNull()) {
        outgoingReferrer = frameLoader.outgoingReferrer();
        outgoingOrigin = frameLoader.outgoingOrigin();
    } else {
        outgoingReferrer = request.httpReferrer();
        outgoingOrigin = SecurityOrigin::createFromString(outgoingReferrer)->toString();
    }

    // FIXME: Refactor SecurityPolicy::generateReferrerHeader to align with new terminology used in https://w3c.github.io/webappsec-referrer-policy.
    switch (resource.options().referrerPolicy) {
    case FetchOptions::ReferrerPolicy::EmptyString: {
        ReferrerPolicy referrerPolicy = cachedResourceLoader.document() ? cachedResourceLoader.document()->referrerPolicy() : ReferrerPolicy::Default;
        outgoingReferrer = SecurityPolicy::generateReferrerHeader(referrerPolicy, request.url(), outgoingReferrer);
        break; }
    case FetchOptions::ReferrerPolicy::NoReferrerWhenDowngrade:
        outgoingReferrer = SecurityPolicy::generateReferrerHeader(ReferrerPolicy::Default, request.url(), outgoingReferrer);
        break;
    case FetchOptions::ReferrerPolicy::NoReferrer:
        outgoingReferrer = String();
        break;
    case FetchOptions::ReferrerPolicy::Origin:
        outgoingReferrer = SecurityPolicy::generateReferrerHeader(ReferrerPolicy::Origin, request.url(), outgoingReferrer);
        break;
    case FetchOptions::ReferrerPolicy::OriginWhenCrossOrigin:
        if (resource.isCrossOrigin())
            outgoingReferrer = SecurityPolicy::generateReferrerHeader(ReferrerPolicy::Origin, request.url(), outgoingReferrer);
        break;
    case FetchOptions::ReferrerPolicy::UnsafeUrl:
        break;
    };

    if (outgoingReferrer.isEmpty())
        request.clearHTTPReferrer();
    else
        request.setHTTPReferrer(outgoingReferrer);
    FrameLoader::addHTTPOriginIfNeeded(request, outgoingOrigin);

    frameLoader.addExtraFieldsToSubresourceRequest(request);
}

void CachedResource::addAdditionalRequestHeaders(CachedResourceLoader& loader)
{
    addAdditionalRequestHeadersToRequest(m_resourceRequest, loader, *this);
}

void CachedResource::load(CachedResourceLoader& cachedResourceLoader)
{
    if (!cachedResourceLoader.frame()) {
        RELEASE_LOG_IF_ALLOWED("load: No associated frame");
        failBeforeStarting();
        return;
    }
    Frame& frame = *cachedResourceLoader.frame();

    // Prevent new loads if we are in the PageCache or being added to the PageCache.
    // We query the top document because new frames may be created in pagehide event handlers
    // and their pageCacheState will not reflect the fact that they are about to enter page
    // cache.
    if (auto* topDocument = frame.mainFrame().document()) {
        if (topDocument->pageCacheState() != Document::NotInPageCache) {
            RELEASE_LOG_IF_ALLOWED("load: Already in page cache or being added to it (frame = %p)", &frame);
            failBeforeStarting();
            return;
        }
    }

    FrameLoader& frameLoader = frame.loader();
    if (m_options.securityCheck == DoSecurityCheck && (frameLoader.state() == FrameStateProvisional || !frameLoader.activeDocumentLoader() || frameLoader.activeDocumentLoader()->isStopping())) {
        if (frameLoader.state() == FrameStateProvisional)
            RELEASE_LOG_IF_ALLOWED("load: Failed security check -- state is provisional (frame = %p)", &frame);
        else if (!frameLoader.activeDocumentLoader())
            RELEASE_LOG_IF_ALLOWED("load: Failed security check -- not active document (frame = %p)", &frame);
        else if (frameLoader.activeDocumentLoader()->isStopping())
            RELEASE_LOG_IF_ALLOWED("load: Failed security check -- active loader is stopping (frame = %p)", &frame);
        failBeforeStarting();
        return;
    }

    m_loading = true;

#if USE(QUICK_LOOK)
    if (!m_resourceRequest.isNull() && m_resourceRequest.url().protocolIs(QLPreviewProtocol())) {
        // When QuickLook is invoked to convert a document, it returns a unique URL in the
        // NSURLReponse for the main document. To make safeQLURLForDocumentURLAndResourceURL()
        // work, we need to use the QL URL not the original URL.
        const URL& documentURL = frameLoader.documentLoader()->response().url();
        m_resourceRequest.setURL(safeQLURLForDocumentURLAndResourceURL(documentURL, url()));
    }
#endif

    if (isCacheValidator()) {
        CachedResource* resourceToRevalidate = m_resourceToRevalidate;
        ASSERT(resourceToRevalidate->canUseCacheValidator());
        ASSERT(resourceToRevalidate->isLoaded());
        const String& lastModified = resourceToRevalidate->response().httpHeaderField(HTTPHeaderName::LastModified);
        const String& eTag = resourceToRevalidate->response().httpHeaderField(HTTPHeaderName::ETag);
        if (!lastModified.isEmpty() || !eTag.isEmpty()) {
            ASSERT(cachedResourceLoader.cachePolicy(type()) != CachePolicyReload);
            if (cachedResourceLoader.cachePolicy(type()) == CachePolicyRevalidate)
                m_resourceRequest.setHTTPHeaderField(HTTPHeaderName::CacheControl, "max-age=0");
            if (!lastModified.isEmpty())
                m_resourceRequest.setHTTPHeaderField(HTTPHeaderName::IfModifiedSince, lastModified);
            if (!eTag.isEmpty())
                m_resourceRequest.setHTTPHeaderField(HTTPHeaderName::IfNoneMatch, eTag);
        }
    }

#if ENABLE(LINK_PREFETCH)
    if (type() == CachedResource::LinkPrefetch || type() == CachedResource::LinkSubresource)
        m_resourceRequest.setHTTPHeaderField(HTTPHeaderName::Purpose, "prefetch");
#endif
    m_resourceRequest.setPriority(loadPriority());

    addAdditionalRequestHeaders(cachedResourceLoader);

    // FIXME: It's unfortunate that the cache layer and below get to know anything about fragment identifiers.
    // We should look into removing the expectation of that knowledge from the platform network stacks.
    ResourceRequest request(m_resourceRequest);
    if (!m_fragmentIdentifierForRequest.isNull()) {
        URL url = request.url();
        url.setFragmentIdentifier(m_fragmentIdentifierForRequest);
        request.setURL(url);
        m_fragmentIdentifierForRequest = String();
    }

    m_loader = platformStrategies()->loaderStrategy()->loadResource(frame, *this, request, m_options);
    if (!m_loader) {
        RELEASE_LOG_IF_ALLOWED("load: Unable to create SubresourceLoader (frame = %p)", &frame);
        failBeforeStarting();
        return;
    }

    m_status = Pending;
}

void CachedResource::loadFrom(const CachedResource& resource)
{
    ASSERT(url() == resource.url());
    ASSERT(type() == resource.type());
    ASSERT(resource.status() == Status::Cached);

    if (isCrossOrigin() && m_options.mode == FetchOptions::Mode::Cors) {
        ASSERT(m_origin);
        String errorMessage;
        if (!WebCore::passesAccessControlCheck(resource.response(), m_options.allowCredentials, *m_origin, errorMessage)) {
            setResourceError(ResourceError(String(), 0, url(), errorMessage, ResourceError::Type::AccessControl));
            return;
        }
    }

    setBodyDataFrom(resource);
    setStatus(Status::Cached);
    setLoading(false);
}

void CachedResource::setBodyDataFrom(const CachedResource& resource)
{
    m_data = resource.m_data;
}

void CachedResource::checkNotify()
{
    if (isLoading() || stillNeedsLoad())
        return;

    CachedResourceClientWalker<CachedResourceClient> walker(m_clients);
    while (CachedResourceClient* client = walker.next())
        client->notifyFinished(this);
}

void CachedResource::addDataBuffer(SharedBuffer&)
{
    ASSERT(dataBufferingPolicy() == BufferData);
}

void CachedResource::addData(const char*, unsigned)
{
    ASSERT(dataBufferingPolicy() == DoNotBufferData);
}

void CachedResource::finishLoading(SharedBuffer*)
{
    setLoading(false);
    checkNotify();
}

void CachedResource::error(CachedResource::Status status)
{
    setStatus(status);
    ASSERT(errorOccurred());
    m_data = nullptr;

    setLoading(false);
    checkNotify();
}
    
void CachedResource::cancelLoad()
{
    if (!isLoading() && !stillNeedsLoad())
        return;

    setStatus(LoadError);
    setLoading(false);
    checkNotify();
}

void CachedResource::finish()
{
    if (!errorOccurred())
        m_status = Cached;
}

bool CachedResource::passesAccessControlCheck(SecurityOrigin& securityOrigin)
{
    String errorDescription;
    return WebCore::passesAccessControlCheck(response(), resourceRequest().allowCookies() ? AllowStoredCredentials : DoNotAllowStoredCredentials, securityOrigin, errorDescription);
}

bool CachedResource::passesSameOriginPolicyCheck(SecurityOrigin& securityOrigin)
{
    if (securityOrigin.canRequest(responseForSameOriginPolicyChecks().url()))
        return true;
    return passesAccessControlCheck(securityOrigin);
}

void CachedResource::setCrossOrigin()
{
    ASSERT(m_options.mode != FetchOptions::Mode::SameOrigin);
    m_responseTainting = (m_options.mode == FetchOptions::Mode::Cors) ? ResourceResponse::Tainting::Cors : ResourceResponse::Tainting::Opaque;
}

bool CachedResource::isCrossOrigin() const
{
    return m_responseTainting != ResourceResponse::Tainting::Basic;
}

bool CachedResource::isClean() const
{
    // https://html.spec.whatwg.org/multipage/infrastructure.html#cors-same-origin
    return !loadFailedOrCanceled() && m_responseTainting != ResourceResponse::Tainting::Opaque;
}

bool CachedResource::isExpired() const
{
    if (m_response.isNull())
        return false;

    return computeCurrentAge(m_response, m_responseTimestamp) > freshnessLifetime(m_response);
}

static inline bool shouldCacheSchemeIndefinitely(const String& scheme)
{
#if PLATFORM(COCOA)
    if (equalLettersIgnoringASCIICase(scheme, "applewebdata"))
        return true;
#endif
#if USE(SOUP)
    if (equalLettersIgnoringASCIICase(scheme, "resource"))
        return true;
#endif
    return equalLettersIgnoringASCIICase(scheme, "data");
}

std::chrono::microseconds CachedResource::freshnessLifetime(const ResourceResponse& response) const
{
    if (!response.url().protocolIsInHTTPFamily()) {
        String protocol = response.url().protocol();
        if (!shouldCacheSchemeIndefinitely(protocol)) {
            // Don't cache non-HTTP main resources since we can't check for freshness.
            // FIXME: We should not cache subresources either, but when we tried this
            // it caused performance and flakiness issues in our test infrastructure.
            if (m_type == MainResource || SchemeRegistry::shouldAlwaysRevalidateURLScheme(protocol))
                return 0us;
        }

        return std::chrono::microseconds::max();
    }

    return computeFreshnessLifetimeForHTTPFamily(response, m_responseTimestamp);
}

void CachedResource::redirectReceived(ResourceRequest& request, const ResourceResponse& response)
{
    m_requestedFromNetworkingLayer = true;
    if (response.isNull())
        return;

    // Redirect to data: URL uses the last HTTP response for SOP.
    if (response.isHTTP() && request.url().protocolIsData())
        m_redirectResponseForSameOriginPolicyChecks = response;

    updateRedirectChainStatus(m_redirectChainCacheStatus, response);
}

const ResourceResponse& CachedResource::responseForSameOriginPolicyChecks() const
{
    return m_redirectResponseForSameOriginPolicyChecks.isNull() ? m_response : m_redirectResponseForSameOriginPolicyChecks;
}

void CachedResource::setResponse(const ResourceResponse& response)
{
    ASSERT(m_response.type() == ResourceResponse::Type::Default);
    m_response = response;
    m_response.setRedirected(m_redirectChainCacheStatus.status != RedirectChainCacheStatus::NoRedirection);

    m_varyingHeaderValues = collectVaryingRequestHeaders(m_resourceRequest, m_response, m_sessionID);
}

void CachedResource::responseReceived(const ResourceResponse& response)
{
    setResponse(response);
    m_responseTimestamp = std::chrono::system_clock::now();
    String encoding = response.textEncodingName();
    if (!encoding.isNull())
        setEncoding(encoding);
}

void CachedResource::clearLoader()
{
    ASSERT(m_loader);
    m_identifierForLoadWithoutResourceLoader = m_loader->identifier();
    m_loader = nullptr;
    deleteIfPossible();
}

void CachedResource::addClient(CachedResourceClient* client)
{
    if (addClientToSet(client))
        didAddClient(client);
}

void CachedResource::didAddClient(CachedResourceClient* client)
{
    if (m_decodedDataDeletionTimer.isActive())
        m_decodedDataDeletionTimer.stop();

    if (m_clientsAwaitingCallback.remove(client))
        m_clients.add(client);
    if (!isLoading() && !stillNeedsLoad())
        client->notifyFinished(this);
}

bool CachedResource::addClientToSet(CachedResourceClient* client)
{
    if (m_preloadResult == PreloadNotReferenced) {
        if (isLoaded())
            m_preloadResult = PreloadReferencedWhileComplete;
        else if (m_requestedFromNetworkingLayer)
            m_preloadResult = PreloadReferencedWhileLoading;
        else
            m_preloadResult = PreloadReferenced;
    }
    if (allowsCaching() && !hasClients() && inCache())
        MemoryCache::singleton().addToLiveResourcesSize(*this);

    if ((m_type == RawResource || m_type == MainResource) && !m_response.isNull() && !m_proxyResource) {
        // Certain resources (especially XHRs and main resources) do crazy things if an asynchronous load returns
        // synchronously (e.g., scripts may not have set all the state they need to handle the load).
        // Therefore, rather than immediately sending callbacks on a cache hit like other CachedResources,
        // we schedule the callbacks and ensure we never finish synchronously.
        ASSERT(!m_clientsAwaitingCallback.contains(client));
        m_clientsAwaitingCallback.add(client, std::make_unique<Callback>(*this, *client));
        return false;
    }

    m_clients.add(client);
    return true;
}

void CachedResource::removeClient(CachedResourceClient* client)
{
    auto callback = m_clientsAwaitingCallback.take(client);
    if (callback) {
        ASSERT(!m_clients.contains(client));
        callback->cancel();
        callback = nullptr;
    } else {
        ASSERT(m_clients.contains(client));
        m_clients.remove(client);
        didRemoveClient(client);
    }

    if (deleteIfPossible()) {
        // `this` object is dead here.
        return;
    }

    if (hasClients())
        return;

    auto& memoryCache = MemoryCache::singleton();
    if (allowsCaching() && inCache()) {
        memoryCache.removeFromLiveResourcesSize(*this);
        memoryCache.removeFromLiveDecodedResourcesList(*this);
    }
    if (!m_switchingClientsToRevalidatedResource)
        allClientsRemoved();
    destroyDecodedDataIfNeeded();

    if (!allowsCaching())
        return;

    if (response().cacheControlContainsNoStore() && url().protocolIs("https")) {
        // RFC2616 14.9.2:
        // "no-store: ... MUST make a best-effort attempt to remove the information from volatile storage as promptly as possible"
        // "... History buffers MAY store such responses as part of their normal operation."
        // We allow non-secure content to be reused in history, but we do not allow secure content to be reused.
        memoryCache.remove(*this);
    }
    memoryCache.pruneSoon();
}

void CachedResource::destroyDecodedDataIfNeeded()
{
    if (!m_decodedSize)
        return;
    if (!MemoryCache::singleton().deadDecodedDataDeletionInterval().count())
        return;
    m_decodedDataDeletionTimer.restart();
}

void CachedResource::decodedDataDeletionTimerFired()
{
    destroyDecodedData();
}

bool CachedResource::deleteIfPossible()
{
    if (canDelete()) {
        if (!inCache()) {
            InspectorInstrumentation::willDestroyCachedResource(*this);
            delete this;
            return true;
        }
        if (m_data)
            m_data->hintMemoryNotNeededSoon();
    }
    return false;
}

void CachedResource::setDecodedSize(unsigned size)
{
    if (size == m_decodedSize)
        return;

    int delta = size - m_decodedSize;

    // The object must be moved to a different queue, since its size has been changed.
    // Remove before updating m_decodedSize, so we find the resource in the correct LRU list.
    if (allowsCaching() && inCache())
        MemoryCache::singleton().removeFromLRUList(*this);
    
    m_decodedSize = size;
   
    if (allowsCaching() && inCache()) {
        auto& memoryCache = MemoryCache::singleton();
        // Now insert into the new LRU list.
        memoryCache.insertInLRUList(*this);
        
        // Insert into or remove from the live decoded list if necessary.
        // When inserting into the LiveDecodedResourcesList it is possible
        // that the m_lastDecodedAccessTime is still zero or smaller than
        // the m_lastDecodedAccessTime of the current list head. This is a
        // violation of the invariant that the list is to be kept sorted
        // by access time. The weakening of the invariant does not pose
        // a problem. For more details please see: https://bugs.webkit.org/show_bug.cgi?id=30209
        bool inLiveDecodedResourcesList = memoryCache.inLiveDecodedResourcesList(*this);
        if (m_decodedSize && !inLiveDecodedResourcesList && hasClients())
            memoryCache.insertInLiveDecodedResourcesList(*this);
        else if (!m_decodedSize && inLiveDecodedResourcesList)
            memoryCache.removeFromLiveDecodedResourcesList(*this);

        // Update the cache's size totals.
        memoryCache.adjustSize(hasClients(), delta);
    }
}

void CachedResource::setEncodedSize(unsigned size)
{
    if (size == m_encodedSize)
        return;

    int delta = size - m_encodedSize;

    // The object must be moved to a different queue, since its size has been changed.
    // Remove before updating m_encodedSize, so we find the resource in the correct LRU list.
    if (allowsCaching() && inCache())
        MemoryCache::singleton().removeFromLRUList(*this);

    m_encodedSize = size;

    if (allowsCaching() && inCache()) {
        auto& memoryCache = MemoryCache::singleton();
        memoryCache.insertInLRUList(*this);
        memoryCache.adjustSize(hasClients(), delta);
    }
}

void CachedResource::didAccessDecodedData(double timeStamp)
{
    m_lastDecodedAccessTime = timeStamp;
    
    if (allowsCaching() && inCache()) {
        auto& memoryCache = MemoryCache::singleton();
        if (memoryCache.inLiveDecodedResourcesList(*this)) {
            memoryCache.removeFromLiveDecodedResourcesList(*this);
            memoryCache.insertInLiveDecodedResourcesList(*this);
        }
        memoryCache.pruneSoon();
    }
}
    
void CachedResource::setResourceToRevalidate(CachedResource* resource) 
{ 
    ASSERT(resource);
    ASSERT(!m_resourceToRevalidate);
    ASSERT(resource != this);
    ASSERT(m_handlesToRevalidate.isEmpty());
    ASSERT(resource->type() == type());
    ASSERT(!resource->m_proxyResource);

    LOG(ResourceLoading, "CachedResource %p setResourceToRevalidate %p", this, resource);

    resource->m_proxyResource = this;
    m_resourceToRevalidate = resource;
}

void CachedResource::clearResourceToRevalidate() 
{
    ASSERT(m_resourceToRevalidate);
    ASSERT(m_resourceToRevalidate->m_proxyResource == this);

    if (m_switchingClientsToRevalidatedResource)
        return;

    m_resourceToRevalidate->m_proxyResource = nullptr;
    m_resourceToRevalidate->deleteIfPossible();

    m_handlesToRevalidate.clear();
    m_resourceToRevalidate = nullptr;
    deleteIfPossible();
}
    
void CachedResource::switchClientsToRevalidatedResource()
{
    ASSERT(m_resourceToRevalidate);
    ASSERT(m_resourceToRevalidate->inCache());
    ASSERT(!inCache());

    LOG(ResourceLoading, "CachedResource %p switchClientsToRevalidatedResource %p", this, m_resourceToRevalidate);

    m_switchingClientsToRevalidatedResource = true;
    for (auto& handle : m_handlesToRevalidate) {
        handle->m_resource = m_resourceToRevalidate;
        m_resourceToRevalidate->registerHandle(handle);
        --m_handleCount;
    }
    ASSERT(!m_handleCount);
    m_handlesToRevalidate.clear();

    Vector<CachedResourceClient*> clientsToMove;
    for (auto& entry : m_clients) {
        CachedResourceClient* client = entry.key;
        unsigned count = entry.value;
        while (count) {
            clientsToMove.append(client);
            --count;
        }
    }

    for (auto& client : clientsToMove)
        removeClient(client);
    ASSERT(m_clients.isEmpty());

    for (auto& client : clientsToMove)
        m_resourceToRevalidate->addClientToSet(client);
    for (auto& client : clientsToMove) {
        // Calling didAddClient may do anything, including trying to cancel revalidation.
        // Assert that it didn't succeed.
        ASSERT(m_resourceToRevalidate);
        // Calling didAddClient for a client may end up removing another client. In that case it won't be in the set anymore.
        if (m_resourceToRevalidate->m_clients.contains(client))
            m_resourceToRevalidate->didAddClient(client);
    }
    m_switchingClientsToRevalidatedResource = false;
}

void CachedResource::updateResponseAfterRevalidation(const ResourceResponse& validatingResponse)
{
    m_responseTimestamp = std::chrono::system_clock::now();

    updateResponseHeadersAfterRevalidation(m_response, validatingResponse);
}

void CachedResource::registerHandle(CachedResourceHandleBase* h)
{
    ++m_handleCount;
    if (m_resourceToRevalidate)
        m_handlesToRevalidate.add(h);
}

void CachedResource::unregisterHandle(CachedResourceHandleBase* h)
{
    ASSERT(m_handleCount > 0);
    --m_handleCount;

    if (m_resourceToRevalidate)
         m_handlesToRevalidate.remove(h);

    if (!m_handleCount)
        deleteIfPossible();
}

bool CachedResource::canUseCacheValidator() const
{
    if (m_loading || errorOccurred())
        return false;

    if (m_response.cacheControlContainsNoStore())
        return false;
    return m_response.hasCacheValidatorFields();
}

CachedResource::RevalidationDecision CachedResource::makeRevalidationDecision(CachePolicy cachePolicy) const
{    
    switch (cachePolicy) {
    case CachePolicyHistoryBuffer:
        return RevalidationDecision::No;

    case CachePolicyReload:
    case CachePolicyRevalidate:
        return RevalidationDecision::YesDueToCachePolicy;

    case CachePolicyVerify:
        if (m_response.cacheControlContainsNoCache())
            return RevalidationDecision::YesDueToNoCache;
        // FIXME: Cache-Control:no-store should prevent storing, not reuse.
        if (m_response.cacheControlContainsNoStore())
            return RevalidationDecision::YesDueToNoStore;

        if (isExpired())
            return RevalidationDecision::YesDueToExpired;

        return RevalidationDecision::No;
    };
    ASSERT_NOT_REACHED();
    return RevalidationDecision::No;
}

bool CachedResource::redirectChainAllowsReuse(ReuseExpiredRedirectionOrNot reuseExpiredRedirection) const
{
    return WebCore::redirectChainAllowsReuse(m_redirectChainCacheStatus, reuseExpiredRedirection);
}

bool CachedResource::varyHeaderValuesMatch(const ResourceRequest& request, const CachedResourceLoader& cachedResourceLoader)
{
    if (m_varyingHeaderValues.isEmpty())
        return true;

    ResourceRequest requestWithFullHeaders(request);
    addAdditionalRequestHeadersToRequest(requestWithFullHeaders, cachedResourceLoader, *this);

    return verifyVaryingRequestHeaders(m_varyingHeaderValues, requestWithFullHeaders, m_sessionID);
}

unsigned CachedResource::overheadSize() const
{
    static const int kAverageClientsHashMapSize = 384;
    return sizeof(CachedResource) + m_response.memoryUsage() + kAverageClientsHashMapSize + m_resourceRequest.url().string().length() * 2;
}

bool CachedResource::areAllClientsXMLHttpRequests() const
{
    if (type() != RawResource)
        return false;

    for (auto& client : m_clients) {
        if (!client.key->isXMLHttpRequest())
            return false;
    }
    return true;
}

void CachedResource::setLoadPriority(const Optional<ResourceLoadPriority>& loadPriority)
{
    if (loadPriority)
        m_loadPriority = loadPriority.value();
    else
        m_loadPriority = defaultPriorityForResourceType(type());
}

inline CachedResource::Callback::Callback(CachedResource& resource, CachedResourceClient& client)
    : m_resource(resource)
    , m_client(client)
    , m_timer(*this, &Callback::timerFired)
{
    m_timer.startOneShot(0);
}

inline void CachedResource::Callback::cancel()
{
    if (m_timer.isActive())
        m_timer.stop();
}

void CachedResource::Callback::timerFired()
{
    m_resource.didAddClient(&m_client);
}

#if USE(FOUNDATION) || USE(SOUP)

void CachedResource::tryReplaceEncodedData(SharedBuffer& newBuffer)
{
    if (!m_data)
        return;
    
    if (!mayTryReplaceEncodedData())
        return;

    // We have to do the memcmp because we can't tell if the replacement file backed data is for the
    // same resource or if we made a second request with the same URL which gave us a different
    // resource. We have seen this happen for cached POST resources.
    if (m_data->size() != newBuffer.size() || memcmp(m_data->data(), newBuffer.data(), m_data->size()))
        return;

    if (m_data->tryReplaceContentsWithPlatformBuffer(newBuffer))
        didReplaceSharedBufferContents();
}

#endif

}