xref: /external/chromium_org/third_party/WebKit/Source/core/fetch/Resource.cpp

/*
    Copyright (C) 1998 Lars Knoll (knoll (at) mpi-hd.mpg.de)
    Copyright (C) 2001 Dirk Mueller (mueller (at) kde.org)
    Copyright (C) 2002 Waldo Bastian (bastian (at) kde.org)
    Copyright (C) 2006 Samuel Weinig (sam.weinig (at) gmail.com)
    Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 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 "core/fetch/Resource.h"

#include "core/fetch/CachedMetadata.h"
#include "core/fetch/CrossOriginAccessControl.h"
#include "core/fetch/MemoryCache.h"
#include "core/fetch/ResourceClient.h"
#include "core/fetch/ResourceClientWalker.h"
#include "core/fetch/ResourceFetcher.h"
#include "core/fetch/ResourceLoader.h"
#include "core/fetch/ResourcePtr.h"
#include "core/inspector/InspectorInstrumentation.h"
#include "platform/Logging.h"
#include "platform/PurgeableBuffer.h"
#include "platform/SharedBuffer.h"
#include "platform/weborigin/KURL.h"
#include "public/platform/Platform.h"
#include "wtf/CurrentTime.h"
#include "wtf/MathExtras.h"
#include "wtf/RefCountedLeakCounter.h"
#include "wtf/StdLibExtras.h"
#include "wtf/Vector.h"
#include "wtf/text/CString.h"

using namespace WTF;

namespace WebCore {

// These response headers are not copied from a revalidated response to the
// cached response headers. For compatibility, this list is based on Chromium's
// net/http/http_response_headers.cc.
const char* const headersToIgnoreAfterRevalidation[] = {
    "allow",
    "connection",
    "etag",
    "expires",
    "keep-alive",
    "last-modified"
    "proxy-authenticate",
    "proxy-connection",
    "trailer",
    "transfer-encoding",
    "upgrade",
    "www-authenticate",
    "x-frame-options",
    "x-xss-protection",
};

// Some header prefixes mean "Don't copy this header from a 304 response.".
// Rather than listing all the relevant headers, we can consolidate them into
// this list, also grabbed from Chromium's net/http/http_response_headers.cc.
const char* const headerPrefixesToIgnoreAfterRevalidation[] = {
    "content-",
    "x-content-",
    "x-webkit-"
};

static inline bool shouldUpdateHeaderAfterRevalidation(const AtomicString& header)
{
    for (size_t i = 0; i < WTF_ARRAY_LENGTH(headersToIgnoreAfterRevalidation); i++) {
        if (equalIgnoringCase(header, headersToIgnoreAfterRevalidation[i]))
            return false;
    }
    for (size_t i = 0; i < WTF_ARRAY_LENGTH(headerPrefixesToIgnoreAfterRevalidation); i++) {
        if (header.startsWith(headerPrefixesToIgnoreAfterRevalidation[i], false))
            return false;
    }
    return true;
}

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

Resource::Resource(const ResourceRequest& request, Type type)
    : m_resourceRequest(request)
    , m_responseTimestamp(currentTime())
    , m_cancelTimer(this, &Resource::cancelTimerFired)
    , m_lastDecodedAccessTime(0)
    , m_loadFinishTime(0)
    , m_identifier(0)
    , m_encodedSize(0)
    , m_decodedSize(0)
    , m_accessCount(0)
    , m_handleCount(0)
    , m_preloadCount(0)
    , m_protectorCount(0)
    , m_preloadResult(PreloadNotReferenced)
    , m_cacheLiveResourcePriority(CacheLiveResourcePriorityLow)
    , m_inLiveDecodedResourcesList(false)
    , m_requestedFromNetworkingLayer(false)
    , m_inCache(false)
    , m_loading(false)
    , m_switchingClientsToRevalidatedResource(false)
    , m_type(type)
    , m_status(Pending)
#ifndef NDEBUG
    , m_deleted(false)
    , m_lruIndex(0)
#endif
    , m_nextInAllResourcesList(0)
    , m_prevInAllResourcesList(0)
    , m_nextInLiveResourcesList(0)
    , m_prevInLiveResourcesList(0)
    , m_resourceToRevalidate(0)
    , m_proxyResource(0)
{
    ASSERT(m_type == unsigned(type)); // m_type is a bitfield, so this tests careless updates of the enum.
#ifndef NDEBUG
    cachedResourceLeakCounter.increment();
#endif

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

Resource::~Resource()
{
    ASSERT(!m_resourceToRevalidate); // Should be true because canDelete() checks this.
    ASSERT(canDelete());
    ASSERT(!inCache());
    ASSERT(!m_deleted);
    ASSERT(url().isNull() || memoryCache()->resourceForURL(KURL(ParsedURLString, url())) != this);

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

void Resource::failBeforeStarting()
{
    WTF_LOG(ResourceLoading, "Cannot start loading '%s'", url().string().latin1().data());
    error(Resource::LoadError);
}

void Resource::load(ResourceFetcher* fetcher, const ResourceLoaderOptions& options)
{
    if (!fetcher->frame()) {
        failBeforeStarting();
        return;
    }

    m_options = options;
    m_loading = true;

    if (!accept().isEmpty())
        m_resourceRequest.setHTTPAccept(accept());

    // 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()) {
        KURL url = request.url();
        url.setFragmentIdentifier(m_fragmentIdentifierForRequest);
        request.setURL(url);
        m_fragmentIdentifierForRequest = String();
    }
    m_status = Pending;
    if (m_loader) {
        RELEASE_ASSERT(m_options.synchronousPolicy == RequestSynchronously);
        m_loader->changeToSynchronous();
        return;
    }
    m_loader = ResourceLoader::create(fetcher, this, request, options);
    m_loader->start();
}

void Resource::checkNotify()
{
    if (isLoading())
        return;

    ResourceClientWalker<ResourceClient> w(m_clients);
    while (ResourceClient* c = w.next())
        c->notifyFinished(this);
}

void Resource::appendData(const char* data, int length)
{
    TRACE_EVENT0("webkit", "Resource::appendData");
    ASSERT(!m_resourceToRevalidate);
    ASSERT(!errorOccurred());
    if (m_options.dataBufferingPolicy == DoNotBufferData)
        return;
    if (m_data)
        m_data->append(data, length);
    else
        m_data = SharedBuffer::create(data, length);
    setEncodedSize(m_data->size());
}

void Resource::setResourceBuffer(PassRefPtr<SharedBuffer> resourceBuffer)
{
    ASSERT(!m_resourceToRevalidate);
    ASSERT(!errorOccurred());
    ASSERT(m_options.dataBufferingPolicy == BufferData);
    m_data = resourceBuffer;
    setEncodedSize(m_data->size());
}

void Resource::error(Resource::Status status)
{
    if (m_resourceToRevalidate)
        revalidationFailed();

    if (!m_error.isNull() && (m_error.isCancellation() || !isPreloaded()))
        memoryCache()->remove(this);

    setStatus(status);
    ASSERT(errorOccurred());
    m_data.clear();

    setLoading(false);
    checkNotify();
}

void Resource::finishOnePart()
{
    setLoading(false);
    checkNotify();
}

void Resource::finish(double finishTime)
{
    ASSERT(!m_resourceToRevalidate);
    ASSERT(!errorOccurred());
    m_loadFinishTime = finishTime;
    finishOnePart();
    if (!errorOccurred())
        m_status = Cached;
}

bool Resource::passesAccessControlCheck(SecurityOrigin* securityOrigin)
{
    String ignoredErrorDescription;
    return passesAccessControlCheck(securityOrigin, ignoredErrorDescription);
}

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

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

    return currentAge() > freshnessLifetime();
}

double Resource::currentAge() const
{
    // RFC2616 13.2.3
    // No compensation for latency as that is not terribly important in practice
    double dateValue = m_response.date();
    double apparentAge = std::isfinite(dateValue) ? std::max(0., m_responseTimestamp - dateValue) : 0;
    double ageValue = m_response.age();
    double correctedReceivedAge = std::isfinite(ageValue) ? std::max(apparentAge, ageValue) : apparentAge;
    double residentTime = currentTime() - m_responseTimestamp;
    return correctedReceivedAge + residentTime;
}

double Resource::freshnessLifetime() const
{
#if !OS(ANDROID)
    // On desktop, local files should be reloaded in case they change.
    if (m_response.url().isLocalFile())
        return 0;
#endif

    // Cache other non-http resources liberally.
    if (!m_response.url().protocolIsInHTTPFamily())
        return std::numeric_limits<double>::max();

    // RFC2616 13.2.4
    double maxAgeValue = m_response.cacheControlMaxAge();
    if (std::isfinite(maxAgeValue))
        return maxAgeValue;
    double expiresValue = m_response.expires();
    double dateValue = m_response.date();
    double creationTime = std::isfinite(dateValue) ? dateValue : m_responseTimestamp;
    if (std::isfinite(expiresValue))
        return expiresValue - creationTime;
    double lastModifiedValue = m_response.lastModified();
    if (std::isfinite(lastModifiedValue))
        return (creationTime - lastModifiedValue) * 0.1;
    // If no cache headers are present, the specification leaves the decision to the UA. Other browsers seem to opt for 0.
    return 0;
}

void Resource::responseReceived(const ResourceResponse& response)
{
    setResponse(response);
    m_responseTimestamp = currentTime();
    String encoding = response.textEncodingName();
    if (!encoding.isNull())
        setEncoding(encoding);

    if (!m_resourceToRevalidate)
        return;
    if (response.httpStatusCode() == 304)
        revalidationSucceeded(response);
    else
        revalidationFailed();
}

void Resource::setSerializedCachedMetadata(const char* data, size_t size)
{
    // We only expect to receive cached metadata from the platform once.
    // If this triggers, it indicates an efficiency problem which is most
    // likely unexpected in code designed to improve performance.
    ASSERT(!m_cachedMetadata);
    ASSERT(!m_resourceToRevalidate);

    m_cachedMetadata = CachedMetadata::deserialize(data, size);
}

void Resource::setCachedMetadata(unsigned dataTypeID, const char* data, size_t size)
{
    // Currently, only one type of cached metadata per resource is supported.
    // If the need arises for multiple types of metadata per resource this could
    // be enhanced to store types of metadata in a map.
    ASSERT(!m_cachedMetadata);

    m_cachedMetadata = CachedMetadata::create(dataTypeID, data, size);
    const Vector<char>& serializedData = m_cachedMetadata->serialize();
    blink::Platform::current()->cacheMetadata(m_response.url(), m_response.responseTime(), serializedData.data(), serializedData.size());
}

CachedMetadata* Resource::cachedMetadata(unsigned dataTypeID) const
{
    if (!m_cachedMetadata || m_cachedMetadata->dataTypeID() != dataTypeID)
        return 0;
    return m_cachedMetadata.get();
}

void Resource::setCacheLiveResourcePriority(CacheLiveResourcePriority priority)
{
    if (inCache() && m_inLiveDecodedResourcesList && cacheLiveResourcePriority() != static_cast<unsigned>(priority)) {
        memoryCache()->removeFromLiveDecodedResourcesList(this);
        m_cacheLiveResourcePriority = priority;
        memoryCache()->insertInLiveDecodedResourcesList(this);
        memoryCache()->prune();
    }
}

void Resource::clearLoader()
{
    m_loader = 0;
}

void Resource::addClient(ResourceClient* client)
{
    if (addClientToSet(client))
        didAddClient(client);
}

void Resource::didAddClient(ResourceClient* c)
{
    if (!isLoading() && !stillNeedsLoad())
        c->notifyFinished(this);
}

static bool shouldSendCachedDataSynchronouslyForType(Resource::Type type)
{
    // Some resources types default to return data synchronously.
    // For most of these, it's because there are layout tests that
    // expect data to return synchronously in case of cache hit. In
    // the case of fonts, there was a performance regression.
    // FIXME: Get to the point where we don't need to special-case sync/async
    // behavior for different resource types.
    if (type == Resource::Image)
        return true;
    if (type == Resource::CSSStyleSheet)
        return true;
    if (type == Resource::Script)
        return true;
    if (type == Resource::Font)
        return true;
    return false;
}

bool Resource::addClientToSet(ResourceClient* client)
{
    ASSERT(!isPurgeable());

    if (m_preloadResult == PreloadNotReferenced) {
        if (isLoaded())
            m_preloadResult = PreloadReferencedWhileComplete;
        else if (m_requestedFromNetworkingLayer)
            m_preloadResult = PreloadReferencedWhileLoading;
        else
            m_preloadResult = PreloadReferenced;
    }
    if (!hasClients() && inCache())
        memoryCache()->addToLiveResourcesSize(this);

    // If we have existing data to send to the new client and the resource type supprts it, send it asynchronously.
    if (!m_response.isNull() && !m_proxyResource && !shouldSendCachedDataSynchronouslyForType(type())) {
        m_clientsAwaitingCallback.add(client);
        ResourceCallback::callbackHandler()->schedule(this);
        return false;
    }

    m_clients.add(client);
    return true;
}

void Resource::removeClient(ResourceClient* client)
{
    if (m_clientsAwaitingCallback.contains(client)) {
        ASSERT(!m_clients.contains(client));
        m_clientsAwaitingCallback.remove(client);
        if (m_clientsAwaitingCallback.isEmpty())
            ResourceCallback::callbackHandler()->cancel(this);
    } else {
        ASSERT(m_clients.contains(client));
        m_clients.remove(client);
        didRemoveClient(client);
    }

    bool deleted = deleteIfPossible();
    if (!deleted && !hasClients()) {
        if (inCache()) {
            memoryCache()->removeFromLiveResourcesSize(this);
            memoryCache()->removeFromLiveDecodedResourcesList(this);
        }
        if (!m_switchingClientsToRevalidatedResource)
            allClientsRemoved();
        if (response().cacheControlContainsNoStore()) {
            // 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.
            if (url().protocolIs("https"))
                memoryCache()->remove(this);
        } else {
            memoryCache()->prune(this);
        }
    }
    // This object may be dead here.
}

void Resource::allClientsRemoved()
{
    if (!m_loader)
        return;
    if (m_type == MainResource || m_type == Raw)
        cancelTimerFired(&m_cancelTimer);
    else if (!m_cancelTimer.isActive())
        m_cancelTimer.startOneShot(0);
}

void Resource::cancelTimerFired(Timer<Resource>* timer)
{
    ASSERT_UNUSED(timer, timer == &m_cancelTimer);
    if (hasClients() || !m_loader)
        return;
    ResourcePtr<Resource> protect(this);
    m_loader->cancelIfNotFinishing();
    if (m_status != Cached)
        memoryCache()->remove(this);
}

bool Resource::deleteIfPossible()
{
    if (canDelete() && !inCache()) {
        InspectorInstrumentation::willDestroyResource(this);
        delete this;
        return true;
    }
    return false;
}

void Resource::setDecodedSize(size_t size)
{
    if (size == m_decodedSize)
        return;

    ptrdiff_t delta = size - m_decodedSize;

    // The object must now be moved to a different queue, since its size has been changed.
    // We have to remove explicitly before updating m_decodedSize, so that we find the correct previous
    // queue.
    if (inCache())
        memoryCache()->removeFromLRUList(this);

    m_decodedSize = size;

    if (inCache()) {
        // 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
        if (m_decodedSize && !m_inLiveDecodedResourcesList && hasClients())
            memoryCache()->insertInLiveDecodedResourcesList(this);
        else if (!m_decodedSize && m_inLiveDecodedResourcesList)
            memoryCache()->removeFromLiveDecodedResourcesList(this);

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

void Resource::setEncodedSize(size_t size)
{
    if (size == m_encodedSize)
        return;

    ptrdiff_t delta = size - m_encodedSize;

    // The object must now be moved to a different queue, since its size has been changed.
    // We have to remove explicitly before updating m_encodedSize, so that we find the correct previous
    // queue.
    if (inCache())
        memoryCache()->removeFromLRUList(this);

    m_encodedSize = size;

    if (inCache()) {
        // Now insert into the new LRU list.
        memoryCache()->insertInLRUList(this);

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

void Resource::didAccessDecodedData(double timeStamp)
{
    m_lastDecodedAccessTime = timeStamp;
    if (inCache()) {
        if (m_inLiveDecodedResourcesList) {
            memoryCache()->removeFromLiveDecodedResourcesList(this);
            memoryCache()->insertInLiveDecodedResourcesList(this);
        }
        memoryCache()->prune();
    }
}

void Resource::finishPendingClients()
{
    while (!m_clientsAwaitingCallback.isEmpty()) {
        ResourceClient* client = m_clientsAwaitingCallback.begin()->key;
        m_clientsAwaitingCallback.remove(client);
        m_clients.add(client);
        didAddClient(client);
    }
}

void Resource::setResourceToRevalidate(Resource* resource)
{
    ASSERT(resource);
    ASSERT(!m_resourceToRevalidate);
    ASSERT(resource != this);
    ASSERT(m_handlesToRevalidate.isEmpty());
    ASSERT(resource->type() == type());

    WTF_LOG(ResourceLoading, "Resource %p setResourceToRevalidate %p", this, resource);

    // The following assert should be investigated whenever it occurs. Although it should never fire, it currently does in rare circumstances.
    // https://bugs.webkit.org/show_bug.cgi?id=28604.
    // So the code needs to be robust to this assert failing thus the "if (m_resourceToRevalidate->m_proxyResource == this)" in Resource::clearResourceToRevalidate.
    ASSERT(!resource->m_proxyResource);

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

void Resource::clearResourceToRevalidate()
{
    ASSERT(m_resourceToRevalidate);
    if (m_switchingClientsToRevalidatedResource)
        return;

    // A resource may start revalidation before this method has been called, so check that this resource is still the proxy resource before clearing it out.
    if (m_resourceToRevalidate->m_proxyResource == this) {
        m_resourceToRevalidate->m_proxyResource = 0;
        m_resourceToRevalidate->deleteIfPossible();
    }
    m_handlesToRevalidate.clear();
    m_resourceToRevalidate = 0;
    deleteIfPossible();
}

void Resource::switchClientsToRevalidatedResource()
{
    ASSERT(m_resourceToRevalidate);
    ASSERT(m_resourceToRevalidate->inCache());
    ASSERT(!inCache());

    WTF_LOG(ResourceLoading, "Resource %p switchClientsToRevalidatedResource %p", this, m_resourceToRevalidate);

    m_resourceToRevalidate->m_identifier = m_identifier;

    m_switchingClientsToRevalidatedResource = true;
    HashSet<ResourcePtrBase*>::iterator end = m_handlesToRevalidate.end();
    for (HashSet<ResourcePtrBase*>::iterator it = m_handlesToRevalidate.begin(); it != end; ++it) {
        ResourcePtrBase* handle = *it;
        handle->m_resource = m_resourceToRevalidate;
        m_resourceToRevalidate->registerHandle(handle);
        --m_handleCount;
    }
    ASSERT(!m_handleCount);
    m_handlesToRevalidate.clear();

    Vector<ResourceClient*> clientsToMove;
    HashCountedSet<ResourceClient*>::iterator end2 = m_clients.end();
    for (HashCountedSet<ResourceClient*>::iterator it = m_clients.begin(); it != end2; ++it) {
        ResourceClient* client = it->key;
        unsigned count = it->value;
        while (count) {
            clientsToMove.append(client);
            --count;
        }
    }

    unsigned moveCount = clientsToMove.size();
    for (unsigned n = 0; n < moveCount; ++n)
        removeClient(clientsToMove[n]);
    ASSERT(m_clients.isEmpty());

    for (unsigned n = 0; n < moveCount; ++n)
        m_resourceToRevalidate->addClientToSet(clientsToMove[n]);
    for (unsigned n = 0; n < moveCount; ++n) {
        // 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(clientsToMove[n]))
            m_resourceToRevalidate->didAddClient(clientsToMove[n]);
    }
    m_switchingClientsToRevalidatedResource = false;
}

void Resource::updateResponseAfterRevalidation(const ResourceResponse& validatingResponse)
{
    m_responseTimestamp = currentTime();

    // RFC2616 10.3.5
    // Update cached headers from the 304 response
    const HTTPHeaderMap& newHeaders = validatingResponse.httpHeaderFields();
    HTTPHeaderMap::const_iterator end = newHeaders.end();
    for (HTTPHeaderMap::const_iterator it = newHeaders.begin(); it != end; ++it) {
        // Entity headers should not be sent by servers when generating a 304
        // response; misconfigured servers send them anyway. We shouldn't allow
        // such headers to update the original request. We'll base this on the
        // list defined by RFC2616 7.1, with a few additions for extension headers
        // we care about.
        if (!shouldUpdateHeaderAfterRevalidation(it->key))
            continue;
        m_response.setHTTPHeaderField(it->key, it->value);
    }
}

void Resource::revalidationSucceeded(const ResourceResponse& response)
{
    ASSERT(m_resourceToRevalidate);
    ASSERT(!m_resourceToRevalidate->inCache());
    ASSERT(m_resourceToRevalidate->isLoaded());
    ASSERT(inCache());

    // Calling evict() can potentially delete revalidatingResource, which we use
    // below. This mustn't be the case since revalidation means it is loaded
    // and so canDelete() is false.
    ASSERT(!canDelete());

    m_resourceToRevalidate->updateResponseAfterRevalidation(response);
    memoryCache()->replace(m_resourceToRevalidate, this);

    switchClientsToRevalidatedResource();
    ASSERT(!m_deleted);
    // clearResourceToRevalidate deletes this.
    clearResourceToRevalidate();
}

void Resource::revalidationFailed()
{
    ASSERT(WTF::isMainThread());
    WTF_LOG(ResourceLoading, "Revalidation failed for %p", this);
    ASSERT(resourceToRevalidate());
    clearResourceToRevalidate();
}

void Resource::updateForAccess()
{
    ASSERT(inCache());

    // Need to make sure to remove before we increase the access count, since
    // the queue will possibly change.
    memoryCache()->removeFromLRUList(this);

    // If this is the first time the resource has been accessed, adjust the size of the cache to account for its initial size.
    if (!m_accessCount)
        memoryCache()->adjustSize(hasClients(), size());

    m_accessCount++;
    memoryCache()->insertInLRUList(this);
}

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

void Resource::unregisterHandle(ResourcePtrBase* h)
{
    ASSERT(m_handleCount > 0);
    --m_handleCount;

    if (m_resourceToRevalidate)
        m_handlesToRevalidate.remove(h);

    if (!m_handleCount)
        deleteIfPossible();
}

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

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

bool Resource::mustRevalidateDueToCacheHeaders() const
{
    if (m_response.cacheControlContainsNoCache() || m_response.cacheControlContainsNoStore()) {
        WTF_LOG(ResourceLoading, "Resource %p mustRevalidate because of m_response.cacheControlContainsNoCache() || m_response.cacheControlContainsNoStore()\n", this);
        return true;
    }

    if (isExpired()) {
        WTF_LOG(ResourceLoading, "Resource %p mustRevalidate because of isExpired()\n", this);
        return true;
    }

    return false;
}

bool Resource::isSafeToMakePurgeable() const
{
    return !hasClients() && !m_proxyResource && !m_resourceToRevalidate;
}

bool Resource::makePurgeable(bool purgeable)
{
    if (purgeable) {
        ASSERT(isSafeToMakePurgeable());

        if (m_purgeableData) {
            ASSERT(!m_data);
            return true;
        }
        if (!m_data)
            return false;

        // Should not make buffer purgeable if it has refs other than this since we don't want two copies.
        if (!m_data->hasOneRef())
            return false;

        m_data->createPurgeableBuffer();
        if (!m_data->hasPurgeableBuffer())
            return false;

        m_purgeableData = m_data->releasePurgeableBuffer();
        m_purgeableData->unlock();
        m_data.clear();
        return true;
    }

    if (!m_purgeableData)
        return true;

    ASSERT(!m_data);
    ASSERT(!hasClients());

    if (!m_purgeableData->lock())
        return false;

    m_data = SharedBuffer::adoptPurgeableBuffer(m_purgeableData.release());
    return true;
}

bool Resource::isPurgeable() const
{
    return m_purgeableData && m_purgeableData->isPurgeable();
}

bool Resource::wasPurged() const
{
    return m_purgeableData && m_purgeableData->wasPurged();
}

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

void Resource::didChangePriority(ResourceLoadPriority loadPriority)
{
    if (m_loader)
        m_loader->didChangePriority(loadPriority);
}

Resource::ResourceCallback* Resource::ResourceCallback::callbackHandler()
{
    DEFINE_STATIC_LOCAL(ResourceCallback, callbackHandler, ());
    return &callbackHandler;
}

Resource::ResourceCallback::ResourceCallback()
    : m_callbackTimer(this, &ResourceCallback::timerFired)
{
}

void Resource::ResourceCallback::schedule(Resource* resource)
{
    if (!m_callbackTimer.isActive())
        m_callbackTimer.startOneShot(0);
    m_resourcesWithPendingClients.add(resource);
}

void Resource::ResourceCallback::cancel(Resource* resource)
{
    m_resourcesWithPendingClients.remove(resource);
    if (m_callbackTimer.isActive() && m_resourcesWithPendingClients.isEmpty())
        m_callbackTimer.stop();
}

void Resource::ResourceCallback::timerFired(Timer<ResourceCallback>*)
{
    HashSet<Resource*>::iterator end = m_resourcesWithPendingClients.end();
    Vector<ResourcePtr<Resource> > resources;
    for (HashSet<Resource*>::iterator it = m_resourcesWithPendingClients.begin(); it != end; ++it)
        resources.append(*it);
    m_resourcesWithPendingClients.clear();
    for (size_t i = 0; i < resources.size(); i++)
        resources[i]->finishPendingClients();
}

#if !LOG_DISABLED
const char* ResourceTypeName(Resource::Type type)
{
    switch (type) {
    case Resource::MainResource:
        return "MainResource";
    case Resource::Image:
        return "Image";
    case Resource::CSSStyleSheet:
        return "CSSStyleSheet";
    case Resource::Script:
        return "Script";
    case Resource::Font:
        return "Font";
    case Resource::Raw:
        return "Raw";
    case Resource::SVGDocument:
        return "SVGDocument";
    case Resource::XSLStyleSheet:
        return "XSLStyleSheet";
    case Resource::LinkPrefetch:
        return "LinkPrefetch";
    case Resource::LinkSubresource:
        return "LinkSubresource";
    case Resource::TextTrack:
        return "TextTrack";
    case Resource::Shader:
        return "Shader";
    case Resource::ImportResource:
        return "ImportResource";
    }
    ASSERT_NOT_REACHED();
    return "Unknown";
}
#endif // !LOG_DISABLED

}