WebKit内核分析之FrameLoader

参考地址：http://blog.csdn.net/dlmu2001/article/details/6168545

FrameLoader类负责一个Frame的加载，在Frame的流程中起到非常重要的作用，同很多组件都有交互，本文将分析FrameLoader类的代码

1. 概述

顾名思义，FrameLoader是一个Frame的loader，它的作用就是为客户端提供一个下载一个Frame的一系列的接口。这里的客户指的是类的客户，比如Frame类，间接客户是上层应用，比如 qwebframe

从它的定义看，最容易想到的是一个load接口，用来将一个frame load下来。任何一个页面都需要一个mainframe，因此一个页面的下载一般就是从load 一个 mainframe开始

在 load frame的过程中，通过FrameLoaderClient接口将load过程的不同阶段告知客户

FrameLoader通过 setDocumentLoader相当于把load的工作委托给了 DocumentLoader类

FrameLoader同 DocumentLoader是has-a的关系。一般在load的时候创建 DocumentLoader。Frame调用DocumentLoader的startLoadingMainResource开始 load frame

类数据代码：

 class FrameLoader {
     WTF_MAKE_NONCOPYABLE(FrameLoader);
 private:
     Frame* m_frame;
     FrameLoaderClient* m_client;
 
     mutable PolicyChecker m_policyChecker;
     mutable HistoryController m_history;
     mutable ResourceLoadNotifier m_notifer;
     mutable SubframeLoader m_subframeLoader;
     mutable FrameLoaderStateMachine m_stateMachine;
 
     FrameState m_state;
     FrameLoadType m_loadType;
 
     // Document loaders for the three phases of frame loading. Note that while
     // a new request is being loaded, the old document loader may still be referenced.
     // E.g. while a new request is in the "policy" state, the old document loader may
     // be consulted in particular as it makes sense to imply certain settings on the new loader.
     RefPtr<DocumentLoader> m_documentLoader;
     RefPtr<DocumentLoader> m_provisionalDocumentLoader;
     RefPtr<DocumentLoader> m_policyDocumentLoader;
 
     bool m_delegateIsHandlingProvisionalLoadError;
 
     bool m_quickRedirectComing;
     bool m_sentRedirectNotification;
     bool m_inStopAllLoaders;
 
     String m_outgoingReferrer;
 
     bool m_isExecutingJavaScriptFormAction;
 
     bool m_didCallImplicitClose;
     bool m_wasUnloadEventEmitted;
     bool m_pageDismissalEventBeingDispatched;
     bool m_isComplete;
     bool m_isLoadingMainResource;
 
     RefPtr<SerializedScriptValue> m_pendingStateObject;
 
     KURL m_workingURL;
 
     OwnPtr<IconLoader> m_iconLoader;
     bool m_mayLoadIconLater;
 
     bool m_needsClear;
 
     KURL m_submittedFormURL;
 
     Timer<FrameLoader> m_checkTimer;
     bool m_shouldCallCheckCompleted;
     bool m_shouldCallCheckLoadComplete;
 
     Frame* m_opener;
     HashSet<Frame*> m_openedFrames;
 
     bool m_didPerformFirstNavigation;
     bool m_loadingFromCachedPage;
     bool m_suppressOpenerInNewFrame;
 
     SandboxFlags m_sandboxFlags;
     SandboxFlags m_forcedSandboxFlags;
 
     RefPtr<FrameNetworkingContext> m_networkingContext;
 
     KURL m_previousUrl;
 }

2. 类关系

1，Frame 和 FrameLoader 是 contain-a的关系，在 Frame的构造函数中调用 FraomeLoader的构造函数，调用时传入参数 Frame指针 和 FrameLoaderClient指针

 inline Frame::Frame(Page* page, HTMLFrameOwnerElement* ownerElement, FrameLoaderClient* frameLoaderClient)
     : m_page(page)
     , m_treeNode(this, parentFromOwnerElement(ownerElement))
     , m_loader(this, frameLoaderClient)
     , m_navigationScheduler(this)
     , m_ownerElement(ownerElement)
     , m_script(this)
     , m_editor(this)
     , m_selectionController(this)
     , m_eventHandler(this)
     , m_animationController(this)
     , m_lifeSupportTimer(this, &Frame::lifeSupportTimerFired)
     , m_pageZoomFactor(parentPageZoomFactor(this))
     , m_textZoomFactor(parentTextZoomFactor(this))
     , m_pageScaleFactor()
 #if ENABLE(ORIENTATION_EVENTS)
     , m_orientation()
 #endif
     , m_inViewSourceMode(false)
     , m_isDisconnected(false)
     , m_excludeFromTextSearch(false)
 #if ENABLE(MEDIA_STREAM)
     , m_mediaStreamFrameController(RuntimeEnabledFeatures::mediaStreamEnabled() ? adoptPtr(new MediaStreamFrameController(this)) : PassOwnPtr<MediaStreamFrameController>())
 #endif
 {
      ....
 }

2，Frame 有可能有子Frame， 所以维护 SubFrameLoader对象 m_subframeLoader来管理子 Frame 的load。  Frame可以对应 xml document，也可以对应html document，等。跟Document相关的子resource的load不在FrameLoader的职责范围内。

3，包含一个DocumentWriter类对象 m_writer，当Frame的数据 load finish的时候，将数据传给 DocumentWriter类，进行下一步的处理（比如解码）

4，FrameLoader维护三个 DocumentLoader对象，分别对应不同的阶段。

     RefPtr<DocumentLoader> m_documentLoader;
     RefPtr<DocumentLoader> m_provisionalDocumentLoader;
     RefPtr<DocumentLoader> m_policyDocumentLoader;

m_policyDocumentLoader 对应于 收到用户 load 调用，进行 policy check 阶段

m_provisionalDocumentLoader 对应于 policy check 通过之后，Frame数据还没有到来之前，它会负责 startLoadingMainResource的调用

m_documentLoader 则是 Frame第一个数据到来以后使用的 DocumentLoader，这个时候，前一个主 Frame 的 DocumentLoader已经不能再用（user agent开始白屏，刷掉前一个页面的显示）

 inline void Frame::init()
 {
     m_loader.init();
 }
 
 void FrameLoader::init()
 {
     // Propagate sandbox attributes to this Frameloader and its descendants.
     // This needs to be done early, so that an initial document gets correct sandbox flags in its SecurityOrigin.
     updateSandboxFlags();
 
     // this somewhat odd set of steps is needed to give the frame an initial empty document
     m_stateMachine.advanceTo(FrameLoaderStateMachine::CreatingInitialEmptyDocument);
     setPolicyDocumentLoader(m_client->createDocumentLoader(ResourceRequest(KURL(ParsedURLString, "")), SubstituteData()).get());
     setProvisionalDocumentLoader(m_policyDocumentLoader.get());
     setState(FrameStateProvisional);
     m_provisionalDocumentLoader->setResponse(ResourceResponse(KURL(), "text/html", , String(), String()));
     m_provisionalDocumentLoader->finishedLoading();
     m_documentLoader->writer()->begin(KURL(), false);
     m_documentLoader->writer()->end();
     m_frame->document()->cancelParsing();
     m_stateMachine.advanceTo(FrameLoaderStateMachine::DisplayingInitialEmptyDocument);
     m_didCallImplicitClose = true;
 
     m_networkingContext = m_client->createNetworkingContext();
 }

从上面代码可以看出，在Frame初始化的时候，仅仅调用FrameLoader的初始化函数

然后FrameLoader初始化的时候，首先把状态机的状态标识成 FrameLoaderStateMachine::CreatingInitialEmptyDocument ，然后调用客户端实现创建一个DocumentLoader，然后设置为PolicyDocumentLoader，并且设置ProvisionalDocumentLoader和PolicyDocumentLoader为同一个loader，并且设置FrameState状态为 Provisional（初始化为commitPage状态）

然后把状态机状态更新为  FrameLoaderStateMachine::DisplayingInitialEmptyDocument  完成初始化

后面还有一次load的变迁：

 void FrameLoader::transitionToCommitted(PassRefPtr<CachedPage> cachedPage)
 {
     ASSERT(m_client->hasWebView());
     ASSERT(m_state == FrameStateProvisional);
 
     if (m_state != FrameStateProvisional)
         return;
 
     if (m_frame->view())
         m_frame->view()->scrollAnimator()->cancelAnimations();
 
     m_client->setCopiesOnScroll();
     history()->updateForCommit();
 
     // The call to closeURL() invokes the unload event handler, which can execute arbitrary
     // JavaScript. If the script initiates a new load, we need to abandon the current load,
     // or the two will stomp each other.
     DocumentLoader* pdl = m_provisionalDocumentLoader.get();
     if (m_documentLoader)
         closeURL();
     if (pdl != m_provisionalDocumentLoader)
         return;
 
     // Nothing else can interupt this commit - set the Provisional->Committed transition in stone
     if (m_documentLoader)
         m_documentLoader->stopLoadingSubresources();
     if (m_documentLoader)
         m_documentLoader->stopLoadingPlugIns();
 
     setDocumentLoader(m_provisionalDocumentLoader.get());
     setProvisionalDocumentLoader();
     setState(FrameStateCommittedPage);
 
     // Handle adding the URL to the back/forward list.
     DocumentLoader* dl = m_documentLoader.get();
 
     switch (m_loadType) {
         case FrameLoadTypeForward:
         case FrameLoadTypeBack:
         case FrameLoadTypeIndexedBackForward:
             if (m_frame->page()) {
                 // If the first load within a frame is a navigation within a back/forward list that was attached
                 // without any of the items being loaded then we need to update the history in a similar manner as
                 // for a standard load with the exception of updating the back/forward list (<rdar://problem/8091103>).
                 if (!m_stateMachine.committedFirstRealDocumentLoad())
                     history()->updateForStandardLoad(HistoryController::UpdateAllExceptBackForwardList);
 
                 history()->updateForBackForwardNavigation();
 
                 // For cached pages, CachedFrame::restore will take care of firing the popstate event with the history item's state object
                 if (history()->currentItem() && !cachedPage)
                     m_pendingStateObject = history()->currentItem()->stateObject();
 
                 // Create a document view for this document, or used the cached view.
                 if (cachedPage) {
                     DocumentLoader* cachedDocumentLoader = cachedPage->documentLoader();
                     ASSERT(cachedDocumentLoader);
                     cachedDocumentLoader->setFrame(m_frame);
                     m_client->transitionToCommittedFromCachedFrame(cachedPage->cachedMainFrame());
 
                 } else
                     m_client->transitionToCommittedForNewPage();
             }
             break;
 
         case FrameLoadTypeReload:
         case FrameLoadTypeReloadFromOrigin:
         case FrameLoadTypeSame:
         case FrameLoadTypeReplace:
             history()->updateForReload();
             m_client->transitionToCommittedForNewPage();
             break;
 
         case FrameLoadTypeStandard:
             history()->updateForStandardLoad();
             if (m_frame->view())
                 m_frame->view()->setScrollbarsSuppressed(true);
             m_client->transitionToCommittedForNewPage();
             break;
 
         case FrameLoadTypeRedirectWithLockedBackForwardList:
             history()->updateForRedirectWithLockedBackForwardList();
             m_client->transitionToCommittedForNewPage();
             break;
 
         // FIXME Remove this check when dummy ds is removed (whatever "dummy ds" is).
         // An exception should be thrown if we're in the FrameLoadTypeUninitialized state.
         default:
             ASSERT_NOT_REACHED();
     }
 
     m_documentLoader->writer()->setMIMEType(dl->responseMIMEType());
 
     // Tell the client we've committed this URL.
     ASSERT(m_frame->view());
 
     if (m_stateMachine.creatingInitialEmptyDocument())
         return;
 
     if (!m_stateMachine.committedFirstRealDocumentLoad())
         m_stateMachine.advanceTo(FrameLoaderStateMachine::DisplayingInitialEmptyDocumentPostCommit);
 
     if (!m_client->hasHTMLView())
         receivedFirstData();
 }

5，包含一个HistoryController对象，用于操作历史记录相关的接口，保存或者恢复Document和View相关的状态，维护前进后退队列，以实现前进后退功能，前进后退本质上是同Page对象关联的，FrameLoader通过HistoryController操作 m_backForwardController对象

6，包含一个 ResourceLoadNotifier 对象， 主要用于同 ResourceLoader及FrameLoaderClient打交道，可以理解为 ResourceLoader有事件变化或者发生的时候，通知 FrameLoader 的一个手段

7，包含一个SubframeLoader对象，当FrameLoader下载的Document有子帧需要请求的时候（比如 HTMLDocument中解析到 iframe），用于处理子帧请求

8，将FrameLoader的状态封装到 FrameLoaderStateMachine 中，这个状态同 FrameState不同。 FrameState倾向于判断Frame涉及的Document的下载状态，是出于发起状态（Provisional），还是出于已经收到响应但不全（CommitedPage），还是响应收全状态，倾向于同HTTP相关。而 FrameLoaderStateMachine 倾向于同DocumentLoader相关，用来描述FrameLoader处理DocumentLoader的节点，是处于已经创建，还是显示状态。

9，PolicyChecker主要用来对FrameLoader进行一些校验。包括三种校验： NewWindow，Navigation和Content。

NewWindow对应于浏览器需要打开一个tab页或新窗口的时候

Navigation 对应于一个页面请求发起的时候

Content校验对应于收到数据之后（判断 Mime type等）

PolicyChecker通过提供对应的接口，由FrameLoaderClient来对这些请求进行校验，以确定是否允许继续，护着需要其他的动作

3.   主要接口

 void FrameLoader::init()

功能：

FrameLoader的初始化

实现：

 void FrameLoader::init()
 {
     // Propagate sandbox attributes to this Frameloader and its descendants.
     // This needs to be done early, so that an initial document gets correct sandbox flags in its SecurityOrigin.
     updateSandboxFlags();
 
     // this somewhat odd set of steps is needed to give the frame an initial empty document
     m_stateMachine.advanceTo(FrameLoaderStateMachine::CreatingInitialEmptyDocument);
     setPolicyDocumentLoader(m_client->createDocumentLoader(ResourceRequest(KURL(ParsedURLString, "")), SubstituteData()).get());
     setProvisionalDocumentLoader(m_policyDocumentLoader.get());
     setState(FrameStateProvisional);
     m_provisionalDocumentLoader->setResponse(ResourceResponse(KURL(), "text/html", , String(), String()));
     m_provisionalDocumentLoader->finishedLoading();
     m_documentLoader->writer()->begin(KURL(), false);
     m_documentLoader->writer()->end();
     m_frame->document()->cancelParsing();
     m_stateMachine.advanceTo(FrameLoaderStateMachine::DisplayingInitialEmptyDocument);
     m_didCallImplicitClose = true;
 
     m_networkingContext = m_client->createNetworkingContext();
 }

函数调用系列：

 QWebFrame::QWebFrame(QwebPage* parent,QWebFrameData *frameData)
 QWebFramePrivate::init(QWebFrame* qwebframe,QWebFrameData* frameData)
 Frame::init()
 FrameLoader::init()

源码追踪：

1，QWebFrame::QWebFrame(QWebPage *parent, QWebFrameData *frameData)

 QWebFrame::QWebFrame(QWebPage *parent, QWebFrameData *frameData)
     : QObject(parent)
     , d(new QWebFramePrivate)
 {
     d->page = parent;
     d->init(this, frameData);
 
     if (!frameData->url.isEmpty()) {
         WebCore::ResourceRequest request(frameData->url, frameData->referrer);
         d->frame->loader()->load(request, frameData->name, false);
     }
 #if ENABLE(ORIENTATION_EVENTS) && ENABLE(DEVICE_ORIENTATION)
     connect(&d->m_orientation, SIGNAL(readingChanged()), this, SLOT(_q_orientationChanged()));
     d->m_orientation.start();
 #endif
 }

2，QWebFramePrivate::init(QWebFrame *qframe, QWebFrameData *frameData)

 void QWebFramePrivate::init(QWebFrame *qframe, QWebFrameData *frameData)
 {
     q = qframe;
 
     allowsScrolling = frameData->allowsScrolling;
     marginWidth = frameData->marginWidth;
     marginHeight = frameData->marginHeight;
     frame = frameData->frame.get();
     frameLoaderClient = frameData->frameLoaderClient;
     frameLoaderClient->setFrame(qframe, frame);
 
     frame->init();
 }

3，Frame::init()

 inline void Frame::init()
 {
     m_loader.init();
 }

4， FrameLoader::init()

OK，源码跟踪到此

说明：

主要做一些自身的初始化工作，比如初始化状态机，Sandbox Flags，创建DocumentLoader被设置为 PolicyDocumentLoader  和  Provisional DocumentLoader，调用 DocumentLoader  和 documentWriter等的接口进行初始化操作

FrameLoader::commitProvisionalLoad

功能：

提交Provisional阶段下载的数据

实现：

 void FrameLoader::commitProvisionalLoad()
 {
     RefPtr<CachedPage> cachedPage = m_loadingFromCachedPage ? pageCache()->get(history()->provisionalItem()) : ;
     RefPtr<DocumentLoader> pdl = m_provisionalDocumentLoader;
 
     LOG(PageCache, "WebCoreLoading %s: About to commit provisional load from previous URL '%s' to new URL '%s'", m_frame->tree()->uniqueName().string().utf8().data(),
         m_frame->document() ? m_frame->document()->url().string().utf8().data() : "",
         pdl ? pdl->url().string().utf8().data() : "<no provisional DocumentLoader>");
 
     // Check to see if we need to cache the page we are navigating away from into the back/forward cache.
     // We are doing this here because we know for sure that a new page is about to be loaded.
     HistoryItem* item = history()->currentItem();
     if (!m_frame->tree()->parent() && PageCache::canCache(m_frame->page()) && !item->isInPageCache())
         pageCache()->add(item, m_frame->page());
 
     if (m_loadType != FrameLoadTypeReplace)
         closeOldDataSources();
 
     if (!cachedPage && !m_stateMachine.creatingInitialEmptyDocument())
         m_client->makeRepresentation(pdl.get());
 
     transitionToCommitted(cachedPage);
 
     if (pdl) {
         // Check if the destination page is allowed to access the previous page's timing information.
         RefPtr<SecurityOrigin> securityOrigin = SecurityOrigin::create(pdl->request().url());
         m_documentLoader->timing()->hasSameOriginAsPreviousDocument = securityOrigin->canRequest(m_previousUrl);
     }
 
     // Call clientRedirectCancelledOrFinished() here so that the frame load delegate is notified that the redirect's
     // status has changed, if there was a redirect.  The frame load delegate may have saved some state about
     // the redirect in its -webView:willPerformClientRedirectToURL:delay:fireDate:forFrame:.  Since we are
     // just about to commit a new page, there cannot possibly be a pending redirect at this point.
     if (m_sentRedirectNotification)
         clientRedirectCancelledOrFinished(false);
 
     if (cachedPage && cachedPage->document()) {
         prepareForCachedPageRestore();
         cachedPage->restore(m_frame->page());
 
         dispatchDidCommitLoad();
 
         // If we have a title let the WebView know about it.
         StringWithDirection title = m_documentLoader->title();
         if (!title.isNull())
             m_client->dispatchDidReceiveTitle(title);
 
         checkCompleted();
     } else {
         KURL url = pdl->substituteData().responseURL();
         if (url.isEmpty())
             url = pdl->url();
         if (url.isEmpty())
             url = pdl->responseURL();
         if (url.isEmpty())
             url = blankURL();
 
         didOpenURL(url);
     }
 
     LOG(Loading, "WebCoreLoading %s: Finished committing provisional load to URL %s", m_frame->tree()->uniqueName().string().utf8().data(),
         m_frame->document() ? m_frame->document()->url().string().utf8().data() : "");
 
     if (m_loadType == FrameLoadTypeStandard && m_documentLoader->isClientRedirect())
         history()->updateForClientRedirect();
 
     if (m_loadingFromCachedPage) {
         m_frame->document()->documentDidBecomeActive();
 
         // Force a layout to update view size and thereby update scrollbars.
         m_frame->view()->forceLayout();
 
         const ResponseVector& responses = m_documentLoader->responses();
         size_t count = responses.size();
         for (size_t i = ; i < count; i++) {
             const ResourceResponse& response = responses[i];
             // FIXME: If the WebKit client changes or cancels the request, this is not respected.
             ResourceError error;
             unsigned long identifier;
             ResourceRequest request(response.url());
             requestFromDelegate(request, identifier, error);
             // FIXME: If we get a resource with more than 2B bytes, this code won't do the right thing.
             // However, with today's computers and networking speeds, this won't happen in practice.
             // Could be an issue with a giant local file.
             notifier()->sendRemainingDelegateMessages(m_documentLoader.get(), identifier, response, static_cast<int>(response.expectedContentLength()), , error);
         }
 
         pageCache()->remove(history()->currentItem());
 
         m_documentLoader->setPrimaryLoadComplete(true);
 
         // FIXME: Why only this frame and not parent frames?
         checkLoadCompleteForThisFrame();
     }
 }

函数调用系列：（两种情况）

 DocumentLoader::finishLoading
 DocumentLoader::commitIfReady
 FrameLoader::commitProvisionalLoad
 
 ResourceLoader::didReceiveData
 MainResourceLoader::addData
 DocumentLoader::receiveData
 DocumentLoader::commitLoad
 DocumentLoader::commitIfReady
 DocumentLoader::commitProvisionalLoad

源码跟踪：

情况一

1，MainResourceLoader::didFinishLoading(double finishTime)

 void MainResourceLoader::didFinishLoading(double finishTime)
 {
     // There is a bug in CFNetwork where callbacks can be dispatched even when loads are deferred.
     // See <rdar://problem/6304600> for more details.
 #if !USE(CF)
     ASSERT(shouldLoadAsEmptyDocument(frameLoader()->activeDocumentLoader()->url()) || !defersLoading());
 #endif
 
     // The additional processing can do anything including possibly removing the last
     // reference to this object.
     RefPtr<MainResourceLoader> protect(this);
 
 #if ENABLE(OFFLINE_WEB_APPLICATIONS)
     RefPtr<DocumentLoader> dl = documentLoader();
 #endif
 
     ASSERT(!documentLoader()->timing()->responseEnd);
     documentLoader()->timing()->responseEnd = finishTime ? finishTime : (m_timeOfLastDataReceived ? m_timeOfLastDataReceived : currentTime());
     frameLoader()->finishedLoading();
     ResourceLoader::didFinishLoading(finishTime);
 
 #if ENABLE(OFFLINE_WEB_APPLICATIONS)
     dl->applicationCacheHost()->finishedLoadingMainResource();
 #endif
 }

2，FrameLoader::finishedLoading()

 void FrameLoader::finishedLoading()
 {
     // Retain because the stop may release the last reference to it.
     RefPtr<Frame> protect(m_frame);
 
     RefPtr<DocumentLoader> dl = activeDocumentLoader();
     dl->finishedLoading();
     if (!dl->mainDocumentError().isNull() || !dl->frameLoader())
         return;
     dl->setPrimaryLoadComplete(true);
     m_client->dispatchDidLoadMainResource(dl.get());
     checkLoadComplete();
 }

3，DocumentLoader::finishedLoading()

 void DocumentLoader::finishedLoading()
 {
     m_gotFirstByte = true;
     commitIfReady();
     if (FrameLoader* loader = frameLoader()) {
         loader->finishedLoadingDocument(this);
         m_writer.end();
     }
 }

4， DocumentLoader::commitIfReady()

 void DocumentLoader::commitIfReady()
 {
     if (m_gotFirstByte && !m_committed) {
         m_committed = true;
         frameLoader()->commitProvisionalLoad();
     }
 }

5， FrameLoader::commitProvisionalLoad()

OK！

情况二：

1，MainResourceLoader::didReceiveData(const char* data, int length, long long encodedDataLength, bool allAtOnce)

 void MainResourceLoader::didReceiveData(const char* data, int length, long long encodedDataLength, bool allAtOnce)
 {
     ASSERT(data);
     ASSERT(length != );
 
     ASSERT(!m_response.isNull());
 
 #if USE(CFNETWORK) || PLATFORM(MAC)
     // Workaround for <rdar://problem/6060782>
     if (m_response.isNull()) {
         m_response = ResourceResponse(KURL(), "text/html", , String(), String());
         if (DocumentLoader* documentLoader = frameLoader()->activeDocumentLoader())
             documentLoader->setResponse(m_response);
     }
 #endif
 
     // There is a bug in CFNetwork where callbacks can be dispatched even when loads are deferred.
     // See <rdar://problem/6304600> for more details.
 #if !USE(CF)
     ASSERT(!defersLoading());
 #endif
 
  #if ENABLE(OFFLINE_WEB_APPLICATIONS)
     documentLoader()->applicationCacheHost()->mainResourceDataReceived(data, length, encodedDataLength, allAtOnce);
 #endif
 
     // The additional processing can do anything including possibly removing the last
     // reference to this object; one example of this is 3266216.
     RefPtr<MainResourceLoader> protect(this);
 
     m_timeOfLastDataReceived = currentTime();
 
     ResourceLoader::didReceiveData(data, length, encodedDataLength, allAtOnce);
 }

2，ResourceLoader::didReceiveData(const char* data, int length, long long encodedDataLength, bool allAtOnce)

 void ResourceLoader::didReceiveData(const char* data, int length, long long encodedDataLength, bool allAtOnce)
 {
     // The following assertions are not quite valid here, since a subclass
     // might override didReceiveData in a way that invalidates them. This
     // happens with the steps listed in 3266216
     // ASSERT(con == connection);
     // ASSERT(!m_reachedTerminalState);
 
     // Protect this in this delegate method since the additional processing can do
     // anything including possibly derefing this; one example of this is Radar 3266216.
     RefPtr<ResourceLoader> protector(this);
 
     addData(data, length, allAtOnce);
     // FIXME: If we get a resource with more than 2B bytes, this code won't do the right thing.
     // However, with today's computers and networking speeds, this won't happen in practice.
     // Could be an issue with a giant local file.
     if (m_sendResourceLoadCallbacks && m_frame)
         frameLoader()->notifier()->didReceiveData(this, data, length, static_cast<int>(encodedDataLength));
 }

3，MainResourceLoader::addData(const char* data, int length, bool allAtOnce)

 void MainResourceLoader::addData(const char* data, int length, bool allAtOnce)
 {
     ResourceLoader::addData(data, length, allAtOnce);
     documentLoader()->receivedData(data, length);
 }

4，DocumentLoader::receivedData(const char* data, int length)

 void DocumentLoader::receivedData(const char* data, int length)
 {
     m_gotFirstByte = true;
     if (doesProgressiveLoad(m_response.mimeType()))
         commitLoad(data, length);
 }

5，DocumentLoader::commitLoad(const char* data, int length)

 void DocumentLoader::commitLoad(const char* data, int length)
 {
     // Both unloading the old page and parsing the new page may execute JavaScript which destroys the datasource
     // by starting a new load, so retain temporarily.
     RefPtr<Frame> protectFrame(m_frame);
     RefPtr<DocumentLoader> protectLoader(this);
 
     commitIfReady();
     FrameLoader* frameLoader = DocumentLoader::frameLoader();
     if (!frameLoader)
         return;
 #if ENABLE(WEB_ARCHIVE)
     if (ArchiveFactory::isArchiveMimeType(response().mimeType()))
         return;
 #endif
     frameLoader->client()->committedLoad(this, data, length);
 }

6， DocumentLoader::commitIfReady()

 void DocumentLoader::commitIfReady()
 {
     if (m_gotFirstByte && !m_committed) {
         m_committed = true;
         frameLoader()->commitProvisionalLoad();
     }
 }

7，FrameLoader::commitProvisionalLoad()

OK， 跟踪over！！

说明： 这个接口主要的操作是将Provisional DocumentLoader设置成 DocumentLoader，因为已经收到数据，所以FrameState也会跃迁到FrameStateCommittedPage。还有历史记录，PageCache相关的操作。另外，这个接口会间接调用 FrameLoaderClientQt::transitionToCommittedForNewPage，通过Frame::createView 创建出 FrameView来。

Frame::finishedLoading

功能：

frame请求网络加载完成的时候调用此接口

实现：

 void FrameLoader::finishedLoading()
 {
     // Retain because the stop may release the last reference to it.
     RefPtr<Frame> protect(m_frame);
 
     RefPtr<DocumentLoader> dl = activeDocumentLoader();
     dl->finishedLoading();
     if (!dl->mainDocumentError().isNull() || !dl->frameLoader())
         return;
     dl->setPrimaryLoadComplete(true);
     m_client->dispatchDidLoadMainResource(dl.get());
     checkLoadComplete();
 }

函数调用系列：

 ResourceLoader::didFinishLoading
 MainResourceLoader::didFinishLoading
 FrameLoader::finishedLoading
 FrameLoader::init()

说明：

检查是否有网络错误，告诉DocumentLoader和DocumentWriter下载完成，以便进行后续操作（提交数据，解析）

FrameLoader::finishedParsing

功能：

解析完成调用此接口

函数调用系列：

 DocumentWritter::end
 ….
 Document::finishParsing
 ….
 Document::finishedParsing
 FrameLoader::finishedParsing

源码跟踪：

1，DocumentLoader::finishedLoading()

 void DocumentLoader::finishedLoading()
 {
     m_gotFirstByte = true;
     commitIfReady();
     if (FrameLoader* loader = frameLoader()) {
         loader->finishedLoadingDocument(this);
         m_writer.end();
     }
 }

2， DocumentWriter::end()

 void DocumentWriter::end()
 {
     m_frame->loader()->didEndDocument();
     endIfNotLoadingMainResource();
 }

3，DocumentWriter::endIfNotLoadingMainResource()

 void DocumentWriter::endIfNotLoadingMainResource()
 {
     if (m_frame->loader()->isLoadingMainResource() || !m_frame->page() || !m_frame->document())
         return;
 
     // http://bugs.webkit.org/show_bug.cgi?id=10854
     // The frame's last ref may be removed and it can be deleted by checkCompleted(),
     // so we'll add a protective refcount
     RefPtr<Frame> protector(m_frame);
 
     // make sure nothing's left in there
     addData(, , true);
     m_frame->document()->finishParsing();
 }

4，Document::finishedParsing()

 void Document::finishedParsing()
 {
     ASSERT(!scriptableDocumentParser() || !m_parser->isParsing());
     ASSERT(!scriptableDocumentParser() || m_readyState != Loading);
     setParsing(false);
     if (!m_documentTiming.domContentLoadedEventStart)
         m_documentTiming.domContentLoadedEventStart = currentTime();
     dispatchEvent(Event::create(eventNames().DOMContentLoadedEvent, true, false));
     if (!m_documentTiming.domContentLoadedEventEnd)
         m_documentTiming.domContentLoadedEventEnd = currentTime();
 
     if (RefPtr<Frame> f = frame()) {
         // FrameLoader::finishedParsing() might end up calling Document::implicitClose() if all
         // resource loads are complete. HTMLObjectElements can start loading their resources from
         // post attach callbacks triggered by recalcStyle().  This means if we parse out an <object>
         // tag and then reach the end of the document without updating styles, we might not have yet
         // started the resource load and might fire the window load event too early.  To avoid this
         // we force the styles to be up to date before calling FrameLoader::finishedParsing().
         // See https://bugs.webkit.org/show_bug.cgi?id=36864 starting around comment 35.
         updateStyleIfNeeded();
 
         f->loader()->finishedParsing();
 
         InspectorInstrumentation::domContentLoadedEventFired(f.get(), url());
     }
 }

5，FrameLoader::finishedParsing()

FrameLoader::load(const ResourceRequest& request,bool lockHistory)

功能：

加载一个Frame请求，Frame请求相关的数据，封装成ResourceRequest传入

函数调用系列：

一般由应用触发

源码跟踪：

见前文

说明：

这个接口调用FrameLoaderClientQt::createDocumentLoader创建出DocumentLoader，并以此DocumentLoader为Policy  DocumentLoder，进入Policy check流程