谷歌浏览器的源码分析 26

消息的流通过程，是一个不同类相互交流的过程，如果不了解这个过程，根本就不知道这些类是怎么样相互协作的。由于上一次说到ViewHostMsg_RequestResource消息已经发送出来，它的处理过徎其实就是一般资源的消息处理过程，下面就来看看这个消息的处理过程，如下：<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

1.       base::MessagePumpWin::Run函数消息

2.       base::MessagePumpWin::RunWithDispatcher

3.       base::MessagePumpWin::DoRunLoop

4.       base::MessagePumpWin::WaitForWork

5.       base::MessagePumpWin::SignalWatcher

6.       IPC::Channel::OnObjectSignaled 通道的消息处理。

7.       IPC::Channel::ProcessIncomingMessages

8.       IPC::SyncChannel::SyncContext::OnMessageReceived

9.       IPC::ChannelProxy::Context::TryFilters

10.    ResourceMessageFilter::OnMessageReceived

11.    IPC::MessageWithTuple<Tuple2<int,ViewHostMsg_Resource_Request> >::Dispatch<ResourceMessageFilter,int,ViewHostMsg_Resource_Request const &>

12.    ResourceMessageFilter::OnRequestResource

13.    ResourceDispatcherHost::BeginRequest

消息通过上面12个函数的流转，到达到处理这个消息的函数ResourceDispatcherHost::BeginRequest，它在里面就会把消息变成一个网络下载请求，函数代码如下：

#001  void ResourceDispatcherHost::BeginRequest(

#002      Receiver* receiver,

#003      HANDLE render_process_handle,

#004      int render_process_host_id,

#005      int render_view_id,

#006      int request_id,

#007      const ViewHostMsg_Resource_Request& request_data,

#008      URLRequestContext* request_context,

#009      IPC::Message* sync_result) {

是否已经传送完成，或者关闭。

#010    if (is_shutdown_ ||

#011        !ShouldServiceRequest(render_process_host_id, request_data)) {

#012      // Tell the renderer that this request was disallowed.

#013      receiver->Send(new ViewMsg_Resource_RequestComplete(

#014          render_view_id,

#015          request_id,

#016          URLRequestStatus(URLRequestStatus::FAILED, net::ERR_ABORTED)));

#017      return;

#018    }

#019 

保证所有插件已经加载。

#020    // Ensure the Chrome plugins are loaded, as they may intercept network

#021    // requests.  Does nothing if they are already loaded.

#022    // TODO(mpcomplete): This takes 200 ms!  Investigate parallelizing this by

#023    // starting the load earlier in a BG thread.

#024    plugin_service_->LoadChromePlugins(this);

#025 

构造事件处理器。

#026    // Construct the event handler.

#027    scoped_refptr<EventHandler> handler;

#028    if (sync_result) {

#029      handler = new SyncEventHandler(receiver, request_data.url, sync_result);

#030    } else {

#031      handler = new AsyncEventHandler(receiver,

#032                                      render_process_host_id,

#033                                      render_view_id,

#034                                      render_process_handle,

#035                                      request_data.url,

#036                                      this);

#037    }

#038 

#039    if (HandleExternalProtocol(request_id, render_process_host_id, render_view_id,

#040                               request_data.url, request_data.resource_type,

#041                               handler)) {

#042      return;

#043    }

#044 

构造下载请求。

#045    // Construct the request.

#046    URLRequest* request = new URLRequest(request_data.url, this);

#047    request->set_method(request_data.method);

#048    request->set_policy_url(request_data.policy_url);

#049    request->set_referrer(request_data.referrer.spec());

#050    request->SetExtraRequestHeaders(request_data.headers);

#051    request->set_load_flags(request_data.load_flags);

#052    request->set_context(request_context);

#053    request->set_origin_pid(request_data.origin_pid);

#054 

设置上传数据。

#055    // Set upload data.

#056    uint64 upload_size = 0;

#057    if (!request_data.upload_content.empty()) {

#058      scoped_refptr<net::UploadData> upload = new net::UploadData();

#059      upload->set_elements(request_data.upload_content);  // Deep copy.

#060      request->set_upload(upload);

#061      upload_size = upload->GetContentLength();

#062    }

#063 

安装一个CrossSiteEventHandler事件处理器。

#064    // Install a CrossSiteEventHandler if this request is coming from a

#065    // RenderViewHost with a pending cross-site request.  We only check this for

#066    // MAIN_FRAME requests.

#067    // TODO(mpcomplete): remove "render_process_host_id != -1"

#068    //                   when http://b/viewIssue?id=1080959 is fixed.

#069    if (request_data.resource_type == ResourceType::MAIN_FRAME &&

#070        render_process_host_id != -1 &&

#071        Singleton<CrossSiteRequestManager>::get()->

#072            HasPendingCrossSiteRequest(render_process_host_id, render_view_id)) {

#073      // Wrap the event handler to be sure the current page‘s onunload handler

#074      // has a chance to run before we render the new page.

#075      handler = new CrossSiteEventHandler(handler,

#076                                          render_process_host_id,

#077                                          render_view_id,

#078                                          this);

#079    }

#080 

#081    if (safe_browsing_->enabled() &&

#082        safe_browsing_->CanCheckUrl(request_data.url)) {

#083      handler = new SafeBrowsingEventHandler(handler,

#084                                             render_process_host_id,

#085                                             render_view_id,

#086                                             request_data.url,

#087                                             request_data.resource_type,

#088                                             safe_browsing_,

#089                                             this);

#090    }

#091 

创建一个缓冲区处理。

#092    // Insert a buffered event handler before the actual one.

#093    handler = new BufferedEventHandler(handler, this, request);

#094 

#095    // Make extra info and read footer (contains request ID).

#096    ExtraRequestInfo* extra_info =

#097        new ExtraRequestInfo(handler,

#098                             request_id,

#099                             render_process_host_id,

#100                             render_view_id,

#101                             request_data.mixed_content,

#102                             request_data.resource_type,

#103                             upload_size);

#104    extra_info->allow_download =

#105        ResourceType::IsFrame(request_data.resource_type);

#106    request->set_user_data(extra_info);  // takes pointer ownership

#107 

开始调用内部处理请求函数。

#108    BeginRequestInternal(request, request_data.mixed_content);

#109  }

通过上面的分析，已经知道消息转换为一个请求任务URLRequest，这个任务就需要交给后面的工作进程来处理了，它是通过函数BeginRequestInternal来把任务进一步发送出去。