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上一次說(shuō)到怎么樣開(kāi)始把任務(wù)發(fā)送出去，也就是調(diào)用函數(shù) BeginRequestInternal 來(lái)把 URL 請(qǐng)求發(fā)送，它的代碼如下：

#001 ? void ResourceDispatcherHost::BeginRequestInternal(URLRequest* request,

#002 ??????????????????????????????????????????????????? bool mixed_content) {

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獲取請(qǐng)求信息。

#003 ??? ExtraRequestInfo* info = ExtraInfoForRequest(request);

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生成全局 ID ，然后保存到正在下載請(qǐng)求隊(duì)列里。

#004 ??? GlobalRequestID global_id(info->render_process_host_id, info->request_id);

#005 ??? pending_requests_[global_id] = request;

#006 ??? if (mixed_content) {

#007 ????? // We don't start the request in that case. ? The SSLManager will potentially

#008 ????? // change the request (potentially to indicate its content should be

#009 ????? // filtered) and start it itself.

#010 ????? SSLManager::OnMixedContentRequest(this, request, ui_loop_);

#011 ????? return;

#012 ??? }

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這里開(kāi)始處理請(qǐng)求。

#013 ??? request->Start();

#014 ?

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啟動(dòng)上傳狀態(tài)更新定時(shí)器。

#015 ??? // Make sure we have the load state monitor running

#016 ??? if (!update_load_states_timer_.IsRunning()) {

#017 ????? update_load_states_timer_.Start(

#018 ????????? TimeDelta::FromMilliseconds(kUpdateLoadStatesIntervalMsec),

#019 ????????? this, &ResourceDispatcherHost::UpdateLoadStates);

#020 ??? }

#021 ? }

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通過(guò)上面的函數(shù)可以看到主要調(diào)用 URLRequest::Start() 來(lái)處理下載的請(qǐng)求，它的代碼如下：

#001 ? void URLRequest::Start() {

#002 ??? DCHECK(!is_pending_);

#003 ??? DCHECK(!job_);

#004 ?

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創(chuàng)建一個(gè)下載的工作任務(wù)。

#005 ??? job_ = GetJobManager()->CreateJob(this);

#006 ??? job_->SetExtraRequestHeaders(extra_request_headers_);

#007 ?

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判斷是否有數(shù)據(jù)需要上傳。

#008 ??? if (upload_.get())

#009 ????? job_->SetUpload(upload_.get());

#010 ?

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設(shè)置請(qǐng)下開(kāi)始下載的時(shí)間，以便后面檢查超時(shí)的狀態(tài)。

#011 ??? is_pending_ = true;

#012 ??? response_info_.request_time = Time::Now();

#013 ?

#014 ??? // Don't allow errors to be sent from within Start().

#015 ??? // TODO(brettw) this may cause NotifyDone to be sent synchronously,

#016 ??? // we probably don't want this: they should be sent asynchronously so

#017 ??? // the caller does not get reentered.

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這里把工作任務(wù)啟動(dòng)運(yùn)行。

#018 ??? job_->Start();

#019 ? }

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由于這里是對(duì) URL 的 HTTP 請(qǐng)求下載數(shù)據(jù)，所以這里的 job_ 是類(lèi) URLRequestHttpJob 的實(shí)例，也就是調(diào)用函數(shù) URLRequestHttpJob::Start() ，在函數(shù) URLRequestHttpJob::Start() 的處理過(guò)程序如下：

1. ?????? URLRequestHttpJob::StartTransaction()

2. ?????? net::HttpCache::Transaction::Start

3. ?????? net::HttpCache::Transaction::BeginNetworkRequest()

4. ?????? net::HttpTransactionWinHttp::Start

5. ?????? net::HttpTransactionWinHttp::DidResolveProxy()

6. ?????? net::HttpTransactionWinHttp::OpenRequest

7. ?????? net::HttpTransactionWinHttp::SendRequest()

8. ?????? net::WinHttpRequestThrottle::SubmitRequest

9. ?????? net::WinHttpRequestThrottle::SendRequest

通過(guò)上面 9 個(gè)函數(shù)的調(diào)用處理，然后就會(huì)通過(guò) Windows 的 HTTP API 進(jìn)行發(fā)送請(qǐng)求和下載數(shù)據(jù)。我們來(lái)分析一下最后的函數(shù) WinHttpRequestThrottle::SendRequest ，看看怎么樣調(diào)用 Windows HTTP API 函數(shù)來(lái)獲取數(shù)據(jù)的，它的代碼如下：

#001 ? BOOL WinHttpRequestThrottle::SendRequest(HINTERNET request_handle,

#002 ?????????????????????????????????????????? DWORD total_size,

#003 ?????????????????????????????????????????? DWORD_PTR context,

#004 ?????????????????????????????????????????? bool report_async_error) {

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下面就是調(diào)用 Windows 的 API 函數(shù) WinHttpSendRequest 來(lái)發(fā)送請(qǐng)求，當(dāng)然在調(diào)用這個(gè)函數(shù)之前，需要調(diào)用函數(shù) WinHttpOpenRequest 先打開(kāi)一個(gè) TCP 連接。

#005 ??? BOOL ok = WinHttpSendRequest(request_handle,

#006 ???????????????????????????????? WINHTTP_NO_ADDITIONAL_HEADERS,

#007 ???????????????????????????????? 0,

#008 ???????????????????????????????? WINHTTP_NO_REQUEST_DATA,

#009 ???????????????????????????????? 0,

#010 ???????????????????????????????? total_size,

#011 ???????????????????????????????? context);

#012 ??? if (!ok && report_async_error) {

#013 ????? WINHTTP_ASYNC_RESULT async_result = { API_SEND_REQUEST, GetLastError() };

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出錯(cuò)處理，就調(diào)用外面的回調(diào)函數(shù)。

#014 ????? HttpTransactionWinHttp::StatusCallback(

#015 ????????? request_handle, context,

#016 ????????? WINHTTP_CALLBACK_STATUS_REQUEST_ERROR,

#017 ????????? &async_result, sizeof(async_result));

#018 ??? }

#019 ??? return ok;

#020 ? }

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通過(guò)前面一系列的分析學(xué)會(huì) chrome 瀏覽器怎么樣輸入 URL 地址，以及怎么樣進(jìn)行 URL 自動(dòng)完成，然后把 URL 發(fā)送到渲染進(jìn)程去處理，最后渲染進(jìn)程又把資源下載請(qǐng)求發(fā)送到資源下載進(jìn)程里處理，最后資源下載進(jìn)程通過(guò) Windows HTTP API 函數(shù)進(jìn)行 TCP 連接，以及 HTTP 數(shù)據(jù)的上傳和下載。瀏覽器向網(wǎng)站發(fā)送請(qǐng)求的過(guò)程已經(jīng)分析完成了，那么 HTTP API 收到網(wǎng)頁(yè)的數(shù)據(jù)后，又是怎么樣處理的呢？下一次再來(lái)分析這個(gè)問(wèn)題。

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谷歌瀏覽器的源碼分析(27)