谷歌浏览器的源码分析 29

Posted 2021-02-12 skiwnchh

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上一次说到通过WinHTTP来接收网络数据，但没有具体介绍怎么样接收，现在就来分析这方面的代码。首先是通过函数WinHttpQueryHeaders来查询HTTP协议头的大小，接着还是通过函数WinHttpQueryHeaders把数据接收到缓冲区里。下面这段代码，就是做这样的事情：<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

#001  int HttpTransactionWinHttp::DidReceiveHeaders() {

 

#002    session_callback_->set_load_state(LOAD_STATE_IDLE);

 

#003 

 

 

 

第一次调用函数WinHttpQueryHeaders查看接收到协议头的大小。

 

#004    DWORD size = 0;

 

#005    if (!WinHttpQueryHeaders(request_handle_,

 

#006                             WINHTTP_QUERY_RAW_HEADERS,

 

#007                             WINHTTP_HEADER_NAME_BY_INDEX,

 

#008                             NULL,

 

#009                             &size,

 

#010                             WINHTTP_NO_HEADER_INDEX)) {

 

#011      DWORD error = GetLastError();

 

#012      if (error != ERROR_INSUFFICIENT_BUFFER) {

 

#013        DLOG(ERROR) << "WinHttpQueryHeaders failed: " << GetLastError();

 

#014        return TranslateLastOSError();

 

#015      }

 

#016      // OK, size should tell us how much to allocate...

 

#017      DCHECK(size > 0);

 

#018    }

 

#019 

 

 

 

第二次调用函数WinHttpQueryHeaders来接收协议头的数据。

 

#020    std::wstring raw_headers;

 

#021 

 

#022    // ‘size‘ is the number of bytes rather than the number of characters.

 

#023    DCHECK(size % 2 == 0);

 

#024    if (!WinHttpQueryHeaders(request_handle_,

 

#025                             WINHTTP_QUERY_RAW_HEADERS,

 

#026                             WINHTTP_HEADER_NAME_BY_INDEX,

 

#027                             WriteInto(&raw_headers, size/2 + 1),

 

#028                             &size,

 

#029                             WINHTTP_NO_HEADER_INDEX)) {

 

#030      DLOG(ERROR) << "WinHttpQueryHeaders failed: " << GetLastError();

 

#031      return TranslateLastOSError();

 

#032    }

 

#033 

 

 

 

设置回应的一些状态。

 

#034    response_.response_time = Time::Now();

 

#035 

 

#036    // From experimentation, it appears that WinHttp translates non-ASCII bytes

 

#037    // found in the response headers to UTF-16 assuming that they are encoded

 

#038    // using the default system charset.  We attempt to undo that here.

 

#039    response_.headers =

 

#040        new HttpResponseHeaders(base::SysWideToNativeMB(raw_headers));

 

#041 

 

#042    // WinHTTP truncates a response longer than 2GB.  Perhaps it stores the

 

#043    // response‘s content length in a signed 32-bit integer.  We fail rather

 

#044    // than reading a truncated response.

 

#045    if (response_.headers->GetContentLength() > 0x80000000)

 

#046      return ERR_FILE_TOO_BIG;

 

#047 

 

#048    response_.vary_data.Init(*request_, *response_.headers);

 

#049    PopulateAuthChallenge();

 

#050 

 

#051    // Unfortunately, WinHttp does not close the connection when a non-keepalive

 

#052    // response is _not_ followed by the server closing the connection.  So, we

 

#053    // attempt to hack around this bug.

 

#054    if (!response_.headers->IsKeepAlive())

 

#055      content_length_remaining_ = response_.headers->GetContentLength();

 

#056 

 

#057    return OK;

 

#058  }

 

 

 

通过上面的函数处理，就可以收到HTTP协议头的数据，这样就可以进一步处理了。那么接着下来就是收到HTTP协议里的数据，这个主要通过下面的函数来接收到的，如下：

 

#001  BOOL HttpTransactionWinHttp::SessionCallback::ReadData(

 

#002      HINTERNET request_handle) {

 

#003    DCHECK(bytes_available_ >= 0);

 

#004    char* buf = read_buf_;

 

#005    read_buf_ = NULL;

 

#006    int bytes_to_read = std::min(bytes_available_, read_buf_len_);

 

#007    read_buf_len_ = 0;

 

#008    if (!bytes_to_read)

 

#009      bytes_to_read = 1;

 

#010 

 

#011    // Because of how WinHTTP fills memory when used asynchronously, Purify isn‘t

 

#012    // able to detect that it‘s been initialized, so it scans for 0xcd in the

 

#013    // buffer and reports UMRs (uninitialized memory reads) for those individual

 

#014    // bytes. We override that to avoid the false error reports.

 

#015    // See http://b/issue?id=1173916.

 

#016    base::MemoryDebug::MarkAsInitialized(buf, bytes_to_read);

 

#017    return WinHttpReadData(request_handle, buf, bytes_to_read, NULL);

 

#018  }

 

上面通过判断可以接收到多少字节，然后通过函数WinHttpReadData把数据保存到缓冲区read_buf_里，在这个缓冲区里保存了所有网络接收到的数据，那么这些数据又将要流向何方呢？下一次再来分析这个问题。

 

再分享一下我老师大神的人工智能教程吧。零基础！通俗易懂！风趣幽默！还带黄段子！希望你也加入到我们人工智能的队伍中来！http://www.captainbed.net