?

上一次說到通過 WinHTTP 來接收網絡數據，但沒有具體介紹怎么樣接收，現在就來分析這方面的代碼。首先是通過函數 WinHttpQueryHeaders 來查詢 HTTP 協議頭的大小，接著還是通過函數 WinHttpQueryHeaders 把數據接收到緩沖區里。下面這段代碼，就是做這樣的事情：

#001 ? int HttpTransactionWinHttp::DidReceiveHeaders() {

#002 ??? session_callback_->set_load_state(LOAD_STATE_IDLE);

#003 ?

?

第一次調用函數 WinHttpQueryHeaders 查看接收到協議頭的大小。

#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 ?

?

第二次調用函數 WinHttpQueryHeaders 來接收協議頭的數據。

#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 ?

?

設置回應的一些狀態。

#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 ? }

?

通過上面的函數處理，就可以收到 HTTP 協議頭的數據，這樣就可以進一步處理了。那么接著下來就是收到 HTTP 協議里的數據，這個主要通過下面的函數來接收到的，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 ? }

上面通過判斷可以接收到多少字節，然后通過函數 WinHttpReadData 把數據保存到緩沖區 read_buf_ 里，在這個緩沖區里保存了所有網絡接收到的數據，那么這些數據又將要流向何方呢？下一次再來分析這個問題。

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