Windows中有一組WinINet函數(http://msdn.microsoft.com/en-us/library/aa385473(v=VS.85).aspx),其中關於向Internet發送/接受請求的函數比較奇怪,尤其是HttpSendRequest函數問題更是詭異,下面是代碼示例(該代碼只是分析出問題,但沒找到原因)
這組測試代碼假設網絡都是正常的.
1. BOOL SendHttpHeaderTest()
2. {
3. BOOL bRet = FALSE;
4. if (ERROR_SUCCESS != ::InternetAttemptConnect(0))
5. return FALSE;
6.
7. if (!::InternetCheckConnection(_T("http://www.baidu.com"), FLAG_ICC_FORCE_CONNECTION, 0))
8. return FALSE;
9.
10. TCHAR szModuleFile[MAX_PATH] = {0};
11. ::GetModuleFileName(::GetInstance(), szModuleFile, MAX_PATH);
12. LPCTSTR lpPath = ::PathFindFileName(szModuleFile);
13. HINTERNET hOpen = ::InternetOpen(lpPath, INTERNET_OPEN_TYPE_PRECONFIG_WITH_NO_AUTOPROXY, NULL, NULL, 0);
14. DWORD dwErr = ::GetLastError();//返回0
15.
16. HINTERNET hConnect = ::InternetConnect(hOpen, _T("www.baidu.com"), INTERNET_DEFAULT_HTTP_PORT, NULL, NULL, INTERNET_SERVICE_HTTP, 0, 0);
17. dwErr = ::GetLastError();//返回0
18.
19. #if 1
20. DWORD dwFlag = INTERNET_FLAG_KEEP_CONNECTION | INTERNET_FLAG_NO_AUTO_REDIRECT | INTERNET_FLAG_NO_CACHE_WRITE | INTERNET_FLAG_NO_COOKIES;
21. HINTERNET hOpenRequest = ::HttpOpenRequest(hConnect, _T("GET"), _T("img/baidu_sylogo1.gif"), _T("HTTP/1.1"), _T("http://www.baidu.com/"), NULL, dwFlag, 0);
22. dwErr = ::GetLastError();//返回122
23.
24.
25. bRet = ::HttpSendRequest(hOpenRequest, NULL, 0, NULL, 0);
26. dwErr = ::GetLastError();//返回0
27. #endif
28.
29. TCHAR szBuff[BUFF_LEN_1024] = {0};
30. DWORD dwBuffSize = BUFF_LEN_1024;
31. bRet = ::HttpQueryInfo(hOpenRequest, HTTP_QUERY_STATUS_CODE, (LPVOID)szBuff, &dwBuffSize, NULL);
32. dwErr = ::GetLastError();//返回0
33.
34. //Reference to http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
35. int nStatusCode = _tstoi(szBuff);// 值為200,證明請求數據baidu_sylogo1.gif是成功的.
36. if (nStatusCode<200 || 206<nStatusCode)
37. bRet = FALSE;
38.
39. bRet = TRUE;
40. ::InternetCloseHandle(hConnect);
41.
42. ::InternetCloseHandle(hOpen);
43.
44. return bRet;
45. }
#if 1 ... #endif HttpOpenRequest說明要向www.baidu.com請求baidu_sylogo1.gif,但這個函數是不會向www.baidu.com發送任何數據的,只有調用HttpSendRequest時才會發送這個請求.
HttpOpenRequest函數的返回值很有意思,可以看到它的返回值是有效的,證明對該函數的調用是成功的,但問題dwErr返回值是122,它的含義是ERROR_INSUFFICIENT_BUFFER: The data area passed to a system call is too small,但不知道什麼意思,也不知到如何才能使dwErr成為0.
根據msdn中的描述,這段代碼可以用下面一段代碼替換:
1. #if 2
2. HINTERNET hOpenRequest = ::HttpOpenRequest(hConnect, NULL, NULL, NULL, NULL, NULL, dwFlag, 0);
3. dwErr = ::GetLastError();//仍然返回122
4.
5. LPCTSTR lpHeader =
6. _T("GET /img/baidu_sylogo1.gif /HTTP/1.1")//A line
7. _T("Referer: http://www.baidu.com/\r\n") //B line
8. _T("Host: www.baidu.com") //C line
9. _T("\r\n\r\n"); //D line
10.
11. bRet = ::HttpSendRequest(hOpenRequest, NULL, 0, NULL, 0);
12. dwErr = ::GetLastError();//返回0
13. #endif
14. // 注意觀察lpHeaer的值,有如下幾個特點:1)它的結尾D行有兩個"\r\n\r\n";2)A行結尾沒有\r\n;3)B行結尾有\r\n;4)C行結尾沒有\r\n.
15. // 下面測試一下這4個特點究竟哪個會對HttpSendRequest的調用產生影響.
16. Test1: // A行結尾有\r\n
17. LPCTSTR lpHeader = _T("GET /img/baidu_sylogo1.gif /HTTP/1.1\r\n")_T("Referer: http://www.baidu.com/")_T("Host: www.baidu.com")_T("\r\n\r\n");
18. // HttpSendRequest返回0, dwErr = 12150, 含義ERROR_HTTP_HEADER_NOT_FOUND:The requested header could not be located.
19. Test2: // A/B/C行結尾沒有\r\n
20. LPCTSTR lpHeader = _T("GET /img/baidu_sylogo1.gif /HTTP/1.1")_T("Referer: http://www.baidu.com/")_T("Host: www.baidu.com")_T("\r\n\r\n");
21. // HttpSendRequest返回1, dwErr = 0
22. Test3: // D行結尾一個\r\n
23. LPCTSTR lpHeader = _T("GET /img/baidu_sylogo1.gif /HTTP/1.1")_T("Referer: http://www.baidu.com/")_T("Host: www.baidu.com")_T("\r\n");
24. // HttpSendRequest返回1, dwErr = 0
25. Test4: // D行結尾沒有\r\n
26. LPCTSTR lpHeader = _T("GET /img/baidu_sylogo1.gif /HTTP/1.1")_T("Referer: http://www.baidu.com/")_T("Host: www.baidu.com");
27. // HttpSendRequest返回1, dwErr = 0
從以上4個測試可以看出,HttpSendRequest的第二個參數header是一個字符串,A行必須不能有\r\n,其它行可以有,也可以沒有.
在測試中還發現,僅僅只有A行會導致HttpSendRequest調用失敗,必須得有B行.
其實lpHeader的值A行剛好對應HttpOpenRequest的參數lpszVerb,lpszObjectName和lpszVersion;B行對應參數lpszReferer.所以,#if 2...endif 還可以用下面的代碼代替:
1. #if 3
2. hOpenRequestHandle = ::HttpOpenRequest(hConnectHandle, NULL, NULL, NULL, NULL, NULL, dwFlag, dwContext);
3. LPCTSTR lpHeader = _T("GET /img/baidu_sylogo1.gif /HTTP/1.1")_T("Referer: http://www.baidu.com/");
4. DWORD dwLen = _tcslen(lpHeader);
5. bRet = ::HttpAddRequestHeaders(hOpenRequestHandle, lpHeader, nLen, HTTP_ADDREQ_FLAG_REPLACE|HTTP_ADDREQ_FLAG_ADD);//返回1
6. bRet = ::HttpSendRequest(hOpenRequestHandle, NULL, 0, NULL, 0);//返回1
7. #endif
以上這些測試都是在VS2008系統中測試出來的,如果有誰發現HttpSendRequest發送的HTTP頭結構文檔及其它特點,還請告訴我,不勝感激
