Windows中有一组WinINet函数(http://msdn.microsoft.com/en-us/library/aa385473(v=VS.85).aspx),其中关于向Internet发送/接受请求的函数比较奇怪,尤其是HttpSendRequest函数问题更是诡异,下面是代码示例(该代码只是分析出问题,但没找到原因)
这组测试代码假设网络都是正常的.
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);// 值为200,证明请求数据baidu_sylogo1.gif是成功的.
36. if (nStatusCode<200 || 206
37. bRet = FALSE;
38.
39. bRet = TRUE;
40. ::InternetCloseHandle(hConnect);
41.
42. ::InternetCloseHandle(hOpen);
43.
44. return bRet;
45. }
#if 1 ... #endif HttpOpenRequest说明要向www.baidu.com请求baidu_sylogo1.gif,但这个函数是不会向www.baidu.com发送任何数据的,只有调用HttpSendRequest时才会发送这个请求.
HttpOpenRequest函数的返回值很有意思,可以看到它的返回值是有效的,证明对该函数的调用是成功的,但问题dwErr返回值是122,它的含义是ERROR_INSUFFICIENT_BUFFER: The data area passed to a system call is too small,但不知道什么意思,也不知到如何才能使dwErr成为0.
根据msdn中的描述,这段代码可以用下面一段代码替换:
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. // 注意观察lpHeaer的值,有如下几个特点:1)它的结尾D行有两个"\r\n\r\n";2)A行结尾没有\r\n;3)B行结尾有\r\n;4)C行结尾没有\r\n.
15. // 下面测试一下这4个特点究竟哪个会对HttpSendRequest的调用产生影响.
16. Test1: // A行结尾有\r\n
17.