How to simulate a Form POST request by using WinInet

This article was previously published under Q165298 On this Page SUMMARY MORE INFORMATION REFERENCES SUMMARY To properly simulate a Form submission using WinInet, you need to send a header that indicates the proper Content-Type. For Forms, the proper Content-Type header is:

Content-Type: application/x-www-form-urlencoded MORE INFORMATION In many cases, the server does not respond appropriately if a Content-Type is not specified. For example, the Active Server Pages component of IIS 3.0 actually checks this header specifically for 'application/x-www-form- urlencoded' before adding form variables to the "Request.Form" object. This MIME/Content-Type indicates that the data of the request is a list of URL- encoded form variables. URL-encoding means that space character (ASCII 32) is encoded as '+', special character such '!' encoded in hexadecimal form as '%21'.

Here is a snippet of code that uses the MFC WinInet classes to simulate a Form POST request:

CString strHeaders = _T("Content-Type: application/x-www-form-urlencoded"); // URL-encoded form variables - // name = "John Doe", userid = "hithere", other = "P&Q" CString strFormData = _T("name=John+Doe&userid=hithere&other=P%26Q"); CInternetSession session; CHttpConnection* pConnection = session.GetHttpConnection(_T("ServerNameHere")); CHttpFile* pFile = pConnection->OpenRequest(CHttpConnection::HTTP_VERB_POST, _T("FormActionHere")); BOOL result = pFile->SendRequest(strHeaders, (LPVOID)(LPCTSTR)strFormData, strFormData.GetLength()); Without MFC, the same code translates to straight SDK calls as follows:

static TCHAR hdrs[] = _T("Content-Type: application/x-www-form-urlencoded"); static TCHAR frmdata[] = _T("name=John+Doe&userid=hithere&other=P%26Q"); static LPSTR accept[2]={"*/*", NULL}; // for clarity, error-checking has been removed HINTERNET hSession = InternetOpen("MyAgent", INTERNET_OPEN_TYPE_PRECONFIG, NULL, NULL, 0); HINTERNET hConnect = InternetConnect(hSession, _T("ServerNameHere"), INTERNET_DEFAULT_HTTP_PORT, NULL, NULL, INTERNET_SERVICE_HTTP, 0, 1); HINTERNET hRequest = HttpOpenRequest(hConnect, "POST", _T("FormActionHere"), NULL, NULL, accept, 0, 1); HttpSendRequest(hRequest, hdrs, strlen(hdrs), frmdata, strlen(frmdata)); // close any valid internet-handles REFERENCES For more information about URL-encoding and the format of a Form POST request, see section 8.2 in RFC 1866.

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