HOWTO: Simulate a Form POST Request Using WinInet

• The Microsoft Foundation Classes (MFC) included with: - Microsoft Visual C++, 32-bit Editions, versions 4.2, 5.0
• Microsoft Internet Client SDK, versions 4.0, 4.01

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 hexadecemal 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());

   static TCHAR hdrs[] =
      _T("Content-Type: application/x-www-form-urlencoded");
   static TCHAR frmdata[] =
      _T("name=John+Doe&userid=hithere&other=P%26Q");
   statuc TCHAR accept[] =
      _T("Accept: */*");

   // 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 on URL-encoding and the format of a Form POST request, see section 8.2 in RFC 1866.

Keywords          : AXSDKWinInet MfcMisc kbprg
Technology        : kbMfc
Version           : winnt:1.0 4.2 5.0
Platform          : NT WINDOWS
Issue type        : kbhowto