Article ID: 165298 - Last Review: September 20, 2004 - Revision: 2.0

How to simulate a Form POST request by using WinInet

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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
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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
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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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APPLIES TO
  • Microsoft Foundation Class Library 4.2, when used with:
    • Microsoft Visual C++ 4.2 Enterprise Edition
    • Microsoft Visual C++ 4.2 Professional Edition
    • Microsoft Visual C++ 5.0 Enterprise Edition
    • Microsoft Visual C++ 5.0 Professional Edition
    • Microsoft Internet Explorer 4.0 128-Bit Edition
    • Microsoft Internet Explorer 4.01 Service Pack 2
  • Microsoft Windows Internet Services (WinInet)
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Keywords: 
kbhowto kbprogramming KB165298
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Retired KB ArticleRetired KB Content Disclaimer
This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
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