How to simulate a Form POST request by using WinInet
This article was previously published under Q165298
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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
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.