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Environment: ASP.NET, MFC/C++, ISAPI, ISAPI Extensions
Introduction
This article presents a way to retrieve the GET-POST data from a form in an ISAPI extension. Two helpful collections classes of parameters are also provided. Because a non-MFC ISAPI extension is more reliable regarding the speed and the simultaneous number of connections, a non-MFC version is also included.
Functionality
Both the MFC and non-MFC versions use Vector-, Map-, and String STL-based classes, with non-MFC code inside. In the MFC version, the string collection is based on the _bstr_t type. In the non-MFC version, the string collection is based on the STL String type. So, the MFC version is using the ISAPI MFC-based macros to retrieve the server variables and parameters data while the non-MFC version uses the WriteClient
and ServerSupportFunction
HTTP functions.
The default method writes to the browser a complex form with check boxes, edit boxes, radio buttons, text area—even a file type edit box. The idea is to receive all the POST parameters into the same DLL extension. The form is loaded from an HTML string resource using the LoadLongResource
helper function. This reduces the time needed to build the page because the string is loaded into memory on the first call of the extension. How to use the HTML string resources in your Visual Studio project it is show in my ADO Data access from ISAPI article.
The GET data is received very easily because that type of data is sent from the browser to the server using the URL. The POST data variables are transparent to the user and it is possible to transfer large amounts of data. For more information about GET/POST data, see my HTTP GET-POST utility article.
MFC Version
The C++ classes used to store parameters from the data collection are Twin
and TwinVector
. The Default method of the ISAPI MFC version writes to the client browser the IDR_HTML_FORM
resource. FormRequest
is the method that receives the control after you click on the “Submit Query” button.
void CPostDataExtension::FormRequest(CHttpServerContext* pCtxt, void* pVoid, DWORD dwBytes) { //build the STL collection from server variables and POST data TwinVector vecServerCtx(pCtxt, (LPTSTR)pVoid); //write on browser stream the server context variables WriteServerData(pCtxt); //write on browser stream the STL collection of //server context variables and POST data WriteServerVar(pCtxt, vecServerCtx); }
A little problem is to get the control from the DLL entry point to FormRequest
method. Under the MFC, that is done very easily, by using the macros:
DEFAULT_PARSE_COMMAND(FormRequest, CPostDataExtension) ON_PARSE_COMMAND(FormRequest, CPostDataExtension, ITS_RAW)
To correctly know what method will receive the POST data, the MFC wrapper must receive from the HTML form one hidden parameter, which must be in the first place after the FORM HTML tag:
<form action="PostData.dll?" method=post> <input TYPE=hidden NAME="MfcISAPICommand" VALUE="FormRequest">
In the WriteServerVar
helper function, the server context variables collection is written on the HTTP stream. It’s possible to directly obtain the value of a needed parameter:
bstrValue = vecServerCtx.Find(L"Filename"). for (itVec = vecServerCtx.begin(); itVec != vecServerCtx.end(); itVec++) *pCtxt << <itvec->GetName() << " = " <<<itvec-> GetValue() << "br";
In the same WriteServerVar
helper function, the POST data collection is written to the HTTP stream in this way:
bstrToken = L"DATA";
index = vecServerCtx.Find(bstrToken);
if (index > -1)
{
map = vecServerCtx[index].GetValueAsMap();
if (!map.empty()) //we have values
for (itMap = map.begin(); itMap != map.end(); itMap++)
*pCtxt << (*itMap).first << " = "
<< (*itMap).second << "br";
}
It’s possible to directly obtain the value of a needed parameter:
*pCtxt << "Filename = " << map[L"Filename"] << "br".
The TwinVector
class offers the VARIANT GetVariant()
method and TwinVector(VARIANT varSafe)
constructor, to easily transport the collection over a network between COM+ components.
Non-MFC Version
The non-MFC version is based on the MSDN article regarding at GET-POST data in ISAPI extensions.
The C++ extension receives the entry point in the DWORD WINAPI HttpExtensionProc( LPEXTENSION_CONTROL_BLOCK pECB )
method.
Here it launches the Run
method of the CWriteFormExtension class
—there is only one running object in our ISAPI extension.
The C++ classes used to keep the parameters in the data collection are MultipartParser
and MultipartEntry
. The cParser
variable of the inherited Map STL type receives the entire collection of POST data. That is done in the Initialize
method. GetParam
is a helper method that returns the value of a needed parameter.
String CWriteFormExtension::GetParam(MultipartParser& cParser, String sName) { String sValue; //the output string MultipartEntry* pEntry = cParser[sName.c_str()]; if(pEntry != NULL) //we have data { sValue = (LPCTSTR) pEntry->Data(); //get value from collection int nLen = sValue.size(); if(sValue[nLen - 1] == '\n' && sValue[nLen - 2] == '\r') sValue = sValue.substr(0, nLen - 2); } return sValue; }
This is the result of the Run
method:
The LoadLongResource
private function is a little modified, compared with the MFC version. The input/output str
string parameter is of the STL string type. In the szPath
char variable, we must put the name of the DLL file to load the correct resource library.
BOOL CWriteLayoutExtension::LoadLongResource(String &str, UINT nID) { HRSRC hRes; BOOL bResult = FALSE; CHAR szPath[MAX_PATH]; strcpy(szPath, "WriteForm.dll"); HINSTANCE hInst = LoadLibrary(szPath); //if you want standard HTML type hRes = FindResource(hInst, MAKEINTRESOURCE(nID), RT_HTML); if (hRes == NULL) { //trace error str = "Error: Resource could not be found\r\n"; } else { DWORD dwSize = SizeofResource(hInst, hRes); if (dwSize == 0) { str.empty(); bResult = TRUE; } else { HGLOBAL hGlob = LoadResource(hInst, hRes); if (hGlob != NULL) { LPVOID lpData = LockResource(hGlob); if (lpData != NULL) { str = (LPCTSTR)lpData; bResult = TRUE; } FreeResource(hGlob); } } if (!bResult) str = "Error: Resource could not be load\r\n"; } return bResult; }