Discover ISAPI. Working with GET-POST data

• Download ISAPI MFC source files - 34 Kb
• Download ISAPI NonMFC source files - 107 Kb

Introduction

Functionality

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 a 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 easy since 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 amount of data. For more information about GET/POST data see my HTTP GET-POST utility article.

MFC version

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 easy, using the macros:

DEFAULT_PARSE_COMMAND(FormRequest,    CPostDataExtension)
ON_PARSE_COMMAND(FormRequest,        CPostDataExtension, ITS_RAW)

<form action="PostData.dll?" method=post>
<input TYPE=hidden NAME="MfcISAPICommand" VALUE="FormRequest">

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 offer the VARIANT GetVariant() method and TwinVector(VARIANT varSafe) constructor, to easy transport the collection over 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 receive the entry point in the DWORD WINAPI HttpExtensionProc( LPEXTENSION_CONTROL_BLOCK pECB ) method.

Here it launches the Run method of the CWriteFormExtension class - there isonly 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 inherited Map STL type receive the entire collection of POST data. That is done in Initialize method. The GetParam is a helper method who return 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:

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;
}

History

16 July 2002 - updated MFC.zip download (was missing a class)

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