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Discover ISAPI. Working with GET-POST data

, 15 Jul 2002
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That article present a way to retrieve the GET-POST data from a form into an ISAPI extension.
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Introduction

This article presents a way to retrieve the GET-POST data from a form in an ISAPI extension. Two helpful collections class 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 included.

Functionality

Both 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 are based on _bstr_t type. In Non MFC version the string collection are based on 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 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

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 easy, 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";
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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";
}
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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:

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The LoadLongResource private function is a little modified compared with the MFC version. The input/output str string parameter is of STL string type. In the szPath char variable we must put the name of the DLL file in order 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;
}

History

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

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

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About the Author

Adrian Bacaianu
Web Developer
Romania Romania
I make programming for over 4 years and extensive experience in C++, ASP, Pascal, MFC, COM+, ATL, TCP/IP, HTTP protocols, XML, XSL, SOAP and SQL.
For the last 2 years i working extensively at the background of financial sites (databases, n tier architecture).
 
I’m available for contracts and/or outsourcing (adrian_bacaianu@yahoo.com).

Comments and Discussions

 
GeneralMy vote of 5 Pinmembermanoj kumar choubey28-Feb-12 19:54 
GeneralEnBSTR.h PinmemberHughJampton12-Oct-05 1:53 
GeneralHTTP OK header missing PinmemberKrotow8-Sep-04 13:05 
GeneralRe: HTTP OK header missing PinmemberAdrian Bacaianu8-Sep-04 21:21 
GeneralVery Nice! PinsussAnonymous14-Jul-02 14:31 
It's a very nice article, i finnaly find how to receive POST data in ISAPI!!!

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