PRB: Parse Maps Do Not Handle Multi-select List Boxes

ID: Q169109

The information in this article applies to:

The Microsoft Foundation Classes (MFC), included with:
- Microsoft Visual C++, 32-bit Editions, versions 4.1, 4.2, 5.0

SYMPTOMS

MFC ISAPI extension cannot handle a multiple-select list box on a form. The following error message may appear in Internet Explorer 3.0 when multiple items are selected:

BAD REQUEST

Your client sent a request that this server didn't understand.

CAUSE

MFC ISAPI parse maps are not designed to handle multiple-select list boxes.

RESOLUTION

One way of handling multiple selections is to override CallFunction and do the all the parsing in CallFunction without calling the base class. This involves writing the code for parsing the input from the browser.

Another method involves modifying the input to a format that can be handled by the parse maps. The sample code in the MORE INFORMATION section of this article overrides CallFunction and modifies the input in a way that the parse maps can handle.

MORE INFORMATION

If you select multiple items in the list box, the following is sent when you use the HTML in the Sample Code section:


   MFCIsapiCommand=WorksOn&Name=ssm&Days=Monday&Days=Tuesday

The code in CallFunction below modifies the input as follows:


   MFCIsapiCommand=WorksOn&Name=ssm&Days=Monday,Tuesday

In the parse map function, the variable associated with the list box contains a string with all the selected items in the list box, delimited by ','. If a comma is not a good delimiter then change the line:


   #define DELIMITER  ','

and specify a different character. Note that &, ?, =, + have special meanings and should not be used as delimiters.

Sample Code

HTML Form that calls the sample dll:


   <HTML>

   <form action="/scripts/MyIsapi.dll?" method="Post">
   <input type=hidden Name=MFCIsapiCommand Value=WorksOn>
   Name <input name="Name" >
   <p>
   Works on
   <SELECT MULTIPLE NAME="Days">
   <OPTION VALUE="">NONE
   <OPTION>Sunday
   <OPTION>Monday
   <OPTION>Tuesday
   <OPTION>Wednesday
   <OPTION>Thursday
   <OPTION>Friday
   <OPTION>Saturday
   </SELECT>
   <p>
   <input type=submit>
   </form>

   </HTML>

MFC ISAPI PARSE_MAP entries and function for the above:


   ON_PARSE_COMMAND(WorksOn, CMyIsapiExtension, ITS_PSTR ITS_PSTR)
   ON_PARSE_COMMAND_PARAMS("Name=~ Days=~")

   void CFirstISAPIExtension::WorksOn (CHttpServerContext* pCtxt,
       LPCTSTR Name, LPTSTR Days)
   {
       StartContent(pCtxt);
       *pCtxt << Name << " works on the following Days : <p>" << Days;
       EndContent(pCtxt);

   }

The code above generates the error message when more than one day is selected in the list box.

The following override of CallFunction modifies the input so that the parse maps can handle multiple selections:


   #define DELIMITER ","

   int CMyIsapiExtension::CallFunction(CHttpServerContext* pCtxt,
       LPTSTR pszQuery, LPTSTR pszCommand)
   {
       LPTSTR queryIn = pszQuery;
       LPTSTR queryOut = new TCHAR[_tcslen(queryIn) + sizeof(TCHAR)];
       LPTSTR pOut = queryOut;
       *pOut = NULL;

       LPTSTR pIn = queryIn;
       // Copy everything till the first ?
       if (_tcschr(pIn, '?'))
       {
           pIn = _tcschr(pIn, '?');
           pIn++;
           memcpy(pOut, queryIn, (pIn - queryIn)); //copy till the ?
           pOut += (pIn - queryIn);
           *pOut = NULL;
       }

       LPTSTR lastParameter = NULL;
       int nLastParameterLen = 0;

       while (pIn && *pIn)
       {
           // Is there a '=' in the input string
           LPTSTR q = _tcschr(pIn, '=');
           if (!q)
           {
               // No. Copy till end of the buffer and break out
               // No more parameter/value pairs.
               _tcscpy(pOut, pIn);
               break;
           }

           int paramLen = (q - pIn);

           // Is the last parameter name the same as the present
           // parameter name?
           if (paramLen &&
               nLastParameterLen == paramLen &&
               _tcsncmp(lastParameter, pIn, nLastParameterLen) == 0)
           {
               // Yes! replace & with , and just copy the value
               // of the parameter.
               q++;
               if (*q)
               {
                   LPTSTR r = _tcschr(q, '&');
                   *(pOut - 1) = ',';
                   //copy the value
                   if (r)
                   {
                       _tcsncpy(pOut, q, (r - q) + 1);
                       pOut+=(r - q) + 1;
                       pIn = r + 1;
                   }
                   else
                   {
                       _tcscpy(pOut, q);
                       break;
                   }
               }
               else
               {
                   *(pOut - 1) = ',';
                   *pOut = NULL;
                   break;
               }
           }
           else
           {
               nLastParameterLen = paramLen;
               lastParameter = pIn;

               q = _tcschr(pIn, '&');
               if (q)
               {
                   if (paramLen)
                   {
                       _tcsncpy(pOut, pIn, (q - pIn) + 1);
                       pOut += (q - pIn) + 1;
                   }
                   pIn = q + 1;
               }
               else
               {
                   if (paramLen)
                   {
                       _tcscpy(pOut, pIn);
                       break;
                   }
                   else
                   {
                       if (pOut == queryOut)
                           *pOut = NULL;
                       else
                           *(pOut - 1) = NULL;
                       break;
                   }
               }
           }
       }

       pszQuery = queryOut;

       int nRet = CHttpServer::CallFunction(pCtxt,
           pszQuery, pszCommand);

       delete []queryOut;

       return nRet;
   }

The following modification to the WorksOn function prints the days on different lines:


   void CMyIsapiExtension::WorksOn (CHttpServerContext* pCtxt,
       LPCTSTR Name, LPTSTR Days)
   {
       StartContent(pCtxt);
       *pCtxt << Name << " works on the following Days<p>";
       LPTSTR p = (LPTSTR)Days;
       while (p)
       {
           LPCTSTR q = p;
           p = _tcschr(p, ',');
           if (p)
               *p++ = NULL;

           *pCtxt << q << "<p>";
       }

       EndContent(pCtxt);

   }

Additional query words: multiple select listbox list box mfcisapi form

Keywords : kbcode kbprg kbnokeyword kbISAPI kbMFC kbVC
Version : winnt:4.1,4.2,5.0
Platform : winnt
Issue type : kbprb