ISAPI Filter Code

This is a discussion on ISAPI Filter Code within the C++ Programming forums, part of the General Programming Boards category; I know very little about C++ but I'm trying to tackle something for work and need some help... I'm using ...

  1. #1
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    ISAPI Filter Code

    I know very little about C++ but I'm trying to tackle something for work and need some help...

    I'm using this C++ ISAPI filter code to add a message to the top of a page on a IIS web server running ASP and CFML. This is a web server that will be going away and need a way to notify the users without modifying tons of pages.

    This code works for the most part, however it only displays this message if the page is large (or maybe it's intermittent, but I thought it was only doing it on large pages). I understand the code is compressing a bit (eliminating sending pieces of the page in smaller sections). However, I can't figure out why it doesn't get added when the page is small.

    Here's a link to the code: http://examples.oreilly.com/97807356...ifier/main.cpp

    The code isn't very long and I think it would take a seasoned C++ developer about a minute to tell me what is going wrong and what I can try to do to fix it.

  2. #2
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    view-source:http://examples.oreilly.com/9780735621695/cd_contents/sdk/samples/WebFilters/webresponsemodifier/main.cpp

    Code:
    /*++
    
       Copyright (c) 2000 Microsoft Corporation.  All rights reserved.
    
    --*/
    
    /*
     *
     *  This filter is a flavor of the filter IIS uses for compression.
     * (Original filter written by David Treadwell on July 1997.)
     *
     * ISA and IIS let you accumulate Requests chunks into a complete
     * Request.
     * The following filter is an example to a filter that collects the
     * response chunks and then allows you to change them depending on the
     * complete response.
    
     * This filter works with 2 notifications.
     * In Send Raw Data it collects the response's chunks, sends 0 bytes
     * instead of them (i.e. sends nothing).
    
     * Then, when all the chunks of this response passed Send Raw Data
     * notification, ISA thinks the complete response was sent. So
     * it calls End Of Request Notification. End Of Request Notification
     * will be the place where we will send the complete response.
     *
     */
    
    
    #include <windows.h>
    #include <httpfilt.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <errno.h>
    
    const char LINE_TO_INSERT[] = "<h3>Brought to you by an ISA Web Filter</h3>\r\n";
    const char CONTENT_LENGTH[] = "Content-Length:";
    
    static DWORD OnSendRawData(PHTTP_FILTER_CONTEXT pfc, PHTTP_FILTER_RAW_DATA pRawData);
    static DWORD OnEndOfRequest(PHTTP_FILTER_CONTEXT pfc);
    static void DisableNotifications(PHTTP_FILTER_CONTEXT pfc, DWORD   flags);
    static int strnstr(const char *string, const char *strCharSet , int n);
    static bool InsertOurHTMLHeader(PHTTP_FILTER_CONTEXT pfc,LPBYTE *ppBuffer,LPDWORD lpdwLen);
    static DWORD dwfnContentLen(LPSTR ContentLenLine,int iLineLen);
    
    
    BOOL WINAPI TerminateFilter ( DWORD dwFlags )
    {
        UNREFERENCED_PARAMETER(dwFlags);
        return TRUE;
    }
    
    
    BOOL WINAPI GetFilterVersion ( PHTTP_FILTER_VERSION pVer )
    {
        if (pVer == NULL) 
        {
            SetLastError( ERROR_INVALID_PARAMETER); 
            return FALSE;
        }
        
        pVer->dwFilterVersion = HTTP_FILTER_REVISION;
    
        pVer->dwFlags =  SF_NOTIFY_ORDER_HIGH | SF_NOTIFY_SECURE_PORT | SF_NOTIFY_NONSECURE_PORT
                        | SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA ;
    
        return TRUE;
    }
    
    
    DWORD WINAPI HttpFilterProc (
        PHTTP_FILTER_CONTEXT pfc,
        DWORD NotificationType,
        LPVOID pvNotification
    )
    {
    
        DWORD dwRet = SF_STATUS_REQ_NEXT_NOTIFICATION;
    
        switch (NotificationType)
        {
            case SF_NOTIFY_SEND_RAW_DATA:
                dwRet = OnSendRawData(pfc, (PHTTP_FILTER_RAW_DATA)pvNotification);
                break;
            case SF_NOTIFY_END_OF_REQUEST:
                dwRet = OnEndOfRequest(pfc);
                break;
            default:
                // We cannot reach here, unless Web Filter support has a BAD ERROR.
                SetLastError( ERROR_INVALID_PARAMETER); 
                dwRet = SF_STATUS_REQ_ERROR;
                break;
        }
    
        return dwRet;
    }
    
    /*
     * OnSendRawData():
     * During Send Raw Data Notification we do the following:
     * 1) Append each chunk to an accumulation buffer (pRawData->cvInData).
     * 2) Resize the Current chunk to 0 ( don't send anything.)
     */
    static DWORD OnSendRawData ( PHTTP_FILTER_CONTEXT pfc, PHTTP_FILTER_RAW_DATA pInRawData )
    {
    
        if ( NULL == pfc || NULL == pInRawData)
        {
            SetLastError( ERROR_INVALID_PARAMETER); 
            return SF_STATUS_REQ_ERROR;
        }
      
        /*
         * Called first time for this request - then allocate pRawData.
         */
        DWORD dwReserved = 0;
    
        if ( NULL == pfc->pFilterContext )
        {
            pfc->pFilterContext = (LPVOID)pfc->AllocMem( pfc, sizeof(HTTP_FILTER_RAW_DATA), dwReserved);
            if ( NULL == pfc->pFilterContext )
            {
                DisableNotifications( pfc, SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA);
                SetLastError( ERROR_NOT_ENOUGH_MEMORY );
                return SF_STATUS_REQ_ERROR;
            }
    
            PHTTP_FILTER_RAW_DATA pRawData = (PHTTP_FILTER_RAW_DATA)pfc->pFilterContext;
    
            pRawData->cbInBuffer = pInRawData->cbInBuffer;
            pRawData->pvInData = (LPVOID)pfc->AllocMem( pfc, pRawData->cbInBuffer, dwReserved);
            if ( NULL == pRawData->pvInData )
            {
                DisableNotifications(pfc,SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA);
                SetLastError( ERROR_NOT_ENOUGH_MEMORY );
                return SF_STATUS_REQ_ERROR;
            }
    
            pRawData->cbInData = 0;
            pRawData->dwReserved = pInRawData->dwReserved ;
        }
    
    
        /*
         * Get the pRawData from the Request Context.
         */
        PHTTP_FILTER_RAW_DATA pRawData = (PHTTP_FILTER_RAW_DATA)pfc->pFilterContext;
    
        /*
         * If Not enough buffer in pRawData -> increase buffer.
         */
        if ( pInRawData->cbInData + pRawData->cbInData > pRawData->cbInBuffer)
        {
            pRawData->cbInBuffer = pInRawData->cbInData + pRawData->cbInBuffer ;
            LPBYTE lpBuffer = (LPBYTE)pfc->AllocMem(pfc,pRawData->cbInBuffer, dwReserved);
            if ( NULL == lpBuffer )
            {
                DisableNotifications(pfc,SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA);
                SetLastError( ERROR_NOT_ENOUGH_MEMORY );
                return SF_STATUS_REQ_ERROR;
            }
    
            memcpy((LPVOID)lpBuffer, pRawData->pvInData, pRawData->cbInData);
            pRawData->pvInData = (void *)lpBuffer;
        }
    
        /*
         * Append InRawData ( new chunk )  to accumulation buffer.
         */
        LPBYTE lpBuffer = (LPBYTE)pRawData->pvInData;
        memcpy((LPVOID)(&lpBuffer[pRawData->cbInData]), pInRawData->pvInData, pInRawData->cbInData);
        pRawData->cbInData = pRawData->cbInData + pInRawData->cbInData;
    
        /*
         * Mark current chunk as size 0 ( i.e. Don't send enything. )
         */
        pInRawData->cbInData = 0;
    
    
        return SF_STATUS_REQ_NEXT_NOTIFICATION;
    }
    
    
    
    /*
     * OnEndOfRequest():
     * During End Of Request Notification we:
     * 1) Get the complete response from the filter Request Specific Data.
     * 2) May manipulate that response.
     * 3) Send that response.
     */
    static DWORD OnEndOfRequest ( PHTTP_FILTER_CONTEXT pfc )
    {
    
        if ( NULL == pfc)
        {
            SetLastError( ERROR_INVALID_PARAMETER); 
            return SF_STATUS_REQ_ERROR;
        }
      
        /*
         * Block the following SEND_RESPONSE and END_OF_REQUEST notifications for
         * this request. ( WriteClient() bellow will generate them.)
         *
         */
        DisableNotifications( pfc, SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA);
    
    
        /*
         * OK all data was accumulated. Now extract from Request Data
         * the response buffer. (which now contains the complete response).
         */
        PHTTP_FILTER_RAW_DATA pRawData = (PHTTP_FILTER_RAW_DATA)pfc->pFilterContext;
        if ( NULL == pRawData)
        {
            return SF_STATUS_REQ_NEXT_NOTIFICATION;
        }
    
        LPBYTE lpBuffer = (LPBYTE)pRawData->pvInData;
        DWORD bytesToSend = pRawData->cbInData;
        /*
         * Empty Request data to make it ready for next response
         * in case the connection is kept alive
         */
        pfc->pFilterContext = NULL;
    
        /*
         * Add here code to modify the response. It is now the complete response.
         * any decisions and changes that demand the complete Response in hand
         * should be done here.
         */
         if (!InsertOurHTMLHeader( pfc, &lpBuffer, &bytesToSend))
         {
            SetLastError( ERROR_NOT_ENOUGH_MEMORY );
            return SF_STATUS_REQ_ERROR;
         }
    
    
        /*
         * Send the complete response in one chunk.
         */
        DWORD dwReserved = 0 ;
        if ( pfc->WriteClient(pfc,(LPVOID)lpBuffer,&bytesToSend,dwReserved) )
        {
            return SF_STATUS_REQ_NEXT_NOTIFICATION;
        }
        else
        {
            return SF_STATUS_REQ_ERROR;
        }
    
    
    }
    
    
    #define STRING_SIZE(str)    (sizeof(str) - 1)
    /*
     *
     * InsertOurHTMLHeader()
     * Given the full response chunk, test if the response is in HTML format (has
     * <HTML>...</HTML> in it). If so, insert an HTML header line into the response
     * HTML. To do that we look at the input HTML as made of 3 chunks:
     * Chunk1 from start till "Content-Length: ..." header ( if exist.)
     * Chunk2 from "\r\n" after "Content-Length:" header untill last character of
     * "<HTML>".
     * Chunk3 from first character after "<HTML>" till the end of the response.
     * We then calculate the new Content-Length value by adding the length of the
     * line we will insert to the original content length, and finally allocate a new
     * buffer and paste into it the chunks in the following order:
     * Chunk1, Updateded-Content-Length-Header, Chunk2, Line-we-wish-to-insert, chunk3.
     *
     */
    static bool InsertOurHTMLHeader ( PHTTP_FILTER_CONTEXT pfc, LPBYTE *ppBuffer, LPDWORD lpdwLen )
    {
        LPSTR lpBuffer = (LPSTR)*ppBuffer;
        DWORD dwLen = *lpdwLen;
        bool bStatus = true;
    
        if ( 0 < strnstr( lpBuffer, "<HTML>", dwLen)  &&
            0 < strnstr( lpBuffer, "</HTML>", dwLen) )
        {
            /*
             *
             * Find first chunk. If no Content-Length header then first chunk will be
             * zero sized.
             *
             */
            int iStartChunk1 = 0;
            int iEndChunk1 = strnstr( lpBuffer, CONTENT_LENGTH, dwLen);
            if ( 0 >= iEndChunk1 )
                iEndChunk1 = 0;
    
    
            int iTmp = 0;
    
            if ( 0 < iEndChunk1 )
            {
                /*
                 *
                 * If we are here then there is a Content-Length header, so we
                 * find the first "\r\n" after the the Content-Length header.
                 *
                 */
                iTmp = strnstr( lpBuffer + iEndChunk1, "\r\n" , dwLen - iEndChunk1);
                if ( 0 >= iTmp ) 
                    goto ReturnBuffer;
            }
    
            /*
             *
             * Find the second chunk. It starts on the "\r\n" after the Content-Length
             * Header, and ends after the first "<HTML>".
             *
             */
            int iStartChunk2 = iEndChunk1 + iTmp;
            iTmp = strnstr( lpBuffer + iStartChunk2, "<HTML>", dwLen - iStartChunk2);
            if ( 0 >= iTmp ) 
                goto ReturnBuffer;
            int iEndChunk2 = iStartChunk2 + iTmp + STRING_SIZE("<HTML>");
    
            /*
             *
             * The third and last chunk starts after the first "<HTML>" and goes till
             * the end of the input response.
             *
             */
            int iStartChunk3 = iEndChunk2;
            int iEndChunk3 = (int)dwLen;
    
    
            char szContentLen[100];
            if ( 0 < iEndChunk1 )
            {
                /*
                 *
                 * If there is Content-Length Header then find the Input Content Length,
                 * and add to it the length of the inserted line.
                 *
                 */
                DWORD dwContentLen =
                    dwfnContentLen( lpBuffer + iEndChunk1, iStartChunk2 - iEndChunk1) +
                    STRING_SIZE(LINE_TO_INSERT);
                char *p = (char *) memcpy( szContentLen, CONTENT_LENGTH, STRING_SIZE(CONTENT_LENGTH)) + 
                    STRING_SIZE(CONTENT_LENGTH);
                *p++ = ' ';
                _ultoa( dwContentLen, p, 10);
            }
            else
            {
                szContentLen[0] = 0;
            }
    
            /*
             *
             * Allocate a buffer for the new response.
             *
             */
            iTmp = iEndChunk1 - iStartChunk1 + strlen(szContentLen) + iEndChunk2 - iStartChunk2 +
                   STRING_SIZE(LINE_TO_INSERT) + iEndChunk3 - iStartChunk3 + 1;
            DWORD dwReserved = 0;
            LPSTR lpNewBuffer = (LPSTR)pfc->AllocMem(pfc,iTmp, dwReserved);
            if ( !lpNewBuffer )
            {
                bStatus = false;
                goto ReturnBuffer;
            }
    
    #define MEMCAT(lpTarget,lpSource,SourceLen,TargetLen) \
            memcpy(lpTarget,lpSource,SourceLen); TargetLen += SourceLen;
    
    
            DWORD dwNewLen = 0;
    
            MEMCAT( lpNewBuffer + dwNewLen, lpBuffer + iStartChunk1, iEndChunk1 - iStartChunk1, dwNewLen);
    
            MEMCAT( lpNewBuffer + dwNewLen, szContentLen, strlen(szContentLen), dwNewLen);
    
            MEMCAT( lpNewBuffer + dwNewLen, lpBuffer + iStartChunk2, iEndChunk2 - iStartChunk2, dwNewLen);
    
            MEMCAT( lpNewBuffer + dwNewLen, LINE_TO_INSERT, strlen(LINE_TO_INSERT), dwNewLen);
    
            MEMCAT( lpNewBuffer + dwNewLen, lpBuffer + iStartChunk3, iEndChunk3 - iStartChunk3, dwNewLen);
    
    
            /*
             * We don't have to do that, but making it a string is good for debugging
             */
            lpNewBuffer[dwNewLen] = 0;
    
            lpBuffer = lpNewBuffer;
            dwLen = dwNewLen;
        }
    
    ReturnBuffer:
        *ppBuffer = (LPBYTE)lpBuffer;
        *lpdwLen = dwLen;
        return bStatus;
    }
    
    /*
     *
     * Extract the input Content-Length value.
     *
     */
    static ULONG dwfnContentLen(LPSTR ContentLenLine, int iLineLen)
    {
        int iColumn = strnstr(ContentLenLine,":",iLineLen) + strlen(":");
        char *s = new char[iLineLen - iColumn + 1];
        if (!s)
            return 0;
        strncpy(s, &ContentLenLine[iColumn],iLineLen - iColumn);
        s[iLineLen - iColumn] = 0;
        LPSTR stopstring;
        DWORD dwCL =  strtoul( s, &stopstring, 10 );       
        if (errno == ERANGE) // overflow
        {
            delete [] s;     
            return 0;
        }
    
        delete [] s;
        return dwCL;
    }
    
    /*
     *
     * Utility function to notify that a filter is not to be called
     * to a notification throughout the lifetime of the current Request.
     *
     */
    static void DisableNotifications ( PHTTP_FILTER_CONTEXT pfc, DWORD   flags )
    {
        pfc->ServerSupportFunction(
                          pfc,
                          SF_REQ_DISABLE_NOTIFICATIONS,
                          NULL,
                          flags,
                          0
                          );
    }
    
    /*
     * strnstr()
     * finds first appearance of strCharSet in string ignoring
     * letters case.
     */
    static int strnstr ( const char *string, const char *strCharSet , int n)
    {
        int len = (strCharSet  != NULL ) ? ((int)strlen(strCharSet )) : 0 ;
    
        if ( 0 == n || 0 == len )
        {
            return -1;
        }
    
        int ret = -1;
        BOOLEAN found = FALSE;
        for (int I = 0 ; I <= n - len && !(found) ; I++)
        {
            int J = 0 ;
            for ( ; J < len ; J++ )
            {
                if (toupper(string[I + J]) != toupper(strCharSet [J]))
                {
                    break; // Exit For(J)
                }
            }
    
            if ( J == len)
            {
                found = TRUE;
                ret = I;
            }
        }
    
        return ret;
    }

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