# Connections filtering.

(Appendix 15)

FBB software allows filtering on connection. Filtering is not done by the

    BBS software but by external programs developed by users.

     When the BBS starts, the C_FILTER does not really need to be there.  But at
    the first connect it must exist.  If it does not exist at THAT time, it will
    not be checked again.  So if a C_FILTER is added after that, the BBS must be
    rebooted for the filter to take effect.

     Connection filter may be interactive and allows to incorporate some features
    like dedicated information for predefined callsigns, password filtering,
    etc...

     The C_FILTER program must be found by the PATH of MsDos. Its extension can
    be COM or EXE, and it must be little and fast as multitasking is stopped
    during the activity of this program. If this program is not found, it will
    not be called until the BBS is rebooted.

     The C_FILTER may also be created as a DLL.  Both for WinFBB and DosFBB (!!).
    The filter must be installed in the path (\FBB\BIN) of Dos.

     When receiving the connection, the C_FILTER program (if found) is called
    with some arguments including a level number. This number is incremented each
    time the program is called in the same connection session. The first time the
    level number will be 0.

     The line arguments given to the C_FILTER program are :

    - Callsign (format as F6FBB-8).
    - Level number (0 is the first time, up to 99).
    - Flags of the user (binary number as user's mask of INIT.SRV).
    - New : Flag indicating if the user is unknown in the BBS database.
    - Record number of the user in INF.SYS.
    - New: one more parameter before the optional text. It indicates the
      port where was connected the user.
    - Received data (in one argument).

     The C_FILTER program ends with an exit value. This value is very important
    and tells the BBS what to do :

     Return value (for C_FILTER):
     0 : Connection is accepted
     1 : C_FILTER will called again, level is incremented
     2 : Connection is refused, user is disconnected
     3 : Connection is accepted, but in read-only mode
     4 : Connection is accepted, but messages will be hold.
     100 and up
       : C_FILTER will called again, next level is equal to the return value.

    Example of C_FILTERs.  First C_FILTER.EXE, next C_FILTER.DLL:

    Example C_FILTER.EXE:

    /*
     * C_FILTER.C
     *
     * Connection filter for FBB BBS software. (C) F6FBB 1991.
     *
     */

    #include <stdio.h>

    /*
     * Connexion filter called for each connection.
     * All datas sent to stdout will be sent to the user.
     *
     * Filter is called with some arguments on the command line :
     * C_FILTER CallSign Level Flags New Record ReceivedData....
     *
     * The return value tells the BBS if C_FILTER must be called again or not
     * 0 if the BBS can go on,
     * 1 if the C_FILTER must be called again
     * 2 if the user must be disconnected.
     *
     * Callsign is in the FORM CALLSIGN-SSID (F6FBB-0).
     *
     * The first time C_FILTER is called Level=0, and then will be incremented
     * each time it is called for the same connection.
     *
     * Flags give the flags of the user (MGPBSXLE) in a bit field. as defined
     * in the INIT.SRV user's mask. (0x80=Modem, 0x40=Guest, etc...)
     *
     * If New=1, then this is the first connection of the user on the BBS.
     * Record is the record number in the INF.SYS file.
     *
     * All other arguments are the words sent by the user
     * (password for instance).
     *
     * The number of arguments is variable and depends of the number of words
     * in the answer of the user.
     *
     */

    /*
     * This is only a little example to test the system. It will be called
     * four times and will give the list of arguments.
     *
     * The fourth time, the hand will be given back to the BBS.
     */

    main(int ac, char **av)
    {
      int i;
      int level = atoi(av[2]);            /* Get level from argument list  */
                                          /* and transform it to integer   */

      if (level == 0) {                   /* Is level equal to 0 ?         */
        printf("Connection line :\n");    /* This is the first call        */
        for (i = 0 ; i < ac ; i++)        /* List line arguments           */
        printf("%s ", av[i]);
        putchar('\n');
        return(1);                        /* C_FILTER must be called again */
      }
      else {
        printf("Following line  :\n");    /* These are other lines         */
        for (i = 0 ; i < ac ; i++)        /* List line arguments           */
          printf("%s ", av[i]);
        putchar('\n');
        if (level == 4)                   /* Is it the last time ?         */
          return(0);                      /* Yes, go on BBS                */
        else
          return(1);                      /* No, call once more C_FILTER   */
      }
    }

    Next example, C_FILTER.DLL:

    #define STRICT
    #include <stdio.h>
    #include <windows.h>

    /*
     *    Code (C) F6FBB 1995-1996
     *
     *  C_FILTER example
     *
     *  svc_main is the only exported function. It must exist as WFBB will
     *  look for it. All filters are in the same format. If not NULL,
     *  r_buf allow to give a direct text back to the BBS
     * The size of the buffer is given by the parameter len.
     *
     *  Answers may also go to stdout (slower...).
     *
     *  This code is only an example and was not fully tested. It could
     *  give problems as I am not an expert !
     *
     * The used compiler is a Borland C++ 4.5
     *
     *  The DLL is not linked with the code, but checked and loaded when
     *  needed by WFBB.
     *
     * This is an example of the C_FILTER.DEF file :
     *
     *  LIBRARY        C_FILTER
     *  DESCRIPTION    'C_FILTER DLL for FBB'
     *  EXETYPE        WINDOWS
     *  CODE           PRELOAD MOVEABLE DISCARDABLE
     *  DATA           PRELOAD MOVEABLE SINGLE
     *  HEAPSIZE       1024
     *
     *
     * Parameters are (for C_FILTER):
     * ac[0] : The name of the filter (C_FILTER)
     * ac[1] : The callsign and SSID
     * ac[2] : Level number (from 0)
     * ac[3] : Flags
     * ac[4] : Boolean for new user
     * ac[5] : Recordnumber in INF.SYS
     * ac[6] : Port number
     * ac[7] : Optionnal Command received
     * r_buf : The buffer to put an answer
     * len   : The size of the answer buffer
     *
     * Return value (for C_FILTER):
     * 0 : Connection is accepted
     * 1 : C_FILTER will called again, level is incremented
     * 2 : Connection is refused, user is disconnected
     * 3 : Connection is accepted, but in read-only mode
     * 4 : Connection is accepted, but messages will be hold.
     * 100 and up
     *   : C_FILTER will called again, next level is equal to the return value.
     *
     */

    int _export FAR PASCAL svc_main (int ac, char FAR ** av, char FAR * r_buf, int len)
    {
    	if (len > 20)
    	{
    		sprintf (r_buf, "Inside the C_FILTER\r");
    	}
    	return (0);
    }

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