InfoMagic Internet Tools 1995 April/Internet Tools.iso/dos_win/winsock/maillist/94-03.Z/94-03/text0298.txt

Text File | 1994-03-30 | 7.0 KB | 189 lines

I have a winsock app that used to work fine, but I upgraded a couple of
stacks and the stuff stopped working.  Since it happened on two different
stacks, I figure the problem must be in my code.  Maybe I was using a
marginal practice that an updated stack would not allow.  Anyway maybe I
can get some help here.

The problem has to do with a call to select() on a datagram socket.  I am
implementing a form or RPC (not ONC or DCE or plug in you own acronym) that
sends a packet to a host and then waits up to two seconds for a reply.
Don't do it, I see you reaching for that "Just use the async calls..."
stuff.  I really want to do a synchronous function call across the network.
The call uses select to tell me if any data arrives on the socket.

In the previous versions, this worked quite well.  Now the select always
returns immediately that the fd_set is ready for reading.  Of course, I
then read the socket and the recv_from returns 0 bytes.  How can I code
around this?

I have tried making the socket blocking and non-blocking and the same
behaviour is displayed.  I was thinking maybe I have to just loop on the
recv_from but then the timing gets tough.  I could make a timer callback
that would set a flag, but that would cost a
makeprocinstance/settimer/killtimer for every single packet.

I have the code below that makes these calls.  Please help if you can.  I
will certainly post the resolution if anybody is interested.

------- Begin Code Fragment -------------------

// Background stuff.....
this code uses a UDP socket to receive packets from a server.  The packets
are 608 bytes in size and using a protocol analyzer, I can see them being
returned to the application.  The problem is that the select call below
returns 1 immediately (not SOCKET_ERROR or 0) even though the packet has not
yet arrived.  The recv_from() does not get any data.  We tried all
combinations of blocking and non-blocking sockets to no avail.


cm_recv    FAR PASCAL recv_packet( rpc_conv FAR *conv, char FAR *packet, int FAR *size)
{
  /* Function to receive a response from the server    */

  struct sockaddr_in    sender;
  int                    len;
  int                    rc;
  fd_set                 fdset;
  struct timeval        timer;
  char                    msg_buf[64];

  FD_ZERO(&fdset);
  FD_SET(conv->socknum,&fdset);
  timer.tv_sec = 2;
  timer.tv_usec = 0;
  /* to check if any data is available to be read */
  switch ( select( 0, &fdset, NULL, NULL, &timer) ) {
    case 0:
        return RPC_TIMEOUT;
    case SOCKET_ERROR:
        wsprintf(msg_buf,"Select Error, errno = %d",
                WSAGetLastError());
        MessageBox ( NULL, msg_buf,"CM_API",
                MB_ICONASTERISK | MB_OK);
        return RPC_ERROR; /* Some error other than a wouldblock   */
    default:
        // Code always takes this path even if no data on the socket
        rc = recvfrom (conv->socknum,
                    (LPSTR) packet,
                    *size,
                    0, (LPSOCKADDR) &sender, &len);
        *size = rc;
          return RPC_OK;
  }
}


// Code that creates the socket....

cm_bool FAR PASCAL makesocket( rpc_conv FAR *conv, int flag )
{
  /* Create a socket for communication with the API server    */

  WSADATA     winconfig;
  int         socket_error;
  struct    hostent FAR *hent;
  char        msg_buf[64];
  int         localport, rc;

  if (flag) {
      /* Startup the winsocket DLL */
      if ((socket_error = WSAStartup( 0x0101, (LPWSADATA) &winconfig)) != 0) {
        wsprintf(msg_buf, "WSAStartup Error, errno = %d", socket_error);
        MessageBox ( NULL, msg_buf, "CM_API", MB_ICONASTERISK | MB_OK);
        return CM_FALSE;
      }
  }

  /* Find the UDP server host */
  if ( (hent = gethostbyname( conv->server )) == NULL ) {
    wsprintf(msg_buf, "Cannot locate server %s", (LPSTR)conv->server);
    MessageBox ( NULL, msg_buf, "CM_API", MB_ICONASTERISK | MB_OK);
    return CM_FALSE;
  }
  /* Save the server host in the peer field    */
  conv->peer.sin_family=AF_INET;
  conv->peer.sin_addr.s_addr = *( (unsigned long far *) hent->h_addr_list[0]);
  conv->peer.sin_port = htons(CM_RPC_PORT);

  /* Create a socket to talk to the server    */
  if ( (conv->socknum = socket( AF_INET, SOCK_DGRAM, 0)) == INVALID_SOCKET ) {
    wsprintf(msg_buf, "Cannot create socket, errno = %d", WSAGetLastError());
    MessageBox ( NULL, msg_buf, "CM_API", MB_ICONASTERISK | MB_OK);
    return CM_FALSE;
  }

  /* Set the socket to blocking */
  u_long     block_flag = 0;
  if ( ioctlsocket( conv->socknum,
                    (long)FIONBIO,
                    (unsigned long FAR *)&block_flag) == SOCKET_ERROR ) {
    wsprintf(msg_buf, "Could not make socket blocking, errno = %d",
                WSAGetLastError());
    MessageBox ( NULL, msg_buf, "CM_API", MB_ICONASTERISK | MB_OK);
    return CM_FALSE;
  }


  _fmemset((void FAR *) &conv->myname, 0x00, sizeof(struct sockaddr_in));
  conv->myname.sin_family=AF_INET;
  conv->myname.sin_addr.s_addr = 0;

  for (localport = CM_RPC_PORT; localport < CM_RPC_PORT + MAX_SESSIONS_PC; localport++) {
    conv->myname.sin_port = htons(localport);
    rc = bind ( conv->socknum,
            (struct sockaddr FAR *) &conv->myname,
            sizeof(struct sockaddr_in) );
    if ( rc == 0 ) return CM_TRUE;
    if ( (rc == SOCKET_ERROR) && (WSAGetLastError() != WSAEADDRINUSE) ) {
        wsprintf(msg_buf, "Could not bind name to socket, errno = %d", WSAGetLastError());
        MessageBox ( NULL, msg_buf, "CM_API", MB_ICONASTERISK | MB_OK);
        return CM_FALSE;
    }
  }
  wsprintf(msg_buf, "%s","All Sockets busy, try later.");
  MessageBox ( NULL, msg_buf, "CM_API", MB_ICONASTERISK | MB_OK);
  return CM_FALSE;
}
--
**********************************************************************
* Mike Vargo                    | Centigram Communications Corp      *
*                               | 91 East Tasman Dr.                 *
* Internet: [e-mail]  | San Jose, CA  95134                *
* Compuserve: 72212,3124        | Telephone: [phone]            *
**********************************************************************
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Subject: Re: re. Winsock Providers
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>       There may be others but the people that come to mind as WINSOCK.DLL
>   providers are:
>   NetManage                Chameloen
>   Novell                        Lan WorkPlace
>   Beame & Whiteside  BW-TCP/BW-NFS
>   Wollongong Group    Pathway Access
>   Frontier Technol.       Super TCP/IP

There "may" be others?  :)  I guess it's easy to forget the minor
players like Microsoft, Sun Microsystems, FTP Software and IBM,
to name a few.

--
 Bob Quinn                                             [e-mail]
 FTP Software, Inc.                                No. Andover, MA