BUG: Winsock--Lost FD_WRITE Notifications

• Microsoft Windows Software Development Kit (SDK) versions 3.1

SYMPTOMS

In both of the following situations, the initial FD_WRITE notifications are never received:

• Create a datagram socket and call WSAAsyncSelect() with interest in FD_WRITE notification.

  -or-

• Create a stream socket, call connect() to connect to a TCP server and call WSAAsyncSelect() with interest in FD_WRITE notification.

RESOLUTION

In the first case, call the bind() function in addition to the socket() function as shown:

   SOCKADDR_IN source_sin;

   source_sin.sin_family = AF_INET;
   source_sin.sin_addr.s_addr = htonl(INADDR_ANY);
   source_sin.sin_port = htons(0);

   s = socket(AF_INET, SOCK_DGRAM, 0);
   bind(s, (struct sockaddr FAR *)&source_sin,sizeof(source_sin));
   WSAAsyncSelect(s, hWnd, WSA_WRITE, FD_WRITE);

In second case, call socket() and call connect() asynchronously as shown:

   SOCKADDR_IN dest_sin;

   dest_sin.sin_family = AF_INET;
   dest_sin.sin_addr.s_addr = htonl(SERV_HOST_ADDR);
   dest_sin.sin_port = htons(SERVER_TCP_PORT);

   s = socket(AF_INET, SOCK_STREAM, 0);
   WSAAsyncSelect(s, hWnd, WSA_WRITE, FD_CONNECT | FD_WRITE);
   connect(s, (struct sockaddr FAR *)&dest_sin, sizeof(dest_sin);

STATUS

Microsoft has confirmed this to be a bug in the products listed at the beginning of this article. We are researching this bug and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

If a datagram client is not expecting to receive a response from a server, it can send data without first binding the datagram socket to a specific port. According to this behavior, a datagram socket should be able to receive FD_WRITE notifications after calling socket() and WSAAsyncSelect().