Microsoft KB Archive/129974

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BUG: Winsock--Lost FD_WRITE Notifications

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Q129974

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The information in this article applies to:


 * Microsoft Windows Software Development Kit (SDK) 3.1

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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.

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 * 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); The window specified by hWnd in WSAAsyncSelect will now receive the FD_WRITE notifications properly.

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.

Additional query words:

Keywords : kbnetwork kbAPI kbSDKPlatform kbOSWin310bug kbWinsock kbGrpDSNet

Issue type : kbbug

Technology : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310