[NumLock]

Код:

uses
  WinSock,

const
  SOCK_MSG = WM_APP+$101;

var
  FSocket: TSocket;
...
      if WSAAsyncSelect(FSocket, hwnd, SOCK_MSG, FD_READ)=SOCKET_ERROR then
        SocketError(WSAGetLastError, 'WSAAsyncSelect()');
...
оконная процедура:
var
  SockAddrIn: sockaddr_in;
  Buffer: array [0..$fff] of Byte;
  len: Integer;
  fromlen: Integer;
...
    SOCK_MSG: begin
      if wParam=FSocket then
      begin
        if LOWORD(lParam)=FD_READ then
        begin
          fromlen:=SizeOf(sockaddr_in);
          len:=recvfrom(FSocket, Buffer[0], Length(Buffer), 0, SockAddrIn, fromlen);
          if len<>SOCKET_ERROR then ...