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function ConvertTo255(IP: string):string; // Ermittlung der vermeintlichen Broadcast-IP
var
  loop: integer;
begin
  for loop := length(IP) downto 0 do
    if IP[loop] = '.' then
    begin
      result := copy(IP,1,loop)+'255';
      break;
    end;
end;

procedure SendPing(Info: TInfo); // Routine zum Senden eines Ping-Datenpakets à la "I`m still here"
var
  BroadCastIP: string;
  Stream: TMemoryStream;
begin
  BroadCastIP := Convertto255(Form1.idIPWatch1.LocalIP);
  Form1.UdpClient.Host := BroadCastIP;
  Stream := TMemoryStream.Create;
  Stream.Write(PING, SizeOf(PING));
  Stream.Write(Info, SizeOf(Info));
  Form1.UDPClient.SendStream(Stream);
  Stream.Free;
end;                    

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procedure TForm1.UDPServerInput(Sender: TObject; AData: TStream;
  ABinding: TIdSocketHandle);
var
  Signal: integer;
begin
  AData.Read(Signal, SizeOf(Signal));
  If Signal = PING then
    inProcessPing(Abinding.PeerIP, AData) // Dieser Fall müsste eintreten! Es passiert nichts.
  else if Signal = TEXT_MESSAGE then
    inProcessMessage(Abinding.PeerIP, Adata)
  else if Signal = SHUTDOWN then
    inRemoveClient(ABinding.PeerIP)
  else if Signal = SET_CURSOR then
    inSetCursor(ABinding.PeerIP, AData)
  else if Signal = SET_DESKTOP then
    inSetFalseDesktop;
end;