unit Unit67;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, IdBaseComponent, IdComponent, IdUDPBase, IdUDPServer, IdSocketHandle;

type
  TForm1 = class(TForm)
    IdUDPServer1: TIdUDPServer;
    Button1: TButton;
    Memo1: TMemo;
    procedure IdUDPServer1UDPRead(Sender: TObject; AData: TStream;
      ABinding: TIdSocketHandle);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.IdUDPServer1UDPRead(Sender: TObject; AData: TStream;
  ABinding: TIdSocketHandle);
var
  s : String;
begin
  SetLength(s, AData.Size);
  AData.Read(s[1], AData.Size);
  Memo1.Lines.Add(s);
  //if s = 'GO' then
  begin
    IdUDPServer1.Send(ABinding.PeerIP, 1412, 'Yes!');
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  IdUDPServer1.Send('10.0.1.2', 1412, 'Yes');
end;

end.