unit Main;

interface

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

type
  TForm1 = class(TForm)
    IdUDPServer: TIdUDPServer;
    edInfo: TEdit;
    Label1: TLabel;
    Label2: TLabel;
    lbBytes: TLabel;
    btnListen: TButton;
    edPort: TEdit;
    procedure IdUDPServerUDPRead(Sender: TObject; AData: TStream;
      ABinding: TIdSocketHandle);
    procedure btnListenClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.IdUDPServerUDPRead(Sender: TObject; AData: TStream;
  ABinding: TIdSocketHandle);
var
  Buf : array[1..1024] of char;
  Str : string;
  Len : integer;
begin
  FillChar(Buf, SizeOf(Buf), 0);
  Len := AData.Read(Buf, 1000);
  Str := String(Buf);
  SetLength(Str, Len);
  edInfo.Text := Str;

  lbBytes.Caption := IntToStr(Len);
end;

procedure TForm1.btnListenClick(Sender: TObject);
begin
  IdUDPServer.DefaultPort := StrToInt(edPort.Text);
  IdUDPServer.Active := True;

  btnListen.Enabled := False;
end;

end.