Habari Chat: message exchange for Delphi applications

Habari Chat is a demo application for the Habari Client libraries, available with full source code and as executable in the demo downloads.

Sending broadcast messages

After choosing a chatroom name and a nickname, the user interface allows to send text messages. For system messages – for example when users enter or leave a chatroom – the code below is used:

procedure TMainForm.SendPublicInfo(const MsgText: string);
var
  Msg: IMessage;
begin
  Msg := Session.CreateTextMessage(MsgText);
  Producer.Send(Msg);
end;

Sending messages with nickname

For user messages, the code is almost the same. One additonal line of code sets a custom message property to the sender nickname:

procedure TMainForm.SendPublicInfo(const MsgText: string);
var
  Msg: IMessage;
begin
  Msg := Session.CreateTextMessage(MsgText);
  Msg.SetStringProperty('nickname', NickName);
  Producer.Send(Msg);
end;

Receiving messages

Incoming messages will be handled by an asynchronous event handler. (For real world applications, using a separate receive thread is recommended, which makes handling of lost connections easier.)

procedure TMainForm.OnMessage(const AMessage: IMessage);
var
  SenderNick: string;
  TxtMsg: ITextMessage;
begin
  SenderNick := AMessage.GetStringProperty('nickname');

  if Supports(AMessage, ITextMessage, TxtMsg) then
  begin
    if SenderNick <> '' then
      MemoChat.Lines.Add(SenderNick + ': ' + TxtMsg.Text)
    else
      MemoChat.Lines.Add(TxtMsg.Text)
  end
  else
  begin
    raise Exception.Create('Expected ITextMessage');
  end;
end;

Conclusion

This example application shows that creating Delphi chat applications based on existing open source message brokers requires little code. The complete sourcecode in MainFrm.pas counts less than 200 lines of code.

Such a compact application is possible because Habari Client libraries provide the high level API to create connections, message consumers / message producers and messages, while the message broker process provides the reliable messaging infrastructure.