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:

[sourcecode language=”Delphi”]

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

[/sourcecode]

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:

[sourcecode language=”Delphi” highlight=”6″]

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

[/sourcecode]

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.)

[sourcecode language=”Delphi” highlight=”6″]

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;

[/sourcecode]

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.