Superchat

An online chat for several users using the Java RMI interface, and Swing.

Demonstration

Description

Based on Java RMI default implementation, the chat consists in one server application, and another for clients (i.e. the server application should be launched on a host, before the clients can launch their one). Based on a P2P traffic model, our chat is centralized.

Features:

• Each client can connect/disconnect whenever they want without leaving the application.

• A real-time connected user list is proposed.

• On connection, the client will receive all the messages not received, and will be able to see the connected users.

• Server logs indicate connections/disconnections.

• The server will load messages from last sessions on launch, and will save them all on exit (by using the file $HOME/.superchat/history on the host).

Implementation:

• The Linker class/interface:

  • Created in the Server, and added in the RMI register once.

  • Identifies the clients; each pseudo is unique (among the connected users) and is stored here to ensure this uniqueness.

  • Every message sent is stored here. This allows to have the same source for the date/time (which is associated to the messages) for every client (a client could use the chat in Colombia while another in Japan, this would result in a synchronicity problem at the time level if the time source was not the same). Also, the messages are stored here from the history file on server start, and retrieved to be saved by the server when exiting.

• The Client class/interface:

  • Created in the Application, and added in the RMI register for every user.

  • Saves state (pseudo and messages) on the server side by using the Linker.

  • Communicates with other clients by saving itself in the RMI register (P2P). Thus, each Client will send a message/notify connection/notify disconnection to others by fetching all the clients in the register, and sending them the message. To do all of this, clients are registered in the RMI register with a URI containing their pseudo (which is unique).

• The Application class:

  • The GUI bound with a Client; the one launched by a user.

  • Informs the Client of the user's inputs so that it can act on them.

• The Server class:

  • Creates the RMI register and Linker; needs to be launched only once, before executing any Application.

  • Retrieves/Saves the message history on launch/exit, in the $HOME/.superchat/history file on the host.

Possible improvements

• For security issues, the URI associated to a Client could be improved, and each pseudo associated to a password.

• For backup issues, the message history file should not be stored on the host, but on the client side. We could also save the message history every X minutes or every Y messages to avoid loosing them on a power cut for example.

• For performance issues, limitations should be added (maximum number of clients, maximum length of messages, etc.), and recovery algorithms should be optimized.

• For ethical issues, the chat itself should not be used this way, because it implies a centralization of user data (names, messages, and metadata). Since we have already implemented a P2P traffic model, we could make this chat completely decentralized.

Instructions

1. First you need to compile the source code:

   user:~/Java-RMI-Chat/ $ make

2. Next you need first to start the server. To do this you have to execute the following command:

   • If you are trying to launch the server on localhost:

   user:~/Java-RMI-Chat/ $ java -jar lib/Server.jar 

   Executing the rmiregistry &/start rmiregistry command is not necessary; since the server is launched on localhost everything is done programmatically.

3. Then to start a user connection:

   user:~/Java-RMI-Chat/ $ java -jar lib/Application.jar <host> 
   

   Where host is the machine on which the server was launched. Its default value is localhost if not specified.

Troubleshooting

Error: java.rmi.ConnectException

• You are not using localhost as the server host, and you may be starting rmiregistry from the wrong folder.

Exception in thread "main" java.awt.AWTError: Can't connect to \<X server\> 
using \<IP address:x.x\> as the value of the DISPLAY variable.

• You may need to execute the export DISPLAY=:0 command.

Attributions

Icon made by Flat Icons from www.flaticon.com .