Multicast Chat

Java implementation of a multicast chat guaranteeing:

• causal ordering of the massages using vector clocks
• integrity of the messages using SHA-1 hashing
• reliable message delivery over UDP multicast socket

Introduction

The package is structured with a MVC design pattern, and the view and controller interacts through Event-Listener mechanisms. The causality is ensured by CausalHandler which compares the local vector clock with the vector clock included in the received message; whenever an inconsistency is detected, a retransmission request is sent to the original sender of the lost messages. Every received message is checked against the computed SHA-1 hash and the hash included in the header: if the hashes are different a retransmission request is sent. Retransmission requests are handled by a separate thread in RepeaterHandler.

How to use

In order to test the chat in localhost, two instances of Application should be run having dual Config.REPEATER_PORT_SERVER and Config.REPEATER_PORT_CLIENT. The provided bash script test.sh will compile the code from command line and run two instances of Application using the following interface:

$ Application groupIP groupPort TTL repeaterPortServer repeaterPortClient

where

• groupIP is the IP of the multicast group
• groupPort is the port of the multicast group
• TTL is the time-to-live of the messages
• repeaterPortServer is the port accepting request for message retransmission
• repeaterPortClient is the port sending request for message retransmission

Licence

MIT Licence. Copyright (c) 2015 Matteo Maggioni