2.2 Project 3: chat application using nachos networking module

Objectives:

• Learn to work with Nachos networking for communication among processes.
• Define and implement a “chat” protocol for interaction between a chat server and a chat client.

Problem statement:

Chat rooms have become a popular way to support a forum for n-way conversation or discussion among a set of people with interest in a common topic. Chat applications range from simple, text-based ones to entire virtual worlds with exotic graphics. In this project you are required to implement a simple text-based chat client/server application.

Problem description:

Email, newsgroup and messaging applications provide means for communication among people but these are one-way mechanisms and they do not provide an easy way to carry on a real-time conversation or discussion with people involved. Chat room extends the one-way messaging concept to accommodate multi-way communication among a set of people.

Nachos networking infrastructure

Nachos networking packages implements a very simple Unix domain (not internet domain), datagram socket. The files of importance to this project and their purpose are described below.

threads directory:

lockcond.h, lockcond.cc: for defining and implementing lock and condition synchronization primitives; needed for network applications to work.

machine directory:

network.h, network.cc: Data structures to emulate a physical network connection. The network provides the abstraction of ordered, unreliable, fixed-size packet delivery to other machines on the network.You may note that the interface to the network is similar to the console device -- both are full duplex channels.

sysdep.h, sysdep.cc : Interprocess communication operations, for simulating the network; Unix sockets creation, binding, closing etc. are called here to provide nachos socket functionality.

network directory:

post.h, post.cc: postoffice and mailbox, mail message definition and implementation.

nettest.cc: application to test communication between host id 0 and host id 1 (these are hardcoded!)

Chat architecture:

A chat application consists of a Chat Client (CC) one per person, a Chat Server (CS) and a two-way communication pipeline between the client and the server to send and receive conversational, control and status messages.

• Chat Client:

Typical features of a CC include: (i) select chat server (server id), (ii) select a nickname for interaction and (iii) ability to set and change user preferences such as number of messages displayed, change nickname, etc. You may design your own chat user interface.

Implementation notes:

The server id is specified at command line (nachos –rs 1234 –m selfid –o serverid ) while executing the nachos process representing the client.

Once the client process is running it could interactively ask the user for the nickname of the chat user and update this information locally and if needed by your design on the server.

• Chat Server:

A chat server supports the set of clients for a room, by maintaining client handle (clientid in nachos –rs –m clientId –o serverid), and client name. Server also has a message interpreter that parses the message received from a client and delegates the command to the appropriate module. Sample architecture for the chat application is shown in Figure 2. You may change the architecture to suit your design.