In this lab you will build a simple client-server chat system. To start with, you should follow the guide in this week's third Distributed Systems video to practice sending and receiving messages -- you should write this code yourself, and not use the templates in client and server, which are there for the second part of the lab.

There are two ways to use the lab sheet, you can either:

• create a new repo from this template - this is the recommended way
• download a zip file

Each question is rated to help you balance your work:

• 🔴⚪⚪⚪⚪ - Easy, strictly necessary.
• 🔴🔴⚪⚪⚪ - Medium, still necessary.
• 🔴🔴🔴⚪⚪ - Hard, necessary if you're aiming for higher marks.
• 🔴🔴🔴🔴⚪ - Hard, useful for coursework extensions.
• 🔴🔴🔴🔴🔴 - Hard, beyond what you need for any part of the coursework.

Follow the video, creating a simple client and server that can send messages to each other. This is best tackled in stages. Again, you should write this code from scratch, as this part of the lab does not relate to the code in client and server. You may want to look at the net package for parts of this.

• Stage 1: Achieve client-server interaction, with a server that listens for a single message and then prints it out and terminates, and a client that dials for a connection and sends a single message.

• Stage 2: Modify the server so that it persists and handles new connections, printing out messages from any clients that connect.

• Stage 3: Modify the client so it can send user-defined messages.

• Stage 4: Modify both components so that the server sends replies to the client, which handles and displays them.

• Stage 5: Create a fully interactive client-server loop, with the user prompted for input which is sent to the server and then acknowledged back to the client, without either component exiting or closing the connection.

Using what you have learned so far on the course, fill out the client and server skeleton code to create a text-based chat system that handles multiple clients.

The client needs to (a) process user input and send it to the server on each newline; (b) at the same time, accept messages sent from the server and display them as they arrive.

The server needs to (a) handle new clients connecting; (b) process incoming messages from any connected client; (c) send any received message to all clients except the client that sent it.

The real test of your code will be to communicate with two or more clients via localhost, and see messages passing back and forth between them.

The skeleton code provides a starting point and some hints. You should use go run server.go to run the server, and go run client.go to run the client. The server accepts a -port flag to define a port to listen on, and the client accepts an -ip flag to define an ip:port string to connect to. By default the server launches on :8030 and the client connects to that port on localhost.