Chat C2S in C

by Sharp - 1st Year of Master's in Computer Security

Table of contents

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• Project Context
• Description
  • Program Features
  • Error Management
  • Specific Cases
• Program Structure & Architecture
• Choices made
• How to test?
• License

Project Context

This project is part of a C course in my first year of Master's in Computer Security. The objective of the project is to develop a Chat Client-Server program in C, where multiple clients can communicate with each other through a server acting as an intermediary. The purpose of this project is to gain hands-on experience in C programming and network communication, as well as to understand the concepts of client-server architecture.

Description

This program enables multiple clients to communicate with each other using a server as an intermediary. Clients connect to the server by registering their name and can send messages to other clients through the server.

Program Features

• Registration : Clients can register with the server using a unique name.
• Client Interaction : Clients can request to speak by typing "1".
• Exclusive Speaking : Only one client can speak at a time, ensuring orderly communication.
• Message Broadcasting : The server displays the name of the sending client and their message to all other connected clients.
• Mutex for Socket Access : A mutex is used to protect access to write sockets, preventing competitive errors and ensuring message integrity.

Error Management

The server handles various error cases to ensure smooth operation and graceful termination :

• Client Limit : The server checks if the number of clients has reached the limit before accepting new connections.
• Bind Function Failure : The server handles the case where the bind function fails and exits gracefully.
• Listen Function Failure : The server handles the case where the listen function fails and exits gracefully.
• Send Function Failure : The server handles the case where the send function fails and closes the client socket.

Specific Cases

The program handles specific cases to enhance user experience and prevent issues :

• Reconnection : Clients have the possibility to connect or rejoin the server using the same port number.
• Maximum Client Capacity : The server can handle up to a maximum number of clients specified by MAX_CLIENTS.
• Continuous Listening : The server listens for incoming connections indefinitely until manually terminated.
• Client Notification : The server sends a message to all clients when a new client connects or disconnects.
• Message Truncation : If a client sends a message larger than the buffer size, it will be truncated to fit.
  • Client Connection Refusal : If the server reaches the maximum number of clients, it will refuse new connections and notify the client.

Program Structure & Architecture

.
└─── chat_c2s_c
    ├─── src
           ├─── handle_client.c
           └─── server.c
    ├─── BUILD.md
    └─── README.md

The project is structured as follows:

• handle_client.c : Code for client-side functionality.
• server.c : Code for server-side functionality.

Choices made

• Modular Code : The code is divided into small functions to facilitate code review and maintainability. There are a total of 9 functions, including the main function.

To ensure thread safety and prevent race conditions when accessing write sockets, a mutex is used. This allows only one client to speak at a time, ensuring messages are not lost or corrupted.

How to test?

To use this program, follow these steps:

1. Start the server first.
2. Open multiple terminals and connect to the server using the following command : nc localhost <port> (e.g., nc localhost 1234).
3. Register with the server by providing a unique name.
4. Communicate with other clients by sending messages through the server.
5. Request to speak by typing "1" to indicate the intention to send a message. Only one client can speak at a time.

Please refer to the BUILD.md file for instructions on building and running the program. Ensure dependencies mentioned in the file are installed.

Enjoy using this program and exploring client-server communication in C!

License

Distributed under the MIT License. See LICENSE for more information.