Megaphone

A client-server messaging system implementing a microblogging service with thread-based discussions and real-time notifications over IPv6 UDP multicast.

Overview

Megaphone is a distributed messaging platform where users can:

• Register with a unique pseudo
• Post messages (billets) to discussion threads (fils)
• Subscribe to threads and receive real-time notifications via IPv6 multicast
• Share files within threads

The system uses a custom binary protocol over UDP with bitfield-packed headers for efficient communication.

Architecture

• Server (server.c): Manages user registration, thread creation, message posting, and notification distribution
• Client (client.c): Handles user interactions, message composition, and receives multicast notifications
• Protocol: Custom binary message formats defined in msgcli.h and msgsrv.h
• Data Structures:
  • Users: Linked list of registered users (user.h)
  • Threads (fils): Linked list containing billets, files, and subscribers (fil.h)
  • Messages: Packed binary structures with 5-bit operation codes and 11-bit user IDs

Protocol

Messages use 16-bit headers with:

• 5 bits for operation code (1=register, 2=post, 4=subscribe, 31=error, etc.)
• 11 bits for user ID (max 2047 users)

Setup

Prerequisites

• GCC compiler
• POSIX-compliant system (Linux/Unix)
• IPv6 network support

Build

# Compile server
gcc -o server server.c msgsrv.c msgcli.c user.c fil.c -lpthread

# Compile client
gcc -o client client.c msgsrv.c msgcli.c user.c fil.c -lpthread

Run

# Terminal 1: Start server (port 7777)
./server

# Terminal 2+: Start client(s)
./client

Contributing

Team

See authors.md for project contributors.

Guidelines

1. Fork the repository
2. Create a feature branch (git checkout -b feature/your-feature)
3. Follow existing code style (K&R C conventions)
4. Test with multiple clients and thread subscriptions
5. Commit changes (git commit -m 'Add feature')
6. Push to branch (git push origin feature/your-feature)
7. Open a Pull Request

Code Structure

• Keep protocol definitions in header files (msgcli.h, msgsrv.h)
• Use linked lists for dynamic data (users, threads, messages)
• Handle thread safety for multicast notifications
• Validate all network input to prevent buffer overflows

License

Project developed as part of network programming coursework.