Multi-Threaded TCP Chat System

A high-performance, concurrent Chat Server and Client built in C for Linux. This project demonstrates core systems programming concepts including multi-threading, socket I/O, and inter-process synchronization.

🚀 Key Features

• Concurrent Server: Handles multiple simultaneous client connections using pthreads.
• User Authentication: Secure registration and login system with persistent storage.
• Thread Safety: Uses pthread_mutex to protect shared resources and global client lists.
• File Integrity: Implements flock (advisory locking) to prevent race conditions during database writes.
• Modular Architecture: Clean separation of concerns between authentication, chat logic, and UI handlers.
• Graceful Shutdown: Handles SIGINT and SIGTERM to clean up resources and close sockets properly.

🛠️ Technical Stack

• Language: C (Standard C99/C11)
• Networking: BSD Sockets (TCP/IP)
• Concurrency: POSIX Threads
• Build System: GNU Make
• OS: Linux (tested on Ubuntu/WSL)

📂 Project Structure

.
├── Makefile            # Automated build script
├── include/            # Header files (.h)
│   ├── common.h        # Shared structures and packet types
│   ├── server.h        # Server-side declarations
│   └── client.h        # Client-side declarations
├── src/                # Source files (.c)
│   ├── server/         # Auth manager, chat logic, and main server loop
│   └── client/         # UI handlers and main client loop
└── README.md