Simple IRC Server

A lightweight IRC (Internet Relay Chat) server implementation in C, designed for educational purposes. This server supports basic chat functionality, private messaging, and user management.

Features

• Multiple concurrent client connections using poll()
• Username validation and management
• Broadcast messaging to all connected clients
• Private messaging between users
• User listing functionality
• Signal handling for graceful shutdown
• Maximum of 10 concurrent clients

Technical Specifications

• Port: 2000 (default)
• Maximum clients: 10
• Maximum message buffer: 1024 bytes
• Maximum username length: 20 characters
• Username requirements: Alphanumeric characters only, 1-10 characters long

Building

To compile the server, use gcc:

gcc -o irc_server main.c

Running the Server

Start the server by running:

./irc_server

The server will listen on port 2000 by default.

Client Commands

The following commands are available to clients:

• /list - Shows all currently connected users
• /w username message - Sends a private message to the specified user

Connection Flow

1. Client connects to server
2. Server prompts for username
3. Client sends username
   • If valid: Client joins chat
   • If invalid: Server requests new username
4. Client can now send/receive messages and use commands

Message Types

The server supports several message formats:

• Broadcast messages: username: message
• Private messages: username to you: message
• Server messages: Server to you: message
• System messages: username has joined/disconnected

Error Handling

The server includes error handling for:

• Invalid usernames
• Connection limits
• Client disconnections
• Signal interrupts (SIGINT, SIGTERM)
• Socket errors

Technical Implementation Details

• Uses poll() for non-blocking I/O
• Implements SO_REUSEADDR for socket reuse
• Handles partial reads and writes
• Manages dynamic memory for usernames
• Uses regex for username validation
• Implements graceful shutdown on signals

Security Considerations

• Username validation prevents injection attacks
• Buffer sizes are strictly enforced
• Memory is properly freed on disconnection
• Socket connections are properly closed

Limitations

• No persistent storage
• No channel support
• Basic authentication (username only)
• Fixed buffer sizes
• No encryption
• No file transfer capabilities

Contributing

This is an educational project. Feel free to fork and extend the functionality while maintaining the educational value of the codebase.

Note

README created by leveraging generative AI.