ft_irc

A lightweight IRC (Internet Relay Chat) server implemented in C++98, following the IRC protocol requirements defined in the 42 ft_irc project.

The project focuses on building a high-performance event-driven server using non-blocking sockets and a single I/O multiplexing loop (poll() or equivalent), capable of handling multiple concurrent clients without threads or processes.

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Features

• TCP/IP client-server communication
• Password authentication
• Nickname and username registration
• Channel creation and management
• Private messaging
• Channel broadcasting
• Channel operators
• IRC channel modes
  • Invite-only (+i)
  • Topic restriction (+t)
  • Channel key (+k)
  • Operator privileges (+o)
  • User limit (+l)
• Graceful client disconnection and cleanup

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System Design

The server follows an event-driven architecture based on a single non-blocking event loop.

                +----------------+
                |  TCP Listener  |
                +--------+-------+
                         |
                    accept()
                         |
              +----------v-----------+
              |      poll() Loop     |
              +----------+-----------+
                         |
          +--------------+--------------+
          |                             |
    Read Events                   Write Events
          |                             |
   Command Parser                Message Queue
          |                             |
          +--------------+--------------+
                         |
                  IRC Command Router
                         |
         +---------------+----------------+
         |                                |
      Client Manager               Channel Manager

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Concepts Covered

Networking

• TCP/IP sockets
• Non-blocking I/O
• Socket lifecycle
• Connection management
• Event multiplexing with poll()

Systems Programming

• Event-driven architecture
• File descriptor management
• Resource cleanup
• Memory ownership
• Error handling
• Graceful shutdown

Protocol Design

• IRC command parsing
• Incremental packet buffering
• Handling fragmented TCP packets
• Message routing
• Protocol validation

Software Design

• Separation of concerns
• Object-oriented design (C++98)
• Command dispatcher pattern
• State management
• Encapsulation
• Modular architecture

Concurrency Model

• Single-threaded event loop
• Concurrent client handling without threads
• Fair scheduling through readiness notifications

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Engineering Challenges

• Handling partial TCP packets correctly
• Supporting multiple commands within a single receive buffer
• Preventing blocking operations
• Maintaining channel consistency
• Managing client lifecycle safely
• Ensuring robustness under malformed or unexpected input

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Testing

The server was validated using:

• Multiple simultaneous clients
• Partial packet delivery
• Message flood tests
• Invalid command handling
• Authentication edge cases
• Channel permission validation
• Connection/disconnection stress tests
• Long message handling
• Duplicate nickname scenarios

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Build

make

Run:

./ircserv <port> <password>

Example:

./ircserv 6667 secret

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Tech Stack

• Modern C++
• POSIX Sockets
• poll()
• Make
• Linux / macOS

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Learning Outcomes

This project provides practical experience with:

• Network programming
• Event-driven systems
• Protocol implementation
• High-performance server design
• State management
• Concurrent connection handling
• Defensive programming
• Systems-level debugging