ft_irc — IRC Server in C++98

An IRC server built from scratch in C++98, fully compatible with standard IRC clients like irssi. This project implements the core of the IRC protocol (inspired by RFC 2812), handling real-time multi-client communication through non-blocking I/O and the poll() system call.

A 42 School project.

Authors: Ayoub Diri · Mohammed Akarkaou · Youssef El Bouzidi

Tech stack: C++98, POSIX sockets, poll(), Makefile.

What I learned

Built a fully functional IRC server from scratch with two teammates. The hard parts: getting non-blocking I/O right with poll() so multiple clients can send commands simultaneously without blocking each other, and implementing the IRC state machine (registration → channel membership → modes) so the server behaves correctly under concurrent connections. The CalcBot and DCC relay were bonus features on top. Tested against irssi to make sure real clients could actually connect.

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Features

Core IRC Protocol

• Capability Handshake — CAP LS support for modern IRC client negotiation
• User Registration — PASS, NICK, USER authentication flow
• Channel Management — JOIN, PART, KICK, INVITE, TOPIC
• Messaging — PRIVMSG for both channels and private DMs
• Operator Privileges — MODE with support for +i, +t, +k, +o, +l
• Connection Handling — PING/PONG keepalive, QUIT

Networking

• Non-blocking sockets with poll() multiplexing
• Buffered, event-driven I/O (POLLIN / POLLOUT)
• Handles partial reads and multi-command buffers
• Compatible with both \r\n (IRC standard) and \n (netcat)

Extended Features

CalcBot 🤖 — A built-in channel bot that evaluates math expressions:

<user> !calc 42 + 13 - 5
<CalcBot> user, the answer to 42 + 13 - 5 is 50

DCC File Transfer — The server transparently relays CTCP/DCC messages between clients, enabling peer-to-peer file transfers through IRC clients like irssi.

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Quick Start

Prerequisites

• A C++98-compatible compiler (e.g. g++, clang++)
• make
• An IRC client (irssi recommended) or netcat

Build & Run

make
./ircserv <port> <password>

Where:

• port must be between 1024 and 65535
• password must be 1..128 chars, without spaces/newlines

Example:

./ircserv 6667 mypassword

Connect with irssi

irssi -c 127.0.0.1 -p 6667 -w mypassword

Connect with netcat

nc localhost 6667
PASS mypassword
NICK mynick
USER mynick 0 * :My Name
JOIN #general
PRIVMSG #general :Hello, world!

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Project Structure

ft_irc/
├── includes/           # Header files
│   ├── Server.hpp      # Server class with poll() event loop
│   ├── Client.hpp      # Client state and buffered I/O
│   ├── Channel.hpp     # Channel membership and modes
│   ├── Bot.hpp         # CalcBot
│   ├── Parser.hpp      # IRC message parser
│   ├── Commands.hpp    # Command handler declarations
│   ├── Reply.hpp       # IRC numeric reply formatting
│   └── Utils.hpp       # String utilities
├── srcs/
│   ├── Server.cpp      # Socket setup, poll loop, client management
│   ├── Client.cpp      # Command routing and execution
│   ├── Channel.cpp     # Channel operations and broadcasting
│   ├── Bot.cpp         # Calculator bot logic
│   ├── Parser.cpp      # RFC-compliant message parsing
│   ├── Reply.cpp       # Reply/error code formatting
│   ├── Utils.cpp       # Helper functions
│   ├── main.cpp        # Entry point
│   └── Command/        # Individual command implementations
│       ├── Pass.cpp, Nick.cpp, User.cpp
│       ├── Join.cpp, Part.cpp, Kick.cpp
│       ├── Privmgs.cpp, Mode.cpp
│       ├── Ping.cpp, Quit.cpp
│       ├── invite.cpp, topic.cpp
│       └── Unknown.cpp
└── Makefile

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Supported IRC Commands

Command	Description
CAP	Capability negotiation (CAP LS implemented)
PASS	Set connection password
NICK	Set or change nickname
USER	Complete registration
JOIN	Join a channel
PART	Leave a channel
KICK	Remove a user from a channel
INVITE	Invite a user to a channel
TOPIC	View or set channel topic
MODE	Set channel/user modes (+i, +t, +k, +o, +l)
PRIVMSG	Send a message to a channel or user
PING	Connection keepalive
QUIT	Disconnect from the server

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Implementation Notes (Current Behavior)

• Registration requirement: clients must authenticate with PASS before NICK/USER are accepted.
• Connection is fully registered only after both valid NICK and USER are set.
• Nickname validation: max length 16, must start with a letter, then letters/digits/-/_.
• Channel creation: first JOIN #channel creates the channel and makes that user channel operator.
• JOIN restrictions enforced:
  • invite-only (+i)
  • user limit (+l)
  • key-protected channel (+k) via JOIN #chan <key>
• TOPIC with +t: only channel operators can change topic.
• MODE #channel with no extra args returns active channel modes.
• Unknown commands return standard IRC ERR_UNKNOWNCOMMAND.
• Line handling: both \r\n (IRC standard) and \n are accepted.

MODE flags implemented

• +i / -i — invite-only channel
• +t / -t — only operators may set topic
• +k <key> / -k — channel key
• +o <nick> / -o <nick> — give/remove channel operator
• +l <limit> / -l — user limit

Bot and CTCP/DCC behavior

• Built-in bot runs as CalcBot and responds to !calc in channels.
• CTCP/DCC payloads are relayed transparently through PRIVMSG, enabling client-side DCC workflows.

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Tested With

• irssi v1.4.5
• netcat (nc)
• Verified on Linux (Ubuntu/Debian)