ft_IRC

An IRC server built from scratch in C++ as part of the 42 Berlin curriculum.

A fully functional IRC server written in C++98, built from scratch as part of the 42 Berlin core curriculum (rank 5). Handles multiple simultaneous client connections using a poll-based event loop. Clients connect with any standard IRC client and interact through channels, private messages, and operator commands.

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What it is

ft_IRC implements the server side of the IRC protocol (Internet Relay Chat). Real IRC clients like irssi, WeeChat, or netcat can connect to it and interact through standard IRC commands. The server handles multiple simultaneous connections using a single poll() event loop without the implementation of forking or threads.

Built by Miguel Andrade and Daniela Torretta.

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Build

make        # compiles into ./ircserv
make clean  # removes object files
make fclean # removes objects + binary
make re     # full rebuild

Requires g++-14 on macOS (auto-detected) or any C++98-compatible compiler on Linux.

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Run

./ircserv <port> <password>

Example:

./ircserv 6667 mypassword

• port must be in the range 1024–65535
• password cannot be empty
• Handles SIGINT (Ctrl+C) and SIGTERM for graceful shutdown

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Connect a client

irssi:

irssi
/connect localhost 6667 mypassword

WeeChat:

/server add local localhost/6667 -password=mypassword
/connect local

netcat (best for evaluation — shows raw protocol):

nc localhost 6667
PASS mypassword
NICK alice
USER alice 0 * :Alice

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Supported Commands

Registration (required before anything else)

Command	Description
PASS <password>	Authenticate with the server password. Must be sent first.
NICK <nickname>	Set or change your nickname. Must start with a letter; allows -_[]\^{}.
USER <username> 0 * :<realname>	Complete registration. Required after NICK.
QUIT [:<reason>]	Disconnect from the server. Notifies all joined channels.

Registration order: PASS → NICK → USER. All three are required before any channel commands are available.

Channel Commands

Command	Description
JOIN <#channel>[,<#channel2>] [key]	Join one or more channels. Creates the channel if it doesn't exist. The first user to join becomes the operator. Supports comma-separated list and optional key.
PART <#channel>[,<#channel2>] [:<reason>]	Leave one or more channels.
PRIVMSG <target> :<message>	Send a message to a channel (#channel) or directly to a user (nickname). Supports comma-separated targets.
TOPIC <#channel> [:<new topic>]	View or set the topic. Without a message, shows the current topic. Setting requires operator privileges if mode +t is active.
INVITE <nickname> <#channel>	Invite a user to a channel. Required if channel is in invite-only mode (+i). Only operators can invite to +i channels.
KICK <#channel>[,<#channel2>] <nickname> [:<reason>]	Remove a user from a channel. Operator-only.
MODE <#channel> [<+/-modes> [params]]	View or change channel modes. Without mode flags, shows current active modes. Operator-only for modifications.

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Channel Modes

Modes are set with MODE #channel +<flags> [params] and unset with -<flags>.

Mode	Flag	Description
Invite-only	+i / -i	Only users who have been INVITEd can join the channel.
Topic restricted	+t / -t	Only channel operators can change the topic.
Key (password)	+k <password> / -k <password>	Requires a password to join.
Operator	+o <nick> / -o <nick>	Grant or revoke operator status for a user. Operators are shown with @ in the member list.
User limit	+l <number> / -l	Set a maximum number of users in the channel.

Multiple modes can be combined in a single command: MODE #general +itk secretpass

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Architecture

The server uses a single-threaded, poll-based event loop. All client sockets are monitored simultaneously — the server blocks on poll() and reacts only when a socket has activity.

• Server (sources/core/Server.cpp) — owns the main loop, accepts new connections, and routes incoming commands via two dispatch maps: one for registration commands, one for channel commands.
• Client (sources/core/Client.cpp) — represents a connected user. Tracks authentication state across three flags (_passRegistered, _logedIn, _isQuitting), stores the incoming data buffer, nickname, username, and pending channel invitations.
• Channel (sources/core/Channel.cpp) — represents a chat room. Maintains separate vectors for regular members and operators, active mode flags, topic, password, and user limit. Exposes four broadcast_message overloads to send to all members or all except a given fd.
• Utils (sources/utils/utils.cpp) — signal handling, _sendResponse, buffer parsing, and cleanup logic for clients, channels, and file descriptors.
• Messages (includes/utils/messages.hpp) — all IRC numeric reply codes and response macros, defined against RFC 1459.

Command pipeline

1. Raw data arrives on a client socket
2. Appended to the client's per-connection buffer
3. Complete messages (ending in \r\n) are extracted and split into tokens
4. Each command is normalized to uppercase and dispatched through the appropriate map to its handler

File layout

sources/core/
├── Server.cpp  — main loop: init(), execute(), NewClient(), NewData(), parser()
├── Client.cpp  — per-connection state
└── Channel.cpp — channel state, member management, broadcast

sources/registration/
├── PassCommand.cpp  — PASS
├── NickCommand.cpp  — NICK
└── UserCommand.cpp  — USER

sources/commands/
├── JoinCommand.cpp     — JOIN
├── PartCommand.cpp     — PART
├── PrivmsgCommand.cpp  — PRIVMSG
├── TopicCommand.cpp    — TOPIC
├── InviteCommand.cpp   — INVITE
├── KickCommand.cpp     — KICK
├── ModeCommand.cpp     — MODE
└── QuitCommand.cpp     — QUIT

sources/utils/utils.cpp         — signal handler, response helpers, socket cleanup
includes/utils/messages.hpp     — IRC numeric codes and response macros

Client authentication states

Connected → (PASS) → passRegistered → (NICK + USER) → logedIn (fully registered)

Channel member model

Each Channel holds two separate vectors: _clients (regular members) and _admins (operators). The first user to create a channel is automatically placed in _admins. Operators appear with @ in the names list. Promotion/demotion via MODE +o/-o moves users between the two vectors atomically.

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Contribution split

Daniela Torretta — server core (Server.cpp, Client.cpp), the poll() event loop, connection handshake, client lifecycle, parser scaffolding, and the registration commands (PASS, NICK, USER).

Miguel Andrade — channel architecture (Channel.cpp), all channel commands (JOIN, PART, PRIVMSG, TOPIC, INVITE, KICK, MODE, QUIT), channel modes and permissions system, messages.hpp (all IRC numeric response codes), and overall integration.

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Skills demonstrated

• Socket programming — TCP server from scratch: socket(), bind(), listen(), accept(), non-blocking I/O with fcntl(), SO_REUSEADDR
• Event-driven I/O — single-threaded poll() loop managing N simultaneous connections without threads or forking
• Protocol implementation — IRC protocol parsing (fragmented TCP streams, \r\n framing, prefix/command/params format), RFC 1459 numeric reply codes
• C++98 — function pointer maps (std::map<string, void(Server::*)(string, int)>), orthodox canonical form.
• State machine design — three-stage auth flow (passRegistered → logedIn), dual-vector channel membership model (clients vs operators)
• Systems programming — signal handling (SIGINT/SIGTERM), fd lifecycle management, graceful client disconnection and resource cleanup