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chat — a concurrent TCP chat server

Source on GitHub ↗

A multi-client chat server written directly on IO::Socket::INET, no framework. Every connection is handled on its own start thread; a shared roster of clients is guarded by a Lock, and each message is broadcast to everyone else. Where the pastebin is one request then one response, this keeps many long-lived connections interleaving at once.

Run it

build/rakupp showcase/chat/chat.raku            # listens on 127.0.0.1:6667
# or compile a standalone binary:
build/rakupp --exe -o chat showcase/chat/chat.raku && ./chat
PORT=7000 build/rakupp showcase/chat/chat.raku  # pick a port

Then connect with any line-oriented TCP client — one per terminal, one per person:

nc 127.0.0.1 6667

The first line you send is your nick; everything after it is broadcast to the room. /who lists who's online, /quit disconnects.

A live session

Four terminals: the server, and three people (alice, bob, carol) coming and going. In each client terminal the short lines are what that person typed (their nick, a message, /who, /quit); every other line arrived from the server.

Terminal 1 — the server

$ build/rakupp showcase/chat/chat.raku
rakupp-chat listening on 127.0.0.1:6667  (Ctrl-C to stop)
  + alice (id 0), 1 online
  + bob (id 1), 2 online
  + carol (id 2), 3 online
  - bob (id 1), 2 online
  - carol (id 2), 1 online
  - alice (id 0), 0 online

Terminal 2 — alice (connects first, stays for the whole session)

$ nc 127.0.0.1 6667
Welcome to rakupp-chat! Pick a nick: alice
Hi alice — you're online. /who to list, /quit to leave.
* bob joined
hey bob
bob: hi alice!
* carol joined
carol: hello everyone
/who
* online: alice, bob, carol
* bob left
* carol left
/quit

Terminal 3 — bob (joins second, leaves early)

$ nc 127.0.0.1 6667
Welcome to rakupp-chat! Pick a nick: bob
Hi bob — you're online. /who to list, /quit to leave.
alice: hey bob
hi alice!
* carol joined
carol: hello everyone
/quit

Terminal 4 — carol (joins last, leaves before alice)

$ nc 127.0.0.1 6667
Welcome to rakupp-chat! Pick a nick: carol
Hi carol — you're online. /who to list, /quit to leave.
hello everyone
* bob left
/quit

Notice a sender never receives their own message (broadcast skips the author), so bob's terminal shows the hi alice! he typed but not a bob: hi alice! echo — and alice, still connected at the end, sees both bob and carol leave.

Commands

How it works

• One thread per client. The accept loop does start serve($conn) and goes straight back to accept, so a slow or idle client never blocks the others. A blocking recv releases the interpreter lock, letting other clients flow.
• Shared state under a Lock. The client roster lives in @clients, guarded by $lock.protect { … } for every add / remove / snapshot.
• Broadcast writes outside the lock. broadcast snapshots the target sockets under the lock, then writes to them outside it, so one stalled client can't hold up the rest.
• Survives abrupt disconnects. Every socket write is guarded, and the runtime ignores SIGPIPE, so a client that vanishes mid-write (a dropped connection, a port scan) drops just itself — the server keeps running.