A sketch of a chat service implemented in Lua.

chat.lua

#!/usr/bin/lua

peers = {}
peer_names = {}
reverse_peers = {}

function on_connect(sock)
  local idx = #peers+1
  local newname = string.format("Peer%d", idx)
  peers[idx] = sock
  peer_names[idx] = newname
  reverse_peers[sock] = idx
  broadcast(string.format("%s joined the channel\n",newname), sock)
end

function on_readline(sock, line)
  local num = reverse_peers[sock]
  if string.sub(line,1,6)=="/name " then
    local newname = string.sub(line, 7, #line)
    broadcast(string.format("%s changed his name to %s\n", peer_names[num], newname), nil)
    peer_names[num] = newname
  else
    broadcast(string.format("<%s> %s\n", peer_names[num], line), sock)
  end
end

function broadcast(data, exclude)
  for num=1, #peers do
    sock = peers[num]
    if sock ~= exclude then
      sock:write(data)
      sock:flush()
    end
  end
end

function main_loop()

  while true do

    if ncat.socket_waiting() then
      on_connect(ncat.accept())
    end
    
    --read line loop
    for num=1, #peers do
      sock = peers[num]
      if ncat.has_line(sock) then
        on_readline(sock, sock:read("*line"))
      end
    end
  end
end

on_connect(io.stdout)
on_connect(io.stderr)
on_readline(io.stdout, "Hai")
on_readline(io.stdout, "/name ziomek")
on_readline(io.stdout, "test")

i can't use this on ncat version 6.40
how to use this?!

So this script is able to handle io.stdin, io.stdout and io.stderr. But it doesn't work with the ncat sockets even after some playing around. How do I get on_connect() to work with network connections? That seems to be the main issue for me.
Besides, the script seems to be run per user logging in and doesn't seem to be able to handle multiple users at once.
(Ncat Version 6.40 on a Ubuntu machine)