An ugly question server, written to learn how coroutines work

question-server.lua

local socket = require("socket")
local inspect = require('inspect')

local host = "127.0.0.1"
local port = 9090

if arg then
  host = arg[1] or host
  port = arg[2] or port
end

udp = assert(socket.udp())
assert(udp:setsockname(host, port))
assert(udp:settimeout(2))
ip, port = udp:getsockname()
assert(ip, port)

print("Server started on " .. ip .. ":" .. port .. "...")

local function questioner(dgram, ip, port)
  if dgram:lower() ~= 'hallo\n' then return end

  local questions = {
    'Wie ist dein Name?\n',
    'Wie alt bist du?\n',
    'Wo wohnst du?\n'
  }
  local answers = {}

  for _, q in ipairs(questions) do
    if not answers[q] then
      print('Asking: ' .. q .. 'to' .. ip .. ':' .. port)
      udp:sendto(q, ip, port)
      answers[q] = coroutine.yield():sub(1, -2)
    end
  end

  local final = string.format('Du heißt %s, bist %d Jahre alt und kommst aus %s!\n', answers['Wie ist dein Name?\n'], answers['Wie alt bist du?\n'], answers['Wo wohnst du?\n'])

  udp:sendto(final, ip, port)
end


local CLIENTS = {}

while 1 do
  local dgram, ip, port = udp:receivefrom()
  
  if dgram and dgram ~= '\n' then
    if CLIENTS[port] then
      coroutine.resume(CLIENTS[port], dgram)
    else
      CLIENTS[port] = coroutine.create(questioner)
      
      local s, e = coroutine.resume(CLIENTS[port], dgram, ip, port)
      
      if not s then print(e) end
    end

    if coroutine.status(CLIENTS[port]) == 'dead' then
      CLIENTS[port] = nil
    end
  else
      print(ip)
  end

  print(inspect(CLIENTS))
end