dns.lua

local component = require("component")
local computer = require("computer")
local event = require("event")
local serialization = require("serialization")
local m = component.modem
local isRunning = false
local name = ""
local isServer = false
local dnsList = {}

function start()
  if(isRunning) then
    print("Already running")
    return
  end
  if m == nil then
    print("No modem")
    return
  end
  if not m.isOpen(1) then
    m.open(1)
  end
  dnsList = {}
  event.listen("modem_message", onMessage)
  local c = loadConfig()
  local conf = c or {}
  isServer = conf.isServer or false
  name = conf.name or ""
  saveConfig(setDefault(setDefault(conf, "isServer", isServer),"name", name))
  if isServer then
    m.broadcast(1, "dns")
  else
    m.broadcast(1, "dns", 1, name)
  end
  isRunning = true
end

function stop()
  if not isRunning then
    print("Not running")
    return
  end
  if m == nil then
     print("No modem")
    return
  end
  if m.isOpen(1) then
    m.close()
  end
  event.ignore("modem_message", onMessage)
  isRunning = false
end

function send(address, port, ...)
  if isServer then
    onMessage(nil, m.address, m.address, 1, 0, address, port, ...)
    return
  end
  m.broadcast(1, address, port, ...)
end

function onMessage(_, localAddress, from, port, distance, to, toPort, ...)
  if not isRunning then
    return
  end
  if port ~= 1 then
    return
  end
  if isServer then
    if to == "dns" and toPort == 1 then
      addClient(from, ...)
      return
    end
    if to == name then
      computer.pushSignal("modem_message", localAddress, from, toPort, distance, ...)
      return
    end
    local na  = dnsList[to]
    if na == nil then return end
    m.send(na, toPort, ...)
    return
  else
    if to == "dns" and toPort == nil then
      m.broadcast(1, "dns", 1, name)
    end
  end
end

function addClient(client, na)
  dnsList[na] = client
end

function loadConfig()
  local env = {}
  local result, reason = loadfile('/etc/dns.cfg', 't', env)
  if result then
    result, reason = xpcall(result, debug.traceback)
    if result then
      return env
    end
  end
  return nil, reason
end

function saveConfig(conf)
  local file, reason = io.open('/etc/dns.cfg', 'w')
  if not file then
    return nil, reason
  end
  for key, value in pairs(conf) do
    file:write(tostring(key) .. " = " .. serialization.serialize(value) .. "\n")
  end
  file:close()
  return true
end

function setDefault(conf, name, data)
  conf[name] = data
  return conf
end

function getName(n)
  n.name = name
end