dnsserver.lua

local version=1.0
local args={...}
local fs=require("filesystem")
local serverName="ServerDNS" --dont change
local serial=require("serialization")
local component=require("component")
local computer=require("computer")
local modem=component.modem
local event=require("event")
local liste={}
local runing=false
modem.open(100)

function cleanOld(name, addr)
  for k, v in pairs(liste) do
    if v==addr and k~=name then
      liste[k]=nil
      liste.remove(k)
    end
  end
end

function register(name, addr)
  if liste[name]==nil or liste[name]~=addr then
    liste[name]=addr
    cleanOld(name, addr)
    save()
  end
end

function save()
  local file=io.open("/etc/dnsTable","w")
  file:write(serial.serialize(liste))
  file:close()
end

function load()
  if fs.exists("/etc/dnsTable") then
    local file=io.open("/etc/dnsTable","r")
    local text=file:read("*all")
    file:close()
    liste={}
    liste=serial.unserialize(text)
  end
end

function dnsDrop()
  liste={}
  save()
end

function isRuning()
  if runing then
    computer.pushSignal("dnsServerRuning")
  end
  return runing
end

function getAddr(name)
  if name==serverName then
    return modem.address
  else
    return liste[name]
  end
end

function get(name, addr)
  modem.send(addr, 100, "req", getAddr(name), name)
end

function handler(event, me, from, port, distance, command, value)
  if port==100 then
    if command~=null then
      if command=="set" then
        register(value, from)
      elseif command=="req" then
        --ignore
      else
        get(command, from)
      end
    end
  end
end

function printTable()
  for k, v in pairs(liste) do
    print(k,v)
  end
end

function localGet(e,name, n)
  addr=getAddr(name)
  computer.pushSignal("dnsReq", addr, name)
end

function restart()
  stop()
  start()
end

function start()
  os.sleep(1)
  if not getServerState() then
    load()
    event.listen("modem_message", handler)
    event.listen("dnsServerStop", stop)
    event.listen("dnsServerPrintTable", printTable)
    event.listen("dnsServerStatus", isRuning)
    event.listen("dnsServerDrop", dnsDrop)
    event.listen("dnsGet", localGet)
    runing=true
  else
    print("DNS-Server läuft bereits")
  end
end

function getServerState()
  computer.pushSignal("dnsServerStatus")
  local state=event.pull(1, "dnsServerRuning")
  if state~=nil then
     return true
  else
    return false
  end
end

function stop()
  runing=false
  event.ignore("modem_message", handler)
  event.ignore("dnsServerStop", stop)
  event.ignore("dnsServerPrintTable", printTable)
  event.ignore("dnsServerStatus", isRuning)
  event.ignore("dnsServerDrop", dnsDrop)
  event.ignore("dnsGet", localGet)
  save()
  list={}
end

if args[1]~=null then
  if args[1]=="run" then
    start()
  elseif args[1]=="print" then
    computer.pushSignal("dnsServerPrintTable")
  elseif args[1]=="stop" then
    computer.pushSignal("dnsServerStop")
  elseif args[1]=="restart" then
    computer.pushSignal("dnsServerStop")
    start()
  elseif args[1]=="drop" then
    computer.pushSignal("dnsServerDrop")
  elseif args[1]=="status" then
    if getServerState() then
      print("DNS läuft")
    else
      print("DNS läuft nicht")
    end
  end
end