oc_dns-server

local fs = require "filesystem"
local text = require "text"

local dns = {}

function dns.read_hosts(path)
  local file = io.open(path, "r")
  local t = {}

  if not file then return nil end
  for line in file:lines() do
      table.insert(t, line)
  end
  io.close(file)
  return t
end

function dns.get(path, name)
  local hosts = dns.read_hosts(path)

  if not hosts then return nil end

  for _,v in pairs(hosts) do
    local tab = text.tokenize(v)
    if tab[2] == name then return tab[1] end
  end
  return nil
end

function dns.write_hosts(path, list)
  local file = io.open(path, "w")

  for _,v in pairs(list) do
    file:write(v)
    file:write("\n")
  end

  io.close(file)
end

function dns.unregister(path, hosts, addr)
  local file = io.open(path, "w")

  for _,v in pairs(hosts) do
    if (text.tokenize(v))[1] ~= addr then
      file:write(v)
      file:write("\n")
    end
  end
  io.close(file)
end

function dns.register(path, hosts, addr, name)
  table.insert(hosts, addr .." ".. name)
  dns.write_hosts(path, hosts)
end

function dns.check_errors(hosts, addr, name)
  if not addr then return "dns_addr_error" end
  if not name then return "dns_name_error" end
  for _,v in pairs(hosts) do
    v = text.tokenize(v)
    if addr == v[1] then return "dns_addr_error" end
    if name == v[2] then return "dns_name_error" end
  end
  return nil
end

function dns.is_registered(hosts, addr)
  for _,v in pairs(hosts) do
    v = text.tokenize(v)
    if addr == v[1] then return true end
  end
  return false
end

-- [[                DNS DAEMON                                ]]

local event = require "event"
local modem = require("component").modem

local state = false
local path = "/etc/hosts.dns"

local function callback(_, to, from, port, dist, msg, name)
  if port == 2 then
    local res = "dns_error"
    if msg == "dns_update" then
      res = dns.read_hosts(path)
      res = table.concat(res, "\n")
    elseif msg == "dns_register" then
      local hosts = dns.read_hosts(path)
      local err = dns.check_errors(hosts, from, name)
      if err then
        res = err
      else
        dns.register(path, hosts, from, name)
        res = "dns_register_ok"
      end
    elseif msg == "dns_unregister" then
      local hosts = dns.read_hosts(path)
      if dns.is_registered(hosts, from) then
        dns.unregister(path, hosts, from)
        res = "dns_unregister_ok"
      else res = "dns_unregister_error"
      end
    end
    modem.send(from, 2, res)
  end
end

function start(_)
  if not fs.exists(path) then io.close(io.open(path, "w")) end
  if state then
    print("Server is already started.")
    return
  end
  modem.open(2)
  event.listen("modem_message", callback)
  print("DNS Server started.")
  state = true
end

function stop(_)
  if not state then
    print("Server is already stopped.")
    return
  end
  modem.close(2)
  event.ignore("modem_message", callback)
  print("DNS Server stopped.")
  state = false
end

function status(_)
  if state == true then
    print("DNS Server is ON")
  else
    print("DNS Server is OFF")
  end
end