some kind of web browser in Lua

dofile("tab2file") -- 2 new functions to write and read ini-like files

cls = function()
  term.clear()
  term.setCursorPos(1,1)
end

main = function()
  cls()
  if fs.exists("sec.config") then
    sec = file2tab("sec.config")
  else
    sec = {}
    sec.open = 1
    sec.shutdown = 1
    sec.net = 0
    tab2file(sec,"sec.config")
  end
  print("1. Browse\n2. Security\n3. Exit")
  local ans = read()
  if ans == "1" then
    return browser()
  elseif ans == "2" then
    return security()
  elseif ans == "3" then
    return
  else
    return main()
  end
end

security = function()
  cls()
  print("1. File opening: "..tonumber(sec.file))
  print("2. Shutdown: "..tonumber(sec.shutdown))
  print("3. Rednet access: "..tonumber(sec.net))
  print("4. Exit")
  local num = {sec.file, sec.shutdown, sec.net}
  local ans = tonumber(read())
  if num[ans] then
    if sec[ans] == 1 then
      sec[ans] = 0
    else
      sec[ans] = 1
    end
    tab2file(sec,"sec.config")
    return security()
  elseif ans == 4 then
    return main()
  else
    return security()
  end
end

browser = function()

  write("URL: ")
  local ans = read()
  sleep(1)
  _,_,id = string.find(ans, "^(%d+)$")
  if id == nil then
    _,_,id,path = string.find(ans, "^(%d+)/([/%w]+)$")
  else
    path = ""
  end
  if id == nil then
    print("Incorrect request")
    sleep(1)
    cls()
    return browser()
  end

  rednet.send(tonumber(id),path)
  _, mes = rednet.receive()
  file = fs.open("page.tmp","w")
  file.write(mes)
  file.close()

  sec = file2tab("sec.config")
  local old = {}
  old.open = fs.open
  old.shutdown = os.shutdown
  old.reboot = os.reboot
  old.send = rednet.send
  old.broadcast = rednet.broadcast
  old.pullEventRaw = os.pullEventRaw
  old.write = term.write
  local restore = function()
    fs.open = old.open
    os.shutdown = old.shutdown
    os.reboot = old.reboot
    rednet.send = old.send
    rednet.broadcast = old.broadcast
    os.pullEventRaw = old.pullEventRaw
    term.write = old.write
  end
  local l_error = error -- backup of error() for confirmation
  if sec.file == 1 then
    local firstfile = true -- for "page.tmp" opening in dofile()
    fs.open = function(file,mode)
      if firstfile == false then
        print("Attempt to open file "..file.." at mode "..mode..". Proceed?")
        if read() == "y" then
          return old.open(file,mode)
        else
          return nil
        end
      else
        firstfile = false
        return old.open(file,mode)
      end
    end
  end
  if sec.shutdown == 1 then
    os.shutdown = function()
      print("Attempt to shutdown host. Emergency exit.")
      if l_error ~= error then
        print("ATTEMPT TO BYPASS EMERGENCY EXIT SYSTEM! IMMEDIATE EXIT!")
        error = l_error
        error("security breach attempt")
      end
      error("shutdown attempt")
    end
    os.reboot = function()
      print("Attempt to reboot system. Emergency exit.")
      if l_error ~= error then
        print("ATTEMPT TO BYPASS EMERGENCY EXIT SYSTEM! IMMEDIATE EXIT!")
        error = l_error
        error("security breach attempt")
      end
      error("reboot attempt")
    end
  end
  if sec.net == 1 then
    rednet.send = function(id,mes)
      print("Attempt to send rednet message \""..mes.."\" to host "..tostring(id)..". Proceed?")
      if read() == "y" then
        return old.send(id,mes)
      else
        return nil
      end
    end
    rednet.broadcast = function(mes)
      print("Attempt to send rednet message \""..mes.."\" to broadcasting channel. Proceed?")
      if read() == "y" then
        return old.broadcast(mes)
      else
        return nil
      end
    end
  end
  os.pullEventRaw = function(type)
    if l_error ~= error then
      print("ATTEMPT TO BYPASS EMERGENCY EXIT SYSTEM! IMMEDIATE EXIT!")
      error = l_error
      error("security breach attempt")
    end
    if type == nil then
      res = {old.pullEventRaw()}
      if res[1] == "key" and res[2] == 59 then
        error("break key pressed")
      end
      return unpack(res)
    else
      while true do
        res = {old.pullEventRaw()}
        if res[1] == "key" and res[2] == 59 then
          error("break key pressed")
        end
        if res[1] == type then
          return unpack(res)
        end
      end
    end
  end
  local save = ""
  term.write = function(text)
    save = save..text
    old.write(text)
  end

  local getSave = function()
    return save
  end

  k, mes = pcall(function() dofile("page.tmp") end)

  restore()
  print()
  if k == true then
    print("Program exited correctly.")
  else
    print("Performed emergency exit because of error.")
    print("Error message: "..tostring(mes))
  end
  print("Press E to exit, S to save page and exit")
  while true do
    local c
    _, c = os.pullEventRaw("char")
    if c == "e" then
      break
    elseif c == "s" then
      print("Enter file name: ")
      path = read()
      file = fs.open(path,"w")
      file.write(getSave())
      file.close()
      print("Saved")
      break
    end
  end
  return main()
end

main()