Revise paste slave_switch.lua

local MODEM_SIDE = "bottom"
local PROTOCOL = "rtm_switch"

local CONFIG_FILE = "slave.cfg"
local config = {
  outputs = {
    straight = {},
    cross = {},
  },
  defaultState = "straight",
}

local state = "straight"

local function saveConfig()
  local h = fs.open(CONFIG_FILE, "w")
  h.write(textutils.serialize(config))
  h.close()
end

local function loadConfig()
  if not fs.exists(CONFIG_FILE) then
    saveConfig()
    return
  end
  local h = fs.open(CONFIG_FILE, "r")
  local raw = h.readAll()
  h.close()
  local t = textutils.unserialize(raw)
  if type(t) == "table" then
    config = t
  end
end

local function clearAll()
  for _, side in ipairs({"top","bottom","left","right","front","back"}) do
    if side ~= MODEM_SIDE then
      redstone.setOutput(side, false)
    end
  end
end

local function applyOutputs(list)
  clearAll()
  for _, side in ipairs(list or {}) do
    if side ~= MODEM_SIDE then
      redstone.setOutput(side, true)
    end
  end
end

local function applyState()
  if state == "straight" then
    applyOutputs(config.outputs.straight)
  else
    applyOutputs(config.outputs.cross)
  end
end

local function reply(targetId, extra)
  local payload = {
    ok = true,
    id = os.getComputerID(),
    state = state,
  }
  if type(extra) == "table" then
    for k, v in pairs(extra) do payload[k] = v end
  end
  rednet.send(targetId, payload, PROTOCOL)
end

loadConfig()
state = config.defaultState or "straight"
applyState()
rednet.open(MODEM_SIDE)

while true do
  local senderId, msg, protocol = rednet.receive(PROTOCOL)
  if type(msg) == "table" then
    if msg.cmd == "set" and (msg.state == "straight" or msg.state == "cross") then
      state = msg.state
      applyState()
      reply(senderId)
    elseif msg.cmd == "ping" then
      reply(senderId, {alive = true})
    elseif msg.cmd == "get_config" then
      reply(senderId, {config = config})
    end
  end
end