techage/basis/nodedata_meta.lua

--[[

	TechAge
	=======

	Copyright (C) 2020 Joachim Stolberg

	AGPL v3
	See LICENSE.txt for more information

	Storage backend for node related data as node metadata

]]--

-- for lazy programmers
local M = minetest.get_meta

local storage = techage.storage

-------------------------------------------------------------------
-- Marshaling
-------------------------------------------------------------------
local use_marshal = minetest.settings:get_bool('techage_use_marshal', false)
local MAR_MAGIC = 0x8e

-- default functions
local serialize = minetest.serialize
local deserialize = minetest.deserialize

if use_marshal then
	if not techage.IE then
		error("Please add 'secure.trusted_mods = techage' to minetest.conf!")
	end
	local marshal = techage.IE.require("marshal")
	if not marshal then
		error("Please install marshal via 'luarocks install lua-marshal'")
	end

	serialize = marshal.encode

	deserialize = function(s)
		if s ~= "" then
			if s:byte(1) == MAR_MAGIC then
				return marshal.decode(s)
			else
				return minetest.deserialize(s)
			end
		end
	end
end

-------------------------------------------------------------------
-- API functions
-------------------------------------------------------------------
local api = {}

function api.get_mapblock_data(key)
	return {}
end

function api.store_mapblock_data(key, mapblock_data)
	for key, item in pairs(mapblock_data) do
		if key ~= "in_use" then
			local pos = item and item._POS_
			if pos then
				item._POS_ = nil
				local data = serialize(item)
				item._POS_ = pos
				local meta = M(pos)
				meta:set_string("ta_data", data)
				meta:mark_as_private("ta_data")
			end
		end
	end
end

function api.get_node_data(pos)
	local tbl = {}
	local s = M(pos):get_string("ta_data")

	if s ~= "" then
		tbl = deserialize(s) or {}
	end
	tbl._POS_ = table.copy(pos)

	return tbl
end

-- Meta data can't be written reliable at shutdown,
-- so we have to store/restore the data differently
function api.freeze_at_shutdown(data)
	storage:set_string("shutdown_nodedata", serialize(data))
end

function api.restore_at_startup()
	local s = storage:get_string("shutdown_nodedata")
	if s ~= "" then
		return deserialize(s) or {}
	end
	return {}
end

return api