Implement basic serialization and file opening

1 files changed, 92 insertions, 0 deletions

diff --git a/init.lua b/init.lua
new file mode 100644
index 0000000..7a1a10b
--- /dev/null
+++ b/init.lua
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+-- serialize_lib
+--[[
+	Copyright (C) 2020  Moritz Blei (orwell96) and contributors
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as
+    published by the Free Software Foundation, either version 3 of the
+    License, or (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+]]--
+
+serialize_lib = {}
+
+--[[ Configuration table
+Whenever asked for a "config", the following table structure is expected:
+config = {
+	skip_empty_tables = false	-- if true, does not store empty tables
+								-- On next read, keys that mapped to empty tables resolve to nil
+								-- Used by: write_table_to_file
+}
+Not all functions use all of the parameters, so you can simplify your config sometimes
+]]
+
+-- log utils
+-- =========
+
+
+function serialize_lib.log_error(text)
+	minetest.log("error", "[serialize_lib] "..text)
+end
+function serialize_lib.log_warn(text)
+	minetest.log("warning", "[serialize_lib] "..text)
+end
+function serialize_lib.log_info(text)
+	minetest.log("action", "[serialize_lib] "..text)
+end
+function serialize_lib.log_debug(text)
+	minetest.log("action", "[serialize_lib](debug) "..text)
+end
+
+-- basic serialization/deserialization
+-- ===================================
+
+local ser = dofile("serialize.lua")
+
+-- Opens the passed filename, and returns deserialized table
+-- When an error occurs, logs an error and returns false
+function serialize_lib.read_table_from_file(filename)
+	local succ, err = pcall(ser.read_from_file, filename)
+	if not succ then
+		serialize_lib.log_error("Mod '"..minetest.get_current_modname().."': "..err)
+	end
+	return succ
+end
+
+-- Writes table into file
+-- When an error occurs, logs an error and returns false
+function serialize_lib.write_table_to_file(filename)
+	local succ, err = pcall(ser.write_to_file, filename)
+	if not succ then
+		serialize_lib.log_error("Mod '"..minetest.get_current_modname().."': "..err)
+	end
+	return succ
+end
+
+-- Managing files and backups
+-- ==========================
+
+--[[
+The plain scheme just overwrites the file in place. This however poses problems when we are interrupted right within
+the write, so we have incomplete data. So, the following scheme is applied:
+1. writes to <filename>.new (if .new already exists, try to complete the moving first)
+2. moves <filename> to <filename>.old, possibly overwriting an existing file (special windows behavior)
+3. moves <filename>.new to <filename>
+
+During loading, we apply the following order of precedence:
+1. <filename>.new
+2. <filename>
+3. <filename>.old
+
+Normal case: <filename> and <filename>.old exist, loading <filename>
+Interrupted during write: .new is damaged, loads last regular state
+Interrupted during the move operations: either <filename>.new or <filename> represents the latest state
+Other corruption: at least the .old state may still be present
+
+]]--
+
+