Implement basic serialization and file opening
orwell96
commit
544f8babb5
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-- serialize_lib
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--[[
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Copyright (C) 2020 Moritz Blei (orwell96) and contributors
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU Affero General Public License as
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published by the Free Software Foundation, either version 3 of the
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License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Affero General Public License for more details.
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]]--
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serialize_lib = {}
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--[[ Configuration table
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Whenever asked for a "config", the following table structure is expected:
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config = {
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skip_empty_tables = false -- if true, does not store empty tables
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-- On next read, keys that mapped to empty tables resolve to nil
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-- Used by: write_table_to_file
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}
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Not all functions use all of the parameters, so you can simplify your config sometimes
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]]
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-- log utils
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-- =========
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function serialize_lib.log_error(text)
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minetest.log("error", "[serialize_lib] "..text)
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end
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function serialize_lib.log_warn(text)
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minetest.log("warning", "[serialize_lib] "..text)
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end
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function serialize_lib.log_info(text)
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minetest.log("action", "[serialize_lib] "..text)
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end
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function serialize_lib.log_debug(text)
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minetest.log("action", "[serialize_lib](debug) "..text)
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end
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-- basic serialization/deserialization
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-- ===================================
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local ser = dofile("serialize.lua")
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-- Opens the passed filename, and returns deserialized table
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-- When an error occurs, logs an error and returns false
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function serialize_lib.read_table_from_file(filename)
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local succ, err = pcall(ser.read_from_file, filename)
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if not succ then
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serialize_lib.log_error("Mod '"..minetest.get_current_modname().."': "..err)
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end
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return succ
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end
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-- Writes table into file
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-- When an error occurs, logs an error and returns false
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function serialize_lib.write_table_to_file(filename)
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local succ, err = pcall(ser.write_to_file, filename)
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if not succ then
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serialize_lib.log_error("Mod '"..minetest.get_current_modname().."': "..err)
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end
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return succ
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end
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-- Managing files and backups
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-- ==========================
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--[[
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The plain scheme just overwrites the file in place. This however poses problems when we are interrupted right within
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the write, so we have incomplete data. So, the following scheme is applied:
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1. writes to <filename>.new (if .new already exists, try to complete the moving first)
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2. moves <filename> to <filename>.old, possibly overwriting an existing file (special windows behavior)
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3. moves <filename>.new to <filename>
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During loading, we apply the following order of precedence:
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1. <filename>.new
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2. <filename>
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3. <filename>.old
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Normal case: <filename> and <filename>.old exist, loading <filename>
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Interrupted during write: .new is damaged, loads last regular state
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Interrupted during the move operations: either <filename>.new or <filename> represents the latest state
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Other corruption: at least the .old state may still be present
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]]--
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@ -0,0 +1,7 @@
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# serialize_lib
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A Minetest mod library for safely storing large amounts of data in on-disk files.
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Created out of the need to have a robust data store for advtrains.
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The main purpose is to load and store large Lua table structures into files, without loading everything in memory and exhausting the function constant limit of LuaJIT.
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Also contains various utilities to handle files on disk in a safe manner, retain multiple versions of the same file a.s.o.
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@ -0,0 +1,260 @@
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-- serialize.lua
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-- Lua-conformant library file that has no minetest dependencies
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-- Contains the serialization and deserialization routines
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--[[
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Structure of entry:
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[keytype][key]:[valuetype][val]
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Types:
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B - bool
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-> 0=false, 1=true
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S - string
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-> see below
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N - number
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-> thing compatible with tonumber()
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Table:
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[keytype][key]:T
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... content is nested in table until the matching
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E
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example:
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LUA_SER v=1 {
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Skey:Svalue key = "value",
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N1:Seins [1] = "eins",
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B1:T [true] = {
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Sa:Sb a = "b",
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Sc:B0 c = false,
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E }
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E }
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String representations:
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In strings the following characters are escaped by &
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'&' -> '&&'
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(line break) -> '&n'
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(CR) -> '&r' --> required?
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':' -> '&:'
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All other characters are unchanged as they bear no special meaning.
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]]
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local write_table, literal_to_string, escape_chars, table_is_empty
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function table_is_empty(t)
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for _,_ in pairs(t) do
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return false
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end
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return true
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end
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function write_table(t, file, config)
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local ks, vs, writeit, istable
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for key, value in pairs(t) do
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ks = value_to_string(key, false)
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writeit = true
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istable = type(value)=="table"
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if istable then
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vs = "T"
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if config.skip_empty_tables then
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writeit = not table_is_empty(value)
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end
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else
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vs = value_to_string(value, true)
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end
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if writeit then
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file:write(ks..":"..vs.."\n")
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if istable then
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write_table(value, file, config)
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file:write("E\n")
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end
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end
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end
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end
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function value_to_string(t)
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if type(t)=="table" then
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error("Can not serialize a table in the key position!")
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elseif type(t)=="boolean" then
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if t then
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return "B1"
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else
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return "B0"
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end
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elseif type(t)=="number" then
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return "N"..t
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elseif type(t)=="string" then
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return "S"..escape_chars(t)
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else
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error("Can not serialize '"..type(t).."' type!")
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end
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return str
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end
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function escape_chars(str)
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local rstr = string.gsub(str, "&", "&&")
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rstr = string.gsub(rstr, ":", "&:")
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rstr = string.gsub(rstr, "\n", "&n")
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return rstr
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end
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------
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local read_table, string_to_value, unescape_chars
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function read_table(t, file)
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local line, ks, vs, kv, vv, vt
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while true do
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line = file:read("*l")
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if not line then
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error("Unexpected EOF or read error!")
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end
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if line=="E" then
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-- done with this table
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return
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end
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ks, vs = string.match(line, "^(.+[^&]):(.+)$")
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if not ks or not vs then
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error("Unable to parse line: '"..line.."'!")
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end
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kv = string_to_value(ks)
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vv, vt = string_to_value(vs, true)
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if vt then
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read_table(vv, file)
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end
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-- put read value in table
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t[kv] = vv
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end
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end
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-- returns: value, is_table
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function string_to_value(str, table_allow)
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local first = string.sub(str, 1,1)
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local rest = string.sub(str, 2)
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if first=="T" then
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if table_allow then
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return {}, true
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else
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error("Table not allowed in key component!")
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end
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elseif first=="N" then
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local num = tonumber(rest)
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if num then
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return num
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else
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error("Unable to parse number: '"..rest.."'!")
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end
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elseif first=="B" then
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if rest=="0" then
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return false
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elseif rest=="1" then
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return true
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else
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error("Unable to parse boolean: '"..rest.."'!")
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end
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elseif first=="S" then
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return unescape_chars(rest)
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else
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error("Unknown literal type '"..first.."' for literal '"..str.."'!")
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end
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end
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function unescape_chars(str) --TODO
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local rstr = string.gsub(str, "&:", ":")
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rstr = string.gsub(rstr, "&n", "\n")
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rstr = string.gsub(rstr, "&&", "&")
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return rstr
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end
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------
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--[[
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config = {
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skip_empty_tables = false -- if true, does not store empty tables
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-- On next read, keys that mapped to empty tables resolve to nil
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}
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]]
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-- Writes the passed table into the passed file descriptor, and closes the file afterwards
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local function write_to_fd(root_table, file, config)
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file:write("LUA_SER v=1\n")
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write_table(root_table, file, config)
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file:write("E\nEND_SER\n")
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file:close()
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end
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-- Reads the file contents from the passed file descriptor and returns the table on success
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-- Throws errors when something is wrong.
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-- config: see above
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local function read_from_fd(file)
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local first_line = file:read("*l")
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if first_line ~= "LUA_SER v=1" then
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error("Expected header, got '"..first_line.."' instead!")
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end
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local t = {}
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read_table(t, file)
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local last_line = file:read("*l")
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file:close()
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if last_line ~= "END_SER" then
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error("Missing END_SER, got '"..last_line.."' instead!")
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end
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return t
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end
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-- Opens the passed filename and serializes root_table into it
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-- config: see above
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function write_to_file(root_table, filename, config)
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-- try opening the file
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local file, err = io.open(filename, "w")
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if not file then
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error("Failed opening file '"..filename.."' for write: "..err)
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end
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write_to_fd(root_table, file, config)
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return true
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end
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-- Opens the passed filename, and returns its deserialized contents
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function read_from_file(filename)
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-- try opening the file
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local file, err = io.open(filename, "r")
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if not file then
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error("Failed opening file '"..filename.."' for read: "..err)
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end
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return read_from_fd(file)
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end
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--[[ simple unit test
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local testtable = {
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key = "value",
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[1] = "eins",
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[true] = {
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a = "b",
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c = false,
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},
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["es:cape1"] = "foo:bar",
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["es&ca\npe2"] = "baz&bam\nbim",
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["es&&ca&\npe3"] = "baz&&bam&\nbim",
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["es&:cape4"] = "foo\n:bar"
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}
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local config = {}
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--write_to_file(testtable, "test_out", config)
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local t = read_from_file("test_out")
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write_to_file(t, "test_out_2", config)
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local t2 = read_from_file("test_out_2")
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write_to_file(t2, "test_out_3", config)
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-- test_out_2 and test_out_3 should be equal
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--]]
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return {
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read_from_fd = read_from_fd,
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write_to_fd = write_to_fd,
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read_from_file = read_from_file,
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write_to_file = write_to_file,
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}
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