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--- Lua module to serialize values as Lua code.
-- From: https://github.com/fab13n/metalua/blob/no-dll/src/lib/serialize.lua
-- License: MIT
-- @copyright 2006-2997 Fabien Fleutot <metalua@gmail.com>
-- @author Fabien Fleutot <metalua@gmail.com>
-- @author ShadowNinja <shadowninja@minetest.net>
--------------------------------------------------------------------------------
--- Serialize an object into a source code string. This string, when passed as
-- an argument to deserialize(), returns an object structurally identical to
-- the original one. The following are currently supported:
-- * Booleans, numbers, strings, and nil.
-- * Functions; uses interpreter-dependent (and sometimes platform-dependent) bytecode!
-- * Tables; they can cantain multiple references and can be recursive, but metatables aren't saved.
-- This works in two phases:
-- 1. Recursively find and record multiple references and recursion.
-- 2. Recursively dump the value into a string.
-- @param x Value to serialize (nil is allowed).
-- @return load()able string containing the value.
function core.serialize(x)
local local_index = 1 -- Top index of the "_" local table in the dump
-- table->nil/1/2 set of tables seen.
-- nil = not seen, 1 = seen once, 2 = seen multiple times.
local seen = {}
-- nest_points are places where a table appears within itself, directly
-- or not. For instance, all of these chunks create nest points in
-- table x: "x = {}; x[x] = 1", "x = {}; x[1] = x",
-- "x = {}; x[1] = {y = {x}}".
-- To handle those, two tables are used by mark_nest_point:
-- * nested - Transient set of tables being currently traversed.
-- Used for detecting nested tables.
-- * nest_points - parent->{key=value, ...} table cantaining the nested
-- keys and values in the parent. They're all dumped after all the
-- other table operations have been performed.
--
-- mark_nest_point(p, k, v) fills nest_points with information required
-- to remember that key/value (k, v) creates a nest point in table
-- parent. It also marks "parent" and the nested item(s) as occuring
-- multiple times, since several references to it will be required in
-- order to patch the nest points.
local nest_points = {}
local nested = {}
local function mark_nest_point(parent, k, v)
local nk, nv = nested[k], nested[v]
local np = nest_points[parent]
if not np then
np = {}
nest_points[parent] = np
end
np[k] = v
seen[parent] = 2
if nk then seen[k] = 2 end
if nv then seen[v] = 2 end
end
-- First phase, list the tables and functions which appear more than
-- once in x.
local function mark_multiple_occurences(x)
local tp = type(x)
if tp ~= "table" and tp ~= "function" then
-- No identity (comparison is done by value, not by instance)
return
end
if seen[x] == 1 then
seen[x] = 2
elseif seen[x] ~= 2 then
seen[x] = 1
end
if tp == "table" then
nested[x] = true
for k, v in pairs(x) do
if nested[k] or nested[v] then
mark_nest_point(x, k, v)
else
mark_multiple_occurences(k)
mark_multiple_occurences(v)
end
end
nested[x] = nil
end
end
local dumped = {} -- object->varname set
local local_defs = {} -- Dumped local definitions as source code lines
-- Mutually recursive local functions:
local dump_val, dump_or_ref_val
-- If x occurs multiple times, dump the local variable rather than
-- the value. If it's the first time it's dumped, also dump the
-- content in local_defs.
function dump_or_ref_val(x)
if seen[x] ~= 2 then
return dump_val(x)
end
local var = dumped[x]
if var then -- Already referenced
return var
end
-- First occurence, create and register reference
local val = dump_val(x)
local i = local_index
local_index = local_index + 1
var = "_["..i.."]"
local_defs[#local_defs + 1] = var.." = "..val
dumped[x] = var
return var
end
-- Second phase. Dump the object; subparts occuring multiple times
-- are dumped in local variables which can be referenced multiple
-- times. Care is taken to dump local vars in a sensible order.
function dump_val(x)
local tp = type(x)
if x == nil then return "nil"
elseif tp == "string" then return string.format("%q", x)
elseif tp == "boolean" then return x and "true" or "false"
elseif tp == "function" then
return string.format("loadstring(%q)", string.dump(x))
elseif tp == "number" then
-- Serialize numbers reversibly with string.format
return string.format("%.17g", x)
elseif tp == "table" then
local vals = {}
local idx_dumped = {}
local np = nest_points[x]
for i, v in ipairs(x) do
if not np or not np[i] then
vals[#vals + 1] = dump_or_ref_val(v)
end
idx_dumped[i] = true
end
for k, v in pairs(x) do
if (not np or not np[k]) and
not idx_dumped[k] then
vals[#vals + 1] = "["..dump_or_ref_val(k).."] = "
..dump_or_ref_val(v)
end
end
return "{"..table.concat(vals, ", ").."}"
else
error("Can't serialize data of type "..tp)
end
end
local function dump_nest_points()
for parent, vals in pairs(nest_points) do
for k, v in pairs(vals) do
local_defs[#local_defs + 1] = dump_or_ref_val(parent)
.."["..dump_or_ref_val(k).."] = "
..dump_or_ref_val(v)
end
end
end
mark_multiple_occurences(x)
local top_level = dump_or_ref_val(x)
dump_nest_points()
if next(local_defs) then
return "local _ = {}\n"
..table.concat(local_defs, "\n")
.."\nreturn "..top_level
else
return "return "..top_level
end
end
-- Deserialization
local function safe_loadstring(...)
local func, err = loadstring(...)
if func then
setfenv(func, {})
return func
end
return nil, err
end
local function dummy_func() end
function core.deserialize(str, safe)
if type(str) ~= "string" then
return nil, "Cannot deserialize type '"..type(str)
.."'. Argument must be a string."
end
if str:byte(1) == 0x1B then
return nil, "Bytecode prohibited"
end
local f, err = loadstring(str)
if not f then return nil, err end
-- The environment is recreated every time so deseralized code cannot
-- pollute it with permanent references.
setfenv(f, {loadstring = safe and dummy_func or safe_loadstring})
local good, data = pcall(f)
if good then
return data
else
return nil, data
end
end
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