minetest-mm/mods/advtrains/serialize_lib/serialize.lua

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2021-01-13 21:04:51 +01:00
-- serialize.lua
-- Lua-conformant library file that has no minetest dependencies
-- Contains the serialization and deserialization routines
--[[
Structure of entry:
[keytype][key]:[valuetype][val]
Types:
B - bool
-> 0=false, 1=true
S - string
-> see below
N - number
-> thing compatible with tonumber()
Table:
[keytype][key]:T
... content is nested in table until the matching
E
example:
LUA_SER v=1 {
Skey:Svalue key = "value",
N1:Seins [1] = "eins",
B1:T [true] = {
Sa:Sb a = "b",
Sc:B0 c = false,
E }
E }
String representations:
In strings the following characters are escaped by &
'&' -> '&&'
(line break) -> '&n'
(CR) -> '&r' --> required?
':' -> '&:'
All other characters are unchanged as they bear no special meaning.
]]
local write_table, literal_to_string, escape_chars, table_is_empty
function table_is_empty(t)
for _,_ in pairs(t) do
return false
end
return true
end
function write_table(t, file, config)
local ks, vs, writeit, istable
for key, value in pairs(t) do
ks = value_to_string(key, false)
writeit = true
istable = type(value)=="table"
if istable then
vs = "T"
if config and config.skip_empty_tables then
writeit = not table_is_empty(value)
end
else
vs = value_to_string(value, true)
end
if writeit then
file:write(ks..":"..vs.."\n")
if istable then
write_table(value, file, config)
file:write("E\n")
end
end
end
end
function value_to_string(t)
if type(t)=="table" then
file:close()
error("Can not serialize a table in the key position!")
elseif type(t)=="boolean" then
if t then
return "B1"
else
return "B0"
end
elseif type(t)=="number" then
return "N"..t
elseif type(t)=="string" then
return "S"..escape_chars(t)
else
--error("Can not serialize '"..type(t).."' type!")
return "S<function>"
end
return str
end
function escape_chars(str)
local rstr = string.gsub(str, "&", "&&")
rstr = string.gsub(rstr, ":", "&:")
rstr = string.gsub(rstr, "\n", "&n")
return rstr
end
------
local read_table, string_to_value, unescape_chars
function read_table(t, file)
local line, ks, vs, kv, vv, vt
while true do
line = file:read("*l")
if not line then
file:close()
error("Unexpected EOF or read error!")
end
if line=="E" then
-- done with this table
return
end
ks, vs = string.match(line, "^(.*[^&]):(.+)$")
if not ks or not vs then
file:close()
error("Unable to parse line: '"..line.."'!")
end
kv = string_to_value(ks)
vv, vt = string_to_value(vs, true)
if vt then
read_table(vv, file)
end
-- put read value in table
t[kv] = vv
end
end
-- returns: value, is_table
function string_to_value(str, table_allow)
local first = string.sub(str, 1,1)
local rest = string.sub(str, 2)
if first=="T" then
if table_allow then
return {}, true
else
file:close()
error("Table not allowed in key component!")
end
elseif first=="N" then
local num = tonumber(rest)
if num then
return num
else
file:close()
error("Unable to parse number: '"..rest.."'!")
end
elseif first=="B" then
if rest=="0" then
return false
elseif rest=="1" then
return true
else
file:close()
error("Unable to parse boolean: '"..rest.."'!")
end
elseif first=="S" then
return unescape_chars(rest)
else
file:close()
error("Unknown literal type '"..first.."' for literal '"..str.."'!")
end
end
function unescape_chars(str) --TODO
local rstr = string.gsub(str, "&:", ":")
rstr = string.gsub(rstr, "&n", "\n")
rstr = string.gsub(rstr, "&&", "&")
return rstr
end
------
--[[
config = {
skip_empty_tables = false -- if true, does not store empty tables
-- On next read, keys that mapped to empty tables resolve to nil
}
]]
-- Writes the passed table into the passed file descriptor, and closes the file
local function write_to_fd(root_table, file, config)
file:write("LUA_SER v=1\n")
write_table(root_table, file, config)
file:write("E\nEND_SER\n")
end
-- Reads the file contents from the passed file descriptor and returns the table on success
-- Throws errors when something is wrong. Closes the file.
-- config: see above
local function read_from_fd(file)
local first_line = file:read("*l")
if first_line ~= "LUA_SER v=1" then
file:close()
error("Expected header, got '"..first_line.."' instead!")
end
local t = {}
read_table(t, file)
local last_line = file:read("*l")
file:close()
if last_line ~= "END_SER" then
error("Missing END_SER, got '"..last_line.."' instead!")
end
return t
end
-- Opens the passed filename and serializes root_table into it
-- config: see above
function write_to_file(root_table, filename, config)
-- try opening the file
local file, err = io.open(filename, "w")
if not file then
error("Failed opening file '"..filename.."' for write:\n"..err)
end
write_to_fd(root_table, file, config)
return true
end
-- Opens the passed filename, and returns its deserialized contents
function read_from_file(filename)
-- try opening the file
local file, err = io.open(filename, "r")
if not file then
error("Failed opening file '"..filename.."' for read:\n"..err)
end
return read_from_fd(file)
end
--[[ simple unit test
local testtable = {
key = "value",
[1] = "eins",
[true] = {
a = "b",
c = false,
},
["es:cape1"] = "foo:bar",
["es&ca\npe2"] = "baz&bam\nbim",
["es&&ca&\npe3"] = "baz&&bam&\nbim",
["es&:cape4"] = "foo\n:bar"
}
local config = {}
--write_to_file(testtable, "test_out", config)
local t = read_from_file("test_out")
write_to_file(t, "test_out_2", config)
local t2 = read_from_file("test_out_2")
write_to_file(t2, "test_out_3", config)
-- test_out_2 and test_out_3 should be equal
--]]
return {
read_from_fd = read_from_fd,
write_to_fd = write_to_fd,
read_from_file = read_from_file,
write_to_file = write_to_file,
}