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lua-json/json.lua

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--
-- json.lua
--
-- Copyright (c) 2015 rxi
--
-- This library is free software; you can redistribute it and/or modify it
-- under the terms of the MIT license. See LICENSE for details.
--
local json = { _version = "0.0.0" }
-------------------------------------------------------------------------------
-- Encode
-------------------------------------------------------------------------------
local encode
local escape_char_map = {
[ "\\" ] = "\\\\",
[ "\"" ] = "\\\"",
[ "\b" ] = "\\b",
[ "\f" ] = "\\f",
[ "\n" ] = "\\n",
[ "\r" ] = "\\r",
[ "\t" ] = "\\t",
}
local escape_char_map_inv = { [ "\\/" ] = "/" }
for k, v in pairs(escape_char_map) do
escape_char_map_inv[v] = k
end
local function escape_char(c)
return escape_char_map[c] or string.format("\\u%04x", c:byte())
end
local function encode_nil(val)
return "null"
end
local function encode_table(val, stack)
local res = {}
stack = stack or {}
-- Circular reference?
if stack[val] then error("circular reference") end
stack[val] = true
if val[1] ~= nil then
-- Treat as array -- check keys are valid and it is not sparse
local n = 0
for k in pairs(val) do
if type(k) ~= "number" then
error("invalid table: mixed or invalid key types")
end
n = n + 1
end
if n ~= #val then
error("invalid table: sparse array")
end
-- Encode
for i, v in ipairs(val) do
table.insert(res, encode(v, stack))
end
stack[val] = nil
return "[" .. table.concat(res, ",") .. "]"
else
-- Treat as an object
for k, v in pairs(val) do
if type(k) ~= "string" then
error("invalid table: mixed or invalid key types")
end
table.insert(res, encode(k, stack) .. ":" .. encode(v, stack))
end
stack[val] = nil
return "{" .. table.concat(res, ",") .. "}"
end
end
local function encode_string(val)
return '"' .. val:gsub('[%z\1-\31\\"]', escape_char) .. '"'
end
local function encode_number(val)
-- Check for NaN, -inf and inf
if val ~= val or val <= -math.huge or val >= math.huge then
error("unexpected number value '" .. tostring(val) .. "'")
end
return string.format("%.14g", val)
end
local type_func_map = {
[ "nil" ] = encode_nil,
[ "table" ] = encode_table,
[ "string" ] = encode_string,
[ "number" ] = encode_number,
[ "boolean" ] = tostring,
}
encode = function(val, stack)
local t = type(val)
local f = type_func_map[t]
if f then
return f(val, stack)
end
error("unexpected type '" .. t .. "'")
end
function json.encode(val)
return ( encode(val) )
end
-------------------------------------------------------------------------------
-- Decode
-------------------------------------------------------------------------------
local parse
local function create_set(...)
local res = {}
for i = 1, select("#", ...) do
res[ select(i, ...) ] = true
end
return res
end
local space_chars = create_set(" ", "\t", "\r", "\n")
local delim_chars = create_set(" ", "\t", "\r", "\n", "]", "}", ",")
local escape_chars = create_set("\\", "/", '"', "b", "f", "n", "r", "t", "u")
local literals = create_set("true", "false", "null")
local literal_map = {
[ "true" ] = true,
[ "false" ] = false,
[ "null" ] = nil,
}
local function next_char(str, idx, set, negate)
for i = idx, #str do
if set[str:sub(i, i)] ~= negate then
return i
end
end
return #str + 1
end
local function decode_error(str, idx, msg)
local line_count = 1
local col_count = 1
for i = 1, idx - 1 do
col_count = col_count + 1
if str:sub(i, i) == "\n" then
line_count = line_count + 1
col_count = 1
end
end
error( string.format("%s at line %d col %d", msg, line_count, col_count) )
end
local function codepoint_to_utf8(n)
-- http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=iws-appendixa
local f = math.floor
if n <= 0x7f then
return string.char(n)
elseif n <= 0x7ff then
return string.char(f(n / 64) + 192, n % 64 + 128)
elseif n <= 0xffff then
return string.char(f(n / 4096) + 224, f(n % 4096 / 64) + 128, n % 64 + 128)
elseif n <= 0x10ffff then
return string.char(f(n / 262144) + 240, f(n % 262144 / 4096) + 128,
f(n % 4096 / 64) + 128, n % 64 + 128)
end
error( string.format("invalid unicode codepoint '%x'", n) )
end
local function parse_unicode_escape(s)
local n1 = tonumber( s:sub(3, 6), 16 )
local n2 = tonumber( s:sub(9, 12), 16 )
-- Surrogate pair?
if n2 then
return codepoint_to_utf8((n1 - 0xd800) * 0x400 + (n2 - 0xdc00) + 0x10000)
else
return codepoint_to_utf8(n1)
end
end
local function parse_string(str, i)
local has_unicode_escape = false
local has_surrogate_escape = false
local has_escape = false
local last
for j = i + 1, #str do
local x = str:byte(j)
if x < 32 then
decode_error(str, j, "control character in string")
end
if last == 92 then -- "\\" (escape char)
if x == 117 then -- "u" (unicode escape sequence)
local hex = str:sub(j + 1, j + 5)
if not hex:find("%x%x%x%x") then
decode_error(str, j, "invalid unicode escape in string")
end
if hex:find("^[dD][89aAbB]") then
has_surrogate_escape = true
else
has_unicode_escape = true
end
else
local c = string.char(x)
if not escape_chars[c] then
decode_error(str, j, "invalid escape char '" .. c .. "' in string")
end
has_escape = true
end
last = nil
elseif x == 34 then -- '"' (end of string)
local s = str:sub(i + 1, j - 1)
if has_surrogate_escape then
s = s:gsub("\\u[dD][89aAbB]..\\u....", parse_unicode_escape)
end
if has_unicode_escape then
s = s:gsub("\\u....", parse_unicode_escape)
end
if has_escape then
s = s:gsub("\\.", escape_char_map_inv)
end
return s, j + 1
else
last = x
end
end
decode_error(str, i, "expected closing quote for string")
end
local function parse_number(str, i)
local x = next_char(str, i, delim_chars)
local s = str:sub(i, x - 1)
local n = tonumber(s)
if not n then
decode_error(str, i, "invalid number '" .. s .. "'")
end
return n, x
end
local function parse_literal(str, i)
local x = next_char(str, i, delim_chars)
local word = str:sub(i, x - 1)
if not literals[word] then
decode_error(str, i, "invalid literal '" .. word .. "'")
end
return literal_map[word], x
end
local function parse_array(str, i)
local res = {}
local n = 1
i = i + 1
while 1 do
local x
i = next_char(str, i, space_chars, true)
-- Empty / end of array?
if str:sub(i, i) == "]" then
i = i + 1
break
end
-- Read token
x, i = parse(str, i)
res[n] = x
n = n + 1
-- Next token
i = next_char(str, i, space_chars, true)
local chr = str:sub(i, i)
i = i + 1
if chr == "]" then break end
if chr ~= "," then decode_error(str, i, "expected ']' or ','") end
end
return res, i
end
local function parse_object(str, i)
local res = {}
i = i + 1
while 1 do
local key, val
i = next_char(str, i, space_chars, true)
-- Empty / end of object?
if str:sub(i, i) == "}" then
i = i + 1
break
end
-- Read key
if str:sub(i, i) ~= '"' then
decode_error(str, i, "expected string for key")
end
key, i = parse(str, i)
-- Read ':' delimiter
i = next_char(str, i, space_chars, true)
if str:sub(i, i) ~= ":" then
decode_error(str, i, "expected ':' after key")
end
i = next_char(str, i + 1, space_chars, true)
-- Read value
val, i = parse(str, i)
-- Set
res[key] = val
-- Next token
i = next_char(str, i, space_chars, true)
local chr = str:sub(i, i)
i = i + 1
if chr == "}" then break end
if chr ~= "," then decode_error(str, i, "expected '}' or ','") end
end
return res, i
end
local char_func_map = {
[ '"' ] = parse_string,
[ "0" ] = parse_number,
[ "1" ] = parse_number,
[ "2" ] = parse_number,
[ "3" ] = parse_number,
[ "4" ] = parse_number,
[ "5" ] = parse_number,
[ "6" ] = parse_number,
[ "7" ] = parse_number,
[ "8" ] = parse_number,
[ "9" ] = parse_number,
[ "-" ] = parse_number,
[ "t" ] = parse_literal,
[ "f" ] = parse_literal,
[ "n" ] = parse_literal,
[ "[" ] = parse_array,
[ "{" ] = parse_object,
}
parse = function(str, idx)
local chr = str:sub(idx, idx)
local f = char_func_map[chr]
if f then
return f(str, idx)
end
decode_error(str, idx, "unexpected character '" .. chr .. "'")
end
function json.decode(str)
return ( parse(str, next_char(str, 1, space_chars, true)) )
end
return json
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