JSON is a compact pure-Lua JSON library. The main functions are: json.stringify, json.parse.
json.stringify:
This expects the following to be true of any tables being encoded:
- They only have string or number keys. Number keys must be represented as strings in json; this is part of the json spec.
- They are not recursive. Such a structure cannot be specified in json.
A Lua table is considered to be an array if and only if its set of keys is a consecutive sequence of positive integers starting at 1. Arrays are encoded like so: [2, 3, false, "hi"]. Any other type of Lua table is encoded as a json object, encoded like so: {"key1": 2, "key2": false}.
Because the Lua nil value cannot be a key, and as a table value is considerd equivalent to a missing key, there is no way to express the json "null" value in a Lua table. The only way this will output "null" is if your entire input obj is nil itself.
An empty Lua table, {}, could be considered either a json object or array - it's an ambiguous edge case. We choose to treat this as an object as it is the more general type.
To be clear, none of the above considerations is a limitation of this code. Rather, it is what we get when we completely observe the json specification for as arbitrary a Lua object as json is capable of expressing.
json.parse:
This function parses json, with the exception that it does not pay attention to \u-escaped unicode code points in strings.
It is difficult for Lua to return null as a value. In order to prevent the loss of keys with a null value in a json string, this function uses the one-off table value json.null (which is just an empty table) to indicate null values. This way you can check if a value is null with the conditional val == json.null.
If you have control over the data and are using Lua, I would recommend just avoiding null values in your data to begin with.
Modified from original: https://gist.github.com/tylerneylon/59f4bcf316be525b30ab
Usage
Module
local JSON = require('Module:JSON')
External Links
- See http://lua-users.org/wiki/JsonModules for more JSON (de)serializer Lua modules
Documentation
- Created with Docbunto
See Also
Code
--- '''JSON''' is a compact pure-Lua JSON library.
-- The main functions are: json.stringify, json.parse.
--
-- '''json.stringify:'''
--
-- This expects the following to be true of any tables being encoded:
-- * They only have string or number keys. Number keys must be represented as
-- strings in json; this is part of the json spec.
-- * They are not recursive. Such a structure cannot be specified in json.
--
-- A Lua table is considered to be an array if and only if its set of keys is a
-- consecutive sequence of positive integers starting at 1. Arrays are encoded like
-- so: `[2, 3, false, "hi"]`. Any other type of Lua table is encoded as a json
-- object, encoded like so: `{"key1": 2, "key2": false}`.
--
-- Because the Lua nil value cannot be a key, and as a table value is considerd
-- equivalent to a missing key, there is no way to express the json "null" value in
-- a Lua table. The only way this will output "null" is if your entire input obj is
-- nil itself.
--
-- An empty Lua table, {}, could be considered either a json object or array -
-- it's an ambiguous edge case. We choose to treat this as an object as it is the
-- more general type.
--
-- To be clear, none of the above considerations is a limitation of this code.
-- Rather, it is what we get when we completely observe the json specification for
-- as arbitrary a Lua object as json is capable of expressing.
--
-- '''json.parse:'''
--
-- This function parses json, with the exception that it does not pay attention to
-- \u-escaped unicode code points in strings.
--
-- It is difficult for Lua to return null as a value. In order to prevent the loss
-- of keys with a null value in a json string, this function uses the one-off
-- table value json.null (which is just an empty table) to indicate null values.
-- This way you can check if a value is null with the conditional
-- `val == json.null`.
--
-- If you have control over the data and are using Lua, I would recommend just
-- avoiding null values in your data to begin with.
--
-- Modified from original: https://gist.github.com/tylerneylon/59f4bcf316be525b30ab
--
-- @module JSON
-- @alias json
-- @author [https://gist.github.com/tylerneylon tylerneylon]
-- @release stable
-- <nowiki>
local json = {}
-- Internal functions.
local function kind_of(obj)
if type(obj) ~= 'table' then return type(obj) end
local i = 1
for _ in pairs(obj) do
if obj[i] ~= nil then i = i + 1 else return 'table' end
end
if i == 1 then return 'table' else return 'array' end
end
local function escape_str(s)
local in_char = {'\\', '"', '/', '\b', '\f', '\n', '\r', '\t'}
local out_char = {'\\', '"', '/', 'b', 'f', 'n', 'r', 't'}
for i, c in ipairs(in_char) do
s = s:gsub(c, '\\' .. out_char[i])
end
return s
end
-- Returns pos, did_find; there are two cases:
-- 1. Delimiter found: pos = pos after leading space + delim; did_find = true.
-- 2. Delimiter not found: pos = pos after leading space; did_find = false.
-- This throws an error if err_if_missing is true and the delim is not found.
local function skip_delim(str, pos, delim, err_if_missing)
pos = pos + #str:match('^%s*', pos)
if str:sub(pos, pos) ~= delim then
if err_if_missing then
error('Expected ' .. delim .. ' near position ' .. pos)
end
return pos, false
end
return pos + 1, true
end
-- Expects the given pos to be the first character after the opening quote.
-- Returns val, pos; the returned pos is after the closing quote character.
local function parse_str_val(str, pos, val)
val = val or ''
local early_end_error = 'End of input found while parsing string.'
if pos > #str then error(early_end_error) end
local c = str:sub(pos, pos)
if c == '"' then return val, pos + 1 end
if c ~= '\\' then return parse_str_val(str, pos + 1, val .. c) end
-- We must have a \ character.
local esc_map = {b = '\b', f = '\f', n = '\n', r = '\r', t = '\t'}
local nextc = str:sub(pos + 1, pos + 1)
if not nextc then error(early_end_error) end
return parse_str_val(str, pos + 2, val .. (esc_map[nextc] or nextc))
end
-- Returns val, pos; the returned pos is after the number's final character.
local function parse_num_val(str, pos)
local num_str = str:match('^-?%d+%.?%d*[eE]?[+-]?%d*', pos)
local val = tonumber(num_str)
if not val then error('Error parsing number at position ' .. pos .. '.') end
return val, pos + #num_str
end
-- Public values and functions.
function json.stringify(obj, as_key)
local s = {} -- We'll build the string as an array of strings to be concatenated.
local kind = kind_of(obj) -- This is 'array' if it's an array or type(obj) otherwise.
if kind == 'array' then
if as_key then error('Can\'t encode array as key.') end
s[#s + 1] = '['
for i, val in ipairs(obj) do
if i > 1 then s[#s + 1] = ', ' end
s[#s + 1] = json.stringify(val)
end
s[#s + 1] = ']'
elseif kind == 'table' then
if as_key then error('Can\'t encode table as key.') end
s[#s + 1] = '{'
for k, v in pairs(obj) do
if #s > 1 then s[#s + 1] = ', ' end
s[#s + 1] = json.stringify(k, true)
s[#s + 1] = ':'
s[#s + 1] = json.stringify(v)
end
s[#s + 1] = '}'
elseif kind == 'string' then
return '"' .. escape_str(obj) .. '"'
elseif kind == 'number' then
if as_key then return '"' .. tostring(obj) .. '"' end
return tostring(obj)
elseif kind == 'boolean' then
return tostring(obj)
elseif kind == 'nil' then
return 'null'
else
error('Unjsonifiable type: ' .. kind .. '.')
end
return table.concat(s)
end
json.null = {} -- This is a one-off table to represent the null value.
function json.parse(str, pos, end_delim)
pos = pos or 1
if pos > #str then error('Reached unexpected end of input.') end
local pos = pos + #str:match('^%s*', pos) -- Skip whitespace.
local first = str:sub(pos, pos)
if first == '{' then -- Parse an object.
local obj, key, delim_found = {}, true, true
pos = pos + 1
while true do
key, pos = json.parse(str, pos, '}')
if key == nil then return obj, pos end
if not delim_found then error('Comma missing between object items.') end
pos = skip_delim(str, pos, ':', true) -- true -> error if missing.
obj[key], pos = json.parse(str, pos)
pos, delim_found = skip_delim(str, pos, ',')
end
elseif first == '[' then -- Parse an array.
local arr, val, delim_found = {}, true, true
pos = pos + 1
while true do
val, pos = json.parse(str, pos, ']')
if val == nil then return arr, pos end
if not delim_found then error('Comma missing between array items.') end
arr[#arr + 1] = val
pos, delim_found = skip_delim(str, pos, ',')
end
elseif first == '"' then -- Parse a string.
return parse_str_val(str, pos + 1)
elseif first == '-' or first:match('%d') then -- Parse a number.
return parse_num_val(str, pos)
elseif first == end_delim then -- End of an object or array.
return nil, pos + 1
else -- Parse true, false, or null.
local literals = {['true'] = true, ['false'] = false, ['null'] = json.null}
for lit_str, lit_val in pairs(literals) do
local lit_end = pos + #lit_str - 1
if str:sub(pos, lit_end) == lit_str then return lit_val, lit_end + 1 end
end
local pos_info_str = 'position ' .. pos .. ': ' .. str:sub(pos, pos + 10)
error('Invalid json syntax starting at ' .. pos_info_str)
end
end
return json