Added json.lua
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--[[ json.lua
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Downloaded from: https://gist.github.com/tylerneylon/59f4bcf316be525b30ab
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Owner said:
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> Oh hey @Shujito and @S0lll0s, sorry for the delayed response.
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> Yes, please use it. I put this in the public domain.
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A compact pure-Lua JSON library.
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The main functions are: json.stringify, json.parse.
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## json.stringify:
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This expects the following to be true of any tables being encoded:
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* They only have string or number keys. Number keys must be represented as
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strings in json; this is part of the json spec.
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* They are not recursive. Such a structure cannot be specified in json.
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A Lua table is considered to be an array if and only if its set of keys is a
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consecutive sequence of positive integers starting at 1. Arrays are encoded like
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so: `[2, 3, false, "hi"]`. Any other type of Lua table is encoded as a json
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object, encoded like so: `{"key1": 2, "key2": false}`.
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Because the Lua nil value cannot be a key, and as a table value is considerd
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equivalent to a missing key, there is no way to express the json "null" value in
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a Lua table. The only way this will output "null" is if your entire input obj is
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nil itself.
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An empty Lua table, {}, could be considered either a json object or array -
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it's an ambiguous edge case. We choose to treat this as an object as it is the
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more general type.
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To be clear, none of the above considerations is a limitation of this code.
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Rather, it is what we get when we completely observe the json specification for
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as arbitrary a Lua object as json is capable of expressing.
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## json.parse:
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This function parses json, with the exception that it does not pay attention to
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\u-escaped unicode code points in strings.
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It is difficult for Lua to return null as a value. In order to prevent the loss
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of keys with a null value in a json string, this function uses the one-off
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table value json.null (which is just an empty table) to indicate null values.
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This way you can check if a value is null with the conditional
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`val == json.null`.
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If you have control over the data and are using Lua, I would recommend just
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avoiding null values in your data to begin with.
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--]]
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local json = {}
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-- Internal functions.
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local function kind_of(obj)
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if type(obj) ~= 'table' then return type(obj) end
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local i = 1
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for _ in pairs(obj) do
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if obj[i] ~= nil then i = i + 1 else return 'table' end
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end
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if i == 1 then return 'table' else return 'array' end
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end
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local function escape_str(s)
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local in_char = {'\\', '"', '/', '\b', '\f', '\n', '\r', '\t'}
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local out_char = {'\\', '"', '/', 'b', 'f', 'n', 'r', 't'}
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for i, c in ipairs(in_char) do
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s = s:gsub(c, '\\' .. out_char[i])
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end
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return s
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end
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-- Returns pos, did_find; there are two cases:
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-- 1. Delimiter found: pos = pos after leading space + delim; did_find = true.
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-- 2. Delimiter not found: pos = pos after leading space; did_find = false.
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-- This throws an error if err_if_missing is true and the delim is not found.
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local function skip_delim(str, pos, delim, err_if_missing)
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pos = pos + #str:match('^%s*', pos)
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if str:sub(pos, pos) ~= delim then
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if err_if_missing then
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error('Expected ' .. delim .. ' near position ' .. pos)
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end
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return pos, false
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end
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return pos + 1, true
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end
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-- Expects the given pos to be the first character after the opening quote.
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-- Returns val, pos; the returned pos is after the closing quote character.
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local function parse_str_val(str, pos, val)
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val = val or ''
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local early_end_error = 'End of input found while parsing string.'
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if pos > #str then error(early_end_error) end
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local c = str:sub(pos, pos)
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if c == '"' then return val, pos + 1 end
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if c ~= '\\' then return parse_str_val(str, pos + 1, val .. c) end
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-- We must have a \ character.
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local esc_map = {b = '\b', f = '\f', n = '\n', r = '\r', t = '\t'}
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local nextc = str:sub(pos + 1, pos + 1)
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if not nextc then error(early_end_error) end
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return parse_str_val(str, pos + 2, val .. (esc_map[nextc] or nextc))
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end
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-- Returns val, pos; the returned pos is after the number's final character.
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local function parse_num_val(str, pos)
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local num_str = str:match('^-?%d+%.?%d*[eE]?[+-]?%d*', pos)
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local val = tonumber(num_str)
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if not val then error('Error parsing number at position ' .. pos .. '.') end
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return val, pos + #num_str
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end
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-- Public values and functions.
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function json.stringify(obj, as_key)
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local s = {} -- We'll build the string as an array of strings to be concatenated.
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local kind = kind_of(obj) -- This is 'array' if it's an array or type(obj) otherwise.
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if kind == 'array' then
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if as_key then error('Can\'t encode array as key.') end
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s[#s + 1] = '['
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for i, val in ipairs(obj) do
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if i > 1 then s[#s + 1] = ', ' end
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s[#s + 1] = json.stringify(val)
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end
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s[#s + 1] = ']'
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elseif kind == 'table' then
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if as_key then error('Can\'t encode table as key.') end
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s[#s + 1] = '{'
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for k, v in pairs(obj) do
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if #s > 1 then s[#s + 1] = ', ' end
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s[#s + 1] = json.stringify(k, true)
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s[#s + 1] = ':'
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s[#s + 1] = json.stringify(v)
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end
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s[#s + 1] = '}'
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elseif kind == 'string' then
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return '"' .. escape_str(obj) .. '"'
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elseif kind == 'number' then
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if as_key then return '"' .. tostring(obj) .. '"' end
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return tostring(obj)
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elseif kind == 'boolean' then
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return tostring(obj)
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elseif kind == 'nil' then
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return 'null'
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else
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error('Unjsonifiable type: ' .. kind .. '.')
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end
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return table.concat(s)
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end
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json.null = {} -- This is a one-off table to represent the null value.
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function json.parse(str, pos, end_delim)
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pos = pos or 1
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if pos > #str then error('Reached unexpected end of input.') end
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local pos = pos + #str:match('^%s*', pos) -- Skip whitespace.
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local first = str:sub(pos, pos)
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if first == '{' then -- Parse an object.
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local obj, key, delim_found = {}, true, true
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pos = pos + 1
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while true do
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key, pos = json.parse(str, pos, '}')
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if key == nil then return obj, pos end
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if not delim_found then error('Comma missing between object items.') end
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pos = skip_delim(str, pos, ':', true) -- true -> error if missing.
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obj[key], pos = json.parse(str, pos)
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pos, delim_found = skip_delim(str, pos, ',')
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end
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elseif first == '[' then -- Parse an array.
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local arr, val, delim_found = {}, true, true
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pos = pos + 1
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while true do
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val, pos = json.parse(str, pos, ']')
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if val == nil then return arr, pos end
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if not delim_found then error('Comma missing between array items.') end
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arr[#arr + 1] = val
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pos, delim_found = skip_delim(str, pos, ',')
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end
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elseif first == '"' then -- Parse a string.
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return parse_str_val(str, pos + 1)
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elseif first == '-' or first:match('%d') then -- Parse a number.
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return parse_num_val(str, pos)
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elseif first == end_delim then -- End of an object or array.
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return nil, pos + 1
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else -- Parse true, false, or null.
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local literals = {['true'] = true, ['false'] = false, ['null'] = json.null}
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for lit_str, lit_val in pairs(literals) do
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local lit_end = pos + #lit_str - 1
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if str:sub(pos, lit_end) == lit_str then return lit_val, lit_end + 1 end
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end
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local pos_info_str = 'position ' .. pos .. ': ' .. str:sub(pos, pos + 10)
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error('Invalid json syntax starting at ' .. pos_info_str)
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end
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end
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return json
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