Convert JSON String to Lua Table? - json

Question

I need to convert a Json String to a table data structure in Lua. I am using the following code.
local json = require "json"
local t = {
["name1"] = "value1",
["name2"] = { 1, false, true, 23.54, "a \021 string" },
name3 = json.null
}
local encode = json.encode (t)
print (encode) --> {"name1":"value1","name3":null,"name2":[1,false,true,23.54,"a \u0015 string"]}
local decode = json.decode( encode )
But when I run the script, I get the following errors,
no field package.preload['json']
no file '/usr/local/share/lua/5.2/json.lua'
no file '/usr/local/share/lua/5.2/json/init.lua'
no file '/usr/local/lib/lua/5.2/json.lua'
no file '/usr/local/lib/lua/5.2/json/init.lua'
no file './json.lua'
no file '/usr/local/lib/lua/5.2/json.so'
no file '/usr/local/lib/lua/5.2/loadall.so'
no file './json.so'
So how to convert my json string to lua table?

Answer 1

maybe lua-cjsonis your friend:
install e.g. through luarocks:
$sudo luarocks install lua-cjson
then in lua:
local json = require('cjson')
local tab = json.decode(json_string)
json_string = json.encode(tab)

Answer 2

https://gist.github.com/tylerneylon/59f4bcf316be525b30ab
I found pure lua script file to parse json data (just one file).
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

Answer 3

You can use json-lua. A pure lua implementation of json. First install json-lua using Luarocks. luarocks install json-lua . Then Use this code :
local json = require "json"
local t = {
["name1"] = "value1",
["name2"] = { 1, false, true, 23.54, "a \021 string" },
name3 = json.null
}
local encode = json:encode (t)
print (encode) --> {"name1":"value1","name3":null,"name2":[1,false,true,23.54,"a \u0015 string"]}
local decode = json:decode( encode )
Tested & Verified on win 7 64 bit with lua 5.1. lua-cjson is fine, but it is not a pure lua rock. So, it's installation will not be easier to you.