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qjson
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‎README.md‎

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# `qjson.lua`
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Tiny and Rapid JSON encoding/decoding in pure Lua.
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(Running benchmark by [`rxi/json.lua`](https://github.com/rxi/json.lua))
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```
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Lua version : LuaJIT 2.1.0-beta3
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CPU name : 11th Gen Intel(R) Core(TM) i7-11800H @ 2.30GHz
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../json.lua : 0.00494s [x7.06e+03] (min: 0.00452s, max 0.00526s)
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dkjson.lua : 0.0121s [x1.73e+04] (min: 0.0118s, max 0.0123s)
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jfjson.lua : 0.00993s [x1.42e+04] (min: 0.00954s, max 0.0103s)
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qjson_simple.lua : 4.3e-06s [x6.14] (min: 0s, max 1.6e-05s)
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qjson.lua : 7e-07s [x1] (min: 0s, max 1e-06s)
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```
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## Features
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* Pure lua, should work on every version (5.1-5.4, JIT)
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* Incredibly fast: ~10000x faster than rxi/json at decoding.
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* Actually tiny, < 150 loc.
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* Decent error handling: `Expected : to follow key for object at char 39`
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## Usage
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```lua
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local json = require "qjson"
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print(json.encode {
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hello = "world!",
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})
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--[[
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{"qjson": ["fast","simple","tiny"],"hello": "world!"}
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]]
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print(json.decode([[
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{ "foo": "bar" }
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]]))
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```
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## Notes
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* `true`, `false` and `null` are represented as strings.
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## qjson_simple
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Smaller initial version of `qjson` without all of the optimizations that make it less readable.
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Often runs worse than `qjson`, but can run at around the same speed.
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Doesn't support escaping strings, exponential numbers, or `null`.

‎qjson.lua‎

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local find, sub, gsub, tonumber, error = string.find, string.sub, string.gsub, tonumber, error
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local function decode(json --[[@param json string]]) ---@return table
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local ptr = 0
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local function consume(pattern --[[@param pattern string]]) ---@return string?
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local _, finish, match = find(json, pattern, ptr)
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if finish then
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ptr = finish + 1
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return match or true
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end
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return nil
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end
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local repl = { -- escape characters
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["b"] = "\b", ["f"] = "\f", ["n"] = "\n", ["r"] = "\r",
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["t"] = "\t", ["\\"] = "\\", ["\""] = "\""
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}
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local function slowstring() -- string parser that works with escapes. fallback at very far end of parsing order, since rare case.
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local _, start = find(json, "^%s*\"", ptr)
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if not start then return end
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ptr = start + 1
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while true do
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local _, finish, escapes = find(json, "(\\*)\"", ptr)
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if finish then
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ptr = finish + 1
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if #escapes % 2 == 0 then
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return ( gsub( sub(json, start + 1, finish - 1), "\\([bfnrt\\\"])", repl) )
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end
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else
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error("Missing end quote for string at char " .. ptr)
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end
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end
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end
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local object, array
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local function faststring() -- Parses a string without any escapes. Fastest and most common case.
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return consume("^%s*\"([^\"\\]*)\"")
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end
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--- Parses a JSON value.
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--- Order is important for performance with common cases.
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local function value()
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return faststring()
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or object()
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or tonumber(consume("^%s*(%-?%d+%.%d+)") or consume("^%s*(%-?%d+)"))
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or consume("^%s*(true)") or consume("^%s*(false)") or consume("^%s*(null)")
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or array()
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or tonumber(consume("^%s*(%-?%d+[eE][%+%-]?%d+)")) -- Exponential number.
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or slowstring()
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end
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function object()
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if consume("^%s*{") then
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local fields = {}
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if consume("^%s*}") then return fields end
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repeat
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local key = faststring()
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if not key then
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error("Expected field for object at char " .. ptr)
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end
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if not consume("^%s*:") then
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error("Expected : to follow key for object at char " .. ptr)
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end
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local val = value()
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if val then
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fields[key] = val
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else
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error("Expected value for field " .. key .. " at char " .. ptr)
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end
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consume("^%s*,")
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until consume("^%s*}")
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return fields
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end
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end
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function array()
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if consume("^%s*%[") then
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local values, nvalues = {}, 0
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if consume("^%s*%]") then return values end
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repeat
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nvalues = nvalues + 1
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local value = value()
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if value then
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values[nvalues] = value
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else
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error("Expected value for field #" .. nvalues + 1 .. " at char " .. ptr)
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end
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consume("^%s*,")
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until consume("^%s*%]")
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return values
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end
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end
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return object()
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end
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local concat, tostring, pairs = table.concat, tostring, pairs
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local function isarray(t)
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local i = 1
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for k in pairs(t) do
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if type(k) ~= "number" or k ~= i then
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return false
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end
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i = i + 1
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end
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return true
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end
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local encode
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local function value(v)
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local t = type(v)
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if t == "table" then
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return encode(v)
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elseif t == "string" then
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return "\"" .. v .. "\""
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else
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return tostring(v)
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end
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end
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function encode(tbl --[[@param tbl table]]) ---@return string
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if isarray(tbl) then
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local strs, len = {}, #tbl
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for i = 1, len do
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strs[i] = value(tbl[i])
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end
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return "[" .. concat(strs, ",", 1, len) .. "]"
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else
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local kvs, nkvs = {}, 0
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for k, v in pairs(tbl) do
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nkvs = nkvs + 1
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kvs[nkvs] = "\"" .. tostring(k) .. "\"" .. ": " .. value(v)
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end
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return "{" .. concat(kvs, ",", 1, nkvs) .. "}";
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end
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end
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return {
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encode = encode,
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decode = decode
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}

‎qjson_simple.lua‎

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local function decode(json --[[@param json string]]) ---@return table
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local ptr = 0
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local function consume(pattern --[[@param pattern string]]) ---@return string?
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local start, finish = json:find("^%s+", ptr)
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if start then ptr = finish + 1 end
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local start, finish, match = json:find(pattern, ptr)
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if start then
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ptr = finish + 1
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return match or true
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end
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end
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local table, list
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local function number() return tonumber(consume("^(%d+%.%d+)") or consume("^(%d+)")) end
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local function bool() return consume("^(true)") or consume("^(false)") end
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local function string() return consume("^\"([^\"]*)\"") end
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local function value() return number() or bool() or string() or table() or list() end
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function table()
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if consume("^{") then
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local fields = {}
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if consume("^}") then return fields end
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repeat
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local key = assert(string(), "Expected field for table")
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assert(consume("^:"))
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fields[key] = assert(value(), "Expected value for field " .. key)
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consume("^,")
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until consume("^}")
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return fields
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end
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end
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function list()
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if consume("^%[") then
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local values = {}
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if consume("^%]") then return values end
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repeat
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values[#values + 1] = assert(value(), "Expected value for field #" .. #values + 1)
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consume("^,")
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until consume("^%]")
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return values
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end
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end
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return table()
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end
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local concat, tostring, pairs = table.concat, tostring, pairs
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local function isarray(t)
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local i = 1
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for k in pairs(t) do
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if type(k) ~= "number" or k ~= i then
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return false
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end
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i = i + 1
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end
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return true
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end
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local encode
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local function value(v)
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local t = type(v)
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if t == "table" then
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return encode(v)
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elseif t == "string" then
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return "\"" .. v .. "\""
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else
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return tostring(v)
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end
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end
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function encode(tbl --[[@param tbl table]]) ---@return string
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if isarray(tbl) then
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local strs, len = {}, #tbl
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for i = 1, len do
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strs[i] = value(tbl[i])
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end
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return "[" .. concat(strs, ",", 1, len) .. "]"
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else
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local kvs, nkvs = {}, 0
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for k, v in pairs(tbl) do
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nkvs = nkvs + 1
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kvs[nkvs] = tostring(k) .. ": " .. value(v)
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end
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return "{" .. concat(kvs, ",", 1, nkvs) .. "}";
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end
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end
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return {
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encode = encode,
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decode = decode
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}

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