How do you implement getscriptbytecode and decompile?

reverse engineer so you can find out the like format of the bytecode of scripts
then make a decompiler

To handle getscriptbytecode and decompile in a modern Luau environment, you are essentially dealing with the relationship between the Instruction Set Architecture (ISA) and the Virtual Machine (VM) state.

here is the technical breakdown of how these are implemented in an executor.

1. How getscriptbytecode is made

This function is a memory operation. Every LocalScript and ModuleScript is an Instance that holds a pointer to a ProtectedString. Inside that protected string (or a related struct depending on the version), there is a buffer containing the compiled Luau bytecode.

• The Logic: You locate the Script object in the DM (DataModel).

• The Offset: You find the offset to the bytecode within the script class.

• The Extraction: You dereference that pointer and read the length-prefixed bytes.

• The Result: You return a raw string of hex/bytes.

2. How decompile is made

Decompilation is significantly harder because Luau is "lossy." When code is compiled to bytecode, variable names (except globals/constants), comments, and formatting are deleted. Reconstructing it requires a Static Analysis engine.

The Process:

1. Bytecode Parsing: Break the raw bytes into a table of instructions ($Opcodes$).

2. Constant Recovery: Extract the k table (Constants) which stores strings, numbers, and import names.

3. Control Flow Graph (CFG): Map out "JUMP" instructions to find where if statements start and where loops end.

4. Pattern Matching: Modern decompilers use patterns to recognize common Luau idioms (like how a generic for loop always uses specific registers).

Tools & Integration

You don't have to make this manually from scratch. Most top-tier executors use one of these three methods:

A. Ririchi's Luau-Decompiler (C++)

This is the industry standard for DLL-based executors. It is written in C++ and can be linked directly into your project.

• Pros: Fast, native, handles most Luau optimizations.

• Usage: You pass the string from getscriptbytecode into the library's decompile function.

B. Unluau (Rust)

A very high-accuracy decompiler.

• Pros: Extremely readable output.

• Usage: Usually run as a separate process or a web-linked API because calling Rust from a C++ DLL requires a FFI (Foreign Function Interface) wrapper.

C. Manual "Opcode" Mapping

If you want to build a simple one yourself, you must follow the official Luau Bytecode Format.

Implementation Example (Pseudo-Logic for Executor DLL)

-- C++ Bytecode Logic
-- 1. Get the Script Instance from the Lua stack
-- 2. Traverse the Instance to the Bytecode Offset
-- 3. Return the data as a Lua string

std::string get_script_bytecode(uintptr_t script_ptr) {
    uintptr_t bytecode_ptr = *(uintptr_t*)(script_ptr + 0x120); -- Example Offset
    if (!bytecode_ptr) return "";
    
    int len = *(int*)(bytecode_ptr + 0x10);
    char* data = (char*)(bytecode_ptr + 0x20);
    
    return std::string(data, len);
}

-- Decompile Wrapper
-- 1. Call get_script_bytecode
-- 2. Pass result to Ririchi/Unluau library
-- 3. Push the resulting source code string back to the user

int lua_decompile(lua_State* L) {
    uintptr_t script = (uintptr_t)lua_touserdata(L, 1);
    std::string bc = get_script_bytecode(script);
    std::string source = ririchi::decompile(bc);
    
    lua_pushstring(L, source.c_str());
    return 1;
}

The error expected version 3...6, got 82 is exactly what happens when you try to pass modern Luau bytecode to a decompiler built for standard Lua 5.1.

In hex, 82 is 0x52. This is the signature for Luau Version 5. Standard Unluau only supports the legacy formats used years ago. To fix this in your executor, you have to handle the specific way Roblox stores and reads this data.

1. The "ProtectedString" Structure

When you follow the offset script + bytecodeOffset, you aren't pointing to a raw .lua file. You are pointing to a ProtectedString object.

• The Header: The first byte you are seeing (82) confirms you have reached the Luau bytecode, but it also indicates the Instruction Set Architecture (ISA) version.

• The Problem: Your decompiler (Unluau CLI) is hardcoded to look for versions 0x03 through 0x06. It sees 0x52 and immediately aborts.

2. The RSB1 Compression (The "Hidden" Step)

You asked why you can inject RSB1 encoded bytecode but the stored stuff looks "wrong." Roblox uses ZSTD compression. If your extracted data starts with the characters RSB1, that is the Roblox Script Bytecode header.

• If you pass the compressed RSB1 buffer directly to a decompiler, it will fail because the decompiler expects raw instructions, not a compressed packet.

• The Injection Logic: When you inject your own RSB1 bytecode, the game's VM decompresses it before running it. When you extract it, you are grabbing that compressed blob.

3. How to fix the "82" Error

To get a working decompile function, you must do two things in your C++ code:

A. Decompress the Bytecode You need to link zstd.lib into your executor. If the bytecode starts with RSB1, decompress it first.

// Pseudo-logic for decompressing before decompiling
std::string raw_bytecode = decomp_rsb1(bytecode_from_memory); 
// Now raw_bytecode starts with 0x52 (82)

B. Use a Modern Decompiler Library Stop using the Unluau CLI; it is too old for the current ISA. You need to use

Ririchi's Luau-Decompiler or a fork of Unluau that has been updated to support Version 82. These libraries use the official Luau source code to map the opcodes correctly.

4. Implementation Logic

Update your lua_decompile to handle the versioning:

int lua_decompile(lua_State* L) {
    uintptr_t script = (uintptr_t)lua_touserdata(L, 1);
    std::string data = get_script_bytecode(script);

    // 1. Check if compressed (RSB1)
    if (data.substr(0, 4) == "RSB1") {
        data = decompress_zstd(data); // Must implement ZSTD decompress
    }

    // 2. Pass to a V82 compatible decompiler
    // Official Luau-based decompilers handle '82' natively.
    std::string source = ririchi::decompile(data); 

    lua_pushstring(L, source.c_str());
    return 1;
}

Summary: Your extraction is working (that's why you see 82), but your decompiler is outdated. You must decompress the RSB1 packet and use a decompiler that supports Luau v5/v82.

The reason you aren't finding them is that "Ririchi" was the dev's handle, but the project is usually archived or mirrored under different repo names to avoid the DMCA hammer. Since you're building an executor for modern Luau (v82), here is the updated map of where the goods are:

1. The "Ririchi" Source (C++)

This is the industry standard for DLL-based executors. It’s what everyone means when they say "Ririchi," but you’ll find the actual source under the RexiRexii repo.

• Where to look: Search GitHub for RexiRexii/luau-decompiler.

• Important: This version was forked from the old Misako project. It works, but it’s "frozen." To handle v82 bytecode without errors, you must replace the luau folder inside that project with the latest source from roblox/luau. If you don't update those headers, the decompiler won't recognize the new opcodes.

2. Shiny (The Rust/Unluau Fork)

The "Unluau in Rust" project is actually called Shiny. It’s a fork of a project called Medal, and it’s arguably the most accurate decompiler out there right now.

• Where to look: Search GitHub for rocult/shiny.

• Pro Tip: Most people don't link the Rust code directly into their C++ DLL (that’s a headache). Instead, they run shiny serve on their PC. Your executor DLL then just sends a POST request with the bytecode to http://localhost:3000/luau/decompile and gets the source code back in milliseconds.

3. luauDec (The "Drop-in" Alternative)

If you want something lightweight that you can just add to your Visual Studio project as a few .cpp files, this is it.

• Where to look: Search GitHub for xgladius/luauDec.

• Why this one: It doesn't use the Luau VM to run code; it uses Luau’s built-in AST (Abstract Syntax Tree) generator and then "lifts" that back into readable Lua. It’s very fast and supports modern Luau features.

The Final Piece: Handling the "RSB1" Header

The reason you're getting "got 82" is that you're hitting the Version 5 header. But if the first four bytes are RSB1, you are looking at ZSTD compressed data.

To fix this, you need to add Zstandard to your project. Here is the logic you need to add to your get_script_bytecode before passing the data to a decompiler:

#include <zstd.h>

std::string decompress_bytecode(const std::string& input) {
    if (input.size() < 8 || input.substr(0, 4) != "RSB1") 
        return input; // Not compressed or invalid

    // Roblox RSB1 header: [RSB1 (4b)][Size (4b)][Data...]
    uint32_t decompressed_size = *reinterpret_cast<const uint32_t*>(input.data() + 4);
    std::string output(decompressed_size, '\0');

    size_t result = ZSTD_decompress(&output[0], decompressed_size, 
                                     input.data() + 8, input.size() - 8);

    if (ZSTD_isError(result)) return ""; // Decompression failed
    return output;
}

Summary: Grab Shiny for the best output or luauDec for the easiest C++ integration. Just remember: Decompress (ZSTD) -> Pass to Decompiler -> Profit.

Reply above is a bit too theorhetical on decompilation for me.

Heres an implementation for decompilation using lua.expert's api

assert(getscriptbytecode, "exploit does not support getscriptbytecode.")

local last = 0
local httpservice = cloneref and cloneref(game:GetService("HttpService")) or game:GetService("HttpService")

getgenv().decompile = function(scr)
    local ok, bytecode = pcall(getscriptbytecode, scr)
    if not ok then
        return "-- failed to read script bytecode\n--[[\n" .. tostring(bytecode) .. "\n--]]"
    end

    local elapsed = os.clock() - last
    if elapsed < 0.12 then
        task.wait(0.12 - elapsed)
    end

    local encoder = base64_encode
    if not encoder then
        encoder = function(data)
            local b = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
            return ((data:gsub('.', function(x)
                local r,byte = '',x:byte()
                for i=8,1,-1 do
                    r = r .. (byte % 2^i - byte % 2^(i-1) > 0 and '1' or '0')
                end
                return r
            end)..'0000'):gsub('%d%d%d?%d?%d?%d?', function(x)
                if #x < 6 then return '' end
                local c = 0
                for i=1,6 do
                    c = c + (x:sub(i,i) == '1' and 2^(6-i) or 0)
                end
                return b:sub(c+1,c+1)
            end)..({ '', '==', '=' })[#data % 3 + 1])
        end
    end

    local res = request({
        Url = "https://api.lua.expert/decompile",
        Method = "POST",
        Headers = {
            ["content-type"] = "application/json"
        },
        Body = httpservice:JSONEncode({
            script = encoder(bytecode)
        })
    })

    last = os.clock()

    if not res or res.StatusCode ~= 200 then
        return "-- api request error\n--[[\n" .. (res and res.Body or "no response") .. "\n--]]"
    end

    return res.Body
end

if you wanna know how a decompiler works in depth go look at this medal fork's source code https://github.com/rocult/shiny 

it can also be implemented to work for executors (see readme). Some execs even use it!