@tootallnate/oodle-wasm

A WebAssembly wrapper around RAD Game Tools' Oodle Data Compression decoder, for reading Oodle-compressed Unreal Engine PAK files in the browser.

Why does this package work differently from the others?

Oodle is a high-quality proprietary compression library that ships inside the Unreal Engine source distribution. The source code is publicly available (under EpicGames/UnrealEngine and mirrored in WorkingRobot/OodleUE) but is governed by the Unreal Engine EULA, not an open-source license. Among other things, that EULA does not permit Oodle's source or compiled binaries to be redistributed as standalone tooling.

This repository's licensing policy is MIT/Apache-2.0/public-domain; shipping Oodle bytes here would compromise that policy. So this package contains only:

1. A small MIT-licensed C wrapper (c/wrapper.c) that exposes OodleLZ_Decompress to JavaScript via a stable, no-libc-imports WASM interface.
2. A build recipe (Makefile) that compiles the wrapper + RAD's source using wasi-sdk.
3. A TypeScript wrapper around the resulting WASM (src/index.ts).
4. A setup script (scripts/setup-source.sh) that fetches RAD's source from EpicGames/UnrealEngine for you, after you accept the UE EULA.

The compiled oodle.wasm blob is never committed to or distributed by this repository. You build your own. Callers pass the WASM bytes to this package's API at runtime, the same way you would with any user-supplied resource a project can't redistribute (game ROMs, console BIOSes, signing keys, etc.).

Building from scratch

You'll need:

• A POSIX shell (bash), make, curl, unzip.
• About 200 MB of disk space (wasi-sdk + Oodle source).
• About 5 minutes.

cd packages/oodle-wasm

# 1. Install wasi-sdk into /tmp/wasi-sdk (downloads ~150 MB).
make setup

# 2. Fetch Oodle's source from EpicGames/UnrealEngine.
#    This prints the EULA URL and prompts for confirmation.
make setup-source

# 3. Compile to WebAssembly.
make

# Result: src/oodle.wasm (~500 KB - 1 MB).

After step 3, the WASM file is at src/oodle.wasm. Pass its bytes to this package's TypeScript API:

import { OodleDecoder } from "@tootallnate/oodle-wasm";
import { readFile } from "node:fs/promises";

const wasm = await readFile("./src/oodle.wasm");
const decoder = await OodleDecoder.create(wasm);
const decompressed = decoder.decompress(compressedBytes, expectedSize);
decoder.dispose();

License situation in detail

| Component | License | Where | |---|---|---| | c/wrapper.c, c/wrapper.h | MIT (this repo) | committed | | src/index.ts (TS API) | MIT (this repo) | committed | | Makefile, scripts/setup-source.sh | MIT (this repo) | committed | | RAD's Oodle source | Unreal Engine EULA | fetched by you, lives in c/oodle-src/ after make setup-source. Gitignored, never committed. | | Compiled oodle.wasm | Derived from RAD's source — covered by the UE EULA | built by you. Never committed, never distributed. |

You should read the Unreal Engine EULA before running make setup-source. The setup script prints a confirmation prompt referencing the EULA URL.

We (the switch-tools maintainers) have no relationship with Epic Games or RAD Game Tools and make no warranty about the legal status of your usage. The pattern this package follows — providing build recipes for proprietary software without shipping the artifacts — is well-established (e.g. emulator BIOS prompts, modding tools that require user-supplied SDKs) but it is not zero-risk; if you intend to use this in a commercial product, consult counsel.

Why wasi-sdk instead of Emscripten?

For consistency with the other WASM packages in this repository (zstd-wasm, brotli-wasm, astc-wasm), all of which use wasi-sdk's clang. The resulting module imports nothing from WASI and runs in plain WebAssembly.Module instantiation — works identically in browsers and Node.

We export only the decoder side of Oodle. Encoders are intentionally excluded from the build to keep the WASM small (the decoder is the expensive optimized part, the encoder pulls in another ~2 MB of analysis machinery for the optimal-parser levels). This package can read Oodle-compressed data but cannot create new Oodle data.

Supported compressors

After build, the WASM can decode any UE-PAK-supported Oodle compressor:

• Kraken (most common; modern UE5 default)
• Mermaid, Selkie, Leviathan, Hydra
• Legacy: LZNA, BitKnit (the source still includes their decoders even though encoding is deprecated)

What if I just want to try it without building?

If you have a copy of oodle.wasm someone else built (and you are permitted to use it under their distribution of RAD's source), you can use that directly. The TypeScript wrapper just needs the bytes of the compiled WASM module.