zstddec

zstddec

ZSTD (Zstandard) decoder for Web and Node.js, using WebAssembly.

Installation

npm install --save zstddec

API

import { ZSTDDecoder } from 'zstddec';

const decoder = new ZSTDDecoder();

await decoder.init();

const decompressedArray = decoder.decode( compressedArray, uncompressedSize );

Limitations: The decoder may fail with the error wasm function signature contains illegal type when the uncompressedSize is not known in advance and given to the decode() method. This is presumably a bug in the WASM bindings, which I am not yet sure how to fix.

Contributing

To build the project locally, run:

yarn install
yarn build

To test changes:

yarn test

Building from source

Compiled from https://github.com/facebook/zstd/tree/dev/build/single_file_libs, with the following steps:

# build zstd
make
cd build/single_file_libs
./create_single_file_decoder.sh

# build wasm
emcc zstddeclib.c -s EXPORTED_FUNCTIONS="['_ZSTD_decompress', '_ZSTD_findDecompressedSize', '_ZSTD_isError', '_malloc', '_free']" -Wl,--no-entry -s WASM=1 -Oz -g0 -flto -s ALLOW_MEMORY_GROWTH=1 -s FILESYSTEM=0 -s STANDALONE_WASM=1 -DNDEBUG=1 -s PURE_WASI=0 -o zstddec.wasm

# build streaming wasm
emcc zstddeclib.c -s EXPORTED_FUNCTIONS="['_ZSTD_decompress', '_ZSTD_findDecompressedSize', '_ZSTD_createDCtx', '_ZSTD_decompressStream', '_ZSTD_freeDCtx', '_ZSTD_DStreamInSize', '_ZSTD_DStreamOutSize', '_malloc', '_free']" -Wl,--no-entry -s WASM=1 -Oz -g0 -flto -s ALLOW_MEMORY_GROWTH=1 -s FILESYSTEM=0 -s STANDALONE_WASM=1 -DNDEBUG=1 -s PURE_WASI=0 -o zstddec-stream.wasm

# encode WASM to base64
base64 -i zstddec.wasm > zstddec.txt
base64 -i zstddec-stream.wasm > zstddec-stream.txt

The base64 string written to zstddec.txt is embedded as the wasm variable at the bottom of the source file. The rest of the file is written by hand, in order to avoid an additional JS wrapper generated by Emscripten.

Last built June 2025, zstd v1.5.7 (f8745da6), emscc v4.0.10.

License

JavaScript wrapper is provided under the MIT License, and the WASM ZSTD decoder is provided by Facebook under the BSD 3-Clause License.