pub package

zstandard_web

The web implementation of zstandard.

Installation

Copy zstd.js and zstd.wasm on the web/ folder.

Include the library inside the <head>:

<!DOCTYPE html>
<html>
<head>
  <script src="zstd.js"></script>
</head>
</html>

Usage

void act() async {
  final zstandard = ZstandardWeb();

  Uint8List original = Uint8List.fromList([...]);

  Uint8List? compressed = await zstandard.compress(original);
  
  Uint8List? decompressed = await zstandard.decompress(compressed ?? Uint8List(0));
}

Generation

zstd.js and zstd.wasm generation:

git clone https://github.com/emscripten-core/emsdk.git

git clone https://github.com/facebook/zstd.git

cd emsdk

./emsdk install latest

./emsdk activate latest

source "$HOME/Development/emsdk/emsdk_env.sh"

echo 'source "$HOME/Development/emsdk/emsdk_env.sh"' >> $HOME/.zprofile


cd zstd

emcc -O3 \
    $(find lib/compress -name "*.c") \
    $(find lib/decompress -name "*.c") \
    $(find lib/common -name "*.c") \
    -s WASM=1 \
    -s EXPORT_NAME="zstdWasmModule" \
    -s EXPORTED_FUNCTIONS="['_ZSTD_compress', '_ZSTD_decompress', '_malloc', '_free', '_ZSTD_getFrameContentSize', '_ZSTD_compressBound']" \
    -o zstd.js

Include compressData and decompressData methods in zstd.js:

function compressData(inputData, compressionLevel) {
    let inputPtr = Module._malloc(inputData.length);
    Module.HEAPU8.set(inputData, inputPtr);

    let outputBufferSize = Module._ZSTD_compressBound(inputData.length);
    let outputPtr = Module._malloc(outputBufferSize);

    let compressedSize = Module._ZSTD_compress(
        outputPtr,
        outputBufferSize,
        inputPtr,
        inputData.length,
        compressionLevel
    );

    if (compressedSize < 0) {
        console.error('Compression error, error code: ', compressedSize);
        return null;
    } else {
        let compressedData = new Uint8Array(Module.HEAPU8.buffer, outputPtr, compressedSize);

        Module._free(inputPtr);
        Module._free(outputPtr);

        return compressedData;
    }
}

function decompressData(compressedData) {
    let compressedPtr = Module._malloc(compressedData.length);
    Module.HEAPU8.set(compressedData, compressedPtr);

    let decompressedSize = Module._ZSTD_getFrameContentSize(compressedPtr, compressedData.length);
    if (decompressedSize === -1 || decompressedSize === -2) {
        console.error('Error in obtaining the original size of the data');
        Module._free(compressedPtr);
        return null;
    }

    let decompressedPtr = Module._malloc(decompressedSize);

    let resultSize = Module._ZSTD_decompress(
        decompressedPtr,
        decompressedSize,
        compressedPtr,
        compressedData.length
    );

    if (resultSize < 0) {
        console.error('Decompression error, error code: ', resultSize);
        Module._free(compressedPtr);
        Module._free(decompressedPtr);
        return null;
    } else {
        let decompressedData = new Uint8Array(Module.HEAPU8.buffer, decompressedPtr, resultSize);

        Module._free(compressedPtr);
        Module._free(decompressedPtr);

        return decompressedData;
    }
}

Libraries

zstandard_ext
zstandard_web