Read asar headers and naively unpack them

asar-rn.js

import {read,writeFile,mkdir} from 'react-native-fs';
var Buffer = require('buffer/').Buffer;
import pickle from 'chromium-pickle-js';

// read an asar and return its header data
// expects to take a valid asar path
// returns an object with the file structure, header size and asar path (for later reference)
const readAsarHeader = async archive => {
  let size;
  let headerBuf;
    try {
    const sizeBuf = Buffer.from(await read(archive, 8, 0, 'base64'),'base64');

    const sizePickle = pickle.createFromBuffer(sizeBuf);
    size = sizePickle.createIterator().readUInt32();

    headerBuf = Buffer.from(await read(archive, size, 8, 'base64'),'base64');
  } finally {
  }

  const headerPickle = pickle.createFromBuffer(headerBuf);
  const header = headerPickle.createIterator().readString();
  const files = JSON.parse(header).files;
  return ({files, headerSize: size, path:archive});
};

// unpack an asar file using its header
// used like: unpackAsar(asarHeader,asarHeader.path,'path/to/write/to')
// returns an array of promises, representing the top level directory
const unpackAsar = async ({files,headerSize},asarPath,to) =>  {
  return Object.keys(files).map(async key => {
    if(files[key].files){
      await mkdir(`${to}/${key}`)
      return Promise.all(
        unpackAsar({files:files[key].files,headerSize},asarPath,`${to}/${key}`)
      )
    }
    else{
      const {offset,size} = files[key]
      const contents = await read(asarPath,size,8+parseInt(offset)+parseInt(headerSize),'base64')
      return writeFile(`${to}/${key}`,contents,'base64').then(console.log,console.error)
    }
  })
}

export {readAsarHeader,unpackAsar}