pack and unpack wxvpkg

pack.js

const path = require('path')
const fs = require('fs')
const { execSync } = require('child_process')

let file = path.join(process.cwd(), 'core.wxvpkg')
if (fs.existsSync(file)) {
  execSync(`rmtrash ${file}`)
}

let fd = fs.openSync(file, 'w')
let dest = path.join(__dirname, 'dest')

function writeSync(buf, start) {
  fs.writeSync(fd, buf, 0, buf.length, start)
}

function writeInt32(number, start) {
  let buf = Buffer.alloc(4)
  buf.writeInt32BE(number, 0)
  writeSync(buf, start)
}

let files = fs.readdirSync(dest)
let totalCount = files.length
let buf = Buffer.alloc(4)
buf.writeInt32BE(totalCount, 0)
writeSync(buf, 14)
let start = 18
// 12 + /name.length
let dataOffset = start
for (let file of files) {
  let name = `/${file}`
  let buf = Buffer.from(name, 'utf8')
  dataOffset = dataOffset + 12 + buf.length
}

for (let file of files) {
  let nb = Buffer.from(`/${file}`, 'utf8')
  // write filename byte length
  writeInt32(nb.length, start)
  start += 4
  // write filename
  writeSync(nb, start)
  start += nb.length
  // write offset
  writeInt32(dataOffset, start)
  start += 4
  // write length
  let contentBuf = fs.readFileSync(path.join(dest, file))
  writeInt32(contentBuf.length, start)
  start += 4
  // write content
  writeSync(contentBuf, dataOffset)
  dataOffset += contentBuf.length
}

fs.closeSync(fd)

unpack.js

// Extract core.wxvpkg of current folder to dest folder
const path = require('path')
const fs = require('fs')

let dest = path.join(__dirname, 'dest')
fs.mkdirSync(dest, {recursive: true})
let file = path.join(process.cwd(), 'core.wxvpkg')
let fd = fs.openSync(file, 'r')

// read buffer
function readSync(start, length) {
  const n = Buffer.alloc(length);
  fs.readSync(fd, n, 0, length, start)
  return n
}

const totalCount = readSync(14, 4).readInt32BE(0)
const map = {};
let n = 18;
for (let i = 0; i < totalCount; i++) {
  const e = {};
  // byte length of filename
  const i = readSync(n, 4).readInt32BE(0);
  n += 4;
  e.name = readSync(n, i).toString();
  n += i;
  e.offset = readSync(n, 4).readInt32BE(0);
  n += 4;
  e.length = readSync(n, 4).readInt32BE(0);
  n += 4;
  map[e.name] = e
}

let created = []
for (let item of Object.values(map)) {
  let dir = path.join(dest, path.dirname(item.name))
  if (created.indexOf(dir) == -1) {
    fs.mkdirSync(dir, {recursive: true})
    created.push(dir)
  }
  let buf = readSync(item.offset, item.length)
  let filepath = path.join(dest, item.name)
  fs.writeFileSync(filepath, buf.toString('utf8'), 'utf8')
}

fs.closeSync(fd)