zip-stream-unpack.js

const zlib = require('zlib')
const fs = require('fs')

if (process.argv.length < 3) {
  console.error('./unpack.js filename')
  process.exit(255)
}

let filePath = process.argv[2]

async function main() {
  let fd = fs.openSync(filePath, 'r')
  let header = Buffer.alloc(1024)
  fs.readSync(fd, header, 0, 1024, 0)
  let fileNameLength = header.readUInt16LE(26)
  let extraFieldLength = header.readUInt16LE(28)
  let compressedSize = header.readUInt32LE(18)
  let unCompressedSize = header.readUInt32LE(22)

  console.log(`${compressedSize}, ${unCompressedSize}`)

  let fileName = header.slice(30, 30 + fileNameLength)
  console.log(`fileNameLength: ${fileNameLength}: ${fileName}`)
  console.log(`extraFieldLength: ${extraFieldLength}`)

  let extractedSize = 0
  let inflater = zlib.createInflateRaw()
  let lastChunk = null
  inflater.on('data', chunk => {
    lastChunk = chunk
    extractedSize += chunk.length
    if (extractedSize % (1024 * 1024 * 1024) === 0) {
      console.log(`${(extractedSize / 1024 / 1024).toFixed(2)} MB`)
    }
  })
  inflater.on('error', err => {
    console.error(err)
  })
  inflater.on('end', () => {
    console.log(lastChunk.toString('utf8'))
    console.log(`done after: ${extractedSize}`)
  })

  // Write the first part of the stream that we read with the header
  let data = header.slice(30 + fileNameLength + extraFieldLength)
  inflater.write(data)

  let zipStream = fs.createReadStream(filePath, { start: header.length })
  zipStream.pipe(inflater)
  inflater.writableHighWaterMark
}

main().catch(err => {
  console.log(err)
})