nodejs asynchronous to synchronous

Question

I'm new to nodejs and javascript and I'm currently working on an open source project, since last night I was trying to convert this function from asynchronous to synchronous, but I couldn't, I used async / await but I think that I didn't understand this concept very well, this function encrypts and compresses files using the aes256 algorithm, I works well asynchronously but I want to add this new feature that allows you to encrypt a directory's content recursively.

function encrypt({ file, password }, error_callback, succ_callback) {
    const initVect = crypto.randomBytes(16);

    // Generate a cipher key from the password.
    const CIPHER_KEY = crypto.createHash('sha256').update(password).digest();;
    const readStream = fs.createReadStream(file);
    const gzip = zlib.createGzip();
    const cipher = crypto.createCipheriv('aes-256-cbc', CIPHER_KEY, initVect);
    const appendInitVect = new AppendInitVect(initVect);
    // Create a write stream with a different file extension.
    const writeStream = fs.createWriteStream(path.join(file + ".dnc"));

    readStream
      .pipe(gzip)
      .pipe(cipher)
      .pipe(appendInitVect)
      .pipe(writeStream);

    readStream.on('error', error_callback);
    readStream.on('end', succ_callback);
}

Answer 1

Try using promises. By changing the code slightly you can promisify the function and then wait for all promises to resolve or reject before taking action.

function encrypt({ file, password }) {
  const initVect = crypto.randomBytes(16);

// Generate a cipher key from the password.
  const CIPHER_KEY = crypto.createHash('sha256').update(password).digest();;
  const readStream = fs.createReadStream(file);
  const gzip = zlib.createGzip();
  const cipher = crypto.createCipheriv('aes-256-cbc', CIPHER_KEY, initVect);
  const appendInitVect = new AppendInitVect(initVect);
// Create a write stream with a different file extension.
  const writeStream = fs.createWriteStream(path.join(file + ".dnc"));

  readStream
    .pipe(gzip)
    .pipe(cipher)
    .pipe(appendInitVect)
    .pipe(writeStream);


  const promise = new Promise();
  writeStream.on('error', err => promise.reject(err));
  writeStream.on('end', data => promise.resolve(data));
  return promise;
}

const promise1 = encrypt({file1, password1});
const promise2 = encrypt({file2, password2});

Promise.all([promise1, promise2])
  .then(succ_callback)
  .catch(error_callback);

I have not run this code so it might need some tweaking to make it work, but this is the general gist.