[s3-redeploy]-parallel-hashes-computation

[s3-redeploy]-parallel-hashes-computation.js

const crypto = require('crypto');
const fs = require('fs');

// Limit of files to be processed simultaneously
const concurrency = 3;

// Promisified hash computation with streams
function computeSingleFileHash(fileName) {
  const hash = crypto.createHash('md5');
  const fileStream = fs.createReadStream(fileName);
  // Error handling is intentionally omitted in this snippet
  return new Promise(resolve => {
    fileStream
      .pipe(hash)
      .on('finish', () => {
        hash.end();
        resolve(hash.read());
      });
  });
}

// Compute file hashes in parallel, applying concurrency limit
// Returns a promise
function computeFileHashes(fileNames) {
  // The same function is used in parallel files uploading snippet
  return parallel(
    fileNames,
    computeSingleFileHash,
    concurrency
  );
}