[s3-redeploy]-parallel-files-uploading

[s3-redeploy]-parallel-files-uploading.js

// Limit of promises executed in parallel
// We don't want to upload more than 3 files simultaneously
const concurrency = 3;

// Returns a promise, which means uploading is fired once function is called
function uploadSingleFileToS3(fileName) {
  const fileStream = fs.createReadStream(fileName);
  return s3Client.upload({
    Key: fileName,
    Body: fileStream,
  }).promise();
}

// Perform parallel uploading applying concurrency limit
function uploadFilesToS3(fileNames) {
  // The function, given as a second parameter, should return a promise
  return parallel(
    fileNames,
    uploadSingleFileToS3,
    concurrency
  );
}

// Raw idea of what is done inside
// Returns a promise
function parallel(values, fn, concurrency = 1) {
  // Take 'concurrency' first values and apply 'fn' to each.
  // 'concurrency' files uploading will be fired simultaneously and
  // 'fn' will return a promise for each call.
  // Chain the following to each returned promise:
  // - take a value from 'values'
  // - apply 'fn'
  // - chain again
}