code: function processFile(bucket, key, transform) {
    // get the csv file s3://${bucket}/${key}
    console.log(`Processing s3://${bucket}/${key}`)
    const s3 = new AWS.S3()
    const csvStream = csv.parse({ headers: true, objectMode: true })
    s3.getObject({Bucket: bucket, Key: key}).createReadStream().pipe(csvStream)
    return es.streamToEs(csvStream, transform, esClient, index)
  }
docs: Process single CSV file