Part of https://jacoposalvestrini.medium.com/batch-download-files-from-aws-s3-36e575f30682

AWSS3-BatchDownload-DownloadWithIterator.go

// from (2020-01-14) https://docs.aws.amazon.com/sdk-for-go/api/service/s3/s3manager/#Downloader.DownloadWithIterator
svc := s3manager.NewDownloader(session)

fooFile, err := os.Open("/tmp/foo.file")
if err != nil {
	return err
}

barFile, err := os.Open("/tmp/bar.file")
if err != nil {
	return err
}

objects := []s3manager.BatchDownloadObject {
	{
		Object: &s3.GetObjectInput {
			Bucket: aws.String("bucket"),
			Key: aws.String("foo"),
		},
		Writer: fooFile,
	},
	{
		Object: &s3.GetObjectInput {
			Bucket: aws.String("bucket"),
			Key: aws.String("bar"),
		},
		Writer: barFile,
	},
}

iter := &s3manager.DownloadObjectsIterator{Objects: objects}
if err := svc.DownloadWithIterator(aws.BackgroundContext(), iter); err != nil {
	return err
}