golang s3 download to buffer using s3manager.downloader

I'm using the Amazon s3 SDK to download files like below:

file, err := os.Create("/tmp/download_file")
downloader := s3manager.NewDownloader(session.New(&aws.Config{
                                 Region: aws.String("us-west-2")}))
numBytes, err := downloader.Download(file,
	&s3.GetObjectInput{
		Bucket: aws.String(bucketName),
		Key:    aws.String(fileName),
	})

It downloads to a file.

How do I get the download content into a []byte slice (buffer) directly.
I tried something like:

var tBuf bytes.Buffer
tBufIo := bufio.NewWriter(&tBuf)

instead of "file". But I get an error for io.WriterAt interface

> cannot use *tBufIo (type bufio.Writer) as type io.WriterAt in argument to downloader.Download

Found it from the link
https://groups.google.com/forum/#!topic/Golang-Nuts/4z8rcWEZ8Os

buff := &aws.WriteAtBuffer{}
downloader := s3manager.NewDownloader(session.New(&aws.Config{
                                      Region: aws.String(S3_Region)}))
numBytes, err := downloader.Download(buff,....
data := buff.Bytes() // now data is my []byte array

Works and fits the need.

See also: https://docs.aws.amazon.com/sdk-for-go/api/aws/#WriteAtBuffer

If you are running AWS SDK v2 then you can create a WriterAt like this

import (
	"context"
	"errors"
	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/credentials"
	"github.com/aws/aws-sdk-go-v2/service/s3"
 	"github.com/aws/aws-sdk-go-v2/feature/s3/manager"
)
func DownloadS3File(objectKey string, bucket string, s3Client *s3.Client) ([]byte, error) {

	buffer := manager.NewWriteAtBuffer([]byte{})

	downloader := manager.NewDownloader(s3Client)

	numBytes, err := downloader.Download(context.TODO(), buffer, &s3.GetObjectInput{
		Bucket: aws.String(bucket),
		Key:    aws.String(objectKey),
	})
	if err != nil {
		return nil, err
	}

	if numBytes < 1 {
		return nil, errors.New("zero bytes written to memory")
	}

	return buffer.Bytes(), nil
}