Golang S3 Download and Return as io.Reader

s3.go

package aws

import (
	"bytes"
	"context"
	"io"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/aws/aws-sdk-go/service/s3"
	"github.com/aws/aws-sdk-go/service/s3/s3manager"
)

func Download(ctx context.Context, bucket string, item string, downloadPath string, environment string) (io.Reader, error) {
	cfg := &aws.Config{}
	cfg.WithCredentialsChainVerboseErrors(true)

  	// TODO: Replace with your region name
	cfg.WithRegion(*aws.String("region-name"))

	sess, err := session.NewSession(cfg)
	if err != nil {
		return nil, err
	}

	writeAtBuffer := &aws.WriteAtBuffer{}

	_, err = s3manager.NewDownloader(sess).
		Download(writeAtBuffer,
			&s3.GetObjectInput{
				Bucket: aws.String(bucket),
				Key:    aws.String(item),
			})
	if err != nil {
		return nil, err
	}

	full := writeAtBuffer.Bytes()

	return bytes.NewReader(full), nil
}