Resize JPEG image in AWS S3

main.go

package main

import (
	"bytes"
	"os"
	"path"

	"image/jpeg"

	log "github.com/Sirupsen/logrus"
	"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"
	"github.com/nfnt/resize"
)

func main() {

	if len(os.Args) != 3 {
		log.Fatalf("Bucket name and key required\nUsage: %s bucket_name key", os.Args[0])
	}

	bucket := os.Args[1]
	key := os.Args[2]

	sess := session.Must(session.NewSessionWithOptions(session.Options{
		SharedConfigState: session.SharedConfigEnable,
	}))

	log.Infof("Fetching s3://%v/%v", bucket, key)

	buff := &aws.WriteAtBuffer{}
	s3dl := s3manager.NewDownloader(sess)
	_, err := s3dl.Download(buff, &s3.GetObjectInput{
		Bucket: aws.String(bucket),
		Key:    aws.String(key),
	})

	if err != nil {
		log.Fatalf("Could not download from S3: %v", err)
	}

	log.Infof("Decoding image")

	imageBytes := buff.Bytes()
	reader := bytes.NewReader(imageBytes)

	img, err := jpeg.Decode(reader)
	if err != nil {
		log.Fatalf("bad response: %s", err)
	}

	log.Infof("Generating thumbnail")
	thumbnail := resize.Thumbnail(150, 150, img, resize.Lanczos3)

	log.Infof("Encoding image for upload to S3")
	buf := new(bytes.Buffer)
	err = jpeg.Encode(buf, thumbnail, nil)

	if err != nil {
		log.Fatalf("JPEG encoding error: %v", err)
	}

	// Set filename "filename-thumb.jpg"
	ext := path.Ext(key)
	thumbkey := key[0:len(key)-len(ext)] + "-thumb.jpg"

	log.Infof("Preparing S3 object: %s", thumbkey)

	uploader := s3manager.NewUploader(sess)
	result, err := uploader.Upload(&s3manager.UploadInput{
		Body:   bytes.NewReader(buf.Bytes()),
		Bucket: aws.String(bucket),
		Key:    aws.String(thumbkey),
	})

	if err != nil {
		log.Fatalln("Failed to upload", err)
	}

	log.Println("Successfully uploaded to", result.Location)

}