Golang Converting image.Image to []byte

Question

Having trouble converting an image.Image to []byte. The problem spot is wrapped in dotted lines.

image_data, err := mybucket.Get(key)

if err != nil {
    panic(err.Error())
}

// reset format of data []byte to image.Image

original_image, _, err := image.Decode(bytes.NewReader(image_data))

new_image := resize.Resize(160, 0, original_image, resize.Lanczos3)
- - - - - - - - - - - - - - - - - - - - - - - - - - -
// reset format the image.Image to data []byte here
var send_S3 []byte
var byteWriter = bufio.NewWriter(send_S3)
- - - - - - - - - - - - - - - - - - - - - - - - - -
err = jpeg.Encode(byteWriter, new_image, nil)

new_path := key + "_sm"

err = mybucket.Put(new_path, send_S3, "image/jpg", "aclstring")

Basically, I need new_image to be in []byte format so that I can send it up to my S3 bucket.

Thanks for the help.

Answer 1

You want a bytes.Buffer, not a bufio.Writer. bytes.Buffer is used when you need a writer that writes to memory. bufio.Writer just caches data in memory before forwarding it to another writer.

buf := new(bytes.Buffer)
err := jpeg.Encode(buf, new_image, nil)
send_s3 := buf.Bytes()

Answer 2

Adding on to Stephen's code, if you're using the aws s3 go SDK to put an object, your code would look like:

// create buffer
buff := new(bytes.Buffer)

// encode image to buffer
err = png.Encode(buff, new_image)
if err != nil {
    fmt.Println("failed to create buffer", err)
}

// convert buffer to reader
reader := bytes.NewReader(buf.Bytes())

// use it in `PutObjectInput`
putInput := s3.PutObjectInput{
    Bucket: aws.String("my_bucket"),
    Body:   reader,
}

// send response
resp, err := svc.PutObject(&putInput)