How to Convert an image.Image to []byte in Go for S3 Upload?

Converting image.Image to []byte in Golang

In this article, we address the issue of converting an image.Image to []byte in Go. The pain point lies in the lines indicated by dotted lines in the provided code snippet:

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)
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// reset format the image.Image to data []byte here
var send_S3 []byte
var byteWriter = bufio.NewWriter(send_S3)
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err = jpeg.Encode(byteWriter, new_image, nil)

new_path := key + "_sm"

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

The objective is to transform the image.Image, new_image, into []byte format for uploading to an S3 bucket.

Solution

The key to resolving this issue is to utilize a bytes.Buffer instead of a bufio.Writer. bytes.Buffer is designed to write data in memory, while bufio.Writer simply caches data in memory before passing it along to another writer.

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

By employing bytes.Buffer, we effectively capture the encoded image into a []byte slice named send_s3. This slice can then be used to upload the image to the S3 bucket.

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