How to Convert a Golang `image.Image` to a `[]byte` for S3 Upload?

Converting an Image from image.Image to []byte Format in Golang

This question pertains to converting an image represented as an image.Image object to a byte array, represented as type []byte in Golang. The specific challenge is evident in the provided code snippet, where the conversion step is marked with dotted lines.

// ...

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

new_image := resize.Resize(160, 0, original_image, resize.Lanczos3)

// Convert the image.Image to []byte here

new_path := key + "_sm"

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

To rectify the issue, the intention is to transform the modified image, stored in new_image, into a byte array, allowing it to be transmitted to the S3 bucket via the Put function.

The remedy lies in utilizing the bytes.Buffer type, which offers an in-memory buffer for writing data. This buffer serves as a destination for the JPEG-encoded image data. In contrast, the bufio.Writer used earlier merely caches data before passing it to an underlying writer, without accumulating the data in memory.

Here's how the code should be adjusted:

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

This updated code employs a bytes.Buffer to accumulate the JPEG-encoded image data in memory, which is then retrieved as a byte array by calling the Bytes method on the buffer. This byte array can now be passed to the Put function to upload the image to the S3 bucket.

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