Implement io.Reader from image.RGBA

I need a little hint. I'm creating thumbnails of images in Go and would like to pass them to jpegoptim for crushing.

jpegoptim has the --stdin and --stdout flags, which I would like to use. Now, I don't want to save the generated image to disk first, but convert my *image.RGBA to something that implements io.Reader, so I can pass it to exec.Cmd.Stdin

I'm a little lost on how I could achieve this, would be great if someone can point me in the right direction.

Thanks

In this case, you don't need to implement your own io.Reader. Use io.Pipe and jpeg.Encode, e.g.

func main() {
    //Prepare image ...
    img := ...

    //Prepare output (file etc.) ...
    outFile := ...

    //Use pipe to connect JPEG encoder output to cmd's STDIN
    pr, pw := io.Pipe()

    //Exec jpegoptim in goroutine
    done := make(chan bool, 1)
    go func() {
        //execute command
        cmdErr := bytes.Buffer{}
        cmd := exec.Command("jpegoptim", "--stdin", "--verbose")
        cmd.Stdin = pr       //image input from PIPE
        cmd.Stderr = &cmdErr //message
        cmd.Stdout = outFile //optimize image output

        if err := cmd.Run(); err != nil {
            // handle error
        }
        fmt.Printf("Result: %s\n", cmdErr.String())
        close(done)
    }()

    //ENCODE image to JPEG then write to PIPE
    o := jpeg.Options{Quality: 90}
    jpeg.Encode(pw, img, &o)

    //When done, close the PIPE
    if err := pw.Close(); err != nil {
        // handle error
    }

    //Wait for jpegoptim
    <-done
}