tour: Output doesn't work

[meownoid]

Context: https://tour.golang.org/methods/23

I've solved methods/23 like this:

func (old_reader rot13Reader) Read(b []byte) (int, error) {
    const LEN int = 1024
    tmp_bytes := make([]byte, LEN)
    old_len, err := old_reader.r.Read(tmp_bytes)
    if err == nil {
        tmp_bytes = tmp_bytes[:old_len]
        rot13(tmp_bytes)
        return len(tmp_bytes), nil
    } else {
        return 0, err
    }
}

func main() {
    s := strings.NewReader("Lbh penpxrq gur pbqr!")
    r := rot13Reader{s}
    io.Copy(os.Stdout, &r)
}

where rot13 is correct, but I can't see any output, process just exits. Debug output just before return len(tmp_bytes), nil shows correct string.

[adg]

Please ask about this on one of our discussion forums: https://golang.org/wiki/Questions