copyN.go

type CopyCb func(written int64)
func CopyWithCb(dst io.Writer, src io.Reader, cb CopyCb) (written int64, err error) {
        for {
                n, err := io.CopyN(dst, src, KB)
                written += n
                cb(written)
                if err != nil {
                        if err == io.EOF {
                                return written, nil
                        }
                        return written, err
                }
        }
}