byte[] tmp;
            int new_size = pipe_buf.length * 2;

            if (len > new_size - used) {
                new_size = len + used;
            }
            tmp = pipe_buf;
            pipe_buf = new byte[new_size];
            i = tmp.length - beg_idx;
            if (used > i) { /* 2 chunks */
                System.arraycopy(tmp, beg_idx, pipe_buf, 0, i);