code: public final LogBuffer duplicate(final int pos, final int len) {
          if (pos + len > limit) throw new IllegalArgumentException("limit excceed: " + (pos + len));
  
          // XXX: Do momery copy avoid buffer modified.
          final int off = origin + pos;
          byte[] buf = Arrays.copyOfRange(buffer, off, off + len);
          return new LogBuffer(buf, 0, len);
      }
docs: Return n bytes in this buffer.