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