return Optional.of((long) length);
    }

    @Override
    public byte[] read() {
      return Arrays.copyOfRange(bytes, offset, offset + length);
    }

    @SuppressWarnings("CheckReturnValue") // it doesn't matter what processBytes returns here
    @Override
    @ParametricNullness
    public <T extends @Nullable Object> T read(ByteProcessor<T> processor) throws IOException {