code: private void sendNotModified(ChannelHandlerContext ctx) {
      HttpResponse response = new DefaultHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.NOT_MODIFIED);
      setDateHeader(response);
  
      // Close the connection as soon as the error message is sent.
      ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
    }
docs: /*
  Sends a Not Modified response to the client