code: public static void sendNotModified(ChannelHandlerContext ctx) {
  		FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, NOT_MODIFIED);
  		setDateHeader(response);
  
  		// close the connection as soon as the error message is sent.
  		ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
  	}
docs: Send the "304 Not Modified" response. This response can be used when the
  file timestamp is the same as what the browser is sending up.
  
  @param ctx The channel context to write the response to.