code: private static void onHeadersRead(ChannelHandlerContext ctx, Http2HeadersFrame headers)
              throws Exception {
          if (headers.isEndStream()) {
              ByteBuf content = ctx.alloc().buffer();
              content.writeBytes(RESPONSE_BYTES.duplicate());
              ByteBufUtil.writeAscii(content, " - via HTTP/2");
              sendResponse(ctx, content);
          }
      }
docs: If receive a frame with end-of-stream set, send a pre-canned response.