code: @Override
      public WebSocketFrame readChunk(ByteBufAllocator allocator) throws Exception {
          ByteBuf buf = input.readChunk(allocator);
          if (buf == null) {
              return null;
          }
          return new ContinuationWebSocketFrame(input.isEndOfInput(), rsv, buf);
      }
docs: Fetches a chunked data from the stream. Once this method returns the last chunk
  and thus the stream has reached at its end, any subsequent {@link #isEndOfInput()}
  call must return {@code true}.
  
  @param allocator {@link ByteBufAllocator}
  @return {@link WebSocketFrame} contain chunk of data