code: public static void storeBuffer(ByteBuf buf, Object message, RequestContext ctx) {
          IdentityHashMap<Object, ByteBuf> buffers = ctx.attr(BUFFERS).get();
          if (buffers == null) {
              buffers = new IdentityHashMap<>();
              ctx.attr(BUFFERS).set(buffers);
          }
          buffers.put(message, buf);
      }
docs: Stores the {@link ByteBuf} backing {@link Message} to be released later using
  {@link #releaseBuffer(Object, RequestContext)}.