[MessagePackObject]
    public class TransferCostDto : ITransferCosts
    {
        [Key(0)]
        public ulong UploadQty { get; private set; }
        [Key(1)]
        public ulong DownloadQty { get; private set; }


        [Key(2)]
        private ulong _UploadQty;
        [Key(3)]
        private ulong _DownloadQty;

        public ulong GetUploadQty()
        {
            return _UploadQty;
        }

        public ulong GetDownloadQty()
        {
            return _DownloadQty;
        }


        public virtual void AddUploadQty(ulong bytes)
        {
            _UploadQty += bytes;
            UploadQty += bytes;
        }

        public virtual void AddDownloadQty(ulong bytes)
        {
            _DownloadQty += bytes;
            DownloadQty += bytes;
        }


    }

  [TestMethod]
        public void SerializeTrasferCostsTest() {
            var tr = new TransferCostDto();
            tr.AddDownloadQty(3);
            tr.AddUploadQty(10);
            var trser = MessagePackSerializer.Serialize(tr , MessagePack.Resolvers.ContractlessStandardResolverAllowPrivate.Instance);
            var trdeser = MessagePackSerializer.Deserialize<TransferCostDto>(trser);

            var trser1 = MessagePackSerializer.Serialize(tr, MessagePack.Resolvers.DynamicObjectResolverAllowPrivate.Instance);
            var trdeser1 = MessagePackSerializer.Deserialize<TransferCostDto>(trser1);

            var trser3 = MessagePackSerializer.Serialize(tr, MessagePack.Resolvers.StandardResolverAllowPrivate.Instance);
            var trdeser3 = MessagePackSerializer.Deserialize<TransferCostDto>(trser3);

            trdeser.DownloadQty.Should().Be(3);
            trdeser1.DownloadQty.Should().Be(3);
            trdeser3.DownloadQty.Should().Be(3);
        }

[MessagePack.Union(0, typeof(TransferCostDto))]
    public interface ITransferCosts
    {
        ulong UploadQty { get; }
        ulong DownloadQty { get; }

        void AddUploadQty(ulong bytes);
        void AddDownloadQty(ulong bytes);
    }