[Question] DateTimeOffset? protobuf serialization/deserialization in ASP Core

[odysseus1973]

Hi!

After some investigation and reading posts on SO I found two ways to serialize DateTimeOffset?

1. Shim properties (working, but does not fit in my case)
2. Surrogates. Not working in my case
   In my StartUp file I use

RuntimeTypeModel.Default.Add(typeof(DateTimeOffset),false).SetSurrogate(typeof(DateTimeOffsetSurrogate));
RuntimeTypeModel.Default.Add(typeof(DateTimeOffset?),false).SetSurrogate(typeof(DateTimeOffsetSurrogate));

My surrogate class

    [ProtoContract]
    public class DateTimeOffsetSurrogate
    {
        [ProtoMember(1)]
        public string Date { get; set; }

        //public static implicit operator DateTimeOffsetSurrogate(DateTimeOffset? value)
        //{
        //    return (value.HasValue) ? new DateTimeOffsetSurrogate { Date = value.Value.ToString("o") } : new DateTimeOffsetSurrogate { Date = null };
        //}

        //public static implicit operator DateTimeOffset? (DateTimeOffsetSurrogate value)
        //{
        //    DateTimeOffset? result = null;
        //    if (DateTimeOffset.TryParse(value.Date, out DateTimeOffset date))
        //    {
        //        result = date;
        //    }
        //    return result;
        //}

        public static implicit operator DateTimeOffsetSurrogate(DateTimeOffset value)
        {
            return (value != null) ? new DateTimeOffsetSurrogate { Date = value.ToString("o") } : new DateTimeOffsetSurrogate { Date = null };
        }

        public static implicit operator DateTimeOffset(DateTimeOffsetSurrogate value)
        {
            // DateTimeOffset? result = null;
            // if (
            DateTimeOffset.TryParse(value.Date, out DateTimeOffset date);
            //{
            //    result = date;
            //}
            return date;
        }
    }

My serialized class

    [ProtoContract]
    public class StocksDto
    {
        [JsonIgnore]
        public Guid? StoreId { get; set; }
        [Required]
        public DateTimeOffset? Date { get; set; }
        [JsonIgnore]
        public DateTime DateUtc { get { return Date.HasValue ? Date.Value.UtcDateTime : DateTime.MinValue; } }
        [JsonIgnore]
        public double TimeZoneOffset { get { return Date.HasValue ? Date.Value.Offset.TotalMinutes : 0; } }
        [ProtoMember(1)]
        [Required]
        public bool? Full { get; set; }
        [HasElements(ErrorMessage = "The field Stocks must contain non-empty array of elements")]
        [ProtoMember(2)]
        public IEnumerable<Stock> Stocks { get; set; }
    }

When I try serialize/deserialize StocksDto, Date property return no value (null). As I can see implicit operator in surrogate does not called.
How to use surrogate for DateTimeOffset? in my case?

[rushfrisby]

Your surrogate should be

using System;
using System.Runtime.Serialization;

namespace ProtobufNetTest
{
    [DataContract(Name = nameof(DateTimeOffset))]
    public class DateTimeOffsetSurrogate
    {
        [DataMember(Order = 1)]
        public long? Value { get; set; }

        public static implicit operator DateTimeOffset(DateTimeOffsetSurrogate surrogate)
        {
            return DateTimeOffset.FromUnixTimeMilliseconds(surrogate.Value.Value);
        }

        public static implicit operator DateTimeOffset?(DateTimeOffsetSurrogate surrogate)
        {
            return surrogate != null ? DateTimeOffset.FromUnixTimeMilliseconds(surrogate.Value.Value) : (DateTimeOffset?)null;
        }

        public static implicit operator DateTimeOffsetSurrogate(DateTimeOffset source)
        {
            return new DateTimeOffsetSurrogate
            {
                Value = source.ToUnixTimeMilliseconds()
            };
        }

        public static implicit operator DateTimeOffsetSurrogate(DateTimeOffset? source)
        {
            return new DateTimeOffsetSurrogate
            {
                Value = source?.ToUnixTimeMilliseconds()
            };
        }
    }
}

[odysseus1973]

Thanks! I will try it, but why surrogate can't use string and how to register surrogate correctly? When I was debugging I did not see that the surrogate was called, so i think my problem with surrogate registration.

[rushfrisby]

The way you registered surrogates is correct however your class has a DateTimeOffset? property and your surrogate has no operators for converting between the two. Your surrogate only has operators for DateTimeOffset which is a different type.

Sure you can serialize the value as a string. I used long and the unix time value because the output is smaller than the string representation and faster than converting to/from a string.

[odysseus1973]

Thanks for answer! I specifically did not delete the commented lines in code block in my question, I tried it, but without success. How does converting to UnixTime support the time zone?

[rushfrisby]

By definition it takes into account the time zone since unix time starts at 1/1/1970 00:00:00 (UTC)

[paraboxx]

The purpose of DateTimeOffset is to preserve TimeZone information so it's possible to see at white Offset the timestamp was generated. By convertig to unixtime this information is lost.

[weitzhandler]

The funny thing is that of these two tests, the first passes whereas the second fails, probably because the serializer directly serializes the fields of the DateTimeOffset, tho I wish it would have worked when it's contained as well.

[Fact]
public void Should_serialize_DateTimeOffset()
{
    // arrange
    var now = DateTimeOffset.UtcNow;

    // act
    var clone = Serializer.DeepClone(now);

    // assert
    Assert.Equal(now, clone);
}

[Fact]
public void Should_serialize_DateTimeOffsetContainer()
{
    // arrange
    var container = new DateTimeOffsetContainer(DateTimeOffset.UtcNow);

    // act
    var clone = Serializer.DeepClone(container);

    // assert
    Assert.Equivalent(container, clone);
}

public record DateTimeOffsetContainer(DateTimeOffset Time);