Why can DateTime.MinValue not be serialized in timezones ahead of UTC?

Question

I am experiencing issues with a WCF REST service. The wire object that I try to return has certain properties not set, resulting in DateTime.MinValue for properties of type DateTime. The service returns an empty document (with HTTP status 200 ???). When I try to call JSON serialization myself, the exception that is thrown is:

SerializationException: DateTime values that are greater than DateTime.MaxValue or smaller than DateTime.MinValue when converted to UTC cannot be serialized to JSON.

This can be reproduced by running the following code in a console app:

DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(DateTime));
MemoryStream m = new MemoryStream();
DateTime dt = DateTime.MinValue;

// throws SerializationException in my timezone
ser.WriteObject(m, dt);
string json = Encoding.ASCII.GetString(m.GetBuffer());
Console.WriteLine(json);

Why is this behaviour? I think it is related to my timezone (GMT+1). As DateTime.MinValue is default(DateTime), I would expect that this can be serialized without problems.

Any tips on how to make my REST service behave? I don't want to change my DataContract.

Answer 1

If your time zone is GMT+1, then the UTC value of DateTime.MinValue in your time zone is going to be an hour less than DateTime.MinValue.

Answer 2

The main problem is DateTime.MinValue has DateTimeKind.Unspecified kind. It defined as:

MinValue = new DateTime(0L, DateTimeKind.Unspecified);

But this is not real problem, this definition leads to problem during serialization. JSON DateTime serialization done thru:

System.Runtime.Serialization.Json.JsonWriterDelegator.WriteDateTime(DateTime value)

Unfortunately it defined as:

...

if (value.Kind != DateTimeKind.Utc)
{
    long num = value.Ticks - TimeZone.CurrentTimeZone.GetUtcOffset(value).Ticks;
    if ((num > DateTime.MaxValue.Ticks) || (num < DateTime.MinValue.Ticks))
    {
        throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(XmlObjectSerializer.CreateSerializationException(SR.GetString("JsonDateTimeOutOfRange"), new ArgumentOutOfRangeException("value")));
    }
}

...

So it does'nt take into account Unspecified and treats it as Local. To avoid this situation you can define your own constant:

MinValueUtc = new DateTime(0L, DateTimeKind.Utc);

or

MinValueUtc = DateTime.MinValue.ToUniversalTime();

It looks weird of cause, but it helps.