Parsing DateTime with timezone offset with JSON.net

Question

I make a call to a web service, which returns an item, one property of which is:

"startDate":"/Date(1398859200000+1100)/"

In my C# representation, I have:

public class MyClass 
{
    public DateTimeOffset StartDate {get; set;}
}

In my unit test, I have the following assertion

var expectation = 
    new DateTimeOffset(2014, 04, 30, 12, 0, 0, new TimeSpan(0, 11, 0, 0));

Assert.That(specialOfferContent.End, Is.EqualTo(expectiation).Within(1).Seconds);

(not sure if there's a better way to assert this...)

If deserialize this from JSON using (without specifying DateParseHandling), the result I get is:

Expected: 04/30/2014 12:00:00 +11:00 +/- 00:00:01
But was: 04/30/2014 13:00:00 +01:00

Alternatively, if I specify DateParseHandling as DateParseHandling.DateTimeOffset I get this:

Expected: 04/30/2014 12:00:00 +11:00 +/- 00:00:01
But was: 04/30/2014 23:00:00 +11:00

My question is, what am i doing wrong?
It is ignoring the +1100 part of the date when I do

Jon Skeet · Accepted Answer · 2014-03-18 15:18:39Z

2

Your expectation is incorrect, basically.

The value you've given is 04/30/2014 23:00:00 +11:00 - because it's UTC 04/30/2014T12:00:00 (as verified with Epoch Converter), but with a local offset of +11 hours. So the local time is 11pm.

In your input, there are two pieces of data:

1398859200000: The number of milliseconds since the Unix epoch (this will be the same around the world, at a given instant)
+1100: The local offset from UTC

It's important to distinguish the two parts - in particular understanding that the first part is not affected by the time zone.

answered Mar 18, 2014 at 15:18

Jon Skeet

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4 Comments

Alex Over a year ago

I'm editing my comment each time you edit your answer.. haha! Anyway.. I was using the Epoch Converter, and think that's where my confusion stemmed from - how can I assert that the date time offset has been parsed with the offset (in this instance +1100)

Jon Skeet Over a year ago

@Alex: You'd create it as new DateTimeOffset(2014, 04, 30, 23, 0, 0, new TimeSpan(0, 11, 0, 0)); - because the DateTimeOffset constructor takes the local time and the offset from UTC.

Alex Over a year ago

Thanks Jon, by local time do you mean time on the (in this case) developer machine... for example, if a developer in, let's say, Singapore, checked out the code and run the unit test, it would fail?

Jon Skeet Over a year ago

@Alex: It's the local time represented by the value /Date(1398859200000+1100)/. So it's presumably local to whatever produced that value. It doesn't depend on the system you're running the parsing code on.

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