Change DateTimeOffset.Offset Property?

Question

My end goal is to get universal time from client with NO offset - just UTC time. I try to accomplish this like so:

Javascript: (new Date()).toUTCString(), the output of which logs: Thu, 17 Mar 2016 15:13:23 GMT, which is exactly what I need.

Then I take it to server and try to convert it to DateTimeOffset:

string dateTimeOffsetPattern = "ddd, dd MMM yyyy HH:mm:ss 'GMT'"; 

DateTimeOffset clientLoginTime = DateTimeOffset.ParseExact
    (timeStringFromClient, dateTimeOffsetPattern, CultureInfo.InvariantCulture);

Which results in:

3/17/2016 3:13:23 PM -04:00 

Somehow it adjusts the time for my local (Eastern) offset. I do NOT want this to happen, I want it to just return the UTC time, like so:

3/17/2016 3:13:23 PM +00:00

P.S. I did just ask another question about this, and I apologize, since I feel like it should be easy enough, but I don't get it. This should be really simple, but it looks like offset doesn't have a setter (unless I am completely missing some C# basics as usual):

public TimeSpan Offset { get; }

Answer 1

There's an overload of ParseExact where you can specify a DateTimeStyles. One of the values of DateTimeValues is AssumeUniversal, which says:

If format does not require that input contain an offset value, the returned DateTimeOffset object is given the UTC offset (+00:00).

which basically means "don't assume it's local, assume it's universal." Assuming local is the default, which is why you're seeing the result you are in that it's adjusting to local. Specifying AssumeUniversal should parse it the way you want.

DateTimeOffset clientLoginTime = DateTimeOffset.ParseExact
(timeStringFromClient, dateTimeOffsetPattern, CultureInfo.InvariantCulture, 
    DateTimeStyles.AssumeUniversal);

Answer 2

I would parse from JS normally, then do the following:

• Strip OffSet from DateTimeOffset by returning DateTime
• Set OffSetby instantiating another DateTimeOffset having TimeSpan set to ZERO.

In your case:

var clientLoginTime = new DateTimeOffset(clientLoginTime.DateTime, TimeSpan.FromHours(0));

This can be easily converted into an extension method

public static DateTimeOffset SetOffset(this DateTimeOffset dto, int timeZoneDiff)
{
    return new DateTimeOffset(dto.DateTime, TimeSpan.FromHours(timeZoneDiff));
}