DateTimeOffset does not parse a valid ISO-8601 datetime string

[chris-steema]

Description

DateTimeOffset does not correctly parse a valid ISO-8601 datetime string. Wikipedia claims the current ISO-8601 definition prefers a comma as the decimal mark for the lowest time order present:

However, DateTimeOffset is not capable of parsing a datetime string with a comma decimal mark for the lowest time order when that time order is seconds:

        static void Main(string[] args)
        {
            static void Test()
            {
                var dateString = "2021-04-23T13:04:17,307642270+02:00";

                DateTimeOffset date = DateTimeOffset.MinValue;

                try
                {
                    date = DateTimeOffset.Parse(dateString);
                }
                catch (Exception e)
                {
                    Console.WriteLine($"date: {e.Message}");
                }
                finally
                {
                    Console.WriteLine($"date: {date}");
                }
            }

            Test();
        }

Configuration

Code above running on .NET 5.0.202 on Windows 20H2 (OS Build 19042.928).

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Issue Details

---

Description

DateTimeOffset does not correctly parse a valid ISO-8601 datetime string. Wikipedia claims the current ISO-8601 definition prefers a comma as the decimal mark for the lowest time order present:

However, DateTimeOffset is not capable of parsing a datetime string with a comma decimal mark for the lowest time order when that time order is seconds:

        static void Main(string[] args)
        {
            static void Test()
            {
                var dateString = "2021-04-23T13:04:17,307642270+02:00";

                DateTimeOffset date = DateTimeOffset.MinValue;

                try
                {
                    date = DateTimeOffset.Parse(dateString);
                }
                catch (Exception e)
                {
                    Console.WriteLine($"date: {e.Message}");
                }
                finally
                {
                    Console.WriteLine($"date: {date}");
                }
            }

            Test();
        }

Configuration

Code above running on .NET 5.0.202 on Windows 20H2 (OS Build 19042.928).

Author:	chris-steema
Assignees:	-
Labels:	area-System.Runtime, untriaged
Milestone:	-

[GrabYourPitchforks]

/cc globalization crew (@maryamariyan @michaelgsharp @safern @tarekgh) in case you all have further thoughts

[tarekgh]

@chris-steema You are right that the comma can replace the period in the ISO-8601 but currently we don't support that. We only support the format we use when formatting the DateTimeOffset which always uses the period. You may workaround it by calling ParseExact and passing the format yyyy'-'MM'-'dd'T'HH':'mm':'ss','fffffffzzz.

[KalleOlaviNiemitalo]

XML Schema Part 2: Datatypes Second Edition seems to specify only . for fractional seconds. Thus, even if DateTimeOffset.Parse is changed to support comma as well, I think XmlConvert should be left as is.

[chris-steema]

Thank you @tarekgh, you're right, please let me explain why this is a concern for us. Our .NET app runs on Linux, and collates information from both Linux and Windows systems. In short, the issue is this:

tofol@neptune:~$ date --iso-8601=ns
2021-04-23T22:07:49,016860795+02:00

Linux appears to understand the decimal mark of ISO-8601 as a comma. What this means on our system, when receiving hundreds of inputs a second from both Windows and Linux, is a degradation of performance as we have to call TryParse to determine which interpretation of ISO-8601 is arriving to our system.

[tarekgh]

@chris-steema I am not objecting we try to fix that in the .NET. I was just pointing at some temporary workaround.

[tarekgh]

Also, are all dates you are receiving in ISO format? I am asking because if this is the case, you can check

if (dateString.Length >= 20 && dateString[19] == ',')
{
    DateTimeOffset dto = DateTimeOffset.ParseExact(dateString, "yyyy'-'MM'-'dd'T'HH':'mm':'ss','fffffffzzz", null);
}

This should mitigate the performance concern.