Exception on DateTime.MinValue

[olexandrvynnychenko]

The code to reproduce the issue is very simple:

using Fluid;

var model = new { foo = "bar", date = DateTime.MinValue };

var template = new FluidParser().Parse("{{foo}} {{date}}");

template.Render(new TemplateContext(model))

The exception:

System.ArgumentOutOfRangeException: The UTC time represented when the offset is applied must be between year 0 and 10,000. (Parameter 'offset')
at System.DateTimeOffset.ValidateDate(DateTime dateTime, TimeSpan offset)
at System.DateTimeOffset..ctor(DateTime dateTime)
at System.DateTimeOffset.op_Implicit(DateTime dateTime)
at Fluid.Values.FluidValue.Create(Object value, TemplateOptions options)
at Fluid.Values.ObjectValueBase.GetValueAsync(String name, TemplateContext context)
at Fluid.Ast.IdentifierSegment.ResolveAsync(FluidValue value, TemplateContext context)
at Fluid.Ast.MemberExpression.EvaluateAsync(TemplateContext context)
at Fluid.Ast.OutputStatement.WriteToAsync(TextWriter writer, TextEncoder encoder, TemplateContext context)
at Fluid.Parser.FluidTemplate.RenderAsync(TextWriter writer, TextEncoder encoder, TemplateContext context)
at Fluid.FluidTemplateExtensions.RenderAsync(IFluidTemplate template, TextWriter textWriter, TemplateContext context, TextEncoder encoder, Boolean isolateContext)
at Fluid.FluidTemplateExtensions.RenderAsync(IFluidTemplate template, TemplateContext context, TextEncoder encoder, Boolean isolateContext)
at Program.<Main>$(String[] args)

An exception is thrown only when the tempalte string contains the date field.

I am using .NET 9.

My timezone is (UTC+02:00) Helsinki, Kyiv, Riga, Sofia, Tallinn, Vilnius.

The following workaround makes it work:

using Fluid;

var model = new { foo = "bar", date = DateTime.SpecifyKind(DateTime.MinValue, DateTimeKind.Utc) };    //same value but Kind = Utc

var template = new FluidParser().Parse("{{foo}} {{date}}");

template.Render(new TemplateContext(model))

[sebastienros]

Internally the DateTime is converted to DateTimeOffset. Since you didn't set the Kind it will be unspecified and DateTimeOffset will assume local. So with an offset of 2 (2 hours after UTC). At that point it will fail because you represent the smallest value, but in your timezone. In UTC it's less than the minimal possible value and DateTimeOffset will fail.

In that case I would suggest to use DateTimeOffset.MinValue instead. Fluid could throw a different exception, but it won't be much help, and trying to convert/round any invalid value could be worse.

[olexandrvynnychenko]

I suspected something like that. So I temporarily just 'fix' any context passed to Fluid using the following code:

private static IDictionary FixValuesInContext(object context)
{
    //making a clone to keep the passed object unchanged
    Dictionary<string, object?> dict;
    if (context is IDictionary)
    {
        dict = new();
        foreach (string key in ((IDictionary)context).Keys)
            dict[key] = ((IDictionary)context)[key];
    }
    else
        dict = context.GetType().GetProperties().ToDictionary(p => p.Name, p => p.GetValue(context));

    foreach (var key in dict.Keys)
    {
        if (dict[key] is DateTime && (DateTime)dict[key]! == DateTime.MinValue && ((DateTime)dict[key]!).Kind != DateTimeKind.Utc)
            dict[key] = DateTime.SpecifyKind(DateTime.MinValue, DateTimeKind.Utc);
    }
    
    return dict;
}

But I hope to find something more straightforward. The problem is that DateTime.MinValue is the default value for DateTime. It is not something random. Exactly the same value will be assigned after the following statement:

DateTime a = default;

So I just thought it would be better to be able to handle DateTime.MinValue without an exception.

[sebastienros]

So I just thought it would be better to be able to handle DateTime.MinValue without an exception.

That's something that could be better, check for this specific values, which would match what you put in it and do the DateTimeOffset conversion explicitly by using DateTimeOffset.MinValue. Same for MaxValue for timezeones that are on the other side of UTC.

Obviously it's not something that we are the first to discover ... https://stackoverflow.com/questions/6924198/converting-datetime-minvalue-to-datetimeoffset

So the action to take is to change the conversion to handle these specific cases.

[olexandrvynnychenko]

I came up with a simpler solution.

options.ValueConverters.Add(obj =>
{
	if (obj is DateTime && (DateTime)obj == DateTime.MinValue && ((DateTime)obj).Kind != DateTimeKind.Utc)
		return DateTime.SpecifyKind(DateTime.MinValue, DateTimeKind.Utc);
	return null;
});

It just works.

Thank you for help and thank you for the great lib!

[olexandrvynnychenko]

I looked through the code of Fluid and noticed there is no explicit conversion DateTime to DateTimeOffset. It seems all DateTime values are implicity converted when passed to DateTimeValue constructor.

So there could be one more constructor taking DateTime value as an argument and converting it to DateTimeOffset explicitly.

I've checked it, works fine for me.

Maybe not a super universal solution but it covers the default value edge case. @sebastienros what do you think?

[sksk571]

Possibly related to this issue is that the library performs datetime conversion to UTC in certain cases. This creates inconsistent results when date rendered with and without format filter, for example:

using Fluid;

var context = new TemplateContext();
context.SetValue("somedate", DateTime.Today);

// displays current date
Console.WriteLine(await new FluidParser().Parse("{{ somedate | date: '%B %d, %Y' }}").RenderAsync(context));

// displays current date - UTC offset
Console.WriteLine(await new FluidParser().Parse("{{ somedate }}").RenderAsync(context));

// displays current time
Console.WriteLine(await new FluidParser().Parse("{{ 'now' | date: '%B %d, %Y %H:%M' }}").RenderAsync(context));

// displays current time - UTC offset
Console.WriteLine(await new FluidParser().Parse("{{ 'now' | date }}").RenderAsync(context));