System.Uri does not round trip properly when original string is UNC path

Consider a path in this form:

//fileserver/Framework/NuGet/server.png

This is parsable by System.Uri constructor. In fact, it is parseable with any of the UriKind values. My understanding is that Uri should round trip safely through JSON serialization and deserialization. If this is a bad assumption, perhaps this should be called out in the documentation (or… maybe I missed it).

With the following bit of code, you can see that the Uri become relative after a round trip.

using System;
using Newtonsoft.Json;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            var before = new Uri("//fileserver/Framework/NuGet/server.png", UriKind.Absolute);
            Console.WriteLine("IsAbsoluteUri: " + before.IsAbsoluteUri);
            var json = JsonConvert.SerializeObject(before);
            Console.WriteLine("JSON: " + json);
            var after = JsonConvert.DeserializeObject<Uri>(json);
            Console.WriteLine("IsAbsoluteUri: " + after.IsAbsoluteUri);
        }
    }
}

Output:

IsAbsoluteUri: True
JSON: "//fileserver/Framework/NuGet/server.png"
IsAbsoluteUri: False

I think the crux of the issue is that a UNC path like this works on all forms of the Uri contrustor:

new Uri(value);
new Uri(value, UriKind.Absolute);
new Uri(value, UriKind.RelativeOrAbsolute);
new Uri(value, UriKind.Relative);

… meaning this sort of string is kind of ambiguous given then following parse line: https://github.com/JamesNK/Newtonsoft.Json/blob/cdf10151d507d497a3f9a71d36d544b199f73435/Src/Newtonsoft.Json/Utilities/ConvertUtils.cs#L478

[TylerLeonhardt]

Looks like the root issue is with .NET then… because:

[Uri]::new("/Users/tyler/").IsAbsoluteUri

# gives you

true

# and 

[Uri]::new("/Users/tyler/", [System.UriKind]::RelativeOrAbsolute).IsAbsoluteUri

#gives you

false

[TylerLeonhardt]

I’ve opened an issue on corefx to discuss this further https://github.com/dotnet/corefx/issues/40428