SignalR Core doesn't seem to respect Newtonsoft's TypeNameHandling setting

Question

I'm passing around classes that derive from a common class. I'm finding that, despite passing deserialization valid data, the hub does not respect the TypeNameHandling and completely ignores the $type of the JSON. It deserializes to the base class regardless of what I try.

I event went and took the JSON that I was sending to the hub, pasted it into the hub code as a string, then used JsonConvert.Deserialize to see what would happen and it correctly deserialized to my derived object.

In my startup, I have

JsonConvert.DefaultSettings = () => new JsonSerializerSettings
            {
                TypeNameHandling = TypeNameHandling.Auto
            };

I wasn't sure if this was actually being used, so I had created a test JSON converter and put a debug on the CanRead property (which I had return a static false). That got hit. This also allowed my string deserialization to work.

So what is the hub doing differently that everything seems to work except the hub?

Answer 1

despite passing deserialization valid data, the hub does not respect the TypeNameHandling and completely ignores the $type of the JSON. It deserializes to the base class regardless of what I try.

I did a test with following code snippet, which work for me, you can refer to it.

In Startup:

services.AddSignalR().AddJsonProtocol(options => {
    options.PayloadSerializerSettings = new Newtonsoft.Json.JsonSerializerSettings
    {
        TypeNameHandling = Newtonsoft.Json.TypeNameHandling.Auto
    };
});

Hub method:

public async Task SendMessage1(Business mes)
{
    //code logic here
    //...
}

Classes:

public abstract class Business
{
    public string Name { get; set; }
}

public class Hotel : Business
{
    public int Stars { get; set; }
}

On client, send following JSON data to above hub method:

var ht = { "$type": "MyNamespaceHere.Hotel, NotesRTMSignalR", "Stars": 4, "Name": "Hudson Hotel" };

Test Result: