SignalR's JSON protocol does not support polymorphic serialization on streaming methods

[Tragetaschen]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

In #47859, most of ASP.NET Core learned to serialize a polymorphic JSON hierarchy, but SignalR was omitted and still doesn't include the type discriminator declared on the base type, for example when streaming from server to client.

It would be great if this difference would not exist.

For me, the workaround of declaring the derived classes [JsonPolymorphic] etc. works.

Expected Behavior

Streaming a base type from server to client should include the type discriminator.

Steps To Reproduce

public class MyHub: Hub
{
    public async IAsyncEnumerable<BaseMessage> GetMessages()
    {
        yield return new DerivedMessage();
    }
}

Exceptions (if any)

No response

.NET Version

8.0.2

Anything else?

No response

[BrennanConroy]

Probably dupe of #52342
Polymorphic support is added in 9.0, try that.

[Tragetaschen]

Yes, this looks very much like a dupe, should've searched the PRs as well…