SignalR: Failed to bind arguments when using Clients.All, but works with Clients.Group

[appvity-danhpham]

When invoking the UpdateIncidentReport method on the SignalR server, the message is successfully sent using:
await Clients.All.SendAsync("incidentReportAction", incidentReport);

However, the BE logs the following error after the send is completed:

TState (Log Message):
Failed to bind arguments received in invocation '(null)' of 'incidentReportAction'

Exception message:
System.IO.InvalidDataException: Invocation provides 1 argument(s) but target expects 0.

Additional Notes:

• The client is properly registered to listen for incidentReportAction with 1 parameter, and it still receives the data correctly.
• The error is logged only when using Clients.All. When using Clients.Group, the error does not occur.
• This suggests there may be an issue in how Clients.All internally dispatches messages to clients compared to Clients.Group.

Reproduction:
I have created a minimal reproduction project for this issue on GitHub:

🔗 https://github.com/appvity-danhpham/signalr-incidentReportAction-repro

Additional Information:

• ASP.NET Core SignalR Version: 8.0.18
• .NET Version: 12.0
• Hosting Environment: Windows

[BrennanConroy]

Please provide a repro as a github project, not a zip:
https://github.com/dotnet/aspnetcore/blob/main/docs/repro.md

[appvity-danhpham]

Hi, @BrennanConroy

I have created a minimal reproduction project for this issue on GitHub:

🔗 https://github.com/appvity-danhpham/signalr-incidentReportAction-repro

The repo includes:

SignalRServer - the SignalR hub server.

SignalRClient - a simple client that listens to incidentReportAction.

SignalR_BE - backend that triggers the SignalR call.

Please refer to the README.md for instructions on how to run and reproduce the issue.

Let me know if you need further details. Thank you!

[BrennanConroy]

However, the BE logs the following error after the send is completed:

Your connection in BE doesn't have a handler for incidentReportAction, so the error log is completely expected.
https://github.com/appvity-danhpham/signalr-incidentReportAction-repro/blob/main/SignalR_BE/SignalR_BE/Controllers/HomeController.cs

[appvity-danhpham]

Hi @BrennanConroy
Thank you for the clarification.

Just to confirm my understanding:
Even though the BE does not need to handle the incidentReportAction event, it still needs to register a handler for that event in order to prevent the SignalR runtime from logging the argument binding error.

This is the expected behavior of SignalR (by design), and not a bug — correct?

Please let me know if my understanding is accurate. Thank you!

[BrennanConroy]

Correct. As you noted earlier, if you use groups (or .Client/.Other etc.) you can avoid sending to the connection(s) that don't need the notification.

[appvity-danhpham]

Thank you for confirming, @BrennanConroy
Appreciate your help!