NotSupportedException: 'Cancellation of stream writes is not supported by this gRPC implementation.'

[max-ieremenko]

Grpc.Net 2.46.0, Grpc.Core 2.46.1

Is your feature request related to a problem? Please describe.

As an API user, i want to know if IAsyncStreamWriter supports WriteAsync(message, CancellationToken).
I don't want to guess or to catch NotSupportedException thrown by the default implementation.

Describe the solution you'd like

change the default implementation, remove NotSupportedException:

public interface IAsyncStreamWriter<T>
{
    Task WriteAsync(T message, CancellationToken cancellationToken) => WriteAsync(message);
}

Describe alternatives you've considered

add indicator whether the current AsyncStreamWriter supports WriteAsync(message, CancellationToken)

public interface IAsyncStreamWriter<T>
{
    bool CanCancelWriteAsync => false; // default false;

    Task WriteAsync(T message, CancellationToken cancellationToken)
    {
        if (cancellationToken.CanBeCanceled && !CanCancelWriteAsync)
        {
            throw new NotSupportedException("Cancellation of stream writes is not supported by this gRPC implementation.");
        }

        return WriteAsync(message);
    }
}

Additional context

Few examples of WriteAsync in context of Grpc.Net and Grpc.Core WriteAsyncChallenge.zip.

[JamesNK]

Grpc.Core doesn't support WriteAsync(message, CancellationToken). Grpc.AspNetCore does.

[JamesNK]

Describe alternatives you've considered

add indicator whether the current AsyncStreamWriter supports WriteAsync(message, CancellationToken)\

That means the cancellation token would silently be ignored which isn't good.

[max-ieremenko]

Grpc.Core doesn't support WriteAsync(message, CancellationToken). Grpc.AspNetCore does.

IAsyncStreamWriter.WriteAsync(CancellationToken) is defined in Grpc.Core is visible to developers and code analyzer.
Resharper makes a suggestion "hey, there's an overload with CancellationToken".

Describe alternatives you've considered

add indicator whether the current AsyncStreamWriter supports WriteAsync(message, CancellationToken)\

That means the cancellation token would silently be ignored which isn't good.

Forcing the user to catch "NotSupportedException" is not good either. What about the alternative "bool CanCancelWriteAsync"?

[JamesNK]

A property like that is only useful if you have code that could run on either implementation. That doesn't seem like it would be common. But if more people ask for this, then it could be considered.

If you know WriteAsync with a cancellation token isn't supported then just don't call it.

[JamesNK]

Thank you for your feedback. We're closing this issue as the behavior discussed is by design.

[Falco20019]

This sadly also did bite us... ReSharper is creating warnings that there is a variant with cancellation token support. Our users just applied it (as it's usually useful) and found out later that this is throwing an exception. So I'm also not too happy with the solution. In my opinion, the macro checking for #if NETSTANDARD2_1_OR_GREATER is misleading.

[NorekZ]

I’d personally be fine with the current state if ReSharper isn’t suggesting filling in the cancellation token from context.

What about adding a setting that would suppress the exception? It’s unwatchable that no team member always ignores this overload (and the suggestion).

[Falco20019]

@NorekZ We nowadays pass CancellationToken.None to suppress the warning and also make clear that we intentionally not pass in the real token (as this would throw at runtime). Still not 100% happy since there will always be cases where it's not caught in a review (especially with new people joining), but it's the best that we were able to come up with.

Since Grpc.Core is in maintenance-only mode, I am pretty sure that no one will invest any more time on this. I really hope that dotnet/aspnetcore#35077 gets some traction and that we could finally switch to the new implementation.

[NorekZ]

Thanks for suggestion.

I now realized this issue is for deprecated Grpc.Core.

We use Grpc.AspNetCore, where we are observing the same problem.

Eventually I've found problem in our Interceptor, where I missed the new method. I generated IAsyncStreamWriter<TResponse> method stubs using ReSharper, but it didn't generate the one for WriteAsync(TResponse message, CancellationToken cancellationToken) because it has default implementation.