gRPC server does not get notified about cancellation on client side during non-streaming requests

[alerosmile]

Version

4.5.14

Context

I'm using Quarkus and Mutiny to implement gRPC services and clients. I noticed that a Uni or Multi subscription cancellation does not get forwarded to the server. To solve this, I created a PR on Quarkus. My tests fail if Vert.x gRPC server support is enabled on Quarkus (quarkus.grpc.server.use-separate-server=false) when the request is a Uni. I found that the Http2ServerRequest.handleReset() method is responsible for this because the reset exception is not forwarded to the event handler since the request has already ended.

Shouldn't this event still be forwarded? Otherwise, the server has no way to get notified about cancellation events from the client. In reactive programming, it is crucial for the server to be aware of cancellation events to manage resources effectively and maintain proper communication flow.

Do you have a reproducer?

See the integration tests on my PR on Quarkus. The O2NCancellationTest and VertxCancellationTest need to be enabled, as they currently fail due to this issue.

[vietj]

can you elaborate more on the flow that should happen ? it does not seem clear to given that this involves using gRPC stub machinery

[alerosmile]

@vietj Sorry for my late response. I'm having a hard time to understand what's going on inside Vert.x. I've been using Vert.x indirectly via Quarkus only.

I've created a small example app. It's a copy from the original gRPC cancellation example reduced to the minimum. The example includes two servers, one using the gRPC libs and one using the Vert.x libs. If you start the gRPC server and then the client, you can see that the server sees the cancellation event. This doesn't work the same way using the Vert.x server.