ObservationGrpcServerInterceptor does not store observation in a context

[AleksanderBrzozowski]

Please describe the feature request.
Let's say that we have a gRPC server written in kotlin with coroutines support enabled:

class ExampleServer(private val registry: ObservationRegistry) :ServiceGrpcKt.CoroutineImplBase() {
    override suspend fun exampleMethod(request: Request): Response {
        // logic
    }

And let's assume that ObservationGrpcServerInterceptor was added as an interceptor.

When we try to get the current observation from the registry, it always return null, which is expected as suspended function are ran in a different thread:

override suspend fun exampleMethod(request: Request): Response {
    this.registry.currentObservation // returns null
}

I wonder how we can fix this, so that we can get the current observation the same as we do for blocking API.

It would be nice if the existing function could be used to retrieve the current observation created by the interceptor:

class ExampleServer(private val registry: ObservationRegistry) :ServiceGrpcKt.CoroutineImplBase() {
    override suspend fun exampleMethod(request: Request): Response {
        coroutineContext.currentObservation()
    }

Rationale
It is currently not possible to create a child observation based on the parent one that was created in the gRPC Server Interceptor.

Additional context
#3256

[jonatan-ivanov]

So it seems there is a missing instrumentation and not the existing one having some bugs, right?
This could be related: micrometer-metrics/tracing#174

[AleksanderBrzozowski]

@jonatan-ivanov
Yeah, exactly, you can see my PR to find how this might be added 🙂

I don't think that the discussion you have mentioned is related, though. It seems to be about context propagation to the REST calls, and in my case it is gRPC call 🙂

I will be happy if you can take a look at the PR that I provided 🙂

[marcingrzejszczak]

Thank you @AleksanderBrzozowski for your PR. We will look into that ASAP (we haven't forgotten about your PR :) )

[AleksanderBrzozowski]

@marcingrzejszczak Thanks! 🙂 I haven't forgotten either! 😄

[AleksanderBrzozowski]

@marcingrzejszczak Hello! :) How is it going? Were you able to take a look at the PR? :)

[marcingrzejszczak]

Not yet, the PR however needs some conflict resolution.

[KostadinAlmishev]

@AleksanderBrzozowski Can you fix conflicts, please. I have same problem and I am waiting this fix :)

[AleksanderBrzozowski]

Yup, I will try to fix conflicts today 🙂

[AleksanderBrzozowski]

Conflicts fixed, @marcingrzejszczak you can proceed with review 😃