Micronaut gRPC server endpoint swallows exceptions (other than gRPC's StatusException); how to log them instead?

Question

I'm working on a Micronaut gRPC server in Kotlin. By default, if my gRPC endpoint throws an exception, it's swallowed without any logging (even at debug level), and gRPC returns only a status: UNKNOWN error response with no details.

I'd like all my gRPC endpoints to log any uncaught exceptions with their stack traces at ERROR level. How can I do that? I could see addressing this with Micronaut serving tools (to intercept/log the exception), some gRPC change, or just at the Kotlin language level to efficiently apply the same except-log-rethrow logic to all endpoint functions.

Here's what I've tried and additional docs I've found:

As a workaround, I've added a try-catch with logging in my endpoint, but I don't want to have this boilerplate in every endpoint; I assume there's some more efficient way to add it in an interceptor or something but haven't found that in Micronaut docs.

import mu.KotlinLogging

import javax.inject.Singleton
import javax.sql.DataSource

private val logger = KotlinLogging.logger {}

@Singleton
@Suppress("unused")
class MyEndpoint(val dataSource: DataSource) : MyServiceGrpcKt.MyServiceCoroutineImplBase() {

    override suspend fun search(request: MyRequest): MyResponse {
        try {
            dataSource.getConnection().use { con ->
                con.prepareStatement("SELECT ... some sql ... ").use { stm ->
                    stm.setString(1, request.query)
                    stm.executeQuery().use { rs ->
                        // build RPC response from ResultSet
                      }
                  }
              }
          }
        } catch (e: Throwable) {
            // The question is, how to avoid having to add this try-catch and logger.error
            // call in every Endpoint?
            logger.error(e) { "Error handling $request" }
            throw e
        }

        return MyResponse.newBuilder().setStuff(... from sql ...).build()
    }
}

I've checked the Micronaut gRPC server docs and gRPC error handling guide, but don't see hints there. And the Micronaut error handling docs are for HTTP error pages, not generic interceptors. I also asked on the gitter Micronaut community, but no response.

The abstract base for the gRPC Endpoint class does have this doc on the search RPC method that I'm implementing:

    /**                                                                                              
     * Returns the response to an RPC for valohealth_monocle.model_search.ModelSearchService.Search. 
     *                                                                                               
     * If this method fails with a [StatusException], the RPC will fail with the corresponding       
     * [io.grpc.Status].  If this method fails with a [java.util.concurrent.CancellationException],  
     * the RPC will fail                                                                             
     * with status `Status.CANCELLED`.  If this method fails for any other reason, the RPC will      
     * fail with `Status.UNKNOWN` with the exception as a cause.                                     
     *                                                                                               
     * @param request The request from the client.                                                   
     */                                                                                              
    open suspend fun search...

That comment indicates that it's the expected behavior that gRPC is converting an exception to the UNKNOWN status. But it doesn't point to how I can enable logging of caught exceptions.

Answer 1

For Kotlin, create a ServerInterceptor like this. Note this is different from how it's done in grpc-java.

In Micronaut, install the interceptor simply by annotating the class as a @javax.inject.Singleton.