Spring Webflux: CoRouter CoRouterFunctionDsl (Coroutine)-context not applied to onError

Question

I am running web flux with Kotlin coroutines using spring boot 3.2 and the underlying version 6.1.1 of the spring framework.

I am using micrometer for tracing. With spring's coRouter, I followed the example here: https://github.com/spring-projects/spring-framework/issues/27010 to set the context in my corouter, so all subsequent calls have access to the MdcContext.

But if I define an onError function, the context is not applied to that function. Is there a special way to do that, or do I have to send the context manually as a function parameter?

Example:

@Bean
fun demoRoutes() = coRouter {
    "/rest".nest {
        "v1".nest {
            "/demo".nest {
                context { observationRegistry.asContextElement() }
                GET("", demoHandler::demoCall)
            }
        }
    }
    onError<RuntimeException> { throwable, serverRequest ->
        errorHandler.handleError(throwable, serverRequest)
    }
}

Another additional question: Is there some way to make the context apply for everything? It only applies if it is set in the last nest function. If I define it to a parent or directly within coRouter, it's not working:

@Bean
fun demoRoutes() = coRouter {
    context { observationRegistry.asContextElement() }
    "/rest".nest {
        "v1".nest {
            "/demo".nest {
                GET("", demoHandler::demoCall)
            }
        }
    }
    onError<RuntimeException> { throwable, serverRequest ->
        errorHandler.handleError(throwable, serverRequest)
    }
}

If used like that, the context is lost in the call to demoHandler::demoCall.

Answer 1

The behavior of error handling seems to be ok as far as I can tell, but there is indeed a surprising behavior when combining nested routers and CoroutineContext, this should be fixed by https://github.com/spring-projects/spring-framework/issues/31831.