Missing path pattern in Spring Framework 6 web Observability support

[bclozel]

As of Spring Boot 3.0, the Micrometer metrics support has been deprecated/removed in favor of broader observability support in Spring projects directly. In the case of Spring MVC and Spring WebFlux, specific filters (like ServerHttpObservationFilter) were created in Spring Framework 6.0.

The filters have been implemented in a generic fashion and do not rely on web frameworks specifics. This means that instead of looking into web frameworks internals to know which mapping pattern matched the incoming request, the framework itself needs to provide this information.

More concretely, in Spring Boot 2.x, WebMvcTags and WebFluxTags needed to know about Spring Data REST internals to pick up the matching pattern. With the new infrastructure, things should be done the other way around: Spring Data REST should get the current observation, if present, and set the matching path like this. I guess this should be done in RepositoryRestHandlerMapping and the reactive variant as well?

Sorry for not noticing this before, this has been reported in spring-projects/spring-boot#33673

[odrotbohm]

It looks like the original arrangement (looking up a repository-specific pattern like /somRepo/{id} from a request attribute)stemmed from this ticket. Essentially, users were trying to gather metrics by "HTTP resources exposed per repository" rather than from the general pattern (/{repository}/…) which standard MVC-pattern-based metrics would resolve in. Thus, we need to register the same augmented pattern as path pattern on the ServerRequestObservationContext.