docs: private CompletableFuture<MetadataResponse> metadata(MetadataRequest request) {
      return CompletableFuture.completedFuture(MetadataResponse.ok(services.entrySet().stream()
          .filter(entry -> Futures.get(entry.getValue()).serviceType().name().equals(request.primitiveType()))
          .map(entry -> entry.getKey())
          .collect(Collectors.toSet())));
    }