How can ServerBuilder accept a list of decorators

[evgeny-mordyasov]

I have the following ServerBuilder with decorators. They are common to all REST services. If there are too many of them, it will look ugly. Is there any way to pass a list of decorators at once? I didn't find the serverBuilder.decorators(...) method.

How it looks now:

@Configuration
@Import(ArmeriaCommonConfig.class)
public class ArmeriaConfig {

    @Autowired private RestTaskService restTaskService;
    @Autowired private RestTasksBoardService restTasksBoardService;
    @Autowired private RestTaskStatusService restTaskStatusService;
    @Autowired private RestTaskTypeService restTaskTypeService;

    @Autowired private ProbeService probeService;

    @Autowired private Function<? super HttpService, ThrottlingService> throttlingDecorator;
    @Autowired private Function<? super HttpService, CorsService> corsDecorator;
    @Autowired private Function<? super HttpService, HeadersService> headersDecorator;
    @Autowired private Function<? super HttpService, MetricCollectingService> metricsDecorator;

    @Autowired private PrometheusMeterRegistry registry;

    @Bean
    public ArmeriaServerConfigurator armeriaConfigurator() {
        return serverBuilder ->
                serverBuilder
                        .annotatedService("/internal", probeService)
                        .annotatedService("/tasks", restTaskService)
                        .annotatedService("/tasks-boards", restTasksBoardService)
                        .annotatedService("/types", restTaskTypeService)
                        .annotatedService("/statuses", restTaskStatusService)
                        .serviceUnder("/internal/metrics", PrometheusExpositionService.of(registry.getPrometheusRegistry()))
                        .serviceUnder("/docs", docService())
                        .decorator(LoggingService.newDecorator())
                        .decorator(headersDecorator)
                        .decorator(metricsDecorator)
                        .decorator(corsDecorator)
                        .decorator(throttlingDecorator);
    }

    private DocService docService() {
        return DocService.builder().build();
    }
}

How would I like to do:

@Configuration
@Import(ArmeriaCommonConfig.class)
public class ArmeriaConfig {

    @Autowired private RestTaskService restTaskService;
    @Autowired private RestTasksBoardService restTasksBoardService;
    @Autowired private RestTaskStatusService restTaskStatusService;
    @Autowired private RestTaskTypeService restTaskTypeService;

    @Autowired private ProbeService probeService;

    @Autowired private List<Function<? super HttpService, ? super HttpService>> decorators;

    @Autowired private PrometheusMeterRegistry registry;

    @Bean
    public ArmeriaServerConfigurator armeriaConfigurator() {
        return serverBuilder ->
                serverBuilder
                        .annotatedService("/internal", probeService)
                        .annotatedService("/tasks", restTaskService)
                        .annotatedService("/tasks-boards", restTasksBoardService)
                        .annotatedService("/types", restTaskTypeService)
                        .annotatedService("/statuses", restTaskStatusService)
                        .serviceUnder("/internal/metrics", PrometheusExpositionService.of(registry.getPrometheusRegistry()))
                        .serviceUnder("/docs", docService())
                        .decorators(decorators);
    }

    private DocService docService() {
        return DocService.builder().build();
    }
}

[jrhee17]

For now, the only way I can think of is pre-merging all decorators:

static Function<? super HttpService, ? extends HttpService> compose(
        List<Function<? super HttpService, ? extends HttpService>> decorators) {
    assert !decorators.isEmpty();
    Function<? super HttpService, ? extends HttpService> decorated = decorators.get(0);
    for (int i = 1; i < decorators.size(); i++) {
        decorated = decorators.get(i).andThen(decorated);
    }
    return decorated;
}

Having said this, I think it's reasonable to add some APIs which allow users to add multiple decorators.

e.g.

Server.builder()
      .routeDecorator()
      .path("/decorated2")
      .build(LoggingService.newDecorator(), MetricCollectingService.newDecorator(...));

WebClient.builder()
         .decorators(LoggingClient.newDecorator(), MetricCollectingClient.newDecorator(...));

Let me create an issue for this