Spring Missing CORS Headers for Static Resources in WebFlux

Affects: 5.3.3 Affected component: WebFlux

I created a configuration that roughly looks like this:

@EnableWebFlux
@Configuration
class WebfluxConfig : WebFluxConfigurer {
    override fun addResourceHandlers(registry: ResourceHandlerRegistry) {
        registry.addResourceHandler("/public/**")
            .addResourceLocations("classpath:/public/")
    }

    override fun addCorsMappings(registry: CorsRegistry) {
        registry.addMapping("/public/**")
            .allowedMethods("GET", "OPTIONS")
            .allowedOriginPatterns("*")
    }
}

Expectation: A GET / OPTIONS request to http://localhost:8080/public/path/to/file should return with CORS headers.

Actual result: CORS headers seem to be missing.

Possible cause: In the bean declaration there seems to be no call to setCorsConfigurations() / configureAbstractHandlerMapping(), although there is in case of RequestMappingHandler and RouterFunctionMapping. FWIW, in the MVC counterpart, this call seems to exist.

I tried adding that line using a breakpoint, after which CORS started working for me.

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Sorry if I'm missing something obvious -- I'm just getting started with WebFlux. 😄 For the time being I guess I'll resort to a WebFilter.

Comment From: rstoyanchev

ResourceWebHandler needs to be declared as CorsConfigurationSource in order to be considered as a handler that supports CORS. It looks like that's missing right now unlike the ResourceHttpRequestHandler for Spring MVC.

Comment From: rstoyanchev

Never mind that. It's unrelated to ResourceWebHandler implenting CorsConfigurationSource. It seems that indeed WebFluxConfigurer#addCorsMapping simply doesn't apply to static resources. The Javadoc mentions only annotated controllers and functional endpoints.