Spring WebFlux doesn't handle redirect: directives when media type is requested [SPR-15291]

[spring-projects-issues]

Greg Turnquist opened SPR-15291 and commented

The following code...

@Controller
public class WelcomeController {

    @GetMapping("/")
    @ResponseBody
    public String welcome() {
        return "Hello World";
    }

    @GetMapping("/redir")
    public Mono<String> redir() {
        return Mono.just("redirect:/");
    }
}

generates the following stacktrace...

java.lang.IllegalStateException: Could not resolve view with name 'redirect:/'.
    at org.springframework.web.reactive.result.view.ViewResolutionResultHandler.lambda$resolveViews$5(ViewResolutionResultHandler.java:274)

---

Affects: 5.0 M5

Issue Links:

• Reactive HTTP response based RedirectView [SPR-14534] #19103 Reactive HTTP response based RedirectView

Referenced from: commits 226c9f9, 718162b

[spring-projects-issues]

Greg Turnquist commented

See also #19103

[spring-projects-issues]

Rossen Stoyanchev commented

Greg Turnquist, I've added an integration test for this since we seem to be missing one and it does work with a FreemarkerViewResolver configured through the view resolver registry

Note that the "redirect:" prefix is detected in UrlBasedViewResolver or sub-classes such as FreemarkerViewResolver. So I'm wondering what view resolvers are in use? In other words what options are you invoking on the ViewResolverRegistry?

[spring-projects-issues]

Greg Turnquist commented

The precise code is here => https://github.com/learning-spring-boot/learning-spring-boot-2nd-edition-code/tree/master/3/part2.

It's a Thymeleaf-based project, so I drafted my own configuration here => https://github.com/learning-spring-boot/learning-spring-boot-2nd-edition-code/blob/master/3/part2/src/main/java/com/greglturnquist/learningspringboot/ReactiveThymeleafConfig.java

Spring Boot 2.0 doesn't yet have a Thymeleaf view resolver by default, so I built my own. I presume this is precursor to Boot adding such support?

[spring-projects-issues]

Rossen Stoyanchev commented

Okay thanks. WebFluxAnnotationAutoConfiguraiton appears to have support for auto-configuring ViewResolver beans. So assuming that part works fine. The ThymeleafReactiveViewResolver does not extend UrlBasedViewResolver but it does look for the "redirect:" prefix.

So I'm not sure what's going on. Sorry I did give your code a quick try but had trouble compiling. Perhaps you can debug a little to see why the view resolver does not pick up the prefix?

[spring-projects-issues]

Brian Clozel commented

Thymeleaf is now supported by Spring Boot (see spring-projects/spring-boot#8124). Custom auto-configuration is no longer needed.

I've just tested this against Spring Boot M1 + WebFlux and Thymeleaf starters and this seems to work as expected.

[spring-projects-issues]

Greg Turnquist commented

Okay, I finally tracked down what has been happening.

In the following code:

@DeleteMapping(value = BASE_PATH + "/" + FILENAME)
public Mono<String> deleteFile(@PathVariable String filename) {
	return Mono.just("redirect:/");
}

...WebFlux seeks out "best mediatype" in HandlerResultHandlerSupport. Using the Path-based resolver, a URI of :8080/images/foo.jpg will come up with acceptible type "image/jpeg". However, the producible type of this method, driven by the RedirectView, will generate text/html. These two media types do not align, and thus no "best mediatype" is found, resulting in an HTTP 406 getting thrown.

If the URI is altered to something else, like :8080/images/foo.jpg/delete, evading the Path-based resolver, this mismatch is avoided, and the redirect is carried out.

I couldn't apply anything in @DeleteMapping that seemed to make :8080/images/foo.jpg work properly, implying there is no way for such a URI to generate a redirect, a severe limitation.

Thoughts?

[spring-projects-issues]

Brian Clozel commented

Since you may have multiple file types associated with this endpoint, maybe dealing with the response "manually" is the best choice:

@GetMapping("/image.jpg")
public Mono<Void> redir(ServerWebExchange exchange) {
	ServerHttpResponse response = exchange.getResponse();
	response.setStatusCode(HttpStatus.SEE_OTHER);
	response.getHeaders().add(HttpHeaders.LOCATION, "/");
	return response.setComplete();
}

[spring-projects-issues]

Rossen Stoyanchev commented

This looks like a bug. Arguably content negotiation should not impact redirects and I recall this being an issue once for Spring MVC (see #13254) and WebFlux should be consistent.

On the Spring MVC side SmartView extends View. I think in WebFlux we can add isRedirect to View as a default method and then it should be easy for ViewResolutionResultHandler to check if a candidate view is a redirect.