RenderingResponse must set status code on RedirectView

This commit makes sure that WebFlux's RenderingResponse sets the HTTP
status code when rendering a RedirectView.

Closes: gh-28839

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultRenderingResponseBuilder.java

@@ -39,6 +39,8 @@
 import org.springframework.util.Assert;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
+import org.springframework.web.reactive.result.view.RedirectView;
+import org.springframework.web.reactive.result.view.View;
 import org.springframework.web.reactive.result.view.ViewResolver;
 import org.springframework.web.server.ServerWebExchange;
 
@@ -195,13 +197,24 @@ protected Mono<Void> writeToInternal(ServerWebExchange exchange, Context context
 					.switchIfEmpty(Mono.error(() ->
 							new IllegalArgumentException("Could not resolve view with name '" + name() + "'")))
 					.flatMap(view -> {
+						setStatus(view);
 						List<MediaType> mediaTypes = view.getSupportedMediaTypes();
 						return view.render(model(),
 								contentType == null && !mediaTypes.isEmpty() ? mediaTypes.get(0) : contentType,
 								exchange);
 					});
 		}
 
+		private void setStatus(View view) {
+			if (view instanceof RedirectView) {
+				HttpStatus httpStatus = HttpStatus.resolve(rawStatusCode());
+				if (httpStatus != null && httpStatus.is3xxRedirection()) {
+					RedirectView redirectView = (RedirectView) view;
+					redirectView.setStatusCode(httpStatus);
+				}
+			}
+		}
+
 	}
 
 }

spring-webflux/src/test/java/org/springframework/web/reactive/function/server/DefaultRenderingResponseTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.web.reactive.function.server;
 
+import java.time.Duration;
 import java.time.ZonedDateTime;
 import java.time.format.DateTimeFormatter;
 import java.time.temporal.ChronoUnit;
@@ -37,6 +38,7 @@
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.web.reactive.result.view.AbstractView;
+import org.springframework.web.reactive.result.view.RedirectView;
 import org.springframework.web.reactive.result.view.View;
 import org.springframework.web.reactive.result.view.ViewResolver;
 import org.springframework.web.reactive.result.view.ViewResolverSupport;
@@ -47,8 +49,10 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
 
 /**
  * @author Arjen Poutsma
@@ -155,6 +159,41 @@ public void render() {
 				.verify();
 	}
 
+	@Test
+	public void writeTo() {
+		Map<String, Object> model = Collections.singletonMap("foo", "bar");
+		RenderingResponse renderingResponse = RenderingResponse.create("view")
+				.status(HttpStatus.FOUND)
+				.modelAttributes(model)
+				.build().block(Duration.of(5, ChronoUnit.MILLIS));
+		assertThat(renderingResponse).isNotNull();
+
+		MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("http://localhost"));
+		MediaType contentType = MediaType.APPLICATION_PDF;
+		exchange.getResponse().getHeaders().setContentType(contentType);
+
+		ViewResolver viewResolver = mock(ViewResolver.class);
+		RedirectView view = mock(RedirectView.class);
+		given(viewResolver.resolveViewName(eq("view"), any())).willReturn(Mono.just(view));
+		given(view.render(model, contentType, exchange)).willReturn(Mono.empty());
+
+		List<ViewResolver> viewResolvers = new ArrayList<>();
+		viewResolvers.add(viewResolver);
+
+		HandlerStrategies mockConfig = mock(HandlerStrategies.class);
+		given(mockConfig.viewResolvers()).willReturn(viewResolvers);
+
+		ServerResponse.Context context = mock(ServerResponse.Context.class);
+		given(context.viewResolvers()).willReturn(viewResolvers);
+
+		Mono<Void> result = renderingResponse.writeTo(exchange, context);
+		StepVerifier.create(result)
+				.expectComplete()
+				.verify();
+
+		verify(view).setStatusCode(HttpStatus.FOUND);
+	}
+
 	@Test
 	public void defaultContentType() {
 		Mono<RenderingResponse> result = RenderingResponse.create("view").build();