Fall back on */* during content negotiation for errors

Prior to this commit, gh-31936 enabled content negotiation for
`@ExceptionHandler` annotated methods in Spring MVC and WebFlux.
In the case of WebFlux, HTTP clients sending invalid media types in the
"Accept" request header would fail with a `NotAcceptableStatusException`
This exception would be handled with an HTTP 406 response status,
instead of processing the original exception.

This commit ensures that invalid media types are ignored during the
exception handling phase and that we fall back to "*/*".

Fixes gh-32878

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ControllerMethodResolver.java

@@ -60,6 +60,7 @@ import org.springframework.web.reactive.result.method.HandlerMethodArgumentResol
 import org.springframework.web.reactive.result.method.InvocableHandlerMethod;
 import org.springframework.web.reactive.result.method.SyncHandlerMethodArgumentResolver;
 import org.springframework.web.reactive.result.method.SyncInvocableHandlerMethod;
+import org.springframework.web.server.NotAcceptableStatusException;
 import org.springframework.web.server.ServerWebExchange;
 
 /**
@@ -416,7 +417,15 @@ class ControllerMethodResolver {
 	public InvocableHandlerMethod getExceptionHandlerMethod(Throwable ex, ServerWebExchange exchange, @Nullable HandlerMethod handlerMethod) {
 
 		Class<?> handlerType = (handlerMethod != null ? handlerMethod.getBeanType() : null);
-		List<MediaType> requestedMediaTypes = this.contentTypeResolver.resolveMediaTypes(exchange);
+		List<MediaType> requestedMediaTypes = List.of(MediaType.ALL);
+		try {
+			requestedMediaTypes = this.contentTypeResolver.resolveMediaTypes(exchange);
+		}
+		catch (NotAcceptableStatusException exc) {
+			if (logger.isDebugEnabled()) {
+				logger.debug("Could not parse Accept header for requested media types", exc);
+			}
+		}
 
 		// Controller-local first
 		if (handlerType != null) {

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/ControllerMethodResolverTests.java

@@ -258,6 +258,18 @@ class ControllerMethodResolverTests {
 		assertThat(producibleMediaTypes).isNotEmpty().contains(MediaType.APPLICATION_JSON);
 	}
 
+	@Test
+	void exceptionHandlerWithInvalidAcceptHeader() {
+		Method method = ResolvableMethod.on(ExceptionHandlerController.class).mockCall(ExceptionHandlerController::handle).method();
+		this.handlerMethod = new HandlerMethod(new ExceptionHandlerController(), method);
+		MockServerHttpRequest httpRequest = MockServerHttpRequest.get("/test").header("Accept", "v=12").build();
+		MockServerWebExchange serverWebExchange = MockServerWebExchange.builder(httpRequest).build();
+		InvocableHandlerMethod invocable = this.methodResolver.getExceptionHandlerMethod(
+				new ResponseStatusException(HttpStatus.BAD_REQUEST, "reason"), serverWebExchange, this.handlerMethod);
+
+		assertThat(invocable).as("No match").isNotNull();
+	}
+
 
 	private static HandlerMethodArgumentResolver next(
 			List<? extends HandlerMethodArgumentResolver> resolvers, AtomicInteger index) {