Add RFC-7807 response interception

Closes gh-31822

Author: rstoyanchev

Diff for: framework-docs/modules/ROOT/pages/web/webflux/ann-rest-exceptions.adoc

@@ -44,6 +44,10 @@ has an `@ExceptionHandler` method that handles any `ErrorResponse` exception, wh
 includes all built-in web exceptions. You can add more exception handling methods, and
 use a protected method to map any exception to a `ProblemDetail`.
 
+You can register `ErrorResponse` interceptors through the
+xref:web/webflux/config.adoc[WebFlux Config] with a `WebFluxConfigurer`. Use that to intercept
+any RFC 7807 response and take some action.
+
 
 
 [[webflux-ann-rest-exceptions-non-standard]]

Diff for: framework-docs/modules/ROOT/pages/web/webmvc/mvc-ann-rest-exceptions.adoc

@@ -44,6 +44,10 @@ has an `@ExceptionHandler` method that handles any `ErrorResponse` exception, wh
 includes all built-in web exceptions. You can add more exception handling methods, and
 use a protected method to map any exception to a `ProblemDetail`.
 
+You can register `ErrorResponse` interceptors through the
+xref:web/webmvc/mvc-config.adoc[MVC Config] with a `WebMvcConfigurer`. Use that to intercept
+any RFC 7807 response and take some action.
+
 
 
 [[mvc-ann-rest-exceptions-non-standard]]

Diff for: spring-web/src/main/java/org/springframework/web/ErrorResponse.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -333,4 +333,24 @@ default ErrorResponse build(@Nullable MessageSource messageSource, Locale locale
 
 	}
 
+
+	/**
+	 * Callback to perform an action before an RFC-7807 {@link ProblemDetail}
+	 * response is rendered.
+	 *
+	 * @author Rossen Stoyanchev
+	 * @since 6.2
+	 */
+	interface Interceptor {
+
+		/**
+		 * Handle the given {@code ProblemDetail} that's going to be rendered,
+		 * and the {@code ErrorResponse} it originates from, if applicable.
+		 * @param detail the {@code ProblemDetail} to be rendered
+		 * @param errorResponse the {@code ErrorResponse}, or {@code null} if there isn't one
+		 */
+		void handleError(ProblemDetail detail, @Nullable ErrorResponse errorResponse);
+
+	}
+
 }

Diff for: spring-webflux/src/main/java/org/springframework/web/reactive/config/DelegatingWebFluxConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@
 import org.springframework.util.CollectionUtils;
 import org.springframework.validation.MessageCodesResolver;
 import org.springframework.validation.Validator;
+import org.springframework.web.ErrorResponse;
 import org.springframework.web.reactive.accept.RequestedContentTypeResolverBuilder;
 import org.springframework.web.reactive.result.method.annotation.ArgumentResolverConfigurer;
 import org.springframework.web.reactive.socket.server.WebSocketService;
@@ -99,6 +100,12 @@ protected void configureArgumentResolvers(ArgumentResolverConfigurer configurer)
 		this.configurers.configureArgumentResolvers(configurer);
 	}
 
+	@Override
+	protected void configureErrorResponseInterceptors(List<ErrorResponse.Interceptor> interceptors) {
+		this.configurers.addErrorResponseInterceptors(interceptors);
+	}
+
+
 	@Override
 	protected void addResourceHandlers(ResourceHandlerRegistry registry) {
 		this.configurers.addResourceHandlers(registry);

Diff for: spring-webflux/src/main/java/org/springframework/web/reactive/config/WebFluxConfigurationSupport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 
 package org.springframework.web.reactive.config;
 
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.function.Predicate;
@@ -44,6 +45,7 @@
 import org.springframework.validation.MessageCodesResolver;
 import org.springframework.validation.Validator;
 import org.springframework.validation.beanvalidation.OptionalValidatorFactoryBean;
+import org.springframework.web.ErrorResponse;
 import org.springframework.web.bind.WebDataBinder;
 import org.springframework.web.bind.support.ConfigurableWebBindingInitializer;
 import org.springframework.web.cors.CorsConfiguration;
@@ -98,6 +100,9 @@ public class WebFluxConfigurationSupport implements ApplicationContextAware {
 	@Nullable
 	private BlockingExecutionConfigurer blockingExecutionConfigurer;
 
+	@Nullable
+	private List<ErrorResponse.Interceptor> errorResponseInterceptors;
+
 	@Nullable
 	private ViewResolverRegistry viewResolverRegistry;
 
@@ -498,7 +503,7 @@ public ResponseEntityResultHandler responseEntityResultHandler(
 			@Qualifier("webFluxContentTypeResolver") RequestedContentTypeResolver contentTypeResolver) {
 
 		return new ResponseEntityResultHandler(serverCodecConfigurer.getWriters(),
-				contentTypeResolver, reactiveAdapterRegistry);
+				contentTypeResolver, reactiveAdapterRegistry, getErrorResponseInterceptors());
 	}
 
 	@Bean
@@ -508,7 +513,7 @@ public ResponseBodyResultHandler responseBodyResultHandler(
 			@Qualifier("webFluxContentTypeResolver") RequestedContentTypeResolver contentTypeResolver) {
 
 		return new ResponseBodyResultHandler(serverCodecConfigurer.getWriters(),
-				contentTypeResolver, reactiveAdapterRegistry);
+				contentTypeResolver, reactiveAdapterRegistry, getErrorResponseInterceptors());
 	}
 
 	@Bean
@@ -534,6 +539,29 @@ public ServerResponseResultHandler serverResponseResultHandler(ServerCodecConfig
 		return handler;
 	}
 
+	/**
+	 * Provide access to the list of {@link ErrorResponse.Interceptor}'s to apply
+	 * in result handlers when rendering error responses.
+	 * <p>This method cannot be overridden; use {@link #configureErrorResponseInterceptors(List)} instead.
+	 * @since 6.2
+	 */
+	protected final List<ErrorResponse.Interceptor> getErrorResponseInterceptors() {
+		if (this.errorResponseInterceptors == null) {
+			this.errorResponseInterceptors = new ArrayList<>();
+			configureErrorResponseInterceptors(this.errorResponseInterceptors);
+		}
+		return this.errorResponseInterceptors;
+	}
+
+	/**
+	 * Override this method for control over the {@link ErrorResponse.Interceptor}'s
+	 * to apply in result handling when rendering error responses.
+	 * @param interceptors the list to add handlers to
+	 * @since 6.2
+	 */
+	protected void configureErrorResponseInterceptors(List<ErrorResponse.Interceptor> interceptors) {
+	}
+
 	/**
 	 * Callback for building the {@link ViewResolverRegistry}. This method is final,
 	 * use {@link #configureViewResolvers} to customize view resolvers.

Diff for: spring-webflux/src/main/java/org/springframework/web/reactive/config/WebFluxConfigurer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,13 +16,16 @@
 
 package org.springframework.web.reactive.config;
 
+import java.util.List;
+
 import org.springframework.core.convert.converter.Converter;
 import org.springframework.format.Formatter;
 import org.springframework.format.FormatterRegistry;
 import org.springframework.http.codec.ServerCodecConfigurer;
 import org.springframework.lang.Nullable;
 import org.springframework.validation.MessageCodesResolver;
 import org.springframework.validation.Validator;
+import org.springframework.web.ErrorResponse;
 import org.springframework.web.cors.CorsConfiguration;
 import org.springframework.web.reactive.accept.RequestedContentTypeResolverBuilder;
 import org.springframework.web.reactive.result.method.annotation.ArgumentResolverConfigurer;
@@ -133,6 +136,16 @@ default void configurePathMatching(PathMatchConfigurer configurer) {
 	default void configureArgumentResolvers(ArgumentResolverConfigurer configurer) {
 	}
 
+	/**
+	 * Add to the list of {@link ErrorResponse.Interceptor}'s to invoke when
+	 * rendering an RFC 7807 {@link org.springframework.http.ProblemDetail}
+	 * error response.
+	 * @param interceptors the handlers to use
+	 * @since 6.2
+	 */
+	default void addErrorResponseInterceptors(List<ErrorResponse.Interceptor> interceptors) {
+	}
+
 	/**
 	 * Configure view resolution for rendering responses with a view and a model,
 	 * where the view is typically an HTML template but could also be based on

Diff for: spring-webflux/src/main/java/org/springframework/web/reactive/config/WebFluxConfigurerComposite.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,7 @@
 import org.springframework.util.CollectionUtils;
 import org.springframework.validation.MessageCodesResolver;
 import org.springframework.validation.Validator;
+import org.springframework.web.ErrorResponse;
 import org.springframework.web.reactive.accept.RequestedContentTypeResolverBuilder;
 import org.springframework.web.reactive.result.method.annotation.ArgumentResolverConfigurer;
 import org.springframework.web.reactive.socket.server.WebSocketService;
@@ -95,6 +96,13 @@ public void configureArgumentResolvers(ArgumentResolverConfigurer configurer) {
 		this.delegates.forEach(delegate -> delegate.configureArgumentResolvers(configurer));
 	}
 
+	@Override
+	public void addErrorResponseInterceptors(List<ErrorResponse.Interceptor> interceptors) {
+		for (WebFluxConfigurer delegate : this.delegates) {
+			delegate.addErrorResponseInterceptors(interceptors);
+		}
+	}
+
 	@Override
 	public void configureViewResolvers(ViewResolverRegistry registry) {
 		this.delegates.forEach(delegate -> delegate.configureViewResolvers(registry));

Diff for: spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/AbstractMessageWriterResultHandler.java

@@ -18,6 +18,7 @@
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 import java.util.Set;
 
@@ -40,6 +41,7 @@
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.CollectionUtils;
+import org.springframework.web.ErrorResponse;
 import org.springframework.web.reactive.HandlerMapping;
 import org.springframework.web.reactive.accept.RequestedContentTypeResolver;
 import org.springframework.web.reactive.result.HandlerResultHandlerSupport;
@@ -60,6 +62,8 @@ public abstract class AbstractMessageWriterResultHandler extends HandlerResultHa
 
 	private final List<HttpMessageWriter<?>> messageWriters;
 
+	private final List<ErrorResponse.Interceptor> errorResponseInterceptors = new ArrayList<>();
+
 	private final List<MediaType> problemMediaTypes =
 			Arrays.asList(MediaType.APPLICATION_PROBLEM_JSON, MediaType.APPLICATION_PROBLEM_XML);
 
@@ -86,9 +90,24 @@ protected AbstractMessageWriterResultHandler(List<HttpMessageWriter<?>> messageW
 	protected AbstractMessageWriterResultHandler(List<HttpMessageWriter<?>> messageWriters,
 			RequestedContentTypeResolver contentTypeResolver, ReactiveAdapterRegistry adapterRegistry) {
 
+		this(messageWriters, contentTypeResolver, adapterRegistry, Collections.emptyList());
+	}
+
+	/**
+	 * Variant of
+	 * {@link #AbstractMessageWriterResultHandler(List, RequestedContentTypeResolver, ReactiveAdapterRegistry)}
+	 * with additional list of {@link ErrorResponse.Interceptor}s for return
+	 * value handling.
+	 * @since 6.2
+	 */
+	protected AbstractMessageWriterResultHandler(List<HttpMessageWriter<?>> messageWriters,
+			RequestedContentTypeResolver contentTypeResolver, ReactiveAdapterRegistry adapterRegistry,
+			List<ErrorResponse.Interceptor> interceptors) {
+
 		super(contentTypeResolver, adapterRegistry);
 		Assert.notEmpty(messageWriters, "At least one message writer is required");
 		this.messageWriters = messageWriters;
+		this.errorResponseInterceptors.addAll(interceptors);
 	}
 
 
@@ -99,6 +118,29 @@ public List<HttpMessageWriter<?>> getMessageWriters() {
 		return this.messageWriters;
 	}
 
+	/**
+	 * Return the configured {@link ErrorResponse.Interceptor}'s.
+	 * @since 6.2
+	 */
+	public List<ErrorResponse.Interceptor> getErrorResponseInterceptors() {
+		return this.errorResponseInterceptors;
+	}
+
+
+	/**
+	 * Invoke the configured {@link ErrorResponse.Interceptor}'s.
+	 * @since 6.2
+	 */
+	protected void invokeErrorResponseInterceptors(ProblemDetail detail, @Nullable ErrorResponse errorResponse) {
+		try {
+			for (ErrorResponse.Interceptor handler : this.errorResponseInterceptors) {
+				handler.handleError(detail, errorResponse);
+			}
+		}
+		catch (Throwable ex) {
+			// ignore
+		}
+	}
 
 	/**
 	 * Write a given body to the response with {@link HttpMessageWriter}.

Diff for: spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ResponseBodyResultHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@
 package org.springframework.web.reactive.result.method.annotation;
 
 import java.net.URI;
+import java.util.Collections;
 import java.util.List;
 
 import reactor.core.publisher.Mono;
@@ -27,6 +28,7 @@
 import org.springframework.http.HttpStatusCode;
 import org.springframework.http.ProblemDetail;
 import org.springframework.http.codec.HttpMessageWriter;
+import org.springframework.web.ErrorResponse;
 import org.springframework.web.bind.annotation.ResponseBody;
 import org.springframework.web.reactive.HandlerResult;
 import org.springframework.web.reactive.HandlerResultHandler;
@@ -69,7 +71,21 @@ public ResponseBodyResultHandler(List<HttpMessageWriter<?>> writers, RequestedCo
 	public ResponseBodyResultHandler(List<HttpMessageWriter<?>> writers,
 			RequestedContentTypeResolver resolver, ReactiveAdapterRegistry registry) {
 
-		super(writers, resolver, registry);
+		this(writers, resolver, registry, Collections.emptyList());
+	}
+
+	/**
+	 * Variant of
+	 * {@link #ResponseBodyResultHandler(List, RequestedContentTypeResolver, ReactiveAdapterRegistry)}
+	 * with additional list of {@link ErrorResponse.Interceptor}s for return
+	 * value handling.
+	 * @since 6.2
+	 */
+	public ResponseBodyResultHandler(List<HttpMessageWriter<?>> writers,
+			RequestedContentTypeResolver resolver, ReactiveAdapterRegistry registry,
+			List<ErrorResponse.Interceptor> interceptors) {
+
+		super(writers, resolver, registry, interceptors);
 		setOrder(100);
 	}
 
@@ -92,6 +108,7 @@ public Mono<Void> handleResult(ServerWebExchange exchange, HandlerResult result)
 				URI path = URI.create(exchange.getRequest().getPath().value());
 				detail.setInstance(path);
 			}
+			invokeErrorResponseInterceptors(detail, null);
 		}
 		return writeBody(body, bodyTypeParameter, exchange);
 	}