ResponseStatusException associated headers

A ResponseStatus exception now exposes extra method to return headers
for the response. This is used in ResponseStatusExceptionHandler to
apply the headers to the response.

Closes gh-23741

Author: rstoyanchev

spring-web/src/main/java/org/springframework/web/server/MethodNotAllowedException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -19,12 +19,15 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
+import java.util.Map;
 import java.util.Set;
 
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
+import org.springframework.util.StringUtils;
 
 /**
  * Exception for errors that fit response status 405 (method not allowed).
@@ -37,7 +40,7 @@ public class MethodNotAllowedException extends ResponseStatusException {
 
 	private final String method;
 
-	private final Set<HttpMethod> supportedMethods;
+	private final Set<HttpMethod> httpMethods;
 
 
 	public MethodNotAllowedException(HttpMethod method, Collection<HttpMethod> supportedMethods) {
@@ -51,10 +54,21 @@ public MethodNotAllowedException(String method, @Nullable Collection<HttpMethod>
 			supportedMethods = Collections.emptySet();
 		}
 		this.method = method;
-		this.supportedMethods = Collections.unmodifiableSet(new HashSet<>(supportedMethods));
+		this.httpMethods = Collections.unmodifiableSet(new HashSet<>(supportedMethods));
 	}
 
 
+	/**
+	 * Return a Map with an "Allow" header.
+	 * @since 5.1.11
+	 */
+	@Override
+	public Map<String, String> getHeaders() {
+		return !CollectionUtils.isEmpty(this.httpMethods) ?
+				Collections.singletonMap("Allow", StringUtils.collectionToDelimitedString(this.httpMethods, ", ")) :
+				Collections.emptyMap();
+	}
+
 	/**
 	 * Return the HTTP method for the failed request.
 	 */
@@ -66,6 +80,7 @@ public String getHttpMethod() {
 	 * Return the list of supported HTTP methods.
 	 */
 	public Set<HttpMethod> getSupportedMethods() {
-		return this.supportedMethods;
+		return this.httpMethods;
 	}
+
 }

spring-web/src/main/java/org/springframework/web/server/NotAcceptableStatusException.java

@@ -18,9 +18,11 @@
 
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
+import org.springframework.util.CollectionUtils;
 
 /**
  * Exception for errors that fit response status 406 (not acceptable).
@@ -51,6 +53,17 @@ public NotAcceptableStatusException(List<MediaType> supportedMediaTypes) {
 	}
 
 
+	/**
+	 * Return a Map with an "Accept" header, or an empty map.
+	 * @since 5.1.11
+	 */
+	@Override
+	public Map<String, String> getHeaders() {
+		return !CollectionUtils.isEmpty(this.supportedMediaTypes) ?
+				Collections.singletonMap("Accept", MediaType.toString(this.supportedMediaTypes)) :
+				Collections.emptyMap();
+	}
+
 	/**
 	 * Return the list of supported content types in cases when the Accept
 	 * header is parsed but not supported, or an empty list otherwise.

spring-web/src/main/java/org/springframework/web/server/ResponseStatusException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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 +16,9 @@
 
 package org.springframework.web.server;
 
+import java.util.Collections;
+import java.util.Map;
+
 import org.springframework.core.NestedExceptionUtils;
 import org.springframework.core.NestedRuntimeException;
 import org.springframework.http.HttpStatus;
@@ -72,12 +75,21 @@ public ResponseStatusException(HttpStatus status, @Nullable String reason, @Null
 
 
 	/**
-	 * The HTTP status that fits the exception (never {@code null}).
+	 * Return the HTTP status associated with this exception.
 	 */
 	public HttpStatus getStatus() {
 		return this.status;
 	}
 
+	/**
+	 * Return response headers associated with the exception, possibly required
+	 * for the given status code (e.g. "Allow", "Accept").
+	 * @since 5.1.11
+	 */
+	public Map<String, String> getHeaders() {
+		return Collections.emptyMap();
+	}
+
 	/**
 	 * The reason explaining the exception (potentially {@code null} or empty).
 	 */
@@ -86,6 +98,7 @@ public String getReason() {
 		return this.reason;
 	}
 
+
 	@Override
 	public String getMessage() {
 		String msg = this.status + (this.reason != null ? " \"" + this.reason + "\"" : "");

spring-web/src/main/java/org/springframework/web/server/handler/ResponseStatusExceptionHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -22,6 +22,7 @@
 
 import org.springframework.http.HttpStatus;
 import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.http.server.reactive.ServerHttpResponse;
 import org.springframework.lang.Nullable;
 import org.springframework.web.server.ResponseStatusException;
 import org.springframework.web.server.ServerWebExchange;
@@ -62,8 +63,7 @@ public void setWarnLogCategory(String loggerName) {
 
 	@Override
 	public Mono<Void> handle(ServerWebExchange exchange, Throwable ex) {
-		HttpStatus status = resolveStatus(ex);
-		if (status == null || !exchange.getResponse().setStatusCode(status)) {
+		if (!updateResponse(exchange.getResponse(), ex)) {
 			return Mono.error(ex);
 		}
 
@@ -86,16 +86,25 @@ private String formatError(Throwable ex, ServerHttpRequest request) {
 		return "Resolved [" + reason + "] for HTTP " + request.getMethod() + " " + path;
 	}
 
-	@Nullable
-	private HttpStatus resolveStatus(Throwable ex) {
+	private boolean updateResponse(ServerHttpResponse response, Throwable ex) {
+		boolean result = false;
 		HttpStatus status = determineStatus(ex);
-		if (status == null) {
+		if (status != null) {
+			if (response.setStatusCode(status)) {
+				if (ex instanceof ResponseStatusException) {
+					((ResponseStatusException) ex).getHeaders()
+							.forEach((name, value) -> response.getHeaders().add(name, value));
+				}
+				result = true;
+			}
+		}
+		else {
 			Throwable cause = ex.getCause();
 			if (cause != null) {
-				status = resolveStatus(cause);
+				result = updateResponse(response, cause);
 			}
 		}
-		return status;
+		return result;
 	}
 
 	/**

spring-web/src/test/java/org/springframework/web/server/handler/ResponseStatusExceptionHandlerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -17,18 +17,27 @@
 package org.springframework.web.server.handler;
 
 import java.time.Duration;
+import java.util.Arrays;
 
 import org.junit.Before;
 import org.junit.Test;
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
 
+import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
 import org.springframework.mock.http.server.reactive.test.MockServerHttpRequest;
+import org.springframework.mock.http.server.reactive.test.MockServerHttpResponse;
 import org.springframework.mock.web.test.server.MockServerWebExchange;
+import org.springframework.web.server.MethodNotAllowedException;
+import org.springframework.web.server.NotAcceptableStatusException;
 import org.springframework.web.server.ResponseStatusException;
 
-import static org.junit.Assert.*;
+import static org.hamcrest.collection.IsIterableContainingInOrder.contains;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertThat;
 
 /**
  * Unit tests for {@link ResponseStatusExceptionHandler}.
@@ -67,6 +76,26 @@ public void handleNestedResponseStatusException() {
 		assertEquals(HttpStatus.BAD_REQUEST, this.exchange.getResponse().getStatusCode());
 	}
 
+	@Test // gh-23741
+	public void handleMethodNotAllowed() {
+		Throwable ex = new MethodNotAllowedException(HttpMethod.PATCH, Arrays.asList(HttpMethod.POST, HttpMethod.PUT));
+		this.handler.handle(this.exchange, ex).block(Duration.ofSeconds(5));
+
+		MockServerHttpResponse response = this.exchange.getResponse();
+		assertEquals(HttpStatus.METHOD_NOT_ALLOWED, response.getStatusCode());
+		assertThat(response.getHeaders().getAllow(), contains(HttpMethod.POST, HttpMethod.PUT));
+	}
+
+	@Test // gh-23741
+	public void handleResponseStatusExceptionWithHeaders() {
+		Throwable ex = new NotAcceptableStatusException(Arrays.asList(MediaType.TEXT_PLAIN, MediaType.TEXT_HTML));
+		this.handler.handle(this.exchange, ex).block(Duration.ofSeconds(5));
+
+		MockServerHttpResponse response = this.exchange.getResponse();
+		assertEquals(HttpStatus.NOT_ACCEPTABLE, response.getStatusCode());
+		assertThat(response.getHeaders().getAccept(), contains(MediaType.TEXT_PLAIN, MediaType.TEXT_HTML));
+	}
+
 	@Test
 	public void unresolvedException() {
 		Throwable expected = new IllegalStateException();