Don't render error view if response is committed

This commit prevents the default error view from rendering itself if the
response has been committed already. In this case, it is impossible to
change the HTTP response status and write a proper response - trying to
do so often results in a `IllegalStateException` since the response body
has already been written to.

Fixes gh-11580

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/error/ErrorMvcAutoConfiguration.java

 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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 +25,9 @@ import javax.servlet.Servlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
 import org.springframework.aop.framework.autoproxy.AutoProxyUtils;
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.ObjectProvider;
@@ -206,6 +209,8 @@ public class ErrorMvcAutoConfiguration {
 	 */
 	private static class SpelView implements View {
 
+		private static final Log logger = LogFactory.getLog(SpelView.class);
+
 		private final NonRecursivePropertyPlaceholderHelper helper;
 
 		private final String template;
@@ -225,16 +230,32 @@ public class ErrorMvcAutoConfiguration {
 		@Override
 		public void render(Map<String, ?> model, HttpServletRequest request,
 				HttpServletResponse response) throws Exception {
+			if (response.isCommitted()) {
+				String message = getMessage(model);
+				logger.error(message);
+				return;
+			}
 			if (response.getContentType() == null) {
 				response.setContentType(getContentType());
 			}
-			Map<String, Object> map = new HashMap<>(model);
-			map.put("path", request.getContextPath());
-			PlaceholderResolver resolver = new ExpressionResolver(getExpressions(), map);
+			PlaceholderResolver resolver = new ExpressionResolver(getExpressions(), model);
 			String result = this.helper.replacePlaceholders(this.template, resolver);
 			response.getWriter().append(result);
 		}
 
+		private String getMessage(Map<String, ?> model) {
+			StringBuilder builder = new StringBuilder();
+			builder.append("Cannot render error page for request [")
+					.append(model.get("path")).append("]");
+			if (model.get("message") != null) {
+				builder.append(" and exception [").append(model.get("message"))
+						.append("]");
+			}
+			return builder.append("] as the response has already been committed.")
+					.append("As a result, the response may have the wrong status code.")
+					.toString();
+		}
+
 		private Map<String, Expression> getExpressions() {
 			if (this.expressions == null) {
 				synchronized (this) {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/error/ErrorMvcAutoConfigurationTests.java

+/*
+ * Copyright 2012-2018 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.autoconfigure.web.servlet.error;
+
+import org.junit.Rule;
+import org.junit.Test;
+
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
+import org.springframework.boot.test.rule.OutputCapture;
+import org.springframework.boot.web.servlet.error.ErrorAttributes;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.mock.web.MockHttpServletResponse;
+import org.springframework.web.context.request.WebRequest;
+import org.springframework.web.servlet.View;
+import org.springframework.web.servlet.handler.DispatcherServletWebRequest;
+
+import static org.hamcrest.Matchers.allOf;
+import static org.hamcrest.Matchers.containsString;
+
+/**
+ * Tests for {@link ErrorMvcAutoConfiguration}.
+ *
+ * @author Brian Clozel
+ */
+public class ErrorMvcAutoConfigurationTests {
+
+	private WebApplicationContextRunner contextRunner = new WebApplicationContextRunner()
+			.withConfiguration(AutoConfigurations.of(ErrorMvcAutoConfiguration.class));
+
+	@Rule
+	public OutputCapture outputCapture = new OutputCapture();
+
+	@Test
+	public void testDefaultViewWithResponseAlreadyCommitted() {
+		this.contextRunner.run((context) -> {
+			View errorView = context.getBean("error", View.class);
+			ErrorAttributes errorAttributes = context.getBean(ErrorAttributes.class);
+			DispatcherServletWebRequest webRequest =
+					createCommittedWebRequest(new IllegalStateException("Exception message"));
+			errorView.render(errorAttributes.getErrorAttributes(webRequest, true),
+					webRequest.getRequest(), webRequest.getResponse());
+			this.outputCapture.expect(allOf(
+					containsString("Cannot render error page for request [/path]" +
+							" and exception [Exception message]] as the response has already been committed."),
+					containsString("As a result, the response may have the wrong status code.")));
+		});
+	}
+
+	protected DispatcherServletWebRequest createCommittedWebRequest(Exception e) {
+		MockHttpServletRequest request = new MockHttpServletRequest("GET", "/path");
+		MockHttpServletResponse response = new MockHttpServletResponse();
+		DispatcherServletWebRequest webRequest = new DispatcherServletWebRequest(request, response);
+		webRequest.setAttribute("javax.servlet.error.exception", e, WebRequest.SCOPE_REQUEST);
+		webRequest.setAttribute("javax.servlet.error.request_uri", "/path", WebRequest.SCOPE_REQUEST);
+		response.setCommitted(true);
+		response.setOutputStreamAccessAllowed(false);
+		response.setWriterAccessAllowed(false);
+		return webRequest;
+	}
+}