Error handling for WebFlux should log HTTP 5xx errors

This commit ensures that all errors handled by the
`DefaultErrorWebExceptionHandler` (Spring WebFlux error convetion
support) logs an error with request information and exception
stacktrace.

This is limited to errors that result in an HTTP 5xx error.
Exceptions that extend `ResponseStatusException` and set a non-5xx
status will not be logged.

Closes gh-10904

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/reactive/error/AbstractErrorWebExceptionHandler.java

@@ -114,6 +114,20 @@ public abstract class AbstractErrorWebExceptionHandler
 		return this.errorAttributes.getErrorAttributes(request, includeStackTrace);
 	}
 
+	/**
+	 * Extract the original error from the current request.
+	 * @param request the source request
+	 * @return the error
+	 */
+	protected Throwable getError(ServerRequest request) {
+		return this.errorAttributes.getError(request);
+	}
+
+	/**
+	 * Check whether the trace attribute has been set on the given request.
+	 * @param request the source request
+	 * @return {@code true} if the error trace has been requested, {@code false} otherwise
+	 */
 	protected boolean isTraceEnabled(ServerRequest request) {
 		String parameter = request.queryParam("trace").orElse("false");
 		return !"false".equals(parameter.toLowerCase());

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/reactive/error/DefaultErrorWebExceptionHandler.java

@@ -21,6 +21,8 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
@@ -72,6 +74,9 @@ public class DefaultErrorWebExceptionHandler extends AbstractErrorWebExceptionHa
 
 	private static final Map<HttpStatus.Series, String> SERIES_VIEWS;
 
+	private static final Log logger = LogFactory
+			.getLog(DefaultErrorWebExceptionHandler.class);
+
 	static {
 		Map<HttpStatus.Series, String> views = new HashMap<>();
 		views.put(HttpStatus.Series.CLIENT_ERROR, "4xx");
@@ -117,7 +122,8 @@ public class DefaultErrorWebExceptionHandler extends AbstractErrorWebExceptionHa
 				.just("error/" + errorStatus.toString(),
 						"error/" + SERIES_VIEWS.get(errorStatus.series()), "error/error")
 				.flatMap((viewName) -> renderErrorView(viewName, response, error))
-				.switchIfEmpty(renderDefaultErrorView(response, error)).next();
+				.switchIfEmpty(renderDefaultErrorView(response, error)).next()
+				.doOnNext(resp -> logError(request, errorStatus));
 	}
 
 	/**
@@ -128,9 +134,11 @@ public class DefaultErrorWebExceptionHandler extends AbstractErrorWebExceptionHa
 	protected Mono<ServerResponse> renderErrorResponse(ServerRequest request) {
 		boolean includeStackTrace = isIncludeStackTrace(request, MediaType.ALL);
 		Map<String, Object> error = getErrorAttributes(request, includeStackTrace);
+		HttpStatus errorStatus = getHttpStatus(error);
 		return ServerResponse.status(getHttpStatus(error))
 				.contentType(MediaType.APPLICATION_JSON_UTF8)
-				.body(BodyInserters.fromObject(error));
+				.body(BodyInserters.fromObject(error))
+				.doOnNext(resp -> logError(request, errorStatus));
 	}
 
 	/**
@@ -178,4 +186,18 @@ public class DefaultErrorWebExceptionHandler extends AbstractErrorWebExceptionHa
 		};
 	}
 
+	/**
+	 * Log the original exception if handling it results in a Server Error.
+	 * @param request the source request
+	 * @param errorStatus the HTTP error status
+	 */
+	protected void logError(ServerRequest request, HttpStatus errorStatus) {
+		if (errorStatus.is5xxServerError()) {
+			Throwable error = getError(request);
+			final String message = "Failed to handle request ["
+					+ request.methodName() + " " + request.uri() + "]";
+			logger.error(message, error);
+		}
+	}
+
 }

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/error/DefaultErrorWebExceptionHandlerIntegrationTest.java

@@ -28,6 +28,7 @@ import java.util.List;
 import javax.validation.Valid;
 
 import org.junit.After;
+import org.junit.Rule;
 import org.junit.Test;
 import reactor.core.publisher.Mono;
 
@@ -38,6 +39,7 @@ import org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration
 import org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration;
 import org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerAutoConfiguration;
 import org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration;
+import org.springframework.boot.test.rule.OutputCapture;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
@@ -52,6 +54,9 @@ import org.springframework.web.bind.annotation.RestController;
 import org.springframework.web.server.ResponseStatusException;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.hamcrest.Matchers.allOf;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.not;
 
 /**
  * Integration tests for {@link DefaultErrorWebExceptionHandler}
@@ -64,6 +69,9 @@ public class DefaultErrorWebExceptionHandlerIntegrationTest {
 
 	private WebTestClient webTestClient;
 
+	@Rule
+	public OutputCapture output = new OutputCapture();
+
 	@After
 	public void closeContext() {
 		if (this.context != null) {
@@ -81,6 +89,8 @@ public class DefaultErrorWebExceptionHandlerIntegrationTest {
 				.jsonPath("path").isEqualTo(("/")).jsonPath("message")
 				.isEqualTo("Expected!").jsonPath("exception").doesNotExist()
 				.jsonPath("trace").doesNotExist();
+		this.output.expect(allOf(containsString("Failed to handle request [GET /]"),
+				containsString("IllegalStateException")));
 	}
 
 	@Test
@@ -101,6 +111,8 @@ public class DefaultErrorWebExceptionHandlerIntegrationTest {
 				.expectHeader().contentType(MediaType.TEXT_HTML).expectBody(String.class)
 				.returnResult().getResponseBody();
 		assertThat(body).contains("status: 500").contains("message: Expected!");
+		this.output.expect(allOf(containsString("Failed to handle request [GET /]"),
+				containsString("IllegalStateException")));
 	}
 
 	@Test
@@ -160,6 +172,7 @@ public class DefaultErrorWebExceptionHandlerIntegrationTest {
 				.isEqualTo("400").jsonPath("error")
 				.isEqualTo(HttpStatus.BAD_REQUEST.getReasonPhrase()).jsonPath("exception")
 				.isEqualTo(ResponseStatusException.class.getName());
+		this.output.expect(not(containsString("ResponseStatusException")));
 	}
 
 	@Test
@@ -171,6 +184,8 @@ public class DefaultErrorWebExceptionHandlerIntegrationTest {
 				.returnResult().getResponseBody();
 		assertThat(body).contains("Whitelabel Error Page")
 				.contains("<div>Expected!</div>");
+		this.output.expect(allOf(containsString("Failed to handle request [GET /]"),
+				containsString("IllegalStateException")));
 	}
 
 	private void load(String... arguments) {
@@ -188,10 +203,10 @@ public class DefaultErrorWebExceptionHandlerIntegrationTest {
 	@Target(ElementType.TYPE)
 	@Retention(RetentionPolicy.RUNTIME)
 	@Documented
-	@Import({ ReactiveWebServerAutoConfiguration.class,
+	@Import({ReactiveWebServerAutoConfiguration.class,
 			HttpHandlerAutoConfiguration.class, WebFluxAutoConfiguration.class,
 			ErrorWebFluxAutoConfiguration.class,
-			PropertyPlaceholderAutoConfiguration.class })
+			PropertyPlaceholderAutoConfiguration.class})
 	private @interface MinimalWebConfiguration {
 
 	}