@MessageExceptionHandler supports error signal

Before this change if a controller method returned a Publisher whose
first signal was an error, the error signal would not be delegated to
a @MessageExceptionHandler method as expected.

To make this work for now we use a package private local copy of the
ChannelSendOperator from spring-web.

See gh-21987

spring-messaging/src/test/java/org/springframework/messaging/handler/invocation/reactive/MethodMessageHandlerTests.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.
@@ -26,6 +26,7 @@ import java.util.function.Consumer;
 
 import org.hamcrest.Matchers;
 import org.junit.Test;
+import org.reactivestreams.Publisher;
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
 
@@ -63,7 +64,7 @@ public class MethodMessageHandlerTests {
 
 		assertEquals(5, mappings.keySet().size());
 		assertThat(mappings.keySet(), Matchers.containsInAnyOrder(
-				"/handleMessage", "/handleMessageWithArgument", "/handleMessageAndThrow",
+				"/handleMessage", "/handleMessageWithArgument", "/handleMessageWithError",
 				"/handleMessageMatch1", "/handleMessageMatch2"));
 	}
 
@@ -80,7 +81,7 @@ public class MethodMessageHandlerTests {
 
 		handler.handleMessage(message).block(Duration.ofSeconds(5));
 
-		StepVerifier.create((Mono<Object>) handler.getLastReturnValue())
+		StepVerifier.create((Publisher<Object>) handler.getLastReturnValue())
 				.expectNext("handleMessageMatch1")
 				.verifyComplete();
 	}
@@ -100,7 +101,7 @@ public class MethodMessageHandlerTests {
 
 		handler.handleMessage(message).block(Duration.ofSeconds(5));
 
-		StepVerifier.create((Mono<Object>) handler.getLastReturnValue())
+		StepVerifier.create((Publisher<Object>) handler.getLastReturnValue())
 				.expectNext("handleMessageWithArgument,payload=foo")
 				.verifyComplete();
 	}
@@ -111,11 +112,11 @@ public class MethodMessageHandlerTests {
 		TestMethodMessageHandler handler = initMethodMessageHandler(TestController.class);
 
 		Message<?> message = new GenericMessage<>("body", Collections.singletonMap(
-				DestinationPatternsMessageCondition.LOOKUP_DESTINATION_HEADER, "/handleMessageAndThrow"));
+				DestinationPatternsMessageCondition.LOOKUP_DESTINATION_HEADER, "/handleMessageWithError"));
 
 		handler.handleMessage(message).block(Duration.ofSeconds(5));
 
-		StepVerifier.create((Mono<Object>) handler.getLastReturnValue())
+		StepVerifier.create((Publisher<Object>) handler.getLastReturnValue())
 				.expectNext("handleIllegalStateException,ex=rejected")
 				.verifyComplete();
 	}
@@ -153,7 +154,7 @@ public class MethodMessageHandlerTests {
 			return delay("handleMessageWithArgument,payload=" + payload);
 		}
 
-		public Mono<Void> handleMessageAndThrow() {
+		public Mono<String> handleMessageWithError() {
 			return Mono.delay(Duration.ofMillis(10))
 					.flatMap(aLong -> Mono.error(new IllegalStateException("rejected")));
 		}

spring-messaging/src/test/java/org/springframework/messaging/handler/invocation/reactive/TestReturnValueHandler.java

@@ -15,6 +15,7 @@
  */
 package org.springframework.messaging.handler.invocation.reactive;
 
+import org.reactivestreams.Publisher;
 import reactor.core.publisher.Mono;
 
 import org.springframework.core.MethodParameter;
@@ -43,7 +44,14 @@ public class TestReturnValueHandler implements HandlerMethodReturnValueHandler {
 	}
 
 	@Override
+	@SuppressWarnings("unchecked")
 	public Mono<Void> handleReturnValue(@Nullable Object value, MethodParameter returnType, Message<?> message) {
+		return value instanceof Publisher ?
+				new ChannelSendOperator((Publisher) value, this::saveValue) :
+				saveValue(value);
+	}
+
+	private Mono<Void> saveValue(@Nullable Object value) {
 		this.lastReturnValue = value;
 		return Mono.empty();
 	}

spring-messaging/src/test/java/org/springframework/messaging/rsocket/RSocketClientToServerIntegrationTests.java

@@ -35,9 +35,9 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.codec.CharSequenceEncoder;
 import org.springframework.core.codec.StringDecoder;
-import org.springframework.messaging.MessageDeliveryException;
 import org.springframework.messaging.ReactiveMessageChannel;
 import org.springframework.messaging.ReactiveSubscribableChannel;
+import org.springframework.messaging.handler.annotation.MessageExceptionHandler;
 import org.springframework.messaging.handler.annotation.MessageMapping;
 import org.springframework.messaging.support.DefaultReactiveMessageChannel;
 import org.springframework.stereotype.Controller;
@@ -170,6 +170,26 @@ public class RSocketClientToServerIntegrationTests {
 				.verifyComplete();
 	}
 
+	@Test
+	public void handleWithThrownException() {
+
+		Mono<String> result = requester.route("thrown-exception").data("a").retrieveMono(String.class);
+
+		StepVerifier.create(result)
+				.expectNext("Invalid input error handled")
+				.verifyComplete();
+	}
+
+	@Test
+	public void handleWithErrorSignal() {
+
+		Mono<String> result = requester.route("error-signal").data("a").retrieveMono(String.class);
+
+		StepVerifier.create(result)
+				.expectNext("Invalid input error handled")
+				.verifyComplete();
+	}
+
 	@Test
 	public void noMatchingRoute() {
 		Mono<String> result = requester.route("invalid").data("anything").retrieveMono(String.class);
@@ -208,6 +228,20 @@ public class RSocketClientToServerIntegrationTests {
 			return payloads.delayElements(Duration.ofMillis(10)).map(payload -> payload + " async");
 		}
 
+		@MessageMapping("thrown-exception")
+		Mono<String> handleAndThrow(String payload) {
+			throw new IllegalArgumentException("Invalid input error");
+		}
+
+		@MessageMapping("error-signal")
+		Mono<String> handleAndReturnError(String payload) {
+			return Mono.error(new IllegalArgumentException("Invalid input error"));
+		}
+
+		@MessageExceptionHandler
+		Mono<String> handleException(IllegalArgumentException ex) {
+			return Mono.delay(Duration.ofMillis(10)).map(aLong -> ex.getMessage() + " handled");
+		}
 	}