WebFlux support for "request handled" in controller

Issue: SPR-16087

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java

@@ -18,6 +18,8 @@ package org.springframework.web.reactive.result.method;
 
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
@@ -31,7 +33,10 @@ import reactor.core.publisher.Mono;
 import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ParameterNameDiscoverer;
+import org.springframework.core.ReactiveAdapter;
+import org.springframework.core.ReactiveAdapterRegistry;
 import org.springframework.http.HttpStatus;
+import org.springframework.http.server.reactive.ServerHttpResponse;
 import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ObjectUtils;
@@ -61,6 +66,8 @@ public class InvocableHandlerMethod extends HandlerMethod {
 
 	private ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
 
+	private ReactiveAdapterRegistry reactiveAdapterRegistry = new ReactiveAdapterRegistry();
+
 
 	public InvocableHandlerMethod(HandlerMethod handlerMethod) {
 		super(handlerMethod);
@@ -103,6 +110,18 @@ public class InvocableHandlerMethod extends HandlerMethod {
 		return this.parameterNameDiscoverer;
 	}
 
+	/**
+	 * Configure a reactive registry. This is needed for cases where the response
+	 * is fully handled within the controller in combination with an async void
+	 * return value.
+	 * <p>By default this is an instance of {@link ReactiveAdapterRegistry} with
+	 * default settings.
+	 * @param registry the registry to use
+	 */
+	public void setReactiveAdapterRegistry(ReactiveAdapterRegistry registry) {
+		this.reactiveAdapterRegistry = registry;
+	}
+
 
 	/**
 	 * Invoke the method for the given exchange.
@@ -117,11 +136,21 @@ public class InvocableHandlerMethod extends HandlerMethod {
 		return resolveArguments(exchange, bindingContext, providedArgs).flatMap(args -> {
 			try {
 				Object value = doInvoke(args);
-				HandlerResult result = new HandlerResult(this, value, getReturnType(), bindingContext);
+
 				HttpStatus status = getResponseStatus();
 				if (status != null) {
 					exchange.getResponse().setStatusCode(status);
 				}
+
+				MethodParameter returnType = getReturnType();
+				ReactiveAdapter adapter = this.reactiveAdapterRegistry.getAdapter(returnType.getParameterType());
+				boolean asyncVoid = isAsyncVoidReturnType(returnType, adapter);
+				if ((value == null || asyncVoid) && isResponseHandled(args, exchange)) {
+					logger.debug("Response fully handled in controller method");
+					return asyncVoid ? Mono.from(adapter.toPublisher(value)) : Mono.empty();
+				}
+
+				HandlerResult result = new HandlerResult(this, value, returnType, bindingContext);
 				return Mono.just(result);
 			}
 			catch (InvocationTargetException ex) {
@@ -204,6 +233,7 @@ public class InvocableHandlerMethod extends HandlerMethod {
 				param.getParameterType().getName() + "' on " + getBridgedMethod().toGenericString();
 	}
 
+	@Nullable
 	private Object doInvoke(Object[] args) throws Exception {
 		if (logger.isTraceEnabled()) {
 			logger.trace("Invoking '" + ClassUtils.getQualifiedMethodName(getMethod(), getBeanType()) +
@@ -228,4 +258,34 @@ public class InvocableHandlerMethod extends HandlerMethod {
 				"on " + getBridgedMethod().toGenericString();
 	}
 
+	private boolean isAsyncVoidReturnType(MethodParameter returnType,
+			@Nullable ReactiveAdapter reactiveAdapter) {
+
+		if (reactiveAdapter != null && reactiveAdapter.supportsEmpty()) {
+			if (reactiveAdapter.isNoValue()) {
+				return true;
+			}
+			Type parameterType = returnType.getGenericParameterType();
+			if (parameterType instanceof ParameterizedType) {
+				ParameterizedType type = (ParameterizedType) parameterType;
+				if (type.getActualTypeArguments().length == 1) {
+					return Void.class.equals(type.getActualTypeArguments()[0]);
+				}
+			}
+		}
+		return false;
+	}
+
+	private boolean isResponseHandled(Object[] args, ServerWebExchange exchange) {
+		if (getResponseStatus() != null || exchange.isNotModified()) {
+			return true;
+		}
+		for (Object arg : args) {
+			if (arg instanceof ServerHttpResponse || arg instanceof ServerWebExchange) {
+				return true;
+			}
+		}
+		return false;
+	}
+
 }

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ControllerMethodResolver.java

@@ -82,6 +82,8 @@ class ControllerMethodResolver {
 
 	private final List<HandlerMethodArgumentResolver> exceptionHandlerResolvers;
 
+	private final ReactiveAdapterRegistry reactiveAdapterRegistry;
+
 
 	private final Map<Class<?>, Set<Method>> initBinderMethodCache = new ConcurrentHashMap<>(64);
 
@@ -127,6 +129,8 @@ class ControllerMethodResolver {
 		addResolversTo(registrar, reactiveRegistry, context);
 		this.exceptionHandlerResolvers = registrar.getResolvers();
 
+		this.reactiveAdapterRegistry = reactiveRegistry;
+
 		initControllerAdviceCaches(context);
 	}
 
@@ -214,6 +218,7 @@ class ControllerMethodResolver {
 	public InvocableHandlerMethod getRequestMappingMethod(HandlerMethod handlerMethod) {
 		InvocableHandlerMethod invocable = new InvocableHandlerMethod(handlerMethod);
 		invocable.setArgumentResolvers(this.requestMappingResolvers);
+		invocable.setReactiveAdapterRegistry(this.reactiveAdapterRegistry);
 		return invocable;
 	}
 

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/InvocableHandlerMethodTests.java

@@ -16,26 +16,40 @@
 
 package org.springframework.web.reactive.result.method;
 
+import java.io.UnsupportedEncodingException;
 import java.lang.reflect.Method;
+import java.time.Duration;
+import java.time.Instant;
 import java.util.Arrays;
 
 import org.junit.Test;
+import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
 
+import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.DefaultDataBufferFactory;
 import org.springframework.http.HttpStatus;
+import org.springframework.http.server.reactive.ServerHttpResponse;
+import org.springframework.lang.Nullable;
 import org.springframework.mock.http.server.reactive.test.MockServerHttpRequest;
 import org.springframework.mock.web.test.server.MockServerWebExchange;
 import org.springframework.web.bind.annotation.ResponseStatus;
 import org.springframework.web.reactive.BindingContext;
 import org.springframework.web.reactive.HandlerResult;
+import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.server.UnsupportedMediaTypeStatusException;
 
-import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.*;
+import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.fail;
 import static org.mockito.Mockito.any;
-import static org.mockito.Mockito.*;
-import static org.springframework.web.method.ResolvableMethod.*;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+import static org.springframework.mock.http.server.reactive.test.MockServerHttpRequest.get;
+import static org.springframework.web.method.ResolvableMethod.on;
 
 /**
  * Unit tests for {@link InvocableHandlerMethod}.
@@ -45,10 +59,72 @@ import static org.springframework.web.method.ResolvableMethod.*;
  */
 public class InvocableHandlerMethodTests {
 
-	private final MockServerWebExchange exchange =
-			MockServerWebExchange.from(MockServerHttpRequest.get("http://localhost:8080/path"));
+	private final MockServerWebExchange exchange = MockServerWebExchange.from(get("http://localhost:8080/path"));
 
 
+	@Test
+	public void invokeAndHandle_VoidWithResponseStatus() throws Exception {
+		Method method = on(VoidController.class).mockCall(VoidController::responseStatus).method();
+		HandlerResult result = invoke(new VoidController(), method).block(Duration.ZERO);
+
+		assertNull("Expected no result (i.e. fully handled)", result);
+		assertEquals(HttpStatus.BAD_REQUEST, this.exchange.getResponse().getStatusCode());
+	}
+
+	@Test
+	public void invokeAndHandle_withResponse() throws Exception {
+		ServerHttpResponse response = this.exchange.getResponse();
+		Method method = on(VoidController.class).mockCall(c -> c.response(response)).method();
+		HandlerResult result = invoke(new VoidController(), method, resolverFor(Mono.just(response)))
+				.block(Duration.ZERO);
+
+		assertNull("Expected no result (i.e. fully handled)", result);
+		assertEquals("bar", this.exchange.getResponse().getHeaders().getFirst("foo"));
+	}
+
+	@Test
+	public void invokeAndHandle_withResponseAndMonoVoid() throws Exception {
+		ServerHttpResponse response = this.exchange.getResponse();
+		Method method = on(VoidController.class).mockCall(c -> c.responseMonoVoid(response)).method();
+		HandlerResult result = invoke(new VoidController(), method, resolverFor(Mono.just(response)))
+				.block(Duration.ZERO);
+
+		assertNull("Expected no result (i.e. fully handled)", result);
+		assertEquals("body", this.exchange.getResponse().getBodyAsString().block(Duration.ZERO));
+	}
+
+	@Test
+	public void invokeAndHandle_withExchange() throws Exception {
+		Method method = on(VoidController.class).mockCall(c -> c.exchange(exchange)).method();
+		HandlerResult result = invoke(new VoidController(), method, resolverFor(Mono.just(this.exchange)))
+				.block(Duration.ZERO);
+
+		assertNull("Expected no result (i.e. fully handled)", result);
+		assertEquals("bar", this.exchange.getResponse().getHeaders().getFirst("foo"));
+	}
+
+	@Test
+	public void invokeAndHandle_withExchangeAndMonoVoid() throws Exception {
+		Method method = on(VoidController.class).mockCall(c -> c.exchangeMonoVoid(exchange)).method();
+		HandlerResult result = invoke(new VoidController(), method, resolverFor(Mono.just(this.exchange)))
+				.block(Duration.ZERO);
+
+		assertNull("Expected no result (i.e. fully handled)", result);
+		assertEquals("body", this.exchange.getResponse().getBodyAsString().block(Duration.ZERO));
+	}
+
+	@Test
+	public void invokeAndHandle_withNotModified() throws Exception {
+		ServerWebExchange exchange = MockServerWebExchange.from(
+				MockServerHttpRequest.get("/").ifModifiedSince(10 * 1000 * 1000));
+
+		Method method = on(VoidController.class).mockCall(c -> c.notModified(exchange)).method();
+		HandlerResult result = invoke(new VoidController(), method, resolverFor(Mono.just(exchange)))
+				.block(Duration.ZERO);
+
+		assertNull("Expected no result (i.e. fully handled)", result);
+	}
+
 	@Test
 	public void invokeMethodWithNoArguments() throws Exception {
 		Method method = on(TestController.class).mockCall(TestController::noArgs).method();
@@ -146,7 +222,7 @@ public class InvocableHandlerMethodTests {
 
 
 	private Mono<HandlerResult> invoke(Object handler, Method method) {
-		return this.invoke(handler, method, new HandlerMethodArgumentResolver[0]);
+		return invoke(handler, method, new HandlerMethodArgumentResolver[0]);
 	}
 
 	private Mono<HandlerResult> invoke(Object handler, Method method,
@@ -195,4 +271,45 @@ public class InvocableHandlerMethodTests {
 		}
 	}
 
+	@SuppressWarnings("unused")
+	private static class VoidController {
+
+		@ResponseStatus(HttpStatus.BAD_REQUEST)
+		public void responseStatus() {
+		}
+
+		public void response(ServerHttpResponse response) {
+			response.getHeaders().add("foo", "bar");
+		}
+
+		public Mono<Void> responseMonoVoid(ServerHttpResponse response) {
+			return response.writeWith(getBody("body"));
+		}
+
+		public void exchange(ServerWebExchange exchange) {
+			exchange.getResponse().getHeaders().add("foo", "bar");
+		}
+
+		public Mono<Void> exchangeMonoVoid(ServerWebExchange exchange) {
+			return exchange.getResponse().writeWith(getBody("body"));
+		}
+
+		@Nullable
+		public String notModified(ServerWebExchange exchange) {
+			if (exchange.checkNotModified(Instant.ofEpochMilli(1000 * 1000))) {
+				return null;
+			}
+			return "body";
+		}
+
+		private Flux<DataBuffer> getBody(String body) {
+			try {
+				return Flux.just(new DefaultDataBufferFactory().wrap(body.getBytes("UTF-8")));
+			}
+			catch (UnsupportedEncodingException ex) {
+				throw new IllegalStateException(ex);
+			}
+		}
+	}
+
 }

src/docs/asciidoc/web/webflux.adoc

@@ -1029,8 +1029,14 @@ from the request path.
 |An API for model and view rendering scenarios.
 
 |`void`
-|For use in method that don't write the response body; or methods where the view name is
-supposed to be determined implicitly from the request path.
+|A method with a `void`, possibly async (e.g. `Mono<Void>`), return type (or a `null` return
+value) is considered to have fully handled the response if it also has a `ServerHttpResponse`,
+or a `ServerWebExchange` argument, or an `@ResponseStatus` annotation. The same is true also
+if the controller has made a positive ETag or lastModified timestamp check.
+// TODO (see <<webflux-caching-etag-lastmodified>> for details)
+
+If none of the above is true, a `void` return type may also indicate "no response body" for
+REST controllers, or default view name selection for HTML controllers.
 
 |`Flux<ServerSentEvent>`, `Observable<ServerSentEvent>`, or other reactive type
 |Emit server-sent events; the `SeverSentEvent` wrapper can be omitted when only data needs

src/docs/asciidoc/web/webmvc.adoc

@@ -1684,9 +1684,13 @@ through a `RequestToViewNameTranslator`.
 |The view and model attributes to use, and optionally a response status.
 
 |`void`
-|For use in methods that declare a `ServletResponse` or `OutputStream` argument and write
-to the response body; or if the view name is supposed to be implicitly determined through a
-`RequestToViewNameTranslator`.
+|A method with a `void` return type (or `null` return value) is considered to have fully
+handled the response if it also has a `ServletResponse`, or an `OutputStream` argument, or an
+`@ResponseStatus` annotation. The same is true also if the controller has made a positive
+ETag or lastModified timestamp check (see <<mvc-caching-etag-lastmodified>> for details).
+
+If none of the above is true, a `void` return type may also indicate "no response body" for
+REST controllers, or default view name selection for HTML controllers.
 
 |`Callable<V>`
 |Produce any of the above return values asynchronously in a Spring MVC managed thread.