Fix HttpServiceMethod support for suspending functions

This commit fixes nested type handling for suspending
functions in HttpServiceMethod.

Closes gh-30266

Author: sdeleuze

spring-web/src/main/java/org/springframework/web/service/invoker/HttpServiceMethod.java

@@ -52,6 +52,7 @@
  * by delegating to an {@link HttpClientAdapter} to perform actual requests.
  *
  * @author Rossen Stoyanchev
+ * @author Sebastien Deleuze
  * @since 6.0
  */
 final class HttpServiceMethod {
@@ -311,14 +312,15 @@ public static ResponseFunction create(
 
 			MethodParameter returnParam = new MethodParameter(method, -1);
 			Class<?> returnType = returnParam.getParameterType();
-			if (KotlinDetector.isSuspendingFunction(method)) {
+			boolean isSuspending = KotlinDetector.isSuspendingFunction(method);
+			if (isSuspending) {
 				returnType = Mono.class;
 			}
 
 			ReactiveAdapter reactiveAdapter = reactiveRegistry.getAdapter(returnType);
 
 			MethodParameter actualParam = (reactiveAdapter != null ? returnParam.nested() : returnParam.nestedIfOptional());
-			Class<?> actualType = actualParam.getNestedParameterType();
+			Class<?> actualType = isSuspending ? actualParam.getParameterType() : actualParam.getNestedParameterType();
 
 			Function<HttpRequestValues, Publisher<?>> responseFunction;
 			if (actualType.equals(void.class) || actualType.equals(Void.class)) {
@@ -331,27 +333,27 @@ else if (actualType.equals(HttpHeaders.class)) {
 				responseFunction = client::requestToHeaders;
 			}
 			else if (actualType.equals(ResponseEntity.class)) {
-				MethodParameter bodyParam = actualParam.nested();
+				MethodParameter bodyParam = isSuspending ? actualParam : actualParam.nested();
 				Class<?> bodyType = bodyParam.getNestedParameterType();
 				if (bodyType.equals(Void.class)) {
 					responseFunction = client::requestToBodilessEntity;
 				}
 				else {
 					ReactiveAdapter bodyAdapter = reactiveRegistry.getAdapter(bodyType);
-					responseFunction = initResponseEntityFunction(client, bodyParam, bodyAdapter);
+					responseFunction = initResponseEntityFunction(client, bodyParam, bodyAdapter, isSuspending);
 				}
 			}
 			else {
-				responseFunction = initBodyFunction(client, actualParam, reactiveAdapter);
+				responseFunction = initBodyFunction(client, actualParam, reactiveAdapter, isSuspending);
 			}
 
 			boolean blockForOptional = returnType.equals(Optional.class);
 			return new ResponseFunction(responseFunction, reactiveAdapter, blockForOptional, blockTimeout);
 		}
 
 		@SuppressWarnings("ConstantConditions")
-		private static Function<HttpRequestValues, Publisher<?>> initResponseEntityFunction(
-				HttpClientAdapter client, MethodParameter methodParam, @Nullable ReactiveAdapter reactiveAdapter) {
+		private static Function<HttpRequestValues, Publisher<?>> initResponseEntityFunction(HttpClientAdapter client,
+				MethodParameter methodParam, @Nullable ReactiveAdapter reactiveAdapter, boolean isSuspending) {
 
 			if (reactiveAdapter == null) {
 				return request -> client.requestToEntity(
@@ -362,7 +364,8 @@ private static Function<HttpRequestValues, Publisher<?>> initResponseEntityFunct
 					"ResponseEntity body must be a concrete value or a multi-value Publisher");
 
 			ParameterizedTypeReference<?> bodyType =
-					ParameterizedTypeReference.forType(methodParam.nested().getNestedGenericParameterType());
+					ParameterizedTypeReference.forType(isSuspending ? methodParam.nested().getGenericParameterType() :
+							methodParam.nested().getNestedGenericParameterType());
 
 			// Shortcut for Flux
 			if (reactiveAdapter.getReactiveType().equals(Flux.class)) {
@@ -376,11 +379,12 @@ private static Function<HttpRequestValues, Publisher<?>> initResponseEntityFunct
 					});
 		}
 
-		private static Function<HttpRequestValues, Publisher<?>> initBodyFunction(
-				HttpClientAdapter client, MethodParameter methodParam, @Nullable ReactiveAdapter reactiveAdapter) {
+		private static Function<HttpRequestValues, Publisher<?>> initBodyFunction(HttpClientAdapter client,
+				MethodParameter methodParam, @Nullable ReactiveAdapter reactiveAdapter, boolean isSuspending) {
 
 			ParameterizedTypeReference<?> bodyType =
-					ParameterizedTypeReference.forType(methodParam.getNestedGenericParameterType());
+					ParameterizedTypeReference.forType(isSuspending ? methodParam.getGenericParameterType() :
+							methodParam.getNestedGenericParameterType());
 
 			return (reactiveAdapter != null && reactiveAdapter.isMultiValue() ?
 					request -> client.requestToBodyFlux(request, bodyType) :

spring-web/src/test/kotlin/org/springframework/web/service/invoker/KotlinHttpServiceMethodTests.kt

@@ -0,0 +1,94 @@
+/*
+ * Copyright 2002-2023 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
+ *
+ *      https://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.web.service.invoker
+
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.toList
+import kotlinx.coroutines.runBlocking
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+import org.springframework.core.ParameterizedTypeReference
+import org.springframework.http.HttpStatus
+import org.springframework.http.ResponseEntity
+import org.springframework.lang.Nullable
+import org.springframework.web.service.annotation.GetExchange
+
+/**
+ * Kotlin tests for [HttpServiceMethod].
+ *
+ * @author Sebastien Deleuze
+ */
+class KotlinHttpServiceMethodTests {
+
+	private val client = TestHttpClientAdapter()
+	private val proxyFactory = HttpServiceProxyFactory.builder(client).build()
+
+	@Test
+	fun coroutinesService(): Unit = runBlocking {
+		val service = proxyFactory.createClient(CoroutinesService::class.java)
+
+		val stringBody = service.stringBody()
+		assertThat(stringBody).isEqualTo("requestToBody")
+		verifyClientInvocation("requestToBody", object : ParameterizedTypeReference<String>() {})
+
+		service.listBody()
+		verifyClientInvocation("requestToBody", object : ParameterizedTypeReference<MutableList<String>>() {})
+
+		val flowBody = service.flowBody()
+		assertThat(flowBody.toList()).containsExactly("request", "To", "Body", "Flux")
+		verifyClientInvocation("requestToBodyFlux", object : ParameterizedTypeReference<String>() {})
+
+		val stringEntity = service.stringEntity()
+		assertThat(stringEntity).isEqualTo(ResponseEntity.ok<String>("requestToEntity"))
+		verifyClientInvocation("requestToEntity", object : ParameterizedTypeReference<String>() {})
+
+		service.listEntity()
+		verifyClientInvocation("requestToEntity", object : ParameterizedTypeReference<MutableList<String>>() {})
+
+		val flowEntity = service.flowEntity()
+		assertThat(flowEntity.statusCode).isEqualTo(HttpStatus.OK)
+		assertThat(flowEntity.body!!.toList()).containsExactly("request", "To", "Entity", "Flux")
+		verifyClientInvocation("requestToEntityFlux", object : ParameterizedTypeReference<String>() {})
+	}
+
+	private fun verifyClientInvocation(methodName: String, @Nullable expectedBodyType: ParameterizedTypeReference<*>) {
+		assertThat(client.invokedMethodName).isEqualTo(methodName)
+		assertThat(client.bodyType).isEqualTo(expectedBodyType)
+	}
+
+	private interface CoroutinesService {
+
+		@GetExchange
+		suspend fun stringBody(): String
+
+		@GetExchange
+		suspend fun listBody(): MutableList<String>
+
+		@GetExchange
+		fun flowBody(): Flow<String>
+
+		@GetExchange
+		suspend fun stringEntity(): ResponseEntity<String>
+
+		@GetExchange
+		suspend fun listEntity(): ResponseEntity<MutableList<String>>
+
+		@GetExchange
+		fun flowEntity(): ResponseEntity<Flow<String>>
+	}
+
+}