Polish suspending functions support in RSocketServiceMethod

Closes gh-35473

Author: sdeleuze

spring-messaging/src/main/java/org/springframework/messaging/rsocket/service/RSocketServiceMethod.java

@@ -137,13 +137,11 @@ private static Function<RSocketRequestValues, Object> initResponseFunction(
 
 		MethodParameter returnParam = new MethodParameter(method, -1);
 		Class<?> returnType = returnParam.getParameterType();
-		boolean isFlowReturnType = COROUTINES_FLOW_CLASS_NAME.equals(returnType.getName());
-		boolean isUnwrapped = KotlinDetector.isSuspendingFunction(method) && !isFlowReturnType;
-		if (isUnwrapped) {
-			returnType = Mono.class;
-		}
-		else if (isFlowReturnType) {
-			returnType = Flux.class;
+		boolean isSuspending = KotlinDetector.isSuspendingFunction(method);
+		boolean hasFlowReturnType = COROUTINES_FLOW_CLASS_NAME.equals(returnType.getName());
+		boolean isUnwrapped = isSuspending && !hasFlowReturnType;
+		if (isSuspending) {
+			returnType = (hasFlowReturnType ? Flux.class : Mono.class);
 		}
 
 		ReactiveAdapter reactiveAdapter = reactiveRegistry.getAdapter(returnType);

spring-messaging/src/test/kotlin/org/springframework/messaging/rsocket/service/RSocketServiceMethodKotlinTests.kt

@@ -37,6 +37,7 @@ import reactor.core.publisher.Mono
  * Kotlin tests for [RSocketServiceMethod].
  *
  * @author Dmitry Sulman
+ * @author Sebastien Deleuze
  */
 class RSocketServiceMethodKotlinTests {
 
@@ -95,6 +96,23 @@ class RSocketServiceMethodKotlinTests {
 		assertThat(rsocket.savedPayload?.dataUtf8).isEqualTo(requestPayload)
 	}
 
+	@Test
+	fun nonSuspendingRequestStream(): Unit = runBlocking {
+		val service = proxyFactory.createClient(NonSuspendingFunctionsService::class.java)
+
+		val requestPayload = "request"
+		val responsePayload1 = "response1"
+		val responsePayload2 = "response2"
+		rsocket.setPayloadFluxToReturn(
+			Flux.just(DefaultPayload.create(responsePayload1), DefaultPayload.create(responsePayload2)))
+		val response = service.requestStream(requestPayload).toList()
+
+		assertThat(response).containsExactly(responsePayload1, responsePayload2)
+		assertThat(rsocket.savedMethodName).isEqualTo("requestStream")
+		assertThat(rsocket.savedPayload?.metadataUtf8).isEqualTo("rs")
+		assertThat(rsocket.savedPayload?.dataUtf8).isEqualTo(requestPayload)
+	}
+
 	@Test
 	fun requestChannel(): Unit = runBlocking {
 		val service = proxyFactory.createClient(SuspendingFunctionsService::class.java)
@@ -131,4 +149,11 @@ class RSocketServiceMethodKotlinTests {
 		@RSocketExchange("rc")
 		suspend fun requestChannel(input: Flow<String>): Flow<String>
 	}
+
+	private interface NonSuspendingFunctionsService {
+
+		@RSocketExchange("rs")
+		fun requestStream(input: String): Flow<String>
+	}
+
 }