Support Coroutines in HttpServiceProxyFactory

See gh-29527

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

@@ -28,6 +28,7 @@ import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
 import org.springframework.core.DefaultParameterNameDiscoverer;
+import org.springframework.core.KotlinDetector;
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.core.ReactiveAdapter;
@@ -83,6 +84,11 @@ final class HttpServiceMethod {
 		if (count == 0) {
 			return new MethodParameter[0];
 		}
+
+		if (KotlinDetector.isSuspendingFunction(method)) {
+			count -= 1;
+		}
+
 		DefaultParameterNameDiscoverer nameDiscoverer = new DefaultParameterNameDiscoverer();
 		MethodParameter[] parameters = new MethodParameter[count];
 		for (int i = 0; i < count; i++) {
@@ -306,6 +312,10 @@ final class HttpServiceMethod {
 
 			MethodParameter returnParam = new MethodParameter(method, -1);
 			Class<?> returnType = returnParam.getParameterType();
+			if (KotlinDetector.isSuspendingFunction(method)) {
+				returnType = Mono.class;
+			}
+
 			ReactiveAdapter reactiveAdapter = reactiveRegistry.getAdapter(returnType);
 
 			MethodParameter actualParam = (reactiveAdapter != null ? returnParam.nested() : returnParam.nestedIfOptional());

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

@@ -25,11 +25,15 @@ import java.util.Map;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 
+import kotlin.coroutines.Continuation;
 import org.aopalliance.intercept.MethodInterceptor;
 import org.aopalliance.intercept.MethodInvocation;
+import reactor.core.publisher.Mono;
 
 import org.springframework.aop.framework.ProxyFactory;
 import org.springframework.aop.framework.ReflectiveMethodInvocation;
+import org.springframework.core.CoroutinesUtils;
+import org.springframework.core.KotlinDetector;
 import org.springframework.core.MethodIntrospector;
 import org.springframework.core.ReactiveAdapterRegistry;
 import org.springframework.core.annotation.AnnotatedElementUtils;
@@ -264,10 +268,18 @@ public final class HttpServiceProxyFactory {
 		}
 
 		@Override
+		@SuppressWarnings({"unchecked"})
 		public Object invoke(MethodInvocation invocation) throws Throwable {
 			Method method = invocation.getMethod();
 			HttpServiceMethod httpServiceMethod = this.httpServiceMethods.get(method);
 			if (httpServiceMethod != null) {
+				if (KotlinDetector.isSuspendingFunction(method)) {
+					Object[] arguments = getSuspendedFunctionArgs(invocation.getArguments());
+					Continuation<Object> continuation = resolveContinuationArgument(invocation.getArguments());
+					Mono<Object> wrapped = (Mono<Object>) httpServiceMethod.invoke(arguments);
+					return CoroutinesUtils.awaitSingleOrNull(wrapped, continuation);
+				}
+
 				return httpServiceMethod.invoke(invocation.getArguments());
 			}
 			if (method.isDefault()) {
@@ -278,6 +290,17 @@ public final class HttpServiceProxyFactory {
 			}
 			throw new IllegalStateException("Unexpected method invocation: " + method);
 		}
+
+		@SuppressWarnings({"unchecked"})
+		private static <T> Continuation<T> resolveContinuationArgument(Object[] args) {
+			return (Continuation<T>) args[args.length - 1];
+		}
+
+		private static Object[] getSuspendedFunctionArgs(Object[] args) {
+			Object[] functionArgs = new Object[args.length - 1];
+			System.arraycopy(args, 0, functionArgs, 0, args.length - 1);
+			return functionArgs;
+		}
 	}
 
 }