Add support for Message<Foo> in stream apps

The FunctionInspector needs to be able to distinguish between a
function of Flux<Foo> and a function of Flux<Message<Foo>>. Then
it can do the conversion a level below.

Only supports Message->Message or POJO->POJO (no mixtures), so there
is only one new method in FunctionInspector.

No support in the web endpoints yet. But it's probably not so hard
to add.

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/ContextFunctionCatalogAutoConfiguration.java

@@ -62,6 +62,7 @@ import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.core.io.FileSystemResource;
 import org.springframework.core.type.StandardMethodMetadata;
 import org.springframework.core.type.classreading.MethodMetadataReadingVisitor;
+import org.springframework.messaging.Message;
 import org.springframework.stereotype.Component;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ReflectionUtils;
@@ -108,6 +109,11 @@ public class ContextFunctionCatalogAutoConfiguration {
 			this.processor = processor;
 		}
 
+		@Override
+		public boolean isMessage(String name) {
+			return processor.isMessage(name);
+		}
+
 		@Override
 		public Class<?> getInputWrapper(String name) {
 			return processor.findInputWrapper(name);
@@ -472,14 +478,19 @@ public class ContextFunctionCatalogAutoConfiguration {
 				Type typeArgumentAtIndex = parameterizedType
 						.getActualTypeArguments()[index];
 				if (typeArgumentAtIndex instanceof ParameterizedType
-						&& FunctionInspector.isWrapper(
-								((ParameterizedType) typeArgumentAtIndex).getRawType())
 						&& !paramType.isWrapper()) {
-					param = ((ParameterizedType) typeArgumentAtIndex)
-							.getActualTypeArguments()[0];
+					if (FunctionInspector.isWrapper(
+							((ParameterizedType) typeArgumentAtIndex).getRawType())) {
+						param = ((ParameterizedType) typeArgumentAtIndex)
+								.getActualTypeArguments()[0];
+						param = extractNestedType(paramType, param);
+					}
+					else {
+						param = extractNestedType(paramType, typeArgumentAtIndex);
+					}
 				}
 				else {
-					param = typeArgumentAtIndex;
+					param = extractNestedType(paramType, typeArgumentAtIndex);
 				}
 			}
 			else {
@@ -488,6 +499,16 @@ public class ContextFunctionCatalogAutoConfiguration {
 			return param;
 		}
 
+		private Type extractNestedType(ParamType paramType, Type param) {
+			if (!paramType.isInnerWrapper()
+					&& param.getTypeName().startsWith(Message.class.getName())) {
+				if (param instanceof ParameterizedType) {
+					param = ((ParameterizedType) param).getActualTypeArguments()[0];
+				}
+			}
+			return param;
+		}
+
 		private Object getField(Object target, String name) {
 			Field field = ReflectionUtils.findField(target.getClass(), name);
 			if (field == null) {
@@ -497,6 +518,19 @@ public class ContextFunctionCatalogAutoConfiguration {
 			return ReflectionUtils.getField(field, target);
 		}
 
+		private boolean isMessage(String name) {
+			if (name == null || !registry.containsBeanDefinition(name)) {
+				return false;
+			}
+			return Message.class.isAssignableFrom(findType(name,
+					(AbstractBeanDefinition) registry.getBeanDefinition(name),
+					ParamType.INPUT_INNER_WRAPPER))
+					|| Message.class.isAssignableFrom(findType(name,
+							(AbstractBeanDefinition) registry.getBeanDefinition(name),
+							ParamType.OUTPUT_INNER_WRAPPER));
+
+		}
+
 		private Class<?> findInputWrapper(String name) {
 			if (name == null || !registry.containsBeanDefinition(name)) {
 				return Object.class;
@@ -533,19 +567,25 @@ public class ContextFunctionCatalogAutoConfiguration {
 		}
 
 		static enum ParamType {
-			INPUT, OUTPUT, INPUT_WRAPPER, OUTPUT_WRAPPER;
+			INPUT, OUTPUT, INPUT_WRAPPER, OUTPUT_WRAPPER, INPUT_INNER_WRAPPER, OUTPUT_INNER_WRAPPER;
 
 			public boolean isOutput() {
-				return this == OUTPUT || this == OUTPUT_WRAPPER;
+				return this == OUTPUT || this == OUTPUT_WRAPPER
+						|| this == OUTPUT_INNER_WRAPPER;
 			}
 
 			public boolean isInput() {
-				return this == INPUT || this == INPUT_WRAPPER;
+				return this == INPUT || this == INPUT_WRAPPER
+						|| this == INPUT_INNER_WRAPPER;
 			}
 
 			public boolean isWrapper() {
 				return this == OUTPUT_WRAPPER || this == INPUT_WRAPPER;
 			}
+
+			public boolean isInnerWrapper() {
+				return this == OUTPUT_INNER_WRAPPER || this == INPUT_INNER_WRAPPER;
+			}
 		}
 	}
 }

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/FunctionInspector.java

@@ -28,6 +28,8 @@ import reactor.core.publisher.Mono;
  */
 public interface FunctionInspector {
 
+	boolean isMessage(String name);
+
 	Class<?> getInputType(String name);
 
 	Class<?> getOutputType(String name);