GH-56 Added support for Function<Flux, Mono> and <Mono, Flux>

Resolves #56
Resolves #218

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

@@ -52,9 +52,11 @@ import org.springframework.cloud.function.context.catalog.FunctionUnregistration
 import org.springframework.cloud.function.core.FluxConsumer;
 import org.springframework.cloud.function.core.FluxFunction;
 import org.springframework.cloud.function.core.FluxSupplier;
+import org.springframework.cloud.function.core.FluxToMonoFunction;
 import org.springframework.cloud.function.core.IsolatedConsumer;
 import org.springframework.cloud.function.core.IsolatedFunction;
 import org.springframework.cloud.function.core.IsolatedSupplier;
+import org.springframework.cloud.function.core.MonoToFluxFunction;
 import org.springframework.cloud.function.json.GsonMapper;
 import org.springframework.cloud.function.json.JacksonMapper;
 import org.springframework.context.ApplicationEventPublisher;
@@ -349,7 +351,22 @@ public class ContextFunctionCatalogAutoConfiguration {
 			else if (a instanceof Function && b instanceof Function) {
 				Function<Object, Object> function1 = (Function<Object, Object>) a;
 				Function<Object, Object> function2 = (Function<Object, Object>) b;
-				return function1.andThen(function2);
+				if (function1 instanceof FluxToMonoFunction) {
+					if (function2 instanceof MonoToFluxFunction) {
+						return function1.andThen(function2);
+					}
+					else {
+						throw new IllegalStateException("The provided function is finite (i.e., returns Mono<?>) "
+								+ "therefore it can *only* be composed with compatible function (i.e., Function<Mono, Flux>");
+					}
+				}
+				else if (function2 instanceof FluxToMonoFunction) {
+					return new FluxToMonoFunction<Object, Object>(((Function<Flux<Object>, Flux<Object>>)a)
+							.andThen(((FluxToMonoFunction<Object,Object>) b).getTarget()));
+				}
+				else {
+					return function1.andThen(function2);
+				}
 			}
 			else if (a instanceof Function && b instanceof Consumer) {
 				Function<Object, Object> function = (Function<Object, Object>) a;
@@ -490,6 +507,12 @@ public class ContextFunctionCatalogAutoConfiguration {
 				}
 				registration.target(target);
 			}
+			if (Mono.class.isAssignableFrom(type.getOutputWrapper())) {
+				registration.target(new FluxToMonoFunction<>((Function) target));
+			}
+			else if (Mono.class.isAssignableFrom(type.getInputWrapper())) {
+				registration.target(new MonoToFluxFunction<>((Function) target));
+			}
 			return registration;
 		}
 

spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/config/BeanFactoryFunctionCatalogTests.java

@@ -120,6 +120,33 @@ public class BeanFactoryFunctionCatalogTests {
 		assertThat(foos.apply(Flux.just(2)).blockFirst()).isEqualTo("Hello 4");
 	}
 
+	@Test
+	public void composeWithFiniteFunction() {
+		Function<String, String> func1 = x -> x.toUpperCase();
+		processor.register(new FunctionRegistration<>(func1, "func1"));
+		processor.register(new FunctionRegistration<>(new FluxThenMonoFunction(), "func2"));
+		Function<Flux<String>, Mono<Long>> foos = processor.lookup(Function.class, "func1,func2");
+		assertThat(foos.apply(Flux.fromArray(new String[] {"a", "b", "c"})).block()).isEqualTo(3);
+	}
+
+	@Test
+	public void composeWithFiniteFunctionAndContinueWithCompatible() {
+		Function<String, String> func1 = x -> x.toUpperCase();
+		processor.register(new FunctionRegistration<>(func1, "func1"));
+		processor.register(new FunctionRegistration<>(new FluxThenMonoFunction(), "func2"));
+		processor.register(new FunctionRegistration<>(new MonoThenFluxFunction(), "func3"));
+		Function<Flux<String>, Flux<Integer>> foos = processor.lookup(Function.class, "func1,func2,func3");
+		assertThat(foos.apply(Flux.fromArray(new String[] {"a", "b", "c"})).collectList().block().size()).isEqualTo(3);
+	}
+
+	@Test(expected=IllegalStateException.class)
+	public void composeIncompatibleFunctions() {
+		Function<String, String> func1 = x -> x.toUpperCase();
+		processor.register(new FunctionRegistration<>(func1, "func1"));
+		processor.register(new FunctionRegistration<>(new FluxThenMonoFunction(), "func2"));
+		processor.lookup(Function.class, "func2,func1");
+	}
+
 	@Test
 	public void composeSupplier() {
 		processor.register(new FunctionRegistration<>(new Source(), "numbers"));
@@ -231,4 +258,20 @@ public class BeanFactoryFunctionCatalogTests {
 
 	}
 
+	protected static class FluxThenMonoFunction implements Function<Flux<String>, Mono<Long>> {
+
+		@Override
+		public Mono<Long> apply(Flux<String> t) {
+			return t.count();
+		}
+	}
+
+	protected static class MonoThenFluxFunction implements Function<Mono<Long>, Flux<Integer>> {
+
+		@Override
+		public Flux<Integer> apply(Mono<Long> t) {
+			return Flux.range(0, Integer.parseInt(t.block().toString()));
+		}
+	}
+
 }

spring-cloud-function-core/src/main/java/org/springframework/cloud/function/core/FluxToMonoFunction.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2018 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
+ *
+ *      http://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.cloud.function.core;
+
+import java.util.function.Function;
+
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+/**
+ * Marker wrapper for target Function<Flux, Mono>
+ *
+ * @author Oleg Zhurakousky
+ * @since 2.0
+ *
+ * @param <T> type of {@link Flux} input of the target function
+ * @param <R> type of {@link Mono} output of the target function
+ */
+public class FluxToMonoFunction<I,O> implements Function<Flux<I>, Mono<O>>, FluxWrapper<Function<Flux<I>, Mono<O>>> {
+
+	private final Function<Flux<I>, Mono<O>> function;
+
+	/**
+	 * @param function target function
+	 */
+	public FluxToMonoFunction(Function<Flux<I>, Mono<O>> function) {
+		this.function = function;
+	}
+
+	@Override
+	public Function<Flux<I>, Mono<O>> getTarget() {
+		return function;
+	}
+
+	@Override
+	public Mono<O> apply(Flux<I> input) {
+		return function.apply(input);
+	}
+}

spring-cloud-function-core/src/main/java/org/springframework/cloud/function/core/MonoToFluxFunction.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2018 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
+ *
+ *      http://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.cloud.function.core;
+
+import java.util.function.Function;
+
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+/**
+ * Marker wrapper for target Function<Mono, Flux>
+ *
+ * @author Oleg Zhurakousky
+ * @since 2.0
+ *
+ * @param <T> type of {@link Mono} input of the target function
+ * @param <R> type of {@link Flux} output of the target function
+ */
+public class MonoToFluxFunction<I,O> implements Function<Mono<I>, Flux<O>>, FluxWrapper<Function<Mono<I>, Flux<O>>> {
+
+	private final Function<Mono<I>, Flux<O>> function;
+
+	/**
+	 * @param function target function
+	 * @param names name(s) of the target function (optional)
+	 */
+	public MonoToFluxFunction(Function<Mono<I>, Flux<O>> function) {
+		this.function = function;
+	}
+
+	@Override
+	public Function<Mono<I>, Flux<O>> getTarget() {
+		return function;
+	}
+
+	@Override
+	public Flux<O> apply(Mono<I> input) {
+		return function.apply(input);
+	}
+}