GH-742 Add initial support for gRPC

Resolves #742

spring-cloud-function-grpc/README.md

@@ -0,0 +1,99 @@
+### Introduction 
+
+Spring Cloud Function allows you to invoke function via [RSocket](https://rsocket.io/). While you can read more about RSocket and it’s java 
+implementation [here](https://github.com/rsocket/rsocket-java), this section will describe the parts relevant to Spring Cloud Function integration.
+
+### Programming model
+From the user perspective bringing RSocket does not change the implementation of functions or any of its features, such as type conversion, 
+composition, POJO functions etc.
+And while RSocket allows first class reactive interaction over the network supporting important reactive features such as back pressure, 
+users of Spring Cloud Function still have freedom to implement their business logic using reactive or imperative functions delegating any 
+adjustment needed to apply proper invocation model to the framework.
+
+To use RSocket integration all you need is to add `spring-cloud-function-rsocket` dependency to your classpath
+```
+<dependency>
+	<groupId>org.springframework.cloud</groupId>
+	<artifactId>spring-cloud-function-rsocket</artifactId>
+ </dependency>
+```
+
+To interact with functions via RSocket we rely on Spring Boot support for RSocket and `RSocketRequester.Builder` API.
+The code below shows the key parts and you can get more details on various interaction models 
+from [this test case](https://github.com/spring-cloud/spring-cloud-function/blob/master/spring-cloud-function-rsocket/src/test/java/org/springframework/cloud/function/rsocket/RSocketAutoConfigurationTests.java).
+
+
+```
+@Bean
+public Function<String, String> uppercase() {
+	return v -> v.toUpperCase();
+}
+
+. . .
+
+RSocketRequester.Builder rsocketRequesterBuilder =
+				applicationContext.getBean(RSocketRequester.Builder.class);
+
+rsocketRequesterBuilder.tcp("localhost", port)
+	.route(“uppercase")
+	.data("\"hello\"")
+	.retrieveMono(String.class)
+	.subscribe(System.out::println);
+```
+
+Once connected to RSocket we use `route` operation to specify which function we want to invoke providing the actual 
+payload via `data` operation. Then we use one of the `retrieve` operations that best suits our desired interaction 
+(RSocket supports multiple interaction models such as fire-and-forget, request-reply etc.)
+
+#### Order of priority for routing instructions
+
+As you can see from the preceding examples, we provide function definition as a value to `route(..)` operator of `RSocketRequester.Builder`.
+However that is not the only way. You can also use standard `spring.cloud.function.definition` property as well as `spring.cloud.function.routing-expression` or property or `MessageRoutingCallback` on the server side of the RSocket interaction (see "Function Routing and Filtering" section of reference manual). 
+This raises a question of _order_ and _priorities_ when it comes to reconsiling a conflict in the event several ways of providing definition are used. So it is a mater of clearly stating the rule whcih is:
+
+***1 - MessageRoutingCallback***
+The `MessageRoutingCallback` takes precedence over all other ways of providing function definition resolution.
+
+***2 - spring.cloud.function.routing-expression***
+The `spring.cloud.function.routing-expression` property takes next precedence. So, in the event you may have also use `route(..)` operator or `spring.cloud.function.definition` property, they will be ignored if `spring.cloud.function.routing-expression` property is provided.
+
+***3 - route(..)***
+The next in line is `route(..)` operator. So in the event there are no `spring.cloud.function.routing-expression` property but you defined `spring.cloud.function.definition` property, it will be ignored in favor of definition provided by the `route(..)` operator.
+
+***4 - spring.cloud.function.definition***
+The `spring.cloud.function.definition` property is the last in the list allowing you to simply `route("")` to empty string.
+
+
+### Messaging
+
+If you want to provide and/or receive additional information that you would normally communicate via Message headers you can send and receive Spring `Message`.
+For example, the following tests case demonstrates how you can accomplish that.
+```
+Person p = new Person();
+p.setName("Ricky");
+Message<Person> message = MessageBuilder.withPayload(p).setHeader("someHeader", "foo").build();
+
+Message<Employee> result = rsocketRequesterBuilder.tcp("localhost", port)
+	.route("pojoMessageToPojo")
+	.data(message)
+	.retrieveMono(new ParameterizedTypeReference<Message<Employee>>() {})
+	.block();
+```
+Aside from sending `Message`, note the usage of `ParameterizedTypeReference` to specify that we want not only `Message` in return but also `Message` with specific payload type. 
+
+### Function Composition over RSocket (Distributed Function Composition)
+
+By now you shoudl be familiar with the standard function composition feature (e.g., `functionA|functionB|functionC`). This feature allows you to compose several co-located functions into one. But what if these functions are not co-located and instead separated by the network?
+
+With RSocket and our _distributed function composition_ feature you can still do it. So let's look at the example.
+
+Let's say we have `uppercase` function available to you locally and `reverse` function exposed via separate RSocket and you wan to compose `uppercase` and `reverse` into a single function. Had they been both available locally it would have been as simple as `uppercase|reverse`, but given that `reverse` function is not locally available we need a way to specify that in our composition instruction. For that we're using _redirect_ operator. So it woudl look like this `uppercase>localhost:2222`, where `localhost:2222` is the host/port combination where `reverse` function is hosted. 
+What's interesting is that remote function can in itself be a result of function composition (local or remote), so effectively you are composing `uppercase` with whatever function definition (which could be composition) that is running on `localhost:2222`. 
+
+The complete example is available in [this test case](https://github.com/spring-cloud/spring-cloud-function/blob/0e3a27a392f5c69727d909db26c2ba6aa0344cfd/spring-cloud-function-rsocket/src/test/java/org/springframework/cloud/function/rsocket/RSocketAutoConfigurationTests.java#L371). 
+And as you can see it is a bit more complex to showcase this feature. In this test we are composing `reverse` function with `uppercase|concat` function running remotely and then with `wrap` function running locally as if `reverse|uppercase|concat|wrap`.
+So you can see `--spring.cloud.function.definition=reverse>localhost:" + portA + "|wrap"` where `localhost:" + portA` points to another application context instance with `--spring.cloud.function.definition=uppercase|concat`. The result of the `reverse` function are sent to `uppercase|concat` function via RSocket and the result of that are fed into `wrap` function.
+
+### Samples
+
+You can also look at one of the [RSocket samples](https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-samples/function-sample-cloudevent-rsocket) that is also introduces you to Cloud Events 

spring-cloud-function-grpc/pom.xml

@@ -0,0 +1,92 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		 xmlns="http://maven.apache.org/POM/4.0.0"
+		 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+
+	<artifactId>spring-cloud-function-grpc</artifactId>
+	<packaging>jar</packaging>
+	<name>Spring Cloud Function gRPC Support</name>
+	<description>Spring Cloud Function gRPC Support</description>
+
+	<parent>
+		<groupId>org.springframework.cloud</groupId>
+		<artifactId>spring-cloud-function-parent</artifactId>
+		<version>3.2.0-SNAPSHOT</version>
+	</parent>
+
+	<properties>
+		<grpc.version>1.16.1</grpc.version>
+	</properties>
+
+	<dependencies>
+		<dependency>
+		    <groupId>io.grpc</groupId>
+		    <artifactId>grpc-netty</artifactId>
+		    <version>${grpc.version}</version>
+		</dependency>
+		<dependency>
+		    <groupId>io.grpc</groupId>
+		    <artifactId>grpc-protobuf</artifactId>
+		    <version>${grpc.version}</version>
+		</dependency>
+		<dependency>
+		    <groupId>io.grpc</groupId>
+		    <artifactId>grpc-stub</artifactId>
+		    <version>${grpc.version}</version>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.cloud</groupId>
+			<artifactId>spring-cloud-function-context</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-configuration-processor</artifactId>
+			<optional>true</optional>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-test</artifactId>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+	
+	<build>
+		<extensions>
+		    <extension>
+		      <groupId>kr.motd.maven</groupId>
+		      <artifactId>os-maven-plugin</artifactId>
+		      <version>1.6.1</version>
+		    </extension>
+		</extensions>
+		<plugins>
+			<plugin>
+		      <groupId>org.xolstice.maven.plugins</groupId>
+		      <artifactId>protobuf-maven-plugin</artifactId>
+		      <version>0.6.1</version>
+		      <configuration>
+		        <protocArtifact>
+		          com.google.protobuf:protoc:3.3.0:exe:${os.detected.classifier}
+		        </protocArtifact>
+		        <pluginId>grpc-java</pluginId>
+		        <pluginArtifact>
+		          io.grpc:protoc-gen-grpc-java:1.4.0:exe:${os.detected.classifier}
+		        </pluginArtifact>
+		      </configuration>
+		      <executions>
+		        <execution>
+		          <goals>
+		            <goal>compile</goal>
+		            <goal>compile-custom</goal>
+		          </goals>
+		        </execution>
+		      </executions>
+		    </plugin>
+<!-- 			<plugin> -->
+<!-- 				<groupId>org.springframework.boot</groupId> -->
+<!-- 				<artifactId>spring-boot-maven-plugin</artifactId> -->
+<!-- 			</plugin> -->
+		</plugins>
+	</build>
+
+</project>

spring-cloud-function-grpc/src/main/java/org/springframework/cloud/function/grpc/FunctionGrpcProperties.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2021-2021 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.cloud.function.grpc;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.cloud.function.context.FunctionProperties;
+
+/**
+ *
+ * @author Oleg Zhurakousky
+ * @since 3.2
+ *
+ */
+@ConfigurationProperties(prefix = FunctionProperties.PREFIX + ".grpc")
+public class FunctionGrpcProperties {
+
+	/**
+	 * Default gRPC port.
+	 */
+	public final static int GRPC_PORT = 55555;
+
+	private int port = GRPC_PORT;
+
+	/**
+	 * Grpc Server port.
+	 */
+	public int getPort() {
+		return this.port;
+	}
+
+	public void setPort(int port) {
+		this.port = port;
+	}
+}

spring-cloud-function-grpc/src/main/java/org/springframework/cloud/function/grpc/GrpcAutoConfiguration.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2021-2021 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.cloud.function.grpc;
+
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.cloud.function.context.FunctionCatalog;
+import org.springframework.cloud.function.context.FunctionProperties;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ *
+ * @author Oleg Zhurakousky
+ * @since 3.2
+ */
+@Configuration(proxyBeanMethods = false)
+@EnableConfigurationProperties(FunctionGrpcProperties.class)
+public class GrpcAutoConfiguration {
+
+	@Bean
+	@ConditionalOnProperty(name = "spring.cloud.function.grpc.mode", havingValue = "server", matchIfMissing = false)
+	public GrpcServer grpcServer(FunctionGrpcProperties grpcProperties, GrpcMessagingServiceImpl grpcMessagingService) {
+		return new GrpcServer(grpcProperties, grpcMessagingService);
+	}
+
+
+	@Bean
+	public GrpcMessagingServiceImpl grpcMessageService(FunctionProperties funcProperties, FunctionCatalog functionCatalog) {
+		return new GrpcMessagingServiceImpl(funcProperties, functionCatalog);
+	}
+}

spring-cloud-function-grpc/src/main/java/org/springframework/cloud/function/grpc/GrpcMessagingServiceImpl.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2021-2021 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.
+ */
+
+/*
+ * Copyright 2021-2021 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.cloud.function.grpc;
+
+import io.grpc.stub.StreamObserver;
+
+import org.springframework.cloud.function.context.FunctionCatalog;
+import org.springframework.cloud.function.context.FunctionProperties;
+import org.springframework.cloud.function.context.catalog.SimpleFunctionRegistry.FunctionInvocationWrapper;
+import org.springframework.cloud.function.grpc.MessagingServiceGrpc.MessagingServiceImplBase;
+import org.springframework.messaging.Message;
+
+class GrpcMessagingServiceImpl extends MessagingServiceImplBase {
+
+	private final FunctionInvocationWrapper function;
+
+	GrpcMessagingServiceImpl(FunctionProperties funcProperties, FunctionCatalog functionCatalog) {
+		this.function = functionCatalog.lookup(funcProperties.getDefinition(), "application/json");
+	}
+
+
+	@Override
+	public void requestReply(GrpcMessage request, StreamObserver<GrpcMessage> responseObserver) {
+		Message<byte[]> message = GrpcUtils.fromGrpcMessage(request);
+		Message<byte[]> replyMessage = (Message<byte[]>) this.function.apply(message);
+
+		GrpcMessage reply = GrpcUtils.toGrpcMessage(replyMessage);
+		/*
+		 * The above is effectively echo. This is where we plug in function invocation
+		 */
+		responseObserver.onNext(reply);
+		responseObserver.onCompleted();
+	}
+//
+//	@Override
+//	public void serverStream(GrpcMessage request,
+//			StreamObserver<GrpcMessage> responseObserver) {
+//
+//	}
+//
+//	@Override
+//	public StreamObserver<GrpcMessage> clientStream(
+//			StreamObserver<GrpcMessage> responseObserver) {
+//		return null;
+//	}
+//
+//	@Override
+//	public StreamObserver<GrpcMessage> biStream(
+//			StreamObserver<GrpcMessage> responseObserver) {
+//		return null;
+//	}
+}

spring-cloud-function-grpc/src/main/java/org/springframework/cloud/function/grpc/GrpcServer.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2021-2021 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.cloud.function.grpc;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+import io.grpc.Server;
+import io.grpc.ServerBuilder;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import org.springframework.cloud.function.grpc.MessagingServiceGrpc.MessagingServiceImplBase;
+import org.springframework.context.SmartLifecycle;
+
+class GrpcServer implements SmartLifecycle {
+
+	protected Log logger = LogFactory.getLog(GrpcServer.class);
+
+	private final FunctionGrpcProperties grpcProperties;
+
+	private final MessagingServiceImplBase grpcMessageService;
+
+	private final ExecutorService executor = Executors.newSingleThreadExecutor();
+
+	private Server server;
+
+	GrpcServer(FunctionGrpcProperties grpcProperties, MessagingServiceImplBase grpcMessageService) {
+		this.grpcProperties = grpcProperties;
+		this.grpcMessageService = grpcMessageService;
+	}
+
+	@Override
+	public void start() {
+		this.executor.execute(() -> {
+			try {
+				this.server = ServerBuilder.forPort(this.grpcProperties.getPort())
+						.addService(this.grpcMessageService)
+						.build();
+
+				logger.info("Starting gRPC server");
+				this.server.start();
+				logger.info("gRPC server is listening on port " + this.grpcProperties.getPort());
+			}
+			catch (Exception e) {
+				throw new IllegalStateException(e);
+			}
+		});
+	}
+
+	@Override
+	public void stop() {
+		logger.info("Shutting down gRPC server");
+		this.server.shutdown();
+		this.executor.shutdown();
+	}
+
+	@Override
+	public boolean isRunning() {
+		return this.server != null && !this.server.isShutdown();
+	}
+}

spring-cloud-function-grpc/src/main/java/org/springframework/cloud/function/grpc/GrpcUtils.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2021-2021 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.cloud.function.grpc;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import com.google.protobuf.ByteString;
+import io.grpc.ManagedChannel;
+import io.grpc.ManagedChannelBuilder;
+
+import org.springframework.messaging.Message;
+import org.springframework.messaging.support.MessageBuilder;
+
+/**
+ *
+ * @author Oleg Zhurakousky
+ * @since 3.2
+ *
+ */
+public final class GrpcUtils {
+
+	private GrpcUtils() {
+
+	}
+
+	public static GrpcMessage toGrpcMessage(byte[] payload, Map<String, String> headers) {
+		return GrpcMessage.newBuilder()
+				.setPayload(ByteString.copyFrom(payload))
+				.putAllHeaders(headers)
+				.build();
+	}
+
+	public static GrpcMessage toGrpcMessage(Message<byte[]> message) {
+		Map<String, String> stringHeaders = new HashMap<>();
+		message.getHeaders().forEach((k, v) -> {
+			stringHeaders.put(k, v.toString());
+		});
+		return toGrpcMessage(message.getPayload(), stringHeaders);
+	}
+
+	public static Message<byte[]> fromGrpcMessage(GrpcMessage message) {
+		return MessageBuilder.withPayload(message.getPayload().toByteArray())
+				.copyHeaders(message.getHeadersMap())
+				.build();
+	}
+
+	public static Message<byte[]> requestReply(Message<byte[]> inputMessage) {
+		return requestReply("localhost", FunctionGrpcProperties.GRPC_PORT, inputMessage);
+	}
+
+	public static Message<byte[]> requestReply(String host, int port, Message<byte[]> inputMessage) {
+		ManagedChannel channel = ManagedChannelBuilder.forAddress("localhost", 55555)
+				.usePlaintext().build();
+		MessagingServiceGrpc.MessagingServiceBlockingStub stub = MessagingServiceGrpc
+				.newBlockingStub(channel);
+
+		GrpcMessage response = stub.requestReply(toGrpcMessage(inputMessage));
+		channel.shutdown();
+		return fromGrpcMessage(response);
+	}
+}

spring-cloud-function-grpc/src/main/proto/MessageService.proto

@@ -0,0 +1,18 @@
+syntax = "proto3";
+option java_multiple_files = true;
+package org.springframework.cloud.function.grpc;
+
+message GrpcMessage {
+    bytes payload = 1;
+    map<string, string> headers = 2;
+}
+
+service MessagingService {
+    rpc biStream(stream GrpcMessage) returns (stream GrpcMessage);
+    
+    rpc clientStream(stream GrpcMessage) returns (GrpcMessage);
+    
+    rpc serverStream(GrpcMessage) returns (stream GrpcMessage);
+    
+    rpc requestReply(GrpcMessage) returns (GrpcMessage);
+}

spring-cloud-function-grpc/src/main/resources/META-INF/spring.factories

@@ -0,0 +1,2 @@
+org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
+org.springframework.cloud.function.grpc.GrpcAutoConfiguration

spring-cloud-function-grpc/src/test/java/org/springframework/cloud/function/grpc/GrpcInteractionTests.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2021-2021 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.cloud.function.grpc;
+
+
+
+import java.util.function.Function;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.WebApplicationType;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.builder.SpringApplicationBuilder;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageHeaders;
+import org.springframework.messaging.support.MessageBuilder;
+import org.springframework.util.MimeTypeUtils;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class GrpcInteractionTests {
+
+	@Test
+	public void test() {
+		try (ConfigurableApplicationContext context = new SpringApplicationBuilder(
+				SampleConfiguration.class).web(WebApplicationType.NONE).run(
+						"--spring.jmx.enabled=false",
+						"--spring.cloud.function.definition=uppercase",
+						"--spring.cloud.function.grpc.port=55555",
+						"--spring.cloud.function.grpc.mode=server")) {
+
+			Message<byte[]> message = MessageBuilder.withPayload("hello gRPC".getBytes())
+					.setHeader("foo", "bar")
+					.setHeader(MessageHeaders.CONTENT_TYPE, MimeTypeUtils.TEXT_PLAIN)
+					.build();
+
+			Message<byte[]> reply = GrpcUtils.requestReply(message);
+
+			assertThat(reply.getPayload()).isEqualTo("\"HELLO GRPC\"".getBytes());
+		}
+	}
+
+	@EnableAutoConfiguration
+	public static class SampleConfiguration {
+
+		@Bean
+		public Function<String, String> uppercase() {
+			return v -> v.toUpperCase();
+		}
+	}
+}

spring-cloud-function-grpc/src/test/resources/application.properties

@@ -0,0 +1 @@
+