GH-742 Add initial support for gRPC

Resolves #742

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

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+