Initial commit of Google Function Adapter

implement HttpFunction
add headers processing
Some refactoring [WIP]
Add invoker integration test
Make test classes nested within test.
Add sample and refdoc

Resolves #468

spring-cloud-function-adapters/spring-cloud-function-adapter-gcp/src/main/java/org/springframework/cloud/function/adapter/gcloud/GcfSpringBootHttpRequestHandler.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright 2020-2020 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.adapter.gcloud;
+
+import com.google.cloud.functions.HttpFunction;
+import com.google.cloud.functions.HttpRequest;
+import com.google.cloud.functions.HttpResponse;
+import com.google.gson.Gson;
+import org.reactivestreams.Publisher;
+import reactor.core.publisher.Mono;
+
+import org.springframework.cloud.function.context.AbstractSpringFunctionAdapterInitializer;
+
+/**
+ * Implementation of {@link HttpFunction} for Google Cloud Function (GCF).
+ * This is the Spring Cloud Function adapter for GCF HTTP function.
+ *
+ * @author Dmitry Solomakha
+ * @author Mike Eltsufin
+ */
+public class GcfSpringBootHttpRequestHandler
+	extends AbstractSpringFunctionAdapterInitializer<HttpRequest> implements HttpFunction {
+
+	private final Gson gson = new Gson();
+
+	public GcfSpringBootHttpRequestHandler() {
+		super();
+	}
+
+	public GcfSpringBootHttpRequestHandler(Class<?> configurationClass) {
+		super(configurationClass);
+	}
+
+	/**
+	 * The implementation of a GCF {@link HttpFunction} that will be used as the entrypoint from GCF.
+	 */
+	@Override
+	public void service(HttpRequest httpRequest, HttpResponse httpResponse) throws Exception {
+		Thread.currentThread()
+			.setContextClassLoader(GcfSpringBootHttpRequestHandler.class.getClassLoader());
+
+		initialize(httpRequest);
+
+		Publisher<?> input;
+		if (getInputType() == Void.class) {
+			input = Mono.empty();
+		}
+		else {
+			input = Mono.just(gson.fromJson(httpRequest.getReader(), getInputType()));
+		}
+
+		Publisher<?> output = this.apply(input);
+
+		Object result = this.result(input, output);
+
+		httpResponse.getWriter().write(gson.toJson(result));
+		httpResponse.getWriter().close();
+	}
+}

spring-cloud-function-adapters/spring-cloud-function-adapter-gcp/src/test/java/org/springframework/cloud/function/adapter/gcloud/GcfSpringBootHttpRequestHandlerTests.java

@@ -0,0 +1,142 @@
+/*
+ * Copyright 2020-2020 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.adapter.gcloud;
+
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.StringReader;
+import java.io.StringWriter;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+import com.google.cloud.functions.HttpRequest;
+import com.google.cloud.functions.HttpResponse;
+import com.google.gson.Gson;
+import org.junit.Test;
+import org.mockito.Mockito;
+
+import org.springframework.cloud.function.context.config.ContextFunctionCatalogAutoConfiguration;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Import;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.when;
+
+/**
+ * Unit tests for the HTTP functions adapter for Google Cloud Functions.
+ *
+ * @author Dmitry Solomakha
+ * @author Mike Eltsufin
+ */
+public class GcfSpringBootHttpRequestHandlerTests {
+
+	private static final Gson gson = new Gson();
+
+	@Test
+	public void testHelloWorldSupplier() throws Exception {
+		testFunction(HelloWorldSupplier.class, null, "Hello World!");
+	}
+
+	@Test
+	public void testJsonInputFunction() throws Exception {
+		testFunction(JsonInputFunction.class, new IncomingRequest("hello"),
+			"Thank you for sending the message: hello");
+	}
+
+	@Test
+	public void testJsonInputOutputFunction() throws Exception {
+		testFunction(JsonInputOutputFunction.class, new IncomingRequest("hello"),
+			new OutgoingResponse("Thank you for sending the message: hello"));
+	}
+
+	@Test
+	public void testJsonInputConsumer() throws Exception {
+		testFunction(JsonInputConsumer.class, new IncomingRequest("hello"), null);
+	}
+
+	private <I, O> void testFunction(Class<?> configurationClass, I input, O expectedOutput) throws Exception {
+		GcfSpringBootHttpRequestHandler handler = new GcfSpringBootHttpRequestHandler(configurationClass);
+
+		HttpRequest request = Mockito.mock(HttpRequest.class);
+
+		if (input != null) {
+			when(request.getReader()).thenReturn(new BufferedReader(new StringReader(gson.toJson(input))));
+		}
+
+		HttpResponse response = Mockito.mock(HttpResponse.class);
+		StringWriter writer = new StringWriter();
+		when(response.getWriter()).thenReturn(new BufferedWriter(writer));
+
+		handler.service(request, response);
+
+		assertThat(writer.toString()).isEqualTo(gson.toJson(expectedOutput));
+	}
+
+	@Configuration
+	@Import({ ContextFunctionCatalogAutoConfiguration.class })
+	protected static class HelloWorldSupplier {
+		@Bean
+		public Supplier<String> supplier() {
+			return () -> "Hello World!";
+		}
+	}
+
+	@Configuration
+	@Import({ ContextFunctionCatalogAutoConfiguration.class })
+	protected static class JsonInputFunction {
+		@Bean
+		public Function<IncomingRequest, String> function() {
+			return (in) -> "Thank you for sending the message: " + in.message;
+		}
+	}
+
+	@Configuration
+	@Import({ ContextFunctionCatalogAutoConfiguration.class })
+	protected static class JsonInputOutputFunction {
+		@Bean
+		public Function<IncomingRequest, OutgoingResponse> function() {
+			return (in) -> new OutgoingResponse("Thank you for sending the message: " + in.message);
+		}
+	}
+
+	@Configuration
+	@Import({ ContextFunctionCatalogAutoConfiguration.class })
+	protected static class JsonInputConsumer {
+		@Bean
+		public Consumer<IncomingRequest> function() {
+			return (in) -> System.out.println("Thank you for sending the message: " + in.message);
+		}
+	}
+
+	private static class IncomingRequest {
+		String message;
+
+		IncomingRequest(String message) {
+			this.message = message;
+		}
+	}
+
+	private static class OutgoingResponse {
+		String message;
+
+		OutgoingResponse(String message) {
+			this.message = message;
+		}
+	}
+}