making changes to adapter, including tests and documentation

docs/src/main/asciidoc/adapters/gcp-intro.adoc

@@ -136,6 +136,28 @@ Invoke the HTTP function:
 curl https://REGION-PROJECT_ID.cloudfunctions.net/function-sample-gcp-http -d "hello"
 ----
 
+
+Setting custom HTTP statusCode:
+
+----
+Users can specify the response statusCode that they want to set by wrapping "statusCode" in headers.
+----
+
+[source, java]
+----
+@Bean
+public Function<String, Message<String>> function() {
+
+	String payload = "hello";
+
+	Message<String> message = MessageBuilder.withPayload(payload).setHeader("statusCode", 404).build();
+
+	return input -> message;
+};
+----
+
+
+
 ==== Background Functions
 
 Google Cloud Functions also supports deploying https://cloud.google.com/functions/docs/writing/background[Background Functions] which are invoked indirectly in response to an event, such as a message on a https://cloud.google.com/pubsub[Cloud Pub/Sub] topic, a change in a https://cloud.google.com/storage[Cloud Storage] bucket, or a https://firebase.google.com/[Firebase] event.

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

@@ -95,6 +95,8 @@ public class FunctionInvoker extends AbstractSpringFunctionAdapterInitializer<Ht
 	@Override
 	public void service(HttpRequest httpRequest, HttpResponse httpResponse) throws Exception {
 
+		String httpStatusCode = "statusCode";
+
 		Function<Message<BufferedReader>, Message<byte[]>> function = lookupFunction();
 
 		Message<BufferedReader> message = getInputType() == Void.class || getInputType() == null ? null
@@ -123,8 +125,8 @@ public class FunctionInvoker extends AbstractSpringFunctionAdapterInitializer<Ht
 			}
 			httpRequest.getContentType().ifPresent(contentType -> httpResponse.setContentType(contentType));
 
-			if (headers.containsKey("statusCode")) {
-				httpResponse.setStatusCode((int) headers.get("statusCode"));
+			if (headers.containsKey(httpStatusCode) && (headers.get(httpStatusCode) instanceof Integer)) {
+				httpResponse.setStatusCode((int) headers.get(httpStatusCode));
 			}
 		}
 	}

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

@@ -20,6 +20,8 @@ import java.io.BufferedReader;
 import java.io.BufferedWriter;
 import java.io.StringReader;
 import java.io.StringWriter;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Supplier;
@@ -37,7 +39,9 @@ import org.springframework.context.annotation.Import;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.support.MessageBuilder;
 
+import static java.util.Arrays.asList;
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 /**
@@ -52,27 +56,38 @@ public class FunctionInvokerHttpTests {
 
 	@Test
 	public void testHelloWorldSupplier() throws Exception {
-		testHttpFunction(HelloWorldSupplier.class, null, "Hello World!");
+		testHttpFunction(HelloWorldSupplier.class, null, "Hello World!", false, false);
 	}
 
 	@Test
 	public void testJsonInputFunction() throws Exception {
 		testHttpFunction(JsonInputFunction.class, new IncomingRequest("hello"),
-				"Thank you for sending the message: hello");
+				"Thank you for sending the message: hello", false, false);
 	}
 
 	@Test
 	public void testJsonInputOutputFunction() throws Exception {
 		testHttpFunction(JsonInputOutputFunction.class, new IncomingRequest("hello"),
-				new OutgoingResponse("Thank you for sending the message: hello"));
+				new OutgoingResponse("Thank you for sending the message: hello"), false, false);
 	}
 
 	@Test
 	public void testJsonInputConsumer_Background() throws Exception {
-		testHttpFunction(JsonInputConsumer.class, new IncomingRequest("hello"), null);
+		testHttpFunction(JsonInputConsumer.class, new IncomingRequest("hello"), null, false, false);
 	}
 
-	private <I, O> void testHttpFunction(Class<?> configurationClass, I input, O expectedOutput) throws Exception {
+	@Test
+	public void testStatusCodeSet() throws Exception {
+		testHttpFunction(statusCodeSupplier.class, "hello", "hello", true, false);
+	}
+
+	@Test
+	public void testMultiValueHeaderSupplied() throws Exception {
+		testHttpFunction(multiValueHeaderSupplier.class, "hello", "hello", false, true);
+	}
+
+
+	private <I, O> void testHttpFunction(Class<?> configurationClass, I input, O expectedOutput, boolean statusCodeCheck, boolean multiHeaderCheck) throws Exception {
 		try (FunctionInvoker handler = new FunctionInvoker(configurationClass);) {
 
 			HttpRequest request = Mockito.mock(HttpRequest.class);
@@ -88,6 +103,14 @@ public class FunctionInvokerHttpTests {
 			when(response.getWriter()).thenReturn(bufferedWriter);
 			handler.service(request, response);
 
+			if (statusCodeCheck) {
+				verify(response).setStatusCode(404);
+			}
+
+			if (multiHeaderCheck) {
+				verify(response).appendHeader("multiValueHeader", "123,headerThing");
+			}
+
 			// Closing the writer is done by the Framework/caller.
 			bufferedWriter.close();
 
@@ -108,6 +131,41 @@ public class FunctionInvokerHttpTests {
 
 	}
 
+	@Configuration
+	@Import({ ContextFunctionCatalogAutoConfiguration.class })
+	protected static class statusCodeSupplier {
+
+		@Bean
+		public Function<String, Message<String>> function() {
+
+			String payload = "hello";
+
+			Message<String> msg = MessageBuilder.withPayload(payload).setHeader("statusCode", 404)
+				.build();
+
+			return x -> msg;
+		};
+
+	}
+
+	@Configuration
+	@Import({ ContextFunctionCatalogAutoConfiguration.class })
+	protected static class multiValueHeaderSupplier {
+
+		@Bean
+		public Function<String, Message<String>> function() {
+
+			String payload = "hello";
+			List<Object> li = new ArrayList<Object>(asList(123, "headerThing"));
+
+			Message<String> msg = MessageBuilder.withPayload(payload).setHeader("multiValueHeader", li)
+				.build();
+
+			return x -> msg;
+		};
+
+	}
+
 	@Configuration
 	@Import({ ContextFunctionCatalogAutoConfiguration.class })
 	protected static class JsonInputFunction {
@@ -128,10 +186,9 @@ public class FunctionInvokerHttpTests {
 			return (in) -> {
 				return MessageBuilder
 						.withPayload(new OutgoingResponse("Thank you for sending the message: " + in.message))
-						.setHeader("foo", "bar").build();
+						.setHeader("statusCode", "bar").build();
 			};
 		}
-
 	}
 
 	@Configuration