enabling users to set custom statusCode

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

@@ -18,6 +18,8 @@ package org.springframework.cloud.function.adapter.gcp;
 
 import java.io.BufferedReader;
 import java.nio.charset.StandardCharsets;
+import java.util.Collection;
+import java.util.Iterator;
 import java.util.Map.Entry;
 import java.util.function.Function;
 
@@ -32,6 +34,7 @@ import org.apache.commons.logging.LogFactory;
 import org.springframework.cloud.function.context.AbstractSpringFunctionAdapterInitializer;
 import org.springframework.cloud.function.context.config.ContextFunctionCatalogAutoConfiguration;
 import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageHeaders;
 import org.springframework.messaging.support.MessageBuilder;
 import org.springframework.util.Assert;
 import org.springframework.util.MimeTypeUtils;
@@ -91,18 +94,38 @@ public class FunctionInvoker extends AbstractSpringFunctionAdapterInitializer<Ht
 	 */
 	@Override
 	public void service(HttpRequest httpRequest, HttpResponse httpResponse) throws Exception {
+
 		Function<Message<BufferedReader>, Message<byte[]>> function = lookupFunction();
 
 		Message<BufferedReader> message = getInputType() == Void.class || getInputType() == null ? null
 				: MessageBuilder.withPayload(httpRequest.getReader()).copyHeaders(httpRequest.getHeaders()).build();
+
 		Message<byte[]> result = function.apply(message);
 
 		if (result != null) {
+			MessageHeaders headers = result.getHeaders();
 			httpResponse.getWriter().write(new String(result.getPayload(), StandardCharsets.UTF_8));
-			for (Entry<String, Object> header : result.getHeaders().entrySet()) {
-				httpResponse.appendHeader(header.getKey(), header.getValue().toString());
+			for (Entry<String, Object> header : headers.entrySet()) {
+				Object values = header.getValue();
+				if (values instanceof Collection<?>) {
+					StringBuilder sb = new StringBuilder();
+					for (Iterator iterator = ((Collection<?>) values).iterator(); iterator.hasNext();) {
+						sb.append(iterator.next());
+						if (iterator.hasNext()) {
+							sb.append(",");
+						}
+					}
+					httpResponse.appendHeader(header.getKey(), sb.toString());
+				}
+				else {
+					httpResponse.appendHeader(header.getKey(), header.getValue().toString());
+				}
 			}
 			httpRequest.getContentType().ifPresent(contentType -> httpResponse.setContentType(contentType));
+
+			if (headers.containsKey("statusCode")) {
+				httpResponse.setStatusCode((int) headers.get("statusCode"));
+			}
 		}
 	}