GH-434 Added generic FunctionInvoker for AWS

- Added generic FunctionInvoker capable of handling the request generically without requiring user to implemen specific AWS request handler

Resolves #434

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

@@ -0,0 +1,143 @@
+/*
+ * Copyright 2019-2019 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.aws;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.nio.charset.StandardCharsets;
+import java.util.Calendar;
+import java.util.Collections;
+import java.util.Date;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.Function;
+
+import com.amazonaws.services.lambda.runtime.Context;
+import com.amazonaws.services.lambda.runtime.RequestStreamHandler;
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.JsonDeserializer;
+import com.fasterxml.jackson.databind.MapperFeature;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.module.SimpleModule;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.cloud.function.context.FunctionCatalog;
+import org.springframework.cloud.function.context.catalog.FunctionInspector;
+import org.springframework.cloud.function.utils.FunctionClassUtils;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.core.env.Environment;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.support.MessageBuilder;
+import org.springframework.util.Assert;
+import org.springframework.util.StreamUtils;
+import org.springframework.util.StringUtils;
+
+/**
+ *
+ * @author Oleg Zhurakousky
+ * @since 3.1
+ *
+ *        see
+ *        https://docs.aws.amazon.com/apigateway/latest/developerguide/set-up-lambda-proxy-integrations.html#api-gateway-simple-proxy-for-lambda-output-format
+ */
+public class FunctionInvoker implements RequestStreamHandler {
+
+	private static Log logger = LogFactory.getLog(FunctionInvoker.class);
+
+	private ObjectMapper mapper;
+
+	private boolean started;
+
+	private Function<Message<byte[]>, Message<byte[]>> function;
+
+	@Override
+	public void handleRequest(InputStream input, OutputStream output, Context context) throws IOException {
+		if (!this.started) {
+			this.start();
+		}
+
+		Message<byte[]> requestMessage = this.generateMessage(input, context);
+
+		Message<byte[]> responseMessage = this.function.apply(requestMessage);
+
+		byte[] responseBytes = responseMessage.getPayload();
+		if (requestMessage.getHeaders().containsKey("httpMethod")) {
+			Map<String, Object> response = new HashMap<String, Object>();
+			response.put("isBase64Encoded", false);
+			response.put("statusCode", 200);
+			response.put("body", new String(responseMessage.getPayload(), StandardCharsets.UTF_8));
+			response.put("headers", Collections.singletonMap("foo", "bar"));
+
+			responseBytes = mapper.writeValueAsBytes(response);
+		}
+
+		StreamUtils.copy(responseBytes, output);
+	}
+
+	private void start() {
+		ConfigurableApplicationContext context = SpringApplication.run(FunctionClassUtils.getStartClass());
+		Environment environment = context.getEnvironment();
+		String functionName = environment.getProperty("spring.cloud.function.definition");
+		FunctionCatalog functionCatalog = context.getBean(FunctionCatalog.class);
+		this.mapper = context.getBean(ObjectMapper.class);
+		this.configureObjectMapper();
+
+		if (logger.isInfoEnabled()) {
+			logger.info("Locating function: '" + functionName + "'");
+		}
+
+		this.function = functionCatalog.lookup(functionName, "application/json");
+		Assert.notNull(this.function, "Failed to lookup function " + functionName);
+
+		if (!StringUtils.hasText(functionName)) {
+			FunctionInspector inspector = context.getBean(FunctionInspector.class);
+			functionName = inspector.getRegistration(this.function).getNames().toString();
+		}
+
+		if (logger.isInfoEnabled()) {
+			logger.info("Located function: '" + functionName + "'");
+		}
+		this.started = true;
+	}
+
+	private void configureObjectMapper() {
+		SimpleModule module = new SimpleModule();
+		module.addDeserializer(Date.class, new JsonDeserializer<Date>() {
+			@Override
+			public Date deserialize(JsonParser jsonParser, DeserializationContext deserializationContext)
+					throws IOException {
+				Calendar calendar = Calendar.getInstance();
+				calendar.setTimeInMillis(jsonParser.getValueAsLong());
+				return calendar.getTime();
+			}
+		});
+		mapper.registerModule(module);
+		mapper.configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES, true);
+	}
+
+	private Message<byte[]> generateMessage(InputStream input, Context context) throws IOException {
+		byte[] payload = StreamUtils.copyToByteArray(input);
+
+		Message<byte[]> message = MessageBuilder.withPayload(payload).setHeader("aws-context", context).build();
+
+		return message;
+	}
+}