Example implementation for Aws API Gateway

User can extend SpringBootApiGatewayRequestHandler instead of the
generic SpringBootRequestHandler. It ties the code to AWS and the
API Gateway, but at least it supports the incoming data fully.

Fixes gh-111, closes gh-136

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

@@ -0,0 +1,96 @@
+package org.springframework.cloud.function.adapter.aws;
+
+import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent;
+import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyResponseEvent;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.cloud.function.context.catalog.FunctionInspector;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageHeaders;
+import org.springframework.messaging.support.GenericMessage;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class SpringBootApiGatewayRequestHandler extends SpringBootRequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
+
+	@Autowired
+	private ObjectMapper mapper;
+
+	@Autowired
+	private FunctionInspector inspector;
+
+	public SpringBootApiGatewayRequestHandler(Class<?> configurationClass) {
+		super(configurationClass);
+	}
+
+	public SpringBootApiGatewayRequestHandler() {
+		super();
+	}
+
+	protected Object convertEvent(APIGatewayProxyRequestEvent event) {
+		Object body = deserializeBody(event.getBody());
+		if (functionAcceptsMessage()) {
+			return new GenericMessage<>(body, getHeaders(event));
+		} else {
+			return body;
+		}
+	}
+
+	private boolean functionAcceptsMessage() {
+		return inspector.isMessage(function());
+	}
+
+	private Object deserializeBody(String json) {
+		try {
+			return mapper.readValue(json, getInputType());
+		} catch (Exception e) {
+			throw new IllegalStateException("Cannot convert event", e);
+		}
+	}
+
+	private MessageHeaders getHeaders(APIGatewayProxyRequestEvent event) {
+		Map<String, Object> headers = new HashMap<>();
+		if (event.getHeaders() != null) {
+			headers.putAll(event.getHeaders());
+		}
+		headers.put("request", event);
+		return new MessageHeaders(headers);
+	}
+
+	protected APIGatewayProxyResponseEvent convertOutput(Object output) {
+		if (functionReturnsMessage(output)) {
+			Message message = (Message) output;
+			return new APIGatewayProxyResponseEvent()
+					.withStatusCode((Integer) message.getHeaders().getOrDefault("statusCode", 200))
+					.withHeaders(toResponseHeaders(message.getHeaders()))
+					.withBody(serializeBody(message.getPayload()));
+		} else {
+			return new APIGatewayProxyResponseEvent()
+					.withStatusCode(200)
+					.withBody(serializeBody(output));
+
+
+		}
+	}
+
+	private boolean functionReturnsMessage(Object output) {
+		return output instanceof Message;
+	}
+
+	private Map<String, String> toResponseHeaders(MessageHeaders messageHeaders) {
+		Map<String, String> responseHeaders = new HashMap<>();
+		messageHeaders.forEach((key, value) -> responseHeaders.put(key, value.toString()));
+		return responseHeaders;
+	}
+
+	private String serializeBody(Object body) {
+		try {
+			return mapper.writeValueAsString(body);
+		} catch (JsonProcessingException e) {
+			throw new IllegalStateException("Cannot convert output", e);
+		}
+	}
+
+}

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

@@ -49,7 +49,7 @@ public class SpringBootRequestHandler<E, O> extends SpringFunctionInitializer im
 	private Object result(Object input, Flux<?> output) {
 		List<Object> result = new ArrayList<>();
 		for (Object value : output.toIterable()) {
-			result.add(value);
+			result.add(convertOutput(value));
 		}
 		if (isSingleValue(input) && result.size()==1) {
 			return result.get(0);
@@ -72,4 +72,8 @@ public class SpringBootRequestHandler<E, O> extends SpringFunctionInitializer im
 		return event;
 	}
 
+    protected O convertOutput(Object output) {
+        return (O) output;
+    }
+
 }

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

@@ -136,7 +136,7 @@ public class SpringFunctionInitializer implements Closeable {
 		return Object.class;
 	}
 
-	private Object function() {
+	protected Object function() {
 		return this.function != null ? this.function
 				: (this.consumer != null ? this.consumer : this.supplier);
 	}