Execution failed due to configuration error: Malformed Lambda proxy response in Java

Question

My function is invoked through a proxied API Gateaway. The function executes OK but the API call returns a 502 error:

Mon Dec 30 18:16:25 UTC 2019 : Endpoint response body before transformations: "{}"
Mon Dec 30 18:16:25 UTC 2019 : Execution failed due to configuration error: Malformed Lambda proxy response
Mon Dec 30 18:16:25 UTC 2019 : Method completed with status: 502

The response should be a stringified JSON and should include a statusCode, a body and headers. All these are included below but I still get a Execution failed due to configuration error: Malformed Lambda proxy response . Help?

package example;

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;
import javax.json.Json;
import javax.json.JsonObject;
import javax.json.JsonObjectBuilder;
import javax.json.bind.Jsonb;
import javax.json.bind.JsonbBuilder;
import javax.json.bind.JsonbConfig;

/**
 *
 * @author LEVALLOIS
 */
public class Hello implements RequestHandler<Object, String> {

    public static void main(String[] args) {
        String input = "{\"key\":\"value\"}";
        new Hello().handleRequest(input, null);
    }

    @Override
    public String handleRequest(Object input, Context cntxt) {
        System.out.println("in the lambda");
        String data = input != null ? input.toString() : "{}";
        System.out.println("data is: " + data);

        JsonObjectBuilder job1 = Json.createObjectBuilder();
        job1.add("isBase64Encoded", false);
        job1.add("statusCode", 200);

        JsonObjectBuilder job2 = Json.createObjectBuilder();
        JsonObjectBuilder job3 = Json.createObjectBuilder();
        job3.add("key", "value");

        job2.add("Content-Type", "application/json");
        job1.add("headers", job2.build());
        job1.add("body", job3.build().toString());
        System.out.println(job1.build().toString());

        return job1.build().toString();
    }

}

Answer 1

Sorry, I can't answer the question. I came here to try to find an answer to more or less the same question. Hopefully the below is helpful...

I believe the output should be a valid JSon String with double-quotes and so on? Like this, which I found in another Stack Overflow thread as a valid example?

{"statusCode":200,"headers":{"Content-Type":"application/json"},"multiValueHeaders":null,"body":"{\"msg\":\"Welcome to Belarus! :)\"}","isBase64Encoded":false}

But when I tried returning this string, it still results in a 502 error. I also tried the above without the double-quoted body structure and the 4 backslashes, which looked wrong to me, but that didn't help. And many other variations of that string, but I always get the 502 error.

I did notice that when I test this from the API Gateway,the output shows

Sat Jan 11 22:53:42 UTC 2020 : Received response. Status: 200, Integration latency: 35 ms
Sat Jan 11 22:53:42 UTC 2020 : Endpoint response headers: {Date=Sat, 11 Jan 2020 22:53:42 GMT, Content-Type=application/json, Content-Length=54, Connection=keep-alive, x-amzn-RequestId=9...}
Sat Jan 11 22:53:42 UTC 2020 : Endpoint response body before transformations: "{\"statusCode\":200,\"body\":\"Welcome to xxx! :)\"}"
Sat Jan 11 22:53:42 UTC 2020 : Execution failed due to configuration error: Malformed Lambda proxy response
Sat Jan 11 22:53:42 UTC 2020 : Method completed with status: 502

ie my response message is coming out OK, but then something (the Method Response tab? which I'm pretty sure I never changed, and which the worked examples don't mention) subsequently tries to process the JSon and fails, so changes the statusCode to 502. But I don't know why it's failing.

What does it require the Json to contain?

Answer 2

Try with APIGatewayProxyResponseEvent from lambda-events or create your own class.

<dependency>
    <groupId>com.amazonaws</groupId>
    <artifactId>aws-lambda-java-events</artifactId>
    <version>2.2.9</version>
</dependency>

And inside handler:

public class MyHandler implements RequestHandler<Map<String, Object>, APIGatewayProxyResponseEvent> {

  @Override
  public APIGatewayProxyResponseEvent handleRequest(Map<String, Object> event, Context context) {
    return new APIGatewayProxyResponseEvent()
        .withStatusCode(200)
        .withBody("")
        .withIsBase64Encoded(false);
  }

}

Answer 3

I forgot to "redeploy" after changes I had made in the API Gateway console. So maybe that I had issues with the json in the response of my lambda, but more probably I did some change in my API Gateway settings, which were not taken into account because I did not re-deploy the API to account for these changes.