AWS Java Lambda compressed JSON responses fails: “Execution failed due to configuration error: Malformed Lambda proxy response”

Question

I am invoking a AWS Lambda function from the AWS API Gateway. The returned JSON needs to be zipped since it sometimes became too big (body size too large etc). However, I have some issues getting the response through the API Gateway. This is my Java code:

    @Override
    public JSONObject handleRequest(Object input, Context context) {
        String json_string = "";
        try {
            Gson gson = new Gson();
            json_string = gson.toJson(input, LinkedHashMap.class);
        } catch (ClassCastException ex) {
            json_string = (String) input;
        }

        GenerateJson generateJson = new GenerateJson ();
        String body = "";
        try {
            JSONParser parser = new JSONParser();
            Object jsonObj = parser.parse(json_string);
            JSONObject matchesobj = (JSONObject) jsonObj;

            if (matchesobj.containsKey("body")) {
                body = (String) matchesobj.get("body");
            } else {
                JSONObject error = new JSONObject();
                error.put("error", "No body with Base64 data in Request.");
                System.out.println(error.toJSONString());
                return error;
            }

        } catch (ParseException ex) {
            ex.printStackTrace();
        }

        byte[] decodedBytes = Base64.getDecoder().decode(body);
        String decodedString = new String(decodedBytes);
        // System.out.println(decodedString);

        JSONObject json = generateJson .getJson(decodedString, "", 2);

        JSONObject returnObject = new JSONObject();
        JSONObject headers = new JSONObject();
        returnObject.put("statusCode", 205);
        returnObject.put("isBase64Encoded", true);
        // returnObject.put("Content-Encoding", "gzip");

        returnObject.put("headers", headers);
        returnObject.put("body", compressStringAndReturnBase64(json.toString()));

        return (returnObject);
    }

    public static String compressStringAndReturnBase64(String srcTxt) {

        ByteArrayOutputStream rstBao = new ByteArrayOutputStream();
        GZIPOutputStream zos;
        try {
            zos = new GZIPOutputStream(rstBao);
            zos.write(srcTxt.getBytes());
            IOUtils.closeQuietly(zos);
            byte[] bytes = rstBao.toByteArray();
            String base64comp = Base64.getEncoder().encodeToString(bytes);
            System.out.println("Json String is " + srcTxt.toString().getBytes().length + " compressed " + bytes.length + " compressed Base64 " + base64comp.getBytes().length);

            return base64comp;
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return "";
    }

I've checked the Base64 output and that seems to work fine (pasted it in https://www.base64decode.org/). In addition, when I check with Postman, I get a binary blob which can be unpacked with 7-zip if I save the response to something that ends with .gz.

Under settings, the API Gateway Binary Media Types has been set to / But I'd like to have the client "see" that it is GZIPped and decode it on the fly. However, when I add the line

returnObject.put("Content-Encoding", "gzip");

I get {"message": "Internal server error"} and in the AWS API logs: Execution failed due to configuration error: Malformed Lambda proxy response

The Lambda logs are fine, so it did execute successfully, just wasn't able to be returned.

I am thinking I need some more tweaking on the API Gateway side, any ideas?

Can you show the whole class? I'm looking to see the public class XXXX implements ........ What interface are you implementing? — ᴛʜᴇᴘᴀᴛᴇʟ
Content-Encoding belongs inside headers, not as a top level key in returnObject. It appears you are building a malformed response by putting this in the wrong place. — Michael - sqlbot
Michael, your comment worked! But I can't flag it as the answer? — helloworld

Daniel Cottone Daniel Cottone · Accepted Answer · 2019-04-27T10:07:22

This sounds like the binary support setting on API Gateway isn't configured correctly; API gateway is trying to parse the response from your lambda rather than passing it on directly to the client.

You can update this setting in the console:

AWS Java Lambda compressed JSON responses fails: “Execution failed due to configuration error: Malformed Lambda proxy response”

2 Answers