Execution failed due to configuration error: Malformed Lambda proxy response while sending back nested JSON value

Question

I have a lambda function, which is returning me a value from dynamdb table. The value is in nested jason format.

When I test the lambda in it's own console it is working fine. BUT When I integrate it with API gateway it is giving me an internal server error with this message.

Execution failed due to configuration error: Malformed Lambda proxy response

here is my response body

 return {
            "isBase64Encoded": "true",
            "statusCode": 200,
            "headers": { "Access-Control-Allow-Methods": "*", "Access-Control-Allow-Headers": "*", "Access-Control-Allow-Origin": "*" },
            "body": response
        }

Does anyone know this issue.

I tried with

return {
            "isBase64Encoded": "true",
            "statusCode": 200,
            "headers": { "Access-Control-Allow-Methods": "*", "Access-Control-Allow-Headers": "*", "Access-Control-Allow-Origin": "*" },
            "body": json.dumps(response['Items'])
        }

it seems to be working.

What is the issue causing this? because if I have a normal JSON.

"body": response

works properly. The issue only comes when there is nested JSON

Here is the JSON object:

[
   {
      "time_stamp":"2021-01-13 06:02:42",
      "broker_id":"broker1",
      "load_id":"ab6fd05f-3f54-44dc-ae6d-28e924fe1ae2",
      "messages":[
         {
            "date":"22:32",
            "messanger_id":"[email protected]",
            "message":"Hello",
            "user":"carrier"
         },
         {
            "date":"22:35",
            "messanger_id":"[email protected]",
            "message":"Hi",
            "user":"broker"
         }
      ],
      "carrier_id":"carrier1"
   },
   {
      "time_stamp":"2021-01-13 06:03:32",
      "broker_id":"broker1",
      "load_id":"ab6fd05f-3f54-44dc-ae6d-28e924fe1ae2",
      "messages":[
         {
            "date":"22:32",
            "messanger_id":"[email protected]",
            "message":"Hello",
            "user":"carrier"
         },
         {
            "date":"22:35",
            "messanger_id":"[email protected]",
            "message":"Hi",
            "user":"broker"
         }
      ],
      "carrier_id":"carrier2"
   }
]

Answer 1

It works with json.dumps because you are getting JSON string, which is required for proxy lambda integration. From docs:

With the Lambda proxy integration, the Lambda function must return output of the following format:

{
    statusCode: "...",            // a valid HTTP status code
    headers: { 
        custom-header: "..."      // any API-specific custom header
    },
    body: "...",                  // a JSON string.
    isBase64Encoded:  true|false  // for binary support
}

As you can see JSON string must be used in body. You can't return plain json object as you do when you write "body": response['Items']