AWS lambda api gateway error “Malformed Lambda proxy response” - aws-lambda

Question

My AWS ApiGateway invokes this lambda function :
const handler = (event, context) => {
const theResponse = {
"statusCode": 200,
"isBase64Encoded": false,
"headers": {
"Content-Type": "application/json"
},
"body": "hello, world"
};
switch (event.httpMethod) {
case 'GET':
theResponse["body"] = `method ${event.httpMethod} detected`;
break;
default:
theResponse["statusCode"] = 404;
theResponse["body"] = `Unsupported method ${event.httpMethod} detected`;
break;
}
return theResponse;
};
module.exports = {
handler,
};
Any thoughts to why this errors with :
{"message": "Internal server error"}
Received response. Status: 200, Integration latency: 344 ms
Endpoint response body before transformations: null
Execution failed due to configuration error: Malformed Lambda proxy response
Method completed with status: 502
I tried replacing return (theResponse); with return JSON.stringify(theResponse); but this also returns the same error.
However if I replace return theResponse; with return {"statusCode":200, "body":"hello, world"}; then the API executes without errors.
Looks to me like a lamda_proxy integration issue but I can't see why. thanks.

Answer 1

Bearrider!
I guess it is related to the way you are building your response object:
Try stringify only the body attribute:
case 'GET':
theResponse["body"] = JSON.stringify(`method ${event.httpMethod} detected`);
break;
default:
theResponse["statusCode"] = 404;
theResponse["body"] = JSON.stringify(`Unsupported method ${event.httpMethod} detected`);
break;
}