Customising Responses

API Gateway expects responses in a specific format from Lambda Proxy integrations. The response needs to be a JSON object containing these fields:

• statusCode should be a number containing the numeric HTTP response code. The number 200 means OK.
• body should be a string representing the response contents.
• headers is an optional argument​ and can contain a map of HTTP response headers.

SAM assumes that you’ll use API Gateway to create JSON APIs, so unless the response provides a content type, it assumes that you’ll be sending back a serialised JSON object. That’s why the sample function formats the response object using JSON.stringify: