Serverless Framework Python lambda return JSON directly

Question

I'm trying to find out how can I return the response as a JSON directly using Serverless Framework. This is a function on AWS with Lambda Proxy Integration. All default setting. The goal is to from the python lambda function, the HTTP response client gets is directly a JSON object, instead of a string serialization of a JSON.

The python handler is as simple as this one

    def handle(event, context):
        log.info("Hello Wold")
        log.info(json.dumps(event, indent=2))
        return {
            "statusCode": 200,
            "body": {"foo": "bar"},
            "headers": {
                "Content-Type": "application/json"
            }
        }

The function looks like this:

    functions:
      report:
        handler: handler.handle
        events:
          - http:
              path: api/mypath
              method: post
              authorizer: aws_iam

With these configurations, the response BODY I get in Postman is:

    {
        "statusCode": 200,
        "body": {
            "foo": "bar"
        },
        "headers": {
            "Content-Type": "application/json"
        }
    }

So this is strange, why I get everything as body? How do I configure it properly so that I only get the "real" body?

Answer 1

approach #1

Use json.dumps() to convert JSON to string.

import json
def handle(event, context):
    log.info("Hello Wold")
    log.info(json.dumps(event, indent=2))
    return {
        "statusCode": 200,
        "body": json.dumps({"foo": "bar"}),
        "headers": {
            "Content-Type": "application/json"
        }
    }

approach #2

Use lambda integration and avoid json.dumps(). But this will transform your output as

{ foo = bar}

Answer 2

The body needs to be stringified when working with API Gateway

The pythonish way to do it is to pass the JSON body into the json.dumps function.

def handle(event, context):
  log.info("Hello Wold")
  log.info(json.dumps(event, indent=2))
  return {
      "statusCode": 200,
      "body": json.dumps({"foo": "bar"}),
      "headers": {
          "Content-Type": "application/json"
      }
  }