Error: RIE Gateway expects a `cookies` fields in the responses

[c-gabdalla]

Hello!

I have a lambda that is served using RIE, which was set up using the following docker-compose.yaml:

version: '2.4'

services:
  # https://github.com/eagletmt/aws-lambda-rie-gateway
  apigw:
    image: public.ecr.aws/eagletmt/aws-lambda-rie-gateway
    environment:
      TARGET_URL: http://app:8080
    ports:
      - 8080:8080

  app:
    image: drift_checker
    build: drift_checker
    working_dir: /usr/src
    mem_limit: 128m
    cpus: 0.2

And with the following code:

def handler(event, context):
    return {
        "statusCode": 200,
        "headers": {
            "Content-Type": "application/json"
        },
        "body": {}
    }

The following error is returned:

src-apigw-1  | 2022-11-11T22:39:57.504677Z  INFO aws_lambda_rie_gateway: Send upstream request: {"version":"2.0","routeKey":null,"rawPath":"/","rawQueryString":null,"cookies":null,"headers":{"host":"docker:8080","user-agent":"curl/7.82.0","accept":"*/*","content-length":"197","content-type":"application/x-www-form-urlencoded"},"queryStringParameters":{},"pathParameters":{},"requestContext":{"routeKey":"$default","accountId":"","stage":"$default","requestId":"","authorizer":null,"apiId":"","domainName":"","domainPrefix":"","time":"11/Nov/2022:22:39:57 +0000","timeEpoch":1668206397504,"http":{"method":"POST","path":"/","protocol":"HTTP/1.1","sourceIp":null,"userAgent":null},"authentication":null},"stageVariables":{},"body":"[REDACTED]","isBase64Encoded":true}
src-apigw-1  | 2022-11-11T22:40:03.685465Z ERROR aws_lambda_rie_gateway: error decoding response body: missing field `cookies` at line 1 column 3369

Of course, if I change the implementation to include a cookies field in the response, it works flawlessly =D

Now, I don´t know if there is documentation describing how each response interface should be treated, but I would like to suggest making cookies an optional attribute.

What do you think?