API Gateway decorators for transforming request and response templates to lambda Proxy

handler.py

def handler_pre_dispatch(handler):
    """
    Request decorator to convert APIG Proxy params to the old style
    Merge GET, POST, STAGE into new event dict
    :param handler: resource handler
    :return:
    """
    def request_decorator(event, content):
        event_decorated = {}

        if event['queryStringParameters']:
            event_decorated.update(event['queryStringParameters'])

        if event['pathParameters']:
            event_decorated.update(event['pathParameters'])

        if event['stageVariables']:
            event_decorated.update(event['stageVariables'])

        return handler(event_decorated, content)

    return request_decorator


def handler_callback(handler):
    """
    Response decorator to convert old style exceptions
    and responses to APIG Proxy response format

    :param handler: resource handler
    :return:
    """
    def response_decorator(event, context):
        try:
            response = handler(event, context)
            raise Exception(json.dumps(response))
        except Exception as e:
            exceptions = collections.OrderedDict((
                (400, 'Bad Request:'),
                (422, 'Unprocessable Entity:'),
                (200, '')
            ))

            for code, message in exceptions.items():
                if str(e).startswith(message):
                    message = str(e).replace(message, '') if message else str(e)
                    break

            return {
                "statusCode": code,
                "headers": {
                    "Content-Type": "application/json",
                    "Accept": "application/json"
                },
                "body": message
            }

    return response_decorator
  
 

@handler_pre_dispatch
@handler_callback
def hello_handler(event, context):
    return services.say_hello(event, context)