The update_function_configuration currently returns an empty dict no matter what but certain lambda libraries (ie, Zappa) require a realistic return value... which is simply the current config after being updated.

https://github.com/localstack/localstack/blob/9cba1010dfcbf2b7672df4d7da46b7e8ab287f64/localstack/services/awslambda/lambda_api.py#L872

https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/lambda.html#Lambda.Client.update_function_configuration

There might also be some other magic enriching that result but my quick read-through looks like it's an empty dict.



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""" Create the final response for the given invocation result """
        if isinstance(result, Response):
            return result
        details = {
            'StatusCode': status_code,
            'Payload': result,
            'Headers': {}
        }
        if isinstance(result, dict):
            for key in ('StatusCode', 'Payload', 'FunctionError'):
                if result.get(key):
                    details[key] = result[key]
        
        payload = details['Payload']
        if payload and isinstance(payload, (str, bytes)) and payload[0] in ('[', '{', '"'):
            try:
                details['Payload'] = json.loads(details['Payload'])
            except Exception:
                pass
        
        if details.get('FunctionError'):
            details['Headers']['X-Amz-Function-Error'] = str(details['FunctionError'])
        
        response_obj = details['Payload']
        if isinstance(response_obj, (dict, list, bool)) or is_number(response_obj):