Bug - Amplify/Lambda reporting uninformative errors

I describe my issue at length on Stack Overflow, but I’m unsure if it is an Amplify bug, so I’m reproducing it (more briefly) here.

Basically, when I return a response from an API Gateway/Lambda with an error statusCode (>= 400), Amplify on the frontend catches the error (good), but the error has none of the information in my structured Lambda response. Instead it’s just a Network Error, with no helpful information.

As in, the below is a successful response:

{
    "statusCode": 200,
    "headers": {
        "Access-Control-Allow-Origin": "*",
        "Access-Control-Allow-Credentials": true
    },
    "body": "{ /* whatever */ }"
}

And I’m returning this on the Lambda end like so:

callback(null, objectShownAbove);

But if I change that 200 to a 400 in my Lambda, the catch on the frontend’s Amplify.get promise is called (as it should be), and/but the error argument is a generic Network Error that doesn’t reference my response body or anything.

Error: Network Error
    at createError (createError.js:16)
    at XMLHttpRequest.handleError (xhr.js:87)

Additionally, the frontend console logs some other non-specific errors (complaining about the response headers, which are identical to the success condition):

GET https://abcdefg.execute-api.us-west-2.amazonaws.com/development/my-endpoint 403 ()

Failed to load https://abcdefg.execute-api.us-west-2.amazonaws.com/development/my-endpoint: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:3000' is therefore not allowed access. The response had HTTP status code 403.

And info about CORB issues, which doesn’t seem sensible, given that a success response works, and all that’s changed is the statusCode number.

Cross-Origin Read Blocking (CORB) blocked cross-origin response https://abcdefg.execute-api.us-west-2.amazonaws.com/development/my-endpoint with MIME type application/json.
XHR failed loading: GET "https://abcdefg.execute-api.us-west-2.amazonaws.com/development/my-endpoint".

Is this an Amplify bug? A Lambda bug? Am I doing something wrong?

Thanks.

[mlabieniec]

This does end up depending on how you configure your API Gateway, e.g. Lambda proxy etc. If you are NOT using a Lambda proxy setup, you will need to map these error responses/codes within API Gateway, see extensive post on that here: https://aws.amazon.com/blogs/compute/error-handling-patterns-in-amazon-api-gateway-and-aws-lambda/

If you are using a Lambda Proxy, you will just return as a specific type of proxy response from Lambda: https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-create-api-as-simple-proxy-for-lambda.html

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