How to add custom paramater in error object lb4?

Question

I am using strongloop 4 (lb4). I am facing one issue that in error object I need to one more custom parameter in the error object.

I want it on the global level. On every error, I want to add that custom parameter in every error message.

In loopback4 global error handling is done by src/sequence.ts.

Suppose the error message object is.

{
  "error": {
    "statusCode": 400,
    "name": "xyz",
    "message": "firstName is required"
  }
}

I want error object output like.

{
  "error": {
    "customParam" : "customParam",
    "statusCode": 400,
    "name": "xyz",
    "message": "firstName is required"
  }
}

Post your code and check out how to ask your question on stackoverflow. — kk., May 02 '19 at 11:08

score 2 · Answer 1 · answered May 10 '19 at 13:54

Cross-posting the answer I gave on GitHub in https://github.com/strongloop/loopback-next/issues/1867#issuecomment-434247807

Building HTTP error responses is a tricky business. It's easy to get it wrong and open your application to attacks.

In LoopBack (both 3.x and 4.x), we use our strong-error-handler middleware to take care of this. See Handling Errors in our docs.

Here are the important security constraints to keep in mind:

In production mode, strong-error-handler omits details from error responses to prevent leaking sensitive information:

For 5xx errors, the output contains only the status code and the status name from the HTTP specification.

For 4xx errors, the output contains the full error message (error.message) and the contents of the details property (error.details) that ValidationError typically uses to provide machine-readable details about validation problems. It also includes error.code to allow a machine-readable error code to be passed through which could be used, for example, for translation.

In debug mode, strong-error-handler returns full error stack traces and internal details of any error objects to the client in the HTTP responses.

Now that I have warned you, LoopBack 4 makes it very easy to format the error messages your way. Just provide a custom implementation of the Sequence action reject. See Customizing Sequence Actions in our docs, it explain how to create a custom send action. The solution for reject is pretty much the same, you just need a different signature for the action function.

export class CustomRejectProvider implements Provider<Reject> {
  // ...
  action({request, response}: HandlerContext, error: Error) {
    // handle the error and send back the error response
    // "response" is an Express Response object
  }
}

Caveat: some errors thrown by LB4 have only code set, these errors need a bit of pre-processing to decide what HTTP status code they should trigger. (For example, the error code ENTITY_NOT_FOUND should be mapped to the status code 404). The built-in reject action does not yet expose this pre-processing for consumption by custom reject actions. It's an oversight on our side, l created a new issue https://github.com/strongloop/loopback-next/issues/1942 to keep track of that.

score 0 · Answer 2 · answered Dec 21 '21 at 06:47

I tried adding error object into new object.

                       let error = new Error();
                        error.name = 'Invalid_OTP_AttemptsError';
                        error.status = 422;
                        error.message = 'You’ve exceeded the maximum number of One-Time Password (OTP) attempts';
                        let data={...error};
                        data.retryCount=foundMb.retryCount
                        data.resendCount=foundMb.resendCount
                        return callback(null,data);

How to add custom paramater in error object lb4?

2 Answers2