Customizing error messages

[jangeorgiev]

Feature proposal

I have noticed that currently there are no way of customizing error messages returned from AJV in LB4.
I have found that there is implementation of handling error message already - AJV-Errors.
I'll be very happy to be able to customize error messages, because some of them are extremely ugly.

Example:

See code here

The code above in case of violation of patter will return
"should match pattern "^[a-z]+$""

[shadyanwar]

Related to #1867

[dhmlau]

@jangeorgiev , is #1867 that @shadyanwar mentioned above something you're looking for? If yes, I'd like to continue the discussion over there instead. Thanks.

[jangeorgiev]

No, it's not related to custom errors that are returned from HttpErrors.UnprocessableEntity().
I talk about customizing error messages of predefined validation rules see all rules here

[TomerSalton]

@YaelGit might be relevant to you?

[bajtos]

Based on the issue description and the discussion, I see two incremental steps we can make:

1. Change our validation layer to use ajv-errors to produce the error message, instead of relying on the built-in ajv messages.

2. Create an extensibility point allowing LB4 applications to further customize the error messages.

3. Probably out of scope of this issue, just something to keep in consideration: localize error messages to a different langauge based on server ENV variables and/or request headers.

Does it look like a reasonable plan to you?

I don't think this will become a priority for us in the next 3-6 months, so it's up to you to contribute these improvements. I am happy to help you along the way if you decide so.

See https://loopback.io/doc/en/contrib/code-contrib.html to get started.

[shadyanwar]

Change our validation layer to use ajv-errors to produce the error message, instead of relying on the built-in ajv messages.

@bajtos I hope to find time next weekend to work on this. It would be nice if you tell me where to start.

[bajtos]

@shadyanwar that's great to hear!

Here is the code converting AJV validation errors to an HttpError instance:

https://github.com/strongloop/loopback-next/blob/27b6accace55761d8db15442e5ca7705bab7d9fc/packages/rest/src/validation/request-body.validator.ts#L128-L137

[AaronJan]

Hi @bajtos, I made a PR (#3746 ), advice needed!

[dhmlau]

@jangeorgiev, is this issue good to close? Thanks.