Some example how to return all errors as JSON/HTTP code?

[bapcyk]

I am on LTS-16.4. So, servant-server is 0.16.2. I want to return errors like:

1. unexpected runtime exception like divison on 0, error call and similar as HTTP 500 and some JSON object
2. errors thrown by me as HTTP , JSON object
3. errors from REST endpoints parsing procedure (like wrong URL, missing part of the endpoint, and similar) as some HTTP code and JSON object

and I need to do it in a simple and general way, so not to do 3 different approaches for these 3 cases, but the one simple general solution. I know how to achieve 2, but I don't know how to do 1 and 2. I don't know how https://docs.servant.dev/en/stable/cookbook/custom-errors/CustomErrors.html is relevant, but as I understood already, the servant still is not for production usage , because of breaking changes: I cannot find any Servant.Server.Internal.ErrorFormatter in my 0.16.2 version... So, my question is simple: is any adequate way to do it in servant: I suppose such obvious and simple task should be solved a long time ago and maybe it is just not described in the tutorials and documentation? If it is, then please, add some description in the tutorial - I cannot find any answer for all 3 cases in the Web, if no such a solution at all, please, write somewhere in the documentation that servant still is not for production usage.

[fisx]

will be fixed by #1314 has been fixed in 0.18.

[bapcyk]

OK, if it's planned, then I will close the issue.

The last question: is it possible to do it today in some simple way like a temporary workaround?

[fisx]

Sorry, that was sloppy reading on my side: you already found the solution to your issue, you just need to upgrade servant. 0.16 is quite outdated. I updated my earlier comment.

To render 5xx errors I would go for a middleware. Feel free to open another issue to extend https://docs.servant.dev/en/stable/cookbook/custom-errors/CustomErrors.html; my feeling is we don't want to do that, but I would have to think about it more.