AddCustomAttributes doesn't work in the app.ErrorHandler

[daenney]

I have a custom error handler. In it I do a simple slogfiber.AddCustomAttributes() so I can hopefully add the error itself to the log message. However, none of the attributes added in the error handler ever make it into the output.

func apiErrorHandler(ctx *fiber.Ctx, err error) error {
    slogfiber.AddCustomAttributes(ctx, slog.String("hi", "there"))

    var e *fiber.Error
    code := fiber.StatusInternalServerError
    if errors.As(err, &e) {
        code = e.Code
    }

    return ctx.Status(code).JSON(...)
}

The hi key with value there is always missing, and so is any other attribute added in the error handler.

[samber]

It works when i test with this function. Can you please create a small repository with a short example?

[daenney]

Sorry for the delay in response, life took a busy turn. I suspect I've misunderstood something about setting up the error handler really.

I've tried to recreate a small sample: https://gist.github.com/daenney/19faee34bc7bee79a5569b8604022fad

When doing a request against /found I get:

$ curl http://127.0.0.1:46229/found
found it

time=2023-11-13T17:40:06.712+01:00 level=INFO msg="Incoming request" time=2023-11-13T17:40:06.712+01:00 latency=10.41µs method=GET host=127.0.0.1:46229 path=/found route=/found status=200 ip=127.0.0.1 user-agent=curl/8.4.0 referer=""

$ curl http://127.0.0.1:46229/not-a-route
error handler

time=2023-11-13T17:40:15.528+01:00 level=INFO msg="Incoming request" time=2023-11-13T17:40:15.528+01:00 latency=13.827µs method=GET host=127.0.0.1:46229 path=/not-a-route route=/ status=200 ip=127.0.0.1 user-agent=curl/8.4.0 referer=""
in the api error handler

The go.mod has the following versions:

github.com/gofiber/fiber/v2 v2.50.0
github.com/samber/slog-fiber v1.8.0

[daenney]

Also, on closer inspection the status in the log line isn't correct either. If I print the value of code in the handler, I get a 404. But I consistently get status=200 in the log line.

The HTTP status code returned is a 404 though:

> GET /not-a-route HTTP/1.1
> Host: 127.0.0.1:35109
> User-Agent: curl/8.4.0
> Accept: */*
> 
< HTTP/1.1 404 Not Found
< Date: Mon, 13 Nov 2023 17:13:35 GMT
< Content-Type: text/plain; charset=utf-8
< Content-Length: 13
< 
* Connection #0 to host 127.0.0.1 left intact
error handler⏎    

[samber]

About the 404 error, you should add a "catch-all" handler:

        // ...

    app.Use(slogfiber.NewWithConfig(logger, config))
    app.Use("/found", func(ctx *fiber.Ctx) error {
        return ctx.SendString("found it")
    })

    // Last handler
    app.Use(func(c *fiber.Ctx) error {
        return c.SendStatus(fiber.StatusNotFound)
    })

    app.Listen(":1111")

The logger is executed before error handler, so your custom attribute won't be registred into log record attributes

[daenney]

So custom attributes don't work in the ErrorHandler after all?

For the 404, the error handler does get executed, since the output from the error handler gets returned to the client.

[samber]

We might think about doing both a middleware and error handler.

[samber]

hi @daenney

I just made a proposal here: #14

[daenney]

Ah brilliant, I will take a look!

[samber]

After the merge of #19 this should be fixed.

Can you check and return it to me if it's not working well?