middleware for convenience error handler

[bluebrown]

Hi, I have a middleware that adds some meta headers like request and correlation id to request/response.

I noticed that the middleware is not used on the `NewError handler.

I tested this with request validation error. It would probably work if the handler returns an error or even on response validation. But it would be more useful if it would always run, imo.

Example Code

type correlator interface {
	SetCorrelationID(val uuid.UUID)
	SetRequestID(val uuid.UUID)
}

type contextKeyCorrelationID struct{}
type contextKeyRequestID struct{}

// this middleware is not called on errror, so no logging and no context data is set
func correlationMiddleware(
	req middleware.Request,
	next func(req middleware.Request) (middleware.Response, error),
) (middleware.Response, error) {
	ts := time.Now()
	rid := uuid.New()
	cid := uuid.New()

	req.Context = context.WithValue(req.Context, contextKeyCorrelationID{}, cid)
	req.Context = context.WithValue(req.Context, contextKeyRequestID{}, rid)

	res, err := next(req)

	slog.Info("request", "cid", cid, "rid", rid, "op",
		req.OperationName, "ok", err == nil, "dur", time.Since(ts))

	if err != nil {
		return res, err
	}

	if c, ok := res.Type.(correlator); ok {
		c.SetCorrelationID(cid)
		c.SetRequestID(rid)
	}

	return res, nil
}

type apiError interface {
	StatusCode() int
	Error() string
	ErrorTag() string
	ErrorCode() string
	ErrorURI() *string
}

// the handler does not have access to the context data because it was never populated
func (h *handler) NewError(ctx context.Context, err error) *api.V1ErrorResponseStatusCodeWithHeaders {
	slog.ErrorContext(ctx, "handler", "err", err)

	res := api.V1ErrorResponseStatusCodeWithHeaders{}

	if rid, ok := ctx.Value(contextKeyRequestID{}).(uuid.UUID); ok {
		res.RequestID = rid
	}

	if cid, ok := ctx.Value(contextKeyCorrelationID{}).(uuid.UUID); ok {
		res.CorrelationID = cid
	}

	res.StatusCode = http.StatusInternalServerError

	res.Response = api.V1ErrorResponse{
		Error:            "internal error",
		ErrorDescription: "an internal error occurred",
	}

	var e apiError
	if errors.As(err, &e) {
		res.StatusCode = e.StatusCode()
		res.Response.Code = e.ErrorCode()
		res.Response.Error = e.ErrorTag()
		res.Response.ErrorDescription = e.Error()
	}

	return &res

}

[bluebrown]

I tested with other kinds of errors, i.e. manually returned from the handler. The middleware runs, but the context passed to the error handler is not the one from the request. I have no idea how I could overcome. How to access the requests context from convinience error handler.