upstream-mattermost/server/public/pluginapi/error.go

package pluginapi

import (
	"net/http"

	"github.com/pkg/errors"

	"github.com/mattermost/mattermost/server/public/model"
)

// ErrNotFound is returned by the plugin API when an object is not found.
var ErrNotFound = errors.New("not found")

// normalizeAppErr returns a truly nil error if appErr is nil as well as normalizing a class
// of non-nil AppErrors to simplify use within plugins.
//
// This doesn't happen automatically when a *model.AppError is cast to an error, since the
// resulting error interface has a concrete type with a nil value. This leads to the seemingly
// impossible:
//
//	var err error
//	err = func() *model.AppError { return nil }()
//	if err != nil {
//	    panic("err != nil, which surprises most")
//	}
//
// Fix this problem for all plugin authors by normalizing to special case the handling of a nil
// *model.AppError. See https://golang.org/doc/faq#nil_error for more details.
func normalizeAppErr(appErr *model.AppError) error {
	if appErr == nil {
		return nil
	}

	if appErr.StatusCode == http.StatusNotFound {
		return ErrNotFound
	}

	return appErr
}