if err, ok := err.(*caddy.ControllerArgErr); ok { fmt.Printf("Error with argument on line %d: %v\n", err.Line(), err.ArgErr()) }
func foo(controller *caddy.Controller) error { if controller.Next() { return &caddy.ControllerArgErr{ Controller: controller, Message: "missing required argument", } } // ... }In this example, we define a function that requires a certain argument to be present in the Caddyfile. If the argument is missing, we return a new instance of ControllerArgErr with the error message "missing required argument". Overall, the Controller ArgErr is a useful struct for representing errors related to arguments in Caddyfile directives. It is part of the Caddy web server project, specifically in the github.com/mholt/caddy package.