gofiber/fiber · error

len constraint requires an argument

Error message

len constraint requires an argument

What it means

Error "len constraint requires an argument" thrown in gofiber/fiber.

Source

Thrown at constraint.go:389

func (maxLenConstraintType) Execute(param string, data []any) bool {
	if len(data) == 0 {
		return false
	}
	limit, ok := data[0].(int)
	if !ok {
		return false
	}
	return len(param) <= limit
}

type lenConstraintType struct{}

func (lenConstraintType) Name() string { return ConstraintLen }
func (lenConstraintType) Analyze(args []string) ([]any, error) {
	args = parseConstraintArgs(args)
	if len(args) == 0 {
		return nil, errors.New("len constraint requires an argument")
	}
	n, err := strconv.Atoi(args[0])
	if err != nil {
		return nil, fmt.Errorf("parse constraint arg: %w", err)
	}
	return []any{n}, nil
}

func (lenConstraintType) Execute(param string, data []any) bool {
	if len(data) == 0 {
		return false
	}
	limit, ok := data[0].(int)
	if !ok {
		return false
	}
	return len(param) == limit
}

View on GitHub (pinned to 9a4c7e57fe)

When it happens

Trigger: Thrown at constraint.go:389 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of gofiber/fiber@9a4c7e57fe (2026-08-04). Data as JSON: /data/errors/7a9c339884dcdd58.json. Report an issue: GitHub.