gofiber/fiber · error

range constraint requires two arguments

Error message

range constraint requires two arguments

What it means

The range route-parameter constraint enforces that a matched path segment, parsed as an integer, lies within an inclusive [lo, hi] range. It is declared inline as :param<range(lo,hi)>. Its Analyze method requires two integer arguments; with fewer than two it returns this error. The internal newConstraint call site swallows Analyze errors, so this surfaces only when Analyze is invoked directly or through a delegating custom-constraint wrapper.

Solutions

1. Provide two integer arguments: :param<range(1,100)>.
2. If a single bound suffices, use :param<min(n)> or :param<max(n)>.
3. Confirm the comma separator is not escaped (\, would merge arguments).
4. For length-based ranges use :param<betweenLen(lo,hi)> instead.

Example fix

// before
app.Get("/n/:id<range(10)>", h)
// after
app.Get("/n/:id<range(10,100)>", h)

var rangeArgs = regexp.MustCompile(`:([^<]+)<range\(([^)]*)\)>`)
for _, p := range routePatterns {
    m := rangeArgs.FindStringSubmatch(p)
    if m != nil && len(strings.Split(m[2], ",")) != 2 {
        log.Fatalf("route %q: range needs exactly two integer args", p)
    }
}

typed, err := rangeConstraint.Analyze(args)
if err != nil {
    return fmt.Errorf("route range constraint: %w", err)
}

When it happens

Trigger: Calling Analyze on a range constraint with fewer than two arguments, derived from a route pattern such as :id<range(5)>, :id<range()>, :id<range>, or :id<range(1\,10)> (escaped comma). parseConstraintArgs splits a single-element slice on the comma; without a comma it stays a one-element slice and len(args)<2 trips the guard at constraint.go:504.

Common situations: Forgetting the upper bound; an escaped comma merging two args into one; confusing range (numeric) with betweenLen (string-length).

Related errors

• betweenLen constraint requires two arguments
• max constraint requires an argument
• min constraint requires an argument
• regex constraint requires a pattern argument
• Domain pattern cannot be empty

AI-assisted analysis of gofiber/fiber@a105acad6c (2026-08-11). Data as JSON: /api/errors/0977b9b97e5991d2. Report an issue: GitHub.

Appendix: source

Thrown at constraint.go:504

func (maxConstraintType) Execute(param string, data []any) bool {
	if len(data) == 0 {
		return false
	}
	limit, ok := data[0].(int)
	if !ok {
		return false
	}
	num, err := strconv.Atoi(param)
	return err == nil && num <= limit
}

type rangeConstraintType struct{}

func (rangeConstraintType) Name() string { return ConstraintRange }
func (rangeConstraintType) Analyze(args []string) ([]any, error) {
	args = parseConstraintArgs(args)
	if len(args) < 2 {
		return nil, errors.New("range constraint requires two arguments")
	}
	lo, err := strconv.Atoi(args[0])
	if err != nil {
		return nil, fmt.Errorf("parse constraint arg: %w", err)
	}
	hi, err := strconv.Atoi(args[1])
	if err != nil {
		return nil, fmt.Errorf("parse constraint arg: %w", err)
	}
	return []any{lo, hi}, nil
}

func (rangeConstraintType) Execute(param string, data []any) bool {
	if len(data) < 2 {
		return false
	}
	lo, ok := data[0].(int)
	if !ok {

View on GitHub (pinned to a105acad6c)