gofiber/fiber · error

missing handler/middleware in route: %s

Error message

missing handler/middleware in route: %s

What it means

App.register requires that a regular route (one not created via a Group) has at least one handler or middleware. Calling register with an empty handlers slice and no group panics with "missing handler/middleware in route", because there would be nothing to execute for matching requests.

Source

Thrown at router.go:981

	norm := app.normalizePath(path)

	headStack := app.stack[headIndex]
	for i, headRoute := range slices.Backward(headStack) {
		if headRoute.path != norm || headRoute.mount || headRoute.use || !headRoute.autoHead {
			continue
		}

		app.stack[headIndex] = append(headStack[:i], headStack[i+1:]...)
		app.hasRoutesRefreshed = true
		atomic.AddUint32(&app.handlersCount, ^uint32(len(headRoute.Handlers)-1)) //nolint:gosec // G115 - handler count is always small
		return
	}
}

func (app *App) register(methods []string, pathRaw string, group *Group, handlers ...Handler) {
	// A regular route requires at least one ctx handler
	if len(handlers) == 0 && group == nil {
		panic(fmt.Sprintf("missing handler/middleware in route: %s\n", pathRaw))
	}
	// No nil handlers allowed
	for _, h := range handlers {
		if h == nil {
			panic(fmt.Sprintf("nil handler in route: %s\n", pathRaw))
		}
	}

	// Precompute path normalization ONCE
	if pathRaw == "" {
		pathRaw = "/"
	}
	if pathRaw[0] != '/' {
		pathRaw = "/" + pathRaw
	}
	pathPretty := pathRaw
	if !app.config.CaseSensitive {
		pathPretty = utilsstrings.ToLower(pathPretty)

View on GitHub (pinned to 9a4c7e57fe)

Solutions

1. Provide at least one handler argument to the route registration method, e.g. app.Get("/health", healthHandler).
2. When registering programmatically, assert the handlers slice is non-empty before calling register-equivalents.
3. Use a linter or code review to catch method shortcuts with missing handler args.

Example fix

// before
app.Get("/health")
// after
app.Get("/health", func(c fiber.Ctx) error {
    return c.SendString("ok")
})

handlers := []fiber.Handler{ /* built elsewhere */ }
if len(handlers) == 0 {
    log.Fatalf("route %q has no handler/middleware", path)
}
app.Register(methods, path, handlers...)

When it happens

Trigger: Indirectly via app.Get("/path") with no handler arguments, or any HTTP-method shortcut called with only a path. Internal callers of register that pass no handlers and no group hit this guard too.

Common situations: Typing app.Get("/health") and forgetting the handler. Refactoring that removes the handler argument but leaves the route call. Building routes generically and an empty handler slice slips through.

Related errors

• use: invalid handler %v
• route handler 'fn' cannot be nil
• route handler 'fn' cannot be nil
• nil handler in route: %s
• runtime.Goexit() called in handler or server panic

AI-assisted analysis of gofiber/fiber@9a4c7e57fe (2026-08-04). Data as JSON: /data/errors/be8bfb4da57ee09c.json. Report an issue: GitHub.