{"id":"a427a551eea7adf5","repo":"gofiber/fiber","slug":"nil-handler-in-route-s","errorCode":null,"errorMessage":"nil handler in route: %s\n","messagePattern":"nil handler in route: (.+?)\n","errorType":"panic","errorClass":null,"httpStatus":null,"severity":"error","filePath":"router.go","lineNumber":986,"sourceCode":"\t\t\tcontinue\n\t\t}\n\n\t\tapp.stack[headIndex] = append(headStack[:i], headStack[i+1:]...)\n\t\tapp.hasRoutesRefreshed = true\n\t\tatomic.AddUint32(&app.handlersCount, ^uint32(len(headRoute.Handlers)-1)) //nolint:gosec // G115 - handler count is always small\n\t\treturn\n\t}\n}\n\nfunc (app *App) register(methods []string, pathRaw string, group *Group, handlers ...Handler) {\n\t// A regular route requires at least one ctx handler\n\tif len(handlers) == 0 && group == nil {\n\t\tpanic(fmt.Sprintf(\"missing handler/middleware in route: %s\\n\", pathRaw))\n\t}\n\t// No nil handlers allowed\n\tfor _, h := range handlers {\n\t\tif h == nil {\n\t\t\tpanic(fmt.Sprintf(\"nil handler in route: %s\\n\", pathRaw))\n\t\t}\n\t}\n\n\t// Precompute path normalization ONCE\n\tif pathRaw == \"\" {\n\t\tpathRaw = \"/\"\n\t}\n\tif pathRaw[0] != '/' {\n\t\tpathRaw = \"/\" + pathRaw\n\t}\n\tpathPretty := pathRaw\n\tif !app.config.CaseSensitive {\n\t\tpathPretty = utilsstrings.ToLower(pathPretty)\n\t}\n\tif !app.config.StrictRouting && len(pathPretty) > 1 {\n\t\tpathPretty = utils.TrimRight(pathPretty, '/')\n\t}\n\tpathClean := RemoveEscapeChar(pathPretty)","sourceCodeStart":968,"sourceCodeEnd":1004,"githubUrl":"https://github.com/gofiber/fiber/blob/9a4c7e57fe0b080a04235d28a4b0d2b4b353d58c/router.go#L968-L1004","documentation":"App.register iterates over every handler in the handlers slice and panics with \"nil handler in route\" if any single handler is nil, because a nil handler would panic at request time when the router invokes it. This guard fails fast at registration instead.","triggerScenarios":"Registering a route where one of the variadic handler arguments is a nil fiber.Handler, e.g. app.Get(\"/x\", realHandler, nil). Common when a handler variable is conditionally assigned and ends up nil.","commonSituations":"Conditionally including a middleware (var mw fiber.Handler; if cond { mw = ... }) and passing mw when the condition is false. A handler slice built by appending optional middlewares that include nil. Refactoring that leaves a nil in a handler chain.","solutions":["Ensure every handler/middleware passed to a route is non-nil; filter nils out of slices before registering.","Use a no-op handler (func(c fiber.Ctx) error { return c.Next() }) instead of nil for optional branches.","Initialize handler variables to a concrete value rather than leaving the zero-value nil pointer."],"exampleFix":"// before\nvar auth fiber.Handler\nif enableAuth {\n    auth = jwt.New(...)\n}\napp.Get(\"/secret\", auth, secretHandler)\n// after\nauth := func(c fiber.Ctx) error { return c.Next() }\nif enableAuth {\n    auth = jwt.New(...)\n}\napp.Get(\"/secret\", auth, secretHandler)","handlingStrategy":"validation","validationCode":"filtered := handlers[:0]\nfor _, h := range handlers {\n    if h != nil {\n        filtered = append(filtered, h)\n    }\n}\nif len(filtered) < len(handlers) {\n    log.Printf(\"route %q: dropped %d nil handler(s)\", path, len(handlers)-len(filtered))\n}\napp.Register(methods, path, filtered...)","typeGuard":"func isNonNilHandler(h fiber.Handler) bool {\n    return h != nil\n}","tryCatchPattern":null,"preventionTips":["Initialize optional middlewares to a no-op handler (func(c fiber.Ctx) error { return c.Next() }) instead of nil.","Filter nil entries out of handler slices before passing them to route registration."],"tags":["routing","handler","nil-check","panic"],"analyzedSha":"9a4c7e57fe0b080a04235d28a4b0d2b4b353d58c","analyzedAt":"2026-08-04T21:44:03.395Z","schemaVersion":2}