{"record":{"id":"c8b32ddffb2b4f8c","repo":"gofiber/fiber","slug":"failed-to-convert-w","errorCode":null,"errorMessage":"failed to convert: %w","messagePattern":"failed to convert: %w","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"warning","filePath":"helpers.go","lineNumber":1234,"sourceCode":"\t}\n\n\tswitch m {\n\tcase MethodPut, MethodDelete:\n\t\treturn true\n\tdefault:\n\t\treturn false\n\t}\n}\n\n// Convert a string value to a specified type, handling errors and optional default values.\nfunc Convert[T any](value string, converter func(string) (T, error), defaultValue ...T) (T, error) {\n\tconverted, err := converter(value)\n\tif err != nil {\n\t\tif len(defaultValue) > 0 {\n\t\t\treturn defaultValue[0], nil\n\t\t}\n\n\t\treturn converted, fmt.Errorf(\"failed to convert: %w\", err)\n\t}\n\n\treturn converted, nil\n}\n\nvar (\n\terrParsedEmptyString = errors.New(\"parsed result is empty string\")\n\terrParsedEmptyBytes  = errors.New(\"parsed result is empty bytes\")\n\terrParsedType        = errors.New(\"unsupported generic type\")\n\t// errParseValue flags a failed numeric/bool parse; callers only test err != nil.\n\terrParseValue = errors.New(\"failed to parse value\")\n)\n\n// genericParseType parses str into V. Parse failures return the static errParseValue\n// sentinel: the error is never surfaced (callers only test err != nil), so a flat\n// sentinel is enough and avoids a per-call fmt.Errorf alloc on the hot default path.\nfunc genericParseType[V GenericType](str string) (V, error) {\n\tvar v V","sourceCodeStart":1216,"sourceCodeEnd":1252,"githubUrl":"https://github.com/gofiber/fiber/blob/a105acad6c1e4576a77f01e02973f67e962bb58d/helpers.go#L1216-L1252","documentation":"Returned by the generic helpers.Convert[T] function when the supplied converter returns an error AND no default value was provided. The converter's error is wrapped as 'failed to convert: <err>'. If a default value is passed (variadic defaultValue), Convert swallows the error and returns the default instead, so this error only escapes when the caller did not supply a fallback.","triggerScenarios":"Calling fiber.Convert(value, strconv.Atoi) (no default) where value is not an integer; fiber.Convert(s, strconv.ParseBool) on a non-bool; or any Convert with a custom converter that errors and no defaultValue argument.","commonSituations":"Parsing query/path/header values into typed fields without validation; a missing or malformed env var parsed via Convert; configuration loaded from strings where a value is blank or has stray whitespace; version bumps that change the expected format.","solutions":["Provide a default to make Convert tolerant: fiber.Convert(v, strconv.Atoi, 0).","Validate/trim the input string before calling Convert (strings.TrimSpace, format check).","Switch to an explicit parser with a clear error if you need to distinguish 'missing' from 'malformed'.","At system boundaries (config load), surface Convert errors to fail fast at startup rather than at request time."],"exampleFix":"// before\nport, err := fiber.Convert(os.Getenv(\"PORT\"), strconv.Atoi)\n\n// after\nport, err := fiber.Convert(os.Getenv(\"PORT\"), strconv.Atoi, 8080)","handlingStrategy":"validation","validationCode":"// validate the string parses before calling Convert when you need to fail loudly\nif _, err := strconv.Atoi(strings.TrimSpace(value)); err != nil {\n    return fmt.Errorf(\"invalid integer %q: %w\", value, err)\n}\n// or pass a default so Convert never returns this error at all:\nv, _ := fiber.Convert(value, strconv.Atoi, 0)","typeGuard":"null","tryCatchPattern":"v, err := fiber.Convert(value, strconv.Atoi)\nif err != nil {\n    // converter failed and no default supplied\n    return fmt.Errorf(\"bad value %q: %w\", value, err)\n}","preventionTips":["Pass a defaultValue to Convert when a fallback is acceptable.","Trim whitespace and validate format before Convert when you must distinguish missing vs malformed.","At config/env load time, fail fast on Convert errors instead of deferring to request time.","Reserve the no-default Convert call for inputs whose malformed state is itself a hard error."],"tags":["parsing","validation","helpers","gofiber","generics"],"backgroundTag":null,"analyzedSha":"a105acad6c1e4576a77f01e02973f67e962bb58d","analyzedAt":"2026-08-11T17:33:26.942Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}