{"record":{"id":"257591d2b8dda296","repo":"gofiber/fiber","slug":"binder-custom-binder-not-found-please-be-sure-to","errorCode":null,"errorMessage":"binder: custom binder not found, please be sure to enter the right name","messagePattern":"binder: custom binder not found, please be sure to enter the right name","errorType":"validation","errorClass":null,"httpStatus":null,"severity":"error","filePath":"error.go","lineNumber":56,"sourceCode":"var (\n\t// ErrRangeMalformed is returned for a syntactically invalid Range header,\n\t// which RFC 9110 Section 14.2 allows a server to reject; it carries a\n\t// 400 Bad Request status so propagating it does not surface as a 500.\n\tErrRangeMalformed = NewError(StatusBadRequest, \"range: malformed range header string\")\n\t// ErrRangeUnsupported is returned for a Range header whose range unit is\n\t// not \"bytes\". RFC 9110 Section 14.2 requires an origin server to IGNORE\n\t// a Range header field with a range unit it does not understand, so\n\t// callers receiving this error should serve the full representation\n\t// instead of returning an error response. It still carries a\n\t// 400 Bad Request status as a safety net, so blind propagation does not\n\t// surface as a 500.\n\tErrRangeUnsupported   = NewError(StatusBadRequest, \"range: unsupported range unit\")\n\tErrRangeTooLarge      = NewError(StatusRequestedRangeNotSatisfiable, \"range: too many ranges\")\n\tErrRangeUnsatisfiable = errors.New(\"range: unsatisfiable range\")\n)\n\n// Binder errors\nvar ErrCustomBinderNotFound = errors.New(\"binder: custom binder not found, please be sure to enter the right name\")\n\n// Format errors\nvar (\n\t// ErrNoHandlers is returned when c.Format is called with no arguments.\n\tErrNoHandlers = errors.New(\"format: at least one handler is required, but none were set\")\n)\n\n// gofiber/schema errors\ntype (\n\t// ConversionError Conversion error exposes the internal schema.ConversionError for public use.\n\tConversionError = schema.ConversionError\n\t// UnknownKeyError error exposes the internal schema.UnknownKeyError for public use.\n\tUnknownKeyError = schema.UnknownKeyError\n\t// EmptyFieldError error exposes the internal schema.EmptyFieldError for public use.\n\tEmptyFieldError = schema.EmptyFieldError\n\t// MultiError error exposes the internal schema.MultiError for public use.\n\tMultiError = schema.MultiError\n)","sourceCodeStart":38,"sourceCodeEnd":74,"githubUrl":"https://github.com/gofiber/fiber/blob/a105acad6c1e4576a77f01e02973f67e962bb58d/error.go#L38-L74","documentation":"ErrCustomBinderNotFound is returned by Bind.Custom (bind.go:235) when no previously registered CustomBinder has a matching Name(). Custom binders are registered with App.RegisterCustomBinder and looked up by exact name match in c.Bind().Custom(name, dest).","triggerScenarios":"Calling c.Bind().Custom(\"formBinder\", &v) when app.RegisterCustomBinder was never called with a binder whose Name() returns \"formBinder\", or when the name string is misspelled or has different casing. bind.go:224-236 iterates app.customBinders and falls through to the sentinel.","commonSituations":"Registering the binder on a different App instance (e.g. on a sub-app or test app); typos in the binder name; renaming a binder's Name() method without updating call sites; casing mismatch (Go string comparison is case-sensitive).","solutions":["Register the binder on the same App that serves the request: app.RegisterCustomBinder(&myBinder{}).","Verify Name() returns the exact string passed to Custom; share the name via a constant to avoid drift.","Confirm the binder is registered before the server starts, not after, since registration appends to app.customBinders at call time."],"exampleFix":"// before\napp.RegisterCustomBinder(&jsonBinder{}) // Name() returns \"json\"\n// ...\nc.Bind().Custom(\"form\", &v) // typo: name mismatch\n// after\nconst BinderJSON = \"json\"\napp.RegisterCustomBinder(&jsonBinder{})\n// ...\nc.Bind().Custom(BinderJSON, &v)","handlingStrategy":"validation","validationCode":"// Share binder names via constants and assert the binder is registered\n// before serving requests.\nconst BinderJSON = \"json\"\n\nfunc ensureBinder(app *fiber.App, name string) {\n    for _, b := range app.CustomBinders() {\n        if b.Name() == name {\n            return\n        }\n    }\n    log.Fatalf(\"custom binder %q not registered\", name)\n}","typeGuard":null,"tryCatchPattern":"if err := c.Bind().Custom(BinderJSON, &v); err != nil {\n    if errors.Is(err, fiber.ErrCustomBinderNotFound) {\n        return c.Status(fiber.StatusInternalServerError).\n            SendString(\"binder misconfigured\")\n    }\n    return err\n}","preventionTips":["Register custom binders on the same App that serves the request, before Listen.","Define binder names as constants to avoid typos and casing drift.","Add a startup test that asserts every name used in handlers is registered."],"tags":["binder","binding","config","validation"],"backgroundTag":null,"analyzedSha":"a105acad6c1e4576a77f01e02973f67e962bb58d","analyzedAt":"2026-08-11T17:33:26.942Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}