{"id":"2aa537ca5af1c6e6","repo":"gofiber/fiber","slug":"failed-to-decode-session-data-w","errorCode":null,"errorMessage":"failed to decode session data: %w","messagePattern":"failed to decode session data: %w","errorType":"http","errorClass":null,"httpStatus":null,"severity":"error","filePath":"middleware/session/session.go","lineNumber":588,"sourceCode":"// decodeSessionData decodes session data from raw bytes\n//\n// Parameters:\n//   - rawData: The raw byte data to decode.\n//\n// Returns:\n//   - error: An error if the decoding fails.\n//\n// Usage:\n//\n//\terr := s.decodeSessionData(rawData)\nfunc (s *Session) decodeSessionData(rawData []byte) error {\n\tbyteBuffer := byteBufferPool.Get().(*bytes.Buffer) //nolint:forcetypeassert,errcheck // We store nothing else in the pool\n\tdefer byteBufferPool.Put(byteBuffer)\n\tdefer byteBuffer.Reset()\n\t_, _ = byteBuffer.Write(rawData)\n\tdecCache := gob.NewDecoder(byteBuffer)\n\tif err := decCache.Decode(&s.data.Data); err != nil {\n\t\treturn fmt.Errorf(\"failed to decode session data: %w\", err)\n\t}\n\treturn nil\n}\n\n// encodeSessionData encodes session data to raw bytes\n//\n// Parameters:\n//   - rawData: The raw byte data to encode.\n//\n// Returns:\n//   - error: An error if the encoding fails.\n//\n// Usage:\n//\n//\terr := s.encodeSessionData(rawData)\nfunc (s *Session) encodeSessionData() ([]byte, error) {\n\tbyteBuffer := byteBufferPool.Get().(*bytes.Buffer) //nolint:forcetypeassert,errcheck // We store nothing else in the pool\n\tdefer byteBufferPool.Put(byteBuffer)","sourceCodeStart":570,"sourceCodeEnd":606,"githubUrl":"https://github.com/gofiber/fiber/blob/9a4c7e57fe0b080a04235d28a4b0d2b4b353d58c/middleware/session/session.go#L570-L606","documentation":"Raised by Session.decodeSessionData when gob cannot decode the raw bytes pulled from the session store back into the session's map[any]any (data.Data). Because the value type is a map keyed by any, every concrete value stored in the session must be registered with gob; the wrapped error is typically 'gob: type not registered for interface' or io.ErrUnexpectedEOF for truncated bytes.","triggerScenarios":"Calling code that reads an existing session whose stored payload holds a concrete Go type never passed to Store.RegisterType, or whose struct shape changed since it was written, or whose bytes were truncated by the storage backend (value-size cap).","commonSituations":"Deploying a new struct into the session without RegisterType; rolling out a schema change while old sessions remain in Redis/memstore; one replica registered a type and another did not; storage backend truncating large values.","solutions":["Register every custom type with store.RegisterType(MyType{}) at startup before serving requests.","Invalidate/clear stale sessions in the storage backend after changing any stored type's fields.","Confirm the storage backend is not truncating payloads (raise Redis max value size / memcache item size if needed)."],"exampleFix":"// before\nstore := session.NewStore()\nsess, err := store.Get(c) // err: failed to decode session data: gob: type not registered for interface\n\n// after\nstore := session.NewStore()\nstore.RegisterType(User{})\nstore.RegisterType(Permissions{})\nsess, err := store.Get(c)","handlingStrategy":"validation","validationCode":"// Register every concrete type you will ever store, once at startup.\nfunc registerSessionTypes(s *session.Store) {\n    s.RegisterType(User{})\n    s.RegisterType(time.Time{})\n    // ...one call per concrete value type used in sess.Set\n}","typeGuard":null,"tryCatchPattern":"sess, err := store.Get(c)\nif err != nil {\n    // Treat unreadable session as corrupt: destroy and start fresh.\n    _ = sess.Destroy()\n    sess, err = store.Get(c) // regenerates a fresh session\n    if err != nil {\n        return fiber.ErrInternalServerError\n    }\n}","preventionTips":["Call Store.RegisterType for every custom type before the first request.","Avoid changing the field layout of stored structs without a session migration.","Keep session payloads small to stay under storage value-size limits."],"tags":["session","gob","serialization","fiber"],"analyzedSha":"9a4c7e57fe0b080a04235d28a4b0d2b4b353d58c","analyzedAt":"2026-08-04T21:44:03.395Z","schemaVersion":2}