{"id":"4484f007876b2f63","repo":"gofiber/fiber","slug":"failed-to-encode-session-data-w","errorCode":null,"errorMessage":"failed to encode session data: %w","messagePattern":"failed to encode session data: %w","errorType":"http","errorClass":null,"httpStatus":null,"severity":"error","filePath":"middleware/session/session.go","lineNumber":610,"sourceCode":"\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)\n\tdefer byteBuffer.Reset()\n\tencCache := gob.NewEncoder(byteBuffer)\n\tif err := encCache.Encode(&s.data.Data); err != nil {\n\t\treturn nil, fmt.Errorf(\"failed to encode session data: %w\", err)\n\t}\n\t// Copy the bytes\n\t// Copy the data in buffer\n\tencodedBytes := make([]byte, byteBuffer.Len())\n\tcopy(encodedBytes, byteBuffer.Bytes())\n\n\treturn encodedBytes, nil\n}\n\n// absExpiration returns the session absolute expiration time or a zero time if not set.\n//\n// Returns:\n//   - time.Time: The session absolute expiration time. Zero time if not set.\n//\n// Usage:\n//\n//\texpiration := s.absExpiration()\nfunc (s *Session) absExpiration() time.Time {","sourceCodeStart":592,"sourceCodeEnd":628,"githubUrl":"https://github.com/gofiber/fiber/blob/9a4c7e57fe0b080a04235d28a4b0d2b4b353d58c/middleware/session/session.go#L592-L628","documentation":"Raised by Session.encodeSessionData when gob cannot serialize data.Data (map[any]any) to bytes, which happens on sess.Save(). The encoder must describe each concrete value through the any interface, so an unregistered type or a gob-incompatible value (channels, funcs, unexported-field structs) makes Encode fail.","triggerScenarios":"Calling sess.Set(\"user\", User{}) on an unregistered User, then sess.Save() triggers encodeSessionData and gob.Encode returns an error; or storing a value gob cannot represent.","commonSituations":"Introducing new session data with custom struct types without RegisterType; storing non-gob-encodable values (chan/func/complex); structs with unexported fields gob cannot reach.","solutions":["Register all custom types via store.RegisterType at startup.","Store only gob-compatible values: exported fields, no chan/func/unsafe.Pointer.","If you must store an exotic type, store a registered plain struct or []byte representation instead."],"exampleFix":"// before\nstore := session.NewStore()\nsess, _ := store.Get(c)\nsess.Set(\"profile\", Profile{})\nerr := sess.Save() // failed to encode session data\n\n// after\nstore := session.NewStore()\nstore.RegisterType(Profile{})\nsess, _ := store.Get(c)\nsess.Set(\"profile\", Profile{})\nerr := sess.Save()","handlingStrategy":"validation","validationCode":"var registeredTypes = []any{User{}, Profile{}, time.Time{}}\nfunc registerSessionTypes(s *session.Store) {\n    for _, t := range registeredTypes {\n        s.RegisterType(t)\n    }\n}","typeGuard":"// typeGuard: only allow gob-encodable, pre-registered kinds into the session.\nfunc isGobSafe(v any) bool {\n    if v == nil { return true }\n    switch reflect.TypeOf(v).Kind() {\n    case reflect.Chan, reflect.Func, reflect.UnsafePointer, reflect.Complex64, reflect.Complex128:\n        return false\n    }\n    return true\n}","tryCatchPattern":"if err := sess.Save(); err != nil {\n    log.Errorf(\"session save failed: %v\", err)\n    return fiber.ErrInternalServerError\n}","preventionTips":["Register types once at startup; keep the list in version control.","Never put chan/func/complex values in a session.","Store simple or pre-registered types only."],"tags":["session","gob","serialization","fiber"],"analyzedSha":"9a4c7e57fe0b080a04235d28a4b0d2b4b353d58c","analyzedAt":"2026-08-04T21:44:03.395Z","schemaVersion":2}