{"record":{"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":"exception","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/a105acad6c1e4576a77f01e02973f67e962bb58d/middleware/session/session.go#L570-L606","documentation":"Thrown by decodeSessionData when gob.Decoder.Decode cannot turn the raw bytes from storage back into s.data.Data. The %w carries the gob decoder's complaint (e.g. EOF, unexpected EOF, gob: type mismatch). This indicates the persisted payload is not valid gob, is truncated, or was written with an incompatible/unregistered type set.","triggerScenarios":"The Storage backend returns bytes that are not a valid gob stream, are truncated (e.g. a value-length prefix cut off), or were produced by a build whose registered types differ from the current one; manually tampered session data; switching storage backends or key encodings.","commonSituations":"Deploying a new version that changed a stored struct without keeping gob.Register consistent; storage corruption (Redis eviction/overwrite, DB truncation); sharing one session store between two apps with different schemas; partial writes during a crash.","solutions":["Treat the decode failure as 'session invalid' and destroy/reset the session so the user gets a fresh one.","Verify the Storage backend is not returning truncated or empty payloads (check raw byte length).","Keep gob.Register calls identical and additive across versions; never remove a registered type while old sessions may still reference it.","Clear the affected session ID from storage to stop the recurrence."],"exampleFix":"// before\nsess, err := store.Get(c)\nif err != nil { return err } // propagates decode error, breaks user\n\n// after\nsess, err := store.Get(c)\nif err != nil {\n    log.Printf(\"session decode failed, resetting: %v\", err)\n    sess.Destroy()\n    sess, err = store.Get(c) // fresh session\n    if err != nil { return err }\n}","handlingStrategy":"fallback","validationCode":"// Before trusting stored data, probe-decode it in a scratch buffer.\nfunc probeDecode(storage Storage, id string) error {\n    raw, err := storage.Get(context.Background(), id)\n    if err != nil || raw == nil { return err }\n    var d Data\n    return gob.NewDecoder(bytes.NewReader(raw)).Decode(&d)\n}","typeGuard":null,"tryCatchPattern":"sess, err := store.Get(c)\nif err != nil {\n    // corrupt/incompatible payload — discard and start fresh\n    log.Printf(\"session decode failed, resetting: %v\", err)\n    sess.Destroy()\n    sess, err = store.Get(c)\n}\nif err != nil { return err }","preventionTips":["Keep gob.Register additive across deploys — never remove a registration while old sessions live.","Do not share one session store between apps with different type sets.","Investigate recurring decode errors as storage corruption.","Log the wrapped gob error so you can see whether it is type-mismatch vs truncation."],"tags":["session","serialization","gob","decoding","corruption"],"backgroundTag":null,"analyzedSha":"a105acad6c1e4576a77f01e02973f67e962bb58d","analyzedAt":"2026-08-11T17:33:26.942Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}