{"record":{"id":"d3e0efc3a1f05f3c","repo":"gofiber/fiber","slug":"failed-to-decode-session-data-w-d3e0ef","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/store.go","lineNumber":179,"sourceCode":"\tsess := acquireSession()\n\n\tsess.mu.Lock()\n\n\tsess.ctx = c\n\tsess.config = s\n\tsess.id = id\n\tsess.isFresh = isFresh\n\tsess.extractor = selectedExtractor\n\n\t// Decode session data if found\n\tif rawData != nil {\n\t\tsess.data.Lock()\n\t\terr := sess.decodeSessionData(rawData)\n\t\tsess.data.Unlock()\n\t\tif err != nil {\n\t\t\tsess.mu.Unlock()\n\t\t\tsess.Release()\n\t\t\treturn nil, fmt.Errorf(\"failed to decode session data: %w\", err)\n\t\t}\n\t}\n\n\tsess.mu.Unlock()\n\n\tif isFresh && s.AbsoluteTimeout > 0 {\n\t\tsess.setAbsExpiration(time.Now().Add(s.AbsoluteTimeout))\n\t} else if sess.isAbsExpired() {\n\t\tif err := sess.Reset(); err != nil {\n\t\t\treturn nil, fmt.Errorf(\"failed to reset session: %w\", err)\n\t\t}\n\t\tsess.setAbsExpiration(time.Now().Add(s.AbsoluteTimeout))\n\t}\n\n\treturn sess, nil\n}\n\n// getSessionID returns the session ID using the configured extractor.","sourceCodeStart":161,"sourceCodeEnd":197,"githubUrl":"https://github.com/gofiber/fiber/blob/a105acad6c1e4576a77f01e02973f67e962bb58d/middleware/session/store.go#L161-L197","documentation":"Thrown during session acquisition (store Get/Acquire) when the session ID already has raw data in Storage but decoding that data via decodeSessionData fails. It is the acquisition-path equivalent of 201: the persisted payload for an existing session is corrupt or type-incompatible.","triggerScenarios":"Storage.Get returns non-nil bytes for the session ID, but those bytes fail gob-decoding — truncation, corruption, or a type set mismatch between the writer and reader builds.","commonSituations":"Deploying a version that changed a stored struct without keeping gob.Register additive; storage corruption; one shared session store used by two apps with different schemas; migrating session backends.","solutions":["Handle the error by destroying the session and issuing a fresh one (do not keep retrying the same corrupt payload).","Verify the Storage backend integrity and that it returns full payloads.","Keep gob.Register consistent/additive across deployments."],"exampleFix":"// before\nsess, err := store.Get(c)\nif err != nil { return err } // user locked out by corrupt session\n\n// after\nsess, err := store.Get(c)\nif err != nil {\n    c.Cookie(&fiber.Cookie{Name: store.SessionName, Expires: time.Unix(0,0)})\n    sess, err = store.Get(c)\n    if err != nil { return err }\n}","handlingStrategy":"fallback","validationCode":"// Validate a stored session before handing it to users.\nfunc sessionPayloadValid(raw []byte) bool {\n    if raw == nil { return true }\n    var d Data\n    return gob.NewDecoder(bytes.NewReader(raw)).Decode(&d) == nil\n}","typeGuard":null,"tryCatchPattern":"sess, err := store.Get(c)\nif err != nil {\n    log.Printf(\"acquire decode failed, resetting: %v\", err)\n    store.Storage.Delete(context.Background(), id)\n    sess, err = store.Get(c)\n}","preventionTips":["Treat decode failures as 'session invalid' and regenerate, not as fatal.","Keep gob.Register consistent across versions sharing the store.","Monitor decode-error rates as a storage-health signal."],"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"}