gofiber/fiber · error

fiber: failed to decode shared state

Error message

fiber: failed to decode shared state %s value: %w

What it means

Returned by decodeSharedStateValue() when the configured decoder (json/msgpack/cbor/xml) returns a non-nil error while deserializing stored bytes into the output value during SharedState.GetJSON/GetMsgPack/GetCBOR/GetXML. Panics from the codec are handled separately (sharedStateCodecPanicError).

Solutions

1. Verify the encode and decode codecs match for a given key namespace.
2. Check the wrapped error for syntax/EOF/type messages and reconcile the target struct.
3. If migrating codecs, migrate the stored data or version the key prefix.
4. Confirm storage integrity (no truncation) — re-Set the value from a known-good source.

Example fix

// before — wrote msgpack, read json
app.State().Shared().SetMsgPack("u:1", u, 0)
app.State().Shared().GetJSON("u:1", &u2)
// -> fiber: failed to decode shared state json value: invalid character ...

// after — match codecs
app.State().Shared().SetMsgPack("u:1", u, 0)
app.State().Shared().GetMsgPack("u:1", &u2)

// Version keys by codec to prevent cross-codec reads.
func keyFor(codec, key string) string { return codec + ":" + key }
// On decode failure, fall back to a safe default rather than crashing.
func getOrDefaultJSON(app *fiber.App, key string, out any, def any) {
    _, ok, err := app.State().Shared().GetJSON(key, out)
    if err != nil || !ok { out = def }
}

_, ok, err := app.State().Shared().GetJSON(k, &out)
if err != nil {
    log.Printf("shared state decode failed for %s: %v", k, err)
    // optionally treat as cache miss and rebuild
    out = freshValue()
} else if !ok {
    out = freshValue()
}

When it happens

Trigger: Calling app.State().Shared().GetJSON(key, &out) where the stored bytes are corrupt, truncated, or were encoded with a different codec than the one used to decode (e.g., stored as msgpack, read with json). Also fires on type mismatch — decoding into a struct whose fields do not match the stored payload.

Common situations: Codec migration: data written with JSON is read with MsgPack; schema drift after a struct field rename; partial write left truncated bytes in storage; storage backend returned corrupted data (Redis eviction mid-write); wrong key namespace returning another app's data.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• fiber: failed to encode shared state
• fiber: shared state is not configured
• failed to unmarshal xml
• binder: msgpack is not configured, please check docs…
• binder: must explicitly set up CBOR, please check docs…

AI-assisted analysis of gofiber/fiber@a105acad6c (2026-08-11). Data as JSON: /api/errors/1c9b5ce13bfaf31b. Report an issue: GitHub.

Appendix: source

Thrown at shared_state.go:398

		err       error
		recovered any
	)
	func() {
		// App-configured codecs may be nil or may still use Fiber's
		// binder.Unimplemented* placeholders, which panic instead of returning an
		// error, so recover here and surface a regular error.
		defer func() {
			recovered = recover()
		}()

		err = decoder(data, out)
	}()

	if recovered != nil {
		return sharedStateCodecPanicError("decode", format, recovered)
	}
	if err != nil {
		return fmt.Errorf("fiber: failed to decode shared state %s value: %w", format, err)
	}

	return nil
}

func sharedStateCodecNotConfiguredError(format, direction string) error {
	return fmt.Errorf("fiber: shared state %s %s is not configured", format, direction)
}

func sharedStateCodecPanicError(operation, format string, recovered any) error {
	if err, ok := recovered.(error); ok {
		return fmt.Errorf("fiber: failed to %s shared state %s value: %w", operation, format, err)
	}

	return fmt.Errorf("fiber: failed to %s shared state %s value: %v", operation, format, recovered)
}

func (s *SharedState) storageKey(key string) (string, bool) {

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