hyperledger/fabric · error

error while marshelling snapshot metadata to JSON

Error message

error while marshelling snapshot metadata to JSON

What it means

generateSnapshotMetadataFiles serializes the snapshot's signable metadata (channel name, files and hashes, stateDB type) to JSON via SnapshotSignableMetadata.ToJSON before writing the metadata file. This error wraps a marshalling failure, which is practically only caused by an unsupported field type in the metadata struct.

Source

Thrown at core/ledger/kvledger/snapshot.go:193

		return err
	}

	stateDBType := l.config.StateDBConfig.StateDatabase
	if stateDBType != ledger.CouchDB {
		stateDBType = simpleKeyValueDB
	}
	signableMetadata := &SnapshotSignableMetadata{
		ChannelName:            l.ledgerID,
		LastBlockNumber:        bcInfo.Height - 1,
		LastBlockHashInHex:     hex.EncodeToString(bcInfo.CurrentBlockHash),
		PreviousBlockHashInHex: hex.EncodeToString(bcInfo.PreviousBlockHash),
		FilesAndHashes:         filesAndHashes,
		StateDBType:            stateDBType,
	}

	signableMetadataBytes, err := signableMetadata.ToJSON()
	if err != nil {
		return errors.Wrap(err, "error while marshelling snapshot metadata to JSON")
	}
	if err := fileutil.CreateAndSyncFile(filepath.Join(dir, SnapshotSignableMetadataFileName), signableMetadataBytes, 0o444); err != nil {
		return err
	}

	// generate metadata hash file
	hash, err := l.hashProvider.GetHash(snapshotHashOpts)
	if err != nil {
		return err
	}
	if _, err := hash.Write(signableMetadataBytes); err != nil {
		return err
	}

	additionalMetadata := &snapshotAdditionalMetadata{
		SnapshotHashInHex:        hex.EncodeToString(hash.Sum(nil)),
		LastBlockCommitHashInHex: hex.EncodeToString(l.commitHash),
	}

View on GitHub (pinned to 2736b63f8f)

Solutions

1. If running stock Fabric, capture peer logs and file a bug — this should never fail on unmodified code
2. If you patched snapshot metadata structs, ensure all added fields are JSON-serializable (no channels, funcs, cycles)
3. Verify no unsupported stateDB type or metadata field is being injected via custom builds

Example fix

// before (custom field not serializable)
type SnapshotSignableMetadata struct {
    StateDBType string `json:"stateDBType"`
    Extra func `json:"extra"` // unmarshalable
}
// after
type SnapshotSignableMetadata struct {
    StateDBType string `json:"stateDBType"`
    Extra string `json:"extra"`

b, err := json.Marshal(signableMetadata)
if err != nil { return fmt.Errorf("snapshot metadata not serializable: %w", err) }

err := ledger.GenerateSnapshot()
if err != nil {
    if strings.Contains(err.Error(), "marshelling snapshot metadata") {
        log.Error("snapshot metadata marshalling failed; verify stock Fabric build / struct customizations")
    }
    return err
}

When it happens

Trigger: Called from generateSnapshot during GenerateSnapshot() when SignableMetadata.ToJSON() fails — e.g. non-serializable content slipped into the metadata struct (rare; typically indicates an internal bug or a customization that added unmarshalable fields).

Common situations: Custom/patched Fabric builds adding non-JSON-serializable fields to snapshot metadata; Go json package constraints (channels, funcs, cyclic data) if metadata struct was modified.

Understand the failure class

Background: json.Marshal / "failed to marshal" errors in Go: why "unsupported type" happens and how to fix it — this error's family across 22 libraries.

Related errors

• incorrect number of arguments
• connection.json not found in source folder: %s
• failed to marshal config
• error marshalling proto message to write to the snapshot fil
• could not marshal field %s

AI-assisted analysis of hyperledger/fabric@2736b63f8f (2026-09-04). Data as JSON: /api/errors/43613ad749c9c346. Report an issue: GitHub.