What causes "error while unmarshalling signable metadata" in hyperledger/fabric?

Validate the JSON files inside the snapshot directory (snapshot_signable_metadata.json parses via jq) and regenerate the snapshot if malformed.

hyperledger/fabric · error

error while unmarshalling signable metadata

Error message

error while unmarshalling signable metadata

What it means

SnapshotMetadataJSONs.ToMetadata decodes the signable portion of a snapshot metadata file (snapshot_signable_metadata.json) via json.Unmarshal into SnapshotSignableMetadata. If the JSON is malformed, empty, or missing expected fields/types, the operation fails wrapped with this message. It indicates a corrupt or hand-edited snapshot metadata file.

Source

Thrown at core/ledger/kvledger/snapshot.go:78

func (m *snapshotAdditionalMetadata) ToJSON() ([]byte, error) {
	return json.MarshalIndent(m, "", jsonFileIndent)
}

type SnapshotMetadata struct {
	*SnapshotSignableMetadata
	*snapshotAdditionalMetadata
}

type SnapshotMetadataJSONs struct {
	signableMetadata   string
	additionalMetadata string
}

func (j *SnapshotMetadataJSONs) ToMetadata() (*SnapshotMetadata, error) {
	metadata := &SnapshotSignableMetadata{}
	if err := json.Unmarshal([]byte(j.signableMetadata), metadata); err != nil {
		return nil, errors.Wrap(err, "error while unmarshalling signable metadata")
	}

	additionalMetadata := &snapshotAdditionalMetadata{}
	if err := json.Unmarshal([]byte(j.additionalMetadata), additionalMetadata); err != nil {
		return nil, errors.Wrap(err, "error while unmarshalling additional metadata")
	}
	return &SnapshotMetadata{
		SnapshotSignableMetadata:   metadata,
		snapshotAdditionalMetadata: additionalMetadata,
	}, nil
}

// generateSnapshot generates a snapshot. This function should be invoked when commit on the kvledger are paused
// after committing the last block fully and further the commits should not be resumed till this function finishes
func (l *kvLedger) generateSnapshot() error {
	snapshotsRootDir := l.config.SnapshotsConfig.RootDir
	bcInfo, err := l.GetBlockchainInfo()
	if err != nil {

View on GitHub (pinned to 2736b63f8f)

Solutions

Validate the JSON files inside the snapshot directory (snapshot_signable_metadata.json parses via jq) and regenerate the snapshot if malformed.
Re-transfer or re-generate the snapshot; a truncated copy is the most common cause.
Ensure the snapshot was created by a compatible Fabric version (v2.x snapshot feature) and is not hand-modified.
If the source is reproducible, take a new snapshot from a healthy peer and retry the channel join.

Example fix

// before: hand-edited metadata
{"lastBlockNumber": "not-a-number"}   // json: cannot unmarshal string into Go struct field ... of type uint64
// after: use the metadata exactly as produced by the peer, verify with:
jq . snapshot_signable_metadata.json

Defensive patterns

Strategy: validation

Validate before calling

// validate snapshot metadata before consuming it
func validateSnapshotMetadata(dir string) error {
	for _, f := range []string{"snapshot_signable_metadata.json", "snapshot_additional_metadata.json"} {
		data, err := os.ReadFile(filepath.Join(dir, f))
		if err != nil {
			return fmt.Errorf("missing snapshot metadata %s: %w", f, err)
		}
		var v map[string]interface{}
		if err := json.Unmarshal(data, &v); err != nil {
			return fmt.Errorf("invalid JSON in %s: %w", f, err)
		}
	}
	return nil
}

Try / catch

md, err := jsons.ToMetadata()
if err != nil {
	if strings.Contains(err.Error(), "error while unmarshalling signable metadata") {
		return nil, fmt.Errorf("snapshot metadata corrupt: regenerate or re-transfer the snapshot: %w", err)
	}
	return nil, err
}

Prevention

Never hand-edit files inside a snapshot directory
Verify snapshot transfers with checksums (sha256) before use
Use jq or json.Unmarshal validation on snapshot metadata before joining
Create and consume snapshots with the same compatible Fabric version

When it happens

Trigger: Loading a snapshot's metadata (snapshotMetadataFromMetaFile) when the signable metadata JSON string cannot be parsed — e.g. during 'peer node channel join' from a snapshot or when reconstructing snapshot metadata.

Common situations: Truncated or corrupted snapshot files during transfer (incomplete scp/rsync); manual editing of snapshot metadata; generating snapshots with an incompatible Fabric version and consuming them with another; wrong file passed as the snapshot metadata.

Understand the failure class

Background: "failed to unmarshal" / json.Unmarshal errors: why parsing a response into a Go struct fails and how to fix it — this error's family across 23 libraries.

Related errors

AI-assisted analysis of hyperledger/fabric@2736b63f8f (2026-09-04). Data as JSON: /api/errors/00bb1c29af06656e. Report an issue: GitHub.