hyperledger/fabric · error

unexpected data format: %x

Error message

unexpected data format: %x

What it means

OpenFile validates that the first byte of the snapshot file equals the expectedDataformat the caller requires. This error (built with errors.New, no inner cause) means the file's format byte differs — the snapshot was written with a different data format than the importer expects, or the file is not a valid snapshot at all.

Source

Thrown at common/ledger/snapshot/file.go:149

	reusableByteSlice []byte
}

// OpenFile constructs a FileReader. This function returns an error if the format of the file, stored in the
// first byte, does not match with the expectedDataFormat
func OpenFile(filePath string, expectDataformat byte) (*FileReader, error) {
	file, err := os.Open(filePath)
	if err != nil {
		return nil, errors.Wrapf(err, "error while opening the snapshot file: %s", filePath)
	}
	bufReader := bufio.NewReader(file)
	dataFormat, err := bufReader.ReadByte()
	if err != nil {
		file.Close()
		return nil, errors.Wrapf(err, "error while reading from the snapshot file: %s", filePath)
	}
	if dataFormat != expectDataformat {
		file.Close()
		return nil, errors.New(fmt.Sprintf("unexpected data format: %x", dataFormat))
	}
	return &FileReader{
		file:      file,
		bufReader: bufReader,
	}, nil
}

// DecodeString reads and decodes a string
func (r *FileReader) DecodeString() (string, error) {
	b, err := r.decodeBytes()
	return string(b), err
}

// DecodeBytes reads and decodes bytes
func (r *FileReader) DecodeBytes() ([]byte, error) {
	b, err := r.decodeBytes()
	if err != nil {
		return nil, err

View on GitHub (pinned to 2736b63f8f)

Solutions

1. Verify the snapshot was exported by a compatible Fabric version and re-export if needed
2. Confirm the configured path points to the correct snapshot file (check the format byte with xxd/od)
3. Check what format the importer expects and confirm the snapshot's first byte matches (e.g. hex 00/01)

f, _ := os.Open(path); defer f.Close()
var b [1]byte
io.ReadFull(f, b[:])
if b[0] != expectedFormat { return fmt.Errorf("format %x != expected %x", b[0], expectedFormat) }

fr, err := snapshot.OpenFile(path, expectedFmt)
if err != nil {
    if strings.Contains(err.Error(), "unexpected data format") {
        return fmt.Errorf("snapshot %s incompatible with this peer version", path)
    }
    return err
}

When it happens

Trigger: dataFormat != expectDataformat, e.g. importing a snapshot exported by a different Fabric version, or pointing OpenFile at a non-snapshot file whose first byte happens to be readable.

Common situations: Version skew between the peer that exported the snapshot and the one importing it; accidentally configuring a corrupted or unrelated file as the snapshot; endianness/format changes across releases.

Related errors

• error while opening the snapshot file: %s
• error while reading bootstrappingSnapshotInfo file
• error while unmarshalling bootstrappingSnapshotInfo
• failed to read bootstrappingSnapshotInfo file under blocksto
• dir %s not empty

AI-assisted analysis of hyperledger/fabric@2736b63f8f (2026-09-04). Data as JSON: /api/errors/3cb63c1f2d441cd3. Report an issue: GitHub.