Method Decode

consensus/wal.go:365–419

Decode reads the next custom-encoded value from its reader and returns it.

()

// Decode reads the next custom-encoded value from its reader and returns it.
func (dec *WALDecoder) Decode() (*TimedWALMessage, error) {
	b := make([]byte, 4)

	_, err := dec.rd.Read(b)
	if errors.Is(err, io.EOF) {
		return nil, err
	}
	if err != nil {
		return nil, DataCorruptionError{fmt.Errorf("failed to read checksum: %v", err)}
	}
	crc := binary.BigEndian.Uint32(b)

	b = make([]byte, 4)
	_, err = dec.rd.Read(b)
	if err != nil {
		return nil, DataCorruptionError{fmt.Errorf("failed to read length: %v", err)}
	}
	length := binary.BigEndian.Uint32(b)

	if length > maxMsgSizeBytes {
		return nil, DataCorruptionError{fmt.Errorf(
			"length %d exceeded maximum possible value of %d bytes",
			length,
			maxMsgSizeBytes)}
	}

	data := make([]byte, length)
	n, err := dec.rd.Read(data)
	if err != nil {
		return nil, DataCorruptionError{fmt.Errorf("failed to read data: %v (read: %d, wanted: %d)", err, n, length)}
	}

	// check checksum before decoding data
	actualCRC := crc32.Checksum(data, crc32c)
	if actualCRC != crc {
		return nil, DataCorruptionError{fmt.Errorf("checksums do not match: read: %v, actual: %v", crc, actualCRC)}
	}

	var res = new(tmcons.TimedWALMessage)
	err = proto.Unmarshal(data, res)
	if err != nil {
		return nil, DataCorruptionError{fmt.Errorf("failed to decode data: %v", err)}
	}

	walMsg, err := WALFromProto(res.Msg)
	if err != nil {
		return nil, DataCorruptionError{fmt.Errorf("failed to convert from proto: %w", err)}
	}
	tMsgWal := &TimedWALMessage{
		Time: res.Time,
		Msg:  walMsg,
	}

	return tMsgWal, err
}

type nilWAL struct{}