structs.go

package lotusdb

import (
	"encoding/binary"

	"github.com/rosedblabs/wal"
)

// LogRecordType is the type of the log record.
type LogRecordType = byte

const (
	// LogRecordNormal is the normal log record type.
	LogRecordNormal LogRecordType = iota
	// LogRecordDeleted is the deleted log record type.
	LogRecordDeleted
	// LogRecordBatchFinished is the batch finished log record type.
	LogRecordBatchFinished
)

// type batchId keySize valueSize
//
//	1  +  10  +   5   +   5 = 21
const maxLogRecordHeaderSize = binary.MaxVarintLen32*2 + binary.MaxVarintLen64 + 1

// LogRecord is the log record of the key/value pair.
// It contains the key, the value, the record type and the batch id
// It will be encoded to byte slice and written to the wal.
type LogRecord struct {
	Key     []byte
	Value   []byte
	Type    LogRecordType
	BatchId uint64
}

// IndexRecord is the index record of the key.
// It contains the key, the record type and the position of the record in the wal.
// Only used in start up to rebuild the index.
type IndexRecord struct {
	key        []byte
	recordType LogRecordType
	position   *wal.ChunkPosition
}

// +-------------+-------------+-------------+--------------+-------------+--------------+
// |    type     |  batch id   |   key size  |   value size |      key    |      value   |
// +-------------+-------------+-------------+--------------+-------------+--------------+
//
//	1 byte	      varint(max 10) varint(max 5)  varint(max 5)     varint		varint
func encodeLogRecord(logRecord *LogRecord) []byte {
	header := make([]byte, maxLogRecordHeaderSize)

	header[0] = logRecord.Type
	var index = 1

	// batch id
	index += binary.PutUvarint(header[index:], logRecord.BatchId)
	// key size
	index += binary.PutVarint(header[index:], int64(len(logRecord.Key)))
	// value size
	index += binary.PutVarint(header[index:], int64(len(logRecord.Value)))

	var size = index + len(logRecord.Key) + len(logRecord.Value)
	encBytes := make([]byte, size)

	// copy header
	copy(encBytes[:index], header[:index])
	// copy key
	copy(encBytes[index:], logRecord.Key)
	// copy value
	copy(encBytes[index+len(logRecord.Key):], logRecord.Value)

	return encBytes
}

// decodeLogRecord decodes the log record from the given byte slice.
func decodeLogRecord(buf []byte) *LogRecord {
	recordType := buf[0]

	var index uint32 = 1
	// batch id
	batchId, n := binary.Uvarint(buf[index:])
	index += uint32(n)

	// key size
	keySize, n := binary.Varint(buf[index:])
	index += uint32(n)

	// value size
	valueSize, n := binary.Varint(buf[index:])
	index += uint32(n)

	// copy key
	key := make([]byte, keySize)
	copy(key[:], buf[index:index+uint32(keySize)])
	index += uint32(keySize)

	// copy value
	value := make([]byte, valueSize)
	copy(value[:], buf[index:index+uint32(valueSize)])

	return &LogRecord{Key: key, Value: value,
		BatchId: batchId, Type: recordType}
}