Method ReadLogRecord

engine/data/data_file.go:61–110

ReadLogRecord reads a log record from the data file based on the offset.

(offset int64)

// ReadLogRecord reads a log record from the data file based on the offset.
func (df *DataFile) ReadLogRecord(offset int64) (*LogRecord, int64, error) {
	fileSize, err := df.IoManager.Size()
	if err != nil {
		return nil, 0, err
	}

	var headerBytes int64 = maxLogRecordHeaderSize
	if offset+maxLogRecordHeaderSize > fileSize {
		headerBytes = fileSize - offset
	}

	// Read header information
	headerBuf, err := df.readNBytes(headerBytes, offset)
	if err != nil {
		return nil, 0, err
	}

	header, headerSize := decodeLogRecordHeader(headerBuf)
	// The following conditions indicate reaching the end of the file, directly return EOF
	if header == nil {
		return nil, 0, io.EOF
	}
	if header.crc == 0 && header.keySize == 0 && header.valueSize == 0 {
		return nil, 0, io.EOF
	}

	// Retrieve the lengths of the key and value
	keySize, valueSize := int64(header.keySize), int64(header.valueSize)
	var recordSize = headerSize + keySize + valueSize

	logRecord := &LogRecord{Type: header.recordType}

	// Read the actual user-stored key/value data
	if keySize > 0 || valueSize > 0 {
		kvBuf, err := df.readNBytes(keySize+valueSize, headerSize+offset)
		if err != nil {
			return nil, 0, err
		}
		// Decode
		logRecord.Key = kvBuf[:keySize]
		logRecord.Value = kvBuf[keySize:]
	}

	// Verify CRC (check data integrity)
	crc := getLogRecordCRC(logRecord, headerBuf[crc32.Size:headerSize])
	if crc != header.crc {
		return nil, 0, ErrInvalidCRC
	}
	return logRecord, recordSize, nil
}

func (df *DataFile) Write(buf []byte) error {
	size, err := df.IoManager.Write(buf)