qb/storage/wal_reader.go

package storage

import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io"
	"os"

	bin "gordenko.dev/dima/bin/little"
	"gordenko.dev/dima/qb/util"
)

const readBufferSize = 8 * 1024 * 1024

type WALReader struct {
	file    *os.File
	reader  *bufio.Reader
	current []any
	next    []any
}

type WALReaderOptions struct {
	FileName   string
	BufferSize int
}

func NewWALReader(opt WALReaderOptions) (*WALReader, error) {
	if opt.FileName == "" {
		return nil, errors.New("FileName option is required")
	}
	if opt.BufferSize <= 0 {
		return nil, errors.New("BufferSize option is required")
	}

	file, err := os.Open(opt.FileName)
	if err != nil {
		return nil, err
	}

	return &WALReader{
		file:   file,
		reader: bufio.NewReaderSize(file, readBufferSize),
	}, nil
}

func (s *WALReader) Close() {
	s.file.Close()
}

func (s *WALReader) NextPacket() ([]any, bool, error) {
	var err error
	if s.current == nil {
		s.current, err = s.readPacket()
		if err != nil {
			return nil, false, err
		}
		if len(s.current) > 0 {
			s.next, err = s.readPacket()
			if err != nil {
				return nil, false, err
			}
		}
	}

	current := s.current
	done := s.next == nil

	s.current = s.next
	s.next, err = s.readPacket()
	if err != nil {
		return nil, false, err
	}
	return current, done, nil
}

func (s *WALReader) readPacket() (_ []any, err error) {
	payloadSize, err := bin.ReadVarSize(s.reader)
	if err != nil {
		if err == io.EOF {
			return nil, nil
		} else {
			return
		}
	}

	storedCRC, err := bin.ReadUint32(s.reader)
	if err != nil {
		return
	}

	body, err := bin.ReadN(s.reader, int(payloadSize))
	if err != nil {
		return
	}

	hasher := util.NewHasher()
	hasher.Write(body)

	calculatedCRC := hasher.Sum32()

	if calculatedCRC == storedCRC {
		return s.parseRecords(body)
	}
	//s.logger.Printf("stored CRC %d != calculated CRC %d", storedCRC, calculatedCRC)
	return nil, nil
}

func (s *WALReader) parseRecords(body []byte) ([]any, error) {
	var (
		src     = bytes.NewBuffer(body)
		records []any
	)

	for {
		recordType, err := src.ReadByte()
		if err != nil {
			if err == io.EOF {
				return records, nil
			}
			return nil, err
		}

		switch recordType {
		case CodeMetricAdd:
			rec := new(MetricAddRecord)
			if err = rec.Parse(src); err != nil {
				return nil, err
			}
			records = append(records, rec)

		case CodeMetricDelete:
			rec := new(MetricDeleteRecord)
			if err = rec.Parse(src); err != nil {
				return nil, err
			}
			records = append(records, rec)

		// case CodeAppendedMeasure:
		// 	rec := new(AppendedMeasure)
		// 	if err = rec.Parse(src); err != nil {
		// 		return nil, err
		// 	}
		// 	records = append(records, rec)

		// case CodeAppendedMeasures:
		// 	rec := new(AppendedMeasures)
		// 	if err = rec.Parse(src); err != nil {
		// 		return nil, err
		// 	}
		// 	records = append(records, rec)

		// case CodeAppendedPages:
		// 	rec := new(AppendedPages)
		// 	if err = rec.Parse(src); err != nil {
		// 		return nil, err
		// 	}
		// 	records = append(records, rec)

		case CodeMeasuresDelete:
			rec := new(MeasuresDeleteRecord)
			if err = rec.Parse(src); err != nil {
				return nil, err
			}
			records = append(records, rec)

		default:
			return nil, fmt.Errorf("unknown record type code: %d", recordType)
		}
	}
}

// HELPERS

// func (s *WALReader) Seek(offset int64) error {
// 	ret, err := s.file.Seek(offset, 0)
// 	if err != nil {
// 		return err
// 	}

// 	if ret != offset {
// 		return fmt.Errorf("ret %d != offset %d", ret, offset)
// 	}
// 	return nil
// }