1st

atree/redo/reader.go

@@ -0,0 +1,96 @@
+package redo
+
+import (
+	"fmt"
+	"hash/crc32"
+	"io"
+	"os"
+
+	"gordenko.dev/dima/qb/bin"
+)
+
+type REDOFile struct {
+	MetricID         uint32
+	Timestamp        uint32
+	Value            float64
+	IsDataPageReused bool
+	DataPage         PageToWrite
+	IsRootChanged    bool
+	RootPageNo       uint32
+	ReusedIndexPages []uint32
+	IndexPages       []PageToWrite
+}
+
+type ReadREDOFileReq struct {
+	FileName      string
+	DataPageSize  int
+	IndexPageSize int
+}
+
+func ReadREDOFile(req ReadREDOFileReq) (*REDOFile, error) {
+	buf, err := os.ReadFile(req.FileName)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(buf) < 25 {
+		return nil, io.EOF
+	}
+
+	var (
+		end                = len(buf) - 4
+		payload            = buf[:end]
+		checksum           = bin.GetUint32(buf[end:])
+		calculatedChecksum = crc32.ChecksumIEEE(payload)
+	)
+
+	// Помилка чексуми означає що файл або недописаний, або пошкодженний
+	if checksum != calculatedChecksum {
+		return nil, fmt.Errorf("written checksum %d not equal calculated checksum %d",
+			checksum, calculatedChecksum)
+	}
+
+	var (
+		redoLog = REDOFile{
+			MetricID:         bin.GetUint32(buf[0:]),
+			Timestamp:        bin.GetUint32(buf[4:]),
+			Value:            bin.GetFloat64(buf[8:]),
+			IsDataPageReused: buf[16] == 1,
+			DataPage: PageToWrite{
+				PageNo: bin.GetUint32(buf[17:]),
+				Data:   buf[21 : 21+req.DataPageSize],
+			},
+		}
+		pos = 21 + req.DataPageSize
+	)
+
+	for {
+		if pos == len(payload) {
+			return &redoLog, nil
+		}
+
+		if pos > len(payload) {
+			return nil, io.EOF
+		}
+
+		flags := buf[pos]
+
+		item := PageToWrite{
+			PageNo: bin.GetUint32(buf[pos+1:]),
+		}
+		pos += 5 // flags + pageNo
+		item.Data = buf[pos : pos+req.IndexPageSize]
+		pos += req.IndexPageSize
+
+		redoLog.IndexPages = append(redoLog.IndexPages, item)
+
+		if (flags & FlagReused) == FlagReused {
+			redoLog.ReusedIndexPages = append(redoLog.ReusedIndexPages, item.PageNo)
+		}
+
+		if (flags & FlagNewRoot) == FlagNewRoot {
+			redoLog.IsRootChanged = true
+			redoLog.RootPageNo = item.PageNo
+		}
+	}
+}