jldb/mdb/change/change.go

package change

import (
	"io"

	"git.crumpington.com/public/jldb/lib/errs"
)

// ----------------------------------------------------------------------------
// Change
// ----------------------------------------------------------------------------

// The Change type encodes a change (store / delete) to be applied to a
// pagefile.
type Change struct {
	CollectionID uint64
	ItemID       uint64
	Store        bool
	Data         []byte

	WritePageIDs []uint64
	ClearPageIDs []uint64
}

func (ch Change) writeTo(w io.Writer) error {
	dataSize := int64(len(ch.Data))
	if !ch.Store {
		dataSize = -1
	}

	err := writeBin(w,
		ch.CollectionID,
		ch.ItemID,
		dataSize,
		uint64(len(ch.WritePageIDs)),
		uint64(len(ch.ClearPageIDs)),
		ch.WritePageIDs,
		ch.ClearPageIDs)
	if err != nil {
		return err
	}

	if ch.Store {
		if _, err := w.Write(ch.Data); err != nil {
			return errs.IO.WithErr(err)
		}
	}

	return nil
}

func (ch *Change) readFrom(r io.Reader) error {
	var pageCount, clearCount uint64
	var dataSize int64

	err := readBin(r,
		&ch.CollectionID,
		&ch.ItemID,
		&dataSize,
		&pageCount,
		&clearCount)
	if err != nil {
		return err
	}

	if uint64(cap(ch.WritePageIDs)) < pageCount {
		ch.WritePageIDs = make([]uint64, pageCount)
	}
	ch.WritePageIDs = ch.WritePageIDs[:pageCount]

	if uint64(cap(ch.ClearPageIDs)) < clearCount {
		ch.ClearPageIDs = make([]uint64, clearCount)
	}
	ch.ClearPageIDs = ch.ClearPageIDs[:clearCount]

	if err = readBin(r, ch.WritePageIDs); err != nil {
		return err
	}

	if err = readBin(r, ch.ClearPageIDs); err != nil {
		return err
	}

	ch.Store = dataSize != -1

	if ch.Store {
		if int64(cap(ch.Data)) < dataSize {
			ch.Data = make([]byte, dataSize)
		}
		ch.Data = ch.Data[:dataSize]
		if _, err := r.Read(ch.Data); err != nil {
			return errs.IO.WithErr(err)
		}
	} else {
		ch.Data = ch.Data[:0]
	}

	return nil
}