utils.go

package pqueue

import (
	"container/list"
	"fmt"
	"os"
	"path"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"time"
)

type file struct {
	modTime time.Time
	path    string
}

func load(settings QueueSettings, segHeader segmentHeadWriter) (*queue, error) {
	if settings.MaxEntriesPerSegment <= 0 {
		settings.MaxEntriesPerSegment = DefaultMaxEntriesPerSegment
	}

	files, err := loadFileInfos(settings.DataDir, fileInfoExtractor)
	if err != nil {
		return nil, err
	}

	segments := list.New()
	for i := range files {
		segments.PushBack(&segment{
			readable: false,
			path:     files[i].path,
		})
	}

	// create new segment for upcoming entries
	q := &queue{
		settings:      settings,
		segHeadWriter: segHeader,
	}

	seg, err := q.newSegment()
	if err != nil {
		return nil, err
	}
	segments.PushBack(seg)

	q.segments = segments
	return q, nil
}

func loadFileInfos(dir string, infoExtractor func(os.DirEntry) (os.FileInfo, error)) ([]file, error) {
	fileList, err := os.ReadDir(dir)
	if err != nil {
		return nil, err
	}

	files := make([]file, 0, len(fileList))
	for i := range fileList {
		fileName := fileList[i].Name()

		if strings.HasPrefix(fileName, segPrefix) &&
			!strings.HasSuffix(fileName, segOffsetFileSuffix) {
			// extract file info
			info, e := infoExtractor(fileList[i])
			if e != nil {
				return nil, e
			}

			// add to list
			files = append(files, file{
				path:    filepath.Join(dir, fileList[i].Name()),
				modTime: info.ModTime(),
			})
		}
	}

	sort.Slice(files, func(i, j int) bool {
		return files[i].modTime.Before(files[j].modTime)
	})

	return files, nil
}

func fileInfoExtractor(f os.DirEntry) (os.FileInfo, error) {
	return f.Info()
}

func createFile(dir, prefix string) (f *os.File, err error) {
	prefix = path.Join(dir, prefix)

	for attempt := 0; attempt < 10_000; attempt++ {
		name := prefix + strconv.FormatInt(time.Now().UnixNano(), 10)

		f, err = os.OpenFile(name, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o600)
		if !os.IsExist(err) {
			return
		}
	}

	err = fmt.Errorf("creating file but fail. path: %s", dir)
	return
}