func packIDTester(repo *repository.Repository, inChan <-chan backend.ID, errChan chan<- error, wg *sync.WaitGroup, done <-chan struct{}) {
	debug.Log("Checker.testPackID", "worker start")
	defer debug.Log("Checker.testPackID", "worker done")

	defer wg.Done()

	for id := range inChan {
		ok, err := repo.Backend().Test(backend.Data, id.String())
		if err != nil {
			err = PackError{ID: id, Err: err}
		} else {
			if !ok {
				err = PackError{ID: id, Err: errors.New("does not exist")}
			}
		}

		if err != nil {
			debug.Log("Checker.testPackID", "error checking for pack %s: %v", id.Str(), err)
			select {
			case <-done:
				return
			case errChan <- err:
			}

			continue
		}

		debug.Log("Checker.testPackID", "pack %s exists", id.Str())
	}
}

func (node Node) createFileAt(path string, repo *repository.Repository) error {
	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY, 0600)
	defer f.Close()

	if err != nil {
		return errors.Annotate(err, "OpenFile")
	}

	var buf []byte
	for _, id := range node.Content {
		_, _, _, length, err := repo.Index().Lookup(id)
		if err != nil {
			return err
		}

		buf = buf[:cap(buf)]
		if uint(len(buf)) < length {
			buf = make([]byte, length)
		}

		buf, err := repo.LoadBlob(pack.Data, id, buf)
		if err != nil {
			return errors.Annotate(err, "Load")
		}

		_, err = f.Write(buf)
		if err != nil {
			return errors.Annotate(err, "Write")
		}
	}

	return nil
}

func printTrees(repo *repository.Repository, wr io.Writer) error {
	done := make(chan struct{})
	defer close(done)

	trees := []backend.ID{}

	for _, idx := range repo.Index().All() {
		for blob := range idx.Each(nil) {
			if blob.Type != pack.Tree {
				continue
			}

			trees = append(trees, blob.ID)
		}
	}

	for _, id := range trees {
		tree, err := restic.LoadTree(repo, id)
		if err != nil {
			fmt.Fprintf(os.Stderr, "LoadTree(%v): %v", id.Str(), err)
			continue
		}

		fmt.Fprintf(wr, "tree_id: %v\n", id)

		prettyPrintJSON(wr, tree)
	}

	return nil
}

func findLatestSnapshot(repo *repository.Repository, targets []string) (backend.ID, error) {
	var (
		latest   time.Time
		latestID backend.ID
		found    bool
	)

	for snapshotID := range repo.List(backend.Snapshot, make(chan struct{})) {
		snapshot, err := restic.LoadSnapshot(repo, snapshotID)
		if err != nil {
			return backend.ID{}, fmt.Errorf("Error listing snapshot: %v", err)
		}
		if snapshot.Time.After(latest) && samePaths(snapshot.Paths, targets) {
			latest = snapshot.Time
			latestID = snapshotID
			found = true
		}
	}

	if !found {
		return backend.ID{}, errNoSnapshotFound
	}

	return latestID, nil
}

// FindSnapshot takes a string and tries to find a snapshot whose ID matches
// the string as closely as possible.
func FindSnapshot(repo *repository.Repository, s string) (backend.ID, error) {
	// find snapshot id with prefix
	name, err := backend.Find(repo.Backend(), backend.Snapshot, s)
	if err != nil {
		return nil, err
	}

	return backend.ParseID(name)
}

func LoadSnapshot(repo *repository.Repository, id backend.ID) (*Snapshot, error) {
	sn := &Snapshot{id: id}
	err := repo.LoadJSONUnpacked(backend.Snapshot, id, sn)
	if err != nil {
		return nil, err
	}

	return sn, nil
}

// LoadLock loads and unserializes a lock from a repository.
func LoadLock(repo *repository.Repository, id backend.ID) (*Lock, error) {
	lock := &Lock{}
	if err := repo.LoadJSONUnpacked(backend.Lock, id, lock); err != nil {
		return nil, err
	}
	lock.lockID = &id

	return lock, nil
}

func createFakeLock(repo *repository.Repository, t time.Time, pid int) (backend.ID, error) {
	hostname, err := os.Hostname()
	if err != nil {
		return backend.ID{}, err
	}

	newLock := &restic.Lock{Time: t, PID: pid, Hostname: hostname}
	return repo.SaveJSONUnpacked(backend.Lock, &newLock)
}

func TeardownRepo(t testing.TB, repo *repository.Repository) {
	if !TestCleanup {
		l := repo.Backend().(*local.Local)
		t.Logf("leaving local backend at %s\n", l.Location())
		return
	}

	OK(t, repo.Delete())
}

func LoadTree(repo *repository.Repository, id backend.ID) (*Tree, error) {
	tree := &Tree{}
	err := repo.LoadJSONPack(pack.Tree, id, tree)
	if err != nil {
		return nil, err
	}

	return tree, nil
}

func (cmd CmdKey) addKey(repo *repository.Repository) error {
	id, err := repository.AddKey(repo, cmd.getNewPassword(), repo.Key())
	if err != nil {
		return fmt.Errorf("creating new key failed: %v\n", err)
	}

	cmd.global.Verbosef("saved new key as %s\n", id)

	return nil
}

func list(repo *repository.Repository, t backend.Type) (IDs []string) {
	done := make(chan struct{})
	defer close(done)

	for id := range repo.List(t, done) {
		IDs = append(IDs, id.String())
	}

	return IDs
}

// FindBlobsForPacks returns the set of blobs contained in a pack of packs.
func FindBlobsForPacks(repo *repository.Repository, packs backend.IDSet) (backend.IDSet, error) {
	blobs := backend.NewIDSet()

	for packID := range packs {
		for _, packedBlob := range repo.Index().ListPack(packID) {
			blobs.Insert(packedBlob.ID)
		}
	}

	return blobs, nil
}

func TeardownRepo(repo *repository.Repository) {
	if !TestCleanup {
		l := repo.Backend().(*local.Local)
		fmt.Printf("leaving local backend at %s\n", l.Location())
		return
	}

	err := repo.Delete()
	if err != nil {
		panic(err)
	}
}

// saveRandomDataBlobs generates random data blobs and saves them to the repository.
func saveRandomDataBlobs(t testing.TB, repo *repository.Repository, num int, sizeMax int) {
	for i := 0; i < num; i++ {
		size := mrand.Int() % sizeMax

		buf := make([]byte, size)
		_, err := io.ReadFull(rand.Reader, buf)
		OK(t, err)

		_, err = repo.SaveAndEncrypt(pack.Data, buf, nil)
		OK(t, err)
	}
}

func (cmd CmdKey) deleteKey(repo *repository.Repository, name string) error {
	if name == repo.KeyName() {
		return errors.New("refusing to remove key currently used to access repository")
	}

	err := repo.Backend().Remove(backend.Key, name)
	if err != nil {
		return err
	}

	cmd.global.Verbosef("removed key %v\n", name)
	return nil
}

// RemoveStaleLocks deletes all locks detected as stale from the repository.
func RemoveStaleLocks(repo *repository.Repository) error {
	return eachLock(repo, func(id backend.ID, lock *Lock, err error) error {
		// ignore locks that cannot be loaded
		if err != nil {
			return nil
		}

		if lock.Stale() {
			return repo.Backend().Remove(backend.Lock, id.String())
		}

		return nil
	})
}

func eachLock(repo *repository.Repository, f func(backend.ID, *Lock, error) error) error {
	done := make(chan struct{})
	defer close(done)

	for id := range repo.List(backend.Lock, done) {
		lock, err := LoadLock(repo, id)
		err = f(id, lock, err)
		if err != nil {
			return err
		}
	}

	return nil
}

// FindPacksForBlobs returns the set of packs that contain the blobs.
func FindPacksForBlobs(repo *repository.Repository, blobs backend.IDSet) (backend.IDSet, error) {
	packs := backend.NewIDSet()
	idx := repo.Index()
	for id := range blobs {
		blob, err := idx.Lookup(id)
		if err != nil {
			return nil, err
		}

		packs.Insert(blob.PackID)
	}

	return packs, nil
}

// RepackBlobs reads all blobs in blobIDs from src and saves them into new pack
// files in dst. Source and destination repo may be the same.
func RepackBlobs(src, dst *repository.Repository, blobIDs backend.IDSet) (err error) {
	for id := range blobIDs {
		err = repackBlob(src, dst, id)
		if err != nil {
			return err
		}
	}

	err = dst.Flush()
	if err != nil {
		return err
	}

	return nil
}