restic/internal/cache/cache.go

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package cache
import (
"fmt"
"io/ioutil"
"os"
"path/filepath"
"strconv"
"time"
"github.com/pkg/errors"
"github.com/restic/restic/internal/debug"
"github.com/restic/restic/internal/fs"
"github.com/restic/restic/internal/restic"
)
// Cache manages a local cache.
type Cache struct {
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Path string
Base string
PerformReadahead func(restic.Handle) bool
}
const dirMode = 0700
const fileMode = 0600
func readVersion(dir string) (v uint, err error) {
buf, err := ioutil.ReadFile(filepath.Join(dir, "version"))
if os.IsNotExist(err) {
return 0, nil
}
if err != nil {
return 0, errors.Wrap(err, "ReadFile")
}
ver, err := strconv.ParseUint(string(buf), 10, 32)
if err != nil {
return 0, errors.Wrap(err, "ParseUint")
}
return uint(ver), nil
}
const cacheVersion = 1
// ensure Cache implements restic.Cache
var _ restic.Cache = &Cache{}
var cacheLayoutPaths = map[restic.FileType]string{
restic.DataFile: "data",
restic.SnapshotFile: "snapshots",
restic.IndexFile: "index",
}
const cachedirTagSignature = "Signature: 8a477f597d28d172789f06886806bc55\n"
func writeCachedirTag(dir string) error {
if err := fs.MkdirAll(dir, dirMode); err != nil {
return err
}
f, err := fs.OpenFile(filepath.Join(dir, "CACHEDIR.TAG"), os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0644)
if err != nil {
if os.IsExist(errors.Cause(err)) {
return nil
}
return errors.Wrap(err, "OpenFile")
}
debug.Log("Create CACHEDIR.TAG at %v", dir)
if _, err := f.Write([]byte(cachedirTagSignature)); err != nil {
_ = f.Close()
return errors.Wrap(err, "Write")
}
return f.Close()
}
// New returns a new cache for the repo ID at basedir. If basedir is the empty
// string, the default cache location (according to the XDG standard) is used.
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//
// For partial files, the complete file is loaded and stored in the cache when
// performReadahead returns true.
func New(id string, basedir string) (c *Cache, err error) {
if basedir == "" {
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basedir, err = DefaultDir()
if err != nil {
return nil, err
}
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}
err = mkdirCacheDir(basedir)
if err != nil {
return nil, err
}
// create base dir and tag it as a cache directory
if err = writeCachedirTag(basedir); err != nil {
return nil, err
}
cachedir := filepath.Join(basedir, id)
debug.Log("using cache dir %v", cachedir)
v, err := readVersion(cachedir)
if err != nil {
return nil, err
}
if v > cacheVersion {
return nil, errors.New("cache version is newer")
}
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// create the repo cache dir if it does not exist yet
if err = fs.MkdirAll(cachedir, dirMode); err != nil {
return nil, err
}
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// update the timestamp so that we can detect old cache dirs
err = updateTimestamp(cachedir)
if err != nil {
return nil, err
}
if v < cacheVersion {
err = ioutil.WriteFile(filepath.Join(cachedir, "version"), []byte(fmt.Sprintf("%d", cacheVersion)), 0644)
if err != nil {
return nil, errors.Wrap(err, "WriteFile")
}
}
for _, p := range cacheLayoutPaths {
if err = fs.MkdirAll(filepath.Join(cachedir, p), dirMode); err != nil {
return nil, err
}
}
c = &Cache{
Path: cachedir,
Base: basedir,
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PerformReadahead: func(restic.Handle) bool {
// do not perform readahead by default
return false
},
}
return c, nil
}
// updateTimestamp sets the modification timestamp (mtime and atime) for the
// directory d to the current time.
func updateTimestamp(d string) error {
t := time.Now()
return fs.Chtimes(d, t, t)
}
const maxCacheAge = 30 * 24 * time.Hour
// Old returns a list of cache directories with a modification time of more
// than 30 days ago.
func Old(basedir string) ([]string, error) {
var oldCacheDirs []string
f, err := fs.Open(basedir)
if err != nil {
return nil, err
}
entries, err := f.Readdir(-1)
if err != nil {
return nil, err
}
oldest := time.Now().Add(-maxCacheAge)
for _, fi := range entries {
if !fi.IsDir() {
continue
}
if !fi.ModTime().Before(oldest) {
continue
}
oldCacheDirs = append(oldCacheDirs, fi.Name())
}
err = f.Close()
if err != nil {
return nil, err
}
debug.Log("%d old cache dirs found", len(oldCacheDirs))
return oldCacheDirs, nil
}
// errNoSuchFile is returned when a file is not cached.
type errNoSuchFile struct {
Type string
Name string
}
func (e errNoSuchFile) Error() string {
return fmt.Sprintf("file %v (%v) is not cached", e.Name, e.Type)
}
// IsNotExist returns true if the error was caused by a non-existing file.
func (c *Cache) IsNotExist(err error) bool {
_, ok := errors.Cause(err).(errNoSuchFile)
return ok
}
// Wrap returns a backend with a cache.
func (c *Cache) Wrap(be restic.Backend) restic.Backend {
return newBackend(be, c)
}
// BaseDir returns the base directory.
func (c *Cache) BaseDir() string {
return c.Base
}