restic/internal/cache/cache.go

165 lines
3.6 KiB
Go

package cache
import (
"fmt"
"io/ioutil"
"os"
"path/filepath"
"strconv"
"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 {
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.
//
// 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 == "" {
basedir, err = defaultCacheDir()
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")
}
// create the repo cache dir if it does not exist yet
if err = fs.MkdirAll(cachedir, dirMode); 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,
PerformReadahead: func(restic.Handle) bool {
// do not perform readahead by default
return false
},
}
return c, 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
}