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restic/internal/cache/backend.go

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package cache
import (
"context"
"io"
"github.com/restic/restic/internal/debug"
"github.com/restic/restic/internal/restic"
)
// Backend wraps a restic.Backend and adds a cache.
type Backend struct {
restic.Backend
restic.Cache
}
// ensure cachedBackend implements restic.Backend
var _ restic.Backend = &Backend{}
// Remove deletes a file from the backend and the cache if it has been cached.
func (b *Backend) Remove(ctx context.Context, h restic.Handle) error {
debug.Log("cache Remove(%v)", h)
err := b.Backend.Remove(ctx, h)
if err != nil {
return err
}
return b.Cache.Remove(h)
}
type teeReader struct {
rd io.Reader
wr io.Writer
err error
}
func (t *teeReader) Read(p []byte) (n int, err error) {
n, err = t.rd.Read(p)
if t.err == nil && n > 0 {
_, t.err = t.wr.Write(p[:n])
}
return n, err
}
var autoCacheTypes = map[restic.FileType]struct{}{
restic.IndexFile: struct{}{},
restic.SnapshotFile: struct{}{},
}
// Save stores a new file is the backend and the cache.
func (b *Backend) Save(ctx context.Context, h restic.Handle, rd io.Reader) (err error) {
debug.Log("cache Save(%v)", h)
if _, ok := autoCacheTypes[h.Type]; !ok {
return b.Backend.Save(ctx, h, rd)
}
wr, err := b.Cache.SaveWriter(h)
if err != nil {
debug.Log("unable to save object to cache: %v", err)
return b.Backend.Save(ctx, h, rd)
}
tr := &teeReader{rd: rd, wr: wr}
err = b.Backend.Save(ctx, h, tr)
if err != nil {
wr.Close()
b.Cache.Remove(h)
return err
}
err = wr.Close()
if err != nil {
debug.Log("cache writer returned error: %v", err)
b.Cache.Remove(h)
}
return nil
}
var autoCacheFiles = map[restic.FileType]bool{
restic.IndexFile: true,
restic.SnapshotFile: true,
}
// Load loads a file from the cache or the backend.
func (b *Backend) Load(ctx context.Context, h restic.Handle, length int, offset int64) (io.ReadCloser, error) {
if b.Cache.Has(h) {
debug.Log("Load(%v, %v, %v) from cache", h, length, offset)
return b.Cache.Load(h, length, offset)
}
debug.Log("Load(%v, %v, %v) delegated to backend", h, length, offset)
rd, err := b.Backend.Load(ctx, h, length, offset)
if err != nil {
if b.Backend.IsNotExist(err) {
// try to remove from the cache, ignore errors
_ = b.Cache.Remove(h)
}
return nil, err
}
// only cache complete files
if offset != 0 || length != 0 {
debug.Log("won't store partial file %v", h)
return rd, err
}
if _, ok := autoCacheFiles[h.Type]; !ok {
debug.Log("wrong type for auto store %v", h)
return rd, nil
}
debug.Log("auto-store %v in the cache", h)
// cache the file, then return cached copy
if err = b.Cache.Save(h, rd); err != nil {
return nil, err
}
if err = rd.Close(); err != nil {
// try to remove from the cache, ignore errors
_ = b.Cache.Remove(h)
return nil, err
}
// load from the cache and save in the backend
return b.Cache.Load(h, 0, 0)
}
// Stat tests whether the backend has a file. If it does not exist but still
// exists in the cache, it is removed from the cache.
func (b *Backend) Stat(ctx context.Context, h restic.Handle) (restic.FileInfo, error) {
debug.Log("cache Stat(%v)", h)
fi, err := b.Backend.Stat(ctx, h)
if err != nil {
if b.Backend.IsNotExist(err) {
// try to remove from the cache, ignore errors
_ = b.Cache.Remove(h)
}
return fi, err
}
return fi, err
}
// IsNotExist returns true if the error is caused by a non-existing file.
func (b *Backend) IsNotExist(err error) bool {
return b.Backend.IsNotExist(err)
}