package cache import ( "context" "io" "sync" "github.com/restic/restic/internal/backend" "github.com/restic/restic/internal/debug" ) // Backend wraps a restic.Backend and adds a cache. type Backend struct { backend.Backend *Cache // inProgress contains the handle for all files that are currently // downloaded. The channel in the value is closed as soon as the download // is finished. inProgressMutex sync.Mutex inProgress map[backend.Handle]chan struct{} } // ensure Backend implements backend.Backend var _ backend.Backend = &Backend{} func newBackend(be backend.Backend, c *Cache) *Backend { return &Backend{ Backend: be, Cache: c, inProgress: make(map[backend.Handle]chan struct{}), } } // Remove deletes a file from the backend and the cache if it has been cached. func (b *Backend) Remove(ctx context.Context, h backend.Handle) error { debug.Log("cache Remove(%v)", h) err := b.Backend.Remove(ctx, h) if err != nil { return err } err = b.Cache.remove(h) return err } func autoCacheTypes(h backend.Handle) bool { switch h.Type { case backend.IndexFile, backend.SnapshotFile: return true case backend.PackFile: return h.IsMetadata } return false } // Save stores a new file in the backend and the cache. func (b *Backend) Save(ctx context.Context, h backend.Handle, rd backend.RewindReader) error { if !autoCacheTypes(h) { return b.Backend.Save(ctx, h, rd) } debug.Log("Save(%v): auto-store in the cache", h) // make sure the reader is at the start err := rd.Rewind() if err != nil { return err } // first, save in the backend err = b.Backend.Save(ctx, h, rd) if err != nil { return err } // next, save in the cache err = rd.Rewind() if err != nil { return err } err = b.Cache.save(h, rd) if err != nil { debug.Log("unable to save %v to cache: %v", h, err) return err } return nil } func (b *Backend) cacheFile(ctx context.Context, h backend.Handle) error { finish := make(chan struct{}) b.inProgressMutex.Lock() other, alreadyDownloading := b.inProgress[h] if !alreadyDownloading { b.inProgress[h] = finish } b.inProgressMutex.Unlock() if alreadyDownloading { debug.Log("readahead %v is already performed by somebody else, delegating...", h) <-other debug.Log("download %v finished", h) return nil } defer func() { // signal other waiting goroutines that the file may now be cached close(finish) // remove the finish channel from the map b.inProgressMutex.Lock() delete(b.inProgress, h) b.inProgressMutex.Unlock() }() // test again, maybe the file was cached in the meantime if !b.Cache.Has(h) { // nope, it's still not in the cache, pull it from the repo and save it err := b.Backend.Load(ctx, h, 0, 0, func(rd io.Reader) error { return b.Cache.save(h, rd) }) if err != nil { // try to remove from the cache, ignore errors _ = b.Cache.remove(h) } return err } return nil } // loadFromCache will try to load the file from the cache. func (b *Backend) loadFromCache(h backend.Handle, length int, offset int64, consumer func(rd io.Reader) error) (bool, error) { rd, inCache, err := b.Cache.load(h, length, offset) if err != nil { return inCache, err } err = consumer(rd) if err != nil { _ = rd.Close() // ignore secondary errors return true, err } return true, rd.Close() } // Load loads a file from the cache or the backend. func (b *Backend) Load(ctx context.Context, h backend.Handle, length int, offset int64, consumer func(rd io.Reader) error) error { b.inProgressMutex.Lock() waitForFinish, inProgress := b.inProgress[h] b.inProgressMutex.Unlock() if inProgress { debug.Log("downloading %v is already in progress, waiting for finish", h) <-waitForFinish debug.Log("downloading %v finished", h) } // try loading from cache without checking that the handle is actually cached inCache, err := b.loadFromCache(h, length, offset, consumer) if inCache { debug.Log("error loading %v from cache: %v", h, err) // the caller must explicitly use cache.Forget() to remove the cache entry return err } // if we don't automatically cache this file type, fall back to the backend if !autoCacheTypes(h) { debug.Log("Load(%v, %v, %v): delegating to backend", h, length, offset) return b.Backend.Load(ctx, h, length, offset, consumer) } debug.Log("auto-store %v in the cache", h) err = b.cacheFile(ctx, h) if err != nil { return err } inCache, err = b.loadFromCache(h, length, offset, consumer) if inCache { debug.Log("error loading %v from cache: %v", h, err) return err } debug.Log("error caching %v: %v, falling back to backend", h, err) return b.Backend.Load(ctx, h, length, offset, consumer) } // 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 backend.Handle) (backend.FileInfo, error) { debug.Log("cache Stat(%v)", h) fi, err := b.Backend.Stat(ctx, h) if err != nil && b.Backend.IsNotExist(err) { // try to remove from the cache, ignore errors _ = b.Cache.remove(h) } 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) } func (b *Backend) Unwrap() backend.Backend { return b.Backend }