backend: refactor backend Connections and HasAtomicReplace into Properties

internal/backend/azure/azure.go

@@ -217,8 +217,11 @@ func (be *Backend) IsPermanentError(err error) bool {
 	return false
 }
 
-func (be *Backend) Connections() uint {
-	return be.connections
+func (be *Backend) Properties() backend.Properties {
+	return backend.Properties{
+		Connections:      be.connections,
+		HasAtomicReplace: true,
+	}
 }
 
 // Hasher may return a hash function for calculating a content hash for the backend
@@ -226,11 +229,6 @@ func (be *Backend) Hasher() hash.Hash {
 	return md5.New()
 }
 
-// HasAtomicReplace returns whether Save() can atomically replace files
-func (be *Backend) HasAtomicReplace() bool {
-	return true
-}
-
 // Path returns the path in the bucket that is used for this backend.
 func (be *Backend) Path() string {
 	return be.prefix

internal/backend/b2/b2.go

@@ -154,8 +154,11 @@ func (be *b2Backend) SetListMaxItems(i int) {
 	be.listMaxItems = i
 }
 
-func (be *b2Backend) Connections() uint {
-	return be.cfg.Connections
+func (be *b2Backend) Properties() backend.Properties {
+	return backend.Properties{
+		Connections:      be.cfg.Connections,
+		HasAtomicReplace: true,
+	}
 }
 
 // Hasher may return a hash function for calculating a content hash for the backend
@@ -163,11 +166,6 @@ func (be *b2Backend) Hasher() hash.Hash {
 	return nil
 }
 
-// HasAtomicReplace returns whether Save() can atomically replace files
-func (be *b2Backend) HasAtomicReplace() bool {
-	return true
-}
-
 // IsNotExist returns true if the error is caused by a non-existing file.
 func (be *b2Backend) IsNotExist(err error) bool {
 	// blazer/b2 does not export its error types and values,

internal/backend/backend.go

@@ -17,15 +17,12 @@ var ErrNoRepository = fmt.Errorf("repository does not exist")
 // the context package need not be wrapped, as context cancellation is checked
 // separately by the retrying logic.
 type Backend interface {
-	// Connections returns the maximum number of concurrent backend operations.
-	Connections() uint
+	// Properties returns information about the backend
+	Properties() Properties
 
 	// Hasher may return a hash function for calculating a content hash for the backend
 	Hasher() hash.Hash
 
-	// HasAtomicReplace returns whether Save() can atomically replace files
-	HasAtomicReplace() bool
-
 	// Remove removes a File described by h.
 	Remove(ctx context.Context, h Handle) error
 
@@ -92,6 +89,14 @@ type Backend interface {
 	WarmupWait(ctx context.Context, h []Handle) error
 }
 
+type Properties struct {
+	// Connections states the maximum number of concurrent backend operations.
+	Connections uint
+
+	// HasAtomicReplace states whether Save() can atomically replace files
+	HasAtomicReplace bool
+}
+
 type Unwrapper interface {
 	// Unwrap returns the underlying backend or nil if there is none.
 	Unwrap() Backend

internal/backend/dryrun/dry_backend.go

@@ -42,8 +42,8 @@ func (be *Backend) Remove(_ context.Context, _ backend.Handle) error {
 	return nil
 }
 
-func (be *Backend) Connections() uint {
-	return be.b.Connections()
+func (be *Backend) Properties() backend.Properties {
+	return be.b.Properties()
 }
 
 // Delete removes all data in the backend.
@@ -59,10 +59,6 @@ func (be *Backend) Hasher() hash.Hash {
 	return be.b.Hasher()
 }
 
-func (be *Backend) HasAtomicReplace() bool {
-	return be.b.HasAtomicReplace()
-}
-
 func (be *Backend) IsNotExist(err error) bool {
 	return be.b.IsNotExist(err)
 }

internal/backend/gs/gs.go

@@ -186,8 +186,11 @@ func (be *Backend) IsPermanentError(err error) bool {
 	return false
 }
 
-func (be *Backend) Connections() uint {
-	return be.connections
+func (be *Backend) Properties() backend.Properties {
+	return backend.Properties{
+		Connections:      be.connections,
+		HasAtomicReplace: true,
+	}
 }
 
 // Hasher may return a hash function for calculating a content hash for the backend
@@ -195,11 +198,6 @@ func (be *Backend) Hasher() hash.Hash {
 	return md5.New()
 }
 
-// HasAtomicReplace returns whether Save() can atomically replace files
-func (be *Backend) HasAtomicReplace() bool {
-	return true
-}
-
 // Path returns the path in the bucket that is used for this backend.
 func (be *Backend) Path() string {
 	return be.prefix

internal/backend/local/local.go

@@ -84,8 +84,11 @@ func Create(_ context.Context, cfg Config) (*Local, error) {
 	return be, nil
 }
 
-func (b *Local) Connections() uint {
-	return b.Config.Connections
+func (b *Local) Properties() backend.Properties {
+	return backend.Properties{
+		Connections:      b.Config.Connections,
+		HasAtomicReplace: true,
+	}
 }
 
 // Hasher may return a hash function for calculating a content hash for the backend
@@ -93,11 +96,6 @@ func (b *Local) Hasher() hash.Hash {
 	return nil
 }
 
-// HasAtomicReplace returns whether Save() can atomically replace files
-func (b *Local) HasAtomicReplace() bool {
-	return true
-}
-
 // IsNotExist returns true if the error is caused by a non existing file.
 func (b *Local) IsNotExist(err error) bool {
 	return errors.Is(err, os.ErrNotExist)

internal/backend/mem/mem_backend.go

@@ -218,8 +218,11 @@ func (be *MemoryBackend) List(ctx context.Context, t backend.FileType, fn func(b
 	return ctx.Err()
 }
 
-func (be *MemoryBackend) Connections() uint {
-	return connectionCount
+func (be *MemoryBackend) Properties() backend.Properties {
+	return backend.Properties{
+		Connections:      connectionCount,
+		HasAtomicReplace: false,
+	}
 }
 
 // Hasher may return a hash function for calculating a content hash for the backend
@@ -227,11 +230,6 @@ func (be *MemoryBackend) Hasher() hash.Hash {
 	return xxhash.New()
 }
 
-// HasAtomicReplace returns whether Save() can atomically replace files
-func (be *MemoryBackend) HasAtomicReplace() bool {
-	return false
-}
-
 // Delete removes all data in the backend.
 func (be *MemoryBackend) Delete(ctx context.Context) error {
 	be.m.Lock()

internal/backend/mock/backend.go

@@ -22,9 +22,8 @@ type Backend struct {
 	DeleteFn           func(ctx context.Context) error
 	WarmupFn           func(ctx context.Context, h []backend.Handle) ([]backend.Handle, error)
 	WarmupWaitFn       func(ctx context.Context, h []backend.Handle) error
-	ConnectionsFn      func() uint
+	PropertiesFn       func() backend.Properties
 	HasherFn           func() hash.Hash
-	HasAtomicReplaceFn func() bool
 }
 
 // NewBackend returns new mock Backend instance
@@ -42,12 +41,15 @@ func (m *Backend) Close() error {
 	return m.CloseFn()
 }
 
-func (m *Backend) Connections() uint {
-	if m.ConnectionsFn == nil {
-		return 2
+func (m *Backend) Properties() backend.Properties {
+	if m.PropertiesFn == nil {
+		return backend.Properties{
+			Connections:      2,
+			HasAtomicReplace: false,
+		}
 	}
 
-	return m.ConnectionsFn()
+	return m.PropertiesFn()
 }
 
 // Hasher may return a hash function for calculating a content hash for the backend
@@ -59,14 +61,6 @@ func (m *Backend) Hasher() hash.Hash {
 	return m.HasherFn()
 }
 
-// HasAtomicReplace returns whether Save() can atomically replace files
-func (m *Backend) HasAtomicReplace() bool {
-	if m.HasAtomicReplaceFn == nil {
-		return false
-	}
-	return m.HasAtomicReplaceFn()
-}
-
 // IsNotExist returns true if the error is caused by a missing file.
 func (m *Backend) IsNotExist(err error) bool {
 	if m.IsNotExistFn == nil {

internal/backend/rest/rest.go

@@ -116,8 +116,12 @@ func Create(ctx context.Context, cfg Config, rt http.RoundTripper) (*Backend, er
 	return be, nil
 }
 
-func (b *Backend) Connections() uint {
-	return b.connections
+func (b *Backend) Properties() backend.Properties {
+	return backend.Properties{
+		Connections: b.connections,
+		// rest-server prevents overwriting
+		HasAtomicReplace: false,
+	}
 }
 
 // Hasher may return a hash function for calculating a content hash for the backend
@@ -125,12 +129,6 @@ func (b *Backend) Hasher() hash.Hash {
 	return nil
 }
 
-// HasAtomicReplace returns whether Save() can atomically replace files
-func (b *Backend) HasAtomicReplace() bool {
-	// rest-server prevents overwriting
-	return false
-}
-
 // Save stores data in the backend at the handle.
 func (b *Backend) Save(ctx context.Context, h backend.Handle, rd backend.RewindReader) error {
 	ctx, cancel := context.WithCancel(ctx)

internal/backend/retry/backend_retry.go

@@ -166,7 +166,7 @@ func (be *Backend) Save(ctx context.Context, h backend.Handle, rd backend.Rewind
 			return nil
 		}
 
-		if be.Backend.HasAtomicReplace() {
+		if be.Backend.Properties().HasAtomicReplace {
 			debug.Log("Save(%v) failed with error: %v", h, err)
 			// there is no need to remove files from backends which can atomically replace files
 			// in fact if something goes wrong at the backend side the delete operation might delete the wrong instance of the file

internal/backend/retry/backend_retry_test.go

@@ -69,7 +69,12 @@ func TestBackendSaveRetryAtomic(t *testing.T) {
 			calledRemove = true
 			return nil
 		},
-		HasAtomicReplaceFn: func() bool { return true },
+		PropertiesFn: func() backend.Properties {
+			return backend.Properties{
+				Connections:      2,
+				HasAtomicReplace: true,
+			}
+		},
 	}
 
 	TestFastRetries(t)

internal/backend/s3/s3.go

@@ -261,8 +261,11 @@ func (be *Backend) IsPermanentError(err error) bool {
 	return false
 }
 
-func (be *Backend) Connections() uint {
-	return be.cfg.Connections
+func (be *Backend) Properties() backend.Properties {
+	return backend.Properties{
+		Connections:      be.cfg.Connections,
+		HasAtomicReplace: true,
+	}
 }
 
 // Hasher may return a hash function for calculating a content hash for the backend
@@ -270,11 +273,6 @@ func (be *Backend) Hasher() hash.Hash {
 	return nil
 }
 
-// HasAtomicReplace returns whether Save() can atomically replace files
-func (be *Backend) HasAtomicReplace() bool {
-	return true
-}
-
 // Path returns the path in the bucket that is used for this backend.
 func (be *Backend) Path() string {
 	return be.cfg.Prefix

internal/backend/sema/backend.go

@@ -22,7 +22,7 @@ type connectionLimitedBackend struct {
 
 // NewBackend creates a backend that limits the concurrent operations on the underlying backend
 func NewBackend(be backend.Backend) backend.Backend {
-	sem, err := newSemaphore(be.Connections())
+	sem, err := newSemaphore(be.Properties().Connections)
 	if err != nil {
 		panic(err)
 	}

internal/backend/sema/backend_test.go

@@ -106,7 +106,12 @@ func concurrencyTester(t *testing.T, setup func(m *mock.Backend), handler func(b
 
 	m := mock.NewBackend()
 	setup(m)
-	m.ConnectionsFn = func() uint { return uint(expectBlocked) }
+	m.PropertiesFn = func() backend.Properties {
+		return backend.Properties{
+			Connections:      uint(expectBlocked),
+			HasAtomicReplace: false,
+		}
+	}
 	be := sema.NewBackend(m)
 
 	var wg errgroup.Group
@@ -206,7 +211,12 @@ func TestFreeze(t *testing.T) {
 		atomic.AddInt64(&counter, 1)
 		return nil
 	}
-	m.ConnectionsFn = func() uint { return 2 }
+	m.PropertiesFn = func() backend.Properties {
+		return backend.Properties{
+			Connections:      2,
+			HasAtomicReplace: false,
+		}
+	}
 	be := sema.NewBackend(m)
 	fb := be.(backend.FreezeBackend)
 

internal/backend/sftp/sftp.go

@@ -264,8 +264,11 @@ func Create(ctx context.Context, cfg Config) (*SFTP, error) {
 	return open(sftp, cfg)
 }
 
-func (r *SFTP) Connections() uint {
-	return r.Config.Connections
+func (r *SFTP) Properties() backend.Properties {
+	return backend.Properties{
+		Connections:      r.Config.Connections,
+		HasAtomicReplace: r.posixRename,
+	}
 }
 
 // Hasher may return a hash function for calculating a content hash for the backend
@@ -273,11 +276,6 @@ func (r *SFTP) Hasher() hash.Hash {
 	return nil
 }
 
-// HasAtomicReplace returns whether Save() can atomically replace files
-func (r *SFTP) HasAtomicReplace() bool {
-	return r.posixRename
-}
-
 // tempSuffix generates a random string suffix that should be sufficiently long
 // to avoid accidental conflicts
 func tempSuffix() string {

internal/backend/swift/swift.go

@@ -111,8 +111,11 @@ func (be *beSwift) createContainer(ctx context.Context, policy string) error {
 	return be.conn.ContainerCreate(ctx, be.container, h)
 }
 
-func (be *beSwift) Connections() uint {
-	return be.connections
+func (be *beSwift) Properties() backend.Properties {
+	return backend.Properties{
+		Connections:      be.connections,
+		HasAtomicReplace: true,
+	}
 }
 
 // Hasher may return a hash function for calculating a content hash for the backend
@@ -120,11 +123,6 @@ func (be *beSwift) Hasher() hash.Hash {
 	return md5.New()
 }
 
-// HasAtomicReplace returns whether Save() can atomically replace files
-func (be *beSwift) HasAtomicReplace() bool {
-	return true
-}
-
 // Load runs fn with a reader that yields the contents of the file at h at the
 // given offset.
 func (be *beSwift) Load(ctx context.Context, h backend.Handle, length int, offset int64, fn func(rd io.Reader) error) error {

internal/repository/repository.go

@@ -552,7 +552,7 @@ func (r *Repository) StartPackUploader(ctx context.Context, wg *errgroup.Group)
 
 	innerWg, ctx := errgroup.WithContext(ctx)
 	r.packerWg = innerWg
-	r.uploader = newPackerUploader(ctx, innerWg, r, r.be.Connections())
+	r.uploader = newPackerUploader(ctx, innerWg, r, r.Connections())
 	r.treePM = newPackerManager(r.key, restic.TreeBlob, r.packSize(), r.uploader.QueuePacker)
 	r.dataPM = newPackerManager(r.key, restic.DataBlob, r.packSize(), r.uploader.QueuePacker)
 
@@ -587,7 +587,7 @@ func (r *Repository) flushPacks(ctx context.Context) error {
 }
 
 func (r *Repository) Connections() uint {
-	return r.be.Connections()
+	return r.be.Properties().Connections
 }
 
 func (r *Repository) LookupBlob(tpe restic.BlobType, id restic.ID) []restic.PackedBlob {

internal/repository/upgrade_repo.go

@@ -33,7 +33,7 @@ func (err *upgradeRepoV2Error) Unwrap() error {
 func upgradeRepository(ctx context.Context, repo *Repository) error {
 	h := backend.Handle{Type: backend.ConfigFile}
 
-	if !repo.be.HasAtomicReplace() {
+	if !repo.be.Properties().HasAtomicReplace {
 		// remove the original file for backends which do not support atomic overwriting
 		err := repo.be.Remove(ctx, h)
 		if err != nil {