backend: Add IsNotExist

src/cmds/restic/cmd_prune.go

@@ -152,6 +152,10 @@ func pruneRepository(gopts GlobalOptions, repo restic.Repository) error {
 
 		err = restic.FindUsedBlobs(ctx, repo, *sn.Tree, usedBlobs, seenBlobs)
 		if err != nil {
+			if repo.Backend().IsNotExist(err) {
+				return errors.Fatal("unable to load a tree from the repo: " + err.Error())
+			}
+
 			return err
 		}
 

src/restic/backend.go

@@ -36,6 +36,10 @@ type Backend interface {
 	// arbitrary order. A goroutine is started for this, which is stopped when
 	// ctx is cancelled.
 	List(ctx context.Context, t FileType) <-chan string
+
+	// IsNotExist returns true if the error was caused by a non-existing file
+	// in the backend.
+	IsNotExist(err error) bool
 }
 
 // FileInfo is returned by Stat() and contains information about a file in the

src/restic/backend/b2/b2.go

@@ -151,6 +151,11 @@ func (wr *wrapReader) Close() error {
 	return err
 }
 
+// IsNotExist returns true if the error is caused by a non-existing file.
+func (be *b2Backend) IsNotExist(err error) bool {
+	return b2.IsNotExist(errors.Cause(err))
+}
+
 // Load returns the data stored in the backend for h at the given offset
 // and saves it in p. Load has the same semantics as io.ReaderAt.
 func (be *b2Backend) Load(ctx context.Context, h restic.Handle, length int, offset int64) (io.ReadCloser, error) {

src/restic/backend/local/local.go

@@ -75,6 +75,11 @@ func (b *Local) Location() string {
 	return b.Path
 }
 
+// IsNotExist returns true if the error is caused by a non existing file.
+func (b *Local) IsNotExist(err error) bool {
+	return os.IsNotExist(errors.Cause(err))
+}
+
 // Save stores data in the backend at the handle.
 func (b *Local) Save(ctx context.Context, h restic.Handle, rd io.Reader) (err error) {
 	debug.Log("Save %v", h)

src/restic/backend/mem/mem_backend.go

@@ -19,6 +19,8 @@ type memMap map[restic.Handle][]byte
 // make sure that MemoryBackend implements backend.Backend
 var _ restic.Backend = &MemoryBackend{}
 
+var errNotFound = errors.New("not found")
+
 // MemoryBackend is a mock backend that uses a map for storing all data in
 // memory. This should only be used for tests.
 type MemoryBackend struct {
@@ -51,6 +53,11 @@ func (be *MemoryBackend) Test(ctx context.Context, h restic.Handle) (bool, error
 	return false, nil
 }
 
+// IsNotExist returns true if the file does not exist.
+func (be *MemoryBackend) IsNotExist(err error) bool {
+	return errors.Cause(err) == errNotFound
+}
+
 // Save adds new Data to the backend.
 func (be *MemoryBackend) Save(ctx context.Context, h restic.Handle, rd io.Reader) error {
 	if err := h.Valid(); err != nil {
@@ -101,7 +108,7 @@ func (be *MemoryBackend) Load(ctx context.Context, h restic.Handle, length int,
 	}
 
 	if _, ok := be.data[h]; !ok {
-		return nil, errors.New("no such data")
+		return nil, errNotFound
 	}
 
 	buf := be.data[h]
@@ -134,7 +141,7 @@ func (be *MemoryBackend) Stat(ctx context.Context, h restic.Handle) (restic.File
 
 	e, ok := be.data[h]
 	if !ok {
-		return restic.FileInfo{}, errors.New("no such data")
+		return restic.FileInfo{}, errNotFound
 	}
 
 	return restic.FileInfo{Size: int64(len(e))}, nil
@@ -148,7 +155,7 @@ func (be *MemoryBackend) Remove(ctx context.Context, h restic.Handle) error {
 	debug.Log("Remove %v", h)
 
 	if _, ok := be.data[h]; !ok {
-		return errors.New("no such data")
+		return errNotFound
 	}
 
 	delete(be.data, h)

src/restic/backend/rest/rest.go

@@ -138,6 +138,23 @@ func (b *restBackend) Save(ctx context.Context, h restic.Handle, rd io.Reader) (
 	return nil
 }
 
+// ErrIsNotExist is returned whenever the requested file does not exist on the
+// server.
+type ErrIsNotExist struct {
+	restic.Handle
+}
+
+func (e ErrIsNotExist) Error() string {
+	return fmt.Sprintf("%v does not exist", e.Handle)
+}
+
+// IsNotExist returns true if the error was caused by a non-existing file.
+func (b *restBackend) IsNotExist(err error) bool {
+	err = errors.Cause(err)
+	_, ok := err.(ErrIsNotExist)
+	return ok
+}
+
 // Load returns a reader that yields the contents of the file at h at the
 // given offset. If length is nonzero, only a portion of the file is
 // returned. rd must be closed after use.
@@ -179,6 +196,11 @@ func (b *restBackend) Load(ctx context.Context, h restic.Handle, length int, off
 		return nil, errors.Wrap(err, "client.Do")
 	}
 
+	if resp.StatusCode == http.StatusNotFound {
+		_ = resp.Body.Close()
+		return nil, ErrIsNotExist{h}
+	}
+
 	if resp.StatusCode != 200 && resp.StatusCode != 206 {
 		_ = resp.Body.Close()
 		return nil, errors.Errorf("unexpected HTTP response (%v): %v", resp.StatusCode, resp.Status)
@@ -205,6 +227,11 @@ func (b *restBackend) Stat(ctx context.Context, h restic.Handle) (restic.FileInf
 		return restic.FileInfo{}, errors.Wrap(err, "Close")
 	}
 
+	if resp.StatusCode == http.StatusNotFound {
+		_ = resp.Body.Close()
+		return restic.FileInfo{}, ErrIsNotExist{h}
+	}
+
 	if resp.StatusCode != 200 {
 		return restic.FileInfo{}, errors.Errorf("unexpected HTTP response (%v): %v", resp.StatusCode, resp.Status)
 	}
@@ -248,6 +275,11 @@ func (b *restBackend) Remove(ctx context.Context, h restic.Handle) error {
 		return errors.Wrap(err, "client.Do")
 	}
 
+	if resp.StatusCode == http.StatusNotFound {
+		_ = resp.Body.Close()
+		return ErrIsNotExist{h}
+	}
+
 	if resp.StatusCode != 200 {
 		return errors.Errorf("blob not removed, server response: %v (%v)", resp.Status, resp.StatusCode)
 	}

src/restic/mock/backend.go

@@ -10,15 +10,16 @@ import (
 
 // Backend implements a mock backend.
 type Backend struct {
-	CloseFn    func() error
-	SaveFn     func(ctx context.Context, h restic.Handle, rd io.Reader) error
-	LoadFn     func(ctx context.Context, h restic.Handle, length int, offset int64) (io.ReadCloser, error)
-	StatFn     func(ctx context.Context, h restic.Handle) (restic.FileInfo, error)
-	ListFn     func(ctx context.Context, t restic.FileType) <-chan string
-	RemoveFn   func(ctx context.Context, h restic.Handle) error
-	TestFn     func(ctx context.Context, h restic.Handle) (bool, error)
-	DeleteFn   func(ctx context.Context) error
-	LocationFn func() string
+	CloseFn      func() error
+	IsNotExistFn func(err error) bool
+	SaveFn       func(ctx context.Context, h restic.Handle, rd io.Reader) error
+	LoadFn       func(ctx context.Context, h restic.Handle, length int, offset int64) (io.ReadCloser, error)
+	StatFn       func(ctx context.Context, h restic.Handle) (restic.FileInfo, error)
+	ListFn       func(ctx context.Context, t restic.FileType) <-chan string
+	RemoveFn     func(ctx context.Context, h restic.Handle) error
+	TestFn       func(ctx context.Context, h restic.Handle) (bool, error)
+	DeleteFn     func(ctx context.Context) error
+	LocationFn   func() string
 }
 
 // Close the backend.
@@ -39,6 +40,15 @@ func (m *Backend) Location() string {
 	return m.LocationFn()
 }
 
+// IsNotExist returns true if the error is caused by a missing file.
+func (m *Backend) IsNotExist(err error) bool {
+	if m.IsNotExistFn == nil {
+		return false
+	}
+
+	return m.IsNotExistFn(err)
+}
+
 // Save data in the backend.
 func (m *Backend) Save(ctx context.Context, h restic.Handle, rd io.Reader) error {
 	if m.SaveFn == nil {