Make file.Read more intelligible

cmd/restic/cmd_mount.go

@@ -275,9 +275,7 @@ type file struct {
 	node *restic.Node
 
 	sizes []uint32
-
-	// cleartext contents
-	clearContent [][]byte
+	blobs [][]byte
 }
 
 func newFile(repo *repository.Repository, node *restic.Node) (*file, error) {
@@ -294,7 +292,7 @@ func newFile(repo *repository.Repository, node *restic.Node) (*file, error) {
 		repo:  repo,
 		node:  node,
 		sizes: sizes,
-		clearContent: make([][]byte, len(node.Content)),
+		blobs: make([][]byte, len(node.Content)),
 	}, nil
 }
 
@@ -305,37 +303,46 @@ func (f *file) Attr(ctx context.Context, a *fuse.Attr) error {
 	return nil
 }
 
-func (f *file) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadResponse) error {
-	off := req.Offset
-	content := make([]byte, req.Size)
-	allContent := content
-
-	for i := range f.node.Content {
-		if off >= int64(f.sizes[i]) {
-			off -= int64(f.sizes[i])
-			continue
+func (f *file) getBlobAt(i int) (blob []byte, err error) {
+	if f.blobs[i] != nil {
+		blob = f.blobs[i]
+	} else {
+		blob, err = f.repo.LoadBlob(pack.Data, f.node.Content[i])
+		if err != nil {
+			return nil, err
+		}
+		f.blobs[i] = blob
 	}
 
-		var subContent []byte
-		if f.clearContent[i] != nil {
-			subContent = f.clearContent[i]
-		} else {
-			var err error
-			subContent, err = f.repo.LoadBlob(pack.Data, f.node.Content[i])
+	return blob, nil
+}
+
+func (f *file) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadResponse) error {
+	off := req.Offset
+
+	// Skip blobs before the offset
+	startContent := 0
+	for off > int64(f.sizes[startContent]) {
+		off -= int64(f.sizes[startContent])
+		startContent++
+	}
+
+	content := make([]byte, req.Size)
+	allContent := content
+	for i := startContent; i < len(f.sizes); i++ {
+		blob, err := f.getBlobAt(i)
 		if err != nil {
 			return err
 		}
-			f.clearContent[i] = subContent
-		}
 
-		subContent = subContent[off:]
+		blob = blob[off:]
 		off = 0
 
 		var copied int
-		if len(subContent) > len(content) {
-			copied = copy(content[0:], subContent[:len(content)])
+		if len(blob) > len(content) {
+			copied = copy(content[0:], blob[:len(content)])
 		} else {
-			copied = copy(content[0:], subContent)
+			copied = copy(content[0:], blob)
 		}
 		content = content[copied:]
 		if len(content) == 0 {