1 files changed, 22 insertions, 0 deletions
diff --git a/object/fetch/treefs_sub.go b/object/fetch/treefs_sub.go
new file mode 100644
index 00000000..faf47092
--- /dev/null
+++ b/object/fetch/treefs_sub.go
@@ -0,0 +1,22 @@
+package fetch
+
+import "io/fs"
+
+// Sub returns a new TreeFS rooted at dir.
+func (treeFS *TreeFS) Sub(dir string) (fs.FS, error) {
+	entry, err := treeFS.resolvePath(treeFSOpSub, dir)
+	if err != nil {
+		return nil, err
+	}
+
+	treeID, err := entry.subtreeID()
+	if err != nil {
+		return nil, treeFSPathError(treeFSOpSub, dir, fs.ErrInvalid)
+	}
+
+	return &TreeFS{
+		resolver:  treeFS.resolver,
+		rootTree:  treeID,
+		rootEntry: entry.treeEntry,
+	}, nil
+}