fix: remove unnecessary parent dir traversal in backend.Walk()

The prefix can contain one or more parent directories. In this case it is not necessary to start traversal at the root dir. Instead start the directory traversal at the last directory component within the prefix.

backend/walk.go

@@ -52,7 +52,15 @@ func Walk(ctx context.Context, fileSystem fs.FS, prefix, delimiter, marker strin
 	var newMarker string
 	var truncated bool
 
-	err := fs.WalkDir(fileSystem, ".", func(path string, d fs.DirEntry, err error) error {
+	root := "."
+	if strings.Contains(prefix, "/") {
+		idx := strings.LastIndex(prefix, "/")
+		if idx > 0 {
+			root = prefix[:idx]
+		}
+	}
+
+	err := fs.WalkDir(fileSystem, root, func(path string, d fs.DirEntry, err error) error {
 		if err != nil {
 			return err
 		}
@@ -222,6 +230,10 @@ func Walk(ctx context.Context, fileSystem fs.FS, prefix, delimiter, marker strin
 		return skipflag
 	})
 	if err != nil {
+		// suppress file not found caused by user's prefix
+		if errors.Is(err, fs.ErrNotExist) {
+			return WalkResults{}, nil
+		}
 		return WalkResults{}, err
 	}