archive: fix listing entries with a leading slash as if they were in the root

The check that an entry returned by an archiver is a direct child of
the directory being listed normalised a parent of "/" to the root, so
an entry named "/x" passed as a child of the root while "x/" and
"dir//x" were rejected.

Decide by stripping the directory prefix and checking what is left
with sanitize.Leaf, which rejects an empty name, ".", ".." and any
name containing a "/". This also covers the leading slash case.

backend/archive/archive.go

@@ -36,6 +36,7 @@ import (
 	"github.com/rclone/rclone/fs/config/configstruct"
 	"github.com/rclone/rclone/fs/fspath"
 	"github.com/rclone/rclone/fs/hash"
+	"github.com/rclone/rclone/lib/sanitize"
 )
 
 // Register with Fs
@@ -529,14 +530,14 @@ func (f *Fs) List(ctx context.Context, dir string) (entries fs.DirEntries, err e
 // isDirectChild reports whether remote names an entry directly in dir
 // ("" being the root), with no ".." or other components in between.
 func isDirectChild(dir, remote string) bool {
-	if remote == "" || remote == "." || remote == ".." || strings.HasSuffix(remote, "/") {
-		return false
+	if dir != "" {
+		var ok bool
+		remote, ok = strings.CutPrefix(remote, dir+"/")
+		if !ok {
+			return false
+		}
 	}
-	parent := path.Dir(remote)
-	if parent == "." || parent == "/" {
-		parent = ""
-	}
-	return parent == dir && path.Clean(remote) == remote
+	return sanitize.Leaf(remote) == nil
 }
 
 // NewObject creates a new remote archive file object

backend/archive/archive_internal_test.go

@@ -379,3 +379,27 @@ func TestArchiveEscapingArchiver(t *testing.T) {
 	_, err = f.NewObject(ctx, "test.escaping/file.txt")
 	assert.ErrorIs(t, err, fs.ErrorObjectNotFound)
 }
+
+// TestIsDirectChild checks the guard which decides whether an entry
+// returned by an archiver belongs directly in the directory listed.
+func TestIsDirectChild(t *testing.T) {
+	for _, test := range []struct {
+		dir, remote string
+		want        bool
+	}{
+		{"", "a.txt", true},
+		{"", "/a.txt", false},
+		{"", "a.txt/", false},
+		{"", "../a.txt", false},
+		{"", "sub/a.txt", false},
+		{"d", "d/a.txt", true},
+		{"d", "d", false},
+		{"d", "d/", false},
+		{"d", "d//a.txt", false},
+		{"d", "d/../a.txt", false},
+		{"d", "dd/a.txt", false},
+		{"d", "a.txt", false},
+	} {
+		assert.Equal(t, test.want, isDirectChild(test.dir, test.remote), "dir=%q remote=%q", test.dir, test.remote)
+	}
+}