archive: fix reading an archive in the root of a remote

Opening an archive in the root of a remote, such as remote:file.zip,
failed with "file does not exist" because the archive's leaf name was
found with path.Base, which doesn't understand remote names. It is now
found with fspath.Split.

backend/archive/archive.go

@@ -194,8 +194,12 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (outFs fs
 		}
 		// Path to the archive
 		archiveRemote := remote[:len(foundArchive.remote)]
-		// Remote is archive leaf name
-		foundArchive.remote = path.Base(archiveRemote)
+		// Remote is archive leaf name. This must understand remote
+		// names as the archive may be in the root, e.g. "remote:file.zip"
+		_, foundArchive.remote, err = fspath.Split(archiveRemote)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse archive path %q: %w", archiveRemote, err)
+		}
 		foundArchive.prefix = ""
 		// Point remote to archive file
 		remote = archiveRemote

backend/archive/archive_internal_test.go

@@ -17,6 +17,7 @@ import (
 	"strings"
 	"testing"
 
+	_ "github.com/rclone/rclone/backend/alias"
 	"github.com/rclone/rclone/backend/archive/archiver"
 	_ "github.com/rclone/rclone/backend/local"
 	"github.com/rclone/rclone/fs"
@@ -323,6 +324,50 @@ func TestArchiveUncleanRoot(t *testing.T) {
 	}
 }
 
+// TestArchiveInRemoteRoot checks that an archive in the root of a
+// remote, with no "/" between the remote name and the archive name, can
+// be read, as can a path within it.
+func TestArchiveInRemoteRoot(t *testing.T) {
+	fstest.Initialise()
+	ctx := context.Background()
+
+	var buf bytes.Buffer
+	zw := zip.NewWriter(&buf)
+	w, err := zw.Create("sub/a.txt")
+	require.NoError(t, err)
+	_, err = w.Write([]byte("data"))
+	require.NoError(t, err)
+	require.NoError(t, zw.Close())
+	dir := t.TempDir()
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "test.zip"), buf.Bytes(), 0600))
+	t.Chdir(dir)
+
+	for _, test := range []struct {
+		name   string
+		remote string
+	}{
+		{name: "plain", remote: ":local:test.zip"},
+		{name: "slash in remote name", remote: ":alias,remote='" + dir + "':test.zip"},
+	} {
+		for _, sub := range []struct {
+			path string
+			want string
+		}{
+			{path: "", want: "sub"},
+			{path: "/sub", want: "a.txt"},
+		} {
+			t.Run(test.name+sub.path, func(t *testing.T) {
+				f, err := cache.Get(ctx, ":archive:"+test.remote+sub.path)
+				require.NoError(t, err)
+				entries, err := f.List(ctx, "")
+				require.NoError(t, err)
+				require.Len(t, entries, 1)
+				assert.Equal(t, sub.want, entries[0].Remote())
+			})
+		}
+	}
+}
+
 // escapingObject is an object whose remote is not where it was asked for.
 type escapingObject struct {
 	fs.Object