Compare cursor serials by identity so returning to an earlier cursor updates

client/vnc/server/session_cursor_test.go

@@ -0,0 +1,80 @@
+//go:build !js && !ios && !android
+
+package server
+
+import (
+	"image"
+	"testing"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// fakeCursorCapturer plays back a scripted sequence of cursor sprites, each
+// with the serial its platform would report.
+type fakeCursorCapturer struct {
+	sprites []fakeSprite
+	next    int
+}
+
+type fakeSprite struct {
+	serial uint64
+	err    error
+}
+
+func (f *fakeCursorCapturer) Width() int  { return 100 }
+func (f *fakeCursorCapturer) Height() int { return 100 }
+
+func (f *fakeCursorCapturer) Capture() (*image.RGBA, error) {
+	return image.NewRGBA(image.Rect(0, 0, 100, 100)), nil
+}
+
+func (f *fakeCursorCapturer) Cursor() (*image.RGBA, int, int, uint64, error) {
+	s := f.sprites[min(f.next, len(f.sprites)-1)]
+	f.next++
+	if s.err != nil {
+		return nil, 0, 0, 0, s.err
+	}
+	return image.NewRGBA(image.Rect(0, 0, 16, 16)), 0, 0, s.serial, nil
+}
+
+func newCursorSession(t *testing.T, cap ScreenCapturer) *session {
+	t.Helper()
+	return &session{
+		capturer:             cap,
+		clientSupportsCursor: true,
+		log:                  log.WithField("test", t.Name()),
+	}
+}
+
+// X11 reports the XFixes cursor-serial, which names the cursor rather than
+// counting upwards: switching back to a cursor shown earlier yields a lower
+// value. Ordering the serials treated that as stale and left the client stuck
+// on whichever cursor had the highest one, typically the I-beam.
+func TestPendingCursorRect_SerialGoingBackwardsStillUpdates(t *testing.T) {
+	cap := &fakeCursorCapturer{sprites: []fakeSprite{
+		{serial: 100}, // arrow
+		{serial: 250}, // I-beam over a text field
+		{serial: 100}, // back to the arrow
+	}}
+	s := newCursorSession(t, cap)
+
+	require.NotNil(t, s.pendingCursorRect(), "the first cursor must be sent")
+	assert.Equal(t, uint64(100), s.lastCursorSerial)
+
+	require.NotNil(t, s.pendingCursorRect(), "a different cursor must be sent")
+	assert.Equal(t, uint64(250), s.lastCursorSerial)
+
+	require.NotNil(t, s.pendingCursorRect(), "returning to an earlier cursor must be sent too")
+	assert.Equal(t, uint64(100), s.lastCursorSerial)
+}
+
+// The same serial twice in a row is the same cursor and carries no update.
+func TestPendingCursorRect_UnchangedSerialIsSkipped(t *testing.T) {
+	cap := &fakeCursorCapturer{sprites: []fakeSprite{{serial: 7}, {serial: 7}}}
+	s := newCursorSession(t, cap)
+
+	require.NotNil(t, s.pendingCursorRect())
+	assert.Nil(t, s.pendingCursorRect(), "an unchanged serial must not re-send the sprite")
+}