Queue UI output and status updates

uiterm/ui.go

@@ -23,6 +23,7 @@ type Ui struct {
 
 	close     chan struct{}
 	closeOnce sync.Once
+	events    chan func()
 	manager   UiManager
 
 	drawCount     int32
@@ -42,6 +43,7 @@ type uiElement struct {
 func New(manager UiManager) *Ui {
 	ui := &Ui{
 		close:            make(chan struct{}),
+		events:           make(chan func(), 256),
 		elements:         make(map[string]*uiElement),
 		manager:          manager,
 		keyListeners:     make(map[Key][]KeyListener),
@@ -55,6 +57,22 @@ func (ui *Ui) Close() {
 	ui.closeOnce.Do(func() { close(ui.close) })
 }
 
+// Post schedules UI work on Run's owning goroutine. It is deliberately
+// bounded: network callbacks must not block behind slow terminal rendering.
+func (ui *Ui) Post(fn func()) bool {
+	if fn == nil {
+		return true
+	}
+	select {
+	case <-ui.close:
+		return false
+	case ui.events <- fn:
+		return true
+	default:
+		return false
+	}
+}
+
 func (ui *Ui) Refresh() {
 	if termbox.IsInit {
 		ui.beginDraw()
@@ -137,6 +155,8 @@ func (ui *Ui) Run(cmds chan string) error {
 		select {
 		case <-ui.close:
 			return nil
+		case fn := <-ui.events:
+			fn()
 		case cmd, ok := <-cmds:
 			if !ok {
 				cmds = nil

uiterm/ui_regression_test.go

@@ -4,6 +4,24 @@ import "testing"
 
 // Regression: Close sent to a bounded channel and could block or enqueue
 // duplicate shutdowns when called more than once.
+// Regression: network callbacks modified terminal state directly. Post gives
+// them a bounded handoff to the UI-owning Run goroutine instead of blocking.
+func TestPostIsBoundedAndRejectsClosedUI(t *testing.T) {
+	ui := New(nil)
+	for i := 0; i < cap(ui.events); i++ {
+		if !ui.Post(func() {}) {
+			t.Fatal("queue filled too early")
+		}
+	}
+	if ui.Post(func() {}) {
+		t.Fatal("Post accepted work past queue capacity")
+	}
+	ui.Close()
+	if ui.Post(func() {}) {
+		t.Fatal("Post accepted work after close")
+	}
+}
+
 func TestCloseIsNonblockingAndIdempotent(t *testing.T) {
 	ui := New(nil)
 	ui.Close()