Sanitize terminal widget text

uiterm/label.go

@@ -40,7 +40,7 @@ func (l *Label) uiDraw() {
 			if ch, _, err := reader.ReadRune(); err != nil {
 				chr = ' '
 			} else {
-				chr = ch
+				chr = safeRune(ch)
 			}
 			termbox.SetCell(x, y, chr, termbox.Attribute(l.Fg), termbox.Attribute(l.Bg))
 		}

uiterm/textbox.go

@@ -63,7 +63,7 @@ func (t *Textbox) uiDraw() {
 			if ch, _, err := reader.ReadRune(); err != nil {
 				chr = ' '
 			} else {
-				chr = ch
+				chr = safeRune(ch)
 			}
 			termbox.SetCell(x, y, chr, termbox.Attribute(t.Fg), termbox.Attribute(t.Bg))
 		}

uiterm/textview.go

@@ -146,7 +146,7 @@ func (t *Textview) uiDraw() {
 			var chr rune = ' '
 			if reader != nil {
 				if ch, _, err := reader.ReadRune(); err == nil {
-					chr = ch
+					chr = safeRune(ch)
 				} //no err
 			} //reader != nil
 			termbox.SetCell(x, y, chr, termbox.Attribute(t.Fg), termbox.Attribute(t.Bg))

uiterm/tree.go

@@ -177,7 +177,7 @@ func (t *Tree) uiDraw() {
 			dx := x - t.x0
 			if reader != nil && level*2 <= dx {
 				if ch, _, err := reader.ReadRune(); err == nil {
-					chr = ch
+					chr = safeRune(ch)
 					fg, bg = item.TreeItemStyle(fg, bg, t.active && t.activeLine == line)
 				}
 			}

uiterm/ui_regression_test.go

@@ -32,3 +32,14 @@ func TestCloseIsNonblockingAndIdempotent(t *testing.T) {
 		t.Fatal("Close did not signal shutdown")
 	}
 }
+
+func TestSafeRuneRemovesTerminalControlCharacters(t *testing.T) {
+	for _, r := range []rune{'\x1b', '\x7f', '\u202e'} {
+		if got := safeRune(r); got != ' ' {
+			t.Errorf("safeRune(%U) = %U, want space", r, got)
+		}
+	}
+	if got := safeRune('A'); got != 'A' {
+		t.Fatalf("safeRune altered printable text: %U", got)
+	}
+}

uiterm/view.go

@@ -1,5 +1,16 @@
 package uiterm
 
+import "unicode"
+
+// safeRune prevents text supplied by a server or another user from being
+// interpreted as a terminal control sequence when termbox flushes its cells.
+func safeRune(r rune) rune {
+	if unicode.IsControl(r) || unicode.Is(unicode.Bidi_Control, r) {
+		return ' '
+	}
+	return r
+}
+
 type View interface {
 	uiInitialize(ui *Ui)
 	uiSetActive(active bool)