ssh/terminal: add Terminal.SetEnterClear(bool)

ssh/terminal/terminal.go

@@ -93,6 +93,11 @@ type Terminal struct {
 	// the incomplete, initial line. That value is stored in
 	// historyPending.
 	historyPending string
+
+	// enterClear will clear the input line on enter, instead of printing a
+	// new line after the input. It's useful for replacing the input with
+	// something else without echoing it.
+	enterClear bool
 }
 
 // NewTerminal runs a VT100 terminal on the given ReadWriter. If the ReadWriter is
@@ -517,14 +522,27 @@ func (t *Terminal) handleKey(key rune) (line string, ok bool) {
 			}
 		}
 	case keyEnter:
-		t.moveCursorToPos(len(t.line))
-		t.queue([]rune("\r\n"))
 		line = string(t.line)
+		if t.enterClear {
+			// Clear line on enter instead of starting a new line.
+			reset := []rune{
+				// Clear whole line
+				keyEscape, '[', '2', 'K',
+				// Clear screen below (for any wrapped lines)
+				keyEscape, '[', 'J',
+			}
+			t.queue(reset)
+		} else {
+			// Pushing the line up resets the cursor to 0,0 and we render a
+			// fresh prompt.
+			t.moveCursorToPos(len(t.line))
+			t.queue([]rune("\r\n"))
+			t.cursorX = 0
+			t.cursorY = 0
+		}
 		ok = true
 		t.line = t.line[:0]
 		t.pos = 0
-		t.cursorX = 0
-		t.cursorY = 0
 		t.maxLine = 0
 	case keyDeleteWord:
 		// Delete zero or more spaces and then one or more characters.
@@ -871,6 +889,17 @@ func (t *Terminal) SetSize(width, height int) error {
 	return err
 }
 
+// SetEnterClear controls whether the input line should be cleared upon
+// pressing Enter. When false (the default), the input line is pushed up with a
+// new-line and the prompt is repainted. When true, the input line is cleared
+// without any new lines.
+func (t *Terminal) SetEnterClear(on bool) {
+	t.lock.Lock()
+	defer t.lock.Unlock()
+
+	t.enterClear = on
+}
+
 type pasteIndicatorError struct{}
 
 func (pasteIndicatorError) Error() string {

ssh/terminal/terminal_test.go

@@ -238,9 +238,10 @@ func TestKeyPresses(t *testing.T) {
 }
 
 var renderTests = []struct {
-	in       string
-	received string
-	err      error
+	in            string
+	received      string
+	err           error
+	setEnterClear bool
 }{
 	{
 		// Cursor move after keyHome (left 4) then enter (right 4, newline)
@@ -257,6 +258,17 @@ var renderTests = []struct {
 			"\x1b[4D" + // Put cursor back in position to insert again
 			"\x1b[4C\r\n", // Put cursor at the end of the line and newline.
 	},
+	{
+		// Write a plain line, enter
+		in:       "abcd\r\n",
+		received: "> abcd\r\n",
+	},
+	{
+		// Write a plain line, enter with setEnterClear enabled
+		in:            "abcd\r\n",
+		received:      "> abcd\x1b[2K\x1b[J",
+		setEnterClear: true,
+	},
 }
 
 func TestRender(t *testing.T) {
@@ -267,6 +279,9 @@ func TestRender(t *testing.T) {
 				bytesPerRead: j,
 			}
 			ss := NewTerminal(c, "> ")
+			if test.setEnterClear {
+				ss.SetEnterClear(true)
+			}
 			_, err := ss.ReadLine()
 			if err != test.err {
 				t.Errorf("Error resulting from test %d (%d bytes per read) was '%v', expected '%v'", i, j, err, test.err)
@@ -405,3 +420,17 @@ func TestOutputNewlines(t *testing.T) {
 		t.Errorf("incorrect output: was %q, expected %q", output, expected)
 	}
 }
+
+func TestCursorStateCrash(t *testing.T) {
+	// If the cursor math is off, reading a bunch of times will inevitably
+	// panic with a slice bounds out of range.
+	buf := bytes.NewBufferString("foo")
+	ss := NewTerminal(buf, "> ")
+	ss.SetEnterClear(true)
+	for i := 0; i < 100; i++ {
+		_, err := ss.ReadLine()
+		if err != nil {
+			t.Errorf("unexpected error: %q", err)
+		}
+	}
+}