ssh/terminal: support home, end, up and down keys.

R=golang-dev, dave
CC=golang-dev
https://golang.org/cl/9777043

ssh/terminal/terminal.go

@@ -75,6 +75,17 @@ type Terminal struct {
 	// a read. It aliases into inBuf.
 	remainder []byte
 	inBuf     [256]byte
+
+	// history contains previously entered commands so that they can be
+	// accessed with the up and down keys.
+	history stRingBuffer
+	// historyIndex stores the currently accessed history entry, where zero
+	// means the immediately previous entry.
+	historyIndex int
+	// When navigating up and down the history it's possible to return to
+	// the incomplete, initial line. That value is stored in
+	// historyPending.
+	historyPending string
 }
 
 // NewTerminal runs a VT100 terminal on the given ReadWriter. If the ReadWriter is
@@ -83,12 +94,13 @@ type Terminal struct {
 // "> ").
 func NewTerminal(c io.ReadWriter, prompt string) *Terminal {
 	return &Terminal{
-		Escape:     &vt100EscapeCodes,
-		c:          c,
-		prompt:     prompt,
-		termWidth:  80,
-		termHeight: 24,
-		echo:       true,
+		Escape:       &vt100EscapeCodes,
+		c:            c,
+		prompt:       prompt,
+		termWidth:    80,
+		termHeight:   24,
+		echo:         true,
+		historyIndex: -1,
 	}
 }
 
@@ -104,6 +116,8 @@ const (
 	keyRight
 	keyAltLeft
 	keyAltRight
+	keyHome
+	keyEnd
 )
 
 // bytesToKey tries to parse a key sequence from b. If successful, it returns
@@ -130,6 +144,15 @@ func bytesToKey(b []byte) (int, []byte) {
 		}
 	}
 
+	if len(b) >= 3 && b[0] == keyEscape && b[1] == 'O' {
+		switch b[2] {
+		case 'H':
+			return keyHome, b[3:]
+		case 'F':
+			return keyEnd, b[3:]
+		}
+	}
+
 	if len(b) >= 6 && b[0] == keyEscape && b[1] == '[' && b[2] == '1' && b[3] == ';' && b[4] == '3' {
 		switch b[5] {
 		case 'C':
@@ -238,6 +261,19 @@ func (t *Terminal) clearLineToRight() {
 
 const maxLineLength = 4096
 
+func (t *Terminal) setLine(newLine []byte, newPos int) {
+	if t.echo {
+		t.moveCursorToPos(0)
+		t.writeLine(newLine)
+		for i := len(newLine); i < len(t.line); i++ {
+			t.writeLine(space)
+		}
+		t.moveCursorToPos(newPos)
+	}
+	t.line = newLine
+	t.pos = newPos
+}
+
 // handleKey processes the given key and, optionally, returns a line of text
 // that the user has entered.
 func (t *Terminal) handleKey(key int) (line string, ok bool) {
@@ -303,6 +339,42 @@ func (t *Terminal) handleKey(key int) (line string, ok bool) {
 		}
 		t.pos++
 		t.moveCursorToPos(t.pos)
+	case keyHome:
+		if t.pos == 0 {
+			return
+		}
+		t.pos = 0
+		t.moveCursorToPos(t.pos)
+	case keyEnd:
+		if t.pos == len(t.line) {
+			return
+		}
+		t.pos = len(t.line)
+		t.moveCursorToPos(t.pos)
+	case keyUp:
+		entry, ok := t.history.NthPreviousEntry(t.historyIndex + 1)
+		if !ok {
+			return "", false
+		}
+		if t.historyIndex == -1 {
+			t.historyPending = string(t.line)
+		}
+		t.historyIndex++
+		t.setLine([]byte(entry), len(entry))
+	case keyDown:
+		switch t.historyIndex {
+		case -1:
+			return
+		case 0:
+			t.setLine([]byte(t.historyPending), len(t.historyPending))
+			t.historyIndex--
+		default:
+			entry, ok := t.history.NthPreviousEntry(t.historyIndex - 1)
+			if ok {
+				t.historyIndex--
+				t.setLine([]byte(entry), len(entry))
+			}
+		}
 	case keyEnter:
 		t.moveCursorToPos(len(t.line))
 		t.queue([]byte("\r\n"))
@@ -320,16 +392,7 @@ func (t *Terminal) handleKey(key int) (line string, ok bool) {
 			t.lock.Lock()
 
 			if newLine != nil {
-				if t.echo {
-					t.moveCursorToPos(0)
-					t.writeLine(newLine)
-					for i := len(newLine); i < len(t.line); i++ {
-						t.writeLine(space)
-					}
-					t.moveCursorToPos(newPos)
-				}
-				t.line = newLine
-				t.pos = newPos
+				t.setLine(newLine, newPos)
 				return
 			}
 		}
@@ -483,6 +546,8 @@ func (t *Terminal) readLine() (line string, err error) {
 		t.c.Write(t.outBuf)
 		t.outBuf = t.outBuf[:0]
 		if lineOk {
+			t.historyIndex = -1
+			t.history.Add(line)
 			return
 		}
 
@@ -501,7 +566,6 @@ func (t *Terminal) readLine() (line string, err error) {
 
 		t.remainder = t.inBuf[:n+len(t.remainder)]
 	}
-	panic("unreachable")
 }
 
 // SetPrompt sets the prompt to be used when reading subsequent lines.
@@ -518,3 +582,43 @@ func (t *Terminal) SetSize(width, height int) {
 
 	t.termWidth, t.termHeight = width, height
 }
+
+// stRingBuffer is a ring buffer of strings.
+type stRingBuffer struct {
+	// entries contains max elements.
+	entries []string
+	max     int
+	// head contains the index of the element most recently added to the ring.
+	head int
+	// size contains the number of elements in the ring.
+	size int
+}
+
+func (s *stRingBuffer) Add(a string) {
+	if s.entries == nil {
+		const defaultNumEntries = 100
+		s.entries = make([]string, defaultNumEntries)
+		s.max = defaultNumEntries
+	}
+
+	s.head = (s.head + 1) % s.max
+	s.entries[s.head] = a
+	if s.size < s.max {
+		s.size++
+	}
+}
+
+// NthPreviousEntry returns the value passed to the nth previous call to Add.
+// If n is zero then the immediately prior value is returned, if one, then the
+// next most recent, and so on. If such an element doesn't exist then ok is
+// false.
+func (s *stRingBuffer) NthPreviousEntry(n int) (value string, ok bool) {
+	if n >= s.size {
+		return "", false
+	}
+	index := s.head - n
+	if index < 0 {
+		index += s.max
+	}
+	return s.entries[index], true
+}

ssh/terminal/terminal_test.go

@@ -52,39 +52,54 @@ func TestClose(t *testing.T) {
 }
 
 var keyPressTests = []struct {
-	in   string
-	line string
-	err  error
+	in             string
+	line           string
+	err            error
+	throwAwayLines int
 }{
 	{
-		"",
-		"",
-		io.EOF,
+		err: io.EOF,
 	},
 	{
-		"\r",
-		"",
-		nil,
+		in:   "\r",
+		line: "",
 	},
 	{
-		"foo\r",
-		"foo",
-		nil,
+		in:   "foo\r",
+		line: "foo",
 	},
 	{
-		"a\x1b[Cb\r", // right
-		"ab",
-		nil,
+		in:   "a\x1b[Cb\r", // right
+		line: "ab",
 	},
 	{
-		"a\x1b[Db\r", // left
-		"ba",
-		nil,
+		in:   "a\x1b[Db\r", // left
+		line: "ba",
 	},
 	{
-		"a\177b\r", // backspace
-		"b",
-		nil,
+		in:   "a\177b\r", // backspace
+		line: "b",
+	},
+	{
+		in: "\x1b[A\r", // up
+	},
+	{
+		in: "\x1b[B\r", // down
+	},
+	{
+		in:   "line\x1b[A\x1b[B\r", // up then down
+		line: "line",
+	},
+	{
+		in:             "line1\rline2\x1b[A\r", // recall previous line.
+		line:           "line1",
+		throwAwayLines: 1,
+	},
+	{
+		// recall two previous lines and append.
+		in:             "line1\rline2\rline3\x1b[A\x1b[Axxx\r",
+		line:           "line1xxx",
+		throwAwayLines: 2,
 	},
 }
 
@@ -96,6 +111,12 @@ func TestKeyPresses(t *testing.T) {
 				bytesPerRead: j,
 			}
 			ss := NewTerminal(c, "> ")
+			for k := 0; k < test.throwAwayLines; k++ {
+				_, err := ss.ReadLine()
+				if err != nil {
+					t.Errorf("Throwaway line %d from test %d resulted in error: %s", k, i, err)
+				}
+			}
 			line, err := ss.ReadLine()
 			if line != test.line {
 				t.Errorf("Line resulting from test %d (%d bytes per read) was '%s', expected '%s'", i, j, line, test.line)