go.crypto/ssh/terminal: fix non-ASCII history.

The length of history buffer entries (which are stored as strings) was
being used as the number of runes. This was correct until ff9ce887b46b,
which allowed unicode entry, but can now cause a panic when editing
history that contains non-ASCII codepoints.

R=golang-dev, sfrithjof, r
CC=golang-dev
https://golang.org/cl/13255050

ssh/terminal/terminal.go

@@ -409,19 +409,22 @@ func (t *Terminal) handleKey(key rune) (line string, ok bool) {
 			t.historyPending = string(t.line)
 		}
 		t.historyIndex++
-		t.setLine([]rune(entry), len(entry))
+		runes := []rune(entry)
+		t.setLine(runes, len(runes))
 	case keyDown:
 		switch t.historyIndex {
 		case -1:
 			return
 		case 0:
-			t.setLine([]rune(t.historyPending), len(t.historyPending))
+			runes := []rune(t.historyPending)
+			t.setLine(runes, len(runes))
 			t.historyIndex--
 		default:
 			entry, ok := t.history.NthPreviousEntry(t.historyIndex - 1)
 			if ok {
 				t.historyIndex--
-				t.setLine([]rune(entry), len(entry))
+				runes := []rune(entry)
+				t.setLine(runes, len(runes))
 			}
 		}
 	case keyEnter:

ssh/terminal/terminal_test.go

@@ -141,6 +141,16 @@ var keyPressTests = []struct {
 		in:   "Ξεσκεπάζω\r",
 		line: "Ξεσκεπάζω",
 	},
+	{
+		in:             "£\r\x1b[A\177\r", // non-ASCII char, enter, up, backspace.
+		line:           "",
+		throwAwayLines: 1,
+	},
+	{
+		in:             "£\r££\x1b[A\x1b[B\177\r", // non-ASCII char, enter, 2x non-ASCII, up, down, backspace, enter.
+		line:           "£",
+		throwAwayLines: 1,
+	},
 }
 
 func TestKeyPresses(t *testing.T) {