Error on dubious characters in ending messages

Curly braces and newlines can allow arbitrary messages to be sent
to an engine. Do not allow these characters to be sent in
end-of-game messages.

Add tests to make sure an exception is raised for invalid characters.

chess/engine.py

@@ -2508,6 +2508,9 @@ async def send_opponent_information(self, *, opponent: Optional[Opponent] = None
     async def send_game_result(self, board: chess.Board, winner: Optional[Color] = None, game_ending: Optional[str] = None, game_complete: bool = True) -> None:
         class XBoardGameResultCommand(BaseCommand[XBoardProtocol, None]):
             def start(self, engine: XBoardProtocol) -> None:
+                if game_ending and any(c in game_ending for c in "{}\n\r"):
+                    raise EngineError(f"invalid line break or curly braces in game ending message: {game_ending!r}")
+
                 engine._new(board, engine.game, {})  # Send final moves to engine.
 
                 outcome = board.outcome(claim_draw=True)

test.py

@@ -3752,6 +3752,22 @@ async def main():
             await protocol.send_game_result(timeout_board, chess.BLACK, "Time forfeiture")
             mock.assert_done()
 
+            error_board = chess.Board()
+            mock.expect("new")
+            mock.expect("force")
+            mock.expect("st 5")
+            mock.expect("nopost")
+            mock.expect("easy")
+            mock.expect("go", ["move e2e4"])
+            mock.expect_ping()
+            result = await protocol.play(error_board, limit, game="error")
+            self.assertEqual(result.move, error_board.parse_uci("e2e4"))
+            error_board.push(result.move)
+            for c in "\n\r{}":
+                with self.assertRaises(chess.engine.EngineError):
+                    await protocol.send_game_result(error_board, chess.BLACK, f"Time{c}forfeiture")
+            mock.assert_done()
+
             material_board = chess.Board("k7/8/8/8/8/8/8/K7 b - - 0 1")
             self.assertTrue(material_board.is_insufficient_material())
             mock.expect("new")