Error when XBoard opponent has newline in name

Use the configuration machinery to send the opponent's information
to the engine instead of using the Opponent class directly. This will
make sure that an exception is raised if the opponent's name has
newlines in it before send_line() is called. This prevents opponents
from injecting commands into the engine. For example, if an
opponent sets their name as "Cheat\neasy", then the following
commands will be sent to the local engine

name Cheat
easy

which would cause the engine to turn off pondering.

Also, add tests to show the change works as expected.

chess/engine.py

@@ -2152,6 +2152,7 @@ def _variant(self, variant: Optional[str]) -> None:
 
     def _new(self, board: chess.Board, game: object, options: ConfigMapping, opponent: Optional[Opponent] = None) -> None:
         self._configure(options)
+        self._configure(self._opponent_configuration(opponent=opponent))
 
         # Set up starting position.
         root = board.root()
@@ -2172,15 +2173,16 @@ def _new(self, board: chess.Board, game: object, options: ConfigMapping, opponen
             if self.config.get("random"):
                 self.send_line("random")
 
-            opponent_name = (opponent.name if opponent else None) or self.target_config.get("name")
+            opponent_name = self.config.get("name")
             if opponent_name and self.features.get("name", True):
                 self.send_line(f"name {opponent_name}")
 
-            opponent_rating = (opponent.rating if opponent else None) or self.target_config.get("opponent_rating") or 0
-            if self.target_config.get("engine_rating") or opponent_rating:
-                self.send_line(f"rating {self.target_config.get('engine_rating') or 0} {opponent_rating}")
+            opponent_rating = self.config.get("opponent_rating")
+            engine_rating = self.config.get("engine_rating")
+            if engine_rating or opponent_rating:
+                self.send_line(f"rating {engine_rating or 0} {opponent_rating or 0}")
 
-            if (opponent and opponent.is_engine) or (self.target_config.get("computer") if self.config.get("computer") is None else self.config.get("computer")):
+            if self.config.get("computer"):
                 self.send_line("computer")
 
         self.send_line("force")
@@ -2518,7 +2520,7 @@ def _opponent_configuration(self, *, opponent: Optional[Opponent] = None, engine
         if opponent is None:
             return {}
 
-        opponent_info: Dict[str, Union[int, bool, str]] = {"engine_rating": engine_rating or 0,
+        opponent_info: Dict[str, Union[int, bool, str]] = {"engine_rating": engine_rating or self.target_config.get("engine_rating") or 0,
                                                            "opponent_rating": opponent.rating or 0,
                                                            "computer": opponent.is_engine or False}
 

test.py

@@ -3688,6 +3688,15 @@ async def main():
             self.assertEqual(result.move, board.parse_san("e5"))
             mock.assert_done()
 
+            bad_opponent = chess.engine.Opponent("New\nLine", "GM", 1, False)
+            with self.assertRaises(chess.engine.EngineError):
+                await protocol.send_opponent_information(opponent=bad_opponent)
+            mock.assert_done()
+
+            with self.assertRaises(chess.engine.EngineError):
+                result = await protocol.play(board, limit, game="bad game", opponent=bad_opponent)
+            mock.assert_done()
+
         asyncio.set_event_loop_policy(chess.engine.EventLoopPolicy())
         asyncio.run(main())