Exception in callback Protocol._line_received('')

[IceboxDev]

I'm experiencing an AssertionError when trying to analyze a chess board using Chessify UCI chess engine. The error occurs after the analysis is completed and seems to be related to the internal state management of engine communication.

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Minimal code to reproduce:

import chess.engine
import constants

engine = chess.engine.SimpleEngine.popen_uci(constants.ENGINE_PATH)

board = chess.Board()
result = engine.analyse(board, chess.engine.Limit(depth=30))
print(result)

Stacktrace:

Exception in callback Protocol._line_received('')
handle: <Handle Protocol._line_received('')>
Traceback (most recent call last):
  File "C:\Users\Manta\AppData\Local\Programs\Python\Python310\lib\asyncio\events.py", line 80, in _run
    self._context.run(self._callback, *self._args)
  File "E:\Projects\UniversalChessTool\.venv\lib\site-packages\chess\engine.py", line 1093, in _line_received
    self.command._line_received(self, line)
  File "E:\Projects\UniversalChessTool\.venv\lib\site-packages\chess\engine.py", line 1385, in _line_received
    assert self.state in [CommandState.ACTIVE, CommandState.CANCELLING]
AssertionError

• self.state has value CommandState.DONE

result:

result = {
    'string': 'NNUE evaluation using nn-b1a57edbea57.nnue',
    'depth': 30,
    'seldepth': 48,
    'multipv': 1,
    'score': 'PovScore(Cp(+32), WHITE)',
    'nodes': 123673136,
    'nps': 9619876,
    'hashfull': 140,
    'tbhits': 0,
    'time': 12.856,
    'pv': [
        'Move.from_uci(e2e4)', 'Move.from_uci(e7e5)', 'Move.from_uci(g1f3)', 'Move.from_uci(b8c6)',
        'Move.from_uci(f1b5)', 'Move.from_uci(g8f6)', 'Move.from_uci(e1g1)', 'Move.from_uci(f6e4)',
        'Move.from_uci(f1e1)', 'Move.from_uci(e4d6)', 'Move.from_uci(f3e5)', 'Move.from_uci(f8e7)',
        'Move.from_uci(b5f1)', 'Move.from_uci(c6e5)', 'Move.from_uci(e1e5)', 'Move.from_uci(e8g8)',
        'Move.from_uci(d2d4)', 'Move.from_uci(e7f6)', 'Move.from_uci(e5e1)', 'Move.from_uci(d6f5)',
        'Move.from_uci(c2c3)', 'Move.from_uci(d7d5)', 'Move.from_uci(b1d2)', 'Move.from_uci(f5d6)',
        'Move.from_uci(a2a4)', 'Move.from_uci(a7a5)', 'Move.from_uci(d2f3)', 'Move.from_uci(c8f5)',
        'Move.from_uci(h2h3)', 'Move.from_uci(f5e4)', 'Move.from_uci(c1f4)', 'Move.from_uci(c7c6)',
        'Move.from_uci(f3e5)', 'Move.from_uci(f8e8)', 'Move.from_uci(f4h2)', 'Move.from_uci(e4f5)',
        'Move.from_uci(d1b3)', 'Move.from_uci(h7h5)', 'Move.from_uci(e1e2)', 'Move.from_uci(g7g6)',
        'Move.from_uci(a1e1)', 'Move.from_uci(h5h4)', 'Move.from_uci(e5g4)', 'Move.from_uci(f5g4)',
        'Move.from_uci(e2e8)', 'Move.from_uci(d6e8)', 'Move.from_uci(h3g4)'
    ],
    'currmove': 'Move.from_uci(h2h4)',
    'currmovenumber': 20
}

Expected Behavior:
The analysis should complete without any errors, and the engine should return the analysis results.

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Environment:
Python version: 3.10
python-chess version: 1.10
Operating System: Windows 10
Chess Engine Used: ChessifyClientStockfish

Additional Context:
The issue occurs consistently with the above setup.
The analysis result is correct; the issue seems to be purely related to internal state handling in the python-chess library.

[niklasf]

Thanks for the detailed report. Can you please also enable debug logging and include the output?