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firestar5683
b06f37e2c7
Define persistent settings, typed schema fields and storage migrations before feature owners consume them. Keep calibration and parameter readers aligned with the shared data contracts.
35 lines
1.1 KiB
Python
35 lines
1.1 KiB
Python
"""Bounded saved-setting reads for the shared feature owner."""
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import os
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import stat
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def read_saved(params, key: str, limit: int) -> tuple[bytes | None, bool]:
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"""Return complete bytes/absence and readability; never authorize a prefix."""
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path = params.get_param_path(key)
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flags = os.O_RDONLY | os.O_NONBLOCK | getattr(os, "O_NOFOLLOW", 0)
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try:
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fd = os.open(path, flags)
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except FileNotFoundError:
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return None, True
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except OSError:
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return b"", False
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try:
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before = os.fstat(fd)
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if not stat.S_ISREG(before.st_mode) or before.st_size > limit:
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return b"", False
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with os.fdopen(fd, "rb", closefd=False) as source:
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raw = source.read(limit + 1)
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after = os.fstat(fd)
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current = os.stat(path, follow_symlinks=False)
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if (len(raw) > limit or not stat.S_ISREG(after.st_mode) or
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(before.st_dev, before.st_ino, before.st_size, before.st_mtime_ns) !=
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(after.st_dev, after.st_ino, after.st_size, after.st_mtime_ns) or
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(current.st_dev, current.st_ino) != (after.st_dev, after.st_ino)):
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return b"", False
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return raw, True
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except OSError:
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return b"", False
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finally:
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os.close(fd)
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