101 lines
2.9 KiB
Python
101 lines
2.9 KiB
Python
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"""Atomic state-file I/O and instance lock.
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The conversation history lives at ``state/conversation.json``. Mutated
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in-memory by the daemon and written via temp+rename to avoid partial
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writes if the process is killed mid-write. A ``state/.lock`` advisory
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file stops two daemons from running against the same directory.
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"""
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from __future__ import annotations
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import errno
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import fcntl
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import json
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import os
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from dataclasses import dataclass
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from pathlib import Path
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from tempfile import NamedTemporaryFile
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class StateError(RuntimeError):
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pass
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@dataclass
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class InstanceLock:
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"""Holds a flock on state/.lock for the daemon's lifetime.
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Released automatically on process exit (kernel closes the fd) or by
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calling ``release()``. ``acquire()`` raises StateError if another
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daemon already holds the lock.
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"""
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lock_path: Path
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_fd: int | None = None
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def acquire(self) -> None:
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self._fd = os.open(self.lock_path, os.O_RDWR | os.O_CREAT, 0o600)
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try:
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fcntl.flock(self._fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
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except OSError as exc:
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os.close(self._fd)
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self._fd = None
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if exc.errno in {errno.EAGAIN, errno.EACCES}:
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raise StateError(
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f"Another daemon is holding {self.lock_path}; refusing to start"
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) from exc
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raise
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os.write(self._fd, str(os.getpid()).encode())
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def release(self) -> None:
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if self._fd is None:
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return
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try:
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fcntl.flock(self._fd, fcntl.LOCK_UN)
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finally:
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os.close(self._fd)
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self._fd = None
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def write_atomic(path: Path, data: str) -> None:
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"""Atomically write text to ``path`` via temp file + rename.
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Crash-safe: a partial write leaves the temp file but does not
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overwrite the target. fsync the data file (not the directory) so the
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rename atomicity gives us durability up to the OS-level rename
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barrier.
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"""
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path.parent.mkdir(parents=True, exist_ok=True)
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with NamedTemporaryFile(
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mode="w",
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encoding="utf-8",
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dir=str(path.parent),
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prefix=f".{path.name}.",
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suffix=".tmp",
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delete=False,
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) as tmp:
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tmp.write(data)
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tmp.flush()
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os.fsync(tmp.fileno())
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tmp_path = Path(tmp.name)
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os.replace(tmp_path, path)
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def write_json_atomic(path: Path, value: object) -> None:
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write_atomic(path, json.dumps(value, indent=2, ensure_ascii=False, sort_keys=False))
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def read_json(path: Path, default: object) -> object:
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"""Read JSON or return default when the file is missing or empty."""
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if not path.exists():
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return default
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raw = path.read_text(encoding="utf-8").strip()
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if not raw:
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return default
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try:
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return json.loads(raw)
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except json.JSONDecodeError as exc:
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raise StateError(f"Corrupt JSON at {path}: {exc}") from exc
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