Odysseus v1.0

core/atomic_io.py

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+"""Atomic JSON file writes.
+
+Use this everywhere a JSON config file is persisted. A plain `open("w") +
+json.dump` truncates the file on first write and only fills it with new
+content afterwards — a kill -9 / power loss / OOM in between produces a
+truncated or empty file. For password DBs (`auth.json`) and live state
+(`sessions.json`, `settings.json`, `integrations.json`, `cookbook_state.json`),
+that's a data-loss event.
+
+`atomic_write_json` writes to a sibling tmp file, fsyncs, then `os.replace`s
+into place. On POSIX `os.replace` is atomic on the same filesystem.
+"""
+
+from __future__ import annotations
+
+import json
+import os
+from typing import Any, Optional
+
+
+def atomic_write_json(path: str, data: Any, *, indent: Optional[int] = None) -> None:
+    """Atomically persist `data` as JSON at `path`.
+
+    The temp file uses the live PID as a suffix so two processes saving the
+    same file (e.g. unit tests) don't collide on the rename target.
+    """
+    os.makedirs(os.path.dirname(path) or ".", exist_ok=True)
+    tmp = f"{path}.tmp.{os.getpid()}"
+    with open(tmp, "w") as f:
+        json.dump(data, f, indent=indent)
+        f.flush()
+        os.fsync(f.fileno())
+    os.replace(tmp, path)
+
+
+def atomic_write_text(path: str, text: str) -> None:
+    os.makedirs(os.path.dirname(path) or ".", exist_ok=True)
+    tmp = f"{path}.tmp.{os.getpid()}"
+    with open(tmp, "w") as f:
+        f.write(text)
+        f.flush()
+        os.fsync(f.fileno())
+    os.replace(tmp, path)