Plan 3: load/save ~/assistant/state/config.json with mode 0600

client/config.py

@@ -0,0 +1,49 @@
+"""Read / write the device config file at ~/assistant/state/config.json."""
+import json
+import os
+from dataclasses import asdict, dataclass
+from pathlib import Path
+
+
+class ConfigMissingError(RuntimeError):
+    """Raised when config.json is missing or malformed."""
+
+
+@dataclass(frozen=True)
+class Config:
+    device_id: str
+    device_token: str
+    backend_ws: str
+
+
+def config_path() -> Path:
+    return Path(os.environ["HOME"]) / "assistant" / "state" / "config.json"
+
+
+def load_config() -> Config:
+    path = config_path()
+    if not path.exists():
+        raise ConfigMissingError(f"{path} not found; run `python -m client.pair` first")
+    try:
+        raw = json.loads(path.read_text())
+    except json.JSONDecodeError as exc:
+        raise ConfigMissingError(f"{path} is not valid JSON: {exc}") from exc
+    try:
+        return Config(
+            device_id=str(raw["device_id"]),
+            device_token=str(raw["device_token"]),
+            backend_ws=str(raw["backend_ws"]),
+        )
+    except KeyError as exc:
+        raise ConfigMissingError(f"{path} missing field: {exc}") from exc
+
+
+def save_config(cfg: Config) -> None:
+    path = config_path()
+    path.parent.mkdir(parents=True, exist_ok=True)
+    # Write to a temp file then atomically rename, so a partial write never
+    # leaves a half-baked config on disk.
+    tmp = path.with_suffix(".json.tmp")
+    tmp.write_text(json.dumps(asdict(cfg), indent=2) + "\n")
+    os.chmod(tmp, 0o600)
+    os.replace(tmp, path)