Reworked cache for news and update manifest.

ptlinux/news.py

@@ -153,6 +153,12 @@ def fetch_news(
 		_write_cache(cache_path, articles)
 		return articles
 	except (OSError, NewsError, UnicodeDecodeError, json.JSONDecodeError):
+		return read_cached_news(cache_path)
+
+
+def read_cached_news(cache_path: Path) -> tuple[NewsArticle, ...]:
+	"""Read the last valid news feed without performing network I/O."""
+
 	return _read_cache(cache_path)
 
 
@@ -179,6 +185,12 @@ def fetch_latest_broadcast(
 		_write_broadcast_cache(cache_path, broadcast)
 		return broadcast
 	except (OSError, NewsError, UnicodeDecodeError, json.JSONDecodeError):
+		return read_cached_broadcast(cache_path)
+
+
+def read_cached_broadcast(cache_path: Path) -> Broadcast | None:
+	"""Read the last valid broadcast without performing network I/O."""
+
 	return _read_broadcast_cache(cache_path)
 
 
@@ -288,7 +300,7 @@ def _read_cache(path: Path) -> tuple[NewsArticle, ...]:
 		if not isinstance(value, list):
 			return ()
 		return tuple(NewsArticle(**item) for item in value if isinstance(item, dict))
-	except (OSError, TypeError, json.JSONDecodeError):
+	except (OSError, UnicodeError, TypeError, json.JSONDecodeError):
 		return ()
 
 
@@ -309,7 +321,7 @@ def _read_broadcast_cache(path: Path) -> Broadcast | None:
 	try:
 		value = json.loads(path.read_text(encoding="utf-8"))
 		return Broadcast(**value) if isinstance(value, dict) else None
-	except (OSError, TypeError, json.JSONDecodeError):
+	except (OSError, UnicodeError, TypeError, json.JSONDecodeError):
 		return None
 
 

ptlinux/self_update.py

@@ -45,6 +45,7 @@ UPDATE_ARCHIVE_PREFIX = "pristontale-eu-linux-update-v"
 _VERSION_PATTERN = re.compile(r"(?:0|[1-9][0-9]*)\.(?:0|[1-9][0-9]*)\.(?:0|[1-9][0-9]*)\Z")
 _SHA256_PATTERN = re.compile(r"[0-9a-f]{64}\Z")
 _ALLOWED_RELEASE_ROOTS = {"ptlinux", "ptdiag", "release.json"}
+UPDATE_CHECK_CACHE_SCHEMA = 1
 
 
 class LauncherUpdateError(RuntimeError):
@@ -143,6 +144,89 @@ def check_for_launcher_update(
 	)
 	_verify_manifest_signature(manifest_bytes, signature_bytes, key)
 	manifest = parse_update_manifest(manifest_bytes)
+	return _evaluate_launcher_update(manifest, current_version, url)
+
+
+def read_cached_launcher_update_check(
+	cache_path: Path,
+	*,
+	current_version: str = __version__,
+	manifest_url: str | None = None,
+	public_key_path: Path | None = None,
+	environment: Mapping[str, str] | None = None,
+) -> LauncherUpdateCheck | None:
+	"""Read a display-only result from the last authenticated live check."""
+
+	url = manifest_url or configured_manifest_url(environment)
+	key = public_key_path or configured_public_key_path(environment)
+	try:
+		_parse_version(current_version, "current launcher version")
+		_require_https_url(url, "update manifest URL")
+		key_sha256 = _sha256_file(key.expanduser().resolve())
+		value = json.loads(cache_path.read_text(encoding="utf-8"))
+	except (
+		OSError,
+		UnicodeError,
+		json.JSONDecodeError,
+		LauncherUpdateError,
+		RuntimeError,
+	):
+		return None
+	if not isinstance(value, dict):
+		return None
+	if value.get("schema") != UPDATE_CHECK_CACHE_SCHEMA:
+		return None
+	if value.get("current_version") != current_version:
+		return None
+	if value.get("manifest_url") != url:
+		return None
+	if value.get("public_key_sha256") != key_sha256:
+		return None
+	manifest_value = value.get("manifest")
+	if not isinstance(manifest_value, dict):
+		return None
+	try:
+		manifest = parse_update_manifest(
+			(json.dumps(manifest_value, sort_keys=True) + "\n").encode("utf-8")
+		)
+	except (LauncherUpdateError, TypeError, ValueError):
+		return None
+	return _evaluate_launcher_update(manifest, current_version, url)
+
+
+def cache_launcher_update_check(
+	cache_path: Path,
+	check: LauncherUpdateCheck,
+	*,
+	public_key_path: Path | None = None,
+	environment: Mapping[str, str] | None = None,
+) -> bool:
+	"""Cache an authenticated result for startup display, never for installation."""
+
+	key = public_key_path or configured_public_key_path(environment)
+	try:
+		key_sha256 = _sha256_file(key.expanduser().resolve())
+		_write_json(
+			cache_path,
+			{
+				"schema": UPDATE_CHECK_CACHE_SCHEMA,
+				"checked_at": datetime.now().astimezone().isoformat(),
+				"current_version": check.current_version,
+				"manifest_url": check.manifest_url,
+				"public_key_sha256": key_sha256,
+				"manifest": asdict(check.manifest),
+			},
+		)
+	except (OSError, RuntimeError):
+		return False
+	return True
+
+
+def _evaluate_launcher_update(
+	manifest: UpdateManifest,
+	current_version: str,
+	manifest_url: str,
+) -> LauncherUpdateCheck:
 	current = _parse_version(current_version, "current launcher version")
 	latest = _parse_version(manifest.version, "manifest version")
 	minimum = _parse_version(
@@ -170,7 +254,7 @@ def check_for_launcher_update(
 		available=available,
 		supported=supported,
 		reason=reason,
-		manifest_url=url,
+		manifest_url=manifest_url,
 		manifest=manifest,
 	)