Version Framey sample settings without losing old data

examples/framey-settings/README.md

@@ -14,6 +14,12 @@ action calls the backend, so it reads the persisted setting rather than a
 browser cache. A missing, damaged, or old non-boolean value reads as the
 caller's default;
 the next save atomically replaces the sample's settings file.
+The current file is `{"schema": 1, "enabled": true|false}`. An unversioned
+`{"enabled": true|false}` file from the first sample release still reads, and
+the next save writes schema 1. A file with another explicit schema returns a
+visible read or save error and remains untouched, so downgrading the sample
+cannot erase settings written by a newer version. Add a deliberate migration
+for each future schema instead of changing this guard silently.
 The panel also guards its own read and write calls synchronously. If two
 controller events arrive before React redraws a disabled control, the second
 event is ignored; after the request settles, a new change can be saved.

examples/framey-settings/main.py

@@ -5,26 +5,41 @@ from pathlib import Path
 import tempfile
 import decky
 
+SETTINGS_SCHEMA = 1
+
 
 def settings_file():
     # Decky provides this per-plugin path through its official Python module.
     return Path(decky.DECKY_PLUGIN_SETTINGS_DIR) / 'settings.json'
 
 
+def read_settings():
+    try:
+        stored = json.loads(settings_file().read_text(encoding='utf-8'))
+    except (FileNotFoundError, json.JSONDecodeError, UnicodeDecodeError):
+        return {}
+    if not isinstance(stored, dict):
+        return {}
+    # The first sample release wrote {"enabled": bool} without a schema.
+    # Keep reading it; the next save writes the current format.
+    schema = stored.get('schema', SETTINGS_SCHEMA)
+    if type(schema) is not int or schema != SETTINGS_SCHEMA:
+        raise ValueError('Settings were written by an unsupported sample version')
+    return stored
+
+
 class Plugin:
     async def get_setting(self, key: str, default=False):
         if key != 'enabled':
             raise ValueError('Unknown setting')
-        try:
-            stored = json.loads(settings_file().read_text(encoding='utf-8'))
-        except (FileNotFoundError, json.JSONDecodeError, UnicodeDecodeError):
-            return default
-        value = stored.get(key) if isinstance(stored, dict) else None
+        value = read_settings().get(key)
         return value if type(value) is bool else default
 
     async def set_setting(self, key: str, value: bool):
         if key != 'enabled' or type(value) is not bool:
             raise ValueError('Expected an enabled boolean')
+        # Refuse to erase settings from a newer plugin after a downgrade.
+        read_settings()
         target = settings_file()
         target.parent.mkdir(mode=0o700, parents=True, exist_ok=True)
         temporary = None
@@ -32,7 +47,7 @@ class Plugin:
             with tempfile.NamedTemporaryFile('w', encoding='utf-8', dir=target.parent,
                                              prefix='.settings-', delete=False) as output:
                 temporary = Path(output.name)
-                json.dump({'enabled': value}, output)
+                json.dump({'schema': SETTINGS_SCHEMA, 'enabled': value}, output)
                 output.write('\n')
             temporary.chmod(0o600)
             os.replace(temporary, target)

tests/test_framey_sample.py

@@ -1,6 +1,7 @@
 """The author example stores settings as a normal Decky user plugin."""
 import asyncio
 import importlib.util
+import json
 from pathlib import Path
 import subprocess
 import sys
@@ -36,7 +37,8 @@ class SamplePlugin(unittest.TestCase):
             self.assertTrue(asyncio.run(first.set_setting('enabled', True)))
             second = backend(folder)
             self.assertTrue(asyncio.run(second.get_setting('enabled', False)))
-            self.assertTrue((Path(folder) / 'settings.json').is_file())
+            self.assertEqual(json.loads((Path(folder) / 'settings.json').read_text()),
+                             {'schema': 1, 'enabled': True})
 
     def test_backend_rejects_unknown_keys_and_non_boolean_values(self):
         with tempfile.TemporaryDirectory() as folder:
@@ -57,6 +59,43 @@ class SamplePlugin(unittest.TestCase):
             self.assertTrue(asyncio.run(plugin.set_setting('enabled', True)))
             self.assertTrue(asyncio.run(backend(folder).get_setting('enabled', False)))
 
+    def test_legacy_boolean_survives_restart_and_migrates_on_save(self):
+        with tempfile.TemporaryDirectory() as folder:
+            path = Path(folder) / 'settings.json'
+            path.write_text('{"enabled": true}\n')
+            self.assertTrue(asyncio.run(backend(folder).get_setting('enabled', False)))
+            self.assertEqual(json.loads(path.read_text()), {'enabled': True},
+                             'Reading must not rewrite a user setting')
+            self.assertTrue(asyncio.run(backend(folder).set_setting('enabled', False)))
+            self.assertEqual(json.loads(path.read_text()), {'schema': 1, 'enabled': False})
+            self.assertFalse(asyncio.run(backend(folder).get_setting('enabled', True)))
+
+    def test_newer_schema_is_preserved_on_read_and_save(self):
+        with tempfile.TemporaryDirectory() as folder:
+            path = Path(folder) / 'settings.json'
+            original = '{"schema": 2, "enabled": true, "future": "keep"}\n'
+            path.write_text(original)
+            plugin = backend(folder)
+            with self.assertRaisesRegex(ValueError, 'unsupported sample version'):
+                asyncio.run(plugin.get_setting('enabled', False))
+            with self.assertRaisesRegex(ValueError, 'unsupported sample version'):
+                asyncio.run(plugin.set_setting('enabled', False))
+            self.assertEqual(path.read_text(), original)
+            self.assertEqual(list(Path(folder).glob('.settings-*')), [])
+
+    def test_failed_atomic_replace_keeps_previous_setting(self):
+        with tempfile.TemporaryDirectory() as folder:
+            path = Path(folder) / 'settings.json'
+            plugin = backend(folder)
+            self.assertTrue(asyncio.run(plugin.set_setting('enabled', True)))
+            previous = path.read_bytes()
+            with patch('os.replace', side_effect=OSError('storage unavailable')):
+                with self.assertRaisesRegex(OSError, 'storage unavailable'):
+                    asyncio.run(plugin.set_setting('enabled', False))
+            self.assertEqual(path.read_bytes(), previous)
+            self.assertEqual(list(Path(folder).glob('.settings-*')), [])
+            self.assertTrue(asyncio.run(backend(folder).get_setting('enabled', False)))
+
 
 if __name__ == '__main__':
     unittest.main()