Fix: re-read the config file before every write

api/src/config.js

@@ -211,35 +211,28 @@ function _backupCorrupt(raw) {
   return _lastBackup;
 }
 
-/* Returns the live cache. Do not write to it. Call loadConfigForUpdate to
-   change the config. A write here survives a failed save. */
-function loadConfig() {
-  if (IS_DEMO) return loadDemoConfig();
-
-  const now = Date.now();
-  if (_cfgCache && now - _cfgCacheAt < CONFIG_TTL_MS) return _cfgCache;
-
+function _readDisk() {
   let raw;
   try {
     raw = fs.readFileSync(CONFIG_PATH, 'utf8');
   } catch (e) {
     if (e.code === 'ENOENT') _clearDamage();
     else _markDamaged('unreadable', e.message);
-    return migrate({ items: [], settings: {} });
+    return null;
   }
 
   let parsed;
   try {
     parsed = JSON.parse(raw);
   } catch (e) {
     _markDamaged('corrupt', e.message, _backupCorrupt(raw));
-    return migrate({ items: [], settings: {} });
+    return null;
   }
 
   const shaped = _normalizeShape(parsed);
   if (!shaped) {
     _markDamaged('corrupt', 'wrong shape', _backupCorrupt(raw));
-    return migrate({ items: [], settings: {} });
+    return null;
   }
 
   _clearDamage();
@@ -254,6 +247,20 @@ function loadConfig() {
         ...(backup ? { backup } : {}),
       });
   }
+  return shaped;
+}
+
+/* Returns the live cache. Do not write to it. Call loadConfigForUpdate to
+   change the config. A write here survives a failed save. */
+function loadConfig() {
+  if (IS_DEMO) return loadDemoConfig();
+
+  const now = Date.now();
+  if (_cfgCache && now - _cfgCacheAt < CONFIG_TTL_MS) return _cfgCache;
+
+  const shaped = _readDisk();
+  if (!shaped) return migrate({ items: [], settings: {} });
+
   const before = shaped._schemaVersion;
   migrate(shaped);
   _cfgCache = shaped;
@@ -269,14 +276,19 @@ function loadConfig() {
   return shaped;
 }
 
+/* Reads the file, not the cache. A hand edit made in the cache window would
+   otherwise be overwritten by the next save. */
 function loadConfigForUpdate() {
+  _cfgCacheAt = 0;
   return structuredClone(loadConfig());
 }
 
 /* keepRev is only for writes the browser never sees. Every open dashboard
    reloads when _rev changes. */
 function saveConfig(data, { keepRev = false } = {}) {
-  if (_damage) loadConfig();
+  /* Check the file, not the cache. A file broken after the last read must be
+     kept, not overwritten. */
+  _readDisk();
   if (_damage) throw new Error('config file cannot be used; refusing to overwrite it');
   if (data && typeof data === 'object') {
     data._schemaVersion = SCHEMA_VERSION;

api/src/routes/config.js

@@ -168,7 +168,7 @@ on('POST', '/api/config', async (req, res) => {
       if ('keepAwake' in data.settings) data.settings.keepAwake = data.settings.keepAwake === true;
       if ('typeToSearch' in data.settings) data.settings.typeToSearch = data.settings.typeToSearch !== false;
     }
-    const existing = loadConfig();
+    const existing = loadConfigForUpdate();
     /* Stale-write check. A client that sends no _rev overwrites. */
     if (data._rev != null && Number(data._rev) !== (Number(existing._rev) || 0))
       return json(res, 409, {

api/test/config-corrupt.test.js

@@ -151,3 +151,31 @@ test('item entries that are not objects are skipped and the file is backed up',
   assert.equal(b.length, 1);
   assert.equal(fs.readFileSync(path.join(DIR, b[0]), 'utf8'), raw);
 });
+
+test('a file broken after the last read is kept, not overwritten by the next save', () => {
+  reset();
+  const cfg = fresh();
+  cfg.saveConfig({ items: [{ id: 'a', type: 'app' }], settings: {} });
+  cfg.loadConfig();
+  fs.writeFileSync(CFG, '{ edited by hand');
+  assert.throws(() => cfg.saveConfig(cfg.loadConfigForUpdate()));
+  assert.equal(fs.readFileSync(CFG, 'utf8'), '{ edited by hand');
+  assert.equal(backups().length, 1);
+});
+
+test('a hand edit made after the last read survives a read-modify-write', () => {
+  reset();
+  const cfg = fresh();
+  cfg.saveConfig({ items: [], settings: { theme: 'dark' } });
+  cfg.loadConfig();
+  fs.writeFileSync(
+    CFG,
+    JSON.stringify({ _schemaVersion: cfg.SCHEMA_VERSION, items: [], settings: { theme: 'light' } }),
+  );
+  const next = cfg.loadConfigForUpdate();
+  next.settings.language = 'de';
+  cfg.saveConfig(next);
+  const onDisk = JSON.parse(fs.readFileSync(CFG, 'utf8'));
+  assert.equal(onDisk.settings.theme, 'light');
+  assert.equal(onDisk.settings.language, 'de');
+});