Issue 6775 - Work around filter data stored in IndexedDB getting lost on Microsoft Edge

lib/indexedDBBackup.js

Index: lib/indexedDBBackup.js
diff --git a/lib/indexedDBBackup.js b/lib/indexedDBBackup.js
new file mode 100644
index 0000000000000000000000000000000000000000..634ac1f059201b9b2a98c805f446d6ea1aa4d76f
--- /dev/null
+++ b/lib/indexedDBBackup.js
@@ -0,0 +1,119 @@
+/*
+ * This file is part of Adblock Plus <https://adblockplus.org/>,
+ * Copyright (C) 2006-present eyeo GmbH
+ *
+ * Adblock Plus is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * Adblock Plus is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+"use strict";
+
+const {FilterNotifier} = require("../adblockpluscore/lib/filterNotifier");
+const {FilterStorage} = require("../adblockpluscore/lib/filterStorage");
+const {DownloadableSubscription, SpecialSubscription} =
+  require("../adblockpluscore/lib/subscriptionClasses");
+
+const BACKUP_NAME = "file:indexedDB-backup";
+
+let minWriteInterval;

[Sebastian Noack, 2018/09/05 14:34:49]

Nit: This is no longer a "min" but a fixed value. Also "backupDelay" seems more
accurately describe it (than write interval).

[geo, 2018/09/05 15:59:08]

Done.
I've also changed the name of `writeInterval` variable in tests/indexedDBBackup
as this change made sense there as well.

+let pendingBackup = false;
+
+function setBackupInterval(backupInterval = 60 * 1000)
+{
+  minWriteInterval = backupInterval;
+}
+
+setBackupInterval();
+
+function scheduleBackup()
+{
+  if (!pendingBackup)
+  {
+    pendingBackup = true;
+
+    setTimeout(
+      () =>
+      {
+        saveToStorage();
+        pendingBackup = false;
+      },
+      minWriteInterval
+    );
+  }
+}
+
+function saveToStorage()
+{
+  browser.storage.local.set({
+    [BACKUP_NAME]: {
+      content: serialize(),
+      lastModified: Date.now()
+    }
+  });
+}
+
+function serialize()
+{
+  let buffer = [];
+
+  for (let subscription of FilterStorage.subscriptions)
+  {
+    if (subscription instanceof SpecialSubscription)
+    {
+      subscription.serialize(buffer);
+      buffer.push("[Subscription filters]");
+      subscription.serializeFilters(buffer);
+    }
+    else if (subscription instanceof DownloadableSubscription)
+    {
+      let {homepage, title, url, disabled} = subscription;
+
+      buffer.push(
+        "[Subscription]",
+        `homepage=${homepage}`,
+        `title=${title}`,
+        `url=${url}`,
+        `disabled=${disabled}`
+      );
+    }
+  }
+  return buffer;
+}
+
+function getBackupData()
+{
+  return browser.storage.local.get(BACKUP_NAME).then(items =>
+  {
+    let entry = items[BACKUP_NAME];
+    if (entry)
+      return entry;
+
+    throw {type: "NoSuchFile"};
+  });
+}
+
+FilterNotifier.on("load", scheduleBackup);
+FilterNotifier.on("subscription.updated", scheduleBackup);
+FilterNotifier.on("subscription.added", scheduleBackup);
+FilterNotifier.on("subscription.removed", scheduleBackup);
+FilterNotifier.on("subscription.disabled", scheduleBackup);
+FilterNotifier.on("filter.added", scheduleBackup);
+FilterNotifier.on("filter.removed", scheduleBackup);
+FilterNotifier.on("filter.moved", scheduleBackup);
+FilterNotifier.on("filter.disabled", scheduleBackup);
+
+exports.IndexedDBBackup =
+{
+  getBackupData,
+  // Non-public API, just for tests.
+  setBackupInterval
+};