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..0a472d08c1ee1eabd5303957d719f097b2ec02bb
--- /dev/null
+++ b/lib/indexedDBBackup.js
@@ -0,0 +1,154 @@
+/*
+ * 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 MIN_WRITE_INTERVAL;
+let pendingUpdate;
+let isSaving;
+let lastBackup;
+let lastRun;
+let saveToStorage;
+
+function init(backupInterval, saveFunction)
+{
+  clearInterval(lastBackup);
+  pendingUpdate = false;
+  isSaving = false;
+  lastRun = false;
+  MIN_WRITE_INTERVAL = backupInterval || 60 * 1000;

[Sebastian Noack, 2018/08/21 20:26:24]

Just out of curiosity? Could you experience any performance difference with vs
without this delay (in terms of measurable CPU usage, and/or irresponsive UI)?

[geo, 2018/08/31 15:49:24]

I've tried to measure CPU usage without too much luck, but when it comes to UI,
it really depends on what the user does.
I don't notice any difference between toggling subscriptions or adding more.
Custom filters are a different story. I've tested with about 433KB. Saving
custom filters is slow at this point, without performing any backup so having a
small delay here is beneficial.
Maybe it would be better to handle different updates separately. I'm not sure.

+  saveToStorage = saveFunction ||

[Sebastian Noack, 2018/08/21 20:26:24]

I'd rather mock browser.storage.local.set() in the tests than passing in this
function.

[geo, 2018/08/31 15:49:24]

Done.

+  function()
+  {
+    return browser.storage.local.set({
+      [BACKUP_NAME]: {
+        content: serialize(),
+        lastModified: Date.now()
+      }
+    });
+  };
+}
+
+init();
+
+function scheduleBackup()
+{
+  pendingUpdate = true;
+  if (!lastRun)
+  {
+    lastRun = performance.now();
+    pendingUpdate = false;
+    isSaving = true;
+
+    saveToStorage().then(() =>
+    {
+      isSaving = false;
+      lastRun = performance.now();
+      if (pendingUpdate)
+        scheduleBackup();
+    });
+  }
+  else
+  {
+    clearInterval(lastBackup);
+
+    lastBackup = setTimeout(() =>
+    {
+      if (!isSaving && (performance.now() - lastRun) >= MIN_WRITE_INTERVAL)
+      {
+        isSaving = true;
+        pendingUpdate = false;
+        lastRun = performance.now();
+        saveToStorage().then(() =>
+        {
+          isSaving = false;
+          lastRun = performance.now();
+          if (pendingUpdate)
+            scheduleBackup();
+        });
+      }
+    }, MIN_WRITE_INTERVAL - (performance.now() - lastRun));
+  }
+}
+
+function serialize(subscriptions = FilterStorage.subscriptions)
+{
+  let buffer = [];
+  for (let subscription of subscriptions)
+  {
+    if (subscription instanceof SpecialSubscription)
+    {
+      buffer.push("");

[Sebastian Noack, 2018/08/21 20:26:24]

Do we have to add an empty line here?

[geo, 2018/08/31 15:49:24]

Done.

+      subscription.serialize(buffer);
+      buffer.push("", "[Subscription filters]");
+      subscription.serializeFilters(buffer);
+    }
+    else if (subscription instanceof DownloadableSubscription)
+    {
+      let {homepage, title, url, disabled} = subscription;
+
+      buffer.push(

[Sebastian Noack, 2018/08/21 20:26:24]

Can't we just use Subscription.serialize() (but without calling
Subscription.serializeFilters()) here?

[geo, 2018/08/31 15:49:24]

As discussed on IRC, I'm leaving the current implementation as it is, since
Subscription.serialize() add some extra fields that we don't need.

+        "",
+        "[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.
+  init,
+  scheduleBackup,

[Sebastian Noack, 2018/08/21 20:26:24]

Can't we just emit one of the above events in the tests rather than calling
sheduleBackup directly?

[geo, 2018/08/31 15:49:24]

Done.

+  serialize
+};