Issue 7015 - Serialize subscriptions for *exportData in one loop

lib/filterStorage.js

 /*
  * 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
@@ skipping 425 matching lines @@
       parser(null);
       return this.saveToDisk();
     });
   },
 
   /**
    * Generator serializing filter data and yielding it line by line.
    */
   *exportData()
   {
-    // Do not persist external subscriptions
-    let subscriptions = [];
-    for (let subscription of this.subscriptions())
-    {
-      if (!(subscription instanceof ExternalSubscription))
-        subscriptions.push(subscription);
-    }
-
     yield "# Adblock Plus preferences";
     yield "version=" + formatVersion;
 
     let saved = new Set();
     let buf = [];
 
     // Save subscriptions
-    for (let subscription of subscriptions)
+    for (let subscription of this.subscriptions())
     {
+      // Do not persist external subscriptions
+      if (subscription instanceof ExternalSubscription)
+        continue;
+
       yield "";
+      subscription.serialize(buf);
 
-      subscription.serialize(buf);
       if (subscription.filters.length)
       {
         buf.push("", "[Subscription filters]");
         subscription.serializeFilters(buf);
       }
+
       for (let line of buf)
         yield line;
+
       buf.splice(0);

[Sebastian Noack, 2018/10/03 16:33:24]

While optimizing this code, you might want consider using `buf = []` which is
used to be much faster than splice(). I didn't benchmark it recently though, so
you might want to double check on recent browser versions.

-    }
 
-    // Save filter data
-    for (let subscription of subscriptions)
-    {
+      // Save filter data
       for (let filter of subscription.filters)
       {
         if (!saved.has(filter.text))
         {
           filter.serialize(buf);
           saved.add(filter.text);
           for (let line of buf)
             yield line;
           buf.splice(0);
         }
@@ skipping 161 matching lines @@
  * @param {Subscription} subscription filter subscription to be removed
  */
 function removeSubscriptionFilters(subscription)
 {
   if (!FilterStorage.knownSubscriptions.has(subscription.url))
     return;
 
   for (let filter of subscription.filters)
     filter.removeSubscription(subscription);
 }