Issue 6559 - Use Map object for known subscriptions

lib/synchronizer.js

Index: lib/synchronizer.js
===================================================================
--- a/lib/synchronizer.js
+++ b/lib/synchronizer.js
@@ -195,21 +195,20 @@
     if (downloadable.redirectURL &&
         downloadable.redirectURL != downloadable.url)
     {
       let oldSubscription = Subscription.fromURL(downloadable.url);
       subscription.title = oldSubscription.title;
       subscription.disabled = oldSubscription.disabled;
       subscription.lastCheck = oldSubscription.lastCheck;
 
-      let listed = (oldSubscription.url in FilterStorage.knownSubscriptions);
-      if (listed)

[kzar, 2018/06/07 13:52:26]

But we already have `listed` here, but now we don't use that and perform the
lookup again in the FilterStorage code? I don't care too much either way, but I
guess I don't understand your reasoning so far.

[Manish Jethani, 2018/06/07 14:29:46]

Yeah I have to admit the last change is not exactly related, let's leave it out
for now (so let's focus on Patch Set 2).

I did it because it made sense that both addSubscription and removeSubscription
would do the same type of check, but let's leave it out. Ideally
removeSubscription would return true if the subscription was actually removed,
which would become the value of "listed" here (so no additional lookup).

-        FilterStorage.removeSubscription(oldSubscription);
+      let listed = FilterStorage.knownSubscriptions.has(oldSubscription.url);
+      FilterStorage.removeSubscription(oldSubscription);
 
-      delete Subscription.knownSubscriptions[oldSubscription.url];
+      Subscription.knownSubscriptions.delete(oldSubscription.url);
 
       if (listed)
         FilterStorage.addSubscription(subscription);
     }
 
     // The download actually succeeded
     subscription.lastSuccess = subscription.lastDownload = Math.round(
       Date.now() / MILLIS_IN_SECOND
@@ -330,17 +329,17 @@
         request.channel.loadFlags = request.channel.loadFlags |
                                     request.channel.INHIBIT_CACHING |
                                     request.channel.VALIDATE_ALWAYS;
         request.addEventListener("load", ev =>
         {
           if (onShutdown.done)
             return;
 
-          if (!(subscription.url in FilterStorage.knownSubscriptions))
+          if (!FilterStorage.knownSubscriptions.has(subscription.url))
             return;
 
           let match = /^(\d+)(?:\s+(\S+))?$/.exec(request.responseText);
           if (match && match[1] == "301" &&    // Moved permanently
               match[2] && /^https?:\/\//i.test(match[2]))
           {
             redirectCallback(match[2]);
           }