Issue 3851 - Implement subscribe link handling via process scripts

lib/child/subscribeLinks.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 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 11 matching lines @@
 Services.obs.addObserver(onContentWindow, "content-document-global-created",
     false);
 onShutdown.add(() =>
 {
   Services.obs.removeObserver(onContentWindow,
       "content-document-global-created");
 });
 
 function onContentWindow(subject, topic, data)
 {
   if (subject instanceof Ci.nsIDOMWindow && subject.top == subject)

[Thomas Greiner, 2016/04/18 15:16:25]

So we're not listening to clicks in subdocuments?

[Wladimir Palant, 2016/04/18 15:38:40]

We do, clicks will bubble up from frames. I verified that.

[Thomas Greiner, 2016/04/18 17:49:43]

Thanks for verifying!

   {
     let eventTarget = subject.QueryInterface(Ci.nsIInterfaceRequestor)
                              .getInterface(Ci.nsIWebNavigation)
                              .QueryInterface(Ci.nsIDocShell)
                              .chromeEventHandler;
-    eventTarget.addEventListener("click", onClick, true);
+    if (eventTarget)

[Wladimir Palant, 2016/04/18 15:38:40]

Not sure when this happens but there are apparently windows without
chromeEventHandler - these must be special-purpose, not to be considered by us.

+      eventTarget.addEventListener("click", onClick, true);
   }
 }
 
 function onClick(event)

[Wladimir Palant, 2016/03/21 19:27:20]

It's mostly an indentation change for this function. The only changes are
onShutdown.done check at the beginning and `link instanceof
content.HTMLAnchorElement` => `link instanceof Ci.nsIDOMHTMLAnchorElement` a bit
further down.

[Wladimir Palant, 2016/03/21 19:29:20]

Heh, forgot the sendAsyncMessage call at the bottom, it has been replaced by
port.emit.

 {
   if (onShutdown.done)
     return;

[Erik, 2016/04/06 03:11:41]

This will stop the function from running after shutdown, but the function is
leaked if it runs after shutdown right?

[Wladimir Palant, 2016/04/18 15:38:40]

Yes, the function itself is leaked - getting the event handler removed after
shutdown would be rather tricky.

 
   // Ignore right-clicks
   if (event.button == 2)
     return;
 
   // Search the link associated with the click
   let link = event.target;
   while (!(link instanceof Ci.nsIDOMHTMLAnchorElement))
   {
     link = link.parentNode;
@@ skipping 52 matching lines @@
     }
   }
 
   port.emit("subscribeLinkClick", {
     title: title,
     url: url,
     mainSubscriptionTitle: mainSubscriptionTitle,
     mainSubscriptionURL: mainSubscriptionURL
   });
 }