Issue 6969 - Implement abort-on-property-read snippet

lib/content/snippets.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 475 matching lines @@
     {
       event.preventDefault();
     }
   },
   true);
 }
 
 exports["prevent-inline-scripts"] = preventInlineScripts;
 
 /**
- * Generate an alpha-numeric id 6 chars long, in the range 100000..zzzzzz.

[Manish Jethani, 2018/10/24 23:02:10]

Some nits:

s/Generate/Generates/

s/an alpha-numeric id 6 chars long .../a random alphanumeric ID consisting of 6
base-36 digits from the range 100000..zzzzzz (both inclusive)./

s/{string} the random id./{string} The random ID./

[hub, 2018/10/25 14:32:27]

Done.

- *
- * @returns {string} the random id.
+ * Generates a random alphanumeric ID consisting of 6 base-36 digits
+ * from the range 100000..zzzzzz (both inclusive).
+ *
+ * @returns {string} The random ID.
  */
 function randomId()
 {
   // 2176782336 is 36^6 which mean 6 chars [a-z0-9]
   // 60466176 is 36^5
   // 2176782336 - 60466176 = 2116316160. This ensure to always have 6
   // chars even if Math.random() returns its minimum value 0.0
+  //
   return Math.floor(Math.random() * 2116316160 + 60466176).toString(36);
 }
 
 function wrapPropertyAccess(object, property, descriptor)
 {
-  // simple property

[Manish Jethani, 2018/10/24 23:02:10]

Do we need this comment? The code is quite straightforward in what it does.

[hub, 2018/10/25 14:32:28]

was carried over from other changes. removed it.

   let currentDescriptor = Object.getOwnPropertyDescriptor(object, property);
-  if (!currentDescriptor)
-    currentDescriptor = {};
-  if (typeof descriptor.get != "undefined")
-  {
-    if (currentDescriptor.get != descriptor.get)

[Manish Jethani, 2018/10/24 23:02:10]

I'm not seeing the point of this check.

[hub, 2018/10/25 14:32:28]

Done.

-      currentDescriptor.get = descriptor.get;
-  }
-  if (typeof descriptor.set != "undefined")
-  {
-    if (currentDescriptor.set != descriptor.set)
-      currentDescriptor.set = descriptor.set;
-  }
-  Object.defineProperty(object, property, currentDescriptor);
-}
-
-/**
- * Will patch a property on the window object to abort when read.
- * It will intercept the onerror callback and block it if tagged.
- *
- * @todo handle properties of properties.
- *
- * @param {string} property the name of the property.
+  if (currentDescriptor && !currentDescriptor.configurable)
+    return false;
+
+  Object.defineProperty(object, property, descriptor);
+  return true;
+}
+
+/**
+ * Patches a property on the window object to abort execution when the
+ * property is read.
+ *
+ * No error is be printed to the console.
+ *
+ * The idea originates from
+ * {@link https://github.com/uBlockOrigin/uAssets/blob/80b195436f8f8d78ba713237bfc268ecfc9d9d2b/filters/resources.txt#L1703 uBlock Origin}.
+ *
+ * @param {string} property The name of the property.
  */
 function abortOnPropertyRead(property)
 {
   if (!property)
     return;
 
   let rid = randomId();
 
   function abort()
   {
     throw new ReferenceError(rid);
   }
 
   let {onerror} = window;
-  window.onerror = (message, ...rest) =>
-  {
-    if (typeof message == "string" && message.includes(rid))
-      return true;
-    if (typeof onerror == "function")
-      return onerror(message, ...rest);
-  };
-
-  wrapPropertyAccess(window, property, {get: abort, set() {}});
+  if (wrapPropertyAccess(window, property, {get: abort, set() {}}))
+  {
+    window.onerror = (message, ...rest) =>
+    {
+      if (typeof message == "string" && message.includes(rid))
+        return true;
+      if (typeof onerror == "function")
+        return (() => {}).call.call(onerror, this, message, ...rest);
+    };
+  }
 }
 
 exports["abort-on-property-read"] = makeInjector(abortOnPropertyRead,
                                                  wrapPropertyAccess,
                                                  randomId);