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 474 matching lines @@
         (!re || re.test(target.textContent)))
     {
       event.preventDefault();
     }
   },
   true);
 }
 
 exports["prevent-inline-scripts"] = preventInlineScripts;
 
+/**
+ * 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 always 6 chars
-  // for when Math.random() returns 0.0
+  // 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);
 }
 
-/**
- * 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} prop the name of the property.
- */
-function abortOnPropertyRead(prop)
-{
-  if (!prop)
+function wrapPropertyAccess(object, property, descriptor)
+{
+  let currentDescriptor = Object.getOwnPropertyDescriptor(object, 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 canceller()
+  function abort()
   {
     throw new ReferenceError(rid);
   }
 
   let {onerror} = window;
-  window.onerror = (message, ...rest) =>
-  {
-    if (typeof message == "string" && message.includes(rid))
-      return true;
-    if (onerror && typeof onerror == "function")
-      return onerror(this, message, ...rest);

[Manish Jethani, 2018/10/23 15:31:24]

This needs to be onerror.call

[hub, 2018/10/23 18:23:17]

Done.

-  };
-
-  (function(o, p)

[Manish Jethani, 2018/10/23 15:31:24]

I think this should be a separate function:

  function wrapPropertyAccess(object, property, descriptor)

If the descriptor does not contain a specific accessor (get or set), it should
be replaced with a passthrough (forward the call to the original descriptor). If
it contains a specific accessor (get or set) but the value is null, it should
use the null value (meaning don't include that accessor).

[hub, 2018/10/23 18:23:17]

Done.

-  {
-    // simple property
-    let d = Object.getOwnPropertyDescriptor(o, p);
-    if (!d || d.get != canceller)
-      Object.defineProperty(o, p, {get: canceller, set() {}});
-  })(window, prop);
-}
-
-exports["abort-on-property-read"] = makeInjector(abortOnPropertyRead, randomId);
+  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);