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 418 matching lines @@
   {
     for (let i = 0; i < times; i++)
       object + "";
 
     if (typeof dir == "function")
       dir.call(this, object);
   };
 }
 
 exports["dir-string"] = makeInjector(dirString);
+
+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
+  return (Math.floor(Math.random() * 2116316160 + 60466176)).toString(36);

[Manish Jethani, 2018/09/25 12:25:22]

Nit: The parentheses around `Math.foor(...)` are unnecessary.

[hub, 2018/09/25 15:40:43]

Done.

+}
+
+/**
+ * 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(...props)
+{
+  if (props.length == 0)
+    return;
+
+  let magic = randomId();
+
+  let abort = function()
+  {
+    throw new ReferenceError(magic);
+  };
+
+  let {onerror} = window;
+  window.onerror = (message, ...rest) =>
+  {
+    if (typeof message == "string" && message.includes(magic))
+      return true;
+    if (onerror && typeof onerro == "function")
+      return onerror(this, message, ...rest);
+  };
+
+  let patch = function(o, p)
+  {
+    // simple property
+    let d = Object.getOwnPropertyDescriptor(o, p);
+    if (!d || d.get != abort)
+      Object.defineProperty(o, p, {get: abort, set() {}});
+  };
+  for (let prop of props)
+    patch(window, prop);
+}
+
+exports["abort-on-property-read"] = makeInjector(abortOnPropertyRead, randomId);