Issue 6791 - Implement abort-current-inline-script 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 90 matching lines @@
 
 function getMagic()
 {
   return String.fromCharCode(Date.now() % 26 + 97) +
          Math.floor(Math.random() * 982451653 + 982451653).toString(36);
 }
 
 function suppressMagicError(magic)
 {
   let {onerror} = window;
   window.onerror = function(message, ...rest)

[kzar, 2018/07/16 16:33:15]

The content script part of our snippet already runs after the page script, so
the injected part definitely does. I wonder what the point of trying to wrap
`onerror` is therefore.

Furthermore this wrapper seems pretty easy to workaround, for example the
website could mess with `String.prototype.includes` so that
`message.includes(magic)` returns `false`.

   {
     if (typeof message == "string" && message.includes(magic))
       return true;
 
     if (typeof onerror instanceof Function)
       return onerror.call(this, message, ...rest);
   };
 }
 
 function log(...args)
 {
   console.log(...args);
 }
 
 exports.log = log;
 
+// This is an implementation of the uabinject-defuser technique used by uBlock
+// Origin
+// https://github.com/uBlockOrigin/uAssets/blob/c091f861b63cd2254b8e9e4628f6bdcd89d43caa/filters/resources.txt#L640
 function uabinjectDefuser()
 {
   window.trckd = true;
   window.uabpdl = true;
   window.uabInject = true;
   window.uabDetect = true;
 }
 
 exports["uabinject-defuser"] = makeInjector(uabinjectDefuser);
 
+// This is an implementation of the abort-current-inline-script technique used
+// by uBlock Origin
+// https://github.com/uBlockOrigin/uAssets/blob/68cf8a364fb55deb96264c4e546b58f4c851d782/filters/resources.txt#L1943
 function abortCurrentInlineScript(target, needle)

[kzar, 2018/07/16 16:33:15]

Could you give me an example of `target` and `needle` with some context? It
would help me grok this logic.

 {
   if (!target)
     return;
 
   let re = null;
 
   if (needle)
   {
     re = new RegExp(/^\/.+\/$/.test(needle) ?
                       needle.slice(1, -1) :
                       regexEscape(needle));
   }
 
   let {owner, property} = findProperty(target) || {};
+
+  if (!owner)
+    return;
 
   let descriptor = Object.getOwnPropertyDescriptor(owner, property);
   if (descriptor && descriptor.get)

[kzar, 2018/07/16 16:33:15]

What's the idea with this check?

     return;
 
   let magic = getMagic();
 
   injectPropertyAccessValidator(owner, property, () =>
   {
     let element = document.currentScript;
     if (element instanceof HTMLScriptElement &&
         element.src == "" && (!re || re.test(element.textContent)))
     {
       throw new ReferenceError(magic);

[kzar, 2018/07/16 16:33:15]

How come you've used `ReferenceError` out of interest?

     }
   });
 
   suppressMagicError(magic);
 }
 
 exports["abort-current-inline-script"] = makeInjector(abortCurrentInlineScript);