Issue 6791 - Implement abort-current-inline-script snippet

lib/content/snippets.js

Index: lib/content/snippets.js
===================================================================
--- a/lib/content/snippets.js
+++ b/lib/content/snippets.js
@@ -15,16 +15,60 @@
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 /* eslint-env webextensions */
 /* eslint no-console: "off" */
 
 "use strict";
 
+function regexEscape(s)
+{
+  return s.replace(/[-/\\^$*+?.()|[\]{}]/g, "\\$&");
+}
+
+function findProperty(path, root = window)
+{
+  let owner = root;
+
+  let chain = path.split(".");
+  let property = chain.pop();
+
+  for (let name of chain)
+  {
+    if (!owner)
+      break;
+
+    owner = owner[name];
+  }
+
+  if (!owner)
+    return null;
+
+  return {owner, property};
+}
+
+function injectPropertyAccessValidator(object, property, validate)
+{
+  let value = object[property];
+
+  Object.defineProperty(object, property, {
+    get()
+    {
+      validate();
+      return value;
+    },
+    set(newValue)
+    {
+      validate();
+      value = newValue;
+    }
+  });
+}
+
 function injectCode(code)
 {
   let script = document.createElement("script");
 
   script.type = "application/javascript";
   script.async = false;
 
   // Firefox 58 only bypasses site CSPs when assigning to 'src',
@@ -50,16 +94,35 @@
   return `"use strict";(${func})(${params.map(JSON.stringify).join(",")});`;
 }
 
 function makeInjector(injectable)
 {
   return (...args) => injectCode(stringifyFunctionCall(injectable, ...args));
 }
 
+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
@@ -69,8 +132,51 @@
 {
   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);