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
@@ -54,21 +54,129 @@
 }
 
 function makeInjector(injectable, ...dependencies)
 {
   return (...args) => injectCode(stringifyFunctionCall(injectable, ...args),
                                  dependencies);
 }
 
+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 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)
+  {
+    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;
 
 function trace(...args)
 {
   log(...args);
 }
 
 exports.trace = makeInjector(trace, log);
+
+// 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)
+{
+  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)
+    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);
+    }
+  });
+
+  suppressMagicError(magic);
+}
+
+exports["abort-current-inline-script"] =
+  makeInjector(abortCurrentInlineScript, regexEscape, findProperty,
+               getMagic, injectPropertyAccessValidator, suppressMagicError);