Issue 5650 - Apply emulation filters to shadow DOMs

lib/content/elemHideEmulation.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 18 matching lines @@
  */
 function positionInParent(node)
 {
   let {children} = node.parentNode;
   for (let i = 0; i < children.length; i++)
     if (children[i] == node)
       return i + 1;
   return 0;
 }
 
+function isShadowRoot(node)
+{
+  return typeof ShadowRoot != "undefined" && node instanceof ShadowRoot;
+}
+
 function makeSelector(node, selector)
 {
   if (node == null)
     return null;
-  if (!node.parentElement)
+
+  // If this is the topmost element in a shadow DOM, climb up one more level
+  // and then use a ":host" prefix.
+  if (!node.parentElement && !isShadowRoot(node.parentNode))
   {
-    let newSelector = ":root";
+    let newSelector = isShadowRoot(node) ? ":host" : ":root";
     if (selector)
       newSelector += " > " + selector;
     return newSelector;
   }
   let idx = positionInParent(node);
   if (idx > 0)
   {
     let newSelector = `${node.tagName}:nth-child(${idx})`;
     if (selector)
       newSelector += " > " + selector;
-    return makeSelector(node.parentElement, newSelector);
+    return makeSelector(node.parentElement || node.parentNode, newSelector);
   }
 
   return selector;
 }
 
 function parseSelectorContent(content, startIndex)
 {
   let parens = 1;
   let quote = null;
   let i = startIndex;
@@ skipping 69 matching lines @@
       yield null;
     else
       yield* evaluate(chain, index + 1, selector, element, styles);
   }
   // Just in case the getSelectors() generator above had to run some heavy
   // document.querySelectorAll() call which didn't produce any results, make
   // sure there is at least one point where execution can pause.
   yield null;
 }
 
+function extractSubtrees(nodes)
+{
+  return nodes.filter(
+    (node, index) => !nodes.some(
+      // The index comparison is based on the fact that a node always appears
+      // in the list before any of its descendants.
+      (otherNode, otherIndex) => otherIndex < index && otherNode.contains(node)
+    )
+  );
+}
+
+function* traverse(nodes)
+{
+  for (let node of nodes)
+  {
+    yield* traverse(node.children);
+    yield node;
+  }
+}
+
+function niceLoop(iterator, callback)
+{
+  let loop = () =>
+  {
+    let cycleStart = performance.now();
+
+    for (let next = iterator.next(); !next.done; next = iterator.next())
+    {
+      callback(next.value);
+
+      if (performance.now() - cycleStart > MAX_SYNCHRONOUS_PROCESSING_TIME)
+      {
+        setTimeout(loop, 0);
+        return;
+      }
+    }
+  };
+
+  loop();
+}
+
 function PlainSelector(selector)
 {
   this._selector = selector;
 }
 
 PlainSelector.prototype = {
   /**
    * Generator function returning a pair of selector
    * string and subtree.
    * @param {string} prefix the prefix for the selector.
@@ skipping 139 matching lines @@
       yield [selector, subtree];
   }
 };
 
 function isSelectorHidingOnlyPattern(pattern)
 {
   return pattern.selectors.some(s => s.preferHideWithSelector) &&
     !pattern.selectors.some(s => s.requiresHiding);
 }
 
-function ElemHideEmulation(addSelectorsFunc, hideElemsFunc)
+function ElemHideEmulation(document, root, addSelectorsFunc, hideElemsFunc,
+                           shadowAttachedEventType)
 {
   this.document = document;
+  this.root = root || document;
   this.addSelectorsFunc = addSelectorsFunc;
   this.hideElemsFunc = hideElemsFunc;
+  this.shadowAttachedEventType = shadowAttachedEventType;
+  this.patterns = [];
   this.observer = new MutationObserver(this.observe.bind(this));
+  this.shadowEmulations = new WeakMap();
+
+  if (shadowAttachedEventType)
+  {
+    this.root.addEventListener(shadowAttachedEventType,
+                               this.onShadowAttached.bind(this), true);
+  }
+
+  if (this.root == this.document)
+    this.document.addEventListener("load", this.onLoad.bind(this), true);
+  else
+    this.findShadowRoots(this.root.children);
 }
 
 ElemHideEmulation.prototype = {
   isSameOrigin(stylesheet)
   {
     try
     {
       return new URL(stylesheet.href).origin == this.document.location.origin;
     }
     catch (e)
@@ skipping 81 matching lines @@
     let selectors = [];
     let selectorFilters = [];
 
     let elements = [];
     let elementFilters = [];
 
     let cssStyles = [];
 
     let stylesheetOnlyChange = !!stylesheets;
     if (!stylesheets)
-      stylesheets = this.document.styleSheets;
+      stylesheets = this.root.styleSheets;
 
     for (let stylesheet of stylesheets)
     {
       // Explicitly ignore third-party stylesheets to ensure consistent behavior
       // between Firefox and Chrome.
       if (!this.isSameOrigin(stylesheet))
         continue;
 
       let rules = stylesheet.cssRules;
       if (!rules)
@@ skipping 29 matching lines @@
 
         pattern = patterns.shift();
 
         if (stylesheetOnlyChange &&
             !pattern.selectors.some(selector => selector.dependsOnStyles))
         {
           pattern = null;
           return processPatterns();
         }
         generator = evaluate(pattern.selectors, 0, "",
-                             this.document, cssStyles);
+                             this.root, cssStyles);
       }
       for (let selector of generator)
       {
         if (selector != null)
         {
           if (isSelectorHidingOnlyPattern(pattern))
           {
             selectors.push(selector);
             selectorFilters.push(pattern.text);
           }
           else
           {
-            for (let element of this.document.querySelectorAll(selector))
+            for (let element of this.root.querySelectorAll(selector))
             {
               elements.push(element);
               elementFilters.push(pattern.text);
             }
           }
         }
         if (performance.now() - cycleStart > MAX_SYNCHRONOUS_PROCESSING_TIME)
         {
           setTimeout(processPatterns, 0);
           return;
@@ skipping 67 matching lines @@
     }
     else
     {
       this._filteringInProgress = true;
       this._addSelectors(stylesheets, completion);
     }
   },
 
   onLoad(event)
   {
+    this.findShadowRoots(this.root.children);
+
+    if (this.patterns.length == 0)
+      return;
+
     let stylesheet = event.target.sheet;
     if (stylesheet)
       this.queueFiltering([stylesheet]);
   },
 
+  onShadowAttached(event)
+  {
+    event.stopImmediatePropagation();
+
+    if (this.patterns.length == 0)
+      return;
+
+    // The shadow root may not be available if it's a closed shadow root.
+    let shadowRoot = event.target.shadowRoot;
+    if (!shadowRoot)
+      return;
+
+    this.addShadowRoot(shadowRoot);
+  },
+
+  addShadowRoot(shadowRoot)
+  {
+    if (!this.shadowEmulations.has(shadowRoot))
+    {
+      let emulation = new ElemHideEmulation(this.document,
+                                            shadowRoot,
+                                            this.addSelectorsFunc,
+                                            this.hideElemsFunc,
+                                            this.shadowAttachedEventType);
+      this.shadowEmulations.set(shadowRoot, emulation);
+      emulation.apply(this.patterns, true);
+    }
+  },
+
+  findShadowRoots(nodes)
+  {
+    niceLoop(traverse(nodes), node =>
+    {
+      let shadowRoot = node.shadowRoot;
+      if (shadowRoot)
+        this.addShadowRoot(shadowRoot);
+    });
+  },
+
   observe(mutations)
   {
+    if (typeof ShadowRoot != "undefined")

[Manish Jethani, 2017/10/20 16:16:42]

Of course we only have to run this code on Chrome.

[hub, 2017/10/20 19:12:50]

Maybe we should set a different mutation observer based on this as the observer
is called quite often.

[Manish Jethani, 2017/10/22 20:01:35]

But both the observers would listen for the same DOM mutations, it's not like
the work would be split between the two. It would be worse because we would have
two observers doing the same work that one could do.

[hub, 2017/10/23 13:30:34]

not saying to observe twice. but when we set up the MutationObserver, we could
setup up a different one if the browser supports ShadowRoot. Feels like a micro
optimisation, maybe.

[Manish Jethani, 2017/10/23 23:04:28]

OK, I see what you mean. I think we're going to end up having to add a lot of
optimizations to that observe function, and that will involve sharing some code
between the shadow roots case and the normal case (e.g. making a list of the
newly added subtree roots). On balance it feels like it's probably best to keep
it all in one function.

If we split the observer, it would make sense to do it based on the mutation
type ("childList", "attributes", and "characterData" can each have their own
observer), but then again let's see how this code evolves as we add support for
user style sheets and so on.

+    {
+      let allAddedElements = [];
+      for (let mutation of mutations)
+      {
+        for (let node of mutation.addedNodes)
+        {
+          if (node instanceof Element)
+            allAddedElements.push(node);
+        }
+      }
+
+      // Find any preattached shadows.
+      this.findShadowRoots(extractSubtrees(allAddedElements));
+    }
+
     this.queueFiltering();
   },
 
-  apply(patterns)
+  apply(patterns, parsed)
   {
-    this.patterns = [];
-    for (let pattern of patterns)
+    if (parsed)
     {
-      let selectors = this.parseSelector(pattern.selector);
-      if (selectors != null && selectors.length > 0)
-        this.patterns.push({selectors, text: pattern.text});
+      this.patterns = patterns;
+    }
+    else
+    {
+      this.patterns = [];
+      for (let pattern of patterns)
+      {
+        let selectors = this.parseSelector(pattern.selector);
+        if (selectors != null && selectors.length > 0)
+          this.patterns.push({selectors, text: pattern.text});
+      }
     }
 
     if (this.patterns.length > 0)
     {
       this.queueFiltering();
       this.observer.observe(
-        this.document,
+        this.root,
         {
           childList: true,
           attributes: true,
           characterData: true,
           subtree: true
         }
       );
-      this.document.addEventListener("load", this.onLoad.bind(this), true);
     }
   }
 };
 
 exports.ElemHideEmulation = ElemHideEmulation;