Issue 6538, 6781 - Implement support for snippet filters

lib/filterClasses.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 66 matching lines @@
   }
 };
 
 /**
  * Cache for known filters, maps string representation to filter objects.
  * @type {Map.<string,Filter>}
  */
 Filter.knownFilters = new Map();
 
 /**
- * Regular expression that element hiding filters should match
+ * Regular expression that content filters should match
  * @type {RegExp}
  */
-Filter.elemhideRegExp = /^([^/*|@"!]*?)#([@?])?#(.+)$/;
+Filter.contentRegExp = /^([^/*|@"!]*?)#([@?$])?#(.+)$/;
 /**
  * Regular expression that RegExp filters specified as RegExps should match
  * @type {RegExp}
  */
 Filter.regexpRegExp = /^(@@)?\/.*\/(?:\$~?[\w-]+(?:=[^,\s]+)?(?:,~?[\w-]+(?:=[^,\s]+)?)*)?$/;
 /**
  * Regular expression that options on a RegExp filter should match
  * @type {RegExp}
  */
 Filter.optionsRegExp = /\$(~?[\w-]+(?:=[^,]+)?(?:,~?[\w-]+(?:=[^,]+)?)*)$/;
 /**
  * Regular expression that matches an invalid Content Security Policy
  * @type {RegExp}
  */
 Filter.invalidCSPRegExp = /(;|^) ?(base-uri|referrer|report-to|report-uri|upgrade-insecure-requests)\b/i;
 
 /**
  * Creates a filter of correct type from its text representation - does the
  * basic parsing and calls the right constructor then.
  *
  * @param {string} text   as in Filter()
  * @return {Filter}
  */
 Filter.fromText = function(text)
 {
   let filter = Filter.knownFilters.get(text);
   if (filter)
     return filter;
 
-  let match = (text.includes("#") ? Filter.elemhideRegExp.exec(text) : null);
+  let match = text.includes("#") ? Filter.contentRegExp.exec(text) : null;
   if (match)
   {
     let propsMatch;
     if (!match[2] &&
         (propsMatch = /\[-abp-properties=(["'])([^"']+)\1\]/.exec(match[3])))
     {
       // This is legacy CSS properties syntax, convert to current syntax
       let prefix = match[3].substr(0, propsMatch.index);
       let expression = propsMatch[2];
       let suffix = match[3].substr(propsMatch.index + propsMatch[0].length);
       return Filter.fromText(`${match[1]}#?#` +
           `${prefix}:-abp-properties(${expression})${suffix}`);
     }
 
-    filter = ElemHideBase.fromText(
-      text, match[1], match[2], match[3]
-    );
+    filter = ContentFilter.fromText(text, match[1], match[2], match[3]);
   }
   else if (text[0] == "!")
     filter = new CommentFilter(text);
   else
     filter = RegExpFilter.fromText(text);
 
   Filter.knownFilters.set(filter.text, filter);
   return filter;
 };
 
@@ skipping 29 matching lines @@
   if (!text)
     return text;
 
   // Remove line breaks, tabs etc
   text = text.replace(/[^\S ]+/g, "");
 
   // Don't remove spaces inside comments
   if (/^ *!/.test(text))
     return text.trim();
 
-  // Special treatment for element hiding filters, right side is allowed to
-  // contain spaces
-  if (Filter.elemhideRegExp.test(text))
-  {
-    let [, domain, separator, selector] = /^(.*?)(#@?#?)(.*)$/.exec(text);
-    return domain.replace(/ +/g, "") + separator + selector.trim();
+  // Special treatment for content filters, right side is allowed to contain
+  // spaces
+  if (Filter.contentRegExp.test(text))
+  {
+    let [, domains, separator, body] = /^(.*?)(#[@?$]?#?)(.*)$/.exec(text);
+    return domains.replace(/ +/g, "") + separator + body.trim();
   }
 
   // For most regexp filters we strip all spaces, but $csp filter options
   // are allowed to contain single (non trailing) spaces.
   let strippedText = text.replace(/ +/g, "");
   if (!strippedText.includes("$") || !/\bcsp=/i.test(strippedText))
     return strippedText;
 
   let optionsMatch = Filter.optionsRegExp.exec(strippedText);
   if (!optionsMatch)
@@ skipping 30 matching lines @@
   return beforeOptions + "$" + options.join();
 };
 
 /**
  * @see filterToRegExp
  */
 Filter.toRegExp = filterToRegExp;
 
 /**
  * Class for invalid filters
- * @param {string} text see Filter()
+ * @param {string} text see {@link Filter Filter()}
  * @param {string} reason Reason why this filter is invalid
  * @constructor
  * @augments Filter
  */
 function InvalidFilter(text, reason)
 {
   Filter.call(this, text);
 
   this.reason = reason;
 }
@@ skipping 10 matching lines @@
 
   /**
    * See Filter.serialize()
    * @inheritdoc
    */
   serialize(buffer) {}
 });
 
 /**
  * Class for comments
- * @param {string} text see Filter()
+ * @param {string} text see {@link Filter Filter()}
  * @constructor
  * @augments Filter
  */
 function CommentFilter(text)
 {
   Filter.call(this, text);
 }
 exports.CommentFilter = CommentFilter;
 
 CommentFilter.prototype = extend(Filter, {
   type: "comment",
 
   /**
    * See Filter.serialize()
    * @inheritdoc
    */
   serialize(buffer) {}
 });
 
 /**
  * Abstract base class for filters that can get hits
  * @param {string} text
- *   see Filter()
+ *   see {@link Filter Filter()}
  * @param {string} [domains]
  *   Domains that the filter is restricted to separated by domainSeparator
  *   e.g. "foo.com|bar.com|~baz.com"
  * @constructor
  * @augments Filter
  */
 function ActiveFilter(text, domains)
 {
   Filter.call(this, text);
 
-  this.domainSource = domains;
+  if (domains)
+    this.domainSource = domains;
 }
 exports.ActiveFilter = ActiveFilter;
 
 ActiveFilter.prototype = extend(Filter, {
   _disabled: false,
   _hitCount: 0,
   _lastHit: 0,
 
   /**
    * Defines whether the filter is disabled
@@ skipping 48 matching lines @@
     {
       let oldValue = this._lastHit;
       this._lastHit = value;
       FilterNotifier.triggerListeners("filter.lastHit", this, value, oldValue);
     }
     return this._lastHit;
   },
 
   /**
    * String that the domains property should be generated from
-   * @type {string}
+   * @type {?string}
    */
   domainSource: null,
 
   /**
    * Separator character used in domainSource property, must be
    * overridden by subclasses
    * @type {string}
    */
   domainSeparator: null,
 
   /**
-   * Determines whether the trailing dot in domain names isn't important and
-   * should be ignored, must be overridden by subclasses.
-   * @type {boolean}
-   */
-  ignoreTrailingDot: true,
-
-  /**
-   * Determines whether domainSource is already upper-case,
+   * Determines whether domainSource is already lower-case,
    * can be overridden by subclasses.
    * @type {boolean}
    */
-  domainSourceIsUpperCase: false,
+  domainSourceIsLowerCase: false,
 
   /**
    * Map containing domains that this filter should match on/not match
    * on or null if the filter should match on all domains
    * @type {?Map.<string,boolean>}
    */
   get domains()
   {
-    // Despite this property being cached, the getter is called
-    // several times on Safari, due to WebKit bug 132872
-    let prop = Object.getOwnPropertyDescriptor(this, "domains");
+    let prop = Object.getOwnPropertyDescriptor(this, "_domains");
     if (prop)
-      return prop.value;
+    {
+      let {value} = prop;
+      return typeof value == "string" ?
+               new Map([[value, true], ["", false]]) : value;
+    }
 
     let domains = null;
 
     if (this.domainSource)
     {
       let source = this.domainSource;
-      if (!this.domainSourceIsUpperCase)
+      if (!this.domainSourceIsLowerCase)
       {
-        // RegExpFilter already have uppercase domains
-        source = source.toUpperCase();
+        // RegExpFilter already have lowercase domains
+        source = source.toLowerCase();
       }
       let list = source.split(this.domainSeparator);
       if (list.length == 1 && list[0][0] != "~")
       {
         // Fast track for the common one-domain scenario
-        if (this.ignoreTrailingDot)
-          list[0] = list[0].replace(/\.+$/, "");
-        domains = new Map([["", false], [list[0], true]]);
+        domains = list[0];
       }
       else
       {
         let hasIncludes = false;
         for (let i = 0; i < list.length; i++)
         {
           let domain = list[i];
-          if (this.ignoreTrailingDot)
-            domain = domain.replace(/\.+$/, "");
           if (domain == "")
             continue;
 
           let include;
           if (domain[0] == "~")
           {
             include = false;
             domain = domain.substr(1);
           }
           else
           {
             include = true;
             hasIncludes = true;
           }
 
           if (!domains)
             domains = new Map();
 
           domains.set(domain, include);
         }
         if (domains)
           domains.set("", !hasIncludes);
       }
 
       this.domainSource = null;
     }
 
-    Object.defineProperty(this, "domains", {value: domains, enumerable: true});
+    Object.defineProperty(this, "_domains", {value: domains});
     return this.domains;
   },
 
   /**
    * Array containing public keys of websites that this filter should apply to
-   * @type {string[]}
+   * @type {?string[]}
    */
   sitekeys: null,
 
   /**
    * Checks whether this filter is active on a domain.
-   * @param {string} docDomain domain name of the document that loads the URL
+   * @param {string} [docDomain] domain name of the document that loads the URL
    * @param {string} [sitekey] public key provided by the document
    * @return {boolean} true in case of the filter being active
    */
   isActiveOnDomain(docDomain, sitekey)
   {
     // Sitekeys are case-sensitive so we shouldn't convert them to
     // upper-case to avoid false positives here. Instead we need to
     // change the way filter options are parsed.
     if (this.sitekeys &&
         (!sitekey || this.sitekeys.indexOf(sitekey.toUpperCase()) < 0))
     {
       return false;
     }
 
     // If no domains are set the rule matches everywhere
     if (!this.domains)
       return true;
 
     // If the document has no host name, match only if the filter
     // isn't restricted to specific domains
     if (!docDomain)
       return this.domains.get("");
 
-    if (this.ignoreTrailingDot)
-      docDomain = docDomain.replace(/\.+$/, "");
-    docDomain = docDomain.toUpperCase();
+    docDomain = docDomain.replace(/\.+$/, "").toLowerCase();
 
     while (true)
     {
       let isDomainIncluded = this.domains.get(docDomain);
       if (typeof isDomainIncluded != "undefined")
         return isDomainIncluded;
 
       let nextDot = docDomain.indexOf(".");
       if (nextDot < 0)
         break;
       docDomain = docDomain.substr(nextDot + 1);
     }
     return this.domains.get("");
   },
 
   /**
    * Checks whether this filter is active only on a domain and its subdomains.
    * @param {string} docDomain
    * @return {boolean}
    */
   isActiveOnlyOnDomain(docDomain)
   {
     if (!docDomain || !this.domains || this.domains.get(""))
       return false;
 
-    if (this.ignoreTrailingDot)
-      docDomain = docDomain.replace(/\.+$/, "");
-    docDomain = docDomain.toUpperCase();
+    docDomain = docDomain.replace(/\.+$/, "").toLowerCase();
 
     for (let [domain, isIncluded] of this.domains)
     {
       if (isIncluded && domain != docDomain)
       {
         if (domain.length <= docDomain.length)
           return false;
 
         if (!domain.endsWith("." + docDomain))
           return false;
@@ skipping 27 matching lines @@
       if (this._hitCount)
         buffer.push("hitCount=" + this._hitCount);
       if (this._lastHit)
         buffer.push("lastHit=" + this._lastHit);
     }
   }
 });
 
 /**
  * Abstract base class for RegExp-based filters
- * @param {string} text see Filter()
+ * @param {string} text see {@link Filter Filter()}
  * @param {string} regexpSource
  *   filter part that the regular expression should be build from
  * @param {number} [contentType]
  *   Content types the filter applies to, combination of values from
  *   RegExpFilter.typeMap
  * @param {boolean} [matchCase]
  *   Defines whether the filter should distinguish between lower and upper case
  *   letters
  * @param {string} [domains]
  *   Domains that the filter is restricted to, e.g. "foo.com|bar.com|~baz.com"
@@ skipping 32 matching lines @@
   else
   {
     // No need to convert this filter to regular expression yet, do it on demand
     this.regexpSource = regexpSource;
   }
 }
 exports.RegExpFilter = RegExpFilter;
 
 RegExpFilter.prototype = extend(ActiveFilter, {
   /**
-   * @see ActiveFilter.domainSourceIsUpperCase
-   */
-  domainSourceIsUpperCase: true,
+   * @see ActiveFilter.domainSourceIsLowerCase
+   */
+  domainSourceIsLowerCase: true,
 
   /**
    * Number of filters contained, will always be 1 (required to
    * optimize Matcher).
    * @type {number}
    */
   length: 1,
 
   /**
    * @see ActiveFilter.domainSeparator
    */
   domainSeparator: "|",
 
   /**
    * Expression from which a regular expression should be generated -
    * for delayed creation of the regexp property
    * @type {string}
    */
   regexpSource: null,
   /**
    * Regular expression to be used when testing against this filter
    * @type {RegExp}
    */
   get regexp()
   {
-    // Despite this property being cached, the getter is called
-    // several times on Safari, due to WebKit bug 132872
-    let prop = Object.getOwnPropertyDescriptor(this, "regexp");
-    if (prop)
-      return prop.value;
-
     let source = Filter.toRegExp(this.regexpSource);
     let regexp = new RegExp(source, this.matchCase ? "" : "i");
     Object.defineProperty(this, "regexp", {value: regexp});
+    this.regexpSource = null;
     return regexp;
   },
   /**
    * Content types the filter applies to, combination of values from
    * RegExpFilter.typeMap
    * @type {number}
    */
   contentType: 0x7FFFFFFF,
   /**
    * Defines whether the filter should distinguish between lower and
    * upper case letters
    * @type {boolean}
    */
   matchCase: false,
   /**
    * Defines whether the filter should apply to third-party or
    * first-party content only. Can be null (apply to all content).
-   * @type {boolean}
+   * @type {?boolean}
    */
   thirdParty: null,
 
   /**
    * String that the sitekey property should be generated from
-   * @type {string}
+   * @type {?string}
    */
   sitekeySource: null,
 
   /**
-   * Array containing public keys of websites that this filter should apply to
-   * @type {string[]}
+   * @see ActiveFilter.sitekeys
    */
   get sitekeys()
   {
-    // Despite this property being cached, the getter is called
-    // several times on Safari, due to WebKit bug 132872
-    let prop = Object.getOwnPropertyDescriptor(this, "sitekeys");
-    if (prop)
-      return prop.value;
-
     let sitekeys = null;
 
     if (this.sitekeySource)
     {
       sitekeys = this.sitekeySource.split("|");
       this.sitekeySource = null;
     }
 
     Object.defineProperty(
       this, "sitekeys", {value: sitekeys, enumerable: true}
     );
     return this.sitekeys;
   },
 
   /**
    * Tests whether the URL matches this filter
    * @param {string} location URL to be tested
    * @param {number} typeMask bitmask of content / request types to match
-   * @param {string} docDomain domain name of the document that loads the URL
-   * @param {boolean} thirdParty should be true if the URL is a third-party
-   *                             request
-   * @param {string} sitekey public key provided by the document
+   * @param {string} [docDomain] domain name of the document that loads the URL
+   * @param {boolean} [thirdParty] should be true if the URL is a third-party
+   *                               request
+   * @param {string} [sitekey] public key provided by the document
    * @return {boolean} true in case of a match
    */
   matches(location, typeMask, docDomain, thirdParty, sitekey)
   {
     if (this.contentType & typeMask &&
         (this.thirdParty == null || this.thirdParty == thirdParty) &&
         this.isActiveOnDomain(docDomain, sitekey) && this.regexp.test(location))
     {
       return true;
     }
     return false;
   }
 });
 
 // Required to optimize Matcher, see also RegExpFilter.prototype.length
 Object.defineProperty(RegExpFilter.prototype, "0", {
   get() { return this; }
 });
 
 /**
  * Creates a RegExp filter from its text representation
  * @param {string} text   same as in Filter()
  * @return {Filter}
  */
 RegExpFilter.fromText = function(text)
 {
   let blocking = true;
   let origText = text;
-  if (text.indexOf("@@") == 0)
+  if (text[0] == "@" && text[1] == "@")
   {
     blocking = false;
     text = text.substr(2);
   }
 
   let contentType = null;
   let matchCase = null;
   let domains = null;
   let sitekeys = null;
   let thirdParty = null;
   let collapse = null;
   let csp = null;
-  let snippets = null;
+  let rewrite = null;
   let options;
-  let match = (text.indexOf("$") >= 0 ? Filter.optionsRegExp.exec(text) : null);
+  let match = text.includes("$") ? Filter.optionsRegExp.exec(text) : null;
   if (match)
   {
     options = match[1].split(",");
     text = match.input.substr(0, match.index);
     for (let option of options)
     {
       let value = null;
       let separatorIndex = option.indexOf("=");
       if (separatorIndex >= 0)
       {
         value = option.substr(separatorIndex + 1);
         option = option.substr(0, separatorIndex);
       }
-      option = option.replace(/-/, "_").toUpperCase();
-      if (option in RegExpFilter.typeMap)
+
+      let inverse = option[0] == "~";
+      if (inverse)
+        option = option.substr(1);
+
+      let type = RegExpFilter.typeMap[option.replace(/-/, "_").toUpperCase()];
+      if (type)
       {
-        if (contentType == null)
-          contentType = 0;
-        contentType |= RegExpFilter.typeMap[option];
-
-        if (option == "CSP" && typeof value != "undefined")
-          csp = value;
-        else if (option == "SNIPPET" && value)
-          snippets = value.split("|");
+        if (inverse)
+        {
+          if (contentType == null)
+            ({contentType} = RegExpFilter.prototype);
+          contentType &= ~type;
+        }
+        else
+        {
+          contentType |= type;
+
+          if (type == RegExpFilter.typeMap.CSP && value)
+            csp = value;
+        }
       }
-      else if (option[0] == "~" && option.substr(1) in RegExpFilter.typeMap)
+      else
       {
-        if (contentType == null)
-          ({contentType} = RegExpFilter.prototype);
-        contentType &= ~RegExpFilter.typeMap[option.substr(1)];
+        switch (option.toLowerCase())
+        {
+          case "match-case":
+            matchCase = !inverse;
+            break;
+          case "domain":
+            if (!value)
+              return new InvalidFilter(origText, "filter_unknown_option");
+            domains = value.toLowerCase();
+            break;
+          case "third-party":
+            thirdParty = !inverse;
+            break;
+          case "collapse":
+            collapse = !inverse;
+            break;
+          case "sitekey":
+            if (!value)
+              return new InvalidFilter(origText, "filter_unknown_option");
+            sitekeys = value.toUpperCase();
+            break;
+          case "rewrite":
+            if (!value)
+              return new InvalidFilter(origText, "filter_unknown_option");
+            rewrite = value;
+            break;
+          default:
+            return new InvalidFilter(origText, "filter_unknown_option");
+        }
       }
-      else if (option == "MATCH_CASE")
-        matchCase = true;
-      else if (option == "~MATCH_CASE")
-        matchCase = false;
-      else if (option == "DOMAIN" && typeof value != "undefined")
-        domains = value.toUpperCase();
-      else if (option == "THIRD_PARTY")
-        thirdParty = true;
-      else if (option == "~THIRD_PARTY")
-        thirdParty = false;
-      else if (option == "COLLAPSE")
-        collapse = true;
-      else if (option == "~COLLAPSE")
-        collapse = false;
-      else if (option == "SITEKEY" && typeof value != "undefined")
-        sitekeys = value.toUpperCase();
-      else
-        return new InvalidFilter(origText, "filter_unknown_option");
-    }
+    }
+  }
+
+  // For security reasons, never match $rewrite filters
+  // against requests that might load any code to be executed.
+  if (rewrite != null)
+  {
+    if (contentType == null)
+      ({contentType} = RegExpFilter.prototype);
+    contentType &= ~(RegExpFilter.typeMap.SCRIPT |
+                     RegExpFilter.typeMap.SUBDOCUMENT |
+                     RegExpFilter.typeMap.OBJECT |
+                     RegExpFilter.typeMap.OBJECT_SUBREQUEST);
   }
 
   try
   {
     if (blocking)
     {
       if (csp && Filter.invalidCSPRegExp.test(csp))
         return new InvalidFilter(origText, "filter_invalid_csp");
 
       return new BlockingFilter(origText, text, contentType, matchCase, domains,
-                                thirdParty, sitekeys, collapse, csp, snippets);
+                                thirdParty, sitekeys, collapse, csp, rewrite);
     }
     return new WhitelistFilter(origText, text, contentType, matchCase, domains,
                                thirdParty, sitekeys);
   }
   catch (e)
   {
     return new InvalidFilter(origText, "filter_invalid_regexp");
   }
 };
 
 /**
  * Maps type strings like "SCRIPT" or "OBJECT" to bit masks
  */
 RegExpFilter.typeMap = {
   OTHER: 1,
   SCRIPT: 2,
   IMAGE: 4,
   STYLESHEET: 8,
   OBJECT: 16,
   SUBDOCUMENT: 32,
   DOCUMENT: 64,
   WEBSOCKET: 128,
   WEBRTC: 256,
   CSP: 512,
   XBL: 1,
   PING: 1024,
   XMLHTTPREQUEST: 2048,
   OBJECT_SUBREQUEST: 4096,
-  SNIPPET: 8192,
   DTD: 1,
   MEDIA: 16384,
   FONT: 32768,
 
   BACKGROUND: 4,    // Backwards compat, same as IMAGE
 
   POPUP: 0x10000000,
   GENERICBLOCK: 0x20000000,
   ELEMHIDE: 0x40000000,
   GENERICHIDE: 0x80000000
 };
 
-// CSP, SNIPPET, DOCUMENT, ELEMHIDE, POPUP, GENERICHIDE and GENERICBLOCK options
+// CSP, DOCUMENT, ELEMHIDE, POPUP, GENERICHIDE and GENERICBLOCK options
 // shouldn't be there by default
 RegExpFilter.prototype.contentType &= ~(RegExpFilter.typeMap.CSP |
-                                        RegExpFilter.typeMap.SNIPPET |
                                         RegExpFilter.typeMap.DOCUMENT |
                                         RegExpFilter.typeMap.ELEMHIDE |
                                         RegExpFilter.typeMap.POPUP |
                                         RegExpFilter.typeMap.GENERICHIDE |
                                         RegExpFilter.typeMap.GENERICBLOCK);
 
 /**
  * Class for blocking filters
- * @param {string} text see Filter()
- * @param {string} regexpSource see RegExpFilter()
- * @param {number} contentType see RegExpFilter()
- * @param {boolean} matchCase see RegExpFilter()
- * @param {string} domains see RegExpFilter()
- * @param {boolean} thirdParty see RegExpFilter()
- * @param {string} sitekeys see RegExpFilter()
- * @param {boolean} collapse
+ * @param {string} text see {@link Filter Filter()}
+ * @param {string} regexpSource see {@link RegExpFilter RegExpFilter()}
+ * @param {number} [contentType] see {@link RegExpFilter RegExpFilter()}
+ * @param {boolean} [matchCase] see {@link RegExpFilter RegExpFilter()}
+ * @param {string} [domains] see {@link RegExpFilter RegExpFilter()}
+ * @param {boolean} [thirdParty] see {@link RegExpFilter RegExpFilter()}
+ * @param {string} [sitekeys] see {@link RegExpFilter RegExpFilter()}
+ * @param {boolean} [collapse]
  *   defines whether the filter should collapse blocked content, can be null
  * @param {string} [csp]
  *   Content Security Policy to inject when the filter matches
- * @param {string} [snippets]
- *   the code snippets to inject when the filter matches
+ * @param {?string} [rewrite]
+ *   The (optional) rule specifying how to rewrite the URL. See
+ *   BlockingFilter.prototype.rewrite.
  * @constructor
  * @augments RegExpFilter
  */
 function BlockingFilter(text, regexpSource, contentType, matchCase, domains,
-                        thirdParty, sitekeys, collapse, csp, snippets)
+                        thirdParty, sitekeys, collapse, csp, rewrite)
 {
   RegExpFilter.call(this, text, regexpSource, contentType, matchCase, domains,
                     thirdParty, sitekeys);
 
-  this.collapse = collapse;
-  this.csp = csp;
-  this.snippets = snippets;
+  if (collapse != null)
+    this.collapse = collapse;
+
+  if (csp != null)
+    this.csp = csp;
+
+  if (rewrite != null)
+    this.rewrite = rewrite;
 }
 exports.BlockingFilter = BlockingFilter;
 
 BlockingFilter.prototype = extend(RegExpFilter, {
   type: "blocking",
 
   /**
    * Defines whether the filter should collapse blocked content.
    * Can be null (use the global preference).
-   * @type {boolean}
+   * @type {?boolean}
    */
   collapse: null,
 
   /**
    * Content Security Policy to inject for matching requests.
-   * @type {string}
+   * @type {?string}
    */
   csp: null,
 
   /**
-   * The code snippets to inject for matching requests.
-   * @type {string[]}
-   */
-  snippets: null
+   * The rule specifying how to rewrite the URL.
+   * The syntax is similar to the one of String.prototype.replace().
+   * @type {?string}
+   */
+  rewrite: null,
+
+  /**
+   * Rewrites an URL.
+   * @param {string} url the URL to rewrite
+   * @return {string} the rewritten URL, or the original in case of failure
+   */
+  rewriteUrl(url)
+  {
+    try
+    {
+      let rewrittenUrl = new URL(url.replace(this.regexp, this.rewrite), url);
+      if (rewrittenUrl.origin == new URL(url).origin)
+        return rewrittenUrl.href;
+    }
+    catch (e)
+    {
+    }
+
+    return url;
+  }
 });
 
 /**
  * Class for whitelist filters
- * @param {string} text see Filter()
- * @param {string} regexpSource see RegExpFilter()
- * @param {number} contentType see RegExpFilter()
- * @param {boolean} matchCase see RegExpFilter()
- * @param {string} domains see RegExpFilter()
- * @param {boolean} thirdParty see RegExpFilter()
- * @param {string} sitekeys see RegExpFilter()
+ * @param {string} text see {@link Filter Filter()}
+ * @param {string} regexpSource see {@link RegExpFilter RegExpFilter()}
+ * @param {number} [contentType] see {@link RegExpFilter RegExpFilter()}
+ * @param {boolean} [matchCase] see {@link RegExpFilter RegExpFilter()}
+ * @param {string} [domains] see {@link RegExpFilter RegExpFilter()}
+ * @param {boolean} [thirdParty] see {@link RegExpFilter RegExpFilter()}
+ * @param {string} [sitekeys] see {@link RegExpFilter RegExpFilter()}
  * @constructor
  * @augments RegExpFilter
  */
 function WhitelistFilter(text, regexpSource, contentType, matchCase, domains,
                          thirdParty, sitekeys)
 {
   RegExpFilter.call(this, text, regexpSource, contentType, matchCase, domains,
                     thirdParty, sitekeys);
 }
 exports.WhitelistFilter = WhitelistFilter;
 
 WhitelistFilter.prototype = extend(RegExpFilter, {
   type: "whitelist"
 });
 
 /**
- * Base class for element hiding filters
- * @param {string} text see Filter()
+ * Base class for content filters
+ * @param {string} text see {@link Filter Filter()}
  * @param {string} [domains] Host names or domains the filter should be
  *                           restricted to
- * @param {string} selector   CSS selector for the HTML elements that should be
- *                            hidden
+ * @param {string} body      The body of the filter
  * @constructor
  * @augments ActiveFilter
  */
+function ContentFilter(text, domains, body)
+{
+  ActiveFilter.call(this, text, domains || null);
+
+  this.body = body;
+}
+exports.ContentFilter = ContentFilter;
+
+ContentFilter.prototype = extend(ActiveFilter, {
+  /**
+   * @see ActiveFilter.domainSeparator
+   */
+  domainSeparator: ",",
+
+  /**
+   * The body of the filter
+   * @type {string}
+   */
+  body: null
+});
+
+/**
+ * Creates a content filter from a pre-parsed text representation
+ *
+ * @param {string} text         same as in Filter()
+ * @param {string} [domains]
+ *   domains part of the text representation
+ * @param {string} [type]
+ *   rule type, either:
+ *     <li>"" for an element hiding filter</li>

[Manish Jethani, 2018/07/11 13:04:26]

Using just "-" doesn't work in the HTML version, but we can use <li> instead.

We should really switch to Markdown in the comments.

[kzar, 2018/07/11 17:17:52]

Acknowledged.

+ *     <li>"@" for an element hiding exception filter</li>
+ *     <li>"?" for an element hiding emulation filter</li>
+ *     <li>"$" for a snippet filter</li>
+ * @param {string} body
+ *   body part of the text representation, either a CSS selector or a snippet
+ *   script
+ * @return {ElemHideFilter|ElemHideException|
+ *          ElemHideEmulationFilter|SnippetFilter|InvalidFilter}
+ */
+ContentFilter.fromText = function(text, domains, type, body)
+{
+  // We don't allow content filters which have any empty domains.
+  // Note: The ContentFilter.prototype.domainSeparator is duplicated here, if
+  // that changes this must be changed too.
+  if (domains && /(^|,)~?(,|$)/.test(domains))
+    return new InvalidFilter(text, "filter_invalid_domain");
+
+  if (type == "@")
+    return new ElemHideException(text, domains, body);
+
+  if (type == "$")
+    return new SnippetFilter(text, domains, body);
+
+  if (type == "?")
+  {
+    // Element hiding emulation filters are inefficient so we need to make sure
+    // that they're only applied if they specify active domains
+    if (!/,[^~][^,.]*\.[^,]/.test("," + domains))
+      return new InvalidFilter(text, "filter_elemhideemulation_nodomain");
+
+    return new ElemHideEmulationFilter(text, domains, body);
+  }
+
+  return new ElemHideFilter(text, domains, body);
+};
+
+/**
+ * Base class for element hiding filters
+ * @param {string} text see {@link Filter Filter()}
+ * @param {string} [domains] see {@link ContentFilter ContentFilter()}
+ * @param {string} selector  CSS selector for the HTML elements that should be
+ *                           hidden
+ * @constructor
+ * @augments ContentFilter
+ */
 function ElemHideBase(text, domains, selector)
 {
-  ActiveFilter.call(this, text, domains || null);
-
-  if (domains)
-  {
-    this.selectorDomain = domains.replace(/,~[^,]+/g, "")
-                                 .replace(/^~[^,]+,?/, "").toLowerCase();
-  }
-
-  // Braces are being escaped to prevent CSS rule injection.
-  this.selector = selector.replace("{", "\\7B ").replace("}", "\\7D ");
+  ContentFilter.call(this, text, domains, selector);
 }
 exports.ElemHideBase = ElemHideBase;
 
-ElemHideBase.prototype = extend(ActiveFilter, {
-  /**
-   * @see ActiveFilter.domainSeparator
-   */
-  domainSeparator: ",",
-
-  /**
-   * @see ActiveFilter.ignoreTrailingDot
-   */
-  ignoreTrailingDot: false,
-
-  /**
-   * Host name or domain the filter should be restricted to (can be null for
-   * no restriction)
-   * @type {string}
-   */
-  selectorDomain: null,
+ElemHideBase.prototype = extend(ContentFilter, {
   /**
    * CSS selector for the HTML elements that should be hidden
    * @type {string}
    */
-  selector: null
-});
-
-/**
- * Creates an element hiding filter from a pre-parsed text representation
- *
- * @param {string} text         same as in Filter()
- * @param {string?} domain
- *   domain part of the text representation
- * @param {string?} type
-*    rule type, either empty or @ (exception) or ? (emulation rule)
- * @param {string} selector     raw CSS selector
- * @return {ElemHideFilter|ElemHideException|
- *          ElemHideEmulationFilter|InvalidFilter}
- */
-ElemHideBase.fromText = function(text, domain, type, selector)
-{
-  // We don't allow ElemHide filters which have any empty domains.
-  // Note: The ElemHide.prototype.domainSeparator is duplicated here, if that
-  // changes this must be changed too.
-  if (domain && /(^|,)~?(,|$)/.test(domain))
-    return new InvalidFilter(text, "filter_invalid_domain");
-
-  if (type == "@")
-    return new ElemHideException(text, domain, selector);
-
-  if (type == "?")
-  {
-    // Element hiding emulation filters are inefficient so we need to make sure
-    // that they're only applied if they specify active domains
-    if (!/,[^~][^,.]*\.[^,]/.test("," + domain))
-      return new InvalidFilter(text, "filter_elemhideemulation_nodomain");
-
-    return new ElemHideEmulationFilter(text, domain, selector);
-  }
-
-  return new ElemHideFilter(text, domain, selector);
-};
+  get selector()
+  {
+    // Braces are being escaped to prevent CSS rule injection.
+    return this.body.replace("{", "\\7B ").replace("}", "\\7D ");
+  }
+});
 
 /**
  * Class for element hiding filters
- * @param {string} text see Filter()
- * @param {string} domains  see ElemHideBase()
- * @param {string} selector see ElemHideBase()
+ * @param {string} text see {@link Filter Filter()}
+ * @param {string} [domains]  see {@link ElemHideBase ElemHideBase()}
+ * @param {string} selector see {@link ElemHideBase ElemHideBase()}
  * @constructor
  * @augments ElemHideBase
  */
 function ElemHideFilter(text, domains, selector)
 {
   ElemHideBase.call(this, text, domains, selector);
 }
 exports.ElemHideFilter = ElemHideFilter;
 
 ElemHideFilter.prototype = extend(ElemHideBase, {
   type: "elemhide"
 });
 
 /**
  * Class for element hiding exceptions
- * @param {string} text see Filter()
- * @param {string} domains  see ElemHideBase()
- * @param {string} selector see ElemHideBase()
+ * @param {string} text see {@link Filter Filter()}
+ * @param {string} [domains]  see {@link ElemHideBase ElemHideBase()}
+ * @param {string} selector see {@link ElemHideBase ElemHideBase()}
  * @constructor
  * @augments ElemHideBase
  */
 function ElemHideException(text, domains, selector)
 {
   ElemHideBase.call(this, text, domains, selector);
 }
 exports.ElemHideException = ElemHideException;
 
 ElemHideException.prototype = extend(ElemHideBase, {
   type: "elemhideexception"
 });
 
 /**
  * Class for element hiding emulation filters
- * @param {string} text           see Filter()
- * @param {string} domains        see ElemHideBase()
- * @param {string} selector       see ElemHideBase()
+ * @param {string} text           see {@link Filter Filter()}
+ * @param {string} domains        see {@link ElemHideBase ElemHideBase()}
+ * @param {string} selector       see {@link ElemHideBase ElemHideBase()}
  * @constructor
  * @augments ElemHideBase
  */
 function ElemHideEmulationFilter(text, domains, selector)
 {
   ElemHideBase.call(this, text, domains, selector);
 }
 exports.ElemHideEmulationFilter = ElemHideEmulationFilter;
 
 ElemHideEmulationFilter.prototype = extend(ElemHideBase, {
   type: "elemhideemulation"
 });
+
+/**
+ * Class for snippet filters
+ * @param {string} text see Filter()
+ * @param {string} [domains] see ContentFilter()
+ * @param {string} script    Script that should be executed
+ * @constructor
+ * @augments ContentFilter
+ */
+function SnippetFilter(text, domains, script)
+{
+  ContentFilter.call(this, text, domains, script);
+}
+exports.SnippetFilter = SnippetFilter;
+
+SnippetFilter.prototype = extend(ContentFilter, {
+  type: "snippet",
+
+  /**
+   * Script that should be executed
+   * @type {string}
+   */
+  get script()
+  {
+    return this.body;
+  }
+});