Issue 6592 - Implement $rewrite filter option

lib/filterClasses.js

Index: lib/filterClasses.js
===================================================================
--- a/lib/filterClasses.js
+++ b/lib/filterClasses.js
@@ -765,16 +765,17 @@
 
   let contentType = null;
   let matchCase = null;
   let domains = null;
   let sitekeys = null;
   let thirdParty = null;
   let collapse = null;
   let csp = null;
+  let rewrite = null;
   let options;
   let match = (text.indexOf("$") >= 0 ? Filter.optionsRegExp.exec(text) : null);
   if (match)
   {
     options = match[1].split(",");
     text = match.input.substr(0, match.index);
     for (let option of options)
     {
@@ -812,30 +813,32 @@
       else if (option == "~THIRD_PARTY")
         thirdParty = false;
       else if (option == "COLLAPSE")
         collapse = true;
       else if (option == "~COLLAPSE")
         collapse = false;
       else if (option == "SITEKEY" && value)
         sitekeys = value.toUpperCase();
+      else if (option == "REWRITE" && value)
+        rewrite = value;
       else
         return new InvalidFilter(origText, "filter_unknown_option");
     }
   }
 
   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);
+                                thirdParty, sitekeys, collapse, csp, rewrite);
     }
     return new WhitelistFilter(origText, text, contentType, matchCase, domains,
                                thirdParty, sitekeys);
   }
   catch (e)
   {
     return new InvalidFilter(origText, "filter_invalid_regexp");
   }
@@ -888,27 +891,31 @@
  * @param {boolean} [matchCase] see RegExpFilter()
  * @param {string} [domains] see RegExpFilter()
  * @param {boolean} [thirdParty] see RegExpFilter()
  * @param {string} [sitekeys] see 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} [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)
+                        thirdParty, sitekeys, collapse, csp, rewrite)
 {
   RegExpFilter.call(this, text, regexpSource, contentType, matchCase, domains,
                     thirdParty, sitekeys);
 
   this.collapse = collapse;
   this.csp = csp;
+  this.rewrite = rewrite;
 }
 exports.BlockingFilter = BlockingFilter;
 
 BlockingFilter.prototype = extend(RegExpFilter, {
   type: "blocking",
 
   /**
    * Defines whether the filter should collapse blocked content.
@@ -916,17 +923,44 @@
    * @type {?boolean}
    */
   collapse: null,
 
   /**
    * Content Security Policy to inject for matching requests.
    * @type {?string}
    */
-  csp: null
+  csp: 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()