Issue 6622 - Implement $rewrite filter option

lib/requestBlocker.js

Index: lib/requestBlocker.js
===================================================================
--- a/lib/requestBlocker.js
+++ b/lib/requestBlocker.js
@@ -184,27 +184,46 @@
     return;
 
   let type = resourceTypes.get(details.type) || "OTHER";
   let [docDomain, sitekey, specificOnly] = getDocumentInfo(page, frame,
                                                            originUrl);
   let [filter, thirdParty] = matchRequest(url, type, docDomain,
                                           sitekey, specificOnly);
 
+  let result;
+  let rewrittenUrl;
+
+  if (filter instanceof BlockingFilter)
+  {
+    if (filter.rewrite)
+    {
+      rewrittenUrl = filter.rewriteUrl(details.url);
+      // If no rewrite happened (error, different origin), we'll
+      // return undefined in order to avoid an "infinite" loop.
+      if (rewrittenUrl != details.url)
+        result = {redirectUrl: rewrittenUrl};
+    }
+    else
+      result = {cancel: true};
+  }
+
   getRelatedTabIds(details).then(tabIds =>
   {
     logRequest(
       tabIds,
-      {url: details.url, type, docDomain, thirdParty, sitekey, specificOnly},
+      {
+        url: details.url, type, docDomain, thirdParty,
+        sitekey, specificOnly, rewrittenUrl
+      },
       filter
     );
   });
 
-  if (filter instanceof BlockingFilter)
-    return {cancel: true};
+  return result;
 }, {urls: ["<all_urls>"]}, ["blocking"]);
 
 port.on("filters.collapse", (message, sender) =>
 {
   let {page, frame} = sender;
 
   if (checkWhitelisted(page, frame))
     return false;