Issue 6622 - Implement $rewrite filter option

lib/requestBlocker.js

Index: lib/requestBlocker.js
===================================================================
--- a/lib/requestBlocker.js
+++ b/lib/requestBlocker.js
@@ -65,17 +65,17 @@
 
   for (let type in browser.webRequest.ResourceType)
     yield resourceTypes.get(browser.webRequest.ResourceType[type]) || "OTHER";
 
   // WEBRTC gets addressed through a workaround, even if the webRequest API is
   // lacking support to block this kind of a request.
   yield "WEBRTC";
 
-  // POPUP, CSP and ELEMHIDE filters aren't mapped to resource types.
+  // These filter types aren't mapped to resource types.
   yield "POPUP";
   yield "ELEMHIDE";
   yield "CSP";
 }());
 
 function getDocumentInfo(page, frame, originUrl)
 {
   return [
@@ -118,25 +118,25 @@
                                      // an origin (proto + host).
   else
     return Promise.resolve([]);
 
   return browser.tabs.query({url}).then(tabs => tabs.map(tab => tab.id));
 }
 
 function logRequest(tabIds, url, type, docDomain, thirdParty,
-                    sitekey, specificOnly, filter)
+                    sitekey, specificOnly, filter, rewrittenTo)
 {
   if (filter)
     FilterNotifier.emit("filter.hitCount", filter, 0, 0, tabIds);
 
   devtools.logRequest(
     tabIds, url, type, docDomain,
     thirdParty, sitekey,
-    specificOnly, filter
+    specificOnly, filter, rewrittenTo
   );
 }
 
 browser.webRequest.onBeforeRequest.addListener(details =>
 {
   // Never block top-level documents.
   if (details.type == "main_frame")
     return;
@@ -189,24 +189,40 @@
     return;
 
   let type = resourceTypes.get(details.type) || "OTHER";
   let [docDomain, sitekey, specificOnly] = getDocumentInfo(page, frame,
                                                            originUrl);
   let [filter, urlString, thirdParty] = matchRequest(url, type, docDomain,
                                                      sitekey, specificOnly);
 
+  let result;
+  let rewritten;
+
+  if (filter instanceof BlockingFilter)
+  {
+    if (filter.rewrite)
+    {
+      rewritten = filter.rewriteUrl(urlString);
+      // If no rewrite happened (error, diff origin), we'll
+      // return undefined in order to avoid an "infinite" loop.
+      if (rewritten != urlString)
+        result = {redirectUrl: rewritten};
+    }
+    else
+      result = {cancel: true};
+  }
+
   getRelatedTabIds(details).then(tabIds =>
   {
     logRequest(tabIds, urlString, type, docDomain,
-               thirdParty, sitekey, specificOnly, filter);
+               thirdParty, sitekey, specificOnly, filter, rewritten);
   });
 
-  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;