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.

[kzar, 2018/05/15 14:30:29]

Nit: Mind removing this unrelated change?

[hub, 2018/05/15 16:31:26]

Done.

   yield "POPUP";
   yield "ELEMHIDE";
   yield "CSP";
 }());
 
 function getDocumentInfo(page, frame, originUrl)
 {
   return [
@@ -180,27 +180,46 @@
     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 rewrittenTo;

[kzar, 2018/05/15 14:30:29]

Nit: I think rewrittenUrl would be a nicer name.

[Manish Jethani, 2018/05/15 14:44:23]

I'll second that.

[Sebastian Noack, 2018/05/15 14:44:36]

Note that the varialbe name here is consistent with the property name expected
by the devtools panel (and therefore also simplifies the object creation below).
So if we change it we should also change the name of the property passed to the
devtools panel. (However, as far as I'm concerned either name would be fine.)

[hub, 2018/05/15 16:31:26]

I'll do that.

+
+  if (filter instanceof BlockingFilter)
+  {
+    if (filter.rewrite)
+    {
+      rewrittenTo = filter.rewriteUrl(details.url);
+      // If no rewrite happened (error, different origin), we'll
+      // return undefined in order to avoid an "infinite" loop.
+      if (rewrittenTo != details.url)
+        result = {redirectUrl: rewrittenTo};
+    }
+    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, rewrittenTo
+      },
       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;