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;

[Sebastian Noack, 2018/05/05 13:46:53]

Nit: Since these variables are no always assigned below, we might want to
initialize them here, to make the behavior more explicit, and for consistency
since we never return or pass along uninitialized variables anywhere.

[hub, 2018/05/07 20:13:04]

In both cases they are undefined which is totally fine. return result that is
undefined is what we want if there is nothing to rewrite and if we don't block.

+
+  if (filter instanceof BlockingFilter)
+  {
+    if (filter.rewrite)
+    {
+      rewritten = filter.rewriteUrl(urlString);
+      // if no rewrite happened (error, diff origin), we'll

[Sebastian Noack, 2018/05/05 13:46:53]

Nit: Capitalize first letter of comment (if it is a sentence).

[hub, 2018/05/07 20:13:04]

Done.

+      // return undefined avoid an "infinite" loop.

[Sebastian Noack, 2018/05/05 13:46:53]

Typo: ... in order to avoid ...

[hub, 2018/05/07 20:13:04]

Done.

+      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);

[Manish Jethani, 2018/05/05 00:54:12]

For what it's worth, I think we should do the logging part as a separate patch.
For now we can just log it as a regular blocked request.

[Sebastian Noack, 2018/05/05 13:46:53]

Without the logging changes, I consider the resulting behavior of the devtools
panel a regression. So I think we should perform those changes simultaneously.

[hub, 2018/05/07 20:13:04]

Without the UI patch, it will just be logged as a blocked request anyway.

   });
 
-  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;