Issue 7250 - Optimize third-party request check

lib/domain.js

Index: lib/domain.js
===================================================================
--- a/lib/domain.js
+++ b/lib/domain.js
@@ -15,16 +15,56 @@
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 "use strict";
 
 const publicSuffixes = require("../data/publicSuffixList.json");
 
 /**
+ * Map of public suffixes to their offsets.
+ * @type {Map.<string,number>}
+ */
+let publicSuffixMap = buildPublicSuffixMap();
+
+/**
+ * Builds a map of public suffixes to their offsets.
+ * @returns {Map.<string,number>}
+ */
+function buildPublicSuffixMap()
+{
+  let map = new Map();
+
+  for (let key in publicSuffixes)
+    map.set(key, publicSuffixes[key]);
+
+  return map;
+}
+
+/**
+ * Yields all suffixes for a domain. For example, given the domain
+ * <code>www.example.com</code>, this function yields
+ * <code>www.example.com</code>, <code>example.com</code>, and
+ * <code>com</code>, in that order.
+ *
+ * @param {string} domain The domain.
+ * @yields {string} The next suffix for the domain.
+ */
+function* suffixes(domain)
+{
+  while (domain != "")
+  {
+    yield domain;
+
+    let dotIndex = domain.indexOf(".");
+    domain = dotIndex == -1 ? "" : domain.substr(dotIndex + 1);
+  }
+}
+
+/**
  * Checks whether the given hostname is a domain.
  *
  * @param {string} hostname
  * @returns {boolean}
  */
 function isDomain(hostname)
 {
   // No hostname or IPv4 address, also considering hexadecimal octets.
@@ -39,48 +79,60 @@
 /**
  * Gets the base domain for the given hostname.
  *
  * @param {string} hostname
  * @returns {string}
  */
 function getDomain(hostname)
 {
-  let bits = hostname.split(".");
-  let cutoff = bits.length - 2;
+  let slices = [];
+  let cutoff = NaN;
 
-  for (let i = 0; i < bits.length; i++)
+  for (let suffix of suffixes(hostname))
   {
-    let offset = publicSuffixes[bits.slice(i).join(".")];
+    slices.push(suffix);
+
+    let offset = publicSuffixMap.get(suffix);
 
     if (typeof offset != "undefined")
     {
-      cutoff = i - offset;
+      cutoff = slices.length - 1 - offset;
       break;
     }
   }
 
+  if (isNaN(cutoff))
+    return slices.length > 2 ? slices[slices.length - 2] : hostname;
+
   if (cutoff <= 0)
     return hostname;
 
-  return bits.slice(cutoff).join(".");
+  return slices[cutoff];
 }
 
+exports.getDomain = getDomain;
+
 /**
  * Checks whether a request's origin is different from its document's origin.
  *
  * @param {URL} url The request URL.
  * @param {string} documentHostname The IDNA-encoded hostname of the document.
  *
  * @returns {boolean}
  */
 function isThirdParty(url, documentHostname)
 {
-  let requestHostname = url.hostname.replace(/\.+$/, "");
-  documentHostname = documentHostname.replace(/\.+$/, "");
+  let requestHostname = url.hostname;
+
+  if (requestHostname[requestHostname.length - 1] == ".")
+    requestHostname = requestHostname.replace(/\.+$/, "");
+
+  if (documentHostname[documentHostname.length - 1] == ".")
+    documentHostname = documentHostname.replace(/\.+$/, "");
 
   if (requestHostname == documentHostname)
     return false;
 
   if (!isDomain(requestHostname) || !isDomain(documentHostname))
     return true;
 
   return getDomain(requestHostname) != getDomain(documentHostname);