hyperobject
diff --git a/‎rewriter/README.md‎ b/‎rewriter/README.md‎
diff --git a/‎rewriter/rewriter.js‎
Lines changed: 16 additions & 3 deletions b/‎rewriter/rewriter.js‎
Lines changed: 16 additions & 3 deletions
@@ -5,11 +5,14 @@
 // Makes a copy of each file at filename.bak.
 //
 // Usage:
-//  (install node and npm)
 //  cd https-everywhere
-//  ./makecrx.sh
+//  ./makecrx.sh # to build default.rulesets
 //  cd rewriter
-//  js rewriter.js ~/path/to/my/webapp
+//  (install node and npm)
+//  npm install
+//  node rewriter.js ~/path/to/my/webapp
+//  cd ~/path/to/my/webapp
+//  git diff
 
 var path = require("path"),
     fs = require("fs"),
@@ -46,6 +49,15 @@ function processDir(dir) {
   }));
 }
 
+// Overwrite the default URI find_uri_expression with a modified one that
+// mitigates a catastrophic backtracking issue common in CSS.
+// The workaround was to insist that URLs start with http, since those are the
+// only ones we want to rewrite anyhow. Note that this may still go exponential
+// on certain inputs. http://www.regular-expressions.info/catastrophic.html
+// Example string that blows up URI.withinString:
+//  image:url(http://img.youtube.com/vi/x7f
+URI.find_uri_expression = /\b((?:http:(?:\/{1,3}|[a-z0-9%])|www\d{0,3}[.]|[a-z0-9.\-]+[.][a-z]{2,4}\/)(?:[^\s()<>]+)+(?:\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s`!()\[\]{};:'".,<>?«»“”‘’]))/ig;
+
 function processFile(filename) {
   var contents = fs.readFileSync(filename, {encoding: 'utf-8'});
   var rewrittenFile = URI.withinString(contents, function(url) {
@@ -74,6 +86,7 @@ function processFile(filename) {
 }
 
 function loadRuleSets() {
+  console.log("Loading rules...");
   var fileContents = fs.readFileSync(path.join(__dirname, '../pkg/crx/rules/default.rulesets'), {encoding: 'utf-8'});
   var xml = new DOMParser().parseFromString(fileContents, 'text/xml');
   ruleSets = new rules.RuleSets("fake user agent", lrucache.LRUCache, xml, {});