Fix a URIError encountered in Chrome when interpreting an X-JSON header with extended characters.

Author: savetheclocktower

src/prototype/ajax/response.js

@@ -151,7 +151,23 @@ Ajax.Response = Class.create({
   _getHeaderJSON: function() {
     var json = this.getHeader('X-JSON');
     if (!json) return null;
-    json = decodeURIComponent(escape(json));
+
+    try {
+      // Browsers expect HTTP headers to be ASCII and nothing else. Running
+      // them through `decodeURIComponent` processes them with the page's
+      // specified encoding.
+      json = decodeURIComponent(escape(json));
+    } catch(e) {
+      // Except Chrome doesn't seem to need this, and calling
+      // `decodeURIComponent` on text that's already in the proper encoding
+      // will throw a `URIError`. The ugly solution is to assume that a
+      // `URIError` raised here signifies that the text is, in fact, already 
+      // in the correct encoding, and treat the failure as a good sign.
+      //
+      // This is ugly, but so too is sending extended characters in an HTTP
+      // header with no spec to back you up.
+    }
+    
     try {
       return json.evalJSON(this.request.options.sanitizeJSON ||
         !this.request.isSameOrigin());