add cmp_tree, in case caja log can't be trusted

(spoiler: it can't)

IPython/html/static/base/js/security.js

@@ -1,57 +1,83 b''
 //----------------------------------------------------------------------------
 //  Copyright (C) 2014  The IPython Development Team
 //
 //  Distributed under the terms of the BSD License.  The full license is in
 //  the file COPYING, distributed as part of this software.
 //----------------------------------------------------------------------------
 
 //============================================================================
 // Utilities
 //============================================================================
 IPython.namespace('IPython.security');
 
 IPython.security = (function (IPython) {
     "use strict";
 
     var utils = IPython.utils;
     
     var noop = function (x) { return x; };
     
+    var cmp_tree = function (a, b) {
+        // compare two HTML trees
+        // only checks the tag structure is preserved,
+        // not any attributes or contents
+        if (a.length !== b.length) {
+            return false;
+        }
+        
+        for (var i = a.length - 1; i >= 0; i--) {
+            if (a[i].tagName && b[i].tagName && a[i].tagName.toLowerCase() != b[i].tagName.toLowerCase()) {
+                return false;
+            }
+        }
+        var ac = a.children();
+        var bc = b.children();
+        if (ac.length === 0 && bc.length === 0) {
+            return true;
+        }
+        return cmp_tree(ac, bc);
+    };
+    
     var sanitize = function (html, log) {
         // sanitize HTML
         // returns a struct of
         // {
         //   src: original_html,
         //   sanitized: the_sanitized_html,
         //   safe: bool // false if the sanitizer made any changes
         // }
         var result = {
             src : html,
             safe : true
         };
         var record_messages = function (msg, opts) {
             console.log("HTML Sanitizer", msg, opts);
             result.safe = false;
         };
         result.sanitized = window.html_sanitize(html, noop, noop, record_messages);
+        // caja can strip whole elements without logging,
+        // so double-check that node structure didn't change
+        if (result.safe) {
+            result.safe = cmp_tree($(result.sanitized), $(result.src));
+        }
         return result;
     };
     
     var sanitize_html = function (html) {
         // shorthand for str-to-str conversion, dropping the struct
         return sanitize(html).sanitized;
     };
     
     var is_safe = function (html) {
         // just return bool for whether an HTML string is safe
         return sanitize(html).safe;
     };
     
     return {
         is_safe: is_safe,
         sanitize: sanitize,
         sanitize_html: sanitize_html
     };
 
 }(IPython));