Iterative traversal of DOM.

There are some deep DOMs you can hit the maximum nesting level
limit in tokenizeDOM (we've experienced this even with maximum nesting
level of 300). Here is an iterative version of the same function with
simple queue/dequeue approach.

Signed-off-by: Maxim Krizhanovsky <darhazer@gmail.com>

NEWS

@@ -20,6 +20,9 @@ NEWS ( CHANGELOG and HISTORY )                                     HTMLPurifier
   when %CSS.Trusted is on.
 ! Add %Cache.SerializerPermissions option for custom serializer
   directory/file permissions
+- Switch to an iterative traversal of the DOM, which prevents us
+  from running out of stack space for deeply nested documents.
+  Thanks Maxim Krizhanovsky for contributing a patch.
 - Make removal of conditional IE comments ungreedy; thanks Bernd
   for reporting.
 - Escape CDATA before removing Internet Explorer comments.

library/HTMLPurifier/Lexer/DOMLex.php

@@ -72,23 +72,57 @@ class HTMLPurifier_Lexer_DOMLex extends HTMLPurifier_Lexer
     }
 
     /**
-     * Recursive function that tokenizes a node, putting it into an accumulator.
-     *
+     * Iterative function that tokenizes a node, putting it into an accumulator.
+     * To iterate is human, to recurse divine - L. Peter Deutsch
      * @param $node     DOMNode to be tokenized.
      * @param $tokens   Array-list of already tokenized tokens.
-     * @param $collect  Says whether or start and close are collected, set to
-     *                  false at first recursion because it's the implicit DIV
-     *                  tag you're dealing with.
      * @returns Tokens of node appended to previously passed tokens.
      */
-    protected function tokenizeDOM($node, &$tokens, $collect = false) {
+    protected function tokenizeDOM($node, &$tokens) {
 
+        $level = 0;
+        $nodes = array($level => array($node));
+        $closingNodes = array();
+        do {
+            while (!empty($nodes[$level])) {
+                $node = array_shift($nodes[$level]); // FIFO
+                $collect = $level > 0 ? true : false;
+                $needEndingTag = $this->createStartNode($node, $tokens, $collect);
+                if ($needEndingTag) {
+                    $closingNodes[$level][] = $node;
+                }
+                if ($node->childNodes && $node->childNodes->length) {
+                    $level++;
+                    $nodes[$level] = array();
+                    foreach ($node->childNodes as $childNode) {
+                        array_push($nodes[$level], $childNode);
+                    }
+                }
+            }
+            $level--;
+            if ($level && isset($closingNodes[$level])) {
+                while($node = array_pop($closingNodes[$level])) {
+                    $this->createEndNode($node, $tokens);
+                }
+            }
+        } while ($level > 0);
+    }
+
+    /**
+     * @param $node  DOMNode to be tokenized.
+     * @param $tokens   Array-list of already tokenized tokens.
+     * @param $collect  Says whether or start and close are collected, set to
+     *                    false at first recursion because it's the implicit DIV
+     *                    tag you're dealing with.
+     * @returns bool if the token needs an endtoken
+     */
+    protected function createStartNode($node, &$tokens, $collect) {
         // intercept non element nodes. WE MUST catch all of them,
         // but we're not getting the character reference nodes because
         // those should have been preprocessed
         if ($node->nodeType === XML_TEXT_NODE) {
             $tokens[] = $this->factory->createText($node->data);
-            return;
+            return false;
         } elseif ($node->nodeType === XML_CDATA_SECTION_NODE) {
             // undo libxml's special treatment of <script> and <style> tags
             $last = end($tokens);
@@ -106,48 +140,44 @@ class HTMLPurifier_Lexer_DOMLex extends HTMLPurifier_Lexer
                 }
             }
             $tokens[] = $this->factory->createText($this->parseData($data));
-            return;
+            return false;
         } elseif ($node->nodeType === XML_COMMENT_NODE) {
             // this is code is only invoked for comments in script/style in versions
             // of libxml pre-2.6.28 (regular comments, of course, are still
             // handled regularly)
             $tokens[] = $this->factory->createComment($node->data);
-            return;
+            return false;
         } elseif (
             // not-well tested: there may be other nodes we have to grab
             $node->nodeType !== XML_ELEMENT_NODE
         ) {
-            return;
+            return false;
         }
 
-        $attr = $node->hasAttributes() ?
-            $this->transformAttrToAssoc($node->attributes) :
-            array();
+        $attr = $node->hasAttributes() ? $this->transformAttrToAssoc($node->attributes) : array();
 
         // We still have to make sure that the element actually IS empty
         if (!$node->childNodes->length) {
             if ($collect) {
                 $tokens[] = $this->factory->createEmpty($node->tagName, $attr);
             }
+            return false;
         } else {
-            if ($collect) { // don't wrap on first iteration
+            if ($collect) {
                 $tokens[] = $this->factory->createStart(
                     $tag_name = $node->tagName, // somehow, it get's dropped
                     $attr
                 );
             }
-            foreach ($node->childNodes as $node) {
-                // remember, it's an accumulator. Otherwise, we'd have
-                // to use array_merge
-                $this->tokenizeDOM($node, $tokens, true);
-            }
-            if ($collect) {
-                $tokens[] = $this->factory->createEnd($tag_name);
-            }
+            return true;
         }
-
     }
 
+    protected function createEndNode($node, &$tokens) {
+        $tokens[] = $this->factory->createEnd($node->tagName);
+    }
+
+
     /**
      * Converts a DOMNamedNodeMap of DOMAttr objects into an assoc array.
      *