src/org/apache/xalan/transformer/StackGuard.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the  "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * $Id$
 */
package org.apache.xalan.transformer;

import javax.xml.transform.TransformerException;

import org.apache.xalan.res.XSLMessages;
import org.apache.xalan.templates.Constants;
import org.apache.xalan.templates.ElemTemplate;
import org.apache.xalan.templates.ElemTemplateElement;
import org.apache.xml.utils.ObjectStack;

/**
 * Class to guard against recursion getting too deep.
 */
public class StackGuard
{

  /**
   * Used for infinite loop check. If the value is -1, do not
   * check for infinite loops. Anyone who wants to enable that
   * check should change the value of this variable to be the
   * level of recursion that they want to check. Be careful setting
   * this variable, if the number is too low, it may report an
   * infinite loop situation, when there is none.
   * Post version 1.0.0, we'll make this a runtime feature.
   */
  private int m_recursionLimit = -1;
  
  TransformerImpl m_transformer;

  /**
   * Get the recursion limit.
   * Used for infinite loop check. If the value is -1, do not
   * check for infinite loops. Anyone who wants to enable that
   * check should change the value of this variable to be the
   * level of recursion that they want to check. Be careful setting
   * this variable, if the number is too low, it may report an
   * infinite loop situation, when there is none.
   * Post version 1.0.0, we'll make this a runtime feature.
   *
   * @return The recursion limit.
   */
  public int getRecursionLimit()
  {
    return m_recursionLimit;
  }

  /**
   * Set the recursion limit.
   * Used for infinite loop check. If the value is -1, do not
   * check for infinite loops. Anyone who wants to enable that
   * check should change the value of this variable to be the
   * level of recursion that they want to check. Be careful setting
   * this variable, if the number is too low, it may report an
   * infinite loop situation, when there is none.
   * Post version 1.0.0, we'll make this a runtime feature.
   *
   * @param limit The recursion limit.
   */
  public void setRecursionLimit(int limit)
  {
    m_recursionLimit = limit;
  }

  /**
   * Constructor StackGuard
   *
   */
  public StackGuard(TransformerImpl transformerImpl)
  {
    m_transformer = transformerImpl;
  }

  /**
   * Overide equal method for StackGuard objects 
   *
   */
  public int countLikeTemplates(ElemTemplate templ, int pos)
  {
  	ObjectStack elems = m_transformer.getCurrentTemplateElements();
  	int count = 1;
    for (int i = pos-1; i >= 0; i--)
    {
    	if((ElemTemplateElement)elems.elementAt(i) == templ)
    		count++;
    }
	
    return count;
  }

  
  /**
   * Get the next named or match template down from and including 
   * the given position.
   * @param pos the current index position in the stack.
   * @return null if no matched or named template found, otherwise 
   * the next named or matched template at or below the position.
   */
  private ElemTemplate getNextMatchOrNamedTemplate(int pos)
  {
  	ObjectStack elems = m_transformer.getCurrentTemplateElements();
    for (int i = pos; i >= 0; i--)
    {
    	ElemTemplateElement elem = (ElemTemplateElement) elems.elementAt(i);
    	if(null != elem)
    	{
	    	if(elem.getXSLToken() == Constants.ELEMNAME_TEMPLATE)
	    	{
	    		return (ElemTemplate)elem;
	    	}
    	}
    }
  	return null;
  }

  /**
   * Check if we are in an infinite loop
   *
   * @throws TransformerException
   */
  public void checkForInfinateLoop() throws TransformerException
  {
    int nTemplates = m_transformer.getCurrentTemplateElementsCount();
    if(nTemplates < m_recursionLimit)
    	return;
    	
    if(m_recursionLimit <= 0)
    	return;  // Safety check.
    	
    // loop from the top index down to the recursion limit (I don't think 
    // there's any need to go below that).
    for (int i = (nTemplates - 1); i >= m_recursionLimit; i--)
    {
    	ElemTemplate template = getNextMatchOrNamedTemplate(i);
    	
    	if(null == template)
    		break;
    		
    	int loopCount = countLikeTemplates(template, i);
    	
    	if (loopCount >= m_recursionLimit)
    	{
    		// throw new TransformerException("Template nesting too deep. nesting = "+loopCount+
    		//   ", template "+((null == template.getName()) ? "name = " : "match = ")+
    		//   ((null != template.getName()) ? template.getName().toString() 
    		//   : template.getMatch().getPatternString()));
    		
    		String idIs = XSLMessages.createMessage(((null != template.getName()) ? "nameIs" : "matchPatternIs"), null);
        	Object[] msgArgs = new Object[]{ new Integer(loopCount), idIs, 
                     ((null != template.getName()) ? template.getName().toString() 
    		   : template.getMatch().getPatternString()) };
        	String msg = XSLMessages.createMessage("recursionTooDeep", msgArgs);

    		throw new TransformerException(msg);
    	}
    }
  }

}