StackGuard


1   /*
2    * Copyright 1999-2004 The Apache Software Foundation.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    *     http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  /*
17   * $Id: StackGuard.java,v 1.12 2004/02/16 20:41:29 minchau Exp $
18   */
19  package org.apache.xalan.transformer;
20  
21  import javax.xml.transform.TransformerException  ;
22  
23  import org.apache.xalan.res.XSLMessages;
24  import org.apache.xalan.templates.Constants;
25  import org.apache.xalan.templates.ElemTemplate;
26  import org.apache.xalan.templates.ElemTemplateElement;
27  import org.apache.xml.utils.ObjectStack;
28  
29  /**
30   * Class to guard against recursion getting too deep.
31   */
32  public class StackGuard
33  {
34  
35    /**
36     * Used for infinite loop check. If the value is -1, do not
37     * check for infinite loops. Anyone who wants to enable that
38     * check should change the value of this variable to be the
39     * level of recursion that they want to check. Be careful setting
40     * this variable, if the number is too low, it may report an
41     * infinite loop situation, when there is none.
42     * Post version 1.0.0, we'll make this a runtime feature.
43     */
44    public static int m_recursionLimit = -1;
45    
46    TransformerImpl m_transformer;
47  
48    /**
49     * Get the recursion limit.
50     * Used for infinite loop check. If the value is -1, do not
51     * check for infinite loops. Anyone who wants to enable that
52     * check should change the value of this variable to be the
53     * level of recursion that they want to check. Be careful setting
54     * this variable, if the number is too low, it may report an
55     * infinite loop situation, when there is none.
56     * Post version 1.0.0, we'll make this a runtime feature.
57     *
58     * @return The recursion limit.
59     */
60    public int getRecursionLimit()
61    {
62      return m_recursionLimit;
63    }
64  
65    /**
66     * Set the recursion limit.
67     * Used for infinite loop check. If the value is -1, do not
68     * check for infinite loops. Anyone who wants to enable that
69     * check should change the value of this variable to be the
70     * level of recursion that they want to check. Be careful setting
71     * this variable, if the number is too low, it may report an
72     * infinite loop situation, when there is none.
73     * Post version 1.0.0, we'll make this a runtime feature.
74     *
75     * @param limit The recursion limit.
76     */
77    public void setRecursionLimit(int limit)
78    {
79      m_recursionLimit = limit;
80    }
81  
82    /**
83     * Constructor StackGuard
84     *
85     *
86     * @param xslTemplate Current template node
87     * @param sourceXML Source Node
88     */
89    public StackGuard(TransformerImpl transformerImpl)
90    {
91      m_transformer = transformerImpl;
92    }
93  
94    /**
95     * Overide equal method for StackGuard objects 
96     *
97     *
98     * @param obj StackGuard object to compare
99     *
100    * @return True if the given object matches this StackGuard object
101    */
102   public int countLikeTemplates(ElemTemplate templ, int pos)
103   {
104     ObjectStack elems = m_transformer.getCurrentTemplateElements();
105     int count = 1;
106     for (int i = pos-1; i >= 0; i--)
107     {
108         if((ElemTemplateElement)elems.elementAt(i) == templ)
109             count++;
110     }
111     
112     return count;
113   }
114 
115   
116   /**
117    * Get the next named or match template down from and including 
118    * the given position.
119    * @param pos the current index position in the stack.
120    * @return null if no matched or named template found, otherwise 
121    * the next named or matched template at or below the position.
122    */
123   private ElemTemplate getNextMatchOrNamedTemplate(int pos)
124   {
125     ObjectStack elems = m_transformer.getCurrentTemplateElements();
126     for (int i = pos; i >= 0; i--)
127     {
128         ElemTemplateElement elem = (ElemTemplateElement) elems.elementAt(i);
129         if(null != elem)
130         {
131             if(elem.getXSLToken() == Constants.ELEMNAME_TEMPLATE)
132             {
133                 return (ElemTemplate)elem;
134             }
135         }
136     }
137     return null;
138   }
139 
140   /**
141    * Check if we are in an infinite loop
142    *
143    *
144    * @param guard Current StackGuard object (matching current template)  
145    *
146    * @throws TransformerException
147    */
148   public void checkForInfinateLoop() throws TransformerException  
149   {
150     int nTemplates = m_transformer.getCurrentTemplateElementsCount();
151     if(nTemplates < m_recursionLimit)
152         return;
153         
154     if(m_recursionLimit <= 0)
155         return;  // Safety check.
156         
157     // loop from the top index down to the recursion limit (I don't think 
158     // there's any need to go below that).
159     for (int i = (nTemplates - 1); i >= m_recursionLimit; i--)
160     {
161         ElemTemplate template = getNextMatchOrNamedTemplate(i);
162         
163         if(null == template)
164             break;
165             
166         int loopCount = countLikeTemplates(template, i);
167         
168         if (loopCount >= m_recursionLimit)
169         {
170             // throw new TransformerException("Template nesting too deep. nesting = "+loopCount+
171             //   ", template "+((null == template.getName()) ? "name = " : "match = ")+
172             //   ((null != template.getName()) ? template.getName().toString() 
173             //   : template.getMatch().getPatternString()));
174             
175             String   idIs = XSLMessages.createMessage(((null != template.getName()) ? "nameIs" : "matchPatternIs"), null);
176             Object  [] msgArgs = new Object  []{ new Integer  (loopCount), idIs, 
177                      ((null != template.getName()) ? template.getName().toString() 
178                : template.getMatch().getPatternString()) };
179             String   msg = XSLMessages.createMessage("recursionTooDeep", msgArgs);
180 
181             throw new TransformerException  (msg);
182         }
183     }
184   }
185 
186 }
187
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