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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    * 
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.lang3.text.translate;
18  
19  import java.io.IOException;
20  import java.io.Writer;
21  
22  /**
23   * Translate escaped octal Strings back to their octal values.
24   *
25   * For example, "\45" should go back to being the specific value (a %).
26   *
27   * Note that this currently only supports the viable range of octal for Java; namely 
28   * 1 to 377. This is because parsing Java is the main use case.
29   * 
30   * @since 3.0
31   */
32  public class OctalUnescaper extends CharSequenceTranslator {
33  
34      /**
35       * {@inheritDoc}
36       */
37      @Override
38      public int translate(final CharSequence input, final int index, final Writer out) throws IOException {
39          final int remaining = input.length() - index - 1; // how many characters left, ignoring the first \
40          final StringBuilder builder = new StringBuilder();
41          if(input.charAt(index) == '\\' && remaining > 0 && isOctalDigit(input.charAt(index + 1)) ) {
42              final int next = index + 1;
43              final int next2 = index + 2;
44              final int next3 = index + 3;
45  
46              // we know this is good as we checked it in the if block above
47              builder.append(input.charAt(next));
48  
49              if(remaining > 1 && isOctalDigit(input.charAt(next2))) {
50                  builder.append(input.charAt(next2));
51                  if(remaining > 2 && isZeroToThree(input.charAt(next)) && isOctalDigit(input.charAt(next3))) {
52                      builder.append(input.charAt(next3));
53                  }
54              }
55  
56              out.write( Integer.parseInt(builder.toString(), 8) );
57              return 1 + builder.length();
58          }
59          return 0;
60      }
61  
62      /**
63       * Checks if the given char is an octal digit. Octal digits are the character representations of the digits 0 to 7.
64       * @param ch the char to check
65       * @return true if the given char is the character representation of one of the digits from 0 to 7
66       */
67      private boolean isOctalDigit(final char ch) {
68          return ch >= '0' && ch <= '7';
69      }
70  
71      /**
72       * Checks if the given char is the character representation of one of the digit from 0 to 3.
73       * @param ch the char to check
74       * @return true if the given char is the character representation of one of the digits from 0 to 3
75       */
76      private boolean isZeroToThree(final char ch) {
77          return ch >= '0' && ch <= '3';
78      }
79  }