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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.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 1.0
31   */
32  public class OctalUnescaper extends CharSequenceTranslator {
33  
34      /**
35       * Tests if the given char is an octal digit. Octal digits are the character representations of the digits 0 to 7.
36       *
37       * @param ch the char to check
38       * @return true if the given char is the character representation of one of the digits from 0 to 7
39       */
40      private boolean isOctalDigit(final char ch) {
41          return ch >= '0' && ch <= '7';
42      }
43  
44      /**
45       * Tests if the given char is the character representation of one of the digit from 0 to 3.
46       *
47       * @param ch the char to check
48       * @return true if the given char is the character representation of one of the digits from 0 to 3
49       */
50      private boolean isZeroToThree(final char ch) {
51          return ch >= '0' && ch <= '3';
52      }
53  
54      /**
55       * {@inheritDoc}
56       */
57      @Override
58      public int translate(final CharSequence input, final int index, final Writer writer) throws IOException {
59          final int remaining = input.length() - index - 1; // how many characters left, ignoring the first \
60          final StringBuilder builder = new StringBuilder();
61          if (input.charAt(index) == '\\' && remaining > 0 && isOctalDigit(input.charAt(index + 1))) {
62              final int next = index + 1;
63              final int next2 = index + 2;
64              final int next3 = index + 3;
65  
66              // we know this is good as we checked it in the if block above
67              builder.append(input.charAt(next));
68  
69              if (remaining > 1 && isOctalDigit(input.charAt(next2))) {
70                  builder.append(input.charAt(next2));
71                  if (remaining > 2 && isZeroToThree(input.charAt(next)) && isOctalDigit(input.charAt(next3))) {
72                      builder.append(input.charAt(next3));
73                  }
74              }
75  
76              writer.write(Integer.parseInt(builder.toString(), 8));
77              return 1 + builder.length();
78          }
79          return 0;
80      }
81  }