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 * https://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 * Creates a new instance.
36 */
37 public OctalUnescaper() {
38 // empty
39 }
40
41 /**
42 * Tests if the given char is an octal digit. Octal digits are the character representations of the digits 0 to 7.
43 *
44 * @param ch the char to check
45 * @return true if the given char is the character representation of one of the digits from 0 to 7
46 */
47 private boolean isOctalDigit(final char ch) {
48 return ch >= '0' && ch <= '7';
49 }
50
51 /**
52 * Tests if the given char is the character representation of one of the digit from 0 to 3.
53 *
54 * @param ch the char to check
55 * @return true if the given char is the character representation of one of the digits from 0 to 3
56 */
57 private boolean isZeroToThree(final char ch) {
58 return ch >= '0' && ch <= '3';
59 }
60
61 /**
62 * {@inheritDoc}
63 */
64 @Override
65 public int translate(final CharSequence input, final int index, final Writer writer) throws IOException {
66 final int remaining = input.length() - index - 1; // how many characters left, ignoring the first \
67 final StringBuilder builder = new StringBuilder();
68 if (input.charAt(index) == '\\' && remaining > 0 && isOctalDigit(input.charAt(index + 1))) {
69 final int next = index + 1;
70 final int next2 = index + 2;
71 final int next3 = index + 3;
72
73 // we know this is good as we checked it in the if block above
74 builder.append(input.charAt(next));
75
76 if (remaining > 1 && isOctalDigit(input.charAt(next2))) {
77 builder.append(input.charAt(next2));
78 if (remaining > 2 && isZeroToThree(input.charAt(next)) && isOctalDigit(input.charAt(next3))) {
79 builder.append(input.charAt(next3));
80 }
81 }
82
83 writer.write(Integer.parseInt(builder.toString(), 8));
84 return 1 + builder.length();
85 }
86 return 0;
87 }
88 }