001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.text.translate;
018
019import java.io.IOException;
020import java.io.Writer;
021
022/**
023 * Translate escaped octal Strings back to their octal values.
024 *
025 * For example, "\45" should go back to being the specific value (a %).
026 *
027 * Note that this currently only supports the viable range of octal for Java; namely
028 * 1 to 377. This is because parsing Java is the main use case.
029 *
030 * @since 1.0
031 */
032public class OctalUnescaper extends CharSequenceTranslator {
033
034    /**
035     * Tests if the given char is an octal digit. Octal digits are the character representations of the digits 0 to 7.
036     *
037     * @param ch the char to check
038     * @return true if the given char is the character representation of one of the digits from 0 to 7
039     */
040    private boolean isOctalDigit(final char ch) {
041        return ch >= '0' && ch <= '7';
042    }
043
044    /**
045     * Tests if the given char is the character representation of one of the digit from 0 to 3.
046     *
047     * @param ch the char to check
048     * @return true if the given char is the character representation of one of the digits from 0 to 3
049     */
050    private boolean isZeroToThree(final char ch) {
051        return ch >= '0' && ch <= '3';
052    }
053
054    /**
055     * {@inheritDoc}
056     */
057    @Override
058    public int translate(final CharSequence input, final int index, final Writer writer) throws IOException {
059        final int remaining = input.length() - index - 1; // how many characters left, ignoring the first \
060        final StringBuilder builder = new StringBuilder();
061        if (input.charAt(index) == '\\' && remaining > 0 && isOctalDigit(input.charAt(index + 1))) {
062            final int next = index + 1;
063            final int next2 = index + 2;
064            final int next3 = index + 3;
065
066            // we know this is good as we checked it in the if block above
067            builder.append(input.charAt(next));
068
069            if (remaining > 1 && isOctalDigit(input.charAt(next2))) {
070                builder.append(input.charAt(next2));
071                if (remaining > 2 && isZeroToThree(input.charAt(next)) && isOctalDigit(input.charAt(next3))) {
072                    builder.append(input.charAt(next3));
073                }
074            }
075
076            writer.write(Integer.parseInt(builder.toString(), 8));
077            return 1 + builder.length();
078        }
079        return 0;
080    }
081}