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     * Creates a new instance.
036     */
037    public OctalUnescaper() {
038        // empty
039    }
040
041    /**
042     * Tests if the given char is an octal digit. Octal digits are the character representations of the digits 0 to 7.
043     *
044     * @param ch the char to check
045     * @return true if the given char is the character representation of one of the digits from 0 to 7
046     */
047    private boolean isOctalDigit(final char ch) {
048        return ch >= '0' && ch <= '7';
049    }
050
051    /**
052     * Tests if the given char is the character representation of one of the digit from 0 to 3.
053     *
054     * @param ch the char to check
055     * @return true if the given char is the character representation of one of the digits from 0 to 3
056     */
057    private boolean isZeroToThree(final char ch) {
058        return ch >= '0' && ch <= '3';
059    }
060
061    /**
062     * {@inheritDoc}
063     */
064    @Override
065    public int translate(final CharSequence input, final int index, final Writer writer) throws IOException {
066        final int remaining = input.length() - index - 1; // how many characters left, ignoring the first \
067        final StringBuilder builder = new StringBuilder();
068        if (input.charAt(index) == '\\' && remaining > 0 && isOctalDigit(input.charAt(index + 1))) {
069            final int next = index + 1;
070            final int next2 = index + 2;
071            final int next3 = index + 3;
072
073            // we know this is good as we checked it in the if block above
074            builder.append(input.charAt(next));
075
076            if (remaining > 1 && isOctalDigit(input.charAt(next2))) {
077                builder.append(input.charAt(next2));
078                if (remaining > 2 && isZeroToThree(input.charAt(next)) && isOctalDigit(input.charAt(next3))) {
079                    builder.append(input.charAt(next3));
080                }
081            }
082
083            writer.write(Integer.parseInt(builder.toString(), 8));
084            return 1 + builder.length();
085        }
086        return 0;
087    }
088}