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 *      https://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
022import org.apache.commons.lang3.CharUtils;
023
024/**
025 * Translate escaped octal Strings back to their octal values.
026 *
027 * For example, "\45" should go back to being the specific value (a %).
028 *
029 * Note that this currently only supports the viable range of octal for Java; namely
030 * 1 to 377. This is because parsing Java is the main use case.
031 *
032 * @since 1.0
033 */
034public class OctalUnescaper extends CharSequenceTranslator {
035
036    /**
037     * Constructs a new instance.
038     */
039    public OctalUnescaper() {
040        // empty
041    }
042
043    /**
044     * Tests if the given char is the character representation of one of the digit from 0 to 3.
045     *
046     * @param ch The char to check.
047     * @return true if the given char is the character representation of one of the digits from 0 to 3.
048     */
049    private boolean isZeroToThree(final char ch) {
050        return ch >= '0' && ch <= '3';
051    }
052
053    /**
054     * {@inheritDoc}
055     */
056    @Override
057    public int translate(final CharSequence input, final int index, final Writer writer) throws IOException {
058        final int remaining = input.length() - index - 1; // how many characters left, ignoring the first \
059        final StringBuilder builder = new StringBuilder();
060        if (input.charAt(index) == '\\' && remaining > 0 && CharUtils.isOctal(input.charAt(index + 1))) {
061            final int next = index + 1;
062            final int next2 = index + 2;
063            final int next3 = index + 3;
064            // we know this is good as we checked it in the if block above
065            builder.append(input.charAt(next));
066            if (remaining > 1 && CharUtils.isOctal(input.charAt(next2))) {
067                builder.append(input.charAt(next2));
068                if (remaining > 2 && isZeroToThree(input.charAt(next)) && CharUtils.isOctal(input.charAt(next3))) {
069                    builder.append(input.charAt(next3));
070                }
071            }
072            writer.write(Integer.parseInt(builder.toString(), 8));
073            return 1 + builder.length();
074        }
075        return 0;
076    }
077}