    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}