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.lang3.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 3.0
031 * @version $Id: OctalUnescaper.java 967237 2010-07-23 20:08:57Z mbenson $
032 */
033public class OctalUnescaper extends CharSequenceTranslator {
034
035    /**
036     * {@inheritDoc}
037     */
038    @Override
039    public int translate(final CharSequence input, final int index, final Writer out) throws IOException {
040        final int remaining = input.length() - index - 1; // how many characters left, ignoring the first \
041        final StringBuilder builder = new StringBuilder();
042        if(input.charAt(index) == '\\' && remaining > 0 && isOctalDigit(input.charAt(index + 1)) ) {
043            final int next = index + 1;
044            final int next2 = index + 2;
045            final int next3 = index + 3;
046
047            // we know this is good as we checked it in the if block above
048            builder.append(input.charAt(next));
049
050            if(remaining > 1 && isOctalDigit(input.charAt(next2))) {
051                builder.append(input.charAt(next2));
052                if(remaining > 2 && isZeroToThree(input.charAt(next)) && isOctalDigit(input.charAt(next3))) {
053                    builder.append(input.charAt(next3));
054                }
055            }
056
057            out.write( Integer.parseInt(builder.toString(), 8) );
058            return 1 + builder.length();
059        }
060        return 0;
061    }
062
063    /**
064     * Checks if the given char is an octal digit. Octal digits are the character representations of the digits 0 to 7.
065     * @param ch the char to check
066     * @return true if the given char is the character representation of one of the digits from 0 to 7
067     */
068    private boolean isOctalDigit(final char ch) {
069        return ch >= '0' && ch <= '7';
070    }
071
072    /**
073     * Checks if the given char is the character representation of one of the digit from 0 to 3.
074     * @param ch the char to check
075     * @return true if the given char is the character representation of one of the digits from 0 to 3
076     */
077    private boolean isZeroToThree(final char ch) {
078        return ch >= '0' && ch <= '3';
079    }
080}