    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.configuration2.convert;
    018
    019import java.util.ArrayList;
    020import java.util.Collection;
    021import java.util.Collections;
    022import java.util.Iterator;
    023import java.util.List;
    024
    025import org.apache.commons.lang3.StringUtils;
    026
    027/**
    028 * <p>
    029 * A specialized implementation of {@code ListDelimiterHandler} which simulates the list delimiter handling as it was
    030 * used by {@code PropertiesConfiguration} in Commons Configuration 1.x.
    031 * </p>
    032 * <p>
    033 * This class mainly exists for compatibility reasons. It is intended to be used by applications which have to deal with
    034 * properties files created by an older version of this library.
    035 * </p>
    036 * <p>
    037 * In the 1.x series of Commons Configuration list handling was not fully consistent. The escaping of property values
    038 * was done in a different way if they contained a list delimiter or not. From version 2.0 on, escaping is more
    039 * stringent which might cause slightly different results when parsing properties files created by or for Configuration
    040 * 1.x. If you encounter such problems, you can switch to this {@code ListDelimiterHandler} implementation rather than
    041 * the default one. In other cases, this class should not be used!
    042 * </p>
    043 * <p>
    044 * Implementation note: An instance of this class can safely be shared between multiple {@code Configuration} instances.
    045 * </p>
    046 *
    047 * @since 2.0
    048 */
    049public class LegacyListDelimiterHandler extends AbstractListDelimiterHandler {
    050    /** Constant for the escaping character. */
    051    private static final String ESCAPE = "\\";
    052
    053    /** Constant for the escaped escaping character. */
    054    private static final String DOUBLE_ESC = ESCAPE + ESCAPE;
    055
    056    /** Constant for a duplicated sequence of escaping characters. */
    057    private static final String QUAD_ESC = DOUBLE_ESC + DOUBLE_ESC;
    058
    059    /** The list delimiter character. */
    060    private final char delimiter;
    061
    062    /**
    063     * Creates a new instance of {@code LegacyListDelimiterHandler} and sets the list delimiter character.
    064     *
    065     * @param listDelimiter the list delimiter character
    066     */
    067    public LegacyListDelimiterHandler(final char listDelimiter) {
    068        delimiter = listDelimiter;
    069    }
    070
    071    /**
    072     * Returns the list delimiter character.
    073     *
    074     * @return the list delimiter character
    075     */
    076    public char getDelimiter() {
    077        return delimiter;
    078    }
    079
    080    /**
    081     * {@inheritDoc} This implementation performs delimiter escaping for a single value (which is not part of a list).
    082     */
    083    @Override
    084    public Object escape(final Object value, final ValueTransformer transformer) {
    085        return escapeValue(value, false, transformer);
    086    }
    087
    088    /**
    089     * {@inheritDoc} This implementation performs a special encoding of backslashes at the end of a string so that they are
    090     * not interpreted as escape character for a following list delimiter.
    091     */
    092    @Override
    093    public Object escapeList(final List<?> values, final ValueTransformer transformer) {
    094        if (!values.isEmpty()) {
    095            final Iterator<?> it = values.iterator();
    096            String lastValue = escapeValue(it.next(), true, transformer);
    097            final StringBuilder buf = new StringBuilder(lastValue);
    098            while (it.hasNext()) {
    099                // if the last value ended with an escape character, it has
    100                // to be escaped itself; otherwise the list delimiter will
    101                // be escaped
    102                if (lastValue.endsWith(ESCAPE) && (countTrailingBS(lastValue) / 2) % 2 != 0) {
    103                    buf.append(ESCAPE).append(ESCAPE);
    104                }
    105                buf.append(getDelimiter());
    106                lastValue = escapeValue(it.next(), true, transformer);
    107                buf.append(lastValue);
    108            }
    109            return buf.toString();
    110        }
    111        return null;
    112    }
    113
    114    /**
    115     * {@inheritDoc} This implementation simulates the old splitting algorithm. The string is split at the delimiter
    116     * character if it is not escaped. If the delimiter character is not found, the input is returned unchanged.
    117     */
    118    @Override
    119    protected Collection<String> splitString(final String s, final boolean trim) {
    120        if (s.indexOf(getDelimiter()) < 0) {
    121            return Collections.singleton(s);
    122        }
    123
    124        final List<String> list = new ArrayList<>();
    125
    126        StringBuilder token = new StringBuilder();
    127        int begin = 0;
    128        boolean inEscape = false;
    129        final char esc = ESCAPE.charAt(0);
    130
    131        while (begin < s.length()) {
    132            final char c = s.charAt(begin);
    133            if (inEscape) {
    134                // last character was the escape marker
    135                // can current character be escaped?
    136                if (c != getDelimiter() && c != esc) {
    137                    // no, also add escape character
    138                    token.append(esc);
    139                }
    140                token.append(c);
    141                inEscape = false;
    142            } else if (c == getDelimiter()) {
    143                // found a list delimiter -> add token and
    144                // resetDefaultFileSystem buffer
    145                String t = token.toString();
    146                if (trim) {
    147                    t = t.trim();
    148                }
    149                list.add(t);
    150                token = new StringBuilder();
    151            } else if (c == esc) {
    152                // eventually escape next character
    153                inEscape = true;
    154            } else {
    155                token.append(c);
    156            }
    157
    158            begin++;
    159        }
    160
    161        // Trailing delimiter?
    162        if (inEscape) {
    163            token.append(esc);
    164        }
    165        // Add last token
    166        String t = token.toString();
    167        if (trim) {
    168            t = t.trim();
    169        }
    170        list.add(t);
    171
    172        return list;
    173    }
    174
    175    /**
    176     * {@inheritDoc} This is just a dummy implementation. It is never called.
    177     */
    178    @Override
    179    protected String escapeString(final String s) {
    180        return null;
    181    }
    182
    183    /**
    184     * Performs the escaping of backslashes in the specified properties value. Because a double backslash is used to escape
    185     * the escape character of a list delimiter, double backslashes also have to be escaped if the property is part of a
    186     * (single line) list. In addition, because the output is written into a properties file, each occurrence of a backslash
    187     * again has to be doubled. This method is called by {@code escapeValue()}.
    188     *
    189     * @param value the value to be escaped
    190     * @param inList a flag whether the value is part of a list
    191     * @return the value with escaped backslashes as string
    192     */
    193    protected String escapeBackslashs(final Object value, final boolean inList) {
    194        String strValue = String.valueOf(value);
    195
    196        if (inList && strValue.indexOf(DOUBLE_ESC) >= 0) {
    197            strValue = StringUtils.replace(strValue, DOUBLE_ESC, QUAD_ESC);
    198        }
    199
    200        return strValue;
    201    }
    202
    203    /**
    204     * Escapes the given property value. This method is called on saving the configuration for each property value. It
    205     * ensures a correct handling of backslash characters and also takes care that list delimiter characters in the value
    206     * are escaped.
    207     *
    208     * @param value the property value
    209     * @param inList a flag whether the value is part of a list
    210     * @param transformer the {@code ValueTransformer}
    211     * @return the escaped property value
    212     */
    213    protected String escapeValue(final Object value, final boolean inList, final ValueTransformer transformer) {
    214        String escapedValue = String.valueOf(transformer.transformValue(escapeBackslashs(value, inList)));
    215        if (getDelimiter() != 0) {
    216            escapedValue = StringUtils.replace(escapedValue, String.valueOf(getDelimiter()), ESCAPE + getDelimiter());
    217        }
    218        return escapedValue;
    219    }
    220
    221    /**
    222     * Returns the number of trailing backslashes. This is sometimes needed for the correct handling of escape characters.
    223     *
    224     * @param line the string to investigate
    225     * @return the number of trailing backslashes
    226     */
    227    private static int countTrailingBS(final String line) {
    228        int bsCount = 0;
    229        for (int idx = line.length() - 1; idx >= 0 && line.charAt(idx) == '\\'; idx--) {
    230            bsCount++;
    231        }
    232
    233        return bsCount;
    234    }
    235}