    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     */
    017    package org.apache.logging.log4j.core.util;
    018
    019    import org.apache.logging.log4j.util.Strings;
    020
    021
    022    /**
    023     * Utility class for transforming strings.
    024     */
    025    public final class Transform {
    026
    027        private static final String CDATA_START = "<![CDATA[";
    028        private static final String CDATA_END = "]]>";
    029        private static final String CDATA_PSEUDO_END = "]]&gt;";
    030        private static final String CDATA_EMBEDED_END = CDATA_END + CDATA_PSEUDO_END + CDATA_START;
    031        private static final int CDATA_END_LEN = CDATA_END.length();
    032
    033        private Transform() {
    034        }
    035
    036        /**
    037         * This method takes a string which may contain HTML tags (ie,
    038         * &lt;b&gt;, &lt;table&gt;, etc) and replaces any
    039         * '&lt;',  '&gt;' , '&amp;' or '&quot;'
    040         * characters with respective predefined entity references.
    041         *
    042         * @param input The text to be converted.
    043         * @return The input string with the special characters replaced.
    044         */
    045        public static String escapeHtmlTags(final String input) {
    046            //Check if the string is null, zero length or devoid of special characters
    047            // if so, return what was sent in.
    048
    049            if (Strings.isEmpty(input)
    050                || (input.indexOf('"') == -1 &&
    051                input.indexOf('&') == -1 &&
    052                input.indexOf('<') == -1 &&
    053                input.indexOf('>') == -1)) {
    054                return input;
    055            }
    056
    057            //Use a StringBuilder in lieu of String concatenation -- it is
    058            //much more efficient this way.
    059
    060            final StringBuilder buf = new StringBuilder(input.length() + 6);
    061            char ch = ' ';
    062
    063            final int len = input.length();
    064            for (int i = 0; i < len; i++) {
    065                ch = input.charAt(i);
    066                if (ch > '>') {
    067                    buf.append(ch);
    068                } else if (ch == '<') {
    069                    buf.append("&lt;");
    070                } else if (ch == '>') {
    071                    buf.append("&gt;");
    072                } else if (ch == '&') {
    073                    buf.append("&amp;");
    074                } else if (ch == '"') {
    075                    buf.append("&quot;");
    076                } else {
    077                    buf.append(ch);
    078                }
    079            }
    080            return buf.toString();
    081        }
    082
    083        /**
    084         * Ensures that embedded CDEnd strings (]]&gt;) are handled properly
    085         * within message, NDC and throwable tag text.
    086         *
    087         * @param buf StringBuilder holding the XML data to this point.  The
    088         *            initial CDStart (&lt;![CDATA[) and final CDEnd (]]&gt;) of the CDATA
    089         *            section are the responsibility of the calling method.
    090         * @param str The String that is inserted into an existing CDATA Section within buf.
    091         */
    092        public static void appendEscapingCData(final StringBuilder buf, final String str) {
    093            if (str != null) {
    094                int end = str.indexOf(CDATA_END);
    095                if (end < 0) {
    096                    buf.append(str);
    097                } else {
    098                    int start = 0;
    099                    while (end > -1) {
    100                        buf.append(str.substring(start, end));
    101                        buf.append(CDATA_EMBEDED_END);
    102                        start = end + CDATA_END_LEN;
    103                        if (start < str.length()) {
    104                            end = str.indexOf(CDATA_END, start);
    105                        } else {
    106                            return;
    107                        }
    108                    }
    109                    buf.append(str.substring(start));
    110                }
    111            }
    112        }
    113
    114        /**
    115         * This method takes a string which may contain JSON reserved chars and
    116         * escapes them.
    117         *
    118         * @param input The text to be converted.
    119         * @return The input string with the special characters replaced.
    120         */
    121        public static String escapeJsonControlCharacters(final String input) {
    122            // Check if the string is null, zero length or devoid of special characters
    123            // if so, return what was sent in.
    124
    125            // TODO: escaped Unicode chars.
    126
    127            if (Strings.isEmpty(input)
    128                || (input.indexOf('"') == -1 &&
    129                input.indexOf('\\') == -1 &&
    130                input.indexOf('/') == -1 &&
    131                input.indexOf('\b') == -1 &&
    132                input.indexOf('\f') == -1 &&
    133                input.indexOf('\n') == -1 &&
    134                input.indexOf('\r') == -1 &&
    135                input.indexOf('\t') == -1)) {
    136                return input;
    137            }
    138
    139            final StringBuilder buf = new StringBuilder(input.length() + 6);
    140
    141            final int len = input.length();
    142            for (int i = 0; i < len; i++) {
    143                final char ch = input.charAt(i);
    144                final String escBs = "\\";
    145                switch (ch) {
    146                case '"':
    147                    buf.append(escBs);
    148                    buf.append(ch);
    149                    break;
    150                case '\\':
    151                    buf.append(escBs);
    152                    buf.append(ch);
    153                    break;
    154                case '/':
    155                    buf.append(escBs);
    156                    buf.append(ch);
    157                    break;
    158                case '\b':
    159                    buf.append(escBs);
    160                    buf.append('b');
    161                    break;
    162                case '\f':
    163                    buf.append(escBs);
    164                    buf.append('f');
    165                    break;
    166                case '\n':
    167                    buf.append(escBs);
    168                    buf.append('n');
    169                    break;
    170                case '\r':
    171                    buf.append(escBs);
    172                    buf.append('r');
    173                    break;
    174                case '\t':
    175                    buf.append(escBs);
    176                    buf.append('t');
    177                    break;
    178                default:
    179                    buf.append(ch);
    180                }
    181            }
    182            return buf.toString();
    183        }
    184    }