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