rgoers/log4j2-core/src/main/java/org/apache/logging/log4j/core/helpers/Transform.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache license, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the license for the specific language governing permissions and
 * limitations under the license.
 */
package org.apache.logging.log4j.core.helpers;


/**
 * Utility class for transforming strings.
 */
public final class Transform {

    private static final String CDATA_START = "<![CDATA[";
    private static final String CDATA_END = "]]>";
    private static final String CDATA_PSEUDO_END = "]]&gt;";
    private static final String CDATA_EMBEDED_END = CDATA_END + CDATA_PSEUDO_END + CDATA_START;
    private static final int CDATA_END_LEN = CDATA_END.length();

    private Transform() {
    }

    /**
     * This method takes a string which may contain HTML tags (ie,
     * &lt;b&gt;, &lt;table&gt;, etc) and replaces any
     * '<',  '>' , '&' or '"'
     * characters with respective predefined entity references.
     *
     * @param input The text to be converted.
     * @return The input string with the special characters replaced.
     */
    public static String escapeTags(final String input) {
        //Check if the string is null, zero length or devoid of special characters
        // if so, return what was sent in.

        if (input == null
            || input.length() == 0
            || (input.indexOf('"') == -1 &&
            input.indexOf('&') == -1 &&
            input.indexOf('<') == -1 &&
            input.indexOf('>') == -1)) {
            return input;
        }

        //Use a StringBuffer in lieu of String concatenation -- it is
        //much more efficient this way.

        StringBuilder buf = new StringBuilder(input.length() + 6);
        char ch = ' ';

        int len = input.length();
        for (int i = 0; i < len; i++) {
            ch = input.charAt(i);
            if (ch > '>') {
                buf.append(ch);
            } else if (ch == '<') {
                buf.append("&lt;");
            } else if (ch == '>') {
                buf.append("&gt;");
            } else if (ch == '&') {
                buf.append("&amp;");
            } else if (ch == '"') {
                buf.append("&quot;");
            } else {
                buf.append(ch);
            }
        }
        return buf.toString();
    }

    /**
     * Ensures that embeded CDEnd strings (]]>) are handled properly
     * within message, NDC and throwable tag text.
     *
     * @param buf StringBuffer holding the XML data to this point.  The
     *            initial CDStart (<![CDATA[) and final CDEnd (]]>) of the CDATA
     *            section are the responsibility of the calling method.
     * @param str The String that is inserted into an existing CDATA Section within buf.
     */
    public static void appendEscapingCDATA(final StringBuilder buf, final String str) {
        if (str != null) {
            int end = str.indexOf(CDATA_END);
            if (end < 0) {
                buf.append(str);
            } else {
                int start = 0;
                while (end > -1) {
                    buf.append(str.substring(start, end));
                    buf.append(CDATA_EMBEDED_END);
                    start = end + CDATA_END_LEN;
                    if (start < str.length()) {
                        end = str.indexOf(CDATA_END, start);
                    } else {
                        return;
                    }
                }
                buf.append(str.substring(start));
            }
        }
    }
}