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The Apache Commons Codec package contains simple encoder and decoders for various formats such as Base64 and Hexadecimal. In addition to these widely used encoders and decoders, the codec package also maintains a collection of phonetic encoding utilities.
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/*   Copyright 2017, 2018 The Apache Software Foundation
 *
 *   Licensed 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.xmlbeans.impl.common;

import java.io.IOException;
import java.io.StringReader;
import java.lang.reflect.Method;
import java.util.concurrent.TimeUnit;

import javax.xml.XMLConstants;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParserFactory;

import org.apache.xmlbeans.XmlOptionsBean;
import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;

/**
 * Provides handy methods for working with SAX parsers and readers
 */
public final class SAXHelper {
    private static final XBLogger logger = XBLogFactory.getLogger(SAXHelper.class);
    private static long lastLog;

    private SAXHelper() {}

    /**
     * Creates a new SAX XMLReader, with sensible defaults
     */
    public static XMLReader newXMLReader(XmlOptionsBean options) throws SAXException, ParserConfigurationException {
        XMLReader xmlReader = saxFactory(options).newSAXParser().getXMLReader();
        xmlReader.setEntityResolver(IGNORING_ENTITY_RESOLVER);
        trySetSAXFeature(xmlReader, XMLConstants.FEATURE_SECURE_PROCESSING);
        trySetXercesSecurityManager(xmlReader, options);
        return xmlReader;
    }
    
    public static final EntityResolver IGNORING_ENTITY_RESOLVER = new EntityResolver() {
        @Override
        public InputSource resolveEntity(String publicId, String systemId)
                throws SAXException, IOException {
            return new InputSource(new StringReader(""));
        }
    };

    static SAXParserFactory saxFactory() {
        return saxFactory(new XmlOptionsBean());
    }

    static SAXParserFactory saxFactory(XmlOptionsBean options) {
        SAXParserFactory saxFactory = SAXParserFactory.newInstance();
        saxFactory.setValidating(false);
        saxFactory.setNamespaceAware(true);
        trySetSAXFeature(saxFactory, XMLConstants.FEATURE_SECURE_PROCESSING, true);
        trySetSAXFeature(saxFactory, XMLBeansConstants.FEATURE_LOAD_DTD_GRAMMAR, options.isLoadDTDGrammar());
        trySetSAXFeature(saxFactory, XMLBeansConstants.FEATURE_LOAD_EXTERNAL_DTD, options.isLoadExternalDTD());
        return saxFactory;
    }

    private static void trySetSAXFeature(SAXParserFactory spf, String feature, boolean flag) {
        try {
            spf.setFeature(feature, flag);
        } catch (Exception e) {
            logger.log(XBLogger.WARN, "SAX Feature unsupported", feature, e);
        } catch (AbstractMethodError ame) {
            logger.log(XBLogger.WARN, "Cannot set SAX feature because outdated XML parser in classpath", feature, ame);
        }
    }

    private static void trySetSAXFeature(XMLReader xmlReader, String feature) {
        try {
            xmlReader.setFeature(feature, true);
        } catch (Exception e) {
            logger.log(XBLogger.WARN, "SAX Feature unsupported", feature, e);
        } catch (AbstractMethodError ame) {
            logger.log(XBLogger.WARN, "Cannot set SAX feature because outdated XML parser in classpath", feature, ame);
        }
    }
    
    private static void trySetXercesSecurityManager(XMLReader xmlReader, XmlOptionsBean options) {
        // Try built-in JVM one first, standalone if not
        for (String securityManagerClassName : new String[] {
                //"com.sun.org.apache.xerces.internal.util.SecurityManager",
                "org.apache.xerces.util.SecurityManager"
        }) {
            try {
                Object mgr = Class.forName(securityManagerClassName).newInstance();
                Method setLimit = mgr.getClass().getMethod("setEntityExpansionLimit", Integer.TYPE);
                setLimit.invoke(mgr, options.getEntityExpansionLimit());
                xmlReader.setProperty(XMLBeansConstants.SECURITY_MANAGER, mgr);
                // Stop once one can be setup without error
                return;
            } catch (Throwable e) {     // NOSONAR - also catch things like NoClassDefError here
                // throttle the log somewhat as it can spam the log otherwise
                if(System.currentTimeMillis() > lastLog + TimeUnit.MINUTES.toMillis(5)) {
                    logger.log(XBLogger.WARN, "SAX Security Manager could not be setup [log suppressed for 5 minutes]", e);
                    lastLog = System.currentTimeMillis();
                }
            }
        }

        // separate old version of Xerces not found => use the builtin way of setting the property
        try {
            xmlReader.setProperty(XMLBeansConstants.ENTITY_EXPANSION_LIMIT, options.getEntityExpansionLimit());
        } catch (SAXException e) {     // NOSONAR - also catch things like NoClassDefError here
            // throttle the log somewhat as it can spam the log otherwise
            if(System.currentTimeMillis() > lastLog + TimeUnit.MINUTES.toMillis(5)) {
                logger.log(XBLogger.WARN, "SAX Security Manager could not be setup [log suppressed for 5 minutes]", e);
                lastLog = System.currentTimeMillis();
            }
        }
    }
}