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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 2004-2018 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.InputStream;
import java.lang.reflect.Method;
import java.util.concurrent.TimeUnit;

import javax.xml.XMLConstants;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.stream.events.Namespace;

import org.apache.xmlbeans.XmlOptionsBean;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.xml.sax.ErrorHandler;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;

public final class DocumentHelper {
    private static XBLogger logger = XBLogFactory.getLogger(DocumentHelper.class);
    private static long lastLog;

    private DocumentHelper() {}

    private static class DocHelperErrorHandler implements ErrorHandler {

        public void warning(SAXParseException exception) throws SAXException {
            printError(XBLogger.WARN, exception);
        }

        public void error(SAXParseException exception) throws SAXException {
            printError(XBLogger.ERROR, exception);
        }

        public void fatalError(SAXParseException exception) throws SAXException {
            printError(XBLogger.FATAL, exception);
            throw exception;
        }

        /** Prints the error message. */
        private void printError(int type, SAXParseException ex) {
            StringBuilder sb = new StringBuilder();
            
            String systemId = ex.getSystemId();
            if (systemId != null) {
                int index = systemId.lastIndexOf('/');
                if (index != -1)
                    systemId = systemId.substring(index + 1);
                sb.append(systemId);
            }
            sb.append(':');
            sb.append(ex.getLineNumber());
            sb.append(':');
            sb.append(ex.getColumnNumber());
            sb.append(": ");
            sb.append(ex.getMessage());

            logger.log(type, sb.toString(), ex);
        }
    }
    
    /**
     * Creates a new document builder, with sensible defaults
     *
     * @param xmlOptions
     * @throws IllegalStateException If creating the DocumentBuilder fails, e.g.
     *  due to {@link ParserConfigurationException}.
     */
    public static DocumentBuilder newDocumentBuilder(XmlOptionsBean xmlOptions) {
        try {
            DocumentBuilder documentBuilder = documentBuilderFactory(xmlOptions).newDocumentBuilder();
            documentBuilder.setEntityResolver(SAXHelper.IGNORING_ENTITY_RESOLVER);
            documentBuilder.setErrorHandler(new DocHelperErrorHandler());
            return documentBuilder;
        } catch (ParserConfigurationException e) {
            throw new IllegalStateException("cannot create a DocumentBuilder", e);
        }
    }

    private static final DocumentBuilderFactory documentBuilderFactory(XmlOptionsBean options) {
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        documentBuilderFactory.setNamespaceAware(true);
        documentBuilderFactory.setValidating(false);
        trySetFeature(documentBuilderFactory, XMLConstants.FEATURE_SECURE_PROCESSING, true);
        trySetFeature(documentBuilderFactory, XMLBeansConstants.FEATURE_LOAD_DTD_GRAMMAR, options.isLoadDTDGrammar());
        trySetFeature(documentBuilderFactory, XMLBeansConstants.FEATURE_LOAD_EXTERNAL_DTD, options.isLoadExternalDTD());
        trySetXercesSecurityManager(documentBuilderFactory, options);
        return documentBuilderFactory;
    }

    private static void trySetFeature(DocumentBuilderFactory dbf, String feature, boolean enabled) {
        try {
            dbf.setFeature(feature, enabled);
        } 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(DocumentBuilderFactory dbf, 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());
                dbf.setAttribute(XMLBeansConstants.SECURITY_MANAGER, mgr);
                // Stop once one can be setup without error
                return;
            } catch (ClassNotFoundException e) {
                // continue without log, this is expected in some setups
            } catch (Throwable e) {     // NOSONAR - also catch things like NoClassDefError here
                if(System.currentTimeMillis() > lastLog + TimeUnit.MINUTES.toMillis(5)) {
                    logger.log(XBLogger.WARN, "DocumentBuilderFactory 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 {
            dbf.setAttribute(XMLBeansConstants.ENTITY_EXPANSION_LIMIT, options.getEntityExpansionLimit());
        } catch (Throwable e) {
            if(System.currentTimeMillis() > lastLog + TimeUnit.MINUTES.toMillis(5)) {
                logger.log(XBLogger.WARN, "DocumentBuilderFactory Entity Expansion Limit could not be setup [log suppressed for 5 minutes]", e);
                lastLog = System.currentTimeMillis();
            }
        }
    }

    /**
     * Parses the given stream via the default (sensible)
     * DocumentBuilder
     * @param inp Stream to read the XML data from
     * @return the parsed Document 
     */
    public static Document readDocument(XmlOptionsBean xmlOptions, InputStream inp) throws IOException, SAXException {
        return newDocumentBuilder(xmlOptions).parse(inp);
    }

    /**
     * Parses the given stream via the default (sensible)
     * DocumentBuilder
     * @param inp sax source to read the XML data from
     * @return the parsed Document 
     */
    public static Document readDocument(XmlOptionsBean xmlOptions, InputSource inp) throws IOException, SAXException {
        return newDocumentBuilder(xmlOptions).parse(inp);
    }

    // must only be used to create empty documents, do not use it for parsing!
    private static final DocumentBuilder documentBuilderSingleton = newDocumentBuilder(new XmlOptionsBean());

    /**
     * Creates a new DOM Document
     */
    public static Document createDocument() {
        return documentBuilderSingleton.newDocument();
    }
}