net.sf.jasperreports.renderers.util.XmlDataSniffer.java Source code

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Here is the source code for net.sf.jasperreports.renderers.util.XmlDataSniffer.java

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/*
 * JasperReports - Free Java Reporting Library.
 * Copyright (C) 2001 - 2019 TIBCO Software Inc. All rights reserved.
 * http://www.jaspersoft.com
 *
 * Unless you have purchased a commercial license agreement from Jaspersoft,
 * the following license terms apply:
 *
 * This program is part of JasperReports.
 *
 * JasperReports is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * JasperReports is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with JasperReports. If not, see <http://www.gnu.org/licenses/>.
 */
package net.sf.jasperreports.renderers.util;

import java.io.ByteArrayInputStream;
import java.io.IOException;

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

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.SAXNotRecognizedException;
import org.xml.sax.SAXNotSupportedException;
import org.xml.sax.helpers.DefaultHandler;

/**
 * Utility class that checks if provided byte data is a valid XML document.
 * It does this by attempting to parse the data using a SAX parser.
 * 
 * @author Teodor Danciu (teodord@users.sourceforge.net)
 */
public class XmlDataSniffer {

    private static final Log log = LogFactory.getLog(XmlDataSniffer.class);

    private static final String SAX_EXCEPTION_MESSAGE_VALID_XML = "something unique";

    private static final String FEATURE_EXTERNAL_GENERAL_ENTITIES = "http://xml.org/sax/features/external-general-entities";
    private static final String FEATURE_EXTERNAL_PARAMETER_ENTITIES = "http://xml.org/sax/features/external-parameter-entities";
    private static final String FEATURE_LOAD_EXTERNAL_DTD = "http://apache.org/xml/features/nonvalidating/load-external-dtd";

    private static class ValidXmlSAXException extends SAXException {
        private static final long serialVersionUID = 1L;

        ValidXmlSAXException() {
            super(SAX_EXCEPTION_MESSAGE_VALID_XML);
        }

        @Override
        public synchronized Throwable fillInStackTrace() {
            // stacktrace is not needed, easing the impact using exceptions
            return this;
        }
    }

    /**
     * 
     */
    public static boolean isXmlData(byte[] data) {
        XmlSniffResult sniffResult = sniffXml(data);
        return sniffResult != null;
    }

    public static XmlSniffResult sniffXml(byte[] data) {
        SAXParserFactory factory = SAXParserFactory.newInstance();
        factory.setValidating(false);
        factory.setNamespaceAware(false);
        factory.setXIncludeAware(false);
        setParserFeature(factory, FEATURE_EXTERNAL_GENERAL_ENTITIES, false);
        setParserFeature(factory, FEATURE_EXTERNAL_PARAMETER_ENTITIES, false);
        setParserFeature(factory, FEATURE_LOAD_EXTERNAL_DTD, false);

        SaxHandler handler = new SaxHandler();

        ByteArrayInputStream bais = new ByteArrayInputStream(data);

        try {
            SAXParser saxParser = factory.newSAXParser();
            saxParser.parse(bais, handler);
            return new XmlSniffResult(handler.rootElementName);
        } catch (ValidXmlSAXException e) {
            return new XmlSniffResult(handler.rootElementName);
        } catch (SAXException | ParserConfigurationException | IOException e) {
            return null;
        }
    }

    protected static void setParserFeature(SAXParserFactory factory, String feature, boolean value) {
        try {
            factory.setFeature(feature, value);
        } catch (SAXNotRecognizedException | SAXNotSupportedException | ParserConfigurationException e) {
            if (log.isDebugEnabled()) {
                log.debug("Failed to set parser feature " + feature + ", error " + e);
            }
        }
    }

    private static class SaxHandler extends DefaultHandler {
        private String rootElementName;

        @Override
        public void startElement(String uri, String localName, String qName, Attributes attributes)
                throws SAXException {
            this.rootElementName = (qName != null && !qName.isEmpty()) ? qName
                    : ((localName != null && !localName.isEmpty()) ? localName : null);
            throw new ValidXmlSAXException();
        }

        @Override
        public InputSource resolveEntity(String publicId, String systemId) throws IOException, SAXException {
            //stop any attempt to load entities
            throw new ValidXmlSAXException();
        }
    }

    public static class XmlSniffResult {
        private final String rootElementName;

        public XmlSniffResult(String rootElementName) {
            this.rootElementName = rootElementName;
        }

        public String getRootElementName() {
            return rootElementName;
        }
    }
}