001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2025 the original author or authors.
004//
005// This library is free software; you can redistribute it and/or
006// modify it under the terms of the GNU Lesser General Public
007// License as published by the Free Software Foundation; either
008// version 2.1 of the License, or (at your option) any later version.
009//
010// This library is distributed in the hope that it will be useful,
011// but WITHOUT ANY WARRANTY; without even the implied warranty of
012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
013// Lesser General Public License for more details.
014//
015// You should have received a copy of the GNU Lesser General Public
016// License along with this library; if not, write to the Free Software
017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
018///////////////////////////////////////////////////////////////////////////////////////////////
019
020package com.puppycrawl.tools.checkstyle;
021
022import java.io.IOException;
023import java.io.InputStream;
024import java.util.Map;
025
026import javax.xml.parsers.ParserConfigurationException;
027import javax.xml.parsers.SAXParserFactory;
028
029import org.xml.sax.InputSource;
030import org.xml.sax.SAXException;
031import org.xml.sax.SAXParseException;
032import org.xml.sax.XMLReader;
033import org.xml.sax.helpers.DefaultHandler;
034
035import com.puppycrawl.tools.checkstyle.utils.UnmodifiableCollectionUtil;
036
037/**
038 * Contains the common implementation of a loader, for loading a configuration
039 * from an XML file.
040 *
041 * <p>
042 * The error handling policy can be described as being austere, dead set,
043 * disciplinary, dour, draconian, exacting, firm, forbidding, grim, hard, hard-
044 * boiled, harsh, harsh, in line, iron-fisted, no-nonsense, oppressive,
045 * persnickety, picky, prudish, punctilious, puritanical, rigid, rigorous,
046 * scrupulous, set, severe, square, stern, stickler, straight, strait-laced,
047 * stringent, stuffy, stuffy, tough, unpermissive, unsparing and uptight.
048 * </p>
049 *
050 * @noinspection ThisEscapedInObjectConstruction
051 * @noinspectionreason ThisEscapedInObjectConstruction - only reference is used and not
052 *      accessed until initialized
053 */
054public class XmlLoader
055    extends DefaultHandler {
056
057    /** Maps public id to resolve to resource name for the DTD. */
058    private final Map<String, String> publicIdToResourceNameMap;
059    /** Parser to read XML files. **/
060    private final XMLReader parser;
061
062    /**
063     * Creates a new instance.
064     *
065     * @param publicIdToResourceNameMap maps public IDs to DTD resource names
066     * @throws SAXException if an error occurs
067     * @throws ParserConfigurationException if an error occurs
068     */
069    protected XmlLoader(Map<String, String> publicIdToResourceNameMap)
070            throws SAXException, ParserConfigurationException {
071        this.publicIdToResourceNameMap =
072                UnmodifiableCollectionUtil.copyOfMap(publicIdToResourceNameMap);
073        parser = createXmlReader(this);
074    }
075
076    /**
077     * Parses the specified input source.
078     *
079     * @param inputSource the input source to parse.
080     * @throws IOException if an error occurs
081     * @throws SAXException in an error occurs
082     */
083    public void parseInputSource(InputSource inputSource)
084            throws IOException, SAXException {
085        parser.parse(inputSource);
086    }
087
088    @Override
089    public InputSource resolveEntity(String publicId, String systemId) {
090        InputSource inputSource = null;
091        if (publicId != null) {
092            final String dtdResourceName = publicIdToResourceNameMap.get(publicId);
093
094            if (dtdResourceName != null) {
095                final ClassLoader loader = getClass().getClassLoader();
096                final InputStream dtdIs = loader.getResourceAsStream(dtdResourceName);
097                inputSource = new InputSource(dtdIs);
098            }
099        }
100        return inputSource;
101    }
102
103    @Override
104    public void error(SAXParseException exception) throws SAXException {
105        throw exception;
106    }
107
108    /**
109     * Helper method to create {@code XMLReader}.
110     *
111     * @param handler the content handler
112     * @return new XMLReader instance
113     * @throws ParserConfigurationException if a parser cannot be created
114     * @throws SAXException for SAX errors
115     */
116    private static XMLReader createXmlReader(DefaultHandler handler)
117            throws SAXException, ParserConfigurationException {
118        final SAXParserFactory factory = SAXParserFactory.newInstance();
119        LoadExternalDtdFeatureProvider.setFeaturesBySystemProperty(factory);
120        factory.setValidating(true);
121        final XMLReader xmlReader = factory.newSAXParser().getXMLReader();
122        xmlReader.setContentHandler(handler);
123        xmlReader.setEntityResolver(handler);
124        xmlReader.setErrorHandler(handler);
125        return xmlReader;
126    }
127
128    /**
129     * Used for setting specific for secure java installations features to SAXParserFactory.
130     * Pulled out as a separate class in order to suppress Pitest mutations.
131     */
132    public static final class LoadExternalDtdFeatureProvider {
133
134        /** System property name to enable external DTD load. */
135        public static final String ENABLE_EXTERNAL_DTD_LOAD = "checkstyle.enableExternalDtdLoad";
136
137        /** Feature that enables loading external DTD when loading XML files. */
138        public static final String LOAD_EXTERNAL_DTD =
139                "http://apache.org/xml/features/nonvalidating/load-external-dtd";
140        /** Feature that enables including external general entities in XML files. */
141        public static final String EXTERNAL_GENERAL_ENTITIES =
142                "http://xml.org/sax/features/external-general-entities";
143        /** Feature that enables including external parameter entities in XML files. */
144        public static final String EXTERNAL_PARAMETER_ENTITIES =
145                "http://xml.org/sax/features/external-parameter-entities";
146
147        /** Stop instances being created. **/
148        private LoadExternalDtdFeatureProvider() {
149        }
150
151        /**
152         * Configures SAXParserFactory with features required
153         * to use external DTD file loading, this is not activated by default to no allow
154         * usage of schema files that checkstyle do not know
155         * it is even security problem to allow files from outside.
156         *
157         * @param factory factory to be configured with special features
158         * @throws SAXException if an error occurs
159         * @throws ParserConfigurationException if an error occurs
160         */
161        public static void setFeaturesBySystemProperty(SAXParserFactory factory)
162                throws SAXException, ParserConfigurationException {
163
164            final boolean enableExternalDtdLoad = Boolean.parseBoolean(
165                System.getProperty(ENABLE_EXTERNAL_DTD_LOAD, "false"));
166
167            factory.setFeature(LOAD_EXTERNAL_DTD, enableExternalDtdLoad);
168            factory.setFeature(EXTERNAL_GENERAL_ENTITIES, enableExternalDtdLoad);
169            factory.setFeature(EXTERNAL_PARAMETER_ENTITIES, enableExternalDtdLoad);
170        }
171
172    }
173
174}