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   1 /**
   2  * Copyright (c) 2010-2023 Contributors to the openHAB project
   3  *
   4  * See the NOTICE file(s) distributed with this work for additional
   5  * information.
   6  *
   7  * This program and the accompanying materials are made available under the
   8  * terms of the Eclipse Public License 2.0 which is available at
   9  * http://www.eclipse.org/legal/epl-2.0
  10  *
  11  * SPDX-License-Identifier: EPL-2.0
  12  */
  13 package org.openhab.transform.xpath.internal;
  14
  15 import java.io.StringReader;
  16
  17 import javax.xml.parsers.DocumentBuilder;
  18 import javax.xml.parsers.DocumentBuilderFactory;
  19 import javax.xml.xpath.XPath;
  20 import javax.xml.xpath.XPathConstants;
  21 import javax.xml.xpath.XPathExpression;
  22 import javax.xml.xpath.XPathFactory;
  23
  24 import org.eclipse.jdt.annotation.NonNullByDefault;
  25 import org.eclipse.jdt.annotation.Nullable;
  26 import org.openhab.core.transform.TransformationException;
  27 import org.openhab.core.transform.TransformationService;
  28 import org.osgi.service.component.annotations.Component;
  29 import org.slf4j.Logger;
  30 import org.slf4j.LoggerFactory;
  31 import org.w3c.dom.Document;
  32 import org.xml.sax.InputSource;
  33
  34 /**
  35  * <p>
  36  * The implementation of {@link TransformationService} which transforms the input by XPath Expressions.
  37  *
  38  * @author Thomas.Eichstaedt-Engelen
  39  */
  40 @NonNullByDefault
  41 @Component(property = { "openhab.transform=XPATH" })
  42 public class XPathTransformationService implements TransformationService {
  43
  44     private final Logger logger = LoggerFactory.getLogger(XPathTransformationService.class);
  45
  46     @Override
  47     public @Nullable String transform(String xpathExpression, String source) throws TransformationException {
  48         if (xpathExpression == null || source == null) {
  49             throw new TransformationException("the given parameters 'xpath' and 'source' must not be null");
  50         }
  51
  52         logger.debug("about to transform '{}' by the function '{}'", source, xpathExpression);
  53
  54         StringReader stringReader = null;
  55
  56         try {
  57             DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
  58             // see https://cheatsheetseries.owasp.org/cheatsheets/XML_External_Entity_Prevention_Cheat_Sheet.html
  59             domFactory.setFeature("http://xml.org/sax/features/external-general-entities", false);
  60             domFactory.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
  61             domFactory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
  62             domFactory.setXIncludeAware(false);
  63             domFactory.setExpandEntityReferences(false);
  64             domFactory.setNamespaceAware(true);
  65             domFactory.setValidating(false);
  66             DocumentBuilder builder = domFactory.newDocumentBuilder();
  67
  68             stringReader = new StringReader(source);
  69             InputSource inputSource = new InputSource(stringReader);
  70             inputSource.setEncoding("UTF-8");
  71
  72             Document doc = builder.parse(inputSource);
  73
  74             XPath xpath = XPathFactory.newInstance().newXPath();
  75             XPathExpression expr = xpath.compile(xpathExpression);
  76
  77             String transformationResult = (String) expr.evaluate(doc, XPathConstants.STRING);
  78
  79             logger.debug("transformation resulted in '{}'", transformationResult);
  80
  81             return transformationResult;
  82         } catch (Exception e) {
  83             throw new TransformationException("transformation throws exceptions", e);
  84         } finally {
  85             if (stringReader != null) {
  86                 stringReader.close();
  87             }
  88         }
  89     }
  90 }