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Apache XML Security for Java supports XML-Signature Syntax and Processing, W3C Recommendation 12 February 2002, and XML Encryption Syntax and Processing, W3C Recommendation 10 December 2002. As of version 1.4, the library supports the standard Java API JSR-105: XML Digital Signature APIs.
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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you 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.xml.security.transforms.implementations;

import javax.xml.transform.TransformerException;

import org.apache.xml.dtm.DTM;
import org.apache.xml.security.utils.I18n;
import org.apache.xml.security.utils.XMLUtils;
import org.apache.xpath.NodeSetDTM;
import org.apache.xpath.XPathContext;
import org.apache.xpath.functions.Function;
import org.apache.xpath.objects.XNodeSet;
import org.apache.xpath.objects.XObject;
import org.apache.xpath.res.XPATHErrorResources;
import org.w3c.dom.Document;
import org.w3c.dom.Node;

/**
 * The 'here()' function returns a node-set containing the attribute or
 * processing instruction node or the parent element of the text node
 * that directly bears the XPath expression.  This expression results
 * in an error if the containing XPath expression does not appear in the
 * same XML document against which the XPath expression is being evaluated.
 *
 * Mainpart is stolen from FuncId.java
 *
 * This does crash under Xalan2.2.D7 and works under Xalan2.2.D9
 *
 * To get this baby to work, a special trick has to be used. The function needs
 * access to the Node where the XPath expression has been defined. This is done
 * by constructing a {@link FuncHere} which has this Node as 'owner'.
 *
 * @see "http://www.w3.org/Signature/Drafts/xmldsig-core/Overview.html#function-here"
 */
public class FuncHere extends Function {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    /**
     * The here function returns a node-set containing the attribute or
     * processing instruction node or the parent element of the text node
     * that directly bears the XPath expression.  This expression results
     * in an error if the containing XPath expression does not appear in the
     * same XML document against which the XPath expression is being evaluated.
     *
     * @param xctxt
     * @return the xobject
     * @throws javax.xml.transform.TransformerException
     */
    public XObject execute(XPathContext xctxt) throws TransformerException {

        Node xpathOwnerNode = (Node) xctxt.getOwnerObject();

        if (xpathOwnerNode == null) {
            return null;
        }

        int xpathOwnerNodeDTM = xctxt.getDTMHandleFromNode(xpathOwnerNode);

        int currentNode = xctxt.getCurrentNode();
        DTM dtm = xctxt.getDTM(currentNode);
        int docContext = dtm.getDocument();

        if (DTM.NULL == docContext) {
            error(xctxt, XPATHErrorResources.ER_CONTEXT_HAS_NO_OWNERDOC, null);
        }

        {
            // check whether currentNode and the node containing the XPath expression
            // are in the same document
            Document currentDoc =
                XMLUtils.getOwnerDocument(dtm.getNode(currentNode));
            Document xpathOwnerDoc = XMLUtils.getOwnerDocument(xpathOwnerNode);

            if (currentDoc != xpathOwnerDoc) {
                throw new TransformerException(I18n.translate("xpath.funcHere.documentsDiffer"));
            }
        }

        XNodeSet nodes = new XNodeSet(xctxt.getDTMManager());
        NodeSetDTM nodeSet = nodes.mutableNodeset();

        {
            int hereNode = DTM.NULL;

            switch (dtm.getNodeType(xpathOwnerNodeDTM)) {

            case Node.ATTRIBUTE_NODE :
            case Node.PROCESSING_INSTRUCTION_NODE : {
                // returns a node-set containing the attribute /  processing instruction node
                hereNode = xpathOwnerNodeDTM;

                nodeSet.addNode(hereNode);

                break;
            }
            case Node.TEXT_NODE : {
                // returns a node-set containing the parent element of the
                // text node that directly bears the XPath expression
                hereNode = dtm.getParent(xpathOwnerNodeDTM);

                nodeSet.addNode(hereNode);

                break;
            }
            default :
                break;
            }
        }

        /** $todo$ Do I have to do this detach() call? */
        nodeSet.detach();

        return nodes;
    }

    /**
     * No arguments to process, so this does nothing.
     * @param vars
     * @param globalsSize
     */
    public void fixupVariables(@SuppressWarnings("rawtypes") java.util.Vector vars, int globalsSize) {
        // do nothing
    }
}