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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.encryption;

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

import javax.xml.XMLConstants;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMResult;
import javax.xml.transform.stream.StreamSource;

import org.apache.xml.security.c14n.Canonicalizer;
import org.apache.xml.security.c14n.InvalidCanonicalizerException;
import org.w3c.dom.Document;
import org.w3c.dom.DocumentFragment;
import org.w3c.dom.Node;

/**
 * Converts Strings into Nodes and visa versa. This requires Xalan to
 * work properly.
 */
public class TransformSerializer extends AbstractSerializer {

    private final TransformerFactory transformerFactory;

    public TransformSerializer(boolean secureValidation) throws InvalidCanonicalizerException, TransformerConfigurationException {
        this(Canonicalizer.ALGO_ID_C14N_PHYSICAL, secureValidation);
    }

    public TransformSerializer(String canonAlg, boolean secureValidation) throws TransformerConfigurationException, InvalidCanonicalizerException {
        super(canonAlg, secureValidation);

        transformerFactory = TransformerFactory.newInstance();
        transformerFactory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, Boolean.TRUE);
        if (secureValidation) {
            try {
                transformerFactory.setAttribute(XMLConstants.ACCESS_EXTERNAL_DTD, "");
                transformerFactory.setAttribute(XMLConstants.ACCESS_EXTERNAL_STYLESHEET, "");
            } catch (IllegalArgumentException ex) {
                // ignore
            }
        }
    }

    /**
     * @param source
     * @param ctx
     * @return the Node resulting from the parse of the source
     * @throws XMLEncryptionException
     */
    @Override
    public Node deserialize(byte[] source, Node ctx) throws XMLEncryptionException, IOException {
        byte[] fragment = createContext(source, ctx);
        try (InputStream is = new ByteArrayInputStream(fragment)) {
            return deserialize(ctx, new StreamSource(is));
        }
    }

    /**
     * @param ctx
     * @param source
     * @return the Node resulting from the parse of the source
     * @throws XMLEncryptionException
     */
    private Node deserialize(Node ctx, Source source) throws XMLEncryptionException {
        try {
            Document contextDocument = null;
            if (Node.DOCUMENT_NODE == ctx.getNodeType()) {
                contextDocument = (Document)ctx;
            } else {
                contextDocument = ctx.getOwnerDocument();
            }

            Transformer transformer = transformerFactory.newTransformer();

            DOMResult res = new DOMResult();

            Node placeholder = contextDocument.createDocumentFragment();
            res.setNode(placeholder);

            transformer.transform(source, res);

            // Skip dummy element
            Node dummyChild = placeholder.getFirstChild();
            Node child = dummyChild.getFirstChild();

            if (child != null && child.getNextSibling() == null) {
                return child;
            }

            DocumentFragment docfrag = contextDocument.createDocumentFragment();
            while (child != null) {
                dummyChild.removeChild(child);
                docfrag.appendChild(child);
                child = dummyChild.getFirstChild();
            }

            return docfrag;
        } catch (Exception e) {
            throw new XMLEncryptionException(e);
        }
    }

}