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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 java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import javax.xml.XMLConstants;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

import org.apache.xml.security.exceptions.XMLSecurityException;
import org.apache.xml.security.signature.XMLSignatureInput;
import org.apache.xml.security.transforms.Transform;
import org.apache.xml.security.transforms.TransformSpi;
import org.apache.xml.security.transforms.TransformationException;
import org.apache.xml.security.transforms.Transforms;
import org.apache.xml.security.utils.XMLUtils;
import org.w3c.dom.Element;

/**
 * Class TransformXSLT
 *
 * Implements the http://www.w3.org/TR/1999/REC-xslt-19991116
 * transform.
 *
 * @author Christian Geuer-Pollmann
 */
public class TransformXSLT extends TransformSpi {

    /** Field implementedTransformURI */
    public static final String implementedTransformURI =
        Transforms.TRANSFORM_XSLT;

    static final String XSLTSpecNS              = "http://www.w3.org/1999/XSL/Transform";
    static final String defaultXSLTSpecNSprefix = "xslt";
    static final String XSLTSTYLESHEET          = "stylesheet";

    private static org.slf4j.Logger log =
        org.slf4j.LoggerFactory.getLogger(TransformXSLT.class);

    /**
     * Method engineGetURI
     *
     * @inheritDoc
     */
    protected String engineGetURI() {
        return implementedTransformURI;
    }

    protected XMLSignatureInput enginePerformTransform(
        XMLSignatureInput input, OutputStream baos, Transform transformObject
    ) throws IOException, TransformationException {
        try {
            Element transformElement = transformObject.getElement();
            
            Element xsltElement =
                XMLUtils.selectNode(transformElement.getFirstChild(), XSLTSpecNS, "stylesheet", 0);

            if (xsltElement == null) {
                Object exArgs[] = { "xslt:stylesheet", "Transform" };

                throw new TransformationException("xml.WrongContent", exArgs);
            }

            TransformerFactory tFactory = TransformerFactory.newInstance();
            // Process XSLT stylesheets in a secure manner
            tFactory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, Boolean.TRUE);

            /*
             * This transform requires an octet stream as input. If the actual
             * input is an XPath node-set, then the signature application should
             * attempt to convert it to octets (apply Canonical XML]) as described
             * in the Reference Processing Model (section 4.3.3.2).
             */
            Source xmlSource =
                new StreamSource(new ByteArrayInputStream(input.getBytes()));
            Source stylesheet;

            /*
             * This complicated transformation of the stylesheet itself is necessary
             * because of the need to get the pure style sheet. If we simply say
             * Source stylesheet = new DOMSource(this.xsltElement);
             * whereby this.xsltElement is not the rootElement of the Document,
             * this causes problems;
             * so we convert the stylesheet to byte[] and use this as input stream
             */
            {
                ByteArrayOutputStream os = new ByteArrayOutputStream();
                Transformer transformer = tFactory.newTransformer();
                DOMSource source = new DOMSource(xsltElement);
                StreamResult result = new StreamResult(os);

                transformer.transform(source, result);

                stylesheet =
                    new StreamSource(new ByteArrayInputStream(os.toByteArray()));
            }

            Transformer transformer = tFactory.newTransformer(stylesheet);

            // Force Xalan to use \n as line separator on all OSes. This 
            // avoids OS specific signature validation failures due to line
            // separator differences in the transformed output. Unfortunately,
            // this is not a standard JAXP property so will not work with non-Xalan
            // implementations.
            try {
                transformer.setOutputProperty("{http://xml.apache.org/xalan}line-separator", "\n");
            } catch (Exception e) {
                log.warn("Unable to set Xalan line-separator property: " + e.getMessage());
            }

            if (baos == null) {
                ByteArrayOutputStream baos1 = new ByteArrayOutputStream();
                StreamResult outputTarget = new StreamResult(baos1);
                transformer.transform(xmlSource, outputTarget);
                XMLSignatureInput output = new XMLSignatureInput(baos1.toByteArray());
                output.setSecureValidation(secureValidation);
                return output;
            }
            StreamResult outputTarget = new StreamResult(baos);

            transformer.transform(xmlSource, outputTarget);         
            XMLSignatureInput output = new XMLSignatureInput((byte[])null);
            output.setSecureValidation(secureValidation);
            output.setOutputStream(baos);
            return output;
        } catch (XMLSecurityException ex) {
            Object exArgs[] = { ex.getMessage() };

            throw new TransformationException("generic.EmptyMessage", exArgs, ex);
        } catch (TransformerConfigurationException ex) {
            Object exArgs[] = { ex.getMessage() };

            throw new TransformationException("generic.EmptyMessage", exArgs, ex);
        } catch (TransformerException ex) {
            Object exArgs[] = { ex.getMessage() };

            throw new TransformationException("generic.EmptyMessage", exArgs, ex);
        }
    }
}