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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.OutputStream;

import org.apache.xml.security.signature.NodeFilter;
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.Constants;
import org.apache.xml.security.utils.XMLUtils;
import org.w3c.dom.Element;
import org.w3c.dom.Node;

/**
 * Implements the http://www.w3.org/2000/09/xmldsig#enveloped-signature
 * transform.
 *
 * @author Christian Geuer-Pollmann
 */
public class TransformEnvelopedSignature extends TransformSpi {

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

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

    /**
     * @inheritDoc
     */
    protected XMLSignatureInput enginePerformTransform(
        XMLSignatureInput input, OutputStream os, Transform transformObject
    ) throws TransformationException {
        /**
         * If the actual input is an octet stream, then the application MUST
         * convert the octet stream to an XPath node-set suitable for use by
         * Canonical XML with Comments. (A subsequent application of the
         * REQUIRED Canonical XML algorithm would strip away these comments.)
         *
         * ...
         *
         * The evaluation of this expression includes all of the document's nodes
         * (including comments) in the node-set representing the octet stream.
         */

        Node signatureElement = transformObject.getElement();

        signatureElement = searchSignatureElement(signatureElement);        
        input.setExcludeNode(signatureElement);   
        input.addNodeFilter(new EnvelopedNodeFilter(signatureElement));
        return input;
    }

    /**
     * @param signatureElement    
     * @return the node that is the signature
     * @throws TransformationException
     */
    private static Node searchSignatureElement(Node signatureElement) 
        throws TransformationException {
        boolean found = false;

        while (true) {
            if (signatureElement == null
                || signatureElement.getNodeType() == Node.DOCUMENT_NODE) {
                break;
            }
            Element el = (Element) signatureElement;
            if (el.getNamespaceURI().equals(Constants.SignatureSpecNS)
                && el.getLocalName().equals(Constants._TAG_SIGNATURE)) {
                found = true;
                break;
            }

            signatureElement = signatureElement.getParentNode();
        }

        if (!found) {
            throw new TransformationException(
                "transform.envelopedSignatureTransformNotInSignatureElement");
        }
        return signatureElement;
    }

    static class EnvelopedNodeFilter implements NodeFilter {
        
        Node exclude;
        
        EnvelopedNodeFilter(Node n) {
            exclude = n;
        }
        
        public int isNodeIncludeDO(Node n, int level) {
            if (n == exclude) {
                return -1;
            }
            return 1;
        }
        
        /**
         * @see org.apache.xml.security.signature.NodeFilter#isNodeInclude(org.w3c.dom.Node)
         */
        public int isNodeInclude(Node n) {
            if (n == exclude || XMLUtils.isDescendantOrSelf(exclude, n)) { 
                return -1;
            }
            return 1;
            //return !XMLUtils.isDescendantOrSelf(exclude,n);
        }
    }
}