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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.c14n.helper;

import org.apache.xml.security.c14n.CanonicalizationException;
import org.w3c.dom.Attr;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NamedNodeMap;

/**
 * Temporary swapped static functions from the normalizer Section
 *
 * @author Christian Geuer-Pollmann
 */
public class C14nHelper {

    /**
     * Constructor C14nHelper
     *
     */
    private C14nHelper() {
        // don't allow instantiation
    }

    /**
     * Method namespaceIsRelative
     *
     * @param namespace
     * @return true if the given namespace is relative. 
     */
    public static boolean namespaceIsRelative(Attr namespace) {
        return !namespaceIsAbsolute(namespace);
    }

    /**
     * Method namespaceIsRelative
     *
     * @param namespaceValue
     * @return true if the given namespace is relative.
     */
    public static boolean namespaceIsRelative(String namespaceValue) {
        return !namespaceIsAbsolute(namespaceValue);
    }

    /**
     * Method namespaceIsAbsolute
     *
     * @param namespace
     * @return true if the given namespace is absolute.
     */
    public static boolean namespaceIsAbsolute(Attr namespace) {
        return namespaceIsAbsolute(namespace.getValue());
    }

    /**
     * Method namespaceIsAbsolute
     *
     * @param namespaceValue
     * @return true if the given namespace is absolute.
     */
    public static boolean namespaceIsAbsolute(String namespaceValue) {
        // assume empty namespaces are absolute
        if (namespaceValue.length() == 0) {
            return true;
        }
        return namespaceValue.indexOf(':') > 0;
    }

    /**
     * This method throws an exception if the Attribute value contains
     * a relative URI.
     *
     * @param attr
     * @throws CanonicalizationException
     */
    public static void assertNotRelativeNS(Attr attr) throws CanonicalizationException {
        if (attr == null) {
            return;
        }

        String nodeAttrName = attr.getNodeName();
        boolean definesDefaultNS = nodeAttrName.equals("xmlns");
        boolean definesNonDefaultNS = nodeAttrName.startsWith("xmlns:");

        if ((definesDefaultNS || definesNonDefaultNS) && namespaceIsRelative(attr)) {
            String parentName = attr.getOwnerElement().getTagName();
            String attrValue = attr.getValue();
            Object exArgs[] = { parentName, nodeAttrName, attrValue };

            throw new CanonicalizationException(
                "c14n.Canonicalizer.RelativeNamespace", exArgs
            );
        }
    }

    /**
     * This method throws a CanonicalizationException if the supplied Document
     * is not able to be traversed using a TreeWalker.
     *
     * @param document
     * @throws CanonicalizationException
     */
    public static void checkTraversability(Document document)
        throws CanonicalizationException {
        if (!document.isSupported("Traversal", "2.0")) {
            Object exArgs[] = {document.getImplementation().getClass().getName() };

            throw new CanonicalizationException(
                "c14n.Canonicalizer.TraversalNotSupported", exArgs
            );
        }
    }

    /**
     * This method throws a CanonicalizationException if the supplied Element
     * contains any relative namespaces.
     *
     * @param ctxNode
     * @throws CanonicalizationException
     * @see C14nHelper#assertNotRelativeNS(Attr)
     */
    public static void checkForRelativeNamespace(Element ctxNode)
        throws CanonicalizationException {
        if (ctxNode != null) {
            NamedNodeMap attributes = ctxNode.getAttributes();

            for (int i = 0; i < attributes.getLength(); i++) {
                C14nHelper.assertNotRelativeNS((Attr) attributes.item(i));
            }
        } else {
            throw new CanonicalizationException("Called checkForRelativeNamespace() on null");
        }
    }
}