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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.utils;

import java.lang.System.Logger;
import java.lang.System.Logger.Level;
import java.math.BigInteger;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.xml.security.exceptions.XMLSecurityException;
import org.w3c.dom.Attr;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.w3c.dom.Text;

/**
 * This is the base class to all Objects which have a direct 1:1 mapping to an
 * Element in a particular namespace.
 */
public abstract class ElementProxy {

    protected static final Logger LOG = System.getLogger(ElementProxy.class.getName());

    /**
     * What XML element does this ElementProxy instance wrap?
     */
    private Element wrappedElement;

    /** Field baseURI */
    protected String baseURI;

    /** Field doc */
    private Document wrappedDoc;

    /** Field prefixMappings */
    private static Map prefixMappings = new ConcurrentHashMap<>();

    /**
     * Constructor ElementProxy
     *
     */
    public ElementProxy() {
    }

    /**
     * Constructor ElementProxy
     *
     * @param doc
     */
    public ElementProxy(Document doc) {
        if (doc == null) {
            throw new RuntimeException("Document is null");
        }

        this.wrappedDoc = doc;
        this.wrappedElement = createElementForFamilyLocal(this.getBaseNamespace(), this.getBaseLocalName());
    }

    /**
     * Constructor ElementProxy
     *
     * @param element
     * @param baseURI
     * @throws XMLSecurityException
     */
    public ElementProxy(Element element, String baseURI) throws XMLSecurityException {
        if (element == null) {
            throw new XMLSecurityException("ElementProxy.nullElement");
        }

        LOG.log(Level.DEBUG, "setElement(\"{0}\", \"{1}\")", element.getTagName(), baseURI);

        setElement(element);
        this.baseURI = baseURI;

        this.guaranteeThatElementInCorrectSpace();
    }

    /**
     * Returns the namespace of the Elements of the sub-class.
     *
     * @return the namespace of the Elements of the sub-class.
     */
    public abstract String getBaseNamespace();

    /**
     * Returns the localname of the Elements of the sub-class.
     *
     * @return the localname of the Elements of the sub-class.
     */
    public abstract String getBaseLocalName();


    protected Element createElementForFamilyLocal(
        String namespace, String localName
    ) {
        Document doc = getDocument();
        Element result = null;
        if (namespace == null) {
            result = doc.createElementNS(null, localName);
        } else {
            String baseName = this.getBaseNamespace();
            String prefix = ElementProxy.getDefaultPrefix(baseName);
            if (prefix == null || prefix.length() == 0) {
                result = doc.createElementNS(namespace, localName);
                result.setAttributeNS(Constants.NamespaceSpecNS, "xmlns", namespace);
            } else {
                result = doc.createElementNS(namespace, prefix + ":" + localName);
                result.setAttributeNS(Constants.NamespaceSpecNS, "xmlns:" + prefix, namespace);
            }
        }
        return result;
    }


    /**
     * This method creates an Element in a given namespace with a given localname.
     * It uses the {@link ElementProxy#getDefaultPrefix} method to decide whether
     * a particular prefix is bound to that namespace.
     * 
     * This method was refactored out of the constructor.
     *
     * @param doc
     * @param namespace
     * @param localName
     * @return The element created.
     */
    public static Element createElementForFamily(Document doc, String namespace, String localName) {
        Element result = null;
        String prefix = ElementProxy.getDefaultPrefix(namespace);

        if (namespace == null) {
            result = doc.createElementNS(null, localName);
        } else {
            if (prefix == null || prefix.length() == 0) {
                result = doc.createElementNS(namespace, localName);
                result.setAttributeNS(Constants.NamespaceSpecNS, "xmlns", namespace);
            } else {
                result = doc.createElementNS(namespace, prefix + ":" + localName);
                result.setAttributeNS(Constants.NamespaceSpecNS, "xmlns:" + prefix, namespace);
            }
        }

        return result;
    }

    /**
     * Method setElement
     *
     * @param element
     * @param baseURI
     * @throws XMLSecurityException
     */
    public void setElement(Element element, String baseURI) throws XMLSecurityException {
        if (element == null) {
            throw new XMLSecurityException("ElementProxy.nullElement");
        }

        LOG.log(Level.DEBUG, "setElement({0}, \"{1}\")", element.getTagName(), baseURI);

        setElement(element);
        this.baseURI = baseURI;
    }

    /**
     * Returns the Element which was constructed by the Object.
     *
     * @return the Element which was constructed by the Object.
     */
    public final Element getElement() {
        return this.wrappedElement;
    }

    /**
     * Returns the Element plus a leading and a trailing CarriageReturn Text node.
     *
     * @return the Element which was constructed by the Object.
     */
    public final NodeList getElementPlusReturns() {

        HelperNodeList nl = new HelperNodeList();

        nl.appendChild(createText("\n"));
        nl.appendChild(getElement());
        nl.appendChild(createText("\n"));

        return nl;
    }

    protected Text createText(String text) {
        return getDocument().createTextNode(text);
    }

    /**
     * Method getDocument
     *
     * @return the Document where this element is contained.
     */
    public Document getDocument() {
        if (wrappedDoc == null) {
            wrappedDoc = XMLUtils.getOwnerDocument(wrappedElement);
        }
        return wrappedDoc;
    }

    /**
     * Method getBaseURI
     *
     * @return the base uri of the namespace of this element
     */
    public String getBaseURI() {
        return this.baseURI;
    }

    /**
     * Method guaranteeThatElementInCorrectSpace
     *
     * @throws XMLSecurityException
     */
    void guaranteeThatElementInCorrectSpace() throws XMLSecurityException {

        String expectedLocalName = this.getBaseLocalName();
        String expectedNamespaceUri = this.getBaseNamespace();

        String actualLocalName = getElement().getLocalName();
        String actualNamespaceUri = getElement().getNamespaceURI();

        if(!expectedNamespaceUri.equals(actualNamespaceUri)
            && !expectedLocalName.equals(actualLocalName)) {
            Object[] exArgs = { actualNamespaceUri + ":" + actualLocalName,
                                expectedNamespaceUri + ":" + expectedLocalName};
            throw new XMLSecurityException("xml.WrongElement", exArgs);
        }
    }

    /**
     * Method addBigIntegerElement
     *
     * @param bi
     * @param localname
     */
    public void addBigIntegerElement(BigInteger bi, String localname) {
        if (bi != null) {
            Element e = XMLUtils.createElementInSignatureSpace(getDocument(), localname);

            byte[] bytes = XMLUtils.getBytes(bi, bi.bitLength());
            String encodedInt = XMLUtils.encodeToString(bytes);

            Document doc = e.getOwnerDocument();
            Text text = doc.createTextNode(encodedInt);

            e.appendChild(text);

            appendSelf(e);
            addReturnToSelf();
        }
    }

    protected void addReturnToSelf() {
        XMLUtils.addReturnToElement(getElement());
    }

    /**
     * Method addBase64Element
     *
     * @param bytes
     * @param localname
     */
    public void addBase64Element(byte[] bytes, String localname) {
        if (bytes != null) {
            addTextElement(XMLUtils.encodeToString(bytes), localname);
        }
    }

    /**
     * Method addTextElement
     *
     * @param text
     * @param localname
     */
    public void addTextElement(String text, String localname) {
        Element e = XMLUtils.createElementInSignatureSpace(getDocument(), localname);
        Text t = createText(text);

        appendOther(e, t);
        appendSelf(e);
        addReturnToSelf();
    }

    /**
     * Method addBase64Text
     *
     * @param bytes
     */
    public void addBase64Text(byte[] bytes) {
        if (bytes != null) {
            Text t = XMLUtils.ignoreLineBreaks()
                ? createText(XMLUtils.encodeToString(bytes))
                : createText("\n" + XMLUtils.encodeToString(bytes) + "\n");
            appendSelf(t);
        }
    }

    protected void appendSelf(ElementProxy toAppend) {
        getElement().appendChild(toAppend.getElement());
    }

    protected void appendSelf(Node toAppend) {
        getElement().appendChild(toAppend);
    }

    protected void appendOther(Element parent, Node toAppend) {
        parent.appendChild(toAppend);
    }

    /**
     * Method addText
     *
     * @param text
     */
    public void addText(String text) {
        if (text != null) {
            Text t = createText(text);

            appendSelf(t);
        }
    }

    /**
     * Method getVal
     *
     * @param localname
     * @param namespace
     * @return The biginteger contained in the given element
     */
    public BigInteger getBigIntegerFromChildElement(
        String localname, String namespace
    ) {
        Node n = XMLUtils.selectNode(getFirstChild(), namespace, localname, 0);
        if (n != null) {
            return new BigInteger(1, XMLUtils.decode(XMLUtils.getFullTextChildrenFromNode(n)));
        }
        return null;
    }

    /**
     * Method getTextFromChildElement
     *
     * @param localname
     * @param namespace
     * @return the Text of the textNode
     */
    public String getTextFromChildElement(String localname, String namespace) {
        return XMLUtils.selectNode(
                getFirstChild(),
                namespace,
                localname,
                0).getTextContent();
    }

    /**
     * Method getBytesFromTextChild
     *
     * @return The base64 bytes from the text children of this element
     * @throws XMLSecurityException
     */
    public byte[] getBytesFromTextChild() throws XMLSecurityException {
        return XMLUtils.decode(getTextFromTextChild());
    }

    /**
     * Method getTextFromTextChild
     *
     * @return the Text obtained by concatenating all the text nodes of this
     *    element
     */
    public String getTextFromTextChild() {
        return XMLUtils.getFullTextChildrenFromNode(getElement());
    }

    /**
     * Method length
     *
     * @param namespace
     * @param localname
     * @return the number of elements {namespace}:localname under this element
     */
    public int length(String namespace, String localname) {
        int number = 0;
        Node sibling = getFirstChild();
        while (sibling != null) {
            if (localname.equals(sibling.getLocalName())
                && namespace.equals(sibling.getNamespaceURI())) {
                number++;
            }
            sibling = sibling.getNextSibling();
        }
        return number;
    }

    /**
     * Adds an xmlns: definition to the Element. This can be called as follows:
     *
     *      * // set namespace with ds prefix
     * xpathContainer.setXPathNamespaceContext("ds", "http://www.w3.org/2000/09/xmldsig#");
     * xpathContainer.setXPathNamespaceContext("xmlns:ds", "http://www.w3.org/2000/09/xmldsig#");
     * 
     *
     * @param prefix
     * @param uri
     * @throws XMLSecurityException
     */
    public void setXPathNamespaceContext(String prefix, String uri)
        throws XMLSecurityException {
        String ns;

        if (prefix == null || prefix.length() == 0) {
            throw new XMLSecurityException("defaultNamespaceCannotBeSetHere");
        } else if ("xmlns".equals(prefix)) {
            throw new XMLSecurityException("defaultNamespaceCannotBeSetHere");
        } else if (prefix.startsWith("xmlns:")) {
            ns = prefix;//"xmlns:" + prefix.substring("xmlns:".length());
        } else {
            ns = "xmlns:" + prefix;
        }

        Attr a = getElement().getAttributeNodeNS(Constants.NamespaceSpecNS, ns);

        if (a != null) {
            if (!a.getNodeValue().equals(uri)) {
                Object[] exArgs = { ns, getElement().getAttributeNS(null, ns) };

                throw new XMLSecurityException("namespacePrefixAlreadyUsedByOtherURI", exArgs);
            }
            return;
        }

        getElement().setAttributeNS(Constants.NamespaceSpecNS, ns, uri);
    }

    /**
     * Method setDefaultPrefix
     *
     * @param namespace
     * @param prefix
     * @throws XMLSecurityException
     * @throws SecurityException if a security manager is installed and the
     *    caller does not have permission to set the default prefix
     */
    public static void setDefaultPrefix(String namespace, String prefix)
        throws XMLSecurityException {
        JavaUtils.checkRegisterPermission();
        setNamespacePrefix(namespace, prefix);
    }

    private static void setNamespacePrefix(String namespace, String prefix)
        throws XMLSecurityException {
        if (prefixMappings.containsValue(prefix)) {
            String storedPrefix = prefixMappings.get(namespace);
            if (!storedPrefix.equals(prefix)) {
                Object[] exArgs = { prefix, namespace, storedPrefix };

                throw new XMLSecurityException("prefix.AlreadyAssigned", exArgs);
            }
        }

        if (Constants.SignatureSpecNS.equals(namespace)) {
            XMLUtils.setDsPrefix(prefix);
        } else if (Constants.SignatureSpec11NS.equals(namespace)) {
            XMLUtils.setDs11Prefix(prefix);
        } else if (EncryptionConstants.EncryptionSpecNS.equals(namespace)) {
            XMLUtils.setXencPrefix(prefix);
        }
        prefixMappings.put(namespace, prefix);
    }

    /**
     * This method registers the default prefixes.
     */
    public static void registerDefaultPrefixes() throws XMLSecurityException {
        setNamespacePrefix("http://www.w3.org/2000/09/xmldsig#", "ds");
        setNamespacePrefix("http://www.w3.org/2001/04/xmlenc#", "xenc");
        setNamespacePrefix("http://www.w3.org/2009/xmlenc11#", "xenc11");
        setNamespacePrefix("http://www.xmlsecurity.org/experimental#", "experimental");
        setNamespacePrefix("http://www.w3.org/2002/04/xmldsig-filter2", "dsig-xpath-old");
        setNamespacePrefix("http://www.w3.org/2002/06/xmldsig-filter2", "dsig-xpath");
        setNamespacePrefix("http://www.w3.org/2001/10/xml-exc-c14n#", "ec");
        setNamespacePrefix(
            "http://www.nue.et-inf.uni-siegen.de/~geuer-pollmann/#xpathFilter", "xx"
        );
        setNamespacePrefix("http://www.w3.org/2009/xmldsig11#", "dsig11");
        setNamespacePrefix("http://www.w3.org/2001/04/xmldsig-more", "rfc4051");
        setNamespacePrefix("http://www.w3.org/2007/05/xmldsig-more#", "rfc6931");
        setNamespacePrefix("http://www.w3.org/2021/04/xmldsig-more#", "rfc9231");
    }

    /**
     * Method getDefaultPrefix
     *
     * @param namespace
     * @return the default prefix bind to this element.
     */
    public static String getDefaultPrefix(String namespace) {
        return prefixMappings.get(namespace);
    }

    /**
     * New value for the wrapped XML element that this object is a proxy for.
     *
     * @param elem  New element
     *
     * @see #getElement()
     */
    protected void setElement(Element elem) {
        wrappedElement = elem;
    }

    /**
     * Set a new value for the wrapped document that this object is a proxy for.
     *
     * @param doc New document object being wrapped.
     *
     * @see #getDocument()
     */
    protected void setDocument(Document doc) {
        wrappedDoc = doc;
    }

    protected String getLocalAttribute(String attrName) {
        return getElement().getAttributeNS(null, attrName);
    }

    protected void setLocalAttribute(String attrName, String value) {
        getElement().setAttributeNS(null, attrName, value);
    }

    protected void setLocalIdAttribute(String attrName, String value) {

        if (value != null) {
            Attr attr = getDocument().createAttributeNS(null, attrName);
            attr.setValue(value);
            getElement().setAttributeNodeNS(attr);
            getElement().setIdAttributeNode(attr, true);
        }
        else {
            getElement().removeAttributeNS(null, attrName);
        }
    }

    protected Node getFirstChild() {
        return getElement().getFirstChild();
    }

}