How can I extract xades signed content in Java xades4j?

Question

I have got xades XML as InputStream. I do not care if certyficates are valid, check sign, etc. I can't provide any CA or any other type of certificate storage/validation. What I need is just get documents embedded in xades file as streams or temporary files on disk so I can process them as they were plain files from disk. Could someone provide snippet that extracts embedded documents? TIA

Answer 1

To extract Base64-encoded signed content from XAdES signed file i use code like below. It doesn't use xades4j at all.

import java.io.InputStream;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import javax.xml.namespace.NamespaceContext;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathFactory;

import org.bouncycastle.util.encoders.Base64;
import org.w3c.dom.Document;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class Utils {

    /**
     * extract ds:Object from .xades file
     *  
     * @param xadesIn .xades file input stream
     * @return base64 decoded bytes
     * @throws Exception
     */
    public static byte[] extractContentFromXadesSignedFile(InputStream xadesIn) throws Exception {
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        dbf.setNamespaceAware(true);
        Document doc = dbf.newDocumentBuilder().parse(xadesIn);
        xadesIn.close();                
        XPathFactory xPathfactory = XPathFactory.newInstance();
        XPath xpath = xPathfactory.newXPath();
        xpath.setNamespaceContext(new SimpleNamespaceContext(new HashMap<String, String>() {{
            put("ds", "http://www.w3.org/2000/09/xmldsig#");
        }}));

        XPathExpression expr = xpath.compile("//ds:SignedInfo/ds:Reference");
        NodeList referenceNodes = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);

        /**
         * loop over all Reference nodes
         * i need to find Object node with Id that fits URI value of Reference
         */
        for(int i=0;i<referenceNodes.getLength();i++){
            Node referenceNode = referenceNodes.item(i);
            NamedNodeMap attributes = referenceNode.getAttributes(); 
            if(attributes != null) {
                Node uri = attributes.getNamedItem("URI");
                if(uri != null) {
                    String objectId = uri.getNodeValue();
                    XPathExpression expr2 = xpath.compile("//ds:Object[@Id='"+objectId.substring(1)+"']");
                    Node contentNode = (Node) expr2.evaluate(doc, XPathConstants.NODE);
                    if(contentNode != null) {
                        String base64 = contentNode.getFirstChild().getNodeValue();
                        return Base64.decode(base64);
                    }
                }
            }
        }

        return null;
    }

    /**
     * http://stackoverflow.com/a/6392700/404395
     */
    private static class SimpleNamespaceContext implements NamespaceContext {
        private final Map<String, String> PREF_MAP = new HashMap<String, String>();

        public SimpleNamespaceContext(final Map<String, String> prefMap) {
            PREF_MAP.putAll(prefMap);       
        }

        @Override
        public String getNamespaceURI(String prefix) {
            return PREF_MAP.get(prefix);
        }

        @Override
        public String getPrefix(String uri) {
            throw new UnsupportedOperationException();
        }

        @Override
        public Iterator getPrefixes(String uri) {
            throw new UnsupportedOperationException();
        }

    }       
}

Sample usage of that:

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;

import org.apache.commons.io.IOUtils;
import org.junit.Assert;
import org.junit.Test;

public class XadesExtractTest {

    @Test
    public void extract() throws Exception {
        InputStream in = XadesExtractTest.class.getClassLoader().getResourceAsStream("test.xades");
        byte[] bytes = Utils.extractContentFromXadesSignedFile(in);
        Assert.assertNotNull(bytes);
        in.close();
        ByteArrayInputStream bin = new ByteArrayInputStream(bytes);
        File f = File.createTempFile("test", ".zip");
        System.out.println(f.getAbsolutePath());
        FileOutputStream fout = new FileOutputStream(f);
        IOUtils.copy(bin, fout);
        bin.close();
        fout.close();
    }
}