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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.
 */
/*
 * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
 */
/*
 * $Id: DigesterOutputStream.java,v 1.5 2005/12/20 20:02:39 mullan Exp $
 */
package org.apache.jcp.xml.dsig.internal;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.MessageDigest;

import org.apache.xml.security.utils.UnsyncByteArrayOutputStream;

/**
 * This class has been modified slightly to use java.security.MessageDigest
 * objects as input, rather than 
 * org.apache.xml.security.algorithms.MessageDigestAlgorithm objects.
 * It also optionally caches the input bytes.
 *
 * @author raul
 * @author Sean Mullan
 */
public class DigesterOutputStream extends OutputStream {
    private static org.slf4j.Logger log = 
        org.slf4j.LoggerFactory.getLogger(DigesterOutputStream.class);
    
    private final boolean buffer;
    private UnsyncByteArrayOutputStream bos;
    private final MessageDigest md;

    /**
     * Creates a DigesterOutputStream.
     *
     * @param md the MessageDigest
     */
    public DigesterOutputStream(MessageDigest md) {
        this(md, false);
    }

    /**
     * Creates a DigesterOutputStream.
     *
     * @param md the MessageDigest
     * @param buffer if true, caches the input bytes
     */
    public DigesterOutputStream(MessageDigest md, boolean buffer) {
        this.md = md;
        this.buffer = buffer;
        if (buffer) {
            bos = new UnsyncByteArrayOutputStream();
        }
    }

    public void write(int input) {
        if (buffer) {
            bos.write(input);
        }
        md.update((byte)input);
    }
    
    @Override
    public void write(byte[] input, int offset, int len) {
        if (buffer) {
            bos.write(input, offset, len);
        }
        if (log.isDebugEnabled()) {
            log.debug("Pre-digested input:");
            StringBuilder sb = new StringBuilder(len);
            for (int i = offset; i < (offset + len); i++) {
                sb.append((char)input[i]);
            }
            log.debug(sb.toString());
        }
        md.update(input, offset, len);
    }
    
    /**
     * @return the digest value 
     */
    public byte[] getDigestValue() {
         return md.digest();   
    }

    /**
     * @return an input stream containing the cached bytes, or
     *    null if not cached
     */
    public InputStream getInputStream() {
        if (buffer) {
            return new ByteArrayInputStream(bos.toByteArray());
        } else {
            return null;
        }
    }
    
    @Override
    public void close() throws IOException {
        if (buffer) {
            bos.close();
        }
    }
}