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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.stax.impl.util;

import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;

/**
 * Trimms the start and the end of a stream
 *
 * @author $Author: coheigea $
 * @version $Revision: 1513098 $ $Date: 2013-08-12 11:28:33 +0100 (Mon, 12 Aug 2013) $
 */
public class TrimmerOutputStream extends FilterOutputStream {

    private byte[] buffer;
    private int bufferedCount;

    private int preTrimmed = 0;
    private int startTrimLength;
    private int endTrimLength;

    public TrimmerOutputStream(OutputStream out, int bufferSize, int startTrimLength, int endTrimLength) {
        super(out);
        if (bufferSize <= 0) {
            throw new IllegalArgumentException("bufferSize <= 0");
        }
        if (bufferSize < endTrimLength) {
            throw new IllegalArgumentException("bufferSize < endTrimLength");
        }
        this.buffer = new byte[bufferSize];
        this.startTrimLength = startTrimLength;
        this.endTrimLength = endTrimLength;
    }

    private void flushBuffer() throws IOException {
        if (bufferedCount >= endTrimLength) {
            //write all but the possible end (endTrimLength)
            out.write(buffer, 0, bufferedCount - endTrimLength);
            System.arraycopy(buffer, bufferedCount - endTrimLength, buffer, 0, endTrimLength);
            bufferedCount = endTrimLength;
        }
    }

    @Override
    public void write(int b) throws IOException {
        if (preTrimmed < startTrimLength) {
            //discard byte
            preTrimmed++;
            return;
        }
        if (bufferedCount >= buffer.length) {
            flushBuffer();
        }
        buffer[bufferedCount++] = (byte) b;
    }

    @Override
    public void write(byte[] b) throws IOException {
        write(b, 0, b.length);
    }

    @Override
    public void write(byte[] b, int off, int len) throws IOException {
        if (preTrimmed < startTrimLength) {
            int missingBytes = startTrimLength - preTrimmed;
            if (missingBytes >= len) {
                //discard bytes
                preTrimmed += len;
                return;
            }
            len -= missingBytes;
            off += missingBytes;
            preTrimmed += missingBytes;
        }

        if (len >= (buffer.length - bufferedCount)) {
            out.write(buffer, 0, bufferedCount);
            out.write(b, off, len - endTrimLength);
            System.arraycopy(b, off + len - endTrimLength, buffer, 0, endTrimLength);
            bufferedCount = endTrimLength;
            return;
        }

        System.arraycopy(b, off, buffer, bufferedCount, len);
        bufferedCount += len;
    }

    @Override
    public void flush() throws IOException {
        flushBuffer();
        out.flush();
    }
}