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The Apache Commons Codec package contains simple encoder and decoders for various formats such as Base64 and Hexadecimal. In addition to these widely used encoders and decoders, the codec package also maintains a collection of phonetic encoding utilities.
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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.commons.codec.binary;

import static org.apache.commons.codec.binary.BaseNCodec.EOF;

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

import org.apache.commons.codec.binary.BaseNCodec.Context;

/**
 * Abstract superclass for Base-N output streams.
 * 
 * To write the EOF marker without closing the stream, call {@link #eof()} or use an Apache Commons IO CloseShieldOutputStream.
 * 
 *
 * @since 1.5
 */
public class BaseNCodecOutputStream extends FilterOutputStream {

    private final boolean doEncode;

    private final BaseNCodec baseNCodec;

    private final byte[] singleByte = new byte[1];

    private final Context context = new Context();

    /**
     * TODO should this be protected?
     *
     * @param output the underlying output or null.
     * @param basedCodec a BaseNCodec.
     * @param doEncode true to encode, false to decode, TODO should be an enum?
     */
    public BaseNCodecOutputStream(final OutputStream output, final BaseNCodec basedCodec, final boolean doEncode) {
        super(output);
        this.baseNCodec = basedCodec;
        this.doEncode = doEncode;
    }

    /**
     * Writes the specified {@code byte} to this output stream.
     *
     * @param i
     *            source byte
     * @throws IOException
     *             if an I/O error occurs.
     */
    @Override
    public void write(final int i) throws IOException {
        singleByte[0] = (byte) i;
        write(singleByte, 0, 1);
    }

    /**
     * Writes {@code len} bytes from the specified {@code b} array starting at {@code offset} to this
     * output stream.
     *
     * @param array
     *            source byte array
     * @param offset
     *            where to start reading the bytes
     * @param len
     *            maximum number of bytes to write
     *
     * @throws IOException
     *             if an I/O error occurs.
     * @throws NullPointerException
     *             if the byte array parameter is null
     * @throws IndexOutOfBoundsException
     *             if offset, len or buffer size are invalid
     */
    @Override
    public void write(final byte array[], final int offset, final int len) throws IOException {
        Objects.requireNonNull(array, "array");
        if (offset < 0 || len < 0) {
            throw new IndexOutOfBoundsException();
        } else if (offset > array.length || offset + len > array.length) {
            throw new IndexOutOfBoundsException();
        } else if (len > 0) {
            if (doEncode) {
                baseNCodec.encode(array, offset, len, context);
            } else {
                baseNCodec.decode(array, offset, len, context);
            }
            flush(false);
        }
    }

    /**
     * Flushes this output stream and forces any buffered output bytes to be written out to the stream. If propagate is
     * true, the wrapped stream will also be flushed.
     *
     * @param propagate
     *            boolean flag to indicate whether the wrapped OutputStream should also be flushed.
     * @throws IOException
     *             if an I/O error occurs.
     */
    private void flush(final boolean propagate) throws IOException {
        final int avail = baseNCodec.available(context);
        if (avail > 0) {
            final byte[] buf = new byte[avail];
            final int c = baseNCodec.readResults(buf, 0, avail, context);
            if (c > 0) {
                out.write(buf, 0, c);
            }
        }
        if (propagate) {
            out.flush();
        }
    }

    /**
     * Flushes this output stream and forces any buffered output bytes to be written out to the stream.
     *
     * @throws IOException
     *             if an I/O error occurs.
     */
    @Override
    public void flush() throws IOException {
        flush(true);
    }

    /**
     * Closes this output stream and releases any system resources associated with the stream.
     * 
     * To write the EOF marker without closing the stream, call {@link #eof()} or use an
     * Apache Commons IO CloseShieldOutputStream.
     * 
     *
     * @throws IOException
     *             if an I/O error occurs.
     */
    @Override
    public void close() throws IOException {
        eof();
        flush();
        out.close();
    }

    /**
     * Writes EOF.
     *
     * @throws IOException
     *             if an I/O error occurs.
     * @since 1.11
     */
    public void eof() throws IOException {
        // Notify encoder of EOF (-1).
        if (doEncode) {
            baseNCodec.encode(singleByte, 0, EOF, context);
        } else {
            baseNCodec.decode(singleByte, 0, EOF, context);
        }
    }

}