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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.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Objects;

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

/**
 * Abstract superclass for Base-N input streams.
 *
 * @since 1.5
 */
public class BaseNCodecInputStream extends FilterInputStream {

    private final BaseNCodec baseNCodec;

    private final boolean doEncode;

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

    private final Context context = new Context();

    protected BaseNCodecInputStream(final InputStream input, final BaseNCodec baseNCodec, final boolean doEncode) {
        super(input);
        this.doEncode = doEncode;
        this.baseNCodec = baseNCodec;
    }

    /**
     * {@inheritDoc}
     *
     * @return {@code 0} if the {@link InputStream} has reached {@code EOF},
     * {@code 1} otherwise
     * @since 1.7
     */
    @Override
    public int available() throws IOException {
        // Note: the logic is similar to the InflaterInputStream:
        //       as long as we have not reached EOF, indicate that there is more
        //       data available. As we do not know for sure how much data is left,
        //       just return 1 as a safe guess.

        return context.eof ? 0 : 1;
    }

    /**
     * Marks the current position in this input stream.
     * The {@link #mark} method of {@link BaseNCodecInputStream} does nothing.
     *
     * @param readLimit the maximum limit of bytes that can be read before the mark position becomes invalid.
     * @see #markSupported()
     * @since 1.7
     */
    @Override
    public synchronized void mark(final int readLimit) {
        // noop
    }

    /**
     * {@inheritDoc}
     *
     * @return Always returns {@code false}
     */
    @Override
    public boolean markSupported() {
        return false; // not an easy job to support marks
    }

    /**
     * Reads one {@code byte} from this input stream.
     *
     * @return the byte as an integer in the range 0 to 255. Returns -1 if EOF has been reached.
     * @throws IOException
     *             if an I/O error occurs.
     */
    @Override
    public int read() throws IOException {
        int r = read(singleByte, 0, 1);
        while (r == 0) {
            r = read(singleByte, 0, 1);
        }
        if (r > 0) {
            final byte b = singleByte[0];
            return b < 0 ? 256 + b : b;
        }
        return EOF;
    }

    /**
     * Attempts to read {@code len} bytes into the specified {@code b} array starting at {@code offset}
     * from this InputStream.
     *
     * @param array
     *            destination byte array
     * @param offset
     *            where to start writing the bytes
     * @param len
     *            maximum number of bytes to read
     *
     * @return number of bytes read
     * @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 int read(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) {
            return 0;
        } else {
            int readLen = 0;
            /*
             Rationale for while-loop on (readLen == 0):
             -----
             Base32.readResults() usually returns > 0 or EOF (-1).  In the
             rare case where it returns 0, we just keep trying.

             This is essentially an undocumented contract for InputStream
             implementors that want their code to work properly with
             java.io.InputStreamReader, since the latter hates it when
             InputStream.read(byte[]) returns a zero.  Unfortunately our
             readResults() call must return 0 if a large amount of the data
             being decoded was non-base32, so this while-loop enables proper
             interop with InputStreamReader for that scenario.
             -----
             This is a fix for CODEC-101
            */
            while (readLen == 0) {
                if (!baseNCodec.hasData(context)) {
                    final byte[] buf = new byte[doEncode ? 4096 : 8192];
                    final int c = in.read(buf);
                    if (doEncode) {
                        baseNCodec.encode(buf, 0, c, context);
                    } else {
                        baseNCodec.decode(buf, 0, c, context);
                    }
                }
                readLen = baseNCodec.readResults(array, offset, len, context);
            }
            return readLen;
        }
    }

    /**
     * Repositions this stream to the position at the time the mark method was last called on this input stream.
     * 
     * The {@link #reset} method of {@link BaseNCodecInputStream} does nothing except throw an {@link IOException}.
     *
     * @throws IOException if this method is invoked
     * @since 1.7
     */
    @Override
    public synchronized void reset() throws IOException {
        throw new IOException("mark/reset not supported");
    }

    /**
     * {@inheritDoc}
     *
     * @throws IllegalArgumentException if the provided skip length is negative
     * @since 1.7
     */
    @Override
    public long skip(final long n) throws IOException {
        if (n < 0) {
            throw new IllegalArgumentException("Negative skip length: " + n);
        }

        // skip in chunks of 512 bytes
        final byte[] b = new byte[512];
        long todo = n;

        while (todo > 0) {
            int len = (int) Math.min(b.length, todo);
            len = this.read(b, 0, len);
            if (len == EOF) {
                break;
            }
            todo -= len;
        }

        return n - todo;
    }
}