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The TwelveMonkeys Core library. Contains common utility classes.
There is a newer version: 2.3
/*
 * Copyright (c) 2008, Harald Kuhr
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name "TwelveMonkeys" nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.twelvemonkeys.io.enc;

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

/**
 * An {@code InputStream} that provides on-the-fly decoding from an underlying
 * stream.
 * 
 * @see EncoderStream
 * @see Decoder
 *
 * @author Harald Kuhr
 * @version $Id: //depot/branches/personal/haraldk/twelvemonkeys/release-2/twelvemonkeys-core/src/main/java/com/twelvemonkeys/io/enc/DecoderStream.java#2 $
 */
public final class DecoderStream extends FilterInputStream {

    protected int mBufferPos;
    protected int mBufferLimit;
    protected final byte[] mBuffer;
    protected final Decoder mDecoder;

    /**
     * Creates a new decoder stream and chains it to the
     * input stream specified by the {@code pStream} argument.
     *
     * @param pStream the underlying input stream.
     * @param pDecoder the decoder that will be used to decode the underlying stream
     *
     * @see java.io.FilterInputStream#in
     */
    public DecoderStream(final InputStream pStream, final Decoder pDecoder) {
        super(pStream);
        mDecoder = pDecoder;
        mBuffer = new byte[1024];
        mBufferPos = 0;
        mBufferLimit = 0;
    }

    public int available() throws IOException {
        return mBufferLimit - mBufferPos + super.available();
    }

    public int read() throws IOException {
        if (mBufferPos == mBufferLimit) {
            mBufferLimit = fill();
        }

        if (mBufferLimit < 0) {
            return -1;
        }

        return mBuffer[mBufferPos++] & 0xff;
    }

    public int read(final byte pBytes[]) throws IOException {
        return read(pBytes, 0, pBytes.length);
    }

    public int read(final byte pBytes[], final int pOffset, final int pLength) throws IOException {
        if (pBytes == null) {
            throw new NullPointerException();
        }
        else if ((pOffset < 0) || (pOffset > pBytes.length) || (pLength < 0) ||
                ((pOffset + pLength) > pBytes.length) || ((pOffset + pLength) < 0)) {
            throw new IndexOutOfBoundsException("bytes.length=" + pBytes.length + " offset=" + pOffset + " length=" + pLength);
        }
        else if (pLength == 0) {
            return 0;
        }

        // End of file?
        if ((mBufferLimit - mBufferPos) < 0) {
            return -1;
        }

        // Read until we have read pLength bytes, or have reached EOF
        int count = 0;
        int off = pOffset;

        while (pLength > count) {
            int avail = mBufferLimit - mBufferPos;

            if (avail <= 0) {
                mBufferLimit = fill();

                if (mBufferLimit < 0) {
                    break;
                }
            }

            // Copy as many bytes as possible
            int dstLen = Math.min(pLength - count, avail);
            System.arraycopy(mBuffer, mBufferPos, pBytes, off, dstLen);

            mBufferPos += dstLen;

            // Update offset (rest)
            off += dstLen;

            // Inrease count
            count += dstLen;
        }

        return count;
    }

    public long skip(final long pLength) throws IOException {
        // End of file?
        if (mBufferLimit - mBufferPos < 0) {
            return 0;
        }

        // Skip until we have skipped pLength bytes, or have reached EOF
        long total = 0;
        
        while (total < pLength) {
            int avail = mBufferLimit - mBufferPos;

            if (avail == 0) {
                mBufferLimit = fill();

                if (mBufferLimit < 0) {
                    break;
                }
            }

            // NOTE: Skipped can never be more than avail, which is
            // an int, so the cast is safe
            int skipped = (int) Math.min(pLength - total, avail);

            mBufferPos += skipped; // Just skip these bytes
            total += skipped;
        }

        return total;
    }

    /**
     * Fills the buffer, by decoding data from the underlying input stream.
     *
     * @return the number of bytes decoded, or {@code -1} if the end of the
     * file is reached
     *
     * @throws IOException if an I/O error occurs
     */
    protected int fill() throws IOException {
        int read = mDecoder.decode(in, mBuffer);

        // TODO: Enforce this in test case, leave here to aid debugging
        if (read > mBuffer.length) {
            throw new AssertionError(
                    String.format(
                            "Decode beyond buffer (%d): %d (using %s decoder)",
                            mBuffer.length, read, mDecoder.getClass().getName()
                    )
            );
        }

        mBufferPos = 0;

        if (read == 0) {
            return -1;
        }

        return read;
    }
}