SeekableInMemoryByteChannel.java

/*
 * 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.compress.utils;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.SeekableByteChannel;
import java.util.Arrays;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * A {@link SeekableByteChannel} implementation that wraps a byte[].
 * <p>
 * When this channel is used for writing an internal buffer grows to accommodate incoming data. The natural size limit is the value of {@link Integer#MAX_VALUE}
 * and it is not possible to {@link #position(long) set the position} or {@link #truncate truncate} to a value bigger than that. Internal buffer can be accessed
 * via {@link SeekableInMemoryByteChannel#array()}.
 * </p>
 *
 * @since 1.13
 * @NotThreadSafe
 */
public class SeekableInMemoryByteChannel implements SeekableByteChannel {

    private static final int NAIVE_RESIZE_LIMIT = Integer.MAX_VALUE >> 1;

    private byte[] data;
    private final AtomicBoolean closed = new AtomicBoolean();
    private int position, size;

    /**
     * Constructs a new instance using a default empty buffer.
     */
    public SeekableInMemoryByteChannel() {
        this(ByteUtils.EMPTY_BYTE_ARRAY);
    }

    /**
     * Constructs a new instance from a byte array.
     * <p>
     * This constructor is intended to be used with pre-allocated buffer or when reading from a given byte array.
     * </p>
     *
     * @param data input data or pre-allocated array.
     */
    public SeekableInMemoryByteChannel(final byte[] data) {
        this.data = data;
        this.size = data.length;
    }

    /**
     * Constructs a new instance from a size of storage to be allocated.
     * <p>
     * Creates a channel and allocates internal storage of a given size.
     * </p>
     *
     * @param size size of internal buffer to allocate, in bytes.
     */
    public SeekableInMemoryByteChannel(final int size) {
        this(new byte[size]);
    }

    /**
     * Obtains the array backing this channel.
     * <p>
     * NOTE: The returned buffer is not aligned with containing data, use {@link #size()} to obtain the size of data stored in the buffer.
     * </p>
     *
     * @return internal byte array.
     */
    public byte[] array() {
        return data;
    }

    @Override
    public void close() {
        closed.set(true);
    }

    private void ensureOpen() throws ClosedChannelException {
        if (!isOpen()) {
            throw new ClosedChannelException();
        }
    }

    @Override
    public boolean isOpen() {
        return !closed.get();
    }

    /**
     * Returns this channel's position.
     * <p>
     * This method violates the contract of {@link SeekableByteChannel#position()} as it will not throw any exception when invoked on a closed channel. Instead
     * it will return the position the channel had when close has been called.
     * </p>
     */
    @Override
    public long position() {
        return position;
    }

    @Override
    public SeekableByteChannel position(final long newPosition) throws IOException {
        ensureOpen();
        if (newPosition < 0L || newPosition > Integer.MAX_VALUE) {
            throw new IOException("Position has to be in range 0.. " + Integer.MAX_VALUE);
        }
        position = (int) newPosition;
        return this;
    }

    @Override
    public int read(final ByteBuffer buf) throws IOException {
        ensureOpen();
        int wanted = buf.remaining();
        final int possible = size - position;
        if (possible <= 0) {
            return -1;
        }
        if (wanted > possible) {
            wanted = possible;
        }
        buf.put(data, position, wanted);
        position += wanted;
        return wanted;
    }

    private void resize(final int newLength) {
        int len = data.length;
        if (len <= 0) {
            len = 1;
        }
        if (newLength < NAIVE_RESIZE_LIMIT) {
            while (len < newLength) {
                len <<= 1;
            }
        } else { // avoid overflow
            len = newLength;
        }
        data = Arrays.copyOf(data, len);
    }

    /**
     * Returns the current size of entity to which this channel is connected.
     * <p>
     * This method violates the contract of {@link SeekableByteChannel#size} as it will not throw any exception when invoked on a closed channel. Instead it
     * will return the size the channel had when close has been called.
     * </p>
     */
    @Override
    public long size() {
        return size;
    }

    /**
     * Truncates the entity, to which this channel is connected, to the given size.
     * <p>
     * This method violates the contract of {@link SeekableByteChannel#truncate} as it will not throw any exception when invoked on a closed channel.
     * </p>
     *
     * @throws IllegalArgumentException if size is negative or bigger than the maximum of a Java integer
     */
    @Override
    public SeekableByteChannel truncate(final long newSize) {
        if (newSize < 0L || newSize > Integer.MAX_VALUE) {
            throw new IllegalArgumentException("Size has to be in range 0.. " + Integer.MAX_VALUE);
        }
        if (size > newSize) {
            size = (int) newSize;
        }
        if (position > newSize) {
            position = (int) newSize;
        }
        return this;
    }

    @Override
    public int write(final ByteBuffer b) throws IOException {
        ensureOpen();
        int wanted = b.remaining();
        final int possibleWithoutResize = size - position;
        if (wanted > possibleWithoutResize) {
            final int newSize = position + wanted;
            if (newSize < 0) { // overflow
                resize(Integer.MAX_VALUE);
                wanted = Integer.MAX_VALUE - position;
            } else {
                resize(newSize);
            }
        }
        b.get(data, position, wanted);
        position += wanted;
        if (size < position) {
            size = position;
        }
        return wanted;
    }

}