    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.io.input.buffer;
    018
    019import java.util.Objects;
    020
    021import org.apache.commons.io.IOUtils;
    022
    023/**
    024 * A buffer, which doesn't need reallocation of byte arrays, because it
    025 * reuses a single byte array. This works particularly well, if reading
    026 * from the buffer takes place at the same time than writing to. Such is the
    027 * case, for example, when using the buffer within a filtering input stream,
    028 * like the {@link CircularBufferInputStream}.
    029 */
    030public class CircularByteBuffer {
    031    private final byte[] buffer;
    032    private int startOffset, endOffset, currentNumberOfBytes;
    033
    034    /**
    035     * Creates a new instance with the given buffer size.
    036     *
    037     * @param pSize the size of buffer to create
    038     */
    039    public CircularByteBuffer(final int pSize) {
    040        buffer = new byte[pSize];
    041        startOffset = 0;
    042        endOffset = 0;
    043        currentNumberOfBytes = 0;
    044    }
    045
    046    /**
    047     * Creates a new instance with a reasonable default buffer size ({@link IOUtils#DEFAULT_BUFFER_SIZE}).
    048     */
    049    public CircularByteBuffer() {
    050        this(IOUtils.DEFAULT_BUFFER_SIZE);
    051    }
    052
    053    /**
    054     * Returns the next byte from the buffer, removing it at the same time, so
    055     * that following invocations won't return it again.
    056     *
    057     * @return The byte, which is being returned.
    058     * @throws IllegalStateException The buffer is empty. Use {@link #hasBytes()},
    059     *                               or {@link #getCurrentNumberOfBytes()}, to prevent this exception.
    060     */
    061    public byte read() {
    062        if (currentNumberOfBytes <= 0) {
    063            throw new IllegalStateException("No bytes available.");
    064        }
    065        final byte b = buffer[startOffset];
    066        --currentNumberOfBytes;
    067        if (++startOffset == buffer.length) {
    068            startOffset = 0;
    069        }
    070        return b;
    071    }
    072
    073    /**
    074     * Returns the given number of bytes from the buffer by storing them in
    075     * the given byte array at the given offset.
    076     *
    077     * @param targetBuffer The byte array, where to add bytes.
    078     * @param targetOffset The offset, where to store bytes in the byte array.
    079     * @param length The number of bytes to return.
    080     * @throws NullPointerException     The byte array {@code pBuffer} is null.
    081     * @throws IllegalArgumentException Either of {@code pOffset}, or {@code pLength} is negative,
    082     *                                  or the length of the byte array {@code pBuffer} is too small.
    083     * @throws IllegalStateException    The buffer doesn't hold the given number
    084     *                                  of bytes. Use {@link #getCurrentNumberOfBytes()} to prevent this
    085     *                                  exception.
    086     */
    087    public void read(final byte[] targetBuffer, final int targetOffset, final int length) {
    088        Objects.requireNonNull(targetBuffer);
    089        if (targetOffset < 0 || targetOffset >= targetBuffer.length) {
    090            throw new IllegalArgumentException("Invalid offset: " + targetOffset);
    091        }
    092        if (length < 0 || length > buffer.length) {
    093            throw new IllegalArgumentException("Invalid length: " + length);
    094        }
    095        if (targetOffset + length > targetBuffer.length) {
    096            throw new IllegalArgumentException("The supplied byte array contains only "
    097                    + targetBuffer.length + " bytes, but offset, and length would require "
    098                    + (targetOffset + length - 1));
    099        }
    100        if (currentNumberOfBytes < length) {
    101            throw new IllegalStateException("Currently, there are only " + currentNumberOfBytes
    102                    + "in the buffer, not " + length);
    103        }
    104        int offset = targetOffset;
    105        for (int i = 0; i < length; i++) {
    106            targetBuffer[offset++] = buffer[startOffset];
    107            --currentNumberOfBytes;
    108            if (++startOffset == buffer.length) {
    109                startOffset = 0;
    110            }
    111        }
    112    }
    113
    114    /**
    115     * Adds a new byte to the buffer, which will eventually be returned by following
    116     * invocations of {@link #read()}.
    117     *
    118     * @param value The byte, which is being added to the buffer.
    119     * @throws IllegalStateException The buffer is full. Use {@link #hasSpace()},
    120     *                               or {@link #getSpace()}, to prevent this exception.
    121     */
    122    public void add(final byte value) {
    123        if (currentNumberOfBytes >= buffer.length) {
    124            throw new IllegalStateException("No space available");
    125        }
    126        buffer[endOffset] = value;
    127        ++currentNumberOfBytes;
    128        if (++endOffset == buffer.length) {
    129            endOffset = 0;
    130        }
    131    }
    132
    133    /**
    134     * Returns, whether the next bytes in the buffer are exactly those, given by
    135     * {@code sourceBuffer}, {@code offset}, and {@code length}. No bytes are being
    136     * removed from the buffer. If the result is true, then the following invocations
    137     * of {@link #read()} are guaranteed to return exactly those bytes.
    138     *
    139     * @param sourceBuffer the buffer to compare against
    140     * @param offset start offset
    141     * @param length length to compare
    142     * @return True, if the next invocations of {@link #read()} will return the
    143     * bytes at offsets {@code pOffset}+0, {@code pOffset}+1, ...,
    144     * {@code pOffset}+{@code pLength}-1 of byte array {@code pBuffer}.
    145     * @throws IllegalArgumentException Either of {@code pOffset}, or {@code pLength} is negative.
    146     * @throws NullPointerException     The byte array {@code pBuffer} is null.
    147     */
    148    public boolean peek(final byte[] sourceBuffer, final int offset, final int length) {
    149        Objects.requireNonNull(sourceBuffer, "Buffer");
    150        if (offset < 0 || offset >= sourceBuffer.length) {
    151            throw new IllegalArgumentException("Invalid offset: " + offset);
    152        }
    153        if (length < 0 || length > buffer.length) {
    154            throw new IllegalArgumentException("Invalid length: " + length);
    155        }
    156        if (length < currentNumberOfBytes) {
    157            return false;
    158        }
    159        int localOffset = startOffset;
    160        for (int i = 0; i < length; i++) {
    161            if (buffer[localOffset] != sourceBuffer[i + offset]) {
    162                return false;
    163            }
    164            if (++localOffset == buffer.length) {
    165                localOffset = 0;
    166            }
    167        }
    168        return true;
    169    }
    170
    171    /**
    172     * Adds the given bytes to the buffer. This is the same as invoking {@link #add(byte)}
    173     * for the bytes at offsets {@code offset+0}, {@code offset+1}, ...,
    174     * {@code offset+length-1} of byte array {@code targetBuffer}.
    175     *
    176     * @param targetBuffer the buffer to copy
    177     * @param offset start offset
    178     * @param length length to copy
    179     * @throws IllegalStateException    The buffer doesn't have sufficient space. Use
    180     *                                  {@link #getSpace()} to prevent this exception.
    181     * @throws IllegalArgumentException Either of {@code pOffset}, or {@code pLength} is negative.
    182     * @throws NullPointerException     The byte array {@code pBuffer} is null.
    183     */
    184    public void add(final byte[] targetBuffer, final int offset, final int length) {
    185        Objects.requireNonNull(targetBuffer, "Buffer");
    186        if (offset < 0 || offset >= targetBuffer.length) {
    187            throw new IllegalArgumentException("Invalid offset: " + offset);
    188        }
    189        if (length < 0) {
    190            throw new IllegalArgumentException("Invalid length: " + length);
    191        }
    192        if (currentNumberOfBytes + length > buffer.length) {
    193            throw new IllegalStateException("No space available");
    194        }
    195        for (int i = 0; i < length; i++) {
    196            buffer[endOffset] = targetBuffer[offset + i];
    197            if (++endOffset == buffer.length) {
    198                endOffset = 0;
    199            }
    200        }
    201        currentNumberOfBytes += length;
    202    }
    203
    204    /**
    205     * Returns, whether there is currently room for a single byte in the buffer.
    206     * Same as {@link #hasSpace(int) hasSpace(1)}.
    207     *
    208     * @return true if there is space for a byte
    209     * @see #hasSpace(int)
    210     * @see #getSpace()
    211     */
    212    public boolean hasSpace() {
    213        return currentNumberOfBytes < buffer.length;
    214    }
    215
    216    /**
    217     * Returns, whether there is currently room for the given number of bytes in the buffer.
    218     *
    219     * @param count the byte count
    220     * @return true if there is space for the given number of bytes
    221     * @see #hasSpace()
    222     * @see #getSpace()
    223     */
    224    public boolean hasSpace(final int count) {
    225        return currentNumberOfBytes + count <= buffer.length;
    226    }
    227
    228    /**
    229     * Returns, whether the buffer is currently holding, at least, a single byte.
    230     *
    231     * @return true if the buffer is not empty
    232     */
    233    public boolean hasBytes() {
    234        return currentNumberOfBytes > 0;
    235    }
    236
    237    /**
    238     * Returns the number of bytes, that can currently be added to the buffer.
    239     *
    240     * @return the number of bytes that can be added
    241     */
    242    public int getSpace() {
    243        return buffer.length - currentNumberOfBytes;
    244    }
    245
    246    /**
    247     * Returns the number of bytes, that are currently present in the buffer.
    248     *
    249     * @return the number of bytes
    250     */
    251    public int getCurrentNumberOfBytes() {
    252        return currentNumberOfBytes;
    253    }
    254
    255    /**
    256     * Removes all bytes from the buffer.
    257     */
    258    public void clear() {
    259        startOffset = 0;
    260        endOffset = 0;
    261        currentNumberOfBytes = 0;
    262    }
    263}