    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;
    033    private int endOffset;
    034    private int currentNumberOfBytes;
    035
    036    /**
    037     * Creates a new instance with a reasonable default buffer size ({@link IOUtils#DEFAULT_BUFFER_SIZE}).
    038     */
    039    public CircularByteBuffer() {
    040        this(IOUtils.DEFAULT_BUFFER_SIZE);
    041    }
    042
    043    /**
    044     * Creates a new instance with the given buffer size.
    045     *
    046     * @param size the size of buffer to create
    047     */
    048    public CircularByteBuffer(final int size) {
    049        buffer = IOUtils.byteArray(size);
    050        startOffset = 0;
    051        endOffset = 0;
    052        currentNumberOfBytes = 0;
    053    }
    054
    055    /**
    056     * Adds a new byte to the buffer, which will eventually be returned by following
    057     * invocations of {@link #read()}.
    058     *
    059     * @param value The byte, which is being added to the buffer.
    060     * @throws IllegalStateException The buffer is full. Use {@link #hasSpace()},
    061     *                               or {@link #getSpace()}, to prevent this exception.
    062     */
    063    public void add(final byte value) {
    064        if (currentNumberOfBytes >= buffer.length) {
    065            throw new IllegalStateException("No space available");
    066        }
    067        buffer[endOffset] = value;
    068        ++currentNumberOfBytes;
    069        if (++endOffset == buffer.length) {
    070            endOffset = 0;
    071        }
    072    }
    073
    074    /**
    075     * Adds the given bytes to the buffer. This is the same as invoking {@link #add(byte)}
    076     * for the bytes at offsets {@code offset+0}, {@code offset+1}, ...,
    077     * {@code offset+length-1} of byte array {@code targetBuffer}.
    078     *
    079     * @param targetBuffer the buffer to copy
    080     * @param offset start offset
    081     * @param length length to copy
    082     * @throws IllegalStateException    The buffer doesn't have sufficient space. Use
    083     *                                  {@link #getSpace()} to prevent this exception.
    084     * @throws IllegalArgumentException Either of {@code offset}, or {@code length} is negative.
    085     * @throws NullPointerException     The byte array {@code pBuffer} is null.
    086     */
    087    public void add(final byte[] targetBuffer, final int offset, final int length) {
    088        Objects.requireNonNull(targetBuffer, "Buffer");
    089        if (offset < 0 || offset >= targetBuffer.length) {
    090            throw new IllegalArgumentException("Illegal offset: " + offset);
    091        }
    092        if (length < 0) {
    093            throw new IllegalArgumentException("Illegal length: " + length);
    094        }
    095        if (currentNumberOfBytes + length > buffer.length) {
    096            throw new IllegalStateException("No space available");
    097        }
    098        for (int i = 0; i < length; i++) {
    099            buffer[endOffset] = targetBuffer[offset + i];
    100            if (++endOffset == buffer.length) {
    101                endOffset = 0;
    102            }
    103        }
    104        currentNumberOfBytes += length;
    105    }
    106
    107    /**
    108     * Removes all bytes from the buffer.
    109     */
    110    public void clear() {
    111        startOffset = 0;
    112        endOffset = 0;
    113        currentNumberOfBytes = 0;
    114    }
    115
    116    /**
    117     * Returns the number of bytes, that are currently present in the buffer.
    118     *
    119     * @return the number of bytes
    120     */
    121    public int getCurrentNumberOfBytes() {
    122        return currentNumberOfBytes;
    123    }
    124
    125    /**
    126     * Returns the number of bytes, that can currently be added to the buffer.
    127     *
    128     * @return the number of bytes that can be added
    129     */
    130    public int getSpace() {
    131        return buffer.length - currentNumberOfBytes;
    132    }
    133
    134    /**
    135     * Returns, whether the buffer is currently holding, at least, a single byte.
    136     *
    137     * @return true if the buffer is not empty
    138     */
    139    public boolean hasBytes() {
    140        return currentNumberOfBytes > 0;
    141    }
    142
    143    /**
    144     * Returns, whether there is currently room for a single byte in the buffer.
    145     * Same as {@link #hasSpace(int) hasSpace(1)}.
    146     *
    147     * @return true if there is space for a byte
    148     * @see #hasSpace(int)
    149     * @see #getSpace()
    150     */
    151    public boolean hasSpace() {
    152        return currentNumberOfBytes < buffer.length;
    153    }
    154
    155    /**
    156     * Returns, whether there is currently room for the given number of bytes in the buffer.
    157     *
    158     * @param count the byte count
    159     * @return true if there is space for the given number of bytes
    160     * @see #hasSpace()
    161     * @see #getSpace()
    162     */
    163    public boolean hasSpace(final int count) {
    164        return currentNumberOfBytes + count <= buffer.length;
    165    }
    166
    167    /**
    168     * Returns, whether the next bytes in the buffer are exactly those, given by
    169     * {@code sourceBuffer}, {@code offset}, and {@code length}. No bytes are being
    170     * removed from the buffer. If the result is true, then the following invocations
    171     * of {@link #read()} are guaranteed to return exactly those bytes.
    172     *
    173     * @param sourceBuffer the buffer to compare against
    174     * @param offset start offset
    175     * @param length length to compare
    176     * @return True, if the next invocations of {@link #read()} will return the
    177     * bytes at offsets {@code pOffset}+0, {@code pOffset}+1, ...,
    178     * {@code pOffset}+{@code length}-1 of byte array {@code pBuffer}.
    179     * @throws IllegalArgumentException Either of {@code pOffset}, or {@code length} is negative.
    180     * @throws NullPointerException     The byte array {@code pBuffer} is null.
    181     */
    182    public boolean peek(final byte[] sourceBuffer, final int offset, final int length) {
    183        Objects.requireNonNull(sourceBuffer, "Buffer");
    184        if (offset < 0 || offset >= sourceBuffer.length) {
    185            throw new IllegalArgumentException("Illegal offset: " + offset);
    186        }
    187        if (length < 0 || length > buffer.length) {
    188            throw new IllegalArgumentException("Illegal length: " + length);
    189        }
    190        if (length < currentNumberOfBytes) {
    191            return false;
    192        }
    193        int localOffset = startOffset;
    194        for (int i = 0; i < length; i++) {
    195            if (buffer[localOffset] != sourceBuffer[i + offset]) {
    196                return false;
    197            }
    198            if (++localOffset == buffer.length) {
    199                localOffset = 0;
    200            }
    201        }
    202        return true;
    203    }
    204
    205    /**
    206     * Returns the next byte from the buffer, removing it at the same time, so
    207     * that following invocations won't return it again.
    208     *
    209     * @return The byte, which is being returned.
    210     * @throws IllegalStateException The buffer is empty. Use {@link #hasBytes()},
    211     *                               or {@link #getCurrentNumberOfBytes()}, to prevent this exception.
    212     */
    213    public byte read() {
    214        if (currentNumberOfBytes <= 0) {
    215            throw new IllegalStateException("No bytes available.");
    216        }
    217        final byte b = buffer[startOffset];
    218        --currentNumberOfBytes;
    219        if (++startOffset == buffer.length) {
    220            startOffset = 0;
    221        }
    222        return b;
    223    }
    224
    225    /**
    226     * Returns the given number of bytes from the buffer by storing them in
    227     * the given byte array at the given offset.
    228     *
    229     * @param targetBuffer The byte array, where to add bytes.
    230     * @param targetOffset The offset, where to store bytes in the byte array.
    231     * @param length The number of bytes to return.
    232     * @throws NullPointerException     The byte array {@code pBuffer} is null.
    233     * @throws IllegalArgumentException Either of {@code pOffset}, or {@code length} is negative,
    234     *                                  or the length of the byte array {@code targetBuffer} is too small.
    235     * @throws IllegalStateException    The buffer doesn't hold the given number
    236     *                                  of bytes. Use {@link #getCurrentNumberOfBytes()} to prevent this
    237     *                                  exception.
    238     */
    239    public void read(final byte[] targetBuffer, final int targetOffset, final int length) {
    240        Objects.requireNonNull(targetBuffer, "targetBuffer");
    241        if (targetOffset < 0 || targetOffset >= targetBuffer.length) {
    242            throw new IllegalArgumentException("Illegal offset: " + targetOffset);
    243        }
    244        if (length < 0 || length > buffer.length) {
    245            throw new IllegalArgumentException("Illegal length: " + length);
    246        }
    247        if (targetOffset + length > targetBuffer.length) {
    248            throw new IllegalArgumentException("The supplied byte array contains only "
    249                    + targetBuffer.length + " bytes, but offset, and length would require "
    250                    + (targetOffset + length - 1));
    251        }
    252        if (currentNumberOfBytes < length) {
    253            throw new IllegalStateException("Currently, there are only " + currentNumberOfBytes
    254                    + "in the buffer, not " + length);
    255        }
    256        int offset = targetOffset;
    257        for (int i = 0; i < length; i++) {
    258            targetBuffer[offset++] = buffer[startOffset];
    259            --currentNumberOfBytes;
    260            if (++startOffset == buffer.length) {
    261                startOffset = 0;
    262            }
    263        }
    264    }
    265}