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