    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;
    018
    019import static org.apache.commons.io.IOUtils.EOF;
    020
    021import java.io.EOFException;
    022import java.io.IOException;
    023import java.io.InputStream;
    024
    025/**
    026 * A functional, light weight {@link InputStream} that emulates
    027 * a stream of a specified size.
    028 * <p>
    029 * This implementation provides a light weight
    030 * object for testing with an {@link InputStream}
    031 * where the contents don't matter.
    032 * </p>
    033 * <p>
    034 * One use case would be for testing the handling of
    035 * large {@link InputStream} as it can emulate that
    036 * scenario without the overhead of actually processing
    037 * large numbers of bytes - significantly speeding up
    038 * test execution times.
    039 * </p>
    040 * <p>
    041 * This implementation returns zero from the method that
    042 * reads a byte and leaves the array unchanged in the read
    043 * methods that are passed a byte array.
    044 * If alternative data is required the {@code processByte()} and
    045 * {@code processBytes()} methods can be implemented to generate
    046 * data, for example:
    047 * </p>
    048 *
    049 * <pre>
    050 *  public class TestInputStream extends NullInputStream {
    051 *      public TestInputStream(int size) {
    052 *          super(size);
    053 *      }
    054 *      protected int processByte() {
    055 *          return ... // return required value here
    056 *      }
    057 *      protected void processBytes(byte[] bytes, int offset, int length) {
    058 *          for (int i = offset; i &lt; length; i++) {
    059 *              bytes[i] = ... // set array value here
    060 *          }
    061 *      }
    062 *  }
    063 * </pre>
    064 *
    065 * @since 1.3
    066 */
    067public class NullInputStream extends InputStream {
    068
    069    /**
    070     * The singleton instance.
    071     *
    072     * @since 2.12.0
    073     */
    074    public static final NullInputStream INSTANCE = new NullInputStream();
    075
    076    private final long size;
    077    private long position;
    078    private long mark = -1;
    079    private long readlimit;
    080    private boolean eof;
    081    private final boolean throwEofException;
    082    private final boolean markSupported;
    083
    084    /**
    085     * Create an {@link InputStream} that emulates a size 0 stream
    086     * which supports marking and does not throw EOFException.
    087     *
    088     * @since 2.7
    089     */
    090    public NullInputStream() {
    091       this(0, true, false);
    092    }
    093
    094    /**
    095     * Create an {@link InputStream} that emulates a specified size
    096     * which supports marking and does not throw EOFException.
    097     *
    098     * @param size The size of the input stream to emulate.
    099     */
    100    public NullInputStream(final long size) {
    101       this(size, true, false);
    102    }
    103
    104    /**
    105     * Create an {@link InputStream} that emulates a specified
    106     * size with option settings.
    107     *
    108     * @param size The size of the input stream to emulate.
    109     * @param markSupported Whether this instance will support
    110     * the {@code mark()} functionality.
    111     * @param throwEofException Whether this implementation
    112     * will throw an {@link EOFException} or return -1 when the
    113     * end of file is reached.
    114     */
    115    public NullInputStream(final long size, final boolean markSupported, final boolean throwEofException) {
    116       this.size = size;
    117       this.markSupported = markSupported;
    118       this.throwEofException = throwEofException;
    119    }
    120
    121    /**
    122     * Return the number of bytes that can be read.
    123     *
    124     * @return The number of bytes that can be read.
    125     */
    126    @Override
    127    public int available() {
    128        final long avail = size - position;
    129        if (avail <= 0) {
    130            return 0;
    131        }
    132        if (avail > Integer.MAX_VALUE) {
    133            return Integer.MAX_VALUE;
    134        }
    135        return (int) avail;
    136    }
    137
    138    /**
    139     * Close this input stream - resets the internal state to
    140     * the initial values.
    141     *
    142     * @throws IOException If an error occurs.
    143     */
    144    @Override
    145    public void close() throws IOException {
    146        eof = false;
    147        position = 0;
    148        mark = -1;
    149    }
    150
    151    /**
    152     * Handle End of File.
    153     *
    154     * @return {@code -1} if {@code throwEofException} is
    155     * set to {@code false}
    156     * @throws EOFException if {@code throwEofException} is set
    157     * to {@code true}.
    158     */
    159    private int doEndOfFile() throws EOFException {
    160        eof = true;
    161        if (throwEofException) {
    162            throw new EOFException();
    163        }
    164        return EOF;
    165    }
    166
    167    /**
    168     * Return the current position.
    169     *
    170     * @return the current position.
    171     */
    172    public long getPosition() {
    173        return position;
    174    }
    175
    176    /**
    177     * Return the size this {@link InputStream} emulates.
    178     *
    179     * @return The size of the input stream to emulate.
    180     */
    181    public long getSize() {
    182        return size;
    183    }
    184
    185    /**
    186     * Mark the current position.
    187     *
    188     * @param readlimit The number of bytes before this marked position
    189     * is invalid.
    190     * @throws UnsupportedOperationException if mark is not supported.
    191     */
    192    @Override
    193    public synchronized void mark(final int readlimit) {
    194        if (!markSupported) {
    195            throw UnsupportedOperationExceptions.mark();
    196        }
    197        mark = position;
    198        this.readlimit = readlimit;
    199    }
    200
    201    /**
    202     * Indicates whether <i>mark</i> is supported.
    203     *
    204     * @return Whether <i>mark</i> is supported or not.
    205     */
    206    @Override
    207    public boolean markSupported() {
    208        return markSupported;
    209    }
    210
    211    /**
    212     * Return a byte value for the  {@code read()} method.
    213     * <p>
    214     * This implementation returns zero.
    215     *
    216     * @return This implementation always returns zero.
    217     */
    218    protected int processByte() {
    219        // do nothing - overridable by subclass
    220        return 0;
    221    }
    222
    223    /**
    224     * Process the bytes for the {@code read(byte[], offset, length)}
    225     * method.
    226     * <p>
    227     * This implementation leaves the byte array unchanged.
    228     *
    229     * @param bytes The byte array
    230     * @param offset The offset to start at.
    231     * @param length The number of bytes.
    232     */
    233    protected void processBytes(final byte[] bytes, final int offset, final int length) {
    234        // do nothing - overridable by subclass
    235    }
    236
    237    /**
    238     * Read a byte.
    239     *
    240     * @return Either The byte value returned by {@code processByte()}
    241     * or {@code -1} if the end of file has been reached and
    242     * {@code throwEofException} is set to {@code false}.
    243     * @throws EOFException if the end of file is reached and
    244     * {@code throwEofException} is set to {@code true}.
    245     * @throws IOException if trying to read past the end of file.
    246     */
    247    @Override
    248    public int read() throws IOException {
    249        if (eof) {
    250            throw new IOException("Read after end of file");
    251        }
    252        if (position == size) {
    253            return doEndOfFile();
    254        }
    255        position++;
    256        return processByte();
    257    }
    258
    259    /**
    260     * Read some bytes into the specified array.
    261     *
    262     * @param bytes The byte array to read into
    263     * @return The number of bytes read or {@code -1}
    264     * if the end of file has been reached and
    265     * {@code throwEofException} is set to {@code false}.
    266     * @throws EOFException if the end of file is reached and
    267     * {@code throwEofException} is set to {@code true}.
    268     * @throws IOException if trying to read past the end of file.
    269     */
    270    @Override
    271    public int read(final byte[] bytes) throws IOException {
    272        return read(bytes, 0, bytes.length);
    273    }
    274
    275    /**
    276     * Read the specified number bytes into an array.
    277     *
    278     * @param bytes The byte array to read into.
    279     * @param offset The offset to start reading bytes into.
    280     * @param length The number of bytes to read.
    281     * @return The number of bytes read or {@code -1}
    282     * if the end of file has been reached and
    283     * {@code throwEofException} is set to {@code false}.
    284     * @throws EOFException if the end of file is reached and
    285     * {@code throwEofException} is set to {@code true}.
    286     * @throws IOException if trying to read past the end of file.
    287     */
    288    @Override
    289    public int read(final byte[] bytes, final int offset, final int length) throws IOException {
    290        if (eof) {
    291            throw new IOException("Read after end of file");
    292        }
    293        if (position == size) {
    294            return doEndOfFile();
    295        }
    296        position += length;
    297        int returnLength = length;
    298        if (position > size) {
    299            returnLength = length - (int)(position - size);
    300            position = size;
    301        }
    302        processBytes(bytes, offset, returnLength);
    303        return returnLength;
    304    }
    305
    306    /**
    307     * Reset the stream to the point when mark was last called.
    308     *
    309     * @throws UnsupportedOperationException if mark is not supported.
    310     * @throws IOException If no position has been marked
    311     * or the read limit has been exceeded since the last position was
    312     * marked.
    313     */
    314    @Override
    315    public synchronized void reset() throws IOException {
    316        if (!markSupported) {
    317            throw UnsupportedOperationExceptions.reset();
    318        }
    319        if (mark < 0) {
    320            throw new IOException("No position has been marked");
    321        }
    322        if (position > mark + readlimit) {
    323            throw new IOException("Marked position [" + mark +
    324                    "] is no longer valid - passed the read limit [" +
    325                    readlimit + "]");
    326        }
    327        position = mark;
    328        eof = false;
    329    }
    330
    331    /**
    332     * Skip a specified number of bytes.
    333     *
    334     * @param numberOfBytes The number of bytes to skip.
    335     * @return The number of bytes skipped or {@code -1}
    336     * if the end of file has been reached and
    337     * {@code throwEofException} is set to {@code false}.
    338     * @throws EOFException if the end of file is reached and
    339     * {@code throwEofException} is set to {@code true}.
    340     * @throws IOException if trying to read past the end of file.
    341     */
    342    @Override
    343    public long skip(final long numberOfBytes) throws IOException {
    344        if (eof) {
    345            throw new IOException("Skip after end of file");
    346        }
    347        if (position == size) {
    348            return doEndOfFile();
    349        }
    350        position += numberOfBytes;
    351        long returnLength = numberOfBytes;
    352        if (position > size) {
    353            returnLength = numberOfBytes - (position - size);
    354            position = size;
    355        }
    356        return returnLength;
    357    }
    358
    359}