    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 light weight {@link InputStream} that emulates a stream of a specified size.
    027 * <p>
    028 * This implementation provides a light weight object for testing with an {@link InputStream} where the contents don't matter.
    029 * </p>
    030 * <p>
    031 * One use case would be for testing the handling of large {@link InputStream} as it can emulate that scenario without the overhead of actually processing large
    032 * numbers of bytes - significantly speeding up test execution times.
    033 * </p>
    034 * <p>
    035 * This implementation returns zero from the method that reads a byte and leaves the array unchanged in the read methods that are passed a byte array. If
    036 * alternative data is required the {@code processByte()} and {@code processBytes()} methods can be implemented to generate data, for example:
    037 * </p>
    038 *
    039 * <pre>
    040 *  public class TestInputStream extends NullInputStream {
    041 *
    042 *      public TestInputStream(int size) {
    043 *          super(size);
    044 *      }
    045 *
    046 *      protected int processByte() {
    047 *          return ... // return required value here
    048 *      }
    049 *
    050 *      protected void processBytes(byte[] bytes, int offset, int length) {
    051 *          for (int i = offset; i &lt; length; i++) {
    052 *              bytes[i] = ... // set array value here
    053 *          }
    054 *      }
    055 *  }
    056 * </pre>
    057 *
    058 * @since 1.3
    059 */
    060public class NullInputStream extends AbstractInputStream {
    061
    062    /**
    063     * The singleton instance.
    064     *
    065     * <p>
    066     * Since instances hold state, call {@link #init()} to reuse.
    067     * </p>
    068     *
    069     * @since 2.12.0
    070     * @deprecated Not reusable without calling {@link #init()} to reset state.
    071     */
    072    @Deprecated
    073    public static final NullInputStream INSTANCE = new NullInputStream();
    074
    075    private final long size;
    076    private long position;
    077    private long mark = -1;
    078    private long readLimit;
    079    private final boolean throwEofException;
    080    private final boolean markSupported;
    081
    082    /**
    083     * Constructs an {@link InputStream} that emulates a size 0 stream which supports marking and does not throw EOFException.
    084     * <p>
    085     * This is an "empty" input stream.
    086     * </p>
    087     *
    088     * @since 2.7
    089     */
    090    public NullInputStream() {
    091        this(0, true, false);
    092    }
    093
    094    /**
    095     * Constructs an {@link InputStream} that emulates a specified size which supports marking and does not throw EOFException.
    096     *
    097     * @param size The size of the input stream to emulate.
    098     */
    099    public NullInputStream(final long size) {
    100        this(size, true, false);
    101    }
    102
    103    /**
    104     * Constructs an {@link InputStream} that emulates a specified size with option settings.
    105     *
    106     * @param size              The size of the input stream to emulate.
    107     * @param markSupported     Whether this instance will support the {@code mark()} functionality.
    108     * @param throwEofException Whether this implementation will throw an {@link EOFException} or return -1 when the end of file is reached.
    109     */
    110    public NullInputStream(final long size, final boolean markSupported, final boolean throwEofException) {
    111        this.size = size;
    112        this.markSupported = markSupported;
    113        this.throwEofException = throwEofException;
    114    }
    115
    116    @Override
    117    public int available() {
    118        if (isClosed()) {
    119            return 0;
    120        }
    121        final long avail = size - position;
    122        if (avail <= 0) {
    123            return 0;
    124        }
    125        if (avail > Integer.MAX_VALUE) {
    126            return Integer.MAX_VALUE;
    127        }
    128        return (int) avail;
    129    }
    130
    131    /**
    132     * Throws {@link EOFException} if {@code throwEofException} is enabled.
    133     *
    134     * @param message The {@link EOFException} message.
    135     * @throws EOFException Thrown if {@code throwEofException} is enabled.
    136     */
    137    private void checkThrowEof(final String message) throws EOFException {
    138        if (throwEofException) {
    139            throw new EOFException(message);
    140        }
    141    }
    142
    143    /**
    144     * Closes this input stream.
    145     *
    146     * @throws IOException If an error occurs.
    147     */
    148    @Override
    149    public void close() throws IOException {
    150        super.close();
    151        mark = -1;
    152    }
    153
    154    /**
    155     * Gets the current position.
    156     *
    157     * @return the current position.
    158     */
    159    public long getPosition() {
    160        return position;
    161    }
    162
    163    /**
    164     * Gets the size this {@link InputStream} emulates.
    165     *
    166     * @return The size of the input stream to emulate.
    167     */
    168    public long getSize() {
    169        return size;
    170    }
    171
    172    /**
    173     * Handles End of File.
    174     *
    175     * @return {@code -1} if {@code throwEofException} is set to {@code false}
    176     * @throws IOException if {@code throwEofException} is set to {@code true}.
    177     */
    178    private int handleEof() throws IOException {
    179        checkThrowEof("handleEof()");
    180        return EOF;
    181    }
    182
    183    /**
    184     * Initializes or re-initializes this instance for reuse.
    185     *
    186     * @return this instance.
    187     * @since 2.17.0
    188     */
    189    public NullInputStream init() {
    190        setClosed(false);
    191        position = 0;
    192        mark = -1;
    193        readLimit = 0;
    194        return this;
    195    }
    196
    197    /**
    198     * Marks the current position.
    199     *
    200     * @param readLimit The number of bytes before this marked position is invalid.
    201     * @throws UnsupportedOperationException if mark is not supported.
    202     */
    203    @Override
    204    public synchronized void mark(final int readLimit) {
    205        if (!markSupported) {
    206            throw UnsupportedOperationExceptions.mark();
    207        }
    208        mark = position;
    209        this.readLimit = readLimit;
    210    }
    211
    212    /**
    213     * Tests whether <em>mark</em> is supported.
    214     *
    215     * @return Whether <em>mark</em> is supported or not.
    216     */
    217    @Override
    218    public boolean markSupported() {
    219        return markSupported;
    220    }
    221
    222    /**
    223     * Returns a byte value for the {@code read()} method.
    224     * <p>
    225     * This implementation returns zero.
    226     *
    227     * @return This implementation always returns zero.
    228     */
    229    protected int processByte() {
    230        // do nothing - overridable by subclass
    231        return 0;
    232    }
    233
    234    /**
    235     * Processes the bytes for the {@code read(byte[], offset, length)} method.
    236     * <p>
    237     * This implementation leaves the byte array unchanged.
    238     * </p>
    239     *
    240     * @param bytes  The byte array
    241     * @param offset The offset to start at.
    242     * @param length The number of bytes.
    243     */
    244    protected void processBytes(final byte[] bytes, final int offset, final int length) {
    245        // do nothing - overridable by subclass
    246    }
    247
    248    /**
    249     * Reads a byte.
    250     *
    251     * @return Either The byte value returned by {@code processByte()} or {@code -1} if the end of file has been reached and {@code throwEofException} is set to
    252     *         {@code false}.
    253     * @throws EOFException if the end of file is reached and {@code throwEofException} is set to {@code true}.
    254     * @throws IOException  if trying to read past the end of file.
    255     */
    256    @Override
    257    public int read() throws IOException {
    258        checkOpen();
    259        if (position == size) {
    260            return handleEof();
    261        }
    262        position++;
    263        return processByte();
    264    }
    265
    266    /**
    267     * Reads some bytes into the specified array.
    268     *
    269     * @param bytes The byte array to read into
    270     * @return The number of bytes read or {@code -1} if the end of file has been reached and {@code throwEofException} is set to {@code false}.
    271     * @throws EOFException if the end of file is reached and {@code throwEofException} is set to {@code true}.
    272     * @throws IOException  if trying to read past the end of file.
    273     */
    274    @Override
    275    public int read(final byte[] bytes) throws IOException {
    276        return read(bytes, 0, bytes.length);
    277    }
    278
    279    /**
    280     * Reads the specified number bytes into an array.
    281     *
    282     * @param bytes  The byte array to read into.
    283     * @param offset The offset to start reading bytes into.
    284     * @param length The number of bytes to read.
    285     * @return The number of bytes read or {@code -1} if the end of file has been reached and {@code throwEofException} is set to {@code false}.
    286     * @throws EOFException if the end of file is reached and {@code throwEofException} is set to {@code true}.
    287     * @throws IOException  if trying to read past the end of file.
    288     */
    289    @Override
    290    public int read(final byte[] bytes, final int offset, final int length) throws IOException {
    291        if (bytes.length == 0 || length == 0) {
    292            return 0;
    293        }
    294        checkOpen();
    295        if (position == size) {
    296            return handleEof();
    297        }
    298        position += length;
    299        int returnLength = length;
    300        if (position > size) {
    301            returnLength = length - (int) (position - size);
    302            position = size;
    303        }
    304        processBytes(bytes, offset, returnLength);
    305        return returnLength;
    306    }
    307
    308    /**
    309     * Resets the stream to the point when mark was last called.
    310     *
    311     * @throws UnsupportedOperationException if mark is not supported.
    312     * @throws IOException                   If no position has been marked or the read limit has been exceeded since the last position was 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 + "] is no longer valid - passed the read limit [" + readLimit + "]");
    324        }
    325        position = mark;
    326        setClosed(false);
    327    }
    328
    329    /**
    330     * Skips a specified number of bytes.
    331     *
    332     * @param numberOfBytes The number of bytes to skip.
    333     * @return The number of bytes skipped or {@code -1} if the end of file has been reached and {@code throwEofException} is set to {@code false}.
    334     * @throws EOFException if the end of file is reached and {@code throwEofException} is set to {@code true}.
    335     * @throws IOException  if trying to read past the end of file.
    336     */
    337    @Override
    338    public long skip(final long numberOfBytes) throws IOException {
    339        if (isClosed()) {
    340            checkThrowEof("skip(long)");
    341            return EOF;
    342        }
    343        if (position == size) {
    344            return handleEof();
    345        }
    346        position += numberOfBytes;
    347        long returnLength = numberOfBytes;
    348        if (position > size) {
    349            returnLength = numberOfBytes - (position - size);
    350            position = size;
    351        }
    352        return returnLength;
    353    }
    354
    355}