    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.IOException;
    022import java.io.InputStream;
    023import java.util.ArrayList;
    024import java.util.Arrays;
    025import java.util.List;
    026
    027import org.apache.commons.io.IOUtils;
    028import org.apache.commons.io.function.IOConsumer;
    029
    030/**
    031 * The {@link ObservableInputStream} allows, that an InputStream may be consumed by other receivers, apart from the
    032 * thread, which is reading it. The other consumers are implemented as instances of {@link Observer}.
    033 * <p>
    034 * A typical application may be the generation of a {@link java.security.MessageDigest} on the fly.
    035 * </p>
    036 * <p>
    037 * <em>Note</em>: The {@link ObservableInputStream} is <em>not</em> thread safe, as instances of InputStream usually
    038 * aren't. If you must access the stream from multiple threads, then synchronization, locking, or a similar means must
    039 * be used.
    040 * </p>
    041 *
    042 * @see MessageDigestInputStream
    043 */
    044public class ObservableInputStream extends ProxyInputStream {
    045
    046    /**
    047     * Abstracts observer callback for {@link ObservableInputStream}s.
    048     */
    049    public static abstract class Observer {
    050
    051        /**
    052         * Called to indicate that the {@link ObservableInputStream} has been closed.
    053         *
    054         * @throws IOException if an I/O error occurs.
    055         */
    056        @SuppressWarnings("unused") // Possibly thrown from subclasses.
    057        public void closed() throws IOException {
    058            // noop
    059        }
    060
    061        /**
    062         * Called to indicate that {@link InputStream#read(byte[])}, or {@link InputStream#read(byte[], int, int)} have
    063         * been called, and are about to invoke data.
    064         *
    065         * @param buffer The byte array, which has been passed to the read call, and where data has been stored.
    066         * @param offset The offset within the byte array, where data has been stored.
    067         * @param length The number of bytes, which have been stored in the byte array.
    068         * @throws IOException if an I/O error occurs.
    069         */
    070        @SuppressWarnings("unused") // Possibly thrown from subclasses.
    071        public void data(final byte[] buffer, final int offset, final int length) throws IOException {
    072            // noop
    073        }
    074
    075        /**
    076         * Called to indicate, that {@link InputStream#read()} has been invoked on the {@link ObservableInputStream},
    077         * and will return a value.
    078         *
    079         * @param value The value, which is being returned. This will never be -1 (EOF), because, in that case,
    080         *        {@link #finished()} will be invoked instead.
    081         * @throws IOException if an I/O error occurs.
    082         */
    083        @SuppressWarnings("unused") // Possibly thrown from subclasses.
    084        public void data(final int value) throws IOException {
    085            // noop
    086        }
    087
    088        /**
    089         * Called to indicate that an error occurred on the underlying stream.
    090         *
    091         * @param exception the exception to throw
    092         * @throws IOException if an I/O error occurs.
    093         */
    094        public void error(final IOException exception) throws IOException {
    095            throw exception;
    096        }
    097
    098        /**
    099         * Called to indicate that EOF has been seen on the underlying stream. This method may be called multiple times,
    100         * if the reader keeps invoking either of the read methods, and they will consequently keep returning EOF.
    101         *
    102         * @throws IOException if an I/O error occurs.
    103         */
    104        @SuppressWarnings("unused") // Possibly thrown from subclasses.
    105        public void finished() throws IOException {
    106            // noop
    107        }
    108    }
    109
    110    private final List<Observer> observers;
    111
    112    /**
    113     * Constructs a new ObservableInputStream for the given InputStream.
    114     *
    115     * @param inputStream the input stream to observe.
    116     */
    117    public ObservableInputStream(final InputStream inputStream) {
    118        this(inputStream, new ArrayList<>());
    119    }
    120
    121    /**
    122     * Constructs a new ObservableInputStream for the given InputStream.
    123     *
    124     * @param inputStream the input stream to observe.
    125     * @param observers List of observer callbacks.
    126     */
    127    private ObservableInputStream(final InputStream inputStream, final List<Observer> observers) {
    128        super(inputStream);
    129        this.observers = observers;
    130    }
    131
    132    /**
    133     * Constructs a new ObservableInputStream for the given InputStream.
    134     *
    135     * @param inputStream the input stream to observe.
    136     * @param observers List of observer callbacks.
    137     * @since 2.9.0
    138     */
    139    public ObservableInputStream(final InputStream inputStream, final Observer... observers) {
    140        this(inputStream, Arrays.asList(observers));
    141    }
    142
    143    /**
    144     * Adds an Observer.
    145     *
    146     * @param observer the observer to add.
    147     */
    148    public void add(final Observer observer) {
    149        observers.add(observer);
    150    }
    151
    152    @Override
    153    public void close() throws IOException {
    154        IOException ioe = null;
    155        try {
    156            super.close();
    157        } catch (final IOException e) {
    158            ioe = e;
    159        }
    160        if (ioe == null) {
    161            noteClosed();
    162        } else {
    163            noteError(ioe);
    164        }
    165    }
    166
    167    /**
    168     * Reads all data from the underlying {@link InputStream}, while notifying the observers.
    169     *
    170     * @throws IOException The underlying {@link InputStream}, or either of the observers has thrown an exception.
    171     */
    172    public void consume() throws IOException {
    173        IOUtils.consume(this);
    174    }
    175
    176    private void forEachObserver(final IOConsumer<Observer> action) throws IOException {
    177        IOConsumer.forAll(action, observers);
    178    }
    179
    180    /**
    181     * Gets a copy of currently registered observers.
    182     *
    183     * @return a copy of the list of currently registered observers.
    184     * @since 2.9.0
    185     */
    186    public List<Observer> getObservers() {
    187        return new ArrayList<>(observers);
    188    }
    189
    190    /**
    191     * Notifies the observers by invoking {@link Observer#finished()}.
    192     *
    193     * @throws IOException Some observer has thrown an exception, which is being passed down.
    194     */
    195    protected void noteClosed() throws IOException {
    196        forEachObserver(Observer::closed);
    197    }
    198
    199    /**
    200     * Notifies the observers by invoking {@link Observer#data(int)} with the given arguments.
    201     *
    202     * @param value Passed to the observers.
    203     * @throws IOException Some observer has thrown an exception, which is being passed down.
    204     */
    205    protected void noteDataByte(final int value) throws IOException {
    206        forEachObserver(observer -> observer.data(value));
    207    }
    208
    209    /**
    210     * Notifies the observers by invoking {@link Observer#data(byte[],int,int)} with the given arguments.
    211     *
    212     * @param buffer Passed to the observers.
    213     * @param offset Passed to the observers.
    214     * @param length Passed to the observers.
    215     * @throws IOException Some observer has thrown an exception, which is being passed down.
    216     */
    217    protected void noteDataBytes(final byte[] buffer, final int offset, final int length) throws IOException {
    218        forEachObserver(observer -> observer.data(buffer, offset, length));
    219    }
    220
    221    /**
    222     * Notifies the observers by invoking {@link Observer#error(IOException)} with the given argument.
    223     *
    224     * @param exception Passed to the observers.
    225     * @throws IOException Some observer has thrown an exception, which is being passed down. This may be the same
    226     *         exception, which has been passed as an argument.
    227     */
    228    protected void noteError(final IOException exception) throws IOException {
    229        forEachObserver(observer -> observer.error(exception));
    230    }
    231
    232    /**
    233     * Notifies the observers by invoking {@link Observer#finished()}.
    234     *
    235     * @throws IOException Some observer has thrown an exception, which is being passed down.
    236     */
    237    protected void noteFinished() throws IOException {
    238        forEachObserver(Observer::finished);
    239    }
    240
    241    private void notify(final byte[] buffer, final int offset, final int result, final IOException ioe) throws IOException {
    242        if (ioe != null) {
    243            noteError(ioe);
    244            throw ioe;
    245        }
    246        if (result == EOF) {
    247            noteFinished();
    248        } else if (result > 0) {
    249            noteDataBytes(buffer, offset, result);
    250        }
    251    }
    252
    253    @Override
    254    public int read() throws IOException {
    255        int result = 0;
    256        IOException ioe = null;
    257        try {
    258            result = super.read();
    259        } catch (final IOException ex) {
    260            ioe = ex;
    261        }
    262        if (ioe != null) {
    263            noteError(ioe);
    264            throw ioe;
    265        }
    266        if (result == EOF) {
    267            noteFinished();
    268        } else {
    269            noteDataByte(result);
    270        }
    271        return result;
    272    }
    273
    274    @Override
    275    public int read(final byte[] buffer) throws IOException {
    276        int result = 0;
    277        IOException ioe = null;
    278        try {
    279            result = super.read(buffer);
    280        } catch (final IOException ex) {
    281            ioe = ex;
    282        }
    283        notify(buffer, 0, result, ioe);
    284        return result;
    285    }
    286
    287    @Override
    288    public int read(final byte[] buffer, final int offset, final int length) throws IOException {
    289        int result = 0;
    290        IOException ioe = null;
    291        try {
    292            result = super.read(buffer, offset, length);
    293        } catch (final IOException ex) {
    294            ioe = ex;
    295        }
    296        notify(buffer, offset, result, ioe);
    297        return result;
    298    }
    299
    300    /**
    301     * Removes an Observer.
    302     *
    303     * @param observer the observer to remove
    304     */
    305    public void remove(final Observer observer) {
    306        observers.remove(observer);
    307    }
    308
    309    /**
    310     * Removes all Observers.
    311     */
    312    public void removeAllObservers() {
    313        observers.clear();
    314    }
    315
    316}