    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     * For subclassing builders from {@link BoundedInputStream} subclassses.
    048     *
    049     * @param <T> The subclass.
    050     * @since 2.18.0
    051     */
    052    public static abstract class AbstractBuilder<T extends AbstractBuilder<T>> extends ProxyInputStream.AbstractBuilder<ObservableInputStream, T> {
    053
    054        private List<Observer> observers;
    055
    056        /**
    057         * Sets the list of observer callbacks.
    058         *
    059         * @param observers The list of observer callbacks.
    060         */
    061        public void setObservers(final List<Observer> observers) {
    062            this.observers = observers;
    063        }
    064
    065    }
    066
    067
    068    /**
    069     * Builds instances of {@link ObservableInputStream}.
    070     *
    071     * @since 2.18.0
    072     */
    073    public static class Builder extends AbstractBuilder<Builder> {
    074
    075        @Override
    076        public ObservableInputStream get() throws IOException {
    077            return new ObservableInputStream(this);
    078        }
    079
    080    }
    081
    082    /**
    083     * Abstracts observer callback for {@link ObservableInputStream}s.
    084     */
    085    public static abstract class Observer {
    086
    087        /**
    088         * Called to indicate that the {@link ObservableInputStream} has been closed.
    089         *
    090         * @throws IOException if an I/O error occurs.
    091         */
    092        @SuppressWarnings("unused") // Possibly thrown from subclasses.
    093        public void closed() throws IOException {
    094            // noop
    095        }
    096
    097        /**
    098         * Called to indicate that {@link InputStream#read(byte[])}, or {@link InputStream#read(byte[], int, int)} have
    099         * been called, and are about to invoke data.
    100         *
    101         * @param buffer The byte array, which has been passed to the read call, and where data has been stored.
    102         * @param offset The offset within the byte array, where data has been stored.
    103         * @param length The number of bytes, which have been stored in the byte array.
    104         * @throws IOException if an I/O error occurs.
    105         */
    106        @SuppressWarnings("unused") // Possibly thrown from subclasses.
    107        public void data(final byte[] buffer, final int offset, final int length) throws IOException {
    108            // noop
    109        }
    110
    111        /**
    112         * Called to indicate, that {@link InputStream#read()} has been invoked on the {@link ObservableInputStream},
    113         * and will return a value.
    114         *
    115         * @param value The value, which is being returned. This will never be -1 (EOF), because, in that case,
    116         *        {@link #finished()} will be invoked instead.
    117         * @throws IOException if an I/O error occurs.
    118         */
    119        @SuppressWarnings("unused") // Possibly thrown from subclasses.
    120        public void data(final int value) throws IOException {
    121            // noop
    122        }
    123
    124        /**
    125         * Called to indicate that an error occurred on the underlying stream.
    126         *
    127         * @param exception the exception to throw
    128         * @throws IOException if an I/O error occurs.
    129         */
    130        public void error(final IOException exception) throws IOException {
    131            throw exception;
    132        }
    133
    134        /**
    135         * Called to indicate that EOF has been seen on the underlying stream. This method may be called multiple times,
    136         * if the reader keeps invoking either of the read methods, and they will consequently keep returning EOF.
    137         *
    138         * @throws IOException if an I/O error occurs.
    139         */
    140        @SuppressWarnings("unused") // Possibly thrown from subclasses.
    141        public void finished() throws IOException {
    142            // noop
    143        }
    144    }
    145
    146    private final List<Observer> observers;
    147
    148    ObservableInputStream(final AbstractBuilder builder) throws IOException {
    149        super(builder);
    150        this.observers = builder.observers;
    151    }
    152
    153    /**
    154     * Constructs a new ObservableInputStream for the given InputStream.
    155     *
    156     * @param inputStream the input stream to observe.
    157     */
    158    public ObservableInputStream(final InputStream inputStream) {
    159        this(inputStream, new ArrayList<>());
    160    }
    161
    162    /**
    163     * Constructs a new ObservableInputStream for the given InputStream.
    164     *
    165     * @param inputStream the input stream to observe.
    166     * @param observers List of observer callbacks.
    167     */
    168    private ObservableInputStream(final InputStream inputStream, final List<Observer> observers) {
    169        super(inputStream);
    170        this.observers = observers;
    171    }
    172
    173    /**
    174     * Constructs a new ObservableInputStream for the given InputStream.
    175     *
    176     * @param inputStream the input stream to observe.
    177     * @param observers List of observer callbacks.
    178     * @since 2.9.0
    179     */
    180    public ObservableInputStream(final InputStream inputStream, final Observer... observers) {
    181        this(inputStream, Arrays.asList(observers));
    182    }
    183
    184    /**
    185     * Adds an Observer.
    186     *
    187     * @param observer the observer to add.
    188     */
    189    public void add(final Observer observer) {
    190        observers.add(observer);
    191    }
    192
    193    @Override
    194    public void close() throws IOException {
    195        IOException ioe = null;
    196        try {
    197            super.close();
    198        } catch (final IOException e) {
    199            ioe = e;
    200        }
    201        if (ioe == null) {
    202            noteClosed();
    203        } else {
    204            noteError(ioe);
    205        }
    206    }
    207
    208    /**
    209     * Reads all data from the underlying {@link InputStream}, while notifying the observers.
    210     *
    211     * @throws IOException The underlying {@link InputStream}, or either of the observers has thrown an exception.
    212     */
    213    public void consume() throws IOException {
    214        IOUtils.consume(this);
    215    }
    216
    217    private void forEachObserver(final IOConsumer<Observer> action) throws IOException {
    218        IOConsumer.forAll(action, observers);
    219    }
    220
    221    /**
    222     * Gets a copy of currently registered observers.
    223     *
    224     * @return a copy of the list of currently registered observers.
    225     * @since 2.9.0
    226     */
    227    public List<Observer> getObservers() {
    228        return new ArrayList<>(observers);
    229    }
    230
    231    /**
    232     * Notifies the observers by invoking {@link Observer#finished()}.
    233     *
    234     * @throws IOException Some observer has thrown an exception, which is being passed down.
    235     */
    236    protected void noteClosed() throws IOException {
    237        forEachObserver(Observer::closed);
    238    }
    239
    240    /**
    241     * Notifies the observers by invoking {@link Observer#data(int)} with the given arguments.
    242     *
    243     * @param value Passed to the observers.
    244     * @throws IOException Some observer has thrown an exception, which is being passed down.
    245     */
    246    protected void noteDataByte(final int value) throws IOException {
    247        forEachObserver(observer -> observer.data(value));
    248    }
    249
    250    /**
    251     * Notifies the observers by invoking {@link Observer#data(byte[],int,int)} with the given arguments.
    252     *
    253     * @param buffer Passed to the observers.
    254     * @param offset Passed to the observers.
    255     * @param length Passed to the observers.
    256     * @throws IOException Some observer has thrown an exception, which is being passed down.
    257     */
    258    protected void noteDataBytes(final byte[] buffer, final int offset, final int length) throws IOException {
    259        forEachObserver(observer -> observer.data(buffer, offset, length));
    260    }
    261
    262    /**
    263     * Notifies the observers by invoking {@link Observer#error(IOException)} with the given argument.
    264     *
    265     * @param exception Passed to the observers.
    266     * @throws IOException Some observer has thrown an exception, which is being passed down. This may be the same
    267     *         exception, which has been passed as an argument.
    268     */
    269    protected void noteError(final IOException exception) throws IOException {
    270        forEachObserver(observer -> observer.error(exception));
    271    }
    272
    273    /**
    274     * Notifies the observers by invoking {@link Observer#finished()}.
    275     *
    276     * @throws IOException Some observer has thrown an exception, which is being passed down.
    277     */
    278    protected void noteFinished() throws IOException {
    279        forEachObserver(Observer::finished);
    280    }
    281
    282    private void notify(final byte[] buffer, final int offset, final int result, final IOException ioe) throws IOException {
    283        if (ioe != null) {
    284            noteError(ioe);
    285            throw ioe;
    286        }
    287        if (result == EOF) {
    288            noteFinished();
    289        } else if (result > 0) {
    290            noteDataBytes(buffer, offset, result);
    291        }
    292    }
    293
    294    @Override
    295    public int read() throws IOException {
    296        int result = 0;
    297        IOException ioe = null;
    298        try {
    299            result = super.read();
    300        } catch (final IOException ex) {
    301            ioe = ex;
    302        }
    303        if (ioe != null) {
    304            noteError(ioe);
    305            throw ioe;
    306        }
    307        if (result == EOF) {
    308            noteFinished();
    309        } else {
    310            noteDataByte(result);
    311        }
    312        return result;
    313    }
    314
    315    @Override
    316    public int read(final byte[] buffer) throws IOException {
    317        int result = 0;
    318        IOException ioe = null;
    319        try {
    320            result = super.read(buffer);
    321        } catch (final IOException ex) {
    322            ioe = ex;
    323        }
    324        notify(buffer, 0, result, ioe);
    325        return result;
    326    }
    327
    328    @Override
    329    public int read(final byte[] buffer, final int offset, final int length) throws IOException {
    330        int result = 0;
    331        IOException ioe = null;
    332        try {
    333            result = super.read(buffer, offset, length);
    334        } catch (final IOException ex) {
    335            ioe = ex;
    336        }
    337        notify(buffer, offset, result, ioe);
    338        return result;
    339    }
    340
    341    /**
    342     * Removes an Observer.
    343     *
    344     * @param observer the observer to remove
    345     */
    346    public void remove(final Observer observer) {
    347        observers.remove(observer);
    348    }
    349
    350    /**
    351     * Removes all Observers.
    352     */
    353    public void removeAllObservers() {
    354        observers.clear();
    355    }
    356
    357}