    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.FilterInputStream;
    022import java.io.IOException;
    023import java.io.InputStream;
    024
    025import org.apache.commons.io.IOUtils;
    026import org.apache.commons.io.build.AbstractStreamBuilder;
    027import org.apache.commons.io.function.Erase;
    028import org.apache.commons.io.function.IOConsumer;
    029import org.apache.commons.io.function.IOIntConsumer;
    030
    031/**
    032 * A proxy stream which acts as a {@link FilterInputStream}, by passing all method calls on to the proxied stream, not changing which methods are called.
    033 * <p>
    034 * It is an alternative base class to {@link FilterInputStream} to increase reusability, because {@link FilterInputStream} changes the methods being called,
    035 * such as read(byte[]) to read(byte[], int, int).
    036 * </p>
    037 * <p>
    038 * In addition, this class allows you to:
    039 * </p>
    040 * <ul>
    041 * <li>notify a subclass that <em>n</em> bytes are about to be read through {@link #beforeRead(int)}</li>
    042 * <li>notify a subclass that <em>n</em> bytes were read through {@link #afterRead(int)}</li>
    043 * <li>notify a subclass that an exception was caught through {@link #handleIOException(IOException)}</li>
    044 * <li>{@link #unwrap()} itself</li>
    045 * </ul>
    046 */
    047public abstract class ProxyInputStream extends FilterInputStream {
    048
    049    /**
    050     * Abstracts builder properties for subclasses.
    051     *
    052     * @param <T> The InputStream type.
    053     * @param <B> The builder type.
    054     * @since 2.18.0
    055     */
    056    protected static abstract class AbstractBuilder<T, B extends AbstractStreamBuilder<T, B>> extends AbstractStreamBuilder<T, B> {
    057
    058        private IOIntConsumer afterRead;
    059
    060        /**
    061         * Gets the {@link ProxyInputStream#afterRead(int)} consumer.
    062         *
    063         * @return the {@link ProxyInputStream#afterRead(int)} consumer.
    064         */
    065        public IOIntConsumer getAfterRead() {
    066            return afterRead;
    067        }
    068
    069        /**
    070         * Sets the {@link ProxyInputStream#afterRead(int)} behavior, null resets to a NOOP.
    071         * <p>
    072         * Setting this value causes the {@link ProxyInputStream#afterRead(int) afterRead} method to delegate to the given consumer.
    073         * </p>
    074         * <p>
    075         * If a subclass overrides {@link ProxyInputStream#afterRead(int) afterRead} and does not call {@code super.afterRead(int)}, then the given consumer is
    076         * not called.
    077         * </p>
    078         * <p>
    079         * This does <em>not</em> override a {@code ProxyInputStream} subclass' implementation of the {@link ProxyInputStream#afterRead(int)} method, it can
    080         * supplement it.
    081         * </p>
    082         *
    083         * @param afterRead the {@link ProxyInputStream#afterRead(int)} behavior.
    084         * @return this instance.
    085         */
    086        public B setAfterRead(final IOIntConsumer afterRead) {
    087            this.afterRead = afterRead;
    088            return asThis();
    089        }
    090
    091    }
    092
    093    /**
    094     * Tracks whether {@link #close()} has been called or not.
    095     */
    096    private boolean closed;
    097
    098    /**
    099     * Handles exceptions.
    100     */
    101    private final IOConsumer<IOException> exceptionHandler;
    102
    103    private final IOIntConsumer afterRead;
    104
    105    /**
    106     * Constructs a new ProxyInputStream.
    107     *
    108     * @param builder  How to build an instance.
    109     * @throws IOException if an I/O error occurs.
    110     * @since 2.18.0
    111     */
    112    @SuppressWarnings("resource")
    113    protected ProxyInputStream(final AbstractBuilder<?, ?> builder) throws IOException {
    114        // the delegate is stored in a protected superclass instance variable named 'in'.
    115        this(builder.getInputStream(), builder);
    116    }
    117
    118    /**
    119     * Constructs a new ProxyInputStream.
    120     *
    121     * @param proxy  the InputStream to proxy.
    122     */
    123    public ProxyInputStream(final InputStream proxy) {
    124        // the delegate is stored in a protected superclass variable named 'in'.
    125        super(proxy);
    126        this.exceptionHandler = Erase::rethrow;
    127        this.afterRead = IOIntConsumer.NOOP;
    128    }
    129
    130    /**
    131     * Constructs a new ProxyInputStream.
    132     *
    133     * @param proxy  the InputStream to proxy.
    134     * @param builder  How to build an instance.
    135     * @since 2.18.0
    136     */
    137    protected ProxyInputStream(final InputStream proxy, final AbstractBuilder<?, ?> builder) {
    138        // the delegate is stored in a protected superclass instance variable named 'in'.
    139        super(proxy);
    140        this.exceptionHandler = Erase::rethrow;
    141        this.afterRead = builder.getAfterRead() != null ? builder.getAfterRead() : IOIntConsumer.NOOP;
    142    }
    143
    144    /**
    145     * Called by the {@code read} methods after the proxied call has returned successfully. The argument is the number of bytes returned to the caller or
    146     * {@link IOUtils#EOF EOF} if the end of stream was reached.
    147     * <p>
    148     * The default delegates to the consumer given to {@link AbstractBuilder#setAfterRead(IOIntConsumer)}.
    149     * </p>
    150     * <p>
    151     * Alternatively, a subclasses can override this method to add post-processing functionality without having to override all the read methods.
    152     * </p>
    153     * <p>
    154     * Note this method is <em>not</em> called from {@link #skip(long)} or {@link #reset()}. You need to explicitly override those methods if you want to add
    155     * post-processing steps also to them.
    156     * </p>
    157     *
    158     * @param n number of bytes read, or {@link IOUtils#EOF EOF} if the end of stream was reached.
    159     * @throws IOException Thrown by a subclass or the consumer given to {@link AbstractBuilder#setAfterRead(IOIntConsumer)}.
    160     * @since 2.0
    161     */
    162    protected void afterRead(final int n) throws IOException {
    163        afterRead.accept(n);
    164    }
    165
    166    /**
    167     * Invokes the delegate's {@link InputStream#available()} method.
    168     *
    169     * @return the number of available bytes, 0 if the stream is closed.
    170     * @throws IOException if an I/O error occurs.
    171     */
    172    @Override
    173    public int available() throws IOException {
    174        if (in != null && !isClosed()) {
    175            try {
    176                return in.available();
    177            } catch (final IOException e) {
    178                handleIOException(e);
    179            }
    180        }
    181        return 0;
    182    }
    183
    184    /**
    185     * Invoked by the {@code read} methods before the call is proxied. The number
    186     * of bytes that the caller wanted to read (1 for the {@link #read()}
    187     * method, buffer length for {@link #read(byte[])}, etc.) is given as
    188     * an argument.
    189     * <p>
    190     * Subclasses can override this method to add common pre-processing
    191     * functionality without having to override all the read methods.
    192     * The default implementation does nothing.
    193     * </p>
    194     * <p>
    195     * Note this method is <em>not</em> called from {@link #skip(long)} or
    196     * {@link #reset()}. You need to explicitly override those methods if
    197     * you want to add pre-processing steps also to them.
    198     * </p>
    199     *
    200     * @since 2.0
    201     * @param n number of bytes that the caller asked to be read.
    202     * @throws IOException if the pre-processing fails in a subclass.
    203     */
    204    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    205    protected void beforeRead(final int n) throws IOException {
    206        // no-op default
    207    }
    208
    209    /**
    210     * Checks if this instance is closed and throws an IOException if so.
    211     *
    212     * @throws IOException if this instance is closed.
    213     */
    214    void checkOpen() throws IOException {
    215        Input.checkOpen(!isClosed());
    216    }
    217
    218    /**
    219     * Invokes the delegate's {@link InputStream#close()} method.
    220     *
    221     * @throws IOException if an I/O error occurs.
    222     */
    223    @Override
    224    public void close() throws IOException {
    225        IOUtils.close(in, this::handleIOException);
    226        closed = true;
    227    }
    228
    229    /**
    230     * Handles any IOExceptions thrown; by default, throws the given exception.
    231     * <p>
    232     * This method provides a point to implement custom exception
    233     * handling. The default behavior is to re-throw the exception.
    234     * </p>
    235     *
    236     * @param e The IOException thrown.
    237     * @throws IOException if an I/O error occurs.
    238     * @since 2.0
    239     */
    240    protected void handleIOException(final IOException e) throws IOException {
    241        exceptionHandler.accept(e);
    242    }
    243
    244    /**
    245     * Tests whether this instance is closed.
    246     *
    247     * @return whether this instance is closed.
    248     */
    249    boolean isClosed() {
    250        return closed;
    251    }
    252
    253    /**
    254     * Invokes the delegate's {@link InputStream#mark(int)} method.
    255     *
    256     * @param readLimit read ahead limit.
    257     */
    258    @Override
    259    public synchronized void mark(final int readLimit) {
    260        if (in != null) {
    261            in.mark(readLimit);
    262        }
    263    }
    264
    265    /**
    266     * Invokes the delegate's {@link InputStream#markSupported()} method.
    267     *
    268     * @return {@code true} if this stream instance supports the mark and reset methods; {@code false} otherwise.
    269     * @see #mark(int)
    270     * @see #reset()
    271     */
    272    @Override
    273    public boolean markSupported() {
    274        return in != null && in.markSupported();
    275    }
    276
    277    /**
    278     * Invokes the delegate's {@link InputStream#read()} method unless the stream is closed.
    279     *
    280     * @return the byte read or {@link IOUtils#EOF EOF} if we reached the end of stream.
    281     * @throws IOException if an I/O error occurs.
    282     */
    283    @Override
    284    public int read() throws IOException {
    285        try {
    286            beforeRead(1);
    287            final int b = in.read();
    288            afterRead(b != EOF ? 1 : EOF);
    289            return b;
    290        } catch (final IOException e) {
    291            handleIOException(e);
    292            return EOF;
    293        }
    294    }
    295
    296    /**
    297     * Invokes the delegate's {@link InputStream#read(byte[])} method.
    298     *
    299     * @param b the buffer to read the bytes into.
    300     * @return the number of bytes read or {@link IOUtils#EOF EOF} if we reached the end of stream.
    301     * @throws IOException
    302     *                     <ul>
    303     *                     <li>If the first byte cannot be read for any reason other than the end of the file,
    304     *                     <li>if the input stream has been closed, or</li>
    305     *                     <li>if some other I/O error occurs.</li>
    306     *                     </ul>
    307     */
    308    @Override
    309    public int read(final byte[] b) throws IOException {
    310        try {
    311            beforeRead(IOUtils.length(b));
    312            final int n = in.read(b);
    313            afterRead(n);
    314            return n;
    315        } catch (final IOException e) {
    316            handleIOException(e);
    317            return EOF;
    318        }
    319    }
    320
    321    /**
    322     * Invokes the delegate's {@link InputStream#read(byte[], int, int)} method.
    323     *
    324     * @param b   the buffer to read the bytes into.
    325     * @param off The start offset.
    326     * @param len The number of bytes to read.
    327     * @return the number of bytes read or {@link IOUtils#EOF EOF} if we reached the end of stream.
    328     * @throws IOException
    329     *                     <ul>
    330     *                     <li>If the first byte cannot be read for any reason other than the end of the file,
    331     *                     <li>if the input stream has been closed, or</li>
    332     *                     <li>if some other I/O error occurs.</li>
    333     *                     </ul>
    334     */
    335    @Override
    336    public int read(final byte[] b, final int off, final int len) throws IOException {
    337        try {
    338            beforeRead(len);
    339            final int n = in.read(b, off, len);
    340            afterRead(n);
    341            return n;
    342        } catch (final IOException e) {
    343            handleIOException(e);
    344            return EOF;
    345        }
    346    }
    347
    348    /**
    349     * Invokes the delegate's {@link InputStream#reset()} method.
    350     *
    351     * @throws IOException if this stream has not been marked or if the mark has been invalidated.
    352     */
    353    @Override
    354    public synchronized void reset() throws IOException {
    355        try {
    356            in.reset();
    357        } catch (final IOException e) {
    358            handleIOException(e);
    359        }
    360    }
    361
    362    /**
    363     * Package-private for testing.
    364     *
    365     * @param in The input stream to set in {@link java.io.FilterInputStream#in}.
    366     */
    367    void setIn(final InputStream in) {
    368        this.in = in;
    369    }
    370
    371    /**
    372     * Invokes the delegate's {@link InputStream#skip(long)} method.
    373     *
    374     * @param n the number of bytes to skip.
    375     * @return the actual number of bytes skipped.
    376     * @throws IOException if the stream does not support seek, or if some other I/O error occurs.
    377     */
    378    @Override
    379    public long skip(final long n) throws IOException {
    380        try {
    381            return in.skip(n);
    382        } catch (final IOException e) {
    383            handleIOException(e);
    384            return 0;
    385        }
    386    }
    387
    388    /**
    389     * Unwraps this instance by returning the underlying {@link InputStream}.
    390     * <p>
    391     * Use with caution; useful to query the underlying {@link InputStream}.
    392     * </p>
    393     *
    394     * @return the underlying {@link InputStream}.
    395     * @since 2.16.0
    396     */
    397    public InputStream unwrap() {
    398        return in;
    399    }
    400
    401}