    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 *      https://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 abstract static class AbstractBuilder<T, B extends AbstractStreamBuilder<T, B>> extends AbstractStreamBuilder<T, B> {
    057
    058        private IOIntConsumer afterRead;
    059
    060        /**
    061         * Constructs a builder of {@code T}.
    062         */
    063        protected AbstractBuilder() {
    064            // empty
    065        }
    066
    067        /**
    068         * Gets the {@link ProxyInputStream#afterRead(int)} consumer.
    069         *
    070         * @return the {@link ProxyInputStream#afterRead(int)} consumer.
    071         */
    072        public IOIntConsumer getAfterRead() {
    073            return afterRead;
    074        }
    075
    076        /**
    077         * Sets the {@link ProxyInputStream#afterRead(int)} behavior, null resets to a NOOP.
    078         * <p>
    079         * Setting this value causes the {@link ProxyInputStream#afterRead(int) afterRead} method to delegate to the given consumer.
    080         * </p>
    081         * <p>
    082         * If a subclass overrides {@link ProxyInputStream#afterRead(int) afterRead} and does not call {@code super.afterRead(int)}, then the given consumer is
    083         * not called.
    084         * </p>
    085         * <p>
    086         * This does <em>not</em> override a {@code ProxyInputStream} subclass' implementation of the {@link ProxyInputStream#afterRead(int)} method, it can
    087         * supplement it.
    088         * </p>
    089         *
    090         * @param afterRead the {@link ProxyInputStream#afterRead(int)} behavior.
    091         * @return this instance.
    092         */
    093        public B setAfterRead(final IOIntConsumer afterRead) {
    094            this.afterRead = afterRead;
    095            return asThis();
    096        }
    097
    098    }
    099
    100    /**
    101     * Tracks whether {@link #close()} has been called or not.
    102     */
    103    private volatile boolean closed;
    104
    105    /**
    106     * Handles exceptions.
    107     */
    108    private final IOConsumer<IOException> exceptionHandler;
    109
    110    private final IOIntConsumer afterRead;
    111
    112    /**
    113     * Constructs a new ProxyInputStream.
    114     *
    115     * @param builder  How to build an instance.
    116     * @throws IOException if an I/O error occurs.
    117     * @since 2.18.0
    118     */
    119    @SuppressWarnings("resource")
    120    protected ProxyInputStream(final AbstractBuilder<?, ?> builder) throws IOException {
    121        // the delegate is stored in a protected superclass instance variable named 'in'.
    122        this(builder.getInputStream(), builder);
    123    }
    124
    125    /**
    126     * Constructs a new ProxyInputStream.
    127     *
    128     * @param proxy  the InputStream to proxy.
    129     */
    130    public ProxyInputStream(final InputStream proxy) {
    131        // the delegate is stored in a protected superclass variable named 'in'.
    132        super(proxy);
    133        this.exceptionHandler = Erase::rethrow;
    134        this.afterRead = IOIntConsumer.NOOP;
    135    }
    136
    137    /**
    138     * Constructs a new ProxyInputStream.
    139     *
    140     * @param proxy  the InputStream to proxy.
    141     * @param builder  How to build an instance.
    142     * @since 2.18.0
    143     */
    144    protected ProxyInputStream(final InputStream proxy, final AbstractBuilder<?, ?> builder) {
    145        // the delegate is stored in a protected superclass instance variable named 'in'.
    146        super(proxy);
    147        this.exceptionHandler = Erase::rethrow;
    148        this.afterRead = builder.getAfterRead() != null ? builder.getAfterRead() : IOIntConsumer.NOOP;
    149    }
    150
    151    /**
    152     * 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
    153     * {@link IOUtils#EOF EOF} if the end of stream was reached.
    154     * <p>
    155     * The default delegates to the consumer given to {@link AbstractBuilder#setAfterRead(IOIntConsumer)}.
    156     * </p>
    157     * <p>
    158     * Alternatively, a subclasses can override this method to add post-processing functionality without having to override all the read methods.
    159     * </p>
    160     * <p>
    161     * 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
    162     * post-processing steps also to them.
    163     * </p>
    164     *
    165     * @param n number of bytes read, or {@link IOUtils#EOF EOF} if the end of stream was reached.
    166     * @throws IOException Thrown by a subclass or the consumer given to {@link AbstractBuilder#setAfterRead(IOIntConsumer)}.
    167     * @since 2.0
    168     */
    169    protected void afterRead(final int n) throws IOException {
    170        afterRead.accept(n);
    171    }
    172
    173    /**
    174     * Invokes the delegate's {@link InputStream#available()} method.
    175     *
    176     * @return the number of available bytes, 0 if the stream is closed.
    177     * @throws IOException if an I/O error occurs.
    178     */
    179    @Override
    180    public int available() throws IOException {
    181        if (in != null && !isClosed()) {
    182            try {
    183                return in.available();
    184            } catch (final IOException e) {
    185                handleIOException(e);
    186            }
    187        }
    188        return 0;
    189    }
    190
    191    /**
    192     * Invoked by the {@code read} methods before the call is proxied. The number
    193     * of bytes that the caller wanted to read (1 for the {@link #read()}
    194     * method, buffer length for {@link #read(byte[])}, etc.) is given as
    195     * an argument.
    196     * <p>
    197     * Subclasses can override this method to add common pre-processing
    198     * functionality without having to override all the read methods.
    199     * The default implementation does nothing.
    200     * </p>
    201     * <p>
    202     * Note this method is <em>not</em> called from {@link #skip(long)} or
    203     * {@link #reset()}. You need to explicitly override those methods if
    204     * you want to add pre-processing steps also to them.
    205     * </p>
    206     *
    207     * @param n number of bytes that the caller asked to be read.
    208     * @throws IOException if the pre-processing fails in a subclass.
    209     * @since 2.0
    210     */
    211    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    212    protected void beforeRead(final int n) throws IOException {
    213        // no-op default
    214    }
    215
    216    /**
    217     * Checks if this instance is closed and throws an IOException if so.
    218     *
    219     * @throws IOException if this instance is closed.
    220     */
    221    void checkOpen() throws IOException {
    222        Input.checkOpen(!isClosed());
    223    }
    224
    225    /**
    226     * Invokes the delegate's {@link InputStream#close()} method.
    227     *
    228     * @throws IOException if an I/O error occurs.
    229     */
    230    @Override
    231    public void close() throws IOException {
    232        IOUtils.close(in, this::handleIOException);
    233        closed = true;
    234    }
    235
    236    /**
    237     * Handles any IOExceptions thrown; by default, throws the given exception.
    238     * <p>
    239     * This method provides a point to implement custom exception
    240     * handling. The default behavior is to re-throw the exception.
    241     * </p>
    242     *
    243     * @param e The IOException thrown.
    244     * @throws IOException if an I/O error occurs.
    245     * @since 2.0
    246     */
    247    protected void handleIOException(final IOException e) throws IOException {
    248        exceptionHandler.accept(e);
    249    }
    250
    251    /**
    252     * Tests whether this instance is closed.
    253     *
    254     * @return whether this instance is closed.
    255     */
    256    boolean isClosed() {
    257        return closed;
    258    }
    259
    260    /**
    261     * Invokes the delegate's {@link InputStream#mark(int)} method.
    262     *
    263     * @param readLimit read ahead limit.
    264     */
    265    @Override
    266    public synchronized void mark(final int readLimit) {
    267        if (in != null) {
    268            in.mark(readLimit);
    269        }
    270    }
    271
    272    /**
    273     * Invokes the delegate's {@link InputStream#markSupported()} method.
    274     *
    275     * @return {@code true} if this stream instance supports the mark and reset methods; {@code false} otherwise.
    276     * @see #mark(int)
    277     * @see #reset()
    278     */
    279    @Override
    280    public boolean markSupported() {
    281        return in != null && in.markSupported();
    282    }
    283
    284    /**
    285     * Invokes the delegate's {@link InputStream#read()} method unless the stream is closed.
    286     *
    287     * @return the byte read or {@link IOUtils#EOF EOF} if we reached the end of stream.
    288     * @throws IOException if an I/O error occurs.
    289     */
    290    @Override
    291    public int read() throws IOException {
    292        try {
    293            beforeRead(1);
    294            final int b = in.read();
    295            afterRead(b != EOF ? 1 : EOF);
    296            return b;
    297        } catch (final IOException e) {
    298            handleIOException(e);
    299            return EOF;
    300        }
    301    }
    302
    303    /**
    304     * Invokes the delegate's {@link InputStream#read(byte[])} method.
    305     *
    306     * @param b the buffer to read the bytes into.
    307     * @return the number of bytes read or {@link IOUtils#EOF EOF} if we reached the end of stream.
    308     * @throws IOException
    309     *                     <ul>
    310     *                     <li>If the first byte cannot be read for any reason other than the end of the file,
    311     *                     <li>if the input stream has been closed, or</li>
    312     *                     <li>if some other I/O error occurs.</li>
    313     *                     </ul>
    314     */
    315    @Override
    316    public int read(final byte[] b) throws IOException {
    317        try {
    318            beforeRead(IOUtils.length(b));
    319            final int n = in.read(b);
    320            afterRead(n);
    321            return n;
    322        } catch (final IOException e) {
    323            handleIOException(e);
    324            return EOF;
    325        }
    326    }
    327
    328    /**
    329     * Invokes the delegate's {@link InputStream#read(byte[], int, int)} method.
    330     *
    331     * @param b   the buffer to read the bytes into.
    332     * @param off The start offset.
    333     * @param len The number of bytes to read.
    334     * @return the number of bytes read or {@link IOUtils#EOF EOF} if we reached the end of stream.
    335     * @throws IOException
    336     *                     <ul>
    337     *                     <li>If the first byte cannot be read for any reason other than the end of the file,
    338     *                     <li>if the input stream has been closed, or</li>
    339     *                     <li>if some other I/O error occurs.</li>
    340     *                     </ul>
    341     */
    342    @Override
    343    public int read(final byte[] b, final int off, final int len) throws IOException {
    344        try {
    345            beforeRead(len);
    346            final int n = in.read(b, off, len);
    347            afterRead(n);
    348            return n;
    349        } catch (final IOException e) {
    350            handleIOException(e);
    351            return EOF;
    352        }
    353    }
    354
    355    /**
    356     * Invokes the delegate's {@link InputStream#reset()} method.
    357     *
    358     * @throws IOException if this stream has not been marked or if the mark has been invalidated.
    359     */
    360    @Override
    361    public synchronized void reset() throws IOException {
    362        try {
    363            in.reset();
    364        } catch (final IOException e) {
    365            handleIOException(e);
    366        }
    367    }
    368
    369    /**
    370     * Sets the underlying input stream.
    371     *
    372     * @param in The input stream to set in {@link java.io.FilterInputStream#in}.
    373     * @return this instance.
    374     * @since 2.19.0
    375     */
    376    public ProxyInputStream setReference(final InputStream in) {
    377        this.in = in;
    378        return this;
    379    }
    380
    381    /**
    382     * Invokes the delegate's {@link InputStream#skip(long)} method.
    383     *
    384     * @param n the number of bytes to skip.
    385     * @return the actual number of bytes skipped.
    386     * @throws IOException if the stream does not support seek, or if some other I/O error occurs.
    387     */
    388    @Override
    389    public long skip(final long n) throws IOException {
    390        try {
    391            return in.skip(n);
    392        } catch (final IOException e) {
    393            handleIOException(e);
    394            return 0;
    395        }
    396    }
    397
    398    /**
    399     * Unwraps this instance by returning the underlying {@link InputStream}.
    400     * <p>
    401     * Use with caution; useful to query the underlying {@link InputStream}.
    402     * </p>
    403     *
    404     * @return the underlying {@link InputStream}.
    405     * @since 2.16.0
    406     */
    407    public InputStream unwrap() {
    408        return in;
    409    }
    410
    411}