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;
026
027/**
028 * 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.
029 * <p>
030 * It is an alternative base class to {@link FilterInputStream} to increase reusability, because {@link FilterInputStream} changes the methods being called,
031 * such as read(byte[]) to read(byte[], int, int).
032 * </p>
033 * <p>
034 * In addition, this class allows you to:
035 * </p>
036 * <ul>
037 * <li>notify a subclass that <em>n</em> bytes are about to be read through {@link #beforeRead(int)}</li>
038 * <li>notify a subclass that <em>n</em> bytes were read through {@link #afterRead(int)}</li>
039 * <li>notify a subclass that an exception was caught through {@link #handleIOException(IOException)}</li>
040 * <li>{@link #unwrap()} itself</li>
041 * </ul>
042 * <p>
043 * This class does not add any state (no additional instance variables).
044 * </p>
045 */
046public abstract class ProxyInputStream extends FilterInputStream {
047
048    /**
049     * Constructs a new ProxyInputStream.
050     *
051     * @param proxy  the InputStream to delegate to
052     */
053    public ProxyInputStream(final InputStream proxy) {
054        super(proxy);
055        // the proxy is stored in a protected superclass variable named 'in'
056    }
057
058    /**
059     * Invoked by the {@code read} methods after the proxied call has returned
060     * successfully. The number of bytes returned to the caller (or -1 if
061     * the end of stream was reached) is given as an argument.
062     * <p>
063     * Subclasses can override this method to add common post-processing
064     * functionality without having to override all the read methods.
065     * The default implementation does nothing.
066     * </p>
067     * <p>
068     * Note this method is <em>not</em> called from {@link #skip(long)} or
069     * {@link #reset()}. You need to explicitly override those methods if
070     * you want to add post-processing steps also to them.
071     * </p>
072     *
073     * @since 2.0
074     * @param n number of bytes read, or -1 if the end of stream was reached.
075     * @throws IOException if the post-processing fails in a subclass.
076     */
077    @SuppressWarnings("unused") // Possibly thrown from subclasses.
078    protected void afterRead(final int n) throws IOException {
079        // no-op default
080    }
081
082    /**
083     * Invokes the delegate's {@code available()} method.
084     *
085     * @return the number of available bytes
086     * @throws IOException if an I/O error occurs.
087     */
088    @Override
089    public int available() throws IOException {
090        try {
091            return super.available();
092        } catch (final IOException e) {
093            handleIOException(e);
094            return 0;
095        }
096    }
097
098    /**
099     * Invoked by the {@code read} methods before the call is proxied. The number
100     * of bytes that the caller wanted to read (1 for the {@link #read()}
101     * method, buffer length for {@link #read(byte[])}, etc.) is given as
102     * an argument.
103     * <p>
104     * Subclasses can override this method to add common pre-processing
105     * functionality without having to override all the read methods.
106     * The default implementation does nothing.
107     * </p>
108     * <p>
109     * Note this method is <em>not</em> called from {@link #skip(long)} or
110     * {@link #reset()}. You need to explicitly override those methods if
111     * you want to add pre-processing steps also to them.
112     * </p>
113     *
114     * @since 2.0
115     * @param n number of bytes that the caller asked to be read.
116     * @throws IOException if the pre-processing fails in a subclass.
117     */
118    @SuppressWarnings("unused") // Possibly thrown from subclasses.
119    protected void beforeRead(final int n) throws IOException {
120        // no-op default
121    }
122
123    /**
124     * Invokes the delegate's {@code close()} method.
125     *
126     * @throws IOException if an I/O error occurs.
127     */
128    @Override
129    public void close() throws IOException {
130        IOUtils.close(in, this::handleIOException);
131    }
132
133    /**
134     * Handles any IOExceptions thrown; by default, throws the given exception.
135     * <p>
136     * This method provides a point to implement custom exception
137     * handling. The default behavior is to re-throw the exception.
138     * </p>
139     *
140     * @param e The IOException thrown
141     * @throws IOException if an I/O error occurs.
142     * @since 2.0
143     */
144    protected void handleIOException(final IOException e) throws IOException {
145        throw e;
146    }
147
148    /**
149     * Invokes the delegate's {@code mark(int)} method.
150     *
151     * @param readLimit read ahead limit
152     */
153    @Override
154    public synchronized void mark(final int readLimit) {
155        in.mark(readLimit);
156    }
157
158    /**
159     * Invokes the delegate's {@code markSupported()} method.
160     *
161     * @return true if mark is supported, otherwise false
162     */
163    @Override
164    public boolean markSupported() {
165        return in.markSupported();
166    }
167
168    /**
169     * Invokes the delegate's {@code read()} method.
170     *
171     * @return the byte read or -1 if the end of stream
172     * @throws IOException if an I/O error occurs.
173     */
174    @Override
175    public int read() throws IOException {
176        try {
177            beforeRead(1);
178            final int b = in.read();
179            afterRead(b != EOF ? 1 : EOF);
180            return b;
181        } catch (final IOException e) {
182            handleIOException(e);
183            return EOF;
184        }
185    }
186
187    /**
188     * Invokes the delegate's {@code read(byte[])} method.
189     *
190     * @param b the buffer to read the bytes into
191     * @return the number of bytes read or EOF if the end of stream
192     * @throws IOException if an I/O error occurs.
193     */
194    @Override
195    public int read(final byte[] b) throws IOException {
196        try {
197            beforeRead(IOUtils.length(b));
198            final int n = in.read(b);
199            afterRead(n);
200            return n;
201        } catch (final IOException e) {
202            handleIOException(e);
203            return EOF;
204        }
205    }
206
207    /**
208     * Invokes the delegate's {@code read(byte[], int, int)} method.
209     *
210     * @param b the buffer to read the bytes into
211     * @param off The start offset
212     * @param len The number of bytes to read
213     * @return the number of bytes read or -1 if the end of stream
214     * @throws IOException if an I/O error occurs.
215     */
216    @Override
217    public int read(final byte[] b, final int off, final int len) throws IOException {
218        try {
219            beforeRead(len);
220            final int n = in.read(b, off, len);
221            afterRead(n);
222            return n;
223        } catch (final IOException e) {
224            handleIOException(e);
225            return EOF;
226        }
227    }
228
229    /**
230     * Invokes the delegate's {@code reset()} method.
231     *
232     * @throws IOException if an I/O error occurs.
233     */
234    @Override
235    public synchronized void reset() throws IOException {
236        try {
237            in.reset();
238        } catch (final IOException e) {
239            handleIOException(e);
240        }
241    }
242
243    /**
244     * Invokes the delegate's {@code skip(long)} method.
245     *
246     * @param n the number of bytes to skip
247     * @return the actual number of bytes skipped
248     * @throws IOException if an I/O error occurs.
249     */
250    @Override
251    public long skip(final long n) throws IOException {
252        try {
253            return in.skip(n);
254        } catch (final IOException e) {
255            handleIOException(e);
256            return 0;
257        }
258    }
259
260    /**
261     * Unwraps this instance by returning the underlying InputStream.
262     * <p>
263     * Use with caution; useful to query the underlying InputStream.
264     * </p>
265     * @return the underlying InputStream.
266     * @since 2.16.0
267     */
268    public InputStream unwrap() {
269        return in;
270    }
271}