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     */
017    package org.apache.commons.io.input;
018    
019    import java.io.EOFException;
020    import java.io.IOException;
021    import java.io.InputStream;
022    
023    /**
024     * A functional, light weight {@link InputStream} that emulates
025     * a stream of a specified size.
026     * <p>
027     * This implementation provides a light weight
028     * object for testing with an {@link InputStream}
029     * where the contents don't matter.
030     * <p>
031     * One use case would be for testing the handling of
032     * large {@link InputStream} as it can emulate that
033     * scenario without the overhead of actually processing
034     * large numbers of bytes - significantly speeding up
035     * test execution times.
036     * <p>
037     * This implementation returns zero from the method that
038     * reads a byte and leaves the array unchanged in the read
039     * methods that are passed a byte array.
040     * If alternative data is required the <code>processByte()</code> and
041     * <code>processBytes()</code> methods can be implemented to generate
042     * data, for example:
043     *
044     * <pre>
045     *  public class TestInputStream extends NullInputStream {
046     *      public TestInputStream(int size) {
047     *          super(size);
048     *      }
049     *      protected int processByte() {
050     *          return ... // return required value here
051     *      }
052     *      protected void processBytes(byte[] bytes, int offset, int length) {
053     *          for (int i = offset; i < length; i++) {
054     *              bytes[i] = ... // set array value here
055     *          }
056     *      }
057     *  }
058     * </pre>
059     *
060     * @since 1.3
061     * @version $Id: NullInputStream.java 1307462 2012-03-30 15:13:11Z ggregory $
062     */
063    public class NullInputStream extends InputStream {
064    
065        private final long size;
066        private long position;
067        private long mark = -1;
068        private long readlimit;
069        private boolean eof;
070        private final boolean throwEofException;
071        private final boolean markSupported;
072    
073        /**
074         * Create an {@link InputStream} that emulates a specified size
075         * which supports marking and does not throw EOFException.
076         *
077         * @param size The size of the input stream to emulate.
078         */
079        public NullInputStream(long size) {
080           this(size, true, false);
081        }
082    
083        /**
084         * Create an {@link InputStream} that emulates a specified
085         * size with option settings.
086         *
087         * @param size The size of the input stream to emulate.
088         * @param markSupported Whether this instance will support
089         * the <code>mark()</code> functionality.
090         * @param throwEofException Whether this implementation
091         * will throw an {@link EOFException} or return -1 when the
092         * end of file is reached.
093         */
094        public NullInputStream(long size, boolean markSupported, boolean throwEofException) {
095           this.size = size;
096           this.markSupported = markSupported;
097           this.throwEofException = throwEofException;
098        }
099    
100        /**
101         * Return the current position.
102         *
103         * @return the current position.
104         */
105        public long getPosition() {
106            return position;
107        }
108    
109        /**
110         * Return the size this {@link InputStream} emulates.
111         *
112         * @return The size of the input stream to emulate.
113         */
114        public long getSize() {
115            return size;
116        }
117    
118        /**
119         * Return the number of bytes that can be read.
120         *
121         * @return The number of bytes that can be read.
122         */
123        @Override
124        public int available() {
125            long avail = size - position;
126            if (avail <= 0) {
127                return 0;
128            } else if (avail > Integer.MAX_VALUE) {
129                return Integer.MAX_VALUE;
130            } else {
131                return (int)avail;
132            }
133        }
134    
135        /**
136         * Close this input stream - resets the internal state to
137         * the initial values.
138         *
139         * @throws IOException If an error occurs.
140         */
141        @Override
142        public void close() throws IOException {
143            eof = false;
144            position = 0;
145            mark = -1;
146        }
147    
148        /**
149         * Mark the current position.
150         *
151         * @param readlimit The number of bytes before this marked position
152         * is invalid.
153         * @throws UnsupportedOperationException if mark is not supported.
154         */
155        @Override
156        public synchronized void mark(int readlimit) {
157            if (!markSupported) {
158                throw new UnsupportedOperationException("Mark not supported");
159            }
160            mark = position;
161            this.readlimit = readlimit;
162        }
163    
164        /**
165         * Indicates whether <i>mark</i> is supported.
166         *
167         * @return Whether <i>mark</i> is supported or not.
168         */
169        @Override
170        public boolean markSupported() {
171            return markSupported;
172        }
173    
174        /**
175         * Read a byte.
176         *
177         * @return Either The byte value returned by <code>processByte()</code>
178         * or <code>-1</code> if the end of file has been reached and
179         * <code>throwEofException</code> is set to {@code false}.
180         * @throws EOFException if the end of file is reached and
181         * <code>throwEofException</code> is set to {@code true}.
182         * @throws IOException if trying to read past the end of file.
183         */
184        @Override
185        public int read() throws IOException {
186            if (eof) {
187                throw new IOException("Read after end of file");
188            }
189            if (position == size) {
190                return doEndOfFile();
191            }
192            position++;
193            return processByte();
194        }
195    
196        /**
197         * Read some bytes into the specified array.
198         *
199         * @param bytes The byte array to read into
200         * @return The number of bytes read or <code>-1</code>
201         * if the end of file has been reached and
202         * <code>throwEofException</code> is set to {@code false}.
203         * @throws EOFException if the end of file is reached and
204         * <code>throwEofException</code> is set to {@code true}.
205         * @throws IOException if trying to read past the end of file.
206         */
207        @Override
208        public int read(byte[] bytes) throws IOException {
209            return read(bytes, 0, bytes.length);
210        }
211    
212        /**
213         * Read the specified number bytes into an array.
214         *
215         * @param bytes The byte array to read into.
216         * @param offset The offset to start reading bytes into.
217         * @param length The number of bytes to read.
218         * @return The number of bytes read or <code>-1</code>
219         * if the end of file has been reached and
220         * <code>throwEofException</code> is set to {@code false}.
221         * @throws EOFException if the end of file is reached and
222         * <code>throwEofException</code> is set to {@code true}.
223         * @throws IOException if trying to read past the end of file.
224         */
225        @Override
226        public int read(byte[] bytes, int offset, int length) throws IOException {
227            if (eof) {
228                throw new IOException("Read after end of file");
229            }
230            if (position == size) {
231                return doEndOfFile();
232            }
233            position += length;
234            int returnLength = length;
235            if (position > size) {
236                returnLength = length - (int)(position - size);
237                position = size;
238            }
239            processBytes(bytes, offset, returnLength);
240            return returnLength;
241        }
242    
243        /**
244         * Reset the stream to the point when mark was last called.
245         *
246         * @throws UnsupportedOperationException if mark is not supported.
247         * @throws IOException If no position has been marked
248         * or the read limit has been exceed since the last position was
249         * marked.
250         */
251        @Override
252        public synchronized void reset() throws IOException {
253            if (!markSupported) {
254                throw new UnsupportedOperationException("Mark not supported");
255            }
256            if (mark < 0) {
257                throw new IOException("No position has been marked");
258            }
259            if (position > mark + readlimit) {
260                throw new IOException("Marked position [" + mark +
261                        "] is no longer valid - passed the read limit [" +
262                        readlimit + "]");
263            }
264            position = mark;
265            eof = false;
266        }
267    
268        /**
269         * Skip a specified number of bytes.
270         *
271         * @param numberOfBytes The number of bytes to skip.
272         * @return The number of bytes skipped or <code>-1</code>
273         * if the end of file has been reached and
274         * <code>throwEofException</code> is set to {@code false}.
275         * @throws EOFException if the end of file is reached and
276         * <code>throwEofException</code> is set to {@code true}.
277         * @throws IOException if trying to read past the end of file.
278         */
279        @Override
280        public long skip(long numberOfBytes) throws IOException {
281            if (eof) {
282                throw new IOException("Skip after end of file");
283            }
284            if (position == size) {
285                return doEndOfFile();
286            }
287            position += numberOfBytes;
288            long returnLength = numberOfBytes;
289            if (position > size) {
290                returnLength = numberOfBytes - (position - size);
291                position = size;
292            }
293            return returnLength;
294        }
295    
296        /**
297         * Return a byte value for the  <code>read()</code> method.
298         * <p>
299         * This implementation returns zero.
300         *
301         * @return This implementation always returns zero.
302         */
303        protected int processByte() {
304            // do nothing - overridable by subclass
305            return 0;
306        }
307    
308        /**
309         * Process the bytes for the <code>read(byte[], offset, length)</code>
310         * method.
311         * <p>
312         * This implementation leaves the byte array unchanged.
313         *
314         * @param bytes The byte array
315         * @param offset The offset to start at.
316         * @param length The number of bytes.
317         */
318        protected void processBytes(byte[] bytes, int offset, int length) {
319            // do nothing - overridable by subclass
320        }
321    
322        /**
323         * Handle End of File.
324         *
325         * @return <code>-1</code> if <code>throwEofException</code> is
326         * set to {@code false}
327         * @throws EOFException if <code>throwEofException</code> is set
328         * to {@code true}.
329         */
330        private int doEndOfFile() throws EOFException {
331            eof = true;
332            if (throwEofException) {
333                throw new EOFException();
334            }
335            return -1;
336        }
337    
338    }