1 /* PushbackInputStream.java -- An input stream that can unread bytes
2 Copyright (C) 1998, 1999, 2001, 2002, 2005 Free Software Foundation, Inc.
4 This file is part of GNU Classpath.
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12 WITHOUT ANY WARRANTY; without even the implied warranty of
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14 General Public License for more details.
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18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
21 Linking this library statically or dynamically with other modules is
22 making a combined work based on this library. Thus, the terms and
23 conditions of the GNU General Public License cover the whole
26 As a special exception, the copyright holders of this library give you
27 permission to link this library with independent modules to produce an
28 executable, regardless of the license terms of these independent
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30 terms of your choice, provided that you also meet, for each linked
31 independent module, the terms and conditions of the license of that
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36 exception statement from your version. */
41 * This subclass of <code>FilterInputStream</code> provides the ability to
42 * unread data from a stream. It maintains an internal buffer of unread
43 * data that is supplied to the next read operation. This is conceptually
44 * similar to mark/reset functionality, except that in this case the
45 * position to reset the stream to does not need to be known in advance.
47 * The default pushback buffer size one byte, but this can be overridden
48 * by the creator of the stream.
51 * @author Aaron M. Renn (arenn@urbanophile.com)
52 * @author Warren Levy (warrenl@cygnus.com)
54 @LATTICE("IN<T,IN<POS,POS<SH,SH<F,SH*,POS*")
55 @METHODDEFAULT("OUT<SH,SH<IN,SH*,THISLOC=OUT,GLOBALLOC=OUT")
56 public class PushbackInputStream extends FilterInputStream
59 * This is the default buffer size
61 @LOC("F") private static final int DEFAULT_BUFFER_SIZE = 1;
64 * This is the buffer that is used to store the pushed back data
66 @LOC("SH") protected byte[] buf;
69 * This is the position in the buffer from which the next byte will be
70 * read. Bytes are stored in reverse order in the buffer, starting from
71 * <code>buf[buf.length - 1]</code> to <code>buf[0]</code>. Thus when
72 * <code>pos</code> is 0 the buffer is full and <code>buf.length</code> when
75 @LOC("POS") protected int pos;
78 * This method initializes a <code>PushbackInputStream</code> to
79 * read from the specified subordinate <code>InputStream</code>
80 * with a default pushback buffer size of 1.
82 * @param in The subordinate stream to read from
84 public PushbackInputStream(InputStream in)
86 this(in, DEFAULT_BUFFER_SIZE);
90 * This method initializes a <code>PushbackInputStream</code> to
91 * read from the specified subordinate <code>InputStream</code> with
92 * the specified buffer size
94 * @param in The subordinate <code>InputStream</code> to read from
95 * @param size The pushback buffer size to use
97 public PushbackInputStream(@LOC("IN")InputStream in, @LOC("IN")int size)
101 throw new IllegalArgumentException();
102 buf = new byte[size];
107 * This method returns the number of bytes that can be read from this
108 * stream before a read can block. A return of 0 indicates that blocking
109 * might (or might not) occur on the very next read attempt.
111 * This method will return the number of bytes available from the
112 * pushback buffer plus the number of bytes available from the
115 * @return The number of bytes that can be read before blocking could occur
117 * @exception IOException If an error occurs
119 public int available() throws IOException
123 return (buf.length - pos) + super.available();
125 catch (NullPointerException npe)
127 throw new IOException ("Stream closed");
132 * This method closes the stream and releases any associated resources.
134 * @exception IOException If an error occurs.
136 public synchronized void close() throws IOException
143 * This method returns <code>false</code> to indicate that it does
144 * not support mark/reset functionality.
146 * @return This method returns <code>false</code> to indicate that
147 * this class does not support mark/reset functionality
149 public boolean markSupported()
155 * This method always throws an IOException in this class because
156 * mark/reset functionality is not supported.
158 * @exception IOException Always thrown for this class
160 public void reset() throws IOException
162 throw new IOException("Mark not supported in this class");
166 * This method reads an unsigned byte from the input stream and returns it
167 * as an int in the range of 0-255. This method also will return -1 if
168 * the end of the stream has been reached. The byte returned will be read
169 * from the pushback buffer, unless the buffer is empty, in which case
170 * the byte will be read from the underlying stream.
172 * This method will block until the byte can be read.
174 * @return The byte read or -1 if end of stream
176 * @exception IOException If an error occurs
178 public synchronized int read() throws IOException
180 if (pos < buf.length)
181 return ((int) buf[pos++]) & 0xFF;
187 * This method read bytes from a stream and stores them into a
188 * caller supplied buffer. It starts storing the data at index
189 * <code>offset</code> into the buffer and attempts to read
190 * <code>len</code> bytes. This method can return before reading the
191 * number of bytes requested. The actual number of bytes read is
192 * returned as an int. A -1 is returned to indicate the end of the
195 * This method will block until some data can be read.
197 * This method first reads bytes from the pushback buffer in order to
198 * satisfy the read request. If the pushback buffer cannot provide all
199 * of the bytes requested, the remaining bytes are read from the
202 * @param b The array into which the bytes read should be stored
203 * @param off The offset into the array to start storing bytes
204 * @param len The requested number of bytes to read
206 * @return The actual number of bytes read, or -1 if end of stream.
208 * @exception IOException If an error occurs.
210 @LATTICE("OUT<THIS,THISLOC=THIS")
212 public synchronized int read(@LOC("OUT") byte[] b,
213 @LOC("THIS,PushbackInputStream.POS") int off,
214 @LOC("THIS,PushbackInputStream.POS") int len) throws IOException
216 @LOC("THIS,PushbackInputStream.POS") int numBytes = Math.min(buf.length - pos,len);
220 System.arraycopy (buf, pos, b, off, numBytes);
228 len = super.read(b, off, len);
230 return numBytes > 0 ? numBytes : -1;
237 * This method pushes a single byte of data into the pushback buffer.
238 * The byte pushed back is the one that will be returned as the first byte
241 * If the pushback buffer is full, this method throws an exception.
243 * The argument to this method is an <code>int</code>. Only the low
244 * eight bits of this value are pushed back.
246 * @param b The byte to be pushed back, passed as an int
248 * @exception IOException If the pushback buffer is full.
250 public synchronized void unread(int b) throws IOException
253 throw new IOException("Insufficient space in pushback buffer");
255 buf[--pos] = (byte) b;
259 * This method pushes all of the bytes in the passed byte array into
260 * the pushback bfer. These bytes are pushed in reverse order so that
261 * the next byte read from the stream after this operation will be
262 * <code>b[0]</code> followed by <code>b[1]</code>, etc.
264 * If the pushback buffer cannot hold all of the requested bytes, an
265 * exception is thrown.
267 * @param b The byte array to be pushed back
269 * @exception IOException If the pushback buffer is full
271 public synchronized void unread(byte[] b) throws IOException
273 unread(b, 0, b.length);
277 * This method pushed back bytes from the passed in array into the
278 * pushback buffer. The bytes from <code>b[offset]</code> to
279 * <code>b[offset + len]</code> are pushed in reverse order so that
280 * the next byte read from the stream after this operation will be
281 * <code>b[offset]</code> followed by <code>b[offset + 1]</code>,
284 * If the pushback buffer cannot hold all of the requested bytes, an
285 * exception is thrown.
287 * @param b The byte array to be pushed back
288 * @param off The index into the array where the bytes to be push start
289 * @param len The number of bytes to be pushed.
291 * @exception IOException If the pushback buffer is full
293 public synchronized void unread(@LOC("IN") byte[] b, @LOC("IN") int off, @LOC("IN") int len)
297 throw new IOException("Insufficient space in pushback buffer");
299 // Note the order that these bytes are being added is the opposite
300 // of what would be done if they were added to the buffer one at a time.
301 // See the Java Class Libraries book p. 1390.
302 System.arraycopy(b, off, buf, pos - len, len);
304 // Don't put this into the arraycopy above, an exception might be thrown
305 // and in that case we don't want to modify pos.
310 * This method skips the specified number of bytes in the stream. It
311 * returns the actual number of bytes skipped, which may be less than the
314 * This method first discards bytes from the buffer, then calls the
315 * <code>skip</code> method on the underlying <code>InputStream</code> to
316 * skip additional bytes if necessary.
318 * @param n The requested number of bytes to skip
320 * @return The actual number of bytes skipped.
322 * @exception IOException If an error occurs
326 public synchronized long skip(long n) throws IOException
328 final long origN = n;
332 int numread = (int) Math.min((long) (buf.length - pos), n);