001    /* PipedInputStream.java -- Read portion of piped streams.
002       Copyright (C) 1998, 1999, 2000, 2001, 2003, 2005  Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010     
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    package java.io;
039    
040    // NOTE: This implementation is very similar to that of PipedReader.  If you 
041    // fix a bug in here, chances are you should make a similar change to the 
042    // PipedReader code.
043    
044    /**
045      * An input stream that reads its bytes from an output stream
046      * to which it is connected. 
047      * <p>
048      * Data is read and written to an internal buffer.  It is highly recommended
049      * that the <code>PipedInputStream</code> and connected 
050      * <code>PipedOutputStream</code>
051      * be part of different threads.  If they are not, the read and write 
052      * operations could deadlock their thread.
053      *
054      * @specnote The JDK implementation appears to have some undocumented 
055      *           functionality where it keeps track of what thread is writing
056      *           to pipe and throws an IOException if that thread susequently
057      *           dies. This behaviour seems dubious and unreliable - we don't
058      *           implement it.
059      *
060      * @author Aaron M. Renn (arenn@urbanophile.com)
061      */
062    public class PipedInputStream extends InputStream
063    {
064      /** PipedOutputStream to which this is connected. Null only if this 
065        * InputStream hasn't been connected yet. */
066      PipedOutputStream source;
067    
068      /** Set to true if close() has been called on this InputStream. */
069      boolean closed;
070    
071    
072      /**
073       * The size of the internal buffer used for input/output.
074       */
075      /* The "Constant Field Values" Javadoc of the Sun J2SE 1.4
076       * specifies 1024.
077       */
078      protected static final int PIPE_SIZE = 1024;
079    
080    
081      /**
082        * This is the internal circular buffer used for storing bytes written
083        * to the pipe and from which bytes are read by this stream
084        */
085      protected byte[] buffer = null;
086    
087      /**
088        * The index into buffer where the next byte from the connected
089        * <code>PipedOutputStream</code> will be written. If this variable is 
090        * equal to <code>out</code>, then the buffer is full. If set to < 0,
091        * the buffer is empty.
092        */
093      protected int in = -1;
094    
095      /**
096        * This index into the buffer where bytes will be read from.
097        */
098      protected int out = 0;
099    
100      /** Buffer used to implement single-argument read/receive */
101      private byte[] read_buf = new byte[1];
102    
103      /**
104        * Creates a new <code>PipedInputStream</code> that is not connected to a 
105        * <code>PipedOutputStream</code>.  It must be connected before bytes can 
106        * be read from this stream.
107        */
108      public PipedInputStream()
109      {
110        this(PIPE_SIZE);
111      }
112    
113      /**
114       * Creates a new <code>PipedInputStream</code> of the given size that is not
115       * connected to a <code>PipedOutputStream</code>.
116       * It must be connected before bytes can be read from this stream.
117       * 
118       * @since 1.6
119       * @since IllegalArgumentException If pipeSize <= 0.
120       */
121      public PipedInputStream(int pipeSize) throws IllegalArgumentException 
122      {
123        if (pipeSize <= 0)
124          throw new IllegalArgumentException("pipeSize must be > 0");
125        
126        this.buffer = new byte[pipeSize];
127      }
128      
129      /**
130        * This constructor creates a new <code>PipedInputStream</code> and connects
131        * it to the passed in <code>PipedOutputStream</code>. The stream is then 
132        * ready for reading.
133        *
134        * @param source The <code>PipedOutputStream</code> to connect this 
135        * stream to
136        *
137        * @exception IOException If <code>source</code> is already connected.
138        */
139      public PipedInputStream(PipedOutputStream source) throws IOException
140      {
141        this();
142        connect(source);
143      }
144    
145      /**
146       * This constructor creates a new <code>PipedInputStream</code> of the given
147       * size and connects it to the passed in <code>PipedOutputStream</code>.
148       * The stream is then ready for reading.
149       *
150       * @param source The <code>PipedOutputStream</code> to connect this 
151       * stream to
152       *
153       * @since 1.6
154       * @exception IOException If <code>source</code> is already connected.
155       */
156     public PipedInputStream(PipedOutputStream source, int pipeSize)
157       throws IOException
158     {
159       this(pipeSize);
160       connect(source);
161     }
162      
163      /**
164        * This method connects this stream to the passed in 
165        * <code>PipedOutputStream</code>.
166        * This stream is then ready for reading.  If this stream is already
167        * connected or has been previously closed, then an exception is thrown
168        *
169        * @param source The <code>PipedOutputStream</code> to connect this stream to
170        *
171        * @exception IOException If this PipedInputStream or <code>source</code> 
172        *                        has been connected already.
173        */
174      public void connect(PipedOutputStream source) throws IOException
175      {
176        // The JDK (1.3) does not appear to check for a previously closed 
177        // connection here.
178        
179        if (this.source != null || source.sink != null)
180          throw new IOException ("Already connected");
181        
182        source.sink = this;
183        this.source = source;
184      }
185      
186      /**
187      * This method receives a byte of input from the source PipedOutputStream.
188      * If the internal circular buffer is full, this method blocks.
189      *
190      * @param val The byte to write to this stream
191      *
192      * @exception IOException if error occurs
193      * @specnote Weird. This method must be some sort of accident.
194      */
195      protected synchronized void receive(int val) throws IOException
196      {
197        read_buf[0] = (byte) (val & 0xff);
198        receive (read_buf, 0, 1);
199      }
200    
201      /**
202        * This method is used by the connected <code>PipedOutputStream</code> to
203        * write bytes into the buffer.
204        *
205        * @param buf The array containing bytes to write to this stream
206        * @param offset The offset into the array to start writing from
207        * @param len The number of bytes to write.
208        *
209        * @exception IOException If an error occurs
210        * @specnote This code should be in PipedOutputStream.write, but we
211        *           put it here in order to support that bizarre recieve(int)
212        *           method.
213        */  
214      synchronized void receive(byte[] buf, int offset, int len)
215        throws IOException
216      {
217        if (closed)
218          throw new IOException ("Pipe closed");
219    
220        int bufpos = offset;
221        int copylen;
222        
223        while (len > 0)
224          {
225            try
226              {
227                while (in == out)
228                  {
229                    // The pipe is full. Wake up any readers and wait for them.
230                    notifyAll();
231                    wait();
232                    // The pipe could have been closed while we were waiting.
233                    if (closed)
234                      throw new IOException ("Pipe closed");
235                  }
236              }
237            catch (InterruptedException ix)
238              {
239                throw new InterruptedIOException ();
240              }
241    
242            if (in < 0) // The pipe is empty.
243              in = 0;
244            
245            // Figure out how many bytes from buf can be copied without 
246            // overrunning out or going past the length of the buffer.
247            if (in < out)
248              copylen = Math.min (len, out - in);
249            else
250              copylen = Math.min (len, buffer.length - in);
251    
252            // Copy bytes until the pipe is filled, wrapping if necessary.
253            System.arraycopy(buf, bufpos, buffer, in, copylen);
254            len -= copylen;
255            bufpos += copylen;
256            in += copylen;
257            if (in == buffer.length)
258              in = 0;
259          }
260        // Notify readers that new data is in the pipe.
261        notifyAll();
262      }
263      
264      /**
265        * This method reads one byte from the stream.
266        * -1 is returned to indicated that no bytes can be read
267        * because the end of the stream was reached.  If the stream is already
268        * closed, a -1 will again be returned to indicate the end of the stream.
269        * 
270        * <p>This method will block if no byte is available to be read.</p>
271        *
272        * @return the value of the read byte value, or -1 of the end of the stream
273        * was reached
274        * 
275        * @throws IOException if an error occured
276        */
277      public int read() throws IOException
278      {
279        // Method operates by calling the multibyte overloaded read method
280        // Note that read_buf is an internal instance variable.  I allocate it
281        // there to avoid constant reallocation overhead for applications that
282        // call this method in a loop at the cost of some unneeded overhead
283        // if this method is never called.
284    
285        int r = read(read_buf, 0, 1);
286        return r != -1 ? (read_buf[0] & 0xff) : -1;
287      }
288      
289      /**
290        * This method reads bytes from the stream into a caller supplied buffer.
291        * It starts storing bytes at position <code>offset</code> into the 
292        * buffer and
293        * reads a maximum of <code>len</code> bytes.  Note that this method 
294        * can actually
295        * read fewer than <code>len</code> bytes.  The actual number of bytes 
296        * read is
297        * returned.  A -1 is returned to indicated that no bytes can be read
298        * because the end of the stream was reached - ie close() was called on the
299        * connected PipedOutputStream.
300        * <p>
301        * This method will block if no bytes are available to be read.
302        *
303        * @param buf The buffer into which bytes will be stored
304        * @param offset The index into the buffer at which to start writing.
305        * @param len The maximum number of bytes to read.
306        *
307        * @exception IOException If <code>close()</code> was called on this Piped
308        *                        InputStream.
309        */  
310      public synchronized int read(byte[] buf, int offset, int len)
311        throws IOException
312      {
313        if (source == null)
314          throw new IOException ("Not connected");
315        if (closed)
316          throw new IOException ("Pipe closed");
317    
318        // Don't block if nothing was requested.
319        if (len == 0)
320          return 0;
321    
322        // If the buffer is empty, wait until there is something in the pipe 
323        // to read.
324        try
325          {
326            while (in < 0)
327              {
328                if (source.closed)
329                  return -1;
330                wait();
331              }
332          }
333        catch (InterruptedException ix)
334          {
335            throw new InterruptedIOException();
336          }
337        
338        int total = 0;
339        int copylen;
340        
341        while (true)
342          {
343            // Figure out how many bytes from the pipe can be copied without 
344            // overrunning in or going past the length of buf.
345            if (out < in)
346              copylen = Math.min (len, in - out);
347            else
348              copylen = Math.min (len, buffer.length - out);
349    
350            System.arraycopy (buffer, out, buf, offset, copylen);
351            offset += copylen;
352            len -= copylen;
353            out += copylen;
354            total += copylen;
355            
356            if (out == buffer.length)
357              out = 0;
358            
359            if (out == in)
360              {
361                // Pipe is now empty.
362                in = -1;
363                out = 0;
364              }
365    
366            // If output buffer is filled or the pipe is empty, we're done.
367            if (len == 0 || in == -1)
368              {
369                // Notify any waiting outputstream that there is now space
370                // to write.
371                notifyAll();
372                return total;
373              }
374          }
375      }
376      
377      /**
378        * This method returns the number of bytes that can be read from this stream
379        * before blocking could occur.  This is the number of bytes that are
380        * currently unread in the internal circular buffer.  Note that once this
381        * many additional bytes are read, the stream may block on a subsequent
382        * read, but it not guaranteed to block.
383        *
384        * @return The number of bytes that can be read before blocking might occur
385        *
386        * @exception IOException If an error occurs
387        */  
388      public synchronized int available() throws IOException
389      {
390        // The JDK 1.3 implementation does not appear to check for the closed or 
391        // unconnected stream conditions here.
392        
393        if (in < 0)
394          return 0;
395        else if (out < in)
396          return in - out;
397        else
398          return (buffer.length - out) + in;
399      }
400      
401      /**
402      * This methods closes the stream so that no more data can be read
403      * from it.
404      *
405      * @exception IOException If an error occurs
406      */
407      public synchronized void close() throws IOException
408      {
409        closed = true;
410        // Wake any thread which may be in receive() waiting to write data.
411        notifyAll();
412      }
413    }
414