com.trilead.ssh2.StreamGobbler Maven / Gradle / Ivy
package com.trilead.ssh2;
import java.io.IOException;
import java.io.InputStream;
/**
* A StreamGobbler is an InputStream that uses an internal worker
* thread to constantly consume input from another InputStream. It uses a buffer
* to store the consumed data. The buffer size is automatically adjusted, if needed.
*
* This class is sometimes very convenient - if you wrap a session's STDOUT and STDERR
* InputStreams with instances of this class, then you don't have to bother about
* the shared window of STDOUT and STDERR in the low level SSH-2 protocol,
* since all arriving data will be immediatelly consumed by the worker threads.
* Also, as a side effect, the streams will be buffered (e.g., single byte
* read() operations are faster).
*
* Other SSH for Java libraries include this functionality by default in
* their STDOUT and STDERR InputStream implementations, however, please be aware
* that this approach has also a downside:
*
* If you do not call the StreamGobbler's read() method often enough
* and the peer is constantly sending huge amounts of data, then you will sooner or later
* encounter a low memory situation due to the aggregated data (well, it also depends on the Java heap size).
* Joe Average will like this class anyway - a paranoid programmer would never use such an approach.
*
* The term "StreamGobbler" was taken from an article called "When Runtime.exec() won't",
* see http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html.
*
* @author Christian Plattner, [email protected]
* @version $Id: StreamGobbler.java,v 1.1 2007/10/15 12:49:56 cplattne Exp $
*/
public class StreamGobbler extends InputStream
{
class GobblerThread extends Thread
{
public void run()
{
byte[] buff = new byte[8192];
while (true)
{
try
{
int avail = is.read(buff);
synchronized (synchronizer)
{
if (avail <= 0)
{
isEOF = true;
synchronizer.notifyAll();
break;
}
int space_available = buffer.length - write_pos;
if (space_available < avail)
{
/* compact/resize buffer */
int unread_size = write_pos - read_pos;
int need_space = unread_size + avail;
byte[] new_buffer = buffer;
if (need_space > buffer.length)
{
int inc = need_space / 3;
inc = (inc < 256) ? 256 : inc;
inc = (inc > 8192) ? 8192 : inc;
new_buffer = new byte[need_space + inc];
}
if (unread_size > 0)
System.arraycopy(buffer, read_pos, new_buffer, 0, unread_size);
buffer = new_buffer;
read_pos = 0;
write_pos = unread_size;
}
System.arraycopy(buff, 0, buffer, write_pos, avail);
write_pos += avail;
synchronizer.notifyAll();
}
}
catch (IOException e)
{
synchronized (synchronizer)
{
exception = e;
synchronizer.notifyAll();
break;
}
}
}
}
}
private InputStream is;
private GobblerThread t;
private Object synchronizer = new Object();
private boolean isEOF = false;
private boolean isClosed = false;
private IOException exception = null;
private byte[] buffer = new byte[2048];
private int read_pos = 0;
private int write_pos = 0;
public StreamGobbler(InputStream is)
{
this.is = is;
t = new GobblerThread();
t.setDaemon(true);
t.start();
}
public int read() throws IOException
{
synchronized (synchronizer)
{
if (isClosed)
throw new IOException("This StreamGobbler is closed.");
while (read_pos == write_pos)
{
if (exception != null)
throw exception;
if (isEOF)
return -1;
try
{
synchronizer.wait();
}
catch (InterruptedException e)
{
}
}
int b = buffer[read_pos++] & 0xff;
return b;
}
}
public int available() throws IOException
{
synchronized (synchronizer)
{
if (isClosed)
throw new IOException("This StreamGobbler is closed.");
return write_pos - read_pos;
}
}
public int read(byte[] b) throws IOException
{
return read(b, 0, b.length);
}
public void close() throws IOException
{
synchronized (synchronizer)
{
if (isClosed)
return;
isClosed = true;
isEOF = true;
synchronizer.notifyAll();
is.close();
}
}
public int read(byte[] b, int off, int len) throws IOException
{
if (b == null)
throw new NullPointerException();
if ((off < 0) || (len < 0) || ((off + len) > b.length) || ((off + len) < 0) || (off > b.length))
throw new IndexOutOfBoundsException();
if (len == 0)
return 0;
synchronized (synchronizer)
{
if (isClosed)
throw new IOException("This StreamGobbler is closed.");
while (read_pos == write_pos)
{
if (exception != null)
throw exception;
if (isEOF)
return -1;
try
{
synchronizer.wait();
}
catch (InterruptedException e)
{
}
}
int avail = write_pos - read_pos;
avail = (avail > len) ? len : avail;
System.arraycopy(buffer, read_pos, b, off, avail);
read_pos += avail;
return avail;
}
}
}