package com.trilead.ssh2;

import java.io.IOException;
import java.io.InputStream;

/**
 * A <code>StreamGobbler</code> 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.
 * <p>
 * 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).
 * <p>
 * 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:
 * <p>
 * If you do not call the StreamGobbler's <code>read()</code> 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.
 * <p>
 * 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, plattner@trilead.com
 * @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;
        }
    }
}