--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/com/trilead/ssh2/channel/Channel.java	Thu May 22 10:41:19 2014 -0700
@@ -0,0 +1,192 @@
+
+package com.trilead.ssh2.channel;
+
+/**
+ * Channel.
+ *
+ * @author Christian Plattner, plattner@trilead.com
+ * @version $Id: Channel.java,v 1.1 2007/10/15 12:49:56 cplattne Exp $
+ */
+public class Channel {
+    /*
+     * OK. Here is an important part of the JVM Specification:
+     * (http://java.sun.com/docs/books/vmspec/2nd-edition/html/Threads.doc.html#22214)
+     *
+     * Any association between locks and variables is purely conventional.
+     * Locking any lock conceptually flushes all variables from a thread's
+     * working memory, and unlocking any lock forces the writing out to main
+     * memory of all variables that the thread has assigned. That a lock may be
+     * associated with a particular object or a class is purely a convention.
+     * (...)
+     *
+     * If a thread uses a particular shared variable only after locking a
+     * particular lock and before the corresponding unlocking of that same lock,
+     * then the thread will read the shared value of that variable from main
+     * memory after the lock operation, if necessary, and will copy back to main
+     * memory the value most recently assigned to that variable before the
+     * unlock operation.
+     *
+     * This, in conjunction with the mutual exclusion rules for locks, suffices
+     * to guarantee that values are correctly transmitted from one thread to
+     * another through shared variables.
+     *
+     * ====> Always keep that in mind when modifying the Channel/ChannelManger
+     * code.
+     *
+     */
+
+    static final int STATE_OPENING = 1;
+    static final int STATE_OPEN = 2;
+    static final int STATE_CLOSED = 4;
+
+    static final int CHANNEL_BUFFER_SIZE = 30000;
+
+    /*
+     * To achieve correctness, the following rules have to be respected when
+     * accessing this object:
+     */
+
+    // These fields can always be read
+    final ChannelManager cm;
+    final ChannelOutputStream stdinStream;
+    final ChannelInputStream stdoutStream;
+    final ChannelInputStream stderrStream;
+
+    // These two fields will only be written while the Channel is in state
+    // STATE_OPENING.
+    // The code makes sure that the two fields are written out when the state is
+    // changing to STATE_OPEN.
+    // Therefore, if you know that the Channel is in state STATE_OPEN, then you
+    // can read these two fields without synchronizing on the Channel. However, make
+    // sure that you get the latest values (e.g., flush caches by synchronizing on any
+    // object). However, to be on the safe side, you can lock the channel.
+
+    int localID = -1;
+    int remoteID = -1;
+
+    /*
+     * Make sure that we never send a data/EOF/WindowChange msg after a CLOSE
+     * msg.
+     *
+     * This is a little bit complicated, but we have to do it in that way, since
+     * we cannot keep a lock on the Channel during the send operation (this
+     * would block sometimes the receiver thread, and, in extreme cases, can
+     * lead to a deadlock on both sides of the connection (senders are blocked
+     * since the receive buffers on the other side are full, and receiver
+     * threads wait for the senders to finish). It all depends on the
+     * implementation on the other side. But we cannot make any assumptions, we
+     * have to assume the worst case. Confused? Just believe me.
+     */
+
+    /*
+     * If you send a message on a channel, then you have to aquire the
+     * "channelSendLock" and check the "closeMessageSent" flag (this variable
+     * may only be accessed while holding the "channelSendLock" !!!
+     *
+     * BTW: NEVER EVER SEND MESSAGES FROM THE RECEIVE THREAD - see explanation
+     * above.
+     */
+
+    final Object channelSendLock = new Object();
+    boolean closeMessageSent = false;
+
+    /*
+     * Stop memory fragmentation by allocating this often used buffer.
+     * May only be used while holding the channelSendLock
+     */
+
+    final byte[] msgWindowAdjust = new byte[9];
+
+    // If you access (read or write) any of the following fields, then you have
+    // to synchronize on the channel.
+
+    int state = STATE_OPENING;
+
+    boolean closeMessageRecv = false;
+
+    /* This is a stupid implementation. At the moment we can only wait
+     * for one pending request per channel.
+     */
+    int successCounter = 0;
+    int failedCounter = 0;
+
+    int localWindow = 0; /* locally, we use a small window, < 2^31 */
+    long remoteWindow = 0; /* long for readable  2^32 - 1 window support */
+
+    int localMaxPacketSize = -1;
+    int remoteMaxPacketSize = -1;
+
+    final byte[] stdoutBuffer = new byte[CHANNEL_BUFFER_SIZE];
+    final byte[] stderrBuffer = new byte[CHANNEL_BUFFER_SIZE];
+
+    int stdoutReadpos = 0;
+    int stdoutWritepos = 0;
+    int stderrReadpos = 0;
+    int stderrWritepos = 0;
+
+    boolean EOF = false;
+
+    Integer exit_status;
+
+    String exit_signal;
+
+    // we keep the x11 cookie so that this channel can be closed when this
+    // specific x11 forwarding gets stopped
+
+    String hexX11FakeCookie;
+
+    // reasonClosed is special, since we sometimes need to access it
+    // while holding the channelSendLock.
+    // We protect it with a private short term lock.
+
+    private final Object reasonClosedLock = new Object();
+    private String reasonClosed = null;
+
+    public Channel(ChannelManager cm) {
+        this.cm = cm;
+        this.localWindow = CHANNEL_BUFFER_SIZE;
+        this.localMaxPacketSize = 35000 - 1024; // leave enough slack
+        this.stdinStream = new ChannelOutputStream(this);
+        this.stdoutStream = new ChannelInputStream(this, false);
+        this.stderrStream = new ChannelInputStream(this, true);
+    }
+
+    /* Methods to allow access from classes outside of this package */
+
+    public ChannelInputStream getStderrStream() {
+        return stderrStream;
+    }
+
+    public ChannelOutputStream getStdinStream() {
+        return stdinStream;
+    }
+
+    public ChannelInputStream getStdoutStream() {
+        return stdoutStream;
+    }
+
+    public String getExitSignal() {
+        synchronized (this) {
+            return exit_signal;
+        }
+    }
+
+    public Integer getExitStatus() {
+        synchronized (this) {
+            return exit_status;
+        }
+    }
+
+    public String getReasonClosed() {
+        synchronized (reasonClosedLock) {
+            return reasonClosed;
+        }
+    }
+
+    public void setReasonClosed(String reasonClosed) {
+        synchronized (reasonClosedLock) {
+            if (this.reasonClosed == null)
+                this.reasonClosed = reasonClosed;
+        }
+    }
+}