terminalinputchaff.java

一个非常好的ssh客户端实现

/******************************************************************************
 *
 * Copyright (c) 1999-2003 AppGate Network Security AB. All Rights Reserved.
 * 
 * This file contains Original Code and/or Modifications of Original Code as
 * defined in and that are subject to the MindTerm Public Source License,
 * Version 2.0, (the 'License'). You may not use this file except in compliance
 * with the License.
 * 
 * You should have received a copy of the MindTerm Public Source License
 * along with this software; see the file LICENSE.  If not, write to
 * AppGate Network Security AB, Otterhallegatan 2, SE-41118 Goteborg, SWEDEN
 *
 *****************************************************************************/

package com.mindbright.terminal;

public abstract class TerminalInputChaff implements TerminalInputListener,
						    Runnable
{
    private Thread           chaffThread;
    private volatile boolean chaffActive;
    private volatile long    chaffLastKeyTime;

    private int[] lastKeyBuf;
    private int   lastKeyROffs;
    private int   lastKeyWOffs;

    public void startChaff() {
	if(!chaffActive) {
	    chaffActive  = true;
	    lastKeyBuf   = new int[4];
	    lastKeyROffs = 0;
	    lastKeyWOffs = 0;
	    chaffThread  = new Thread(this, "SSH2TerminalAdapterImpl.chaff");
	    chaffThread.setDaemon(true);
	    chaffThread.start();
	}
    }

    public void stopChaff() {
	if(chaffActive) {
	    chaffActive = false;
	    synchronized(chaffThread) {
		chaffThread.notify();
	    }
	    chaffThread = null;
	}
    }

    public void typedChar(char c) {
	if(chaffThread == null) {
	    sendTypedChar((int)c);
	} else {
	    synchronized(this) {
		lastKeyBuf[lastKeyWOffs++] = (int)c;
		lastKeyWOffs &= 0x03;
	    }
	    dispenseChaff();
	}
    }

    public void run() {
	long now;
	int  wait;
	while(chaffActive) {
	    try {
		synchronized(chaffThread) {
		    chaffThread.wait();
		}
		wait = (int)(System.currentTimeMillis() ^
			     (new Object()).hashCode()) & 0x1ff;
		do {
		    int lastKeyChar = -1;
		    synchronized(this) {
			if(lastKeyWOffs != lastKeyROffs) {
			    lastKeyChar = lastKeyBuf[lastKeyROffs++];
			    lastKeyROffs &= 0x03;
			}
		    }
		    if(lastKeyChar >= 0) {
			sendTypedChar(lastKeyChar);
		    } else {
			sendFakeChar();
		    }
		    Thread.sleep(30);
		    now = System.currentTimeMillis();
		} while(chaffActive &&
			(now - chaffLastKeyTime) < (1500 + wait));
	    } catch (InterruptedException e) {
		/* don't care... */
	    }
	}
    }

    public void dispenseChaff() {
	if(chaffThread != null) {
	    long now = System.currentTimeMillis();
	    if((now - chaffLastKeyTime) > 1000) {
		chaffLastKeyTime = now;
		synchronized(chaffThread) {
		    chaffThread.notify();
		}
	    }
	}
    }

    protected abstract void sendTypedChar(int c);
    protected abstract void sendFakeChar();

}