/*************************************************************************

"FreePastry" Peer-to-Peer Application Development Substrate 

Copyright 2002, Rice University. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.

- Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

- Neither  the name  of Rice  University (RICE) nor  the names  of its
contributors may be  used to endorse or promote  products derived from
this software without specific prior written permission.

This software is provided by RICE and the contributors on an "as is"
basis, without any representations or warranties of any kind, express
or implied including, but not limited to, representations or
warranties of non-infringement, merchantability or fitness for a
particular purpose. In no event shall RICE or contributors be liable
for any direct, indirect, incidental, special, exemplary, or
consequential damages (including, but not limited to, procurement of
substitute goods or services; loss of use, data, or profits; or
business interruption) however caused and on any theory of liability,
whether in contract, strict liability, or tort (including negligence
or otherwise) arising in any way out of the use of this software, even
if advised of the possibility of such damage.

********************************************************************************/

package rice.p2p.commonapi;

import java.io.*;
import java.util.*;

import rice.p2p.commonapi.rawserialization.OutputBuffer;

/**
 * @(#) NodeHandle.java This class is an abstraction of a node handle from the
 * CommonAPI paper. A node handle is a handle to a known node, which
 * conceptually includes the node's Id, as well as the node's underlying network
 * address (such as IP/port). This class is (unfortunately) an abstact class due
 * to the need to be observable.
 *
 * @version $Id: NodeHandle.java 3274 2006-05-15 16:17:47Z jeffh $
 * @author Alan Mislove
 * @author Peter Druschel
 */
public abstract class NodeHandle extends Observable implements Serializable {

  // constants defining types of observable events
  /**
   * DESCRIBE THE FIELD
   */
  public final static Integer PROXIMITY_CHANGED = new Integer(1);
  /**
   * DESCRIBE THE FIELD
   */
  public final static Integer DECLARED_DEAD = new Integer(2);
  /**
   * DESCRIBE THE FIELD
   */
  public final static Integer DECLARED_LIVE = new Integer(3);

  // serialver
  private final static long serialVersionUID = 4761193998848368227L;

  /**
   * Returns this node's id.
   *
   * @return The corresponding node's id.
   */
  public abstract Id getId();

  /**
   * Returns whether or not this node is currently alive
   *
   * @return Whether or not this node is currently alive
   */
  public abstract boolean isAlive();

  /**
   * Returns the current proximity value of this node
   *
   * @return The current proximity value of this node
   */
  public abstract int proximity();

  /**
   * Requests that the underlying transport layer check to ensure that the
   * remote node is live. If the node is found to be live, nothing happens, but
   * if the node does not respond, the transport layer make take steps to
   * verfify that the node is dead. Such steps could include finding an
   * alteranate route to the node.
   *
   * @return Whether or not the node is currently alive
   */
  public abstract boolean checkLiveness();

  /**
   * DESCRIBE THE METHOD
   *
   * @param buf DESCRIBE THE PARAMETER
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public abstract void serialize(OutputBuffer buf) throws IOException;

}

