pastmessage.java

pastry的java实现的2.0b版

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

"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
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- Redistributions of source code must retain the above copyright
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- Redistributions in binary form must reproduce the above copyright
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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
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whether in contract, strict liability, or tort (including negligence
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********************************************************************************/

package rice.p2p.past.messaging;

import java.io.IOException;

import rice.*;
import rice.environment.Environment;
import rice.p2p.commonapi.*;
import rice.p2p.commonapi.rawserialization.*;
import rice.p2p.past.*;

/**
 * @(#) PastMessage.java This class the abstraction of a message used internally
 * by Past.
 *
 * @version $Id: PastMessage.java 3274 2006-05-15 16:17:47Z jeffh $
 * @author Alan Mislove
 * @author Ansley Post
 * @author Peter Druschel
 */
public abstract class PastMessage implements RawMessage {

  // the unique id for this message
  /**
   * DESCRIBE THE FIELD
   */
  protected int id;

  // the source Id of this message
  /**
   * DESCRIBE THE FIELD
   */
  protected NodeHandle source;

  // the destination of this message
  /**
   * DESCRIBE THE FIELD
   */
  protected Id dest;

  // whether or not this message is a response
  /**
   * DESCRIBE THE FIELD
   */
  protected boolean isResponse;

  // serialver for backward compatibility
  private final static long serialVersionUID = -7195054010358285316L;

  /**
   * Constructor which takes a unique integer Id
   *
   * @param id The unique id
   * @param source The source address
   * @param dest The destination address
   */
  protected PastMessage(int id, NodeHandle source, Id dest) {
    this.id = id;
    this.source = source;
    this.dest = dest;

    isResponse = false;
  }

  /**
   * Constructor for PastMessage.
   *
   * @param buf DESCRIBE THE PARAMETER
   * @param endpoint DESCRIBE THE PARAMETER
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public PastMessage(InputBuffer buf, Endpoint endpoint) throws IOException {
    id = buf.readInt();
//    System.out.println("PM.deserialize()" + endpoint);
    dest = endpoint.readId(buf, buf.readShort());
//    System.out.println("PastMessage dest:"+dest+" id:"+id);
    source = endpoint.readNodeHandle(buf);
    isResponse = buf.readBoolean();
  }

  /**
   * Method which should return the priority level of this message. The messages
   * can range in priority from 0 (highest priority) to Integer.MAX_VALUE
   * (lowest) - when sending messages across the wire, the queue is sorted by
   * message priority. If the queue reaches its limit, the lowest priority
   * messages are discarded. Thus, applications which are very verbose should
   * have LOW_PRIORITY or lower, and applications which are somewhat quiet are
   * allowed to have MEDIUM_PRIORITY or possibly even HIGH_PRIORITY.
   *
   * @return This message's priority
   */
  public byte getPriority() {
    return MEDIUM_HIGH_PRIORITY;
  }

  /**
   * Method which returns this messages' unique id
   *
   * @return The id of this message
   */
  public int getUID() {
    return id;
  }

  /**
   * Method which returns this messages' source address
   *
   * @return The source of this message
   */
  public NodeHandle getSource() {
    return source;
  }

  /**
   * Method which returns this messages' destination address
   *
   * @return The dest of this message
   */
  public Id getDestination() {
    return dest;
  }

  /**
   * Method which returns whether or not this message is a response.
   *
   * @return whether or not this message is a response.
   */
  public boolean isResponse() {
    return isResponse;
  }

  /**
   * Method which builds a response for this message, using the provided object
   * as a result. Should be overriden by subclasses, but with the
   * super.setResponse() called.
   */
  protected void setResponse() {
    isResponse = true;
  }

  /**
   * Method by which this message is supposed to return it's response.
   *
   * @param c The continuation to return the reponse to.
   * @param env DESCRIBE THE PARAMETER
   * @param instance DESCRIBE THE PARAMETER
   */
  public abstract void returnResponse(Continuation c, Environment env, String instance);

  /**
   * Method which is designed to be overridden by subclasses if they need to
   * keep track of where they've been.
   *
   * @param handle The current local handle
   */
  public void addHop(NodeHandle handle) {
  }

  /**
   * DESCRIBE THE METHOD
   *
   * @param buf DESCRIBE THE PARAMETER
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public void serialize(OutputBuffer buf) throws IOException {
    buf.writeInt(id);
//    System.out.println("PM.serialize()" + dest);
    buf.writeShort(dest.getType());
    dest.serialize(buf);
    source.serialize(buf);
    buf.writeBoolean(isResponse);
  }

}