src/java/com/oroinc/net/tftp/TFTPDataPacket.java

/***
 * $Id: TFTPDataPacket.java,v 1.1 2002/04/03 01:04:38 brekke Exp $
 *
 * NetComponents Internet Protocol Library
 * Copyright (C) 1997-2002  Daniel F. Savarese
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library in the LICENSE file; if not, write
 * to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 * Boston, MA  02111-1307  USA
 ***/

package com.oroinc.net.tftp;

import java.net.*;

/***
 * A final class derived from TFTPPacket definiing the TFTP Data
 * packet type.
 * <p>
 * Details regarding the TFTP protocol and the format of TFTP packets can
 * be found in RFC 783.  But the point of these classes is to keep you
 * from having to worry about the internals.  Additionally, only very
 * few people should have to care about any of the TFTPPacket classes
 * or derived classes.  Almost all users should only be concerned with the
 * <a href="com.oroinc.net.tftp.TFTPClient.html#_top_">TFTPClient</a> class
 * <a href="com.oroinc.net.tftp.TFTPClient.html#receiveFile">receiveFile()</a>
 * and
 * <a href="com.oroinc.net.tftp.TFTPClient.html#sendFile">sendFile()</a>
 * methods.
 * <p>
 * <p>
 * @author Daniel F. Savarese
 * @see TFTPPacket
 * @see TFTPPacketException
 * @see TFTP
 ***/

public final class TFTPDataPacket extends TFTPPacket {
  /*** The maximum number of bytes in a TFTP data packet (512) ***/ 
  public static final int MAX_DATA_LENGTH = 512;

  /*** The minimum number of bytes in a TFTP data packet (0) ***/ 
  public static final int MIN_DATA_LENGTH = 0;

  /*** The block number of the packet. ***/
  int _blockNumber;

  /*** The length of the data. ***/
  int _length;

  /*** The offset into the _data array at which the data begins. ***/
  int _offset;

  /*** The data stored in the packet. ***/
  byte[] _data;

  /***
   * Creates a data packet to be sent to a host at a given port
   * with a given block number.  The actual data to be sent is passed as
   * an array, an offset, and a length.  The offset is the offset into
   * the byte array where the data starts.  The length is the length of
   * the data.  If the length is greater than MAX_DATA_LENGTH, it is
   * truncated.
   * <p>
   * @param destination  The host to which the packet is going to be sent.
   * @param port  The port to which the packet is going to be sent.
   * @param blockNumber The block number of the data.
   * @param data The byte array containing the data.
   * @param offset The offset into the array where the data starts.
   * @param length The length of the data.
   ***/
  public TFTPDataPacket(InetAddress destination, int port, int blockNumber,
			byte[] data, int offset, int length){
    super(TFTPPacket.DATA, destination, port);

    _blockNumber = blockNumber;
    _data        = data;
    _offset      = offset;

    if(length > MAX_DATA_LENGTH)
      _length = MAX_DATA_LENGTH;
    else
      _length = length;
  }

  public TFTPDataPacket(InetAddress destination, int port, int blockNumber,
			byte[] data) {
    this(destination, port, blockNumber, data, 0, data.length);
  }


  /***
   * Creates a data packet based from a received
   * datagram.  Assumes the datagram is at least length 4, else an
   * ArrayIndexOutOfBoundsException may be thrown.
   * <p>
   * @param datagram  The datagram containing the received data.
   * @throws TFTPPacketException  If the datagram isn't a valid TFTP
   *         data packet.
   ***/
  TFTPDataPacket(DatagramPacket datagram) throws TFTPPacketException {
    super(TFTPPacket.DATA, datagram.getAddress(), datagram.getPort());

    _data   = datagram.getData();
    _offset = 4;

    if(getType() != _data[1])
      throw new TFTPPacketException("TFTP operator code does not match type.");

    _blockNumber = (((_data[2] & 0xff) << 8) | (_data[3] & 0xff));

    _length      =  datagram.getLength() - 4;

    if(_length > MAX_DATA_LENGTH)
      _length = MAX_DATA_LENGTH;
  }

  /***
   * This is a method only available within the package for
   * implementing efficient datagram transport by elminating buffering.
   * It takes a datagram as an argument, and a byte buffer in which 
   * to store the raw datagram data.  Inside the method, the data
   * is set as the datagram's data and the datagram returned.
   * <p>
   * @param datagram  The datagram to create.
   * @param data The buffer to store the packet and to use in the datagram.
   * @return The datagram argument.
   ***/
  DatagramPacket _newDatagram(DatagramPacket datagram, byte[] data) {
    data[0] = 0; data[1] = (byte)_type;
    data[2] = (byte)((_blockNumber & 0xffff) >> 8);
    data[3] = (byte)(_blockNumber & 0xff);

    // Doublecheck we're not the same
    if(data != _data)
      System.arraycopy(_data, _offset, data, 4, _length);

    datagram.setAddress(_address);
    datagram.setPort(_port);
    datagram.setData(data);
    datagram.setLength(_length + 4);

    return datagram;
  }

  /***
   * This is a method exposed to the programmer in case he
   * wants to implement his own TFTP client instead of using
   * the <a href="com.oroinc.net.tftp.TFTPClient.html#_top_">TFTPClient</a> 
   * class.
   * Under normal circumstances, you should not have a need to call this
   * method.  It creates a UDP datagram containing all the TFTP
   * data packet data in the proper format.
   * <p>
   * @return A UDP datagram containing the TFTP data packet.
   ***/
  public DatagramPacket newDatagram() {
    byte[] data;
    DatagramPacket datagram;

    data    = new byte[_length + 4];
    data[0] = 0; data[1] = (byte)_type;
    data[2] = (byte)((_blockNumber & 0xffff) >> 8);
    data[3] = (byte)(_blockNumber & 0xff);

    System.arraycopy(_data, _offset, data, 4, _length);

    return new DatagramPacket(data, _length + 4, _address, _port);
  }

  /***
   * Returns the block number of the data packet.
   * <p>
   * @return The block number of the data packet.
   ***/
  public int getBlockNumber() { return _blockNumber; }

  /*** Sets the block number of the data packet.  ***/
  public void setBlockNumber(int blockNumber) { _blockNumber = blockNumber; }

  /***
   * Sets the data for the data packet.
   * <p>
   * @param data The byte array containing the data.
   * @param offset The offset into the array where the data starts.
   * @param length The length of the data.
   ***/
  public void setData(byte[] data, int offset, int length) {
    _data = data;
    _offset = offset;
    _length = length;

    if(length > MAX_DATA_LENGTH)
      _length = MAX_DATA_LENGTH;
    else
      _length = length;
  }

  /***
   * Returns the length of the data part of the data packet.
   * <p>
   * @return The length of the data part of the data packet.
   ***/
  public int getDataLength()  { return _length; }

  /***
   * Returns the offset into the byte array where the packet data actually
   * starts.
   * <p>
   * @return The offset into the byte array where the packet data actually
   *         starts.
   ***/
  public int getDataOffset()  { return _offset; }

  /***
   * Returns the byte array containing the packet data.
   * <p>
   * @return The byte array containing the packet data.
   ***/
  public byte[] getData()     { return _data; }
}