Android Open Source - azilink Udp Packet

• Back to Hardware/usb  ↑

From Project

Back to project page azilink.

License

The source code is released under:

GNU General Public License

Java Source Code

/* AziLink: USB tethering for Android
 * Copyright (C) 2009 by James Perry//  w  w  w. j  av  a 2s  . c  o m
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) version 3 of the License.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.lfx.azilink.net;

import java.nio.ByteBuffer;

/**
 * Represents a single UDP packet
 * 
 * @author Jim Perry
 *
 */
public class UdpPacket {
  /**
   * Builds an empty packet with preloaded addresses (REVERSED!)
   * @param nk addresses to preload (reversed)
   */
  UdpPacket( UdpKey nk ) {
    mRaw = ByteBuffer.allocate( 3000 );
    mUdpOffset = 20;
    mDataOffset = mUdpOffset + 8;
    mPacketLength = mDataOffset;
    
    mRaw.putShort( 0, (short) 0x4500 );  // len=20
    mRaw.putInt( 4, 0 );    // no flags, no fragment, no id
    mRaw.putShort( 8, (short) 0xFF11 );  // 255 TTL, UDP
    mRaw.putInt( 12, nk.mDestIp );    // src
    mRaw.putInt( 16, nk.mSrcIp );    // dest
    mRaw.putShort( mUdpOffset, (short) nk.mDestPort );
    mRaw.putShort( mUdpOffset+2, (short) nk.mSrcPort );    
  }
  
  /**
   * Complete a UDP packet (fill in length and compute checksums)
   */
  void complete() {
    mRaw.putShort( 2, (short) mPacketLength );
    mRaw.putShort( 10, (short) 0 );        // zero header checksum for calculation
    mRaw.putShort( mUdpOffset+4, (short) (mPacketLength-mUdpOffset) );
    mRaw.putShort( mUdpOffset+6, (short) 0 );  // zero udp checksum for calculation
    
    byte[] buf = mRaw.array();
    
    // ** IP header **
    {
      int leftSum = 0;
      int rightSum = 0;
      int sum = 0;
      
      int len = mUdpOffset;
      
      for( int i=0 ; i<len ; i+=2 ) {
        leftSum += buf[i] & 0xFF;
        rightSum += buf[i+1] & 0xFF;      
      }
      sum = (leftSum << 8) + rightSum;
      
      while( sum>>>16 != 0 ) {
        sum = (sum & 0xFFFF) + (sum >>> 16);
      }
      sum = ~sum;
      mRaw.putShort( 10, (short) sum );
    }
    
    // *** UDP
    {
      int leftSum = 0;
      int rightSum = 0;
      int sum = 0;
      
      int len = mPacketLength-1;
      
      for( int i=mUdpOffset ; i<len ; i+=2 ) {
        leftSum += buf[i] & 0xFF;
        rightSum += buf[i+1] & 0xFF;      
      }
      if( (mPacketLength&1) != 0) {
        leftSum += buf[ mPacketLength-1 ] & 0xFF;
      }
      sum = (leftSum << 8) + rightSum;
                  
      UdpKey nk = getAddresses();
      sum += (nk.mSrcIp>>>16)&0xFFFF;
      sum += (nk.mSrcIp)&0xFFFF;
      sum += (nk.mDestIp>>>16)&0xFFFF;
      sum += (nk.mDestIp)&0xFFFF;
      sum += mPacketLength - mUdpOffset;
      sum += getProtocol();
      while( (sum>>>16) != 0 ) {
        sum = (sum & 0xFFFF) + (sum >>> 16);
      }
      sum = ~sum;
      mRaw.putShort( mUdpOffset+6, (short) sum );
    }
  }    
  
  /**
   * Import an existing packet (wraps the provided buffer, so don't alter it)
   * @param pkt packet to import (do not alter until UdpPacket is destroyed)
   */
  UdpPacket( byte[] pkt ) {
    mRaw = ByteBuffer.wrap( pkt );
    mUdpOffset = (((int) mRaw.get(0)) & 0x0F) * 4;
    mDataOffset = mUdpOffset + 8;      
    mPacketLength = ((int) mRaw.getShort( 2 )) & 0xFFFF;
    if( mPacketLength > pkt.length ) mPacketLength = pkt.length;
  }
  
  /**
   * Get protocol of packet
   * @return protocol
   */
  int getProtocol() {
    return mRaw.get( 9 ) & 0xFF;
  }
  
  /**
   * Get the addresses used by this packet
   * @return addresses
   */
  UdpKey getAddresses() {
    UdpKey nk = new UdpKey();
    nk.mSrcIp = mRaw.getInt( 12 );
    nk.mDestIp = mRaw.getInt( 16 );
    nk.mSrcPort = ((int) mRaw.getShort( mUdpOffset )) & 0xFFFF;
    nk.mDestPort = ((int) mRaw.getShort( mUdpOffset+2 )) & 0xFFFF;
    return nk;
  }
  
  /**
   * Set the packet payload
   * 
   * @param info payload
   * @param len payload length
   */
  public void setData( byte[] info, int len ) {
    System.arraycopy( info, 0, mRaw.array(), mDataOffset, len );
    mPacketLength = mDataOffset + len;
  }
    
  /**
   * Get the payload length
   * @return payload length
   */
  public int getDataLength() {
    return mPacketLength - mDataOffset;
  }
  
  /**
   * Get the packet payload
   * @return payload
   */
  public byte[] getData() {
    byte[] dd = new byte[ getDataLength() ];
    System.arraycopy( mRaw.array(), mDataOffset, dd, 0, dd.length );
    return dd;
  }
  
  int mUdpOffset;
  int mDataOffset;
  int mPacketLength;
  ByteBuffer mRaw;
}

Java Source Code List

• Back to Hardware/usb  ↑