Android Open Source - azilink Icmp 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 ava 2 s . 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 ICMP packet.
 * 
 * @author Jim Perry
 *
 */
public class IcmpPacket {
  /** Create an empty packet with provided IP addresses.  Since this is used to create a reply packet,
   * the src and dest addresses are reversed during construction.
   * 
   * @param nk src/dest addresses (inverted)
   */
  IcmpPacket( IcmpKey nk ) {
    mRaw = ByteBuffer.allocate( 1500 );
    mIcmpOffset = 20;
    mDataOffset = mIcmpOffset + 8;
    mPacketLength = mDataOffset;
    
    mRaw.putShort( 0, (short) 0x4500 );  // len=20
    mRaw.putInt( 4, 0 );    // no flags, no fragment, no id
    mRaw.putShort( 8, (short) 0xFF01 );  // 255 TTL, ICMP
    mRaw.putInt( 12, nk.mDestIp );    // src
    mRaw.putInt( 16, nk.mSrcIp );    // dest
  }
  
  /** Swap src/dest IP addresses */
  void swapHosts() {
    int src = mRaw.getInt(12);
    mRaw.putInt(12, mRaw.getInt(16));
    mRaw.putInt(16, src);
  }
  
  /** Prepare to send packet.  Store size and compute checksums. */
  void complete() {
    mRaw.putShort( 2, (short) mPacketLength );
    mRaw.putShort( 10, (short) 0 );        // zero header checksum for calculation
    mRaw.putShort( mIcmpOffset+2, (short) 0 );  // zero udp checksum for calculation
    
    // ** IP header **
    int sum = 0;
    for( int i=0 ; i<mIcmpOffset ; i+=2 ) {
      sum += ((int) mRaw.getShort( i )) & 0xFFFF;
    }
    while( sum>>>16 != 0 ) {
      sum = (sum & 0xFFFF) + (sum >>> 16);
    }
    sum = ~sum;
    mRaw.putShort( 10, (short) sum );
    
    // ** ICMP **
    sum = 0;
    // -1 is so we don't scan a final odd byte
    for( int i=mIcmpOffset ; i<mPacketLength-1 ; i+=2 ) {
      sum += ((int) mRaw.getShort( i )) & 0xFFFF;
    }
    if( mPacketLength%2 != 0 ) {
      int val = ((int) mRaw.get( mPacketLength-1 ))&0xFF;
      sum += (val << 8);
    }
    while( (sum>>>16) != 0 ) {
      sum = (sum & 0xFFFF) + (sum >>> 16);
    }
    sum = ~sum;
    mRaw.putShort( mIcmpOffset+2, (short) sum );
  }
  
  /** Load a provided ICMP packet.  Do not alter the passed array until the IcmpPacket is destroyed!
   * 
   * @param pkt ICMP source packet
   */
  IcmpPacket( byte[] pkt ) {
    mRaw = ByteBuffer.wrap( pkt );
    mIcmpOffset = (((int) mRaw.get(0)) & 0x0F) * 4;
    mDataOffset = mIcmpOffset + 8;      
    mPacketLength = ((int) mRaw.getShort( 2 )) & 0xFFFF;
    if( mPacketLength > pkt.length ) mPacketLength = pkt.length;
  }
  
  /** Returns the ICMP protocol 
   * @return protocol
   */
  int getProtocol() {
    return mRaw.get( 9 ) & 0xFF;
  }
  
  /** 
   * Retrieve the IP addresses this packet refers to.
   * @return src/dest addresses
   */
  IcmpKey getAddresses() {
    IcmpKey nk = new IcmpKey();
    nk.mSrcIp = mRaw.getInt( 12 );
    nk.mDestIp = mRaw.getInt( 16 );
    return nk;
  }
  
  /**
   * Set the payload of this ICMP packet.
   * 
   * @param info payload for packet
   * @param len length of payload (if less than the array size)
   */
  public void setData( byte[] info, int len ) {
    int maxlen = Math.min(len, 1500-mDataOffset);
    System.arraycopy( info, 0, mRaw.array(), mDataOffset, maxlen );
    mPacketLength = mDataOffset + maxlen;
  }

  /**
   * Get the length of the payload.
   * @return payload length
   */
  public int getDataLength() {
    return mPacketLength - mDataOffset;
  }
  
  /**
   * Get a copy of the packet's payload (can be modified).
   * @return payload
   */
  public byte[] getData() {
    byte[] dd = new byte[ getDataLength() ];
    System.arraycopy( mRaw.array(), mDataOffset, dd, 0, dd.length );
    return dd;
  }
  
  /**
   * Set the ICMP type.
   * @param v ICMP type
   */
  public void setType(int v) {
    mRaw.put(mIcmpOffset, (byte)v);    
  }
  
  /**
   * Set the ICMP code.
   * @param v ICMP code
   */
  public void setCode(int v) {
    mRaw.put(mIcmpOffset+1, (byte)v);
  }
  
  /**
   * Set the ICMP ID
   * @param v ICMP ID
   */
  public void setId( int v) {
    mRaw.putShort(mIcmpOffset+4, (short)v);
  }
  
  /**
   * Set the packet sequence number.
   * @param v sequence number
   */
  public void setSequence( int v ) {
    mRaw.putShort(mIcmpOffset+6, (short)v);
  }
  
  /**
   * Get the ICMP type.
   * @return icmp type
   */
  public int getType() {
    return mRaw.get(mIcmpOffset) & 0xFF;
  }
  
  /**
   * Get the ICMP code
   * @return icmp code
   */
  public int getCode() {
    return mRaw.get(mIcmpOffset+1) & 0xFF;
  }
  
  /**
   * Get the ICMP ID
   * @return icmp id
   */
  public int getId() {
    return mRaw.getShort(mIcmpOffset+4) & 0xFFFF;
  }
  
  /**
   * Get the packet sequence number.
   * @return packet sequence number
   */
  public int getSequence() {
    return mRaw.getShort(mIcmpOffset+6) & 0xFFFF;
  }
  
  static final int TYPE_ICMP_ECHO_REPLY = 0;
  static final int PROTO_ICMP_ECHO_REPLY = 0;
  
  static final int TYPE_ICMP_UNREACHABLE = 3;
  static final int PROTO_ICMP_UNREACHABLE_PORT = 3;

  static final int TYPE_ICMP_ECHO_REQUEST = 8;
  static final int PROTO_ICMP_ECHO_REQUEST = 0;
  
  /** Offset to the ICMP header */
  int mIcmpOffset;
  /** Offset to the payload */
  int mDataOffset;
  /** Total packet length */
  int mPacketLength;
  /** Buffer containing the raw packet */
  ByteBuffer mRaw;
}

Java Source Code List

• Back to Hardware/usb  ↑